Proto-mammals (probably) didn't look too mammal-like

I would not really consider myself a paleoartist, at least not in a professional sense. I have drawn extinct animals for various projects of mine but I see myself more as a writer. This might make it unusual that now I do not write merely about the history of paleoart but directly comment on paleoartistic tropes and trends and criticize those. But I hope you will see how it came to this point and why I want to talk about it.

My attempt at reconstructing the Early Triassic cynodont Cynognathus crateronotus, which used to be a popular staple in older books but is nowadays only rarely featured for some reason. Is this attempt too conservative? Shouldn't this animal have fur, a distinctive leathery nose, maybe pointy ears, looking basically like a dog with a lizard tail, as many like to reconstruct it? Well, as you will read, maybe not.

At my current job for the Natural History Museum Zürich (NMZ) I help with the research on quite a project, which we call the Great Journey (no relation to the Halo games, sadly), which will be a 60-metre long diorama depicting the last 600 million years of life on Earth. Currently we are working on the prototype, which will be “just” 10 metres and depict “just” a timespan of 100 million years, beginning with the start of the Triassic and ending in the Late Jurassic. This will be populated by around 300 miniature models and my task is to write the research-dossiers for these, which our 3D-artists can then use as reference material to make and 3D-print our models. I can not show those models off just yet, but trust me, you will love them.

Now, as you may guess, the first half of the Mesozoic holds a lot of extremely important events in the history of life. A marine ecosystem revolution, the rise of the archosaurs, including the dinosaurs and pterosaurs, the origin of various marine reptile clades, turtles, lepidosaurs, all our modern conifer families, and, of course, the evolution of mammals as we know them from the more archaic therapsids. Regarding the latter, we of course will have a couple of taxa which show these transitions. More basal therapsids, like the dicynodont Dinodontosaurus, early cynognaths like Cynognathus and Exaeretodon, mammaliamorph tritylodonts like Kayentatherium, famous mammaliaforms like Adelobasileus, Morganucodon and Castorocauda and eventually of course true crown-group Mammalia like Pseudotribos and Juramaia.

Fuzzy, snow-bound dinocephalians and therocephalians of the Middle Permian, as illustrated by Robert Bakker in the famous 1975 Dinosaur Renaissance issue of Scientific American. Are such speculations, which continue being made by paleoartists to this day, reasonable for early therapsids or do we now have sufficient data to doubt them? Source: Bakker 1975.

As you can imagine, my main goal has been figuring out for our artists what any of these animals would have looked like in life. Many artists in recent years (not naming names) have, likely influenced by the All Yesterdays movement, tended to give almost any of these animals features we associate with modern mammals but would rarely, if ever, fossilize: External ear pinnae, a soft, mobile rhinarium, long whiskers, a full fur coat and sometimes even the ability to lactate. But in my research, as well as after talking to experts, I have realized there is a noted discrepancy between how artists traditionally depict these animals and what current data, both directly from fossils as well as palaeoneurological work, says about the soft tissue anatomy of synapsids before the evolution of crown-group mammals. While these synapsids were closely related to or ancestral to mammals, this does not mean that they already possessed every trait we associate with mammals. In many ways these were very unique animals in their own right, not readily comparable with anything that survives today and drawing them in such an altogether too “modern” way may be just as erroneous and overenthusiastic as giving full feather-coats to sauropod dinosaurs. In some ways we might even have to go back and re-evaluate some of the supposedly outdated art that was made back when non-mammal synapsids were still thought of as “mammal-like reptiles” (just in case it needs to be said, synapsids do not descend from reptiles, they just share a common ancestor and are an amniote group of their own).

Let’s just go over a few traits:

The Myth of Thrinaxodon Whiskers

Early cynodonts such as Thrinaxodon and Cynognathus, as well as therocephalians and even gorgonopsians, are popularly depicted as having had whiskers (vibrissae) sprouting from their snouts. The origins of this go all the way back to D.M.S. Watson in 1931, who claimed that the densely arranged pits in the skulls of these animals were in fact anchoring points for vibrissae. This claim has often been repeated, rather uncritically, for the better part of a century. That is despite there being two rather major problems with the whisker-pit-hypothesis: 1) These supposed whisker-pits are in density and form nearly identical to the foramina also seen in various sauropsid reptiles, which obviously do not have whiskers and in which these pits instead house blood vessels that support lips and other facial tissues (Benoit et al. 2019), and, perhaps much more importantly: 2) No mammal today actually has such whisker pits in its skull (Benoit et al. 2019). Therefore, these pits cannot be used as an indicator for the presence of vibrissae. If anything, the foramina are more direct evidence for these animals having had thin, immobile, lizard-like lips, in contrast to modern mammals whose thick, muscly facial tissues are reflected in very smooth skull bone textures (Witton 2018).

Can we use other potential markers to determine when exactly vibrissae would have appeared in synapsids? Indeed, we can. In a series of papers starting in 2016, Julien Benoit et al. have looked at the evolution of the infraorbital nerve in synapsids and came to some rather insightful conclusions on the issue. In simple terms, the infraorbital nerve is what in modern mammals controls the movement and feel of the whiskers, as well as the rhinarium (the fleshy, mobile, wet nose typical of many mammals, more on which later). In mammals, the nerve is short and enters the infraorbital canal under the eye, where it lies unenclosed. This gives it enough space in order to be able to move the whiskers and rhinarium as effective tactile sense organs (Benoit et al. 2016). Reptiles also have this nerve, but it is much longer and passes together as a bundle with other nerves through a fully enclosing maxillary canal, giving it no room for mobility, thereby preventing the complex movement of facial tissues. (Note that the language used in the relevant papers is highly technical and I am not an expert in palaeoneurology, so I am sorry if the details here are a bit too oversimplified).

The evolution of the maxillary canal as well as the Msx2 gene coupled with the pineal eye both suggest that the genetic and neurological prerequisites for whiskers and more mammal-like snouts in general do not appear until the emergence of the derived cynodont clade Probainognathia. Source: Benoit et al. 2016.

How does the situation look alongside the therapsid-mammal spectrum? Here the data shows rather unequivocally that the typical mammalian condition of the infraorbital nerve does not evolve in cynodonts until the appearance of the clade Probainognathia (Benoit et al. 2016 & 2019). This is a rather advanced clade of cynodonts, consisting mainly of mammaliamorphs and their closest relatives, like the puma-like Trucidocynodon. It excludes its sister-group, Cynognathia (which Cynognathus and the large, herbivorous traversodonts are part of) and any earlier cynodonts, like Thrinaxodon. These animals, as well as more basal therapsids like the therocephalians and gorgonopsians, are instead found to have had the reptile-like (or rather ancestral amniote) condition, with the trigeminal nerve fully enclosed by the maxillary canal (Benoit et al. 2016 & 2019). This is not just a strong indicator but actually a direct falsification of the idea that these animals would have had mobile whiskers, as the ossification meant the nerve was immobile and therefore could not have controlled any tactile organs on the face in an effective manner (Benoit et al. 2019). Therefore, it is pretty safe to say, whiskers first appear in Probainognathia, not earlier.

What further supports this is that Probainognathia is the first synapsid clade in which the pineal/parietal eye (a primitive third eye on the forehead ancestral to all vertebrates) is permanently lost (Benoit et al. 2016). Studies on lizards, mice and humans have shown that the evolution and loss of this feature is controlled by the homeogene Msx2, which in mammals also affects the expression of certain skin and brain traits. Mice with a knocked-out Msx2 develop a rudimentary pineal eye, but at the cost of a deficient development of hair follicles and milk glands (Benoit et al. 2016), traits that are elemental to mammals as we know them, alongside other interesting losses, like a diminished cerebellum. The latter is further supported by the enlarged brain endocasts on probainognaths compared to earlier synapsids (Benoit et al. 2016). So, in short, if a synapsid still had a pineal eye, it's very unlikely it had whiskers, full-body fur or mammal-like mental faculties. The fact that we can use simple osteological characters like that to make assessments about the genetics and soft tissue traits of long extinct organisms is quite amazing, if I dare say so myself.

