“The more carefully
they [historians] study, say,
Aristotelian physics, phlogistic chemistry, or caloric thermodynamics, the more
certain they feel that those once current views of nature were, as a whole,
neither less scientific nor more the product of human idiosyncrasy than those
current today. If these out-of-date beliefs are to be called myths, then myths
can be produced by the same sorts of methods and held for the same sorts of
reasons that now lead to scientific knowledge. If, on the other hand, they are
to be called science, then science has included bodies of belief quite
incompatible with the ones we hold today. Given these alternatives, the
historian must choose the latter. Out-of-date- theories are not in principle
unscientific because they have been discarded. That choice, however, makes it
difficult to see scientific development as a process of accretion.”
-Thomas Kuhn in The
Structure of Scientific Revolutions
Fig. 1: Zanclodon,
a dubious taxon only known from teeth, deliberately mis-reconstructed by me as a
carnivorous prosauropod. I added horns because horns are cool.
Paleontology, by virtue of its nature, is a science that
deals with incomplete evidence and extrapolations based on those. This has sometimes
led to things one might call “phantom taxa”, whole groups or types of organisms
that were once thought to exist based on fragmentary evidence that then later
turned out to have been entirely man-made constructs. These are not the same as
a simple phylogenetic misinterpretations. For example, therizinosaur theropods used
to be called segnosaurs and were once interpreted by more than one researcher
as plateosaur-type sauropodomorphs that somehow survived into the Cretaceous. While
this turned out to be wrong, the underlying fossils still were those of a very
real group of saurischian dinosaurs that has simply changed position in that
family tree. In a different example, the mammal order Insectivora is now widely
recognized as an unnatural grouping, but all of its once-constituent clades,
such as shrews and golden moles, obviously still exist. A “phantom taxon” is
instead something that arises from much more fundamental mistakes in the
assessment of the fossil evidence at hand. One of the more dramatic examples in
recent years was the idea that Cretaceous Gondwana was once home to a group of
giant, late-surviving dicynodonts (conventionally thought to have gone extinct
at the end of the Triassic) that took up a similar ecological role as the
contemporary ceratopsian dinosaurs in Laurasia. This idea was based on fossils
from Australia interpreted as such (Thulborn & Turner 2003). While the idea
is, frankly, pretty awesome and the remains did indeed come from synapsids, a recent
reassessment found that the geological layer they were found in was not at all
Cretaceous in age but instead dated to the Pleistocene, the bones probably
coming from giant ice age marsupials similar to Diprotodon (Knutsen & Oerlemans 2020). With one fell swoop, a
whole potential taxon of Cretaceous dicynodonts has evaporated, reduced now to
a curious footnote in history. A related example is that some researchers of
the early twentieth century believed that non-avian theropods may have survived
some time into the Cenozoic of South America (Ameghino 1906), based on teeth
that later turned out to have belonged to sebecid crocodylomorphs.
Today we take a look at just such a “phantom taxon”, but one
which has had a very long stay in mainstream publications and even influenced
earlier ideas of dinosaur taxonomy. This makes it all the more mysterious that
this taxon is today remembered by almost nobody but the most hardcore of
dino-nerds. I am talking about a group interchangeably called either
Palaeopoda/Paleopoda, Palaeosauria or Teratosauria. The idea of the paleopods
was that of large, carnivorous dinosaurs existing during the Triassic, which
were interpreted as either predatory off-shoots of the sauropodomorphs, direct
ancestors of Jurassic mega-theropods like Megalosaurus
and Allosaurus or even both!
Disclaimer: While it is technically an outdated term, for
this post I will still refer to all non-sauropod sauropodomorphs as
“prosauropods”, because it is simply quite useful.
Setting the stage: Early dinosaur classifications and the
prosauropods
Prosauropods, especially the bipedal kind, are not just
underappreciated but also quite peculiar dinosaurs, in that they seem to
combine traits from all of the three major dinosaur groups. Combined with their
great age, they therefore play a crucial role in the wider-scale classification
of dinosaurs, one which was majorly coloured by the concept of the palaeosaurs.
