How to Resurrect a Terror Croc

In the wake of the Great Depression, you would think that dinosaurs would be of no concern to the American government. Who had time to care about prehistoric monsters when the nation had been thrown into crippling economic turmoil? Yet the fossil-rich expanses of the Western states offered unique opportunities for unemployed Americans to get back to work, and at least one project indirectly resulted in the discovery of one of the most formidable predators ever to stalk the coastal swamps of the Late Cretaceous.

Big Bend National Park sits in a little nub of western Texas along the Mexico border. Back in the 1930s, before the land became a national park, the Works Progress Administration and Civilian Conservation Corps put unskilled laborers to work among the 80- to 73-million-year-old strata to search for fossils. The workers weren’t just scrabbling around in the dirt for no reason. The aim of the project was to find a reasonably complete, mountable dinosaur skeleton that could be displayed in a show of regional pride. No luck. Such a skeleton proved elusive, but the project did focus the attention of paleontologists on the area.

In 1940 the famous American Museum of Natural History fossil hunter Barnum Brown and his assistant Erich Schlaikjer were searching the area near the WPA quarries in Big Bend when they discovered the skeletal scraps of an enormous crocodylian. As recounted by paleontologist David Schwimmer in his book King of the Crocodylians, the pieces were placed in the care of another of Brown’s trusted field hands — Roland T. Bird — for preparation and study. The excavated bits of skull were awfully strange. Bird thought that one fragment marked by a large, rounded cup was a partial hip which preserved the socket for the femur, only to discover that the piece was part of the animal’s premaxilla — the depression was actually a tooth socket in the frontmost part of the upper jaw!

Unfortunately, very little of the monstrous crocodylian had been found. Most of the recovered pieces were skull fragments, and even these did not provide a full picture of what the animal’s head looked like. In order to figure that out, Bird teamed up with AMNH paleontologist Edwin Colbert and other museum staff members to describe the animal and reconstruct the entire skull in plaster. The result was a terrifying skull labeled with the appropriate name Phobosuchus riograndensis — roughly the “terror crocodile from the Rio Grande.”

What Bird, Colbert, and the AMNH team created was a rough extrapolation which used living crocodylian species to fill in the considerable missing gaps. The whole thing measured over six feet long — just the tip of what the paleontologists proposed was a 50-foot animal — and was guaranteed nightmare fuel for small children who viewed it in the dark corner of the AMNH, where it sat until the end of the 20th century. As Schwimmer said in his book, though, “[The skull] was really a beautiful job of artistic sculpting.” That’s a compliment and a dig combined. Given the scrappy material, the AMNH crew used the Cuban crocodile — Crocodylus rhombifer — to restore the rest of the Phobosuchus skull, but we now know this was a mistake. As awesome and frightening as the classic bone-and-plaster skull was — a skull that has been reproduced multiple times and remains on display in museums today — it is inconsistent with the nature of the 40-foot, 8-ton Cretaceous crocodylian paleontologists now call Deinosuchus rugosus.

Here’s the skinny on the name change. When Bird and Colbert named the big croc, they decided to place their new species within the previously described genus Phobosuchus. As has often been the case with fossil discoveries, though, previously described fossils that could be referred to the same animal took precedence. In 1909 paleontologist W.J. Holland used a few enormous crocodylian bones and scutes to name the animal Deinosuchus hatcheri. Though the genus name was considered to be an unnecessary synonym of Phobosuchus at the time, paleontologists Jack Horner and Don Baird showed that the opposite was actually the case in a 1979 paper. “Phobosuchus” was a generic wastebasket into which many crocodylians had been dumped, and so had to be tossed.

The change in species name was another matter. Fifty one years before Holland’s paper, the North Carolina paleontologist Ebenezer Emmons used a pair of isolated teeth to establish the name Polyptychodon rugosus. Much like “Phobosuchus”, though, the name “Polyptychodon” was a previously described genus that was often misapplied, but Emmons was correct that the teeth he was looking at represented a then-unknown species which, on the basis of tooth anatomy and additional fossils found in the same place, turned out to be referable to Deinosuchus. Holland’s 1909 genus name and Emmons’ 1858 species name were therefore mashed together to create Deinosuchus rugosus (though I hasten to add that the wide distribution of Deinosuchus fossils makes it possible that there is more than one species hiding within all the fossils attributed to this single recognized name).

The name of “Phobosuchus” was not the only thing to change. Even though Deinosuchus fossils have been found at many quarries from Texas to New Jersey, the enormous crocodylian is primarily known from teeth, bony body armor (scutes), portions of skull, vertebrae, and other elements. Understanding Deinosuchus has always required at least some degree of speculation and reconstruction, and it is especially vexing that no complete skeleton of this huge and widespread animal has yet been found. Nevertheless, the scattered bits and pieces — paired with a deeper understanding of crocodylian evolution — have allowed paleontologists to refine our picture of this monstrous predator.

Contrary to methods used for the 1954 reconstruction, crocodiles were not the best candidates for filling in the missing parts of the Deinosuchus skull. There is a three-way split among modern crocodylians — the gavialoids, the crocodyloids, and the alligatoroids. (These are all technical names, but I’m pretty sure you can guess which name represents which branch.) Rather than being closely related to crocodyloids, as Bird and Colbert inferred, Deinosuchus was actually a broad-skulled alligatoroid more closely related to today’s American alligators than Cuban crocodiles.

This doesn’t mean that Deinosuchus was simply an American alligator writ large, as I often imagined after watching the under-appreciated 1980 horror flick Alligator. Deinosuchus actually exhibited a mosaic of characteristics seen in both alligators and crocodiles. While the creature had a broad, rounded, and alligator-like skull, for example, Deinosuchus also had a pocket in the upper jaw where a large tooth from the lower jaw rested when the animal’s jaws were closed. This is something primarily seen in living crocodiles and not alligators — it’s one of the ways you can tell the two surviving crocodylian lineages apart — but, in the deep past, this feature was present in alligatoroids, too. Even more peculiar is the fact that Deinosuchus had a more varied dental armament than its living relatives. The teeth toward the front half of the jaws were huge, conical stabbers, while the back half of the jaw was arrayed with blunted, low-crowned crushers that would have undoubtedly been useful in busting open turtle shells. (Just imagine the sound of turtle shells being crushed reverberating through the swamps of the Late Cretaceous night.) Deinosuchus truly was an alligatoroid that could have eaten anything it wanted.

Top Image: The reconstructed skull of “Phobosuchus” created by the AMNH in 1954. The darker portions are actual fossil bone — the rest is plaster reconstruction. From Colbert and Bird, 1954.

References:

Colbert, E., and Bird, R. (1954). A Gigantic Crocodile from the Upper Cretaceous Beds of Texas American Museum Novitates (1688), 1-22

Schwimmer, D. 2002. King of the Crocodylians. Bloomington: Indiana University Press. pp. 13-41