Splitting Hairs

So, where does this leave us in regards to one of the most characteristic mammal traits: Hair? Well, that depends on what hypothesis you subscribe to as to the original function of hair. Today, fur’s primary function is thermal insulation, allowing homeothermic endotherms to retain and keep steady the costly body warmth that has been generated by the animal’s elevated metabolism. Therefore, the appearance of fur has often been linked to the emergence of endothermy, which, according to bone histology, may potentially stretch back all the way to Permian pelycosaurs like Ophiacodon (Shelton & Sander 2015). Some recent work suggests that some form of endothermy may even have been ancestral to amniotes as a whole (Grigg et al. 2022). However, evolution does not work with foresight. You cannot go from naked skin to a fully insulating fur-coat overnight. There must have been some intermediate stage in which only part of the body was covered in hair, at which point it could not have had functioned sufficiently as an insulator. Going out at night with nothing on but socks may be kinky, but not good for survival. The original function of hairs must have therefore been something else, it being co-opted for insulation only later. As hair follicles are closely connected to nerves, the most commonly cited hypothesis has therefore been that hairs originally evolved purely as tactile sense organs, in most cases meaning whiskers. So, if you subscribe to the whiskers-first approach, then the paleoneurological works discussed to far seem to indicate that fur coats do not predate the emergence of Probainognathia, something also suggested by the authors. The soft-tissue fossil record seems to corroborate this. Even if endothermic in some form, all known skin imprints and trace fossils from pelycosaurs, including famous taxa like Dimetrodon, seem to show only reptile-like scales or scutes (Niedźwiedzki & Bojanowski 2012, Marchetti et al. 2025). Early therapsids, like the dinocephalian Estemmenosuchus, show only smooth, glandular skin reminiscent of that of big, hairless mammals today (Chudinov 1968), as does the recently described fossil mummy of the famous dicynodont Lystrosaurus from the Karoo Basin (Smith et al. 2022), a more derived neotherapsid. In other words, classic artists like Charles R. Knight and Zdeněk Burian seem to have portrayed these animals more accurately than some have tended to give them credit for. 

A fossilized mummy of a Lystrosaurus, described in 2022 from the Karoo Basin. It shows mainly a leathery skin with some pits and dimples, which may be skin glands. This largely affirms past reconstructions showing these animals as being naked instead of furry. Though taking taphonomy into account, could this animal still have had faint beginnings of hair somewhere on the body that did not preserve? Source: Smith et al. 2022. 

So, if you want to err on the safe side, you should probably not depict synapsids more basal than Probainognathia with fur coats. Sorry, fuzzy dicynodont fans (which sadly includes me). This statement comes with some asterisks, however. Even Benoit et al. do not exclude the possibility that some form of hair could have predated Probainognathia, even if it did not yet form a fur coat or specialized whiskers. While the Msx2 gene controls the density and distribution of hair follicles, it does not control the growth of hair itself, which is tied to different genes (Benoit et al. 2016). It is entirely possible that, instead of specialized whiskers at the front of the snout, the original tactile hairs were instead isolated filaments or strands occurring sporadically across the whole body, a condition that would have been helpful to small, burrowing animals, like Thrinaxodon and Diictodon, to feel their way through dark tunnels. I want to note that this is indeed the condition seen today in the naked mole-rat (Heterocephalus glaber) which has secondarily become almost cold-blooded, but still retains some isolated tactile hairs across the body and tail to aid its burrowing lifestyle. Some artists have indeed been depicting early synapsids with such a naked-mole-rat-look for a long time (good, old Dmitry Bogdanov of Wikimedia fame comes to mind). From this condition, once early probainognaths started trending towards not just a burrowing but also nocturnal life and full warm-bloodedness, the early tactile hairs would have been co-opted into specialized whiskers at the front of the head and isolating fur coats for the rest of the body. If you ascribe to this scenario, then note that such isolated tactile body hairs would only make sense in a burrowing or nocturnal synapsid. Large, above-ground-dwelling animals that were active during the daytime probably had limited or no use for these, so I would still recommend giving the likes of Inostrancevia, Lisowicia and Cynognathus a proper shave.

Isolated tactile hairs along the body could make sense even for a not-wholly-homeothermic, burrowing animal, as evidenced by the modern naked mole-rat. Is it possible such earliest beginnings of hair (which are very unlikely to be preserved, even in mummies) could have been present in some burrowing therapsids like Lystrosaurus? Source: Wikimedia.

 

It is also interesting to note that while probainognaths are the first clade in which all subsequent taxa lack a pineal eye, some individual genera of earlier cynodonts, dicynodonts and therocephalians seem to have convergently also lost this trait at separate points in time (Benoit et al. 2016). Assuming the same mechanisms of a mutated Msx2 gene are at work here, and assuming that some form of hair follicle did exist in the neotherapsid ancestor, I wonder if this meant that these particular genera also independently evolved a denser distribution of hair follicles. So, I am guessing, if you really want to draw a fuzzy dicynodont, only go for the ones known to have definitely lacked a pineal eye, such as Thliptosaurus.

The one fossil piece of evidence for pre-probainognath hairs are coprolites found from the Latest Permian of Russia, which seem to show hair-like filaments alongside half-digested bones of cynodonts and dicynodonts (Bajdek et al. 2015) (the animal that ate and excreted the victims seems to have ominously been a Proterosuchus-like archosauriform). While these are very exciting and suggestive, it cannot be definitively proven that these really are hairs, as the filament-like structures could have also been produced by plants or fungi (Benoit et al. 2016). The case therefore remains ambiguous. I have also heard of rumours that some of the Karoo mummies previously mentioned may not have been as naked as it at first seemed, but so far, that is just it. Rumours.  

The Nose Knows

Another long-standing artistic tradition is equipping theriodont synapsids (gorgonopsians, therocephalians and cynodonts) with a rhinarium. A rhinarium or muzzle is the characteristic mobile, fleshy nose/snout very distinct from the rest of the head that is unique to mammals and not found in any other tetrapods. It’s the wet, leathery nose of your pet cat or dog. At first glance, this might make sense and is a neat way for the artist to make these animals seem more familiar. The skulls of these early therapsids are vaguely dog-like and especially the shape of the front of the snout looks suggestive of a dog-like profile. But the keyword here is profile. The outline of the skull of a gorgonopsian or cynodont looks vaguely like the profile of a living dog, but have you actually compared them to the skull of a dog? There is a night-and-day difference there. Where there is solid bone in the nose region of these animals, in a dog or almost any other therian mammal, there is just nothing. Most mammals in effect only have a single aperture for the nose, with no bone separating the left and right nares (Higashiyama et al. 2019). In contrast, most of everything outside of Theria has clearly separated bony nostrils, and just very “bone-y” snouts in general. This seems to have largely been overlooked by most artists, continuing to equip the likes of Morganucodon with distinct, rodent-like noses, but the fact that this would have massive consequences for the life appearance of these animals was effectively shown by Higashiyama et al. 2019. In their study, they closely looked at the embryological development of the snout across various tetrapods and compared them with fossil synapsids and came to a very significant conclusion: Therian mammals (marsupials + placentals) have completely lost the premaxilla bone, which in all other vertebrates forms the tip of the jaw. 

As can be seen here, all synapsids prior to Mammalia possess a fully intact premaxilla and enclosed, boney nose-ring, much like other early amniotes. Only in therian mammals is the premaxilla completely lost and its function is replaced by an enlarged septomaxilla, which directly correlates with the presence of a rhinarium as an evolutionary novelty in therians. So, no dog-noses for the admittedly dog-like gorgonopsians, therocephalians etc. Source: Higashiyama et al. 2019.