Prosauropods were known from the fossil record before the
word dinosaur even existed. Bones of classic Plateosaurus from
Heroldsberg were already known in 1834 and described by Hermann von
Meyer in 1837, who classified it as some huge saurian. The small prosauropod Thecodontosaurus
was described one year earlier by Henry Riley and Samuel Stutchbury from rocks
of South England. Alongside Thecodontosaurus
they also described two species based solely off single teeth (probably
from phytosaurs): Palaeosaurus platyodon and
Palaeosaurus cylindrodon. Both genera
were interpreted by them as carnivorous squamates or, in other words, big
lizards.
The first attempt at naming that which we now consider
dinosaurs was made in 1932, before Plateosaurus
was known, when Hermann von Meyer united Megalosaurus and Iguanodon in
a group he (only years later) called Pachypoda (Huxley 1870a). When Richard Owen created the Dinosauria in 1842, none of the aforementioned
prosauropod taxa were included. The original genera that made up the Dinosauria
were only Megalosaurus,
Iguanodon and Hylaeosaurus. Plateosaurus
was not mentioned, as Owen named the Dinosauria in a paper that only dealt
with British reptiles, while Thecodontosaurus
and Palaeosaurus were classified by Owen as just some
nondescript “thecodonts”. In the same publication, Owen assigned body
fossils to Palaeosaurus, giving the tooth-taxon a body (which later
turned out to actually be just more Thecodontosaurus remains). With
this, Owen arguably began a long tradition of uniting the teeth of predatory
Triassic reptiles with the postcranial fossils of prosauropods. The exclusion
of prosauropods from the dinosaurs was, from a certain point of view,
rectified in 1845, when Von Meyer expanded his Pachypoda to include Megalosaurus,
Iguanodon, Hylaeosaurus and Plateosaurus.
Fig. 2: Depiction of Teratosaurus
(far left) as a carnosaur, from a 1972 children’s book.
In 1861 emerged another big player in this story, when Von
Meyer first described a toothed maxilla found in Stuttgart. Clearly coming from
a large, predatory reptile, Von Meyer considered it to be one of the
pachypodes, likely related to Megalosaurus, and named it Teratosaurus suevicus.
Many remains that had previously been referred by Theodor Plieninger to Belodon were considered to be referrable
or related to Teratosaurus instead, including
the Swiss prosauropod Gresslyosaurus
(Huxley 1870a).
The first to propose an internal classification scheme for
the dinosaurs was Edward Drinker Cope in 1866 (later worked out in more detail
in 1883). According to Cope, Dinosauria consisted of the following groups:
- Orthopoda (encompasses Scelidosaurus, Hylaeosaurus,
Iguanodon and Hadrosaurus)
-
Goniopoda (enc. Megalosaurus,
Laelaps [Dryptosaurus] and Coelosaurus
[indet. ornithomimid])
-
Symphopoda (named Hallopoda in 1883, enc. Compsognathus and Ornithotarsus [indet. hadrosaurid])
As you can see, prosauropods were not considered in this
classification, while true sauropods (later named Ophistocoela by Cope), still
called cetiosaurs, were thought to be more closely related to crocodilians, as
per Owen. In 1870, Thomas Henry Huxley criticized this scheme on the grounds
that the details of the ankle-bones that Cope used to distinguish orthopods
from goniopods were not sufficient. Huxley instead divided Dinosauria into
three families that clearly reflected Owen’s original definition: Megalosauridae,
Iguanodontidae and Scelidosauridae. Compsognathus
he found to be distinctive enough to be its own thing outside of dinosaurs
proper, but still closely related. The resulting new order of
Dinosauria+Compsognatha he christened Ornithoscelida (“bird-legs”). Huxley
is often stated to be the first to propose that the birds descend from
somewhere within this order, but it should be mentioned that Cope (1867) had
already observed the close relationship between birds and dinosaurs, which
Huxley (1870b) even utilized for his argument, feeling glad and reassured that
“so able an anatomist as Prof. Cope should have been led by the force of
facts to arrive, simultaneously with myself, at conclusions so similar in their
general character with my own.” (Huxley 1870b).
