Sunday 17 March 2024

Paleopods: The Myth of the Predatory Prosauropods that kinda turned out to be true

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 If these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scientific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 Out-of-date- theories are not in principle unscientific because they have been discarded.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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Image sources:

  • Fig. 2: Jackson & Matternes 1972, p. 8.
  • Fig. 3: Hutchinson 1910, Plate XVII.
  • Fig. 4: Moody 1977.
  • Fig. 5: Colber 1964.
  • Fig. 6: Wikimedia
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  • Fig. 9: Martinez & Alcober 2009.
  • Fig. 10: Hallett & Wedel 2016, p. 21.
  • Fig. 11: Wikimedia
  • Fig. 12: Wikimedia