What had long been thought to be the mammalian premaxilla is actually an enlarged septomaxilla, which in other tetrapods is usually a small bone inside the nose. It is the loss of the first bone and the expansion of the latter which allowed the mobile rhinarium to develop in the first place, as a true evolutionary novelty that makes us extremely alien compared to other tetrapods (Higashiyama et al. 2019). Really think about how weird that is for a moment. What does this mean for every animal outside of Theria? The condition is unclear for near-therian Mesozoic mammals like multituberculates (Higashiyama et al. 2019). Monotremes like the echidna and platypus still have an intact premaxilla (at least at an embryonal stage). Their nostrils are leathery but otherwise do not form a special organ separate from the rest of the snout. While an early expansion of the septomaxilla (comparable to what is observed in echidna embryos) can already be seen in early cynodonts and therocephalians, the fact remains that every synapsid outside of crown-group Mammalia retains a fully intact premaxilla even into adulthood, forming a prominent bone ring between the nostrils (Higashiyama et al. 2019). Mammaliaforms like the docodonts and the famous Morganucodon have one, tritylodonts like Kayentatherium have one, every earlier cynodont has one, as does every synapsid that came before them. Their noses must have been immobile and in general quite indistinct from the rest of the head. In other words, their noses would have looked more like those of other tetrapods, such as reptiles and amphibians (Higashiyama et al. 2019). The dog-like heads of some theriodonts are merely an illusion, in the flesh they would have resembled more a reptilian caricature of a dog. Taking Benoit et al. 2016 & 2019 into account, I think it is possible that, starting with Probainognathia, the texture of the nose may have become more distinct, being covered by more sensitive, leathery skin as seen in the echidna and platypus, but that would still not change the fact that most of everything outside of Theria would still have had very “boney” or “shrink-wrapped” immobile noses, with the non-muscular skin adhering close to the shape of the skull’s snout tip. There is surprisingly still little art that accurately reflects this. 

The rhinarium is a structure unique to therian mammals alone that differentiates them from other tetrapods, where the snout is ordinarily formed by the premaxilla. Source: Higashiyama et al. 2019.

 

Can you lend me an ear?

Another typical mammalian trait that has been applied in a rather laissez-faire attitude across various synapsid clades has been the external ear pinna, or “Ohrmuschel”, as it is known in my hood. Like most things discussed so far, this is a purely soft-tissue trait that does not readily fossilize. Though at least one fossil pinna, quite large and mouse-like, is known from the Mesozoic mammals Spinolestes, which lived around 125 million years ago, making it the oldest known example (Martin et al. 2015). Spinolestes was an eutriconodont, a basal clade of theriimorphs (true mammal on the lineage to the marsupials and placentals). As both marsupials and placentals also have pinnae, we can therefore say with reasonable certainty that all theriimorphs would have ancestrally had one too. That includes eutriconodonts, multituberculates, gondwanatheres, dryolestoids and therians. But just that clade? At first glance, monotremes seem to lack this trait, suggesting that, like the rhinarium, this is another unique therian-line adaptation. However, the echidna actually does have pinnae! They are just very small and embedded in the skin of the head (Augee et al. 2006, p. 84). This suggests, at least to me, that they are vestigial, which makes sense, as it is generally thought that the echidna evolved from a platypus-like aquatic ancestor and aquatic mammals tend to reduce their ears for streamlining purposes. It therefore seems likely to me that the last common ancestor of monotremes and therians, meaning the first true crown-group mammal, would have already possessed some form of ear pinnae. 

Illustration of the classic mammaliaform Morganucodon, from a 70s children's book. Prominently featured in such books as the "first mammal", it is often illustrated as here, looking like a shrew or rodent (which are derived placental mammals), with a distinctive, wet button-nose and pointy ears. In reality this animal would in many ways have been more archaic than even a platypus, so we may question such portrayals. Source: McCord 1977.

How does it look outside Mammalia? Probably less optimistic. According to the experts I have asked, the evolution of the external ear pinna is closely linked, for obvious reasons, to that of the typical mammalian inner ear, which was brought about by the distinctive secondary jaw joint that allowed mammals to repurpose two of their jaw bones into ear ossicles. In paleontology, in lieu of milk, the acquisition of this trait is central to distinguishing true mammals from non-mammal synapsids. All earlier mammaliaforms, like Morganucodon or Castorocauda, have the transitional jaw form, where they have both the typical mammalian jaw-joint as well as the earlier tetrapod-typical joint also seen in reptiles. It is possible that the incipient stages of the pinnae may have started somewhere here already, but as their jaw bones were not yet fully integrated into the ear, their hearing was less sensitive than in mammals, so there may not have been a need for them. Everything outside Mammaliaformes still had only the more archaic form of jaw-joint and therefore an even more reptile-like way of hearing. They would have just had simple ear holes with a tympanum right behind the jaw-joint. If you go back far enough, to the pelycosaurs, even ear holes seem to disappear completely, as these animals seem to have picked up vibrations from the ground and air solely with their jaw bones (Olroyd 2022). 

My own attempt at reconstructing Morganucodon (based on the skeletal from Rowe 2022). As you can see, there are no ear pinnae, no distinctive rhinarium for a nose, but added is a (perhaps too prominent) spur on the ankle of the foot (venom optional). An unfamiliar and altogether "archaic" look, but one that seems to be in line with the paleobiology of synapsids before the emergence of true mammals as we know them.

 

In conclusion, I would tend to not give pinnae to anything outside of Mammalia. And even within the crown-group mammals, one has to take into account that burrowing or aquatic lifestyles can lead to a reduction or loss of pinnae.

Greg, could you milk me?

As already alluded to, the most defining mammal trait, when not looking at the skeleton, is the ability to lactate and thereby feed one’s offspring with milk (a few fish and birds also feed their young with milk-like substances secreted from the body, but these are cases of convergent evolution). All living mammals do this in one form or another, so the trait must have already existed when the crown-group Mammalia emerged (though dedicated teats/nipples seem to be unique to the therian-line of mammals, as the monotremes still excrete milk from their bellies as a form of sweat). How old is this elemental link between mother and child? Some paleoartists have stretched lactation all the way back to ancient pelycosaurs like Dimetrodon, though how justified are such projections?

A speculative depiction of Dimetrodon, titled Texan Mama, illustrated by Mike Keesey and first appearing in 2013’s All Your Yesterdays. The animal has the sail covered in a fatty hump, no scales, tufts of hair and feeds its children with proto-milk-like secretions from its skin. How badly has this aged 13 years later?

Even if milk glands do not readily fossilize, we can make some inferences from anatomy and reproductive methods to see how likely it was that a synapsid excreted milk. One of the best starting points are the recently described in-ovo embyros of Lystrosaurus. These show that the chicks of these animals were mostly precocial (able to feed themselves shortly after hatching) and hatched from relatively large eggs, much larger in proportion than those of monotremes (Benoit et al. 2026). The most likely reason for this is that these eggs still contained large yolk sacs, much like turtles or birds, whereas in modern monotremes the lack of a large yolk sac and the resulting small egg size is compensated with lactation from the mother (Benoit et al. 2026). All of this makes it unlikely that Lystrosaurus mothers would have fed their chicks with milk. As Lystrosaurus most likely represents the ancestral condition for therapsids, this is may likely be true for all earlier synapsids (barring convergent evolution of this trait), so, sorry, no Dimetrodon milkshakes for you. At best it seems possible that some of these animals secreted the immediate “ancestor” of milk, a sort of sweat that mothers probably used to coat their leathery-shelled eggs with to protect them from desiccation, as still sometimes observed in monotremes (Benoit et al. 2026).

More intriguing and further up the family tree is the case of Kayentatherium, a tritylodont, a family of superficially rodent-like mammaliamorphs. A famous specimen shows a mother with her nest of about 38 perinates. The large number, curled poses as well as the relatively adult-looking proportions of these offspring were indicated by the original authors as evidence that Kayentatherium still reproduced much like a lizard, laying a large clutch of eggs with precocial offspring able to feed themselves right after hatching (Hoffman et al. 2018), therefore not needing milk. This was further corroborated by the fact that the teeth of some of the offspring already showed signs of use. The authors of the aforementioned Lystrosaurus eggs paper have however called some of these inferences into question. Some modern rodent babies can already be born with wear on their teeth, so this not as clear of a sign for precociality as it at first seems (Benoit et al. 2026). Furthermore, the inferred egg sizes for Kayentatherium must have been exceptionally tiny, much closer to what is seen in modern monotremes, thereby indicating only a very small amount of yolk and a necessity for milk from the mother (Benoit et al. 2026). These arguments are very intriguing, though the sheer size of the clutch to me still suggests a more archaic, reptile-like style of reproduction and I find it hard to imagine feeding up to 40 babies with milk, especially without dedicated teats. For reference, modern monotremes only lay 1 - 2 eggs per breeding season. 