What is fascinating is that, even if it does not look that
way, Huxley was acutely aware of Von Meyer’s Pachypoda. Consequently, prosauropods
and sauropods were included within Ornithoscelida, but split up and shoehorned into
the aforementioned dinosaur families (which I imagine opens up a whole can of
worms for the modern usage of that term as a hypothetical clade name for
Theropoda+Ornithischia). Palaeosaurus and
Teratosaurus were classified by him
within the Megalosauridae. Thecodontosaurus
was put in the Scelidosauridae and
Cetiosaurus in the Iguanodontidae
(that sauropods were long-necked quadrupeds was
not yet known). Plateosaurus was
included by Huxley in the Dinosauria in an earlier lecture, though without
being assigned to a family (Huxley 1870b). Based on his comments on two
skeletons found by Theodor Plieninger in Württemberg, it appears that he
considered these remains (which later turned out to be Plateosaurus) as the bodies that would have attached to the
carnivorous jaw of Teratosaurus (Huxley 1870a), thus again uniting
prosauropod bodies with jaws and teeth of a carnivorous Triassic reptile. This
extended to the two species of Palaeosaurus. The tooth of P. platyodon he
considered to simply belong to Thecodontosaurus, but he found a close
similarity between the tooth of P. cylindrodon and those of Megalosaurus,
hence why he placed the genus in the Megalosauridae (Huxley 1870a). Various
Triassic tooth-taxa, such as Zanclodon and Cladyodon were also
referred by Huxley to Megalosauridae.
Thus, we can
observe the emergence of two general developments by the 1870s. First, there is
the tendency to associate teeth of predatory Triassic reptiles with the bodies
of prosauropods. Second is the belief that megalosaur-type dinosaurs already
existed in the Triassic. Three further taxonomic revisions would cement these
ideas.
Marsh’s Theropoda vs. Von Huene’s Pachypodosauria
In a series of memoirs dating from 1878 to 1884, Othniel
Charles Marsh offered a different model of dinosaur classification. These are
the names you are all familiar with:
- Stegosauria (also
included other armoured dinosaurs like scelidosaurs)
-
Ornithopoda
-
Sauropoda
-
Theropoda
“These names
proposed by Marsh, rather than the names proposed by Cope, are still in use for
four of the six suborders of dinosaurs recognized today, a fact that must
disturb the unquiet spirit of Cope in its eternal sojourn beyond the far banks
of the Styx.”, to quote the eloquent Edwin Colbert (1968, p. 98). Very
fascinating is what Marsh considered the Theropoda to include:
- Megalosauridae
-
Compsognathidae
-
Ornithomimidae
-
Hallopodidae (later turned out to be crocodylomorphs)
-
Plateosauridae
-
Anchisauridae
Most surprising to
us today is that the typical prosauropods were here considered to be theropods.
Indeed, Marsh describes the North American Anchisaurus as an early
carnivore, based on the serrations of its teeth (Marsh 1896). Apparently
feeding on meat yet having small heads compared to later theropods, it became a
popular notion that these small prosauropods were scavengers of the Triassic
wastes (Norman 1985). This of course fit very well with the idea that there
were also larger carnivorous types, teratosaurs, running around during this
time, probably of the more active, predatory kind.
Fig. 3: The small
prosauropod Anchisaurus, depicted
here in 1910 by Joseph Smit as a carnivore preying on small mammals.
In 1887/1888, Harry
Govier Seeley made a long-lasting choice: Based on the difference in the shape
of their pelvis, as well as the presence or absence of skeletal pneumaticity,
he recognized that Marsh’s Stegosauria and Ornithopoda were distinctly
different from Theropoda and Sauropoda and therefore had to be split apart from
them. The former two he thus grouped together in the Ornithischia (bird hips),
the latter two in the Saurischia (lizard hips), the two “grand clans” of
dinosaurs you are all familiar with. However, he found the differences between
the two to be so significant that he did not think they shared a close common
ancestor, instead having developed in parallel out of unrelated “thecodonts”.
