Solved and Unsolved Fossil Enigmas - Part 2

Welcome back to our ongoing look at some of the most (in)famous fossil mysteries. For part 1 go here.

Fig. 1: The supposed paratype of Protoavis texensis. Is this a genuine Triassic bird or something entirely else? Read on and find out.

Paleodictyon

Paleodictyon stands out on this list in that it is not the fossil of an organism, but a trace fossil. It usually consists of a stretch of burrows arranged in a honeycomb-pattern. It starts appearing somewhen during the transition from the Ediacaran to the Cambrian and extends… all the way to modern day. Despite existing since Precambrian times no fossil animal has ever been associated with Paleodictyon and not even samples taken with submersibles from modern specimens were able to find any inhabitant inside them. Who made these? Hypotheses have been quite diverse. The most obvious suggestion is that these were the feeding traces of some burrowing animal that either failed to be fossilized or left the burrow before the samples were taken. Others have suggested bacterial colonies or that these are structures left behind by sponges or xenophyophores. Geologist Mark McMenamin has suggested that Paleodictyon, just like real honeycombs, was/is the nest of some marine organism into which it laid its eggs. He noticed some form of organic pellets inside the fossil, through which some of the burrows cut through. He theorizes that this was probably food left there by the parent and the honeycomb-like structures were made by the larvae as they searched for the pellets. This would explain why no body-fossil or living animal has ever been associated with the structure so far, as a nest would only be occupied for a short time before being discarded. It would be the oldest known example of parental care. Another hypothesis is that these structures were created by the unknown trace-maker as a form of bacterial farm on which to feed. That there is no trace-maker and the structure is of abiotic origin has also been suggested. Only the future can tell.

Fig. 2: A Miocene specimen of Paleodictyon.

Waukesha’s butterfly creature

The Waukesha Lagerstätte is a fossil site from the Brandon Bridge Formation of Wisconsin containing many beautifully preserved soft-body impressions of invertebrates from the Early Silurian. Unlike the Burgess Shale, the majority of the organisms found can be classified into known taxa. However, one fossil that is surprisingly common, but very mysterious is the “butterfly animal”, as it is called (as far as I am aware it still does not have an official taxonomic name). It is obviously not a real butterfly, as those would not appear until 240 million years later. It was instead some type of aquatic arthropod that bore a carapace with wing-like extensions on its side, earning it its nickname. To this day there seems to be still no official classification for this animal beyond being some type of bivalved arthropod. Surprisingly very little is written about it and it was even a bit difficult to get to pictures of it.

Fig. 3: The Waukeshan butterfly creature alongside other members of its ecosystem.

Rutgersella and Protonympha

Remember the Ediacarans from the last post? The idea that they were giant amoebas or para-animals were not the only possible explanations for their identity. Australian paleontologist Greg Retallack proposed that these organisms actually lived in freshwater or even on land and were giant lichen. He came to this hypothesis based on two fossils considerably younger than the Ediacaran biota. One was Rutgersella, an organism from the Silurian of Pennsylvania that looked superficially similar to Dickinsonia. It seems to have lived in or near freshwater and its fossils show pyritized rhizines, the root-structures we know from fungi. The other was Protonympha from the Devonian Gardeau Sandstone. It bears great resemblance to Spriggina, is associated alongside freshwater fish and plants and also possessed rhizoid-like structures. Rutgersella’s association with Dickinsonia has however weakened recently, given that the latter was able to be identified as an animal based on fossilized biomarkers and cladistic analysis. Their similarity may be a taphonomic coincidence. Protonympha’s association with Spriggina is however more open to interpretation. While Protonympha lacks the characteristic head-shield, the segmentation of its body is intriguingly close to that of Spriggina and they are preserved in the same type of sandstone Lagerstätte. If they truly are related, it would mean that Spriggina was neither a proto-trilobite nor some frondomorph vendobiont, but some sort of lichen-mat… or would it? While Protonympha’s rhizines are definitely suggestive of some sort of fungal organism, there is no known group of fungus/lichen that grows like it is trying to mimic a trilobite (at least known to me, though I am admittedly not a mycologist so feel free to correct me on that). Similar structures are also sported by plants and algae and could have maybe also convergently evolved in vendobionts (assuming they possessed cilia like ctenophores). Perhaps the rhizines in Protonympha could also be a misinterpretation or the original organism was overgrown by fungi after death. As always, more research and material is needed to come to a conclusion about the identity of these fossils. Spriggina is definitely in dire need of a biomarker study like was done for Dickinsonia.

Fig. 4: Compare Protonympha (top) with Spriggina (bottom).