Reconstruction of a Lystrosaurus embryo, preserved likely in-ovo (the soft, leathery eggshell unlikely to be preserved). Proportions of the embryo and likely size of the egg indicate that this animal reproduced much more like a tortoise than a platypus, so extended parental care and milk-feeding is very unlikely. Conditions may vary for other therapsids, however. Source: Benoit et al. 2026.

 

Teeth can also give some indication about the evolution of lactation. Most non-mammal synapsids seem to have had polyphyodont teeth, meaning that, just like reptiles, they continually replaced their teeth throughout their whole life. This in turn indicates that their diet must have stayed mostly the same throughout their whole life, without a distinctive milk-feeding stage. This seems to have been the case all the way up to the early mammaliaform Sinoconodon, which would conflict with the more basal Kayentatherium having had milk. Only with more derived mammaliaforms like the morganucodontans do we find clear evidence of diphyodonty (milk teeth being replaced once by a set of permanent teeth), as well as toothless young that clearly would have needed their mother’s milk to survive (Panciroli et al. 2017).

In summary, lactation probably became the status quo in mammaliaforms like Morganucodon and Castorocauda, but perhaps did not have its origins earlier than, at best, Mammaliamorpha, depending on the parenting style of Kayentatherium. Suckling Thrinaxodon, as seen in Walking with Dinosaurs, are therefore very unlikely.

In the spur of the moment

Instead of deducting traits, how about we add one? One feature that is frequently pointed at in the monotremes to show their supposed “freakiness” are the spurs on the ankles of their hindlimbs. In the adult platypus only the males possess these and they are capable of injecting a painful venom. In the echidna both males and females have these, but neither is venomous. What many laypeople do not seem to be aware of is that these spurs are not a unique oddity of the monotremes but used to be the status quo among mammals as a whole and we are actually the weird ones for having lost this trait.

Venomous ankle-spur of the male platypus. It is very likely one of your distant ancestors had one of these too.

This has been well-documented since Hurum et al. 2006 and still remains the consensus view among Mesozoic mammal-researchers today (pers. comm. Elsa Panciroli). What clearly are platypus-like ankle spurs have been found in a wide variety of specimens from pretty much every major group of Mesozoic mammal, including ones on our side of the family tree, such as multituberculates, eutriconodonts and spalacotheriids. It has also been found in earlier docodont mammaliaforms like Castorocauda (Ji et al. 2006). It is very likely that this was a trait ancestral to most or all Mammaliaformes, with it only being lost in the common ancestor of marsupials and placentals (Hurum et al. 2006).

Ankle-spur on the echidna.

Does this mean every individual pre-therian Mesozoic mammaliaform had them? Well, there is obviously some nuance involved here. For one, some lineages could have obviously secondarily lost it, just like our own ancestors did. For the other, the trait is clearly sexually dimorphic. As mentioned, only male platypodes have them and they use them in battles against other males, while the spur is also only vestigial in adult female echidnas. If a Mesozoic mammal is found without them it could just mean you have found a female specimen. On the other hand, this dimorphism may only be unique to the monotremes. Both male and female echidnas possess the spur, while young female platypodes also have the spur before losing it into adulthood, suggesting that both sexes having spurs was the original condition. Furthermore, the spur’s clear main function is as a venom-delivery system. Even if the echidna lacks venom, its spurs still have a hollow tube like in the platypus’, showing that its ancestors most likely had venom running through there too (Hurum et al. 2006). While platypodes mainly use them to fight each other, they can also use them as defensive weapons against predators. Hurum et al. 2006 speculated that in the earliest Mesozoic mammals this was likely the main function of these spurs, as a defensive weapon against small, predatory dinosaurs. If that is the case then it would make sense for this trait to not have originally been sexually dimorphic, as it would have been useful in daily survival for both males and females.

Don’t take this as gospel

A very rough attempt by me to visually summarize everything we have learned so far, starting with the traits already inherent to early "pelycosaur" synapsids and what each successive clade potentially added or subtracted. The resulting image seems to run against popular speculation of synapsids already looking pretty much like mammals by the Late Permian and instead shows a gradual accumulation of typical "mammalian" traits that protracts itself throughout the whole Triassic and probably into the Jurassic.

Ultimately most of what you have read here is speculative to some degree. I do think we have a better idea now of when certain traits appeared than we did two decades ago, but a lot of this is still based on phylogenetic inference and proxy skeletal-traits. These still leave a lot of room open for hypotheticals and unknown unknowns. To know the life appearance of these animals for certain, we really would need perfectly preserved Lagerstätte specimens from the Triassic or Permian. Here I would like to cite Brian Engh, with whom I had a lively email exchange about exactly this topic and who allowed me to directly quote him (afterwards, please be sure to check out his blog Living Relic Productions):

“Overall, I tend to think a lot of these questions come down to how we're interpreting ecospace for extinct animals for which we sometimes aren't 100% certain of the ecospace they actually inhabited (semiaquatic Kayentatherium definitely falls into this category). While in paleontology people often emphasize phylogenetics over soft tissue or behavioral plasticity, the reality here in real life is that there are lots and lots of examples where animals have adapted their soft tissues or behavior in response to niche radiation or other selective pressures, sometimes very very rapidly, and sometimes in ways that can't be detected in their skeletons or in incomplete fossils. People in paleo love to say "only (therian) mammals have motile facial tissues, reptiles do not!" but that's just not true. Crocodiles and several species of lizards have independently evolved muscular nostrils that can close when they dive. Hump-nosed lizards (Lyriocephalus) can retract their lips when feeding. Toad headed agamas (Phrynocephalus) have mobile cheek flaps. Several chameleons have novel motile ear-like "occipital flaps" for display. And birds show all kinds of weird, muscularized cranial kinesis not clearly indicated by their theropod dinosaur ancestors. Many of these features leave no indication on the skeleton (and with regards to some of the lizards, I've looked), and many have not been studied or published on. So, I tend to regard the rigidness with which paleo people interpret soft tissue adaptation according to (skeletal) phylogenies as an artifact of trusting their own preconceptions rather than actually observing nature. For these reasons I'm a mildly "controversial" artist for being willing to explore those unknown spectra of soft tissue adaptations that must have occurred between known fossil data points. There were almost certainly evolutionary intermediaries of all of these features.”

I think the moral of the story is to think critically when applying soft tissue traits, but to not treat skeletal proxies and phylogeny as absolute gospel. I agree with Brian, in the sense that many paleontologists seem to treat animals like engineers do machines, i.e. “this screw only fits with that socket, this hinge is only suited for such and such weights”, while living organisms show us time and time again that they are not bound to such rigidity, like the proverbial bumblebee that fails to adhere to aerodynamics. To every perceived rule there are exceptions at every corner. A prominent example is the recent finding of the early cynodont Chiniquodon, whose neonatal-line growth-rings suggest that it was born live instead of hatching from an egg (Gaetano et al. 2026). The authors go as far as speculating that live birth may have been the original condition in cynodonts, with monotremes somehow secondarily re-evolving egg-laying (Gaetano et al. 2026). I am aware that there are cases where such athing has been proposed for some squamates, but, as far as I am aware, not in any conclusive manner and if, then only within short time-spans after the first loss of oviparity. Therefore, I find this proposal unlikely that monotremes re-evolved egg-laying somehow after around 100 millions of years of viviparity. I find it far more likely that if Chiniquodon was viviparous (“if” because I am not sure if growth rings on an induvial are enough to say this conclusively compared to more direct evidence like a fossil embryo inside a mother), then it evolved this trait independently of later mammals. We have far more evidence for viviparity evolving repeatedly across vertebrates as a whole and I would not be surprised if far more synapsids evolved live birth independently too, even if the “main line” up to therian mammals was oviparous. The same could be the case for a wide variety of other traits. We can use phylogeny and proxies as a general guideline of what to expect at the base-line, but that does not mean various species could not have evolved certain traits independently ahead of the “mainstream”. Though I remain highly skeptical, maybe there were some shaggy dinocephalians or dicynodonts, maybe some gorgonopsians could snarl, maybe there were some pelycosaurs that could excrete some milk-like substance from their bellies. As long as it makes sense for the lifestyle of the respective animal.