This made Dinosauria a polyphyletic (unnatural) grouping and reduced it to
merely an informal term for big Mesozoic reptiles (which may have had an
influence on the misconception many laypeople still have that plesiosaurs,
pterosaurs and such are also dinosaurs). Though the word dinosaur remained
popular, its invalidity in academic circles proved to be tenacious. Until the
late 1970s one can still find educational books confidently stating that there
technically is no such thing as a dinosaur (McLoughlin 1979 for example).
What is significant
for what we are talking about today is that Seeley’s creation of Saurischia
moved the Theropoda and Sauropoda closer together. For some, the close
relationship seems to have blurred the lines. In 1914, Friedrich von Huene
split up the Saurischia into two groups that cut right across Marsh’s
Theropoda. One group consisted of Coelurosauria, which was not the same as the
Coelurosauria you are today familiar with (a specific clade of feathered
dinosaurs from the later Mesozoic, which includes Velociraptor, T. rex and
birds). Instead, Coelurosauria consisted of all the small bipedal
carnivorous dinosaurs and can be imagined as one big lineage starting in the
Triassic with forms like Coelophysis and ending in the Cretaceous with forms like
Struthiomimus. The other big group of Saurischia, which included the big
carnivores and the sauropods, was Pachypodosauria, probably named in
reference to Von Meyer’s Pachypoda. In a series of papers ranging from 1928 to
1956, Von Huene further subdivided Pachypodosauria into three major groups:
Marsh’s Sauropoda, the Carnosauria and the Prosauropoda.
Carnosauria consisted of all the big theropods, from Megalosaurus and
Dilophosaurus to Tyrannosaurus. As the carnosaurs were imagined
by him as more closely related to the prosauropods than to the coelurosaurs, it
must have been no wonder that genera like Teratosaurus and Palaeosaurus,
who appeared to have plateosaur-like bodies combined with megalosaur-like
teeth, seemed to him like perfect transitional forms. This was further aided by
the fact that Von Huene assigned additional bone material to both Teratosaurus
and Palaeosaurus, even erecting new species inside them with T. minor and P. diagnostica.
These new species later turned out to actually be based on the bones of
prosauropod Efraasia (Galton 1984).
Fig. 4: Thecodontosaurus, depicted here as an omnivore scavenging
carcasses, from a 1978 children’s book.
Von Huene’s split of Saurischia into Coelurosauria and Pachypodosauria
was not accepted by most workers, but it did leave an impact. In his papers and
textbooks from the 50s, famous vertebrate paleontologist Alfred Sherwood Romer
maintained the more conservative subdivision of Saurischia into Marsh’s
Theropoda and Sauropoda, however, he subdivided Theropoda into the groups
created by Von Huene:
- Coelurosauria
-
Carnosauria
-
Prosauropoda
And this was largely followed by most researchers the following
decades. The subdivision of the theropods into a uniform “big” and a uniform
“small” group brought with it quite some implications. It meant that one group
never arose from the other and that they instead only share a common ancestor.
Since coelurosaurs were already present in the Triassic with forms like Coelophysis,
it meant the split must have happened earlier and that carnosaurs like Megalosaurus
and must have also had Triassic ancestors that resembled them. Thus was
born the myth of Teratosaurus as the first carnosaur, which menaced the
Triassic fabrosaurs and plateosaurs much like its later descendant T. rex
would do with the herbivores of its time.
Divorcing the Carnosauria from the Palaeopoda
In 1964, Edwin Colbert began to doubt this standard model. Taking
a close look again at the pelves, like Seeley had done, he recognized that
Saurischia could be broadly divided into two main groups: Those who are
brachyiliac (they have a short ilium) and those who are dolichoiliac (they have
a long ilium). Dolichoiliac saurischians, like the coeulurosaurs, evolved this
adaptation because they permanently stood on only two legs, like birds.
Brachyiliac saurischians (prosauropods and sauropods) have a shorter ilium
because they are less well adapted towards bipedalism and instead walked, at
least on occasion, on all fours. Colbert’s observation was furthermore that the
Triassic “carnosaurs” were brachyiliac, while the Jurassic and Cretaceous ones
were dolichoiliac like the coelurosaurs. This led him to conclude:
“It is herein proposed that the name “Carnosauria” be
restricted to these large Jurassic and Cretaceous carnivores of coelurosaurian
origin, and that the large carnivorous dinosaurs of the Triassic be recognized
for what they are, namely, an antecedent and independent adaptation for a
predatory mode of life among the brachyiliac group of saurischians. These
dinosaurs might very logically be designated as Palaeosauria, to
distinguish them from their brachyiliac relatives, the prosauropods or
plateosaurs.” (Colbert 1964, p. 18, emphasis mine).