Typhloesus

We move on in time to the Carboniferous Bear Gulch Limestone of Montana. The formation used to be an estuarine lagoon with an anoxic bottom. When fish and other animals died and sank to the bottom, the environment prevented them from easily decaying, allowing excellent preservation of the soft-bits. One of the creatures that was found here in such a condition was Typhloesus. When it was first discovered some excitement arose, as it was found closely associated with conodont-teeth, making it seem like the infamously elusive conodont-animal (see Part 1) had finally been found. However, when Simon Conway Morris described Typhloesus in detail in 1990, he discovered that the teeth were not located in the organism’s mouth, but rather in its gut-area. Typhloesus was not the conodont-bearer, but a conodont-eater. Morris was however not able to figure out what exactly the animal was. Shapewise, Typhloesus was a sac-like organism with no hard-parts. It had a hooded mouth and a sort of tailfin at the end of its body, giving it a vaguely fish-like shape, however it lacked any traces of sense-organs and limbs. Based on this, Typhloesus might be classified as some sort of primitive, fish-like chordate but Morris objected to such a classification because the animal apparently lacked an anus. Instead of terminating in an anus, the midgut seemingly had no exits. Below the gut was instead a disk of solid iron deposits, the so-called ferrodiscus-organ (which was present in all Typhloesus fossils). Nobody knows what this disk was used for. Most intriguing was the fact that alongside conodonts, fish-scales and worm-jaws have also been found, implying that Typhloesus may have been a quite a successful predator… despite lacking eyes or teeth of any kind.

Fig. 5: A sketch of Typhloesus’ life-appearance, based on Morris’ observations.

Ever since Morris’ description, the fossil has been quite obscure and rarely discussed. In 2016 blogger and taxonomist Christopher Taylor was critical of Morris’ assessment that Typhloesus lacked an anus, instead speculating that the anus was simply obscured by the ferrodiscus organ and that the organism was some type of chordate after all. The most recent speculation comes from a podcast of Turkish paleoartist C.M Kosemen. In it, he notes the strangely close association between Typhloesus and conodonts, like the fact that the only conodont teeth that can be found in the Bear Gulch Formation come from the “guts” of Typhloesus. Based on this he speculates that their relationship may have been more complex than that of predator and prey. Instead of being a predator, Typhloesus may have actually been a life-stage of conodonts, perhaps a sort of egg-sac in which the young developed. Maybe it even was the adult-stage about to give birth, while the classic eel-like conodonts are larvae. Somewhat similar examples of metamorphosis are known from other chordates, such as tunicates. However, the fact that the remains of animals that are not conodonts have also been found inside Typhloesus speaks against the idea that the conodonts were its young and is more in favour of them having been prey. The question then remains how in all hell Typhloesus was so good at catching conodonts.

Tullimonstrum

Also from the Carboniferous, though from the Mazon Creek fossil beds, is Tullimonstrum gregarium. It is perhaps among the most famous, if not the most famous fossil enigma, having even become the state fossil of Illinois. In 1966 there was even a newspaper-hoax that claimed living Tullimonstrum were found in Africa. The Tully Monster, as it is colloquially known, was a cylindrical animal with a tail-fin, two stalked eyes and a trunk-like proboscis with a toothed claw/jaw at its end. For the longest time it was simply classified as an annelid worm of unknown affinity or some other type of invertebrate. A study from 2016 however reclassified it as a basal vertebrate related to modern lampreys and identified several structures that were interpreted as gill-openings, a notochord, vertebrate-like eyes, as well as a vertebrate-like nervous system. In the following year a new study harshly criticized the previous one however, saying many of the identified features have been misinterpretations. This newer study noted similarities between Tullimonstrum and Cambrian animals such as Opabinia and vetulicolians, but also that the organism’s eyes bear resemblance to those of cephalopods and other molluscs. This response-study was however itself met with criticism. There currently is still no clear consensus on what exactly the Tully Monster is, but that does not seem to hinder its growing popularity. It has become a popular subject in paleoart and there are even plastic toys and plushies of it. 

Fig. 6: Tullimonstrum, interpreted here as a type of vertebrate.

On a more funny note, the probably most bizarre speculation about Tullimonstrum comes from British journalist and cryptozoologist Frederick "Ted" William Holiday. In his 1968 book The Great Orm of Ness he proposes that the Loch Ness Monster, as well as many other famous lake and sea monsters, might be based on sightings of large modern relatives of Tullimonstrum. He used the original classification of the Tully Monster as a type of annelid worm as an explanation why many medieval legends of sea-monsters and dragons call the creatures worms, orms or a variation thereof (the Lindwurm Fafnir from the German Nibelungenlied comes to mind). A large Tully Monster swimming close to the surface and sticking its proboscis out of the water would indeed look similar to the classic swan-necked pseudo-plesiosaur silhouette we like to imagine Nessie has. The very first claimed sighting of the monster made by George Spicer in 1933 also does describe it as being a large, blob-like creature with a trunk sticking out of the front of its body. Nonetheless, while it is an interesting and admittedly charming idea, the Monster of Loch Ness is almost certainly not a giant, living Tully Monster, as there is no evidence that Nessie exists in the first place.