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Related articles:

• The Evolution of Fur - A Historic Perspective (Now very outdated)

References:

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• Bajdek, Piotr; Qvarnström, Martin; Owocki, Krysztof et al. 2015: Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites from Russia, in: Lethaia, 49, 4, p. 455 – 477.
• Bakker, Robert 1975: Dinosaur Renaissance, in : Scientific American, 234, 4.
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• Benoit, Julien et al. 2019: The Evolution of the Maxillary Canal in Probainognathia(Cynodontia, Synapsida): Reassessment of the Homology of the Infraorbital Foramenin Mammalian Ancestors, in: Journal of Mammalian Evolution, 27, p. 329 – 348.
• Benoit, Julien et al. 2026: The first non-mammalian synapsid embryo from the Triassic of South Africa, in: PLOS One.
• Chudinov, Peter 1968: Structure of the integuments of theromorphs, in: (Anon., Trans.). Doklady Akademii Nauk SSSR, 179, 1, p. 226-229.
• Gaetano, Leandro Carlos et al. 2026: Early origin of viviparity in the mammalian lineage, in: Frontiers in Mammal Science, 5.
• Grigg, Gordon; Nowack, Julia; Bicudo, José et al. 2022: Whole‐body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians, in: Biological Reviews, 97., p. 766 – 801.
• Higashiyama, Hiroki et al. 2021: Mammalian face as an evolutionary novelty, in: PNAS, 118.
• Hoffman, Eva et al. 2018: Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth, in: Nature, 561.
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• Polonica, 51.
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• Martin, Thomas; Marugan-Lobon, Jesus; Vullo, Romain et al. 2015: A Cretaceous eutriconodont and integument evolution in early mammals, in: Nature, 526, p. 380 – 384.
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• Olroyd, Savannah 2022: The Function of the Reflected Lamina in Therapsids and the Origin of the Mammalian Middle Ear.
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Wilfarth's Great Tides and the Dinosaurs - Part 3

Go here for Part 2!

And so we continue with Martin Wilfarth and his alien visions for the Mesozoic:

“The herbivorous Kickoff-Breathers”

Die herbivoren Abstossatmer (Iguanodontidae)

…and birds?

Coming now to the Ornithischia. Wilfarth imagines the ancestor of the ornithischians as a small “saltopodid” that adapted to living in more isolated but large tidepools that connect with the ocean only for a short time during flow. Plankton was sparse here, and so were the filter-feeding invertebrates that most of the saurischians fed on. So these small dinosaurs instead began feeding on water plants, which was an easy transition, as he notes, because they are softer than terrestrial plants that have woody support-structures (Wilfarth 1949a, p. 54). As the ancestral, pencil-like front teeth were useless for herbivory, they were lost and instead the lips hardened, becoming eventually a true beak supported by a predentary bone. Hence why Wilfarth sees the name Predentata as equally valid as Ornithischia. Being small animals in deep tidal lakes, made even deeper during flow, the animals needed to jump up a far distance to breathe. Grazing underwater in a crouched position, the pubis was already below the femur and could therefore be used to pull the leg back for a powerful upwards jump (see fig. 2). Exploiting this, the early ornithischians retroverted their pubis so that the pubo-femoral muscle could be used even more effectively to help with jumping. The downside of this was that these ornithischians consequently lost the bipedal balancing function of their pelvis and could only move anymore on land either quadrupedally or by hopping (Wilfarth 1949a, p. 54). But as tidal ranges lowered and carnivorous dinosaurs became a bigger threat, some re-developed bipedalism by evolving the additional praebubis or neopubis bone at the anterior base of the pubis, which picked up again the lost lever-function.   

Fig. 1: Underwater Iguanodon. This is one of my favorite illustrations in the book, because of how well-drawn the dinosaurs are here. There is a nice, scaly texture to them that is strangely lacking in the others. Though I am guessing that was to deliberately invoke iguanas? (Source: Wilfarth 1949a, p. 56).

As already mentioned (see part 1), unlike other workers of his time, Wilfarth did not view the ornithischian pelvis as arising independently from the saurischian one:

“That the ancestor of the ornithischians already was a lever-pelvis saurian, one can see by the retroverted pubis already being true levers, meaning longer than they would have to be for a basket-pelvis. If we count all saurians with a lever-pelvis as dinosaurs, so we may conclude that the ornithischians and birds must descend from a saurischian.” (Wilfarth 1949a, p. 52, translated by me).

Apart from speaking in favour of dinosaur monophyly here, your interest must surely be piqued by the mention of birds. I bet you did not see that coming. Yes, indeed, Wilfarth believed that birds descend from dinosaurs, a fact we all know today but an idea that would have been regarded as highly unorthodox in the 1940s, thanks to Gerhard Heilmann and Othenio Abel, who, contra Huxley, had popularized the idea that birds only share a common ancestor with dinosaurs among the Pseudosuchia. Wilfarth goes even further by claiming that the birds actually descend from the hypothetical small tidal proto-ornithischians just discussed:

“The birds probably branch off at the point on the evolutionary line to the ornithischian at which the retroverted pubis had been gained, but the herbivorous diet has not or not fully been adopted yet. In the birds must then have occurred an arboreal episode in their evolutionary line. The little saurischian who was destined to become the progenitor of the birds then probably climbed up the tree as an insectivore. Here a neopubis was not gained, because here there was no necessity for it.” (Wilfarth 1949a, p. 55, translated by me).

The idea that birds might descend from the ornithischian dinosaurs was semi-popular among some paleontologists of the early 1900s, mostly due to the shape of their pelvis, but was strongly rejected by Gerhard Heilmann (1926) on the basis of the ornithischian pelvis only bearing a resemblance to that of ratites, whose skeletons are greatly derived from those of ancestral birds like Archaeopteryx, as well as ornithischians supposedly not having clavicles that could have evolved into the avian furcula. Wilfarth surely was aware of Heilmann’s writings, given that he heavily references his artwork, so it is interesting that he either disagreed with or ignored these conclusions. Sadly, there is no greater elaboration than what you have just read. Wilfarth was not the only one proposing a bird-dinosaur ancestral relationship during the pre-Ostrom “Dinosaur Doldrums”, but those proposals, made by the likes of Carl Vogt, Robert Wiedersheim and Percy Lowe, were even more unorthodox and therefore taken even less seriously. They suggested that birds are actually polyphyletic, with the flying forms descending from Heilmann’s pseudosuchians or even pterosaurs and the ratites directly descending from the ostrich-dinosaurs. So Wilfarth seems a bit saner in comparison, even if he identified the wrong dinosaur group as the bird-ancestors. The bird-ornithischian link would be revived one last time by Peter Galton in 1970, who, just like Wilfarth, concluded that, while true ornithischians with their praepubis were too derived to have been the direct bird-ancestors, they still could have shared a close immediate ancestor similar to Lesothosaurus. Galton himself gave this idea up by the mid-80s (Norman 1985, p. 193).

Fig. 2: The reversion of the ornithischian pubis was to facilitate better jumps, according to Wilfarth (Source: Wilfarth 1949a, p. 53).

The first specific ornithischian group discussed by Wilfarth are the iguanodonts, whom he interprets as larger versions of the ancestral kick-breathers, though now so large that they merely needed to stand up to breathe. Just as with Plateosaurus and the sauropods, the characteristic thumb-claw of Iguanodon he interprets as another tool for the animals to anchor themselves in the sediment while feeding (Wilfarth 1949a, p. 56). During flow, the animal evaded sharks with its strong paddle-tail, during ebb it ran away from the theropods with its strong hindlegs.