Palaeosauria, along with Plateosauria, became an infraorder
inside a new suborder which Colbert named Palaeopoda.
Within Palaeosauria he included the families Palaeosauridae, Teratosauridae
and, interestingly, also Ammosauridae (another name for Anchisauridae).
Probably following Marsh’s original suggestion of Anchisaurus as a scavenger, the “palaeosaur-lore” therefore
expanded to include these prosauropods as a the palaeosaur’s very own radiation
of smaller carnivores. Colbert’s vision of the saurischian family tree looked
as follows:
Fig. 5: Colbert’s family tree of the Saurischia. As you can
see, all the branches sandwiched between Melanorosauridae and Podokesauridae are
considered Palaeopoda, with Palaeosauria being that group’s carnivorous branch.
In 1970, Colbert would rename Palaeosauria into Teratosauria. Interestingly,
Colbert thought (adhering to Seeley’s idea of dinosaur polyphyly) that the
saurischians descended from pseudosuchians like the ornithosuchids and
erpetosuchids.
Colbert also provides us with a reason for why these
carnivorous prosauropods did not make it past the Triassic:
“The palaeosaurs were, by the nature of their skeletons
more “clumsy” than were the carnosaurs, and probably were ill fitted for
survival in a changing world. There is no record in the rock sequence that
shows any contemporaneous existence of palaeosaurs and carnosaurs, for which
reason, among others, it has been supposed that the one group was ancestral to
the other. It seems more logical, however, in view of the structural
resemblances of the palaeosaurs to the prosauropods and of the carnosaurs to
the coelurosaurs, to regard the large Jurassic carnivores as replacements of
and not as descendants from the palaeosaurs, as has been argued. Thus the
palaeosaurs, the large carnivorous dinosaurs of the Triassic period, seem to
take their place in reptilian history as a brief and sterile experiment in
adaptation for predation. They were successful for a time, but, as reptilian
life became more complex during the transition from the Triassic to the
Jurassic (very significant changes were involved during this crucial aspect of
tetrapod evolutionary history), it appears that the palaeosaurs could no longer
hold their own, and they disappeared, while their place and their functions in
the ecology of those distant times were taken over by the better adapted
carnosaurs.” (Colbert 1964, p. 19).
While the idea that the “carnosaurian” theropods were really
just overgrown versions of the “coelurosaurian” theropods would eventually
catch on and be proven right from a certain point of view, the concept of the
palaeosaurs as a dead-end of predatory prosauropods has seen remarkably little
reception, especially when it comes to paleoart. All the way into the 80s, most
textbooks and children’s books went with the more Romerian standard model of
carnosaurs already existing as their own theropod group in the Triassic. Thus,
the overwhelming amount of depictions of Teratosaurus
still showed it as just some stockier, more archaic version of Neave
Parker’s Megalosaurus. Finding any
art that actually shows Teratosaurus or
Palaeosaurus as Colbertian palaeopods
has been remarkably difficult. This might have been because, also in 1964,
Alick Walker observed that none of the alleged palaeosaur skull material could
be definitely linked to the assigned postcranial remains and therefore the
latter should be considered to come from more ordinary prosauropods. This left
only the Ammosauridae standing inside Colbert’s Palaeosauria. While prescient
in that regard, in the same paper, Walker interestingly also considered the
fairly complete croc-line archosaur Ornithosuchus
to be an early carnosaur, alongside Teratosaurus and Sinosaurus, thus giving
new strength to the idea of Triassic carnosaurs.
The complicated death-throes of Palaeosauria
Fig. 6: Torvosaurus
tanneri, apparently once considered as a transitional form between
prosauropods and megalosaurs. Sure, why not?