The “Triassic Kraken”

Apropos sea monster. Another time, another mystery, but curiously again a familiar protagonist. The Berlin-Ichthyosaur State Park is a fossil site from Nevada established in 1957 in which up to 40 skeletons of the giant Triassic marine reptile Shonisaurus popularis have been discovered. What was weird and unique about the site was that many of the skeletons were arranged parallel to each other, while the vertebrae of others were organized in strange spiral-patterns. This arrangement is unique to this fossil site and only comparable to some modern whale “graveyards”. While some odd sea-current was probably the likeliest explanation for this, Mark McMenamin, whom we have already met, claimed that the patterns could not have been made by natural processes and came up with a rather extraordinary explanation. According to him the fossil bed may have been created by a gigantic cephalopod that killed the ichthyosaurs, brought them to its lair and arranged the bones in a certain pattern, perhaps to decorate its nest in order to attract a mate. Somewhat similar behaviour can be seen in modern octopodes. Some of the vertebrae-spirals vaguely resemble the arm of an octopus with suckers, so McMenamin also fancied that this may have also even been an early form of art and self-depiction. As Shonisaurus was a reptile of up to 15 meters length, the cephalopod capable of doing this must have been of enormous size and strength, perhaps even surpassing the modern colossal squid Mesonychoteuthis hamiltoni. There was no evidence for the presence of such a giant mollusc at the site, so his proposal was not taken seriously and largely ignored. That was until 2013, when he went on his own digging expedition at the fossil site and actually found a strange fossil, which, upon comparing it to a modern humboldt squid, McMenamin claims to be the beak of his alleged Triassic Kraken, thus reigniting the debate. Is this the final proof that during Mesozoic times marine reptiles were battling titanic cephalopods, like we think happens today between sperm whales and giant squids? As you probably noticed by my wording, it is not certain if what McMenamin found actually is a beak and even if it is one, the remains are too fragmentary to allow an accurate estimate of the animal’s size. It could have just been an ordinarily sized cephalopod. The evidence is not extraordinary enough to confirm the extraordinary claim.

Fig. 7: Ichthyosaur vertebrae arranged in a sort of carpeting pattern. Was this produced by an odd sea-current or an intelligent force?

While I also think that the most likely explanation are sea-currents, I would still like to offer my own explanation, simply because it is fun and hey, why not? Ichthyosaurs, as many people note, have an uncanny resemblance to dolphins and similar cetaceans due to living in the same habitat. What if the resemblance is more than skin-deep? We know that ichthyosaurs gave live birth and we generally assume that they lived in groups. They therefore may have had a type of sophisticated social intelligence and behaviour, similar to modern marine mammals. We know from cetaceans that they mourn their dead and there is anecdotal evidence from other smart animals, such as elephants, that they recognize the bones of their conspecifics and sometimes rearrange or even carry them around, as if to somehow protect or honor their remains. What if the Berlin Ichthyosaur State Park used to be a type of “graveyard” that was visited by pods of Shonisaurus to bring their dead to and rearrange their bones? My speculation is admittedly rather outlandish as there is no real equivalent in modern animals (the whale and elephant graveyards you sometimes hear of are a myth based on mistaken natural animal traps) and the endocasts of ichthyosaurs suggest brains of similar shape and relative size to those of modern non-bird reptiles, making such complex behaviour improbable. But hey, at least I am not conjuring up a sea monster out of thin air.