“The Backplate Saurians”

Die Rückenplattensaurier (Stegosauridae)

Dinosaurs usually get the short end of the stick in old paleontological texts, but no group ever gets an end as short as the stegosaurs. With their small brains, supposedly useless, extraneous backplates and mismatched legs, many old writers saw these animals as destined for extinction. It is therefore quite refreshing to see that Wilfarth, in his own weird way, actually shows them quite a bit of appreciation, seeing them as expertly adapted to their supposed habitat. It should be noted that Wilfarth here seems to treat ankylosaurs as a type of stegosaur, probably following Marsh’s original definition of Stegosauria.

Fig. 3: Kentrosaurus using its thagomizer as an anchor against the current (Source: Wilfarth 1949a, p. 62).

Especially the backplates have given many early researchers headaches and there have even been some who claimed they were maladaptive traits, a consequence of genetic degeneracy out of control, with Frederic Brewster Loomis writing in 1905 (p. 842): “With such an excessive load of bony weight entailing a drain on vitality, it is little wonder that the family [Stegosauridae] was short-lived”. Wilfarth sees the plates instead as ingenious hydrodynamic structures, a beneficial adaptation for the intertidal zone (which is at least one step above being aerodynamic). To Wilfarth, stegosaurs inhabited shallow waters with strong currents. Feeding against the current, the backplates helped direct the water, so that it would flow over the back and press the animal down, so it could retain a firm grip to the ground instead of being carried away. (Wilfarth 1949a, p. 59 – 60). One wonders if the spikes on Wiwaxia could have worked like that.

Wilfarth is very open to the thagomizer of stegosaurs and ankylosaurs having been used as a defensive weapon (amusingly more against sharks than against theropods), though he thinks that could not have been its only function. Using Kentrosaurus (written here as “Kentrurosaurus”, which was Edwin Hennig’s preferred spelling to avoid confusion with Centrosaurus), Wilfarth notes that many contemporary reconstructions are wrong in showing the tail-spikes of stegosaurs as pointing straight up (Wilfarth 1949a, p. 58 – 59) and instead were splayed more to the side and pointing back. This is still the preferred view today. Where it gets weird is that Wilfarth asserts that therefore the most likely function of the thagomizer was as an anchor or stake in the sediment, as a further countermeasure against strong currents (Wilfarth 1949a, p. 57 – 58). This extends even to the tail-clubs of the ankylosaurs.

The unusually long hindlegs in comparison to the arms are of course another obvious adaptation towards having to rear up in shallow water in order to breathe. Interesting is here that Wilfarth makes special note of the neck-armour many stegosaurs had, which in his view protected the throat during this vulnerable moment (Wilfarth 1949a, p. 63 – 64).

“The Neck-Shield Saurians”

Die Nackenschildsaurier (Ceratopsia)

The earliest ceratopsians, like Leptoceratops, Wilfarth still interprets as primarily aquatic, on account of their deep, laterally flattened tails, something he does for other dinosaurs too. It should be noted that this was pretty common for paleontologists at the time, especially in regards to hadrosaurs, and it took until the Dinosaur Renaissance for some to point out that the dinosaur tail does not resemble the paddle-tails of crocodilians, especially since the deepest sections tend to be close to the body instead of mid- or end-part of the tail.

Fig. 4: Triceratops gracefully grazing in shallow water. In the background an individual lifts its head above the waves to breathe (Source: Wilfarth 1949a, p. 65).

The forms appearing in the Late Cretaceous he however regards as the dinosaurs with the least aquatic adaptations (Wilfarth 1949a, p. 65). Which of course makes sense, because the Great Tides had greatly diminished by this point. Instead of swimming or living submerged, the ceratopsians were merely waders of knee-high waters, grazing on aquatic plants during flow and otherwise prowling the beaches for other plants during ebb. The characteristic neck-frill Wilfarth interprets as a specific adaptation towards that lifestyle. While he does not go full John C. McLoughlin  he does still view the shield as primarily an attachment site for strong neck and shoulder muscles, allowing the skull to quickly pivot around its ball-and-socket-joint with the spine. This “hinge-skull” or “Klappschädel”, as he calls it, allowed the ceratopsians to efficiently lift their snout above water when they needed to take a breath, again according to Wilfarth’s motto that dinosaurs used elaborate bone constructions in order to save on muscle-work. The question of why they would evolve such an unusual hinge-skull instead of simply repositioning their nostrils like other semi-aquatic animals would do, Wilfarth does not address. On the topic of nostrils, Wilfarth writes on the unusually huge ceratopsian nares, believing that, just as with the sauropods, these must have housed elaborate soft tissue structures:

“The bony nasal opening in the ceratopsians is very big. Despite that, this fact has so far been ignored and reconstructions of the neck-shield saurian have always (with the exception of Lull 1933) drawn them a usual small nostril. These ornithischians have simply always been viewed as Mesozoic replacement-rhinoceroses, and for an only-land animal such a huge nasal opening is of course inconceivable. For a shallow-water-dweller and a hinge-skull-breather however, a huge nasal opening, which can be quickly widely opened and then shut close again, was very important.” (Wilfarth 1949a, p. 67, translated by me).

Semi-aquatic interpretations of ceratopsians have popped up here and there again in the decades following Wilfarth, but, as with most dinosaurs, evidence is abundant that these were purely terrestrial animals. However, the large nostrils that he addresses here still present a mystery for paleoartists to this day. While some still continue to reconstruct them with simple, slit-like nostrils, it has become popular to speculate that they may have housed large, inflatable air sacs, used for visual communication as seen in some birds.

Fig. 5: Triceratops using its headshield as a muscle-lever to lift its huge nostrils above the water (Source: Wilfarth 1949a, p. 65).

The nose horn, Wilfarth sees primarily as a means of protecting the large, fleshy and therefore sensitive nostrils. The brow horns in some species, however, he believes primarily evolved as a means of giving the eyes shade, so that they could look more clearly through the water’s surface (Wilfarth 1949a, p. 69), I guess similar to the wings of a black heron. Though he also goes into detail on how the numerous horns on the ceratopsian skull could also be used in defence against sharks, marine reptiles and theropods (Wilfarth 1949a, p. 69 – 70).

That Wilfarth regards the ceratopsians as the least aquatic dinosaurs is of course interesting if we remember (from part 1) his cryptozoological article on the Sanderson reports from Africa. Of course he would view these as the dinosaurs most likely to survive into the modern day, as they would be best suited for coping with the loss of the Great Tides.

“The Trunkbreathers”

Die Rüsselatmer (Hadrosauridae)

The hadrosaurs are the one group that Wilfarth has focussed the most on, writing papers on the supposed hadrosaur-trunk as far back as 1938. His hypothesis has notably changed and evolved over the years in response to criticism. Perhaps responding to Sternberg’s critique, where Sternberg erroneously claimed that Wilfarth imagined the hadrosaurs having a trunk like an elephant, Wilfarth writes:

“That is why I name the sub-family Hadrosaurinae here “Peaktrunkers” [Original: Spitzenrüssler], although the term “trunk” is dangerous. All the world immediately thinks of an elephant’s trunk, which is used as a tool for gathering food. This is obviously not what is meant here. The expanded breathing-nose, which is the subject here, is solely used for respiration. Also in length and mobility the breathing-nose cannot compete with the elephant’s trunk. As is often the case, here too the right word is missing for a previously unknown apparition. Nose is too little, trunk too much. There is nothing left but to use the term trunk here, because it has to be emphasized that we are dealing here with significantly more than a nose.” Wilfarth (1949a, p. 74, translated by me).

I believe the closest that Wilfarth imagined here for the hadrosaurs is something like the breathing proboscis seen on the snouts of modern softshell turtles. It should be noted that, for the time, this was pretty much the only unorthodox idea Wilfarth espoused about the hadrosaurs. Other supposed aquatic features cited by him, such as deep paddle-tails and alleged webbing on the hands of hadrosaur mummies, were also used by plenty of other contemporaneous researchers to support an amphibious lifestyle for these dinosaurs. And unlike other researchers, Wilfarth did not relegate the hadrosaurs to the waters because he thought they could only eat soft aquatic plants. He does mention that the complex tooth-batteries in their jaws would have been just as effective in function as the molars of mammals (Wilfarth 1949a, p. 54), which I think is somewhat notable, as that would later become an important talking point in the Dinosaur Renaissance.