The concept of palaeopods and Triassic carnosaurs proved to
be surprisingly tenacious, even through the Dinosaur Renaissance of the 70s. Indeed,
the 1979 description of the Jurassic giant megalosaur Torvosaurus tanneri from the famous Morrison Formation seems to
have actually tried to revive Von Huene’s idea of the Pachypodosauria. Peter
Galton and James Jensen’s original paper reads:
“In Torvosaurus the ilium is dolichoiliac, but the pubis and ischium are brachyiliac.
This is the first demonstration of this combination in a carnosaurian theropod
from the Upper Jurassic. Bonaparte (1969, p. 480) noted that “the evidence for
linking the Carnosauria with the Coelurosauria (Colbert 1964; Charig and other
1964) is as ambiguous as that linking that linking the Carnosauria with the
Prosauropoda (Huene 1956; Romer 1956).” It should be noted that the division of
the Theropoda into the Coelurosauria and Carnosauria may be artificial (Ostrom
1969, 1978) because Upper Jurassic theropod Compsognathus (family Compsognathidae) is very small, yet it has
many carnosaurlike characters (Ostrom 1978), and the Cretaceous family
Dromaeosauridae show a combination of coelurosaurian and carnosaurian
characters (Ostrom 1969). Colbert and Russell (1969) erected a third theropod
infraorder, the Deinonychosauria, for the last family that probably originated
from a line close to the Upper Jurassic coelurid Ornitholestes (Ostrom
1969). We suggest that the anatomy of the pubis and ischium of Torvosaurus
strengthens the case for regarding the Jurassic Megalosauridae (and the
Carnosauria if this is a natural group) as descendants of the Prosauropoda
rather than of another theropod currently included in the Coelurosauria.
It should be noted that the form of the humerus and phalanx 1 of digit 1 of the
manus of Torvosaurus is more similar to those of prosauropods than those
of coelurosaurs.” (Galton & Jensen 1979, emphasis mine).
Fig. 7: John McLoughlin’s
depiction of Teratosaurus, again as a carnosaur, from his infamous 1979
book Archosauria. It stands out for its quite weird head.
Until 1985 one could also still find books which depicted Teratosaurus and Ornithosuchus as the first carnosaurian dinosaurs.
But the cracks already started to show in 1984, when Peter Galton showed that
the maxilla bone of Teratosaurus suevicus
was not even from a dinosaur, but a rauisuchid, a type of archosaur more
closely related to crocodilians. The other bones assigned to it came from
unassociated prosauropods that were probably of the type Plateosaurus or Efraasia.
One year later, Michael Benton came to the same conclusion in an independent
study. In said paper, he also takes a look at the other supposed carnosaurs:
“The genera other than Teratosaurus that have been
called middle to late Triassic or early Jurassic carnosaurs include such forms
as Palaeosaurus and Cladeiodon from England, Palaeosaurus,
Zanclodon, and Gresslyosaurus from Germany, Orosaurus, Aetonyx,
and Gryponyx from South Africa, Zatomus from North America, and Sinosaurus
from China (Romer 1956). The type specimens of Palaeosaurus and Cladeiodon
from England, and Zatomus, are teeth and, as such, they cannot be
assigned with certainty to a particular group of dinosaurs or thecodontians: they
are effectively indeterminate (Charig et cd. 1965). Palaeosaurus from
Germany is an anchisaurid prosauropod renamed Efraasia (Galton 1973).
The type specimens of the several species of Zanclodon are teeth, again
indeterminate. Gresslyosaurus is a large prosauropod dinosaur, and Orosaurus
has been synonymized with the large prosauropod Euskelosaurus (Van
Heerden 1979). Aetonyx and Gryponyx are also prosauropod
dinosaurs, probably identical to Massospondylus (Galton and Cluver
1976). Sinosaurus was based on a maxilla with teeth (dinosaur or
thecodontian?) and postcranial remains very like those of a melanorosaurid
prosauropod (Charig et al. 1965) [Today, after an additional, more complete
specimen was found, Sinosaurus is
considered to have been a dilophosaur-like theropod]. This leaves no
convincing evidence of large carnivorous dinosaurs in the Triassic.”