Protoavis

We stay in the Triassic, but move from the water to land… or rather the air. It is generally assumed that the dinosaur-group we call birds first emerged in the Mid-to-Late Jurassic about 160 million years ago from animals similar to Anchiornis and Archaeopteryx and that they are members of the coelurosaur-clade Maniraptora. However, since the nineteenth century there have been claims of birds existing as far back as the Triassic, the oldest one coming from Edward Hitchcock who in 1848 claimed that the three-toed footprints of the Triassic New Red Sandstone came from gigantic, moa-sized waterfowl. These “giga-duck”-footprints later turned out to have been produced by early sauropodomorphs similar to Anchisaurus. The most recent claim of Triassic birds came from the 90s. In 1991 Sankar Chatterjee of the Texas Tech University described a fossil animal from the Post Quarry of Late Triassic Texas. He called it Protoavis texensis and claimed it to have been a Triassic bird that was remarkably more advanced and bird-like than the Jurassic Archaeopteryx, despite being about 75 million years older than the Urvogel. He even wanted to identify quill-knobs on the arm-bones of the animal, which would have been a definitive sign of pennaceous wing-feathers. The existence of Protoavis was a rather extraordinary claim and would have pushed the split of birds from the other dinosaurs way further back in time or even questioned the dinosaurian origin of birds. It has thus led to many speculations. In his 1989 book Predatory Dinosaurs of the World, before the official description of the animal was published and working with only informal information, famous paleoartist Gregory S. Paul offered some fascinating speculation on what Protoavis may have been and what role it played in bird-evolution. He tentatively classified it as a close relative of the early theropods such as Herrerasaurus and speculated that it was a bird-imitator that, convergently to real birds, evolved primitive flight or descended from a flying ancestor (In case you are wondering, yes, as far back as the 80s Paul believed that the first theropods already had feathers, something which is only in recent years gradually becoming consensus). He also considered the possibility that Protoavis is a genuine bird-ancestor and that later “proto-birds” like Archaeopteryx and Velociraptor are the actual dead-ends. This he however considered to be unlikely as there is a large gap in the fossil record between Protoavis and Archaeopteryx in which we find no bird-like animals. He also considered the possibility that Protoavis was perhaps a chimaera of dinosaur and pterosaur remains (Paul 1988, p. 251-252). Unfortunately, for history’s sake, Paul did not offer a drawing of how he imagined Chatterjee’s animal to look like.

Fig. 8: Protoavis as reconstructed on Chatterjee’s book about bird evolution. Given how badly preserved and questionable the actual remains are, the artistic license here is very generous.

It should be the latter of Paul’s interpretations that would prove to be prophetic. Later re-examinations by palaeontologists such as Lawrence Witmer showed that Chatterjee’s Triassic “bird” was nowhere near as complete, definitive or genuine as he claimed. The original specimen was severely crushed, heavily jumbled, disarticulated and seemingly composed of several different animals. The arms resembled those of a ceratosaur, the leg bones resembled those of Coelophysis while the neck and cranium seemingly came from a drepanosaur very similar to Megalancosaurus (drepanosaurs were chameleonesque arboreal reptiles that convergently evolved very bird-like heads). The supposed avian features, like the quill-knobs, were either too vague or not discernible at all due to how badly the bones were crushed. It is quite telling that in the book about his own discovery, The Rise of Birds, Chatterjee does not even show photographs of the fossil, instead just presenting the reader with artistic reconstructions. Every sign points towards the Post Quarry having been created by a Triassic flash flood that caught multiple different animals and jumbled their corpses. This archosaur-mess was then very optimistically and prematurely interpreted by Chatterjee as all belonging to the same animal. As such, Protoavis is not seen as a genuine genus by almost all modern palaeontologists, let alone a bird-ancestor, and we can fairly safely place this fossil mystery in the “Solved”-folder.

Fig. 9: Greg Paul unfortunately never drew Protoavis, but he did depict the Cretaceous Avimimus, which he thought looked strikingly similar. Once thought to have been exceptionally bird-like, Avimimus is now recognized as an oviraptorosaur. Then again, some paleontologists, like Michael J. Benton, insist that oviraptorosaurs were secondarily fligthless birds.

Paul’s speculation that flight may have evolved multiple times in dinosaurs is however still material for worthwhile discussions, especially given recent finds. Recently discovered dinosaurs, such as Microraptor (being a dromaeosaur and therefore more closely related to Velociraptor and Utahraptor than to birds) have frequently opened up the question whether feather-based flight may have evolved multiple times among maniraptorans or if all these animals descend from a single flying ancestor with some lineages becoming secondarily flightless. Most intriguing are the scansoriopterygids Yi Qi and Ambopteryx, which, despite being feathered dinosaurs, apparently possessed membranous wings made of skin, more similar to bats or pterosaurs. Who knows, maybe there really was something like a flying herrerasaur somewhere in deep time.

Chilesaurus

There exist three major groups of dinosaurs: Theropoda (bipedal carnivores), Ornithischia (beaked herbivores like Triceratops and Dryosaurus) and Sauropodomorpha (sauropods and close relatives like Plateosaurus). Based on the shape of the pelvis and the presence of pneumatic airsacs, theropods and sauropodomorphs have classically been considered to be more closely related to each other than to ornithischians and are grouped together into Saurischia. Since Harry Govier Seeley, Dinosauria as a whole has therefore been split up into Saurischia and Ornithischia for the better part of the last century and up until very recently. This tradition has however faced a major blow in 2017, when a paper by Matthew Baron, David Norman and Paul Barrett was published. In their analysis they found not only that putative early theropods like Herrerasaurus were more closely related to sauropodomorphs, but also that theropods are more closely related to ornithischians than to sauropodomorphs. This new Theropoda-Ornithischia grouping they gave the name Ornithoscelida, borrowing the name from an old concept of Thomas Henry Huxley. According to this Ornithoscelida-model, ornithischian dinosaurs did not arise in the Triassic alongside the other dinosaur groups from a more primitive dinosauriform, but instead descend from primitive theropods of the Early Jurassic. While it at first seems scandalous and has caused a lot of discussion and outrage, the hypothesis has a lot of interesting things going for it. Early ornithischians, such as Heterodontosaurus, have a lot of similarities to theropods and we have found feather-like filaments in both groups while these are so far unknown from sauropodomorphs. Most intriguing is the fact that we lack any evidence of definitive ornithischian dinosaurs from the Triassic. Almost all putative Triassic ornithischians, most notably Pisanosaurus, have so far been proven to actually be primitive dinosauriforms, such as silesaurids, or to even be pseudosuchians.