Fig. 6: An early, trunk-nosed hadrosaur walking upright across the tidal bottom, feeding on aquatic plants drifting in the water. The pose seems inspired by Charles Knight's original reconstruction of Trachodon (Source: Wilfarth 1949a, p. 74). 

The hadrosaurs he imagines as evolving from an ornithischian similar to Iguanodon, but adapted to the shallow-water conditions of the Late Cretaceous. They no longer needed to rear up or fulfil breath-jumps in order to breathe and instead, convergently to the ceratopsians, evolved adaptations that allowed them to keep their nostrils above the water during feeding. The simplest of these forms were the aforementioned “Spitzenrüssler”, Hadrosaurinae, to which Wilfarth counts forms like Hadrosaurus (synonymous to him with Trachodon), Edmontosaurus and Claosaurus. These differed from the iguanodonts by having deep, vacuous nares, which Wilfarth again sees as an indicator for elaborate soft-tissue structures, in this case an inflatable, short, forward-facing proboscis. That these spaces probably did house some sort of elaborate nostril structure is still a popular speculation today, though, as with the ceratopsians, something like inflatable display sacs were probably more likely. Wilfarth makes special note of the hook-like squamosal bones at the back of the skull of hadrosaurs, which he interprets as a lever-like structure, again similar to the ceratopsian neck-frill, that allowed the animals to quickly clap back their heads for quick breaths (Wilfarth 1949a, p. 83). The zygapophses in the neck vertebrae he interprets as a further stabilizing feature to better make the animal withstand strong currents (Wilfarth 1949a, p. 82 – 83). The general feeding mode of hadrosaurines he imagines as walking bipedally through shallow water and feeding, from below, on drifting plants on the water’s surface.

Fig. 7: Wilfarth's supposed evolution of the hadrosaur trunk. Beginning with forward-facing, extendable nostrils in Claosaurus, pointing backwards in Kritosaurus, becoming a large, fleshy structure in lambeosaurines, before then ossifiying in Parasaurolophus. As the description indicates, Wilfarth was unsure where the fleshy nostrils would have actually connected with the inner skull, speculating if a secondary opening atop the skull was a sort of new naris (Source: Wilfarth 1949a, p. 85).

With the water constantly splashing against the nose, the trunk eventually began facing backwards and started to retract, as seen in supposed transitional forms like Kritosaurus. This eventually resulted in the evolution of the “Helmettrunkers” (Helmrüssler), the Lambeosaurinae. In Wilfarth’s view, the headcrest on animals like Corythosaurus was the basis for a fleshy trunk extending from the top of the head, allowing the animal to feed on plants and breathe in water even in a crouched-over position. Wilfarth remains ambiguous on where he thinks the connection of the fleshy nostrils into the skull would have run. In his sketches he seems to prefer a secondary skull opening in the crest he labelled 5b, but as he cannot find it in every hadrosaur skull, he is also open to the trunk having been connected to the original nares at the front of the snout (Wilfarth 1949a, p. 85), which would seem much more sensible if you asked me.

Fig. 8: Corythosaurus in breathing and feeding position (Source: Wilfarth 1949a, p. 78).

The end-point of this evolution were then eventually forms like Parasaurolophus. The idea that Parasaurolophus’ famous headcrest acted as a form of snorkel is not actually unique to Wilfarth. Alfred Sherwood Romer, yes that Romer, in his famous textbook on vertebrate paleontology, already had this idea in 1933. Though without any fleshy bits, instead thinking there must have been an actual hole at the end of the crest. Wilfarth’s original interpretation was ironically very different. In his 1938 paper on hadrosaurs, he originally speculated that the whole headcrest of this dinosaur was connected by muscles and ligaments to the neck and shoulders, acting similarly to the hinge-skulls of the ceratopsians. This was of course an extreme interpretation he was strongly criticized for (Wiman 1942), though it is interesting from the perspective of the modern discussions on the placement of the nuchal ligaments, such as in Bertozzo et al. 2020. Shortly after publication, Wilfarth gave this idea up (Wiman 1942), so I guess you at least cannot say that he was not receptive to criticism.

Fig. 9: Parasaurolophus, able to breathe and feed at the same time thanks to its crest (Source: Wilfarth 1949a, p. 84).

Instead, again following the idea that dinosaurs preferred replacing muscle-work with bone construction, the crest of Parasaurolophus actually represents an ossification of the breathing trunk that in forms like Corythosaurus was still made out of flesh and muscle (Wilfarth 1949a, p. 82 – 83). This made it the most specialized and efficient of the hadrosaurs, able to feed in shallow water, even on all fours, while being able to breathe at the same time. But even that did not save it from extinction.

The Great Dying

Wilfarth’s assessment of the End-Cretaceous mass extinction is as brief as it is succinct and his evaluation of different hypotheses reads as surprisingly modern, systematically going through all the ideas that were popular during his time before coming to his own conclusions. Funny for us today is that he labels it the Great Dying, which is now a term more reserved for the End-Permian mass extinction.

First Wilfarth addresses the idea that competition with mammals wiped out the dinosaurs, something proposed, for example, by Baron Franz Nopsca. He, quite correctly, counters this with the remark that dinosaurs were not the only animals that went extinct and that mammals could have hardly also been competing with the marine reptiles and pterosaurs.

Next is the idea that disease could have been the main cause, an idea first championed by Roy Lee Moodie and long after even by Robert Bakker. Here again, Wilfarth notes that epidemics could have hardly wiped out both the dinosaurs and also all the other giant reptiles, as well as so many invertebrates like ammonites.

Third is the idea of “racial senility” or “phylogeronty”. This was an idea very popular in the early 20th century, endorsed by some leading paleontologists like Richard Swann Lull and Arthur Smith Woodward, who claimed that whole lineages could “age” like a single person, meaning that the longer they existed the more their genome would deteriorate and grow out of control, leading to the evolution of maladaptive features and eventually extinction (Benton 1990). Proponents of this idea often liked to point at the odd and excessive features on the skulls of dinosaurs, like the hadrosaur headcrests or the ceratopsian neckfrills, or at the strange shell-shapes of the heteromorph ammonites, as evidence that the genetics of these animals had gone awry with age, like the Ottomans and Byzantines growing more decadent as their empire neared its end (Bakker 1986, p. 52). That this idea was once so popular, and that it still subconsciously lingered on in popular imaginings of prehistory long after, is pretty baffling, as it falls apart when you think about it for just a minute. All life on Earth shares the same common ancestor, so at any point in time all lifeforms also share the same evolutionary age of their genes. Wilfarth, who we have seen views all the odd features of dinosaur anatomy as beneficial adaptations for their lifestyle, points exactly this out when he criticizes the concept of racial senility and asks why the dinosaurs should have grown senile, but crocodiles, snakes, lizards and turtles still have not. Adding to that: “Should this senility have extended to the ammonites and so on? Lingula, a brachiopod, has from the Cambrian until today not grown senile” (Wilfarth 1949a, p. 87, translated by me).

The fourth idea he addresses is that other animals ate all the dinosaur eggs. Here he correctly points out that it would be highly unusual for the number of egg-eaters to increase so suddenly and also the obvious fact that many of the marine reptiles did not even lay eggs but gave live birth.

Fifth is the idea that a sudden drop in global temperatures could have led to the extinction of the various cold-blooded animals, which was an idea that would prove to be popular all the way into the 1970s (Benton 1990). Here, Wilfarth brings up the pretty valid point that the early Cenozoic was still just as tropical as the Mesozoic (Wilfarth 1949a, p. 87) and that by the same logic there should also no longer be any snakes and crocodiles today. Indeed, today we know that the Palaeocene and Eocene were actually even warmer than the Cretaceous.

Last, he comes to the also popular idea that orogenies were the main cause, the many new mountain chains building up in the Late Cretaceous draining the swamps that the dinosaurs supposedly inhabited. Again, he points out that many animals went extinct that obviously were not swamp-dwellers, but funnily enough he also points out a very valid inconsistency, which is that many of the proponents of this idea did not view certain dinosaur groups, like the coelurosaurs and carnosaurs, as swamp-dwellers (Wilfarth 1949a, p. 87).