(Benton 1985, emphasis mine)
Furthermore, several experts were now coming to the
conclusion that that Anchisaurus and
relatives were clear herbivores (Norman 1985). This debunked the final vestiges
of the Palaeosauria. While some papers (namely Kurzanov 1989) were still citing
the original placement of Torvosaurus as
a transitional form between prosauropods and megalosaurs, the idea received
little further attention and eventually went extinct. It was replaced by the
realisation that there never were large, predatory dinosaurs during the
Triassic, only herbivores and small carnivores. The ecological role that would
later be taken up by the “carnosaurs” was instead occupied by various lineages
of pseudosuchians, crocodile-relatives such as the rauisuchids and poposaurids.
Only after their extinction at the beginning of the Jurassic were the small
theropods even able to grow in size and become formidable predators themselves.
Though, based on this, the idea of Triassic carnosaurs was revived one last
time in 1985 when Sankar Chatterjee suggested that exactly these pseudosuchians,
namely Postosuchus, were the ancestors of Carnosauria,
making Dinosauria polyphyletic (which was already anachronistic at the time).
But, for obvious reasons, we should leave it at that.
Fig. 8: Peter Zallinger’s depiction of Teratosaurus from his book Dinosaurs
and Other Archosaurs. Being released in 1986, this likely makes it the last
major work to depict Teratosaurus as
a dinosaur.
Possibly the last mention of Palaeopoda in a major
publication was Gregory S. Paul’s Predatory
Dinosaurs of the World, which succinctly reiterates the whole story so far:
“But closer investigation invariably shows that these are
the skeletons of herbivorous prosauropod dinosaurs, mixed in with the teeth and
skull parts of predatory thecodonts or dinosaurs. What often happened is that
predatory thecodonts or dinosaurs shed some of their teeth while they were
killing or feeding on a herbivore. Or, in the case of Teratosaurus, the skull bones turned out
to be those of a big rauisuchid thecodont. Never has a predatory skull actually
been found attached to a prosauropod neck, nor will one ever be since a bulky
herbivore’s body is wholly unsuitable for a hunter. The worst of these mix-ups
are claims that some of the early giant brontosaurs had predatory heads. The
supposed “predatory prosauropods” were often called paleopods, but since they
never really existed the title is best dropped.” (Paul 1988, p. 237
- 238)
Ironically, this section is then followed by Paul’s markedly
aged claim that the segnosaurs (therizinosaurs if you remember) should not be
counted among the theropods but instead were descendants of the prosauropods,
but well, that is the nature of science. I was intrigued by the mention of
there having been proposals of sauropods proper having carnivorous heads. I
actually emailed Paul, asking what he was referring to there at the time. He
kindly replied. Apparently when Early Jurassic sauropod Vulcanodon was first found, it was associated with blade-shaped
teeth, which caused it to originally be classified as a prosauropod. Said teeth
later turned out to have come from a theropod that was scavenging on the
carcass, a tale as old as time as we have now seen.
But wait, weren’t there actual predatory prosauropods?
Fig. 9: Panphagia
protos, an early sauropodomorph with carnivorous traits, albeit a quite tiny one.
… is the question you may be asking yourself at this point.
And indeed, you would be right. As it turns out, there were carnivorous
sauropodomorphs after all. Many of the basalmost prosauropods that have been
discovered since the 90s, namely Panphagia,
Buriolestes, Saturnalia, Pampadromaeus and
Eoraptor clearly have teeth adapted
towards a carnivorous or at least omnivorous diet. Indeed, they look so much
like early theropods that this was what Eoraptor
was originally classified as. These being some of the earliest-diverging
sauropodomorphs interestingly also puts them on roughly the same position on
the family tree as Colbert’s original Palaeosauria (though these genera do
not actually form a monophyletic clade). But these were all pretty tiny
animals, even smaller than Anchisaurus, not exactly comparable to the original vision of palaeosaurs as macropredators.
Indeed, it appears that the early carnivorous sauropodopmorphs were probably
not capable of competing with the pseudosuchians and first theropods for
predatory niches, which is why they tended to evolve more and more towards a
herbivorous diet. Though some of their descendants may still have been
partially omnivorous, as the teeth of Plateosaurus
have been interpreted by some researchers as resembling those of modern
omnivorous lizards.
