Class: Reptilia

Order: Crocodilia

Family: Alligatoridae

Genus: Allognathosuchus

Species: A. haupti, A. mooki, A. polyodon

When and where Allognathosuchus lived: Allognathosuchus is an extinct crocodile that lived from the late Cretaceous through the Oligocene in North and South America, Eurasia and Africa (Brochu, 2004).

General Description

The famous paleontologist E.D. Cope found the first specimen, portions of cranium, teeth and vertebrae, of Allognathosuchus in the Eocene Bridger Formation in 1873 near Green River, Wyoming. However, it was not named as a new genus until 1921 when C.C. Mook re-examined the Cope skeleton. Since its original description, specimens of Allognathosuchus have been found in practically every early Tertiary formation. Significant specimens of skulls and skeletons are known from the Willwood, Wind River, Wasatch and White River formations.

Unlike modern crocodilians which have sharp pointed teeth, Allognathosuchus had large blunt teeth and often times it is called a button-toothed crocodile or alligator. The reptile was smaller than its living relatives, with a maximum length of 1.5 meters (Brochu, 2004). The teeth in the back of the upper and lower jaws have rounded crowns (Mook, 1921), like many other crocodilians and are large compared to the front teeth (Brochu, 2004). The jaw was narrow and more curved than most crocodilians and the skull more slender. Allognathosuchus was aquatic and may have preyed on mollusks, due to the blunt nature of its teeth, but its diet is still unknown. Some scientists believe Allognathosuchus was a specialist eater feeding on turtles whereas other scientists speculate that Allognathosuchus, like modern alligators, was not specific in its food habits, eating fish, turtles, birds and mammals (Simpson, 1930).

Allognathosuchus possessed a modest-sized set of ridges on its snout, though less pronounced than in other alligatoroids (Brochu, 2004).

There is much debate about whether Allognathosuchus is at all related to modern alligators. G.G. Simpson suggested that the Cretaceous Brachychampsa, found in the Hell Creek Formation in Montana was the ancestor of the modern alligator, and the Tertiary Allognathosuchus independently acquired similar teeth and skull attributes. Therefore, they might represent an evolutionary convergence. Simpson overall favored the theory that these commonalities arose from a common ancestor (Simpson, 1930).

In any case, Allognathosuchus represents the emergence and disappearance of