Fig. 10: A cast of the Chilesaurus holotype.

This is where Chilesaurus comes in. It is a roughly three meter long dinosaur from the Late Jurassic of Chile and has been infamous so far for defying any classification attempt. It has a backwards-pointing pelvis and its teeth indicate a herbivore, something we would expect from an ornithischian, however its jaw lacks a predentary bone, the beak that is present in all known ornithischians. Its hands bore similarities to those of early sauropodomorphs such as Anchisaurus, but these were long extinct by the time Chilesaurus lived. Like T. rex it only had two fingers. Originally the dinosaur was classified as an early tetanuran theropod, but in the same year as the Ornithoscelida study, Baron and Barrett also did an analysis of  Chilesaurus and found it to be the earliest diverging ornithischian, having split off before the group evolved the characteristic predentary bone. Chilesaurus would therefore be a transitional form between Jurassic theropods and the earliest ornithischians (though it should be noted that it lived too late to have been the missing link, it would be more like a relic of an earlier point of evolution), therefore being strong evidence in favour of the Ornithoscelida-hypothesis. The following year however there was a study by Müller et al. responding to Baron et al., using the same data, that recovered Chilesaurus as an early sauropodomorph. Baron et al. then informed Müller et al. that they had accidentally used an earlier, inaccurate data-set from their study, meaning the sauropodomorph-classification was a mistake. As far as I am aware, an accident like this is a first in paleontology.

Fig. 11: Chilesaurus as reconstructed by Liam Elward.

The Ornithoscelida-hypothesis as well as the classification of Chilesaurus remain controversial and it remains to be seen if they ever become consensus. Several re-analyses have been done whose results were both in favour and against the Ornithoscelida-hypothesis. Curiously some of these coincidentally recovered a third alternative, which is that ornithischians and sauropodomorphs are more closely related to each other than to theropods. This grouping is called Phytodinosauria, a name first conceived by Robert T. Bakker, who first speculated about such a grouping in the 1980s.

Qinornis and other Paleocene dinosaurs

The only dinosaurs who survived the End-Cretaceous mass extinction 66 million years ago were the crown-group birds. Or were they? There actually do exist fossils of non-avian dinosaurs from the Paleocene, the epoch that immediately succeeded the Cretaceous. The most famous is a hadrosaur thigh-bone from the Ojo Alamo Sandstone of New Mexico which has been dated to about 64.5 million years ago, as well as some theropod remains of the Chatham Islands of New Zealand. Did some non-avian dinosaurs survive the catastrophes at the end of the Cretaceous and live a couple of thousand or million years into the Cenozoic? It is certainly not impossible, though the evidence we have so far is not enough to confirm this. These Paleocene dinosaur fossils could be so-called reworked fossils. It sometimes happens that a fossil gets eroded out of the stone in which it originally fossilized, gets transported to a new sediment and preserved there again, making it appear a lot younger than it actually is. So far all of these Paleocene dinosaurs are only known from singular, fragmentary bones, making such a reworking likely. More compelling evidence for genuine Paleocene dinosaurs would be complete skeletons, but none have been found so far. The only dinosaurs we find in Paleogene Konservat-Lagerstätten, like the Messel Pit of Germany, are birds. In all fairness however, it should be mentioned that the original describers of the Paleocene hadrosaur femur note that the possibility of their bone having been reworked from older sediments is highly unlikely. The bedding surface was very flat, the bone very heavy and it showed no signs of abrasions or erosion, making it very likely that the animal had died on the spot and in the time it was found in, instead of the bone being transported there by water or wind (Fassett et al. 2001). 

Fig. 12: The Ojo Alamo hadrosaur femur and its geologic context. Note how high it is above the K-T Boundary.