Fig. 10: Staurikosaurus, a small herrerasaur, drawn here by Mark
Hallett.
Where things get really funky is Herrerasauria. Why? While
most people may know Herrerasaurus
and Staurikosaurus as archaic
theropods, various researchers of the 60s and 70s (Rozhdestvensky &
Tatarinov 1964; Van Heerden 1978) actually classified them as examples of
predatory sauropodomorphs. Edwin Colbert (1970) in fact classified all of them
within the Teratosauria, making them a firm part of the “palaeosaur-lore”,
indeed the only part that is not based on chimaeras or misidentified herbivores.
This history has largely been forgotten, because, like I mentioned, most later
paleontologists considered them to have obviously been early theropods.
However, with the discovery of even more herrerasaurians,
most cladistic analyses over the past few years have actually recovered a far
more interesting place for them on the family tree. While indeed predatory
dinosaurs (and not pseudosuchians like some have proposed), they seem to have
been outside Theropoda, instead being
their very own group of early saurischians (Novas et al. 2021). The notorious
Ornithoscelida-paper (Baron et al. 2017) even recovers them as the sister-group
of the Sauropodomorpha, putting them again suspiciously close to the vacant
spot left behind by Colbert’s debunked Palaeosauria/Teratosauria. And unlike
the true carnivorous prosauropods, herrerasaurs could actually grow
considerably big. One of the largest found specimens of Herrerasaurus ischigualastensis may have come from an individual
that was an impressive 6 metres in length (Sereno & Novas 1992). Indeed,
until the late 2000s, there even existed the belief that the Triassic had
giant, allosaur-sized herrerasaurs in the form of South African Aliwalia rex, but those bones later turned out to have actually come from herbivorous prosauropod Eucnemesaurus (Yates 2007), which ironically had also once
been part of the “palaeosaur-lore”.
Fig. 11: Herrerasaurus
ischigualastensis, a (for its time) quite impressive and formidable
carnivore. Might it have been a true palaeosaur?
So, in conclusion,
does Palaeosauria live on through the Herrerasauria? Well, obviously not in the
strictest sense, as herrerasaurs were not actually sauropodomorphs… though
Thomas R. Holtz (2017) has actually proposed that, if Baron et al.’s
classification were true, Sauropodomorpha should be redefined to include
herrerasaurs (basically being defined as everything more closely related to Diplodocus than to theropods) or that their “new” Saurischia clade should be
named after Von Huene’s Pachypodosauria. Ignoring Holtz and the
Ornithoscelida-hypothesis, herrerasaurs and the concept of the palaeosaurs
still overlap with each other in the sense that the former were once considered
part of the latter and indeed represent an independent radiation of
macropredatory dinosaurs outside of Theropoda. At least it seems that way at
this point in time. With my luck, a brand-new study will probably be released
tomorrow that overturns everything I just wrote.
One last thing...
Believe it or not, palaeosaurs may have made at least one movie appearance. In 1959 there released the British-American monster movie The Mighty Behemoth. It is, essentially, a copycat of The Beast from 20'000 Fathoms, which itself was an adaptation of the Ray Bradbury novel The Fog Horn. Both movies were even made by the same director, Eugène Lourié. Whereas the monster in Fathoms is a fictional species, "Rhedosaurus", the titular Behemoth is classifed by a scientist in the film as a Paleosaurus which at one point was an alternate name for Palaeosaurus. It is a quadrupedal carnivore with a long neck. This may indeed be a genuine attempt at portraying a predatory sauropodomorph, though this could also be a coincidence, the monster obviously being a stand-in for the also quadrupedal Rhedosaurus. Given that the dinosaur is also marine, electric and radiation-filled, I do not think any attempt was made to adhere to current science and the name could just be a coincidence. The stop-motion was done by Willis O'Brien though, so that is always a plus, even if he apparently did it with a limited time and budget. It was one of the last movies he worked on.
Fig. 12: At long last, paleosaur-art.
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Fig. 11: Wikimedia
- Fig. 12: Wikimedia
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