 Thus, Wilfarth comes to the conclusion that you probably could have imagined. By the beginning of the Cenozoic, the Moon had drifted away so far from the Earth that it led to an end of the Great Tides and therefore also the unique intertidal ecosystem that used to cover a large part of the continents. Thus, it came to a collapse of the shallow-water planktonic community, followed by an extinction of invertebrates and in turn marine reptiles and, of course, the dinosaurs (Wilfarth 1949a, p. 87 – 88), which were then succeeded by the fully terrestrial fauna of the Cenozoic. Wilfarth ends his book poetically: “The Great Tides formed the dinosaurs, with the Great Tides they also faded.” (Wilfarth 1949a, p. 88).

Fig. 10: How you supposedly get a Parasaurolophus out of a Corythosaurus, with a speculative transitional form (Source: Wilfarth 1949a, p. 80).

Of course, the base assumption, that dinosaurs were intertidal-dwellers, is wrong and today we definitely know that a catastrophic asteroid impact spelled doom for the Mesozoic, but on its own, Wilfarth’s conclusion is quite sober, especially compared to the other ideas of the time. Why? Because, normally, the biggest driver for the extinction of species is habitat loss, a fact that is more relevant today than ever. While I think human activity certainly was a factor in the extinction of the mammoth, what is often overlooked is that the entire biome these animals inhabited, the mammoth steppe, is also almost completely gone due to climatic and ecological changes.

On another note, it is interesting that Wilfarth here unknowingly tried to resurrect arguably the first hypothesis for the K-Pg mass extinction. Georges Cuvier (1825) was one of the first naturalists of the early 19th century who recognized a major faunal change between the Secondary and Tertiary ages. However, dinosaurs were barely known by that time and so most of the lifeforms known to him from the Age of Reptiles were plesiosaurs, crocodiles, ichthyosaurs and turtles. So he thought that during this period most life was still aquatic or amphibious and went extinct due to a sudden drop in sea levels, with the mammals of the Tertiary Age being Earth’s first true dry-land fauna. How Cuvier and his ilk imagined their alien Age of Reptiles would be a topic for a whole other series of blogposts, though Mario Lanzas has given a good impression.

Assessing Wilfarth

This ends Wilfarth’s vision of the Mesozoic and the lifestyle of dinosaurs. There are obviously some details I would have liked to know more from him. Like, what was going on on dry land during this time? Is this where the first mammals and birds were biding their time until the fall of the Great Tides? How much more extreme were conditions during the Permian? How exactly do pterosaurs and marine reptiles fit into the Great Tides? Except for an image description there is also a sore lack of any stratigraphical arguments from dinosaur-bearing sites that Wilfarth could have addressed.

But in the end how do we want to evaluate Martin Wilfarth? Obviously, he was quite unorthodox and eccentric and his insistence on the validity of his hypothesis and how it supposedly answers so many questions all at once bears all the hallmarks that we today associate with pseudoscience. And most importantly: He was wrong. At the same time, his hypothesis was based on some true uncertainties of his time and some of the things he used as arguments, such as the supposed aquatic adaptations in sauropods and hadrosaurs, were really not all that different from what leading contemporaneous experts were already claiming. He just dared to go a few steps farther down the aquatic paradigm.

Fig. 11: Wilfarth pointing out the unusually vacuous bony nostrils of Iguanodon and Edmontosaurus, speculating that these must have housed large, unusual, fleshy noses with special functions (Source: Wilfarth 1949a, p. 73).

What I hope I was able to show is that there are also things that can be appreciated about Wilfarth’s body of work. He was one of the few scientists in the 1940s who tried to specialize in dinosaurs, at a time when most vertebrate paleontologists were decidedly neglectful of the group. In a recovering post-war Germany, mind you. In the process, he made some points, which, even if they were ignored by his contemporaries, would prove quite prophetic for later dinosaur research. In Wilfarth’s work we find such prescient ideas, unpopular for his time but very familiar today:

• Dinosaurs were successful, complex animals.
• Dinosaur anatomy was sophisticated and its oddities were efficient adaptations to their environment and lifestyle, not degenerate features brought about by “racial senility”.
• Dinosaurs did not go extinct due to incompetence or due to being inferior to mammals.
• Dinosaurs are monophyletic.
• Birds descend from dinosaurs.
• Dinosaur young changed lifestyle and ecology as they grew up.
• Dinosaurs had stiff backs and balancing tails that worked like a seesaw.
• Dinosaurs did not drag their tails on the ground. 
• Plateosaurus was an obligate biped.
• Sauropods held their spine up in a slight concave curve and regularly reared up onto their hindlegs.
• The large nares on sauropod, ceratopsian and hadrosaur skulls were likely supporting elaborate soft-tissue structures.
• Small theropods were fast and agile.
• Large theropods were active hunters.
• Stegosaurs were competently adapted animals, not mistakes of nature.
• The spikes on thagomizers faced sideways.
• The horns on ceratopsian skulls were formidable defensive weapons.
• Hadrosaur dentition was complex and just as efficient as that of herbivorous mammals.

It is true that a broken clock strikes right twice a day, but this is a bit more than that, don’t you think? While Wilfarth’s framework as a whole was wrong, it is nonetheless fascinating that the lens with which he viewed the dinosaur skeleton still was able to make him see some features that much later researchers would discover, while being ignored by his contemporaries. And does that not say something about the philosophy of science? In his famous work The Structure of Scientific Revolutions, Thomas Kuhn argued that the worldview a scientist operates in is more important than the data he works with, as only with a change in worldview can he sometimes see things he would not have seen otherwise (some interpreters of Kuhn have gone as far as arguing that he claimed that when the worldview changes, it is the world itself that actually changes). Wilfarth pointing out features that other contemporaries seem to have ignored, such as the highly unusual noses of dinosaurs, would seem to support this. But another point Kuhn argued is that, due to the crucial unintelligibility or incommensurability between worldviews (“planet” is a very different term for a geocentrist than it is for a heliocentrist), scientists will ultimately diverge and break away from each other with each revolution, producing not a progress towards what we would call truth, but a progress away from a common starting point, akin to darwinistic speciation. If all sciences were nearing truth, he argued, we would see them converge into a single grand unified theory, instead of what we actually see: Each discipline splitting up into more and more sub-disciplines, some of which incompatible with each other (such as quantum physics vs. relativity theory).

Wilfarth’s tidal paradigm is incompatible with the warmblooded paradigm of the thinkers of the Dinosaur Renaissance. But not necessarily incommensurable, as the word “dinosaur” would have meant pretty much the same to a Wilfarth and a Bob Bakker, but not to an Edwin Colbert. And they both also made common observations that the researchers of the older swamp paradigm did not. Is that then not a notable convergence? Like pterosaurs and birds both evolving wings, just in different configurations, due to adapting to the same constraints of aerodynamics? Maybe, contra Kuhn, worldviews can convergently adapt to the same underlying constraints, some adapting better to reality than others, implying that there is some sort of truth that can be progressed towards. Or maybe I am just waxing philosophical again because I don't know how to end this section. Here's a meme:

Fig. 12: And so the cruel king stands there among the tides, enjoying the crocodile cacophony or perhaps just the aquatic ambiance, awaiting the arrival of his gangplank galleon. 

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Related articles:

• Wilfarth's Great Tides and the Dinosaurs - Part 1
• Wilfarth's Great Tides and the Dinosaurs - Part 2 
• The Alien Prehistoric World Trope - Part 2
• The weirdest things people have thought about pterosaurs
• Unorthodox Ideas about Bird Origins 
• Stegosaurus: A History of Reconstructions 
• Paleopods: The myth of the predatory prosauropods that kinda turned out to be true
• "Hawkinspunk" Spinosaurus

Further Reading:

• Alien Planetology 
• A Vast Quantity of Evidence Confirms that Non-Bird Dinosaurs were not Aquatic by Darren Naish
• Dinosaur Sex Lakes, Too Big to Walk and the Bizarre Theories of Brian Ford by C. M. Kosemen

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