A perhaps less exciting, though still interesting example of a surviving non-avian dinosaur is Qinornis, found in 61 million year old rocks from China. It is an avialan dinosaur only known from a hindlimb and foot, but these show very primitive characteristics that make it hard to classify as a crown-group bird (though some have proposed that the leg and foot looked primitive because the animal found was a juvenile). Based on these characteristics, Qinornis would be a basal ornithuran bird, the only one known to have survived past the Cretaceous. That said, it likely looked a lot like modern birds, with a toothless beak and pygostyle, and is a non-avian dinosaur only in technical terms. It is still fascinating and important, as it has been generally thought that all birds outside Aves went extinct in the Cretaceous, including weird forms like the toothed enantiornitheans and the penguin-like hesperornithids

Eoliths and other Geofacts

Eoliths are a type of flintstone found in Europe that bears sharp chipping edges. In the nineteenth century it had been generally assumed that these had been stone tools produced by prehistoric humans. Eoliths were however so crude that their authenticity was often doubted, as they could have easily been produced by natural processes. They were nonetheless taken seriously for a time as they were found closely associated with the infamous Piltdown Man, a supposed fossil hominin from Britain. But as it was conclusively proven that the Piltdown Man was a forgery and genuine human stone tools were found from the Olduvai Gorge in East Africa, eoliths quickly lost their status and are today recognized as geofacts, geologic artefacts of natural origin.

Fig. 13: An eolith that was once thought to have been a handaxe but is now recognized as a naturally chipped rock.

The story of mistaken stone tools does not end in Victorian times however. Nowadays we still find stories of a similar caliber, mainly from North America. This is in part because the question of when exactly the Americas were first colonized by Homo sapiens remains controversial. The classic estimate has been 16’000 years ago, though some have pushed for earlier dates like 20 to even 30 thousand years ago. There have been some that went even farther. The most recent example was a paper from 2017 about the Cerutti Mastodon Site in California, in which the researchers claim to have found evidence that the mastodon bones found at the site were broken and fractured by humans using cobblestone anvils. The site is around 130’700 years old, which is so far back in time that the humans who killed the elephants may not have even been H. sapiens, but some earlier species of Homo, such as H. erectus, Neanderthals or even Denisovans. This idea has understandably been met with criticism. There are no human remains at the site, there is no definitive sign that the cobblestone was worked by humans and the bone fractures could have been created by a number of different ways, with some researchers noting that similar patterns can even be found in dinosaur fossil beds. Similar problems are met by the Calico Early Man Site, also in California, which initially claimed to have found stone tools that are over 200’000 years old. Consequent studies have found the artefacts to have been seriously misdated, to be of natural origin and far too numerous to have been produced by early humans. There is currently no strong evidence that the peopling of the Americas goes back significantly further than about 20’000 years ago.

What we have learned

At the end of posts like these I like to make an assessment of the things we have observed. What general patterns can be seen in the discussion of fossil problematica? On the previous post a commenter mentioned to me that the study of fossil enigmas like those discussed here reminds him more of cryptozoology than of genuine paleontology. There certainly are some interesting parallels and connections, especially after we have seen at least one example of an enigmatic fossil being connected to a legendary lake monster. While I did not mention it before, the alleged ancient stone tools from Cerutti have also been connected to Bigfoot/Sasquatch by some hacks. Much like cryptids, the mystery of fossil enigmas invites rather fanciful speculation and colourful figures. Most prominently we have seen Mark McMenamin get involved and making claims that range from reasonable, like the Garden of Ediacara hypothesis, to the absurd, like the Triassic Kraken. Outside of paleontology, McMenamin has also made some adventurous claims in archaeology, such as the Carthaginians having discovered America around 250 BCE. He is a contentious figure, to say it mildly. One of McMenamin’s former mentors, Adolf Seilacher also appeared at least in two separate cases. Another reoccurring researcher was Simon Conway Morris, who dealt with at least two possible conodont-candidates. Sankar Chatterjee only appeared once, but stands out for his often criticized and rather unprofessional handling of the Protoavis remains. Outside of Protoavis he has also made similar claims, like the pseudosuchian Shuvosaurus being a Triassic ornithomimid. Arguably some parallels can be drawn between the case of Protoavis and the current discussion around Oculudentavis, a skull found in Burmese blood-amber claimed to be from a very primitive micro-bird, but now thought to have been a lizard by most researchers. When we leave fossils and come to geologic or archaeological artefacts from prehistory, such as the Klerksdorp spheres, the Oklo nuclear reactor or alleged stone tools, we leave semi-serious paleontologists/geologists behind and straight up enter the realm of pseudo-archaeology and ancient alien nonsense. Another similarity between the study of enigmatic fossils and cryptozology is people trying to interconnect fossil mysteries in order to create grand unified theories. The Ediacaran biota was connected to the Paleozoic oddballs Rutgersella and Protonympha, the bizarre Cambrian Opabinia was connected to the Tully Monster and both Odontogriphus and Typhloesus were at one point thought to have been the enigmatic conodont-animal. It is like the discussion of fossil enigmas is its own little, isolated world where the same people, objects and creatures bounce around to always form new connections. The most bizarre case has to be the fact that the mystery of the Gabonionta and of the Oklo natural nuclear reactor occurred basically right next to each other near the town of Franceville, Gabon. Though I think that is just a coincidence. I hope it is a coincidence.

