27 08 2007

One of the aspects I love about the American Museum of Natural History is that no matter how many times I visit, there’s always something new for me to discover, usually something I had previously overlooked. Such was the case during my last visit, as I just happened across a little white skeleton embedded in red sediments. It was the skeleton of Protosuchus.

Skeleton of Protosuchus at the AMNH.

Although it was new to me, however, the remains of the small basal crocodile aren’t fresh out of the ground at all. In 1951, Edwin Colbert and Charles Mook published the paper “The ancestral crocodilian Protosuchus” in the Bulletin of the AMNH, v. 97, although the story of the discovery of this relatively small predator go back to 1930. In that year, the paper tells us that a Navajo Indian discovered the fossil that would eventually be named Protosuchus in an area northeast of Cameron, Arizona. The find was brought to the attention of Hubert Richardson, who owned a trading post in Cameron and was a friend of the famed fossil-hunter Barnum Brown. The following year (1931), Brown visited the site and was able to collect four specimens, all within close proximity (20 feet) to each other, deciding to name the fossil archosaurs Archaeosuchus richardsoni. The fossils were sent back to the AMNH for study, and Brown later returned in 1934 to collect two more specimens from the locality, although by this time it had become known that the genus Archaeosuchus was already occupied by a fossil the famous South African paleontologist Robert Broom had named in 1905. The genus name was thus changed to Protosuchus, and the species name richardsoni remained, honoring the man who gave Brown the tip (a great tradition in paleontological nomenclature).

Part of the problem with Protosuchus, however, was that it was not properly described for nearly two decades. In 1933 Barnum Brown did issue a short communication entitled “An Ancestral Crocodile” in the American Museum Novitates no. 638 describing “Archaeosuchus” and attempting to establish the Archaeosuchidae as a new family, but the paper merely consists of a short summary and three photographs of a wonderfully preserved specimen Brown had unearthed.

Brown’s “Archaeosuchus” (=Protosuchus) from “An Ancestral Crocodile“, American Museum Novitiates no. 638.

Despite this initial release, however, Brown never followed-up with a more detailed study, which had to wait for the diagnosis of Colbert and Mook. Although the exact position of the fossil could be disputed at the time (strong cases could be made for Late Triassic or Early Jurassic, Protosuchus now being considered to be of Early Jurassic age), one thing was certain; Protosuchus was a crocodilian and a basal one at that. Although it had previously been grouped in now-defunct taxonomic wastebaskets, it was clear to the researchers that Protosuchus, if not directly ancestral to later crocodilians, at least represented the type of animal that was ancestral to later forms.

Reconstruction of Protosuchus from “The ancestral crocodilian Protosuchus” Bulletin of the AMNH v. 97, article 3. The well-preserved rows of scutes along the back are not pictured (see illustration from Brown’s paper, above).

Although there are many aspects of the skeleton of Protosuchus that link it to later crocodilians, certain aspects of its skull are quite different from modern forms. Living crocodilians typically have their orbits on the top of their skull, the skull being adapted so only the eyes and nostrils are above water when crocodilians want to see but do not want to be seen. In Protosuchus, however, the eyes are more towards the side of the skull and in a more forward position, the opening at the back of the skull also being much larger in relation to the size of the orbits than in many living crocodilians as well. Protosuchus also looks a bit snub-nosed, lacking the long grin bristling with teeth made famous by large crocodiles in Africa and Australia. Protosuchus lacks a preorbital fenestra, as well, or a large opening in the skull in front of the eye that is so commonly seen in the skulls of theropod dinosaurs, and Colbert & Mook note that such a condition is a specialization seen in crocodilians, making Protosuchus more derived from its “thecodont” ancestors.

Dwarf Caiman
A Dward Caiman at the Reptile House of the Bronx Zoo. The skull is a bit deep dorso-ventrally than other crocodilans compared to the rest of the body, but it still is useful in illustrating the transition of the eyes to the top of the head as an adaptation to a aquatic/semi-aquatic lifestyle.

As discussed in a recent post about Phytosaurs (creatures that occupied the niche crocodiles do today, only much earlier) however, crocodiles as we know them today would not show up until the Cretaceous, many of the all-too-often forgotten crocodilans and their relatives being rather fierce and terrifying terrestrial predators (see Darren Naish’s treatment of the nightmarish Sebecosuchians). As far as Protosuchus goes, however, C.E. Gow’s 2000 paper “The Skull Of Protosuchus haughtoni, An Early Jurassic Crocodyliform From Southern Africa,” the clade to which Protosuchus and its close relatives belong underwent little change from the Early Jurassic to Early Cretaceous, likely remaining terrestrial predators rather than transitioning into the water.

As is evident from this post, however, I’m no expert on crocodilian evolution, and I have a lot left to learn. Even so, there are plenty of absolutely exquisite fossils like those of Protosuchus that are often overlooked, hidden in plain sight in museum galleries. I can only imagine what might be waiting in dusty basements, forgotten storage containers, and other out-of-the-way places, as there always seem to be far more fossils to study than paleontologists to study them. In any event, while superficial in detail, this post serves as a snapshot of an interesting group of animals now long gone, but I hope to be able to build connections to it mentally as I learn more. Next stop, Postosuchus….



6 responses

27 08 2007
Zach Miller

Love those early crocodilians. I printed both AMN papers, and I look forward to reading them.

27 08 2007
Zach Miller

My friend Scott Elyard (of Coherent Lighthouse–he did the Arizonasaurus painting) is putting together an art show that focuses on crurotarians and non-dinosaurian ornithodirs. I think he’s including Protosuchus. If not, I’m going to suggest it to him, as this looks like a well-known taxon.

27 08 2007

Thanks for the comments, Zach. Definitely endorse Protosuchus to Scott; I’d love to see a more up-to-date reconstruction than the one presented in Colbert’s paper. Even though the skull is a bit cracked the preservation seems great overall, and I’m sure Scott could come up with something wonderful. Like I mentioned above, I hope to have a post on Postosuchus up soon, and as I learn more I hope to cover some of the sebecosuchids and other critters in due time. When it’s all done I’ll try to link them all together in a post about croc evolution, but that’ll probably be a long way off.

13 08 2010

director web

28 08 2010

Самые вкусные и кулинарные рецепты с фото и рецептами.

4 09 2010
Lighthouse Paintings

I always wanted to be a paleontologist, but I joined the Army instead 23 years ago, now my son is going to college to live the dream I once had.

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