All that said, most of these cases have been subject to serious, scientific scrutiny, which was eventually able to discredit most of the out-there claims. In short summary:

• Klerksdorp Spheres: Solved – Natural mineral accretions
• Gabonionta: Mostly solved – Most likely of biological origin, probably formed by early eukaryotes
• Oklo nuclear reactor: Solved – A natural fission reactor that formed thanks to unique conditions on Precambrian Earth.
• Ediacaran biota: Partially solved – Most likely an assemblage of early, sessile animals and para-animals. Exact classification of most members remains controversial however.
• Cambrian biota: Mostly solved – Largely consists of stem-group members of existing/known animal groups. Some members remain unclassifiable.
• Conodonts: Solved – Conodonts were early, jawless chordates.
• Paleodicyton: Unresolved – May be a burrow, nest or something entirely else.
• Waukesha “butterfly”: Partially unresolved: An arthropod, but of undetermined affinity.
• Rutgersella/Protonympha: Mostly unresolved – Could be related to Ediacaran biota, could also be coincidentally similar. Likely some type of fungus or lichen.
• Typhloesus: Unresolved – May be a chordate, could also be an entirely different animal.
• Tullimonstrum: Mostly unresolved – Currently considered a vertebrate by some, but this classification is highly contested.
• Triassic Kraken: Mostly solved – Most likely created by sea-currents, arguably not a mystery to begin with.
• Protoavis: Solved – a chimaera of bones from different archosaurs.
• Chilesaurus: Partially unresolved – Possibly a very primitive ornithischian that descends from theropods.
• Qinornis & Co: Partially solved – The former seems to be a genuine non-crown-group bird that survived a few million years into the Paleogene. The latter are more ambiguous.
• Geofacts: Mostly solved: Majority created by geologic processes. Paleoanthropological claims have little evidence that support them.

Out of 16 discussed cases we can consider 10 to have been fully, mostly or partially resolved. Out of the remaining 6 mysteries, 3 in particular, the Waukesha arthropod, Protonympha and Typhloesus, I think remain unresolved to this day because academic interest in them seems to be very lacking. After their initial descriptions very little work has been done on them and the discussion surrounding them has been mostly restricted to amateur online-spheres (like the very blog you are reading right now). Their identity might perhaps be easily resolved after thorough re-examinations with modern methods. Out of the other 3, Chilesaurus is a relatively new discovery, with the controversy around it being even more recent. As it is known from pretty complete remains, we can expect the mystery around it to be resolved in a few years after more analyses have been done. Tullimonstrum has been known for far longer, though scientific interest in it has only gained momentum in recent years and we might expect a similar outcome in the near future. This leaves us with Paleodicyton, whose longevity and origin I regard as truly mysterious. Even if we accept the idea that it represents a nest or a bacterial farm made by some animal, this creature would have had to have existed since Precambrian times until today not only largely unchanged but also without leaving any evidence of its body in the fossil record. The trace-maker of Paleodictyon, if it even was made by a trace-maker, could therefore be regarded as the greatest phantom in Earth’s history.

As a last note I also have to admit that my selection of fossil enigmas for these two posts has been pretty selective on my part. There are still a lot of controversial fossil animals that have gone unmentioned: Weird Triassic reptiles like Longisquama and Sharovipteryx whose classification has been all over the place at one point or another are an example, as is the story of therizinosaur-classification and the ongoing discussion around megaraptors. Recently a photograph of a Protoceratops-mummy has resurfaced that might show signs of cheeks and other facial tissues, but its skin(?) has forever been destroyed by preparation work, leaving us permanently guessing at what it actually represented. Even early fossils discoveries, such as Pterodacytlus (engulfed in a years-long debate over whether it was a flying reptile, a bird, a bat or a monotreme) or Archaeopteryx (variously interpreted by some as a derived drepanosaur, a lizard that evolved feathers convergently to birds or a flying dromaeosaur) could at one point have been considered enigmas. The most recent mystery has been the identity of the recently discovered Oculudentavis, but I consciously did not discuss it in length because I do not think it will remain a mystery for long, but also to avoid the very disheartening discussion around its very unethical discovery. While I do not plan to write a part 3, these are all things I’d like return to in one form or another at some point.

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Related Posts:

• Solved and Unsolved Fossil Enigmas - Part 1
• The weirdest things people have thought about pterosaurs 
• The Alien Prehistoric World Trope: Part 2 - Dinosaurs become movie monsters

Literary Sources:

• Barrett, Paul/ Naish, Darren: Dinosaurs. How they lived and evolved, London 2016 (2. Edition).
• Chatterjee, Sankar: The Rise of Birds. 225 Million years of Evolution, Baltimore 1997.
• Desmond, Adrian: The Hot-Blooded Dinosaurs. A revolution in Paleontology, London 1975.
• Godfrey-Smith, Peter: Other Minds. The Octopus and The Evolution of Intelligent Life, London 2017.
• Gould, Stephen Jay: Wonderful Life. The Burgess Shale and the Nature of History, New York 1989.
• Holiday, Frederick William: The Great Orm of Ness. A Practical Inquiry into the Nature and Habits of Water-Monsters, London 1968.
• McMenamin, Mark: The Garden of Ediacara. Discovering the First Complex Life, New York 1998.
• Paul, Gregory Scott: Predatory Dinosaurs of the World. A Complete Illustrated Guide, New York 1988.
• Witmer, L. M.: The debate on avian ancestry - phylogeny, function and fossils. – In: Mesozoic Birds: Above the Heads of Dinosaurs (eds. Chiappe L.M.& L.M. Witmer), Berkeley 2002, p. 3-30.

Papers:

• Paleobiology and taphonomy of exceptionally preserved organisms from the Waukesha Biota (Silurian), Wisconsin, USA by Wendruff et al.
• A New Exceptionally Preserved Biota from the Lower Silurian of Wisconsin, U.S.A.  by Mikulic et al.
• Reassessment of the Devonian problematicum Protonympha as another post‐Ediacaran vendobiont by Gregory J. Retallack.
• Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont by Gregory J. Retallack. 
• Typhloesus wellsi (Melton and Scott, 1973), a bizarre metazoan from the Carboniferous of Montana, U. S. A by Simon Conway Morris.
• The ‘Tully monster’ is a vertebrate by McCoy et al. 
• The ‘tully monster’ is not a vertebrate by Sallan et al.
• Evidence for a Triassic Kraken: Unusual arrangement of bones at Ichthyosaur State Park in Nevada by Mark McMenamin. 
• Cranial Anatomy and Relationships of a New Triassic Bird from Texas by Sankar Chatterjee.
• The first 85 million years of avian evolution by Luis Chiappe.
• Bird-like Head on a Chameleon Body: New specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of Northern Italy 
• A new hypothesis of dinosaur relationships and early dinosaur evolution by Baron et al.
• Multiple optimality criteria support Ornithoscelida by Baron et al.
• Untangling the dinosaur family tree by Langer et al. and the reply by Baron et al.
• An enigmatic plant-eating theropod from the Late Jurassic period of Chile by Novas et al.
• A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs by Baron and Barrett.
• Comment on ‘A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs' by Müller et al. and the reply by Baron et al.
• Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary
• COMPELLING NEW EVIDENCE FOR PALEOCENE DINOSAURS IN THE OJO ALAMO SANDSTONE, SAN JUAN BASIN, NEW MEXICO AND COLORADO, USA. By Fassett et al.
•  Dinosaur sanctuary on the Chatham Islands, Southwest Pacific: First record of theropods from the K–T boundary Takatika Grit
• A 130,000-year-old archaeological site in southern California, USA

Online Sources:

• Leonardo fossil sketch may depict early nests
• KU Ichnology on Paleodicyton
• Typhloesus: The 'Alien Goldfish' of Bear Gulch by Catalogue of Organisms
• C. M. Kosemen Paleo-Profile: Typhloesus, the Ultimate Paradox Organism
• ‘Tully Monster’ Mystery Is Far From Solved, Penn-led Group Argues
• The Giant, Prehistoric Squid That Ate Common Sense
• Kraken Rises: New Fossil Evidence Revives Sea Monster Debate
• The Protoavis controversy
• The Ruins of the Fabrosaur Empire by Archosaurophilia.
• Humans in California 130,000 Years Ago? Get the Facts by National Geographic
• Ancient Bones Spark Fresh Debate over First Humans in the Americas from Scientific American

Image Sources:

• Fig. 1: Wikimedia
• Fig. 2: Wikimedia
• Fig. 3: Mikulic et al. 1985, plate 2.
• Fig. 4: Wikimedia
• Fig. 5: Morris 1990.
• Fig. 6: Wikimedia
• Fig. 7: The Giant Prehistoric Squid that ate Common sense
• Fig. 8: Chatterjee 1997, cover.
• Fig. 9: Paul 1988, p. 402.
• Fig. 10: Wikimedia
• Fig. 11: Wikimedia
• Fig. 12: Fasset et al. 2001.
• Fig. 13: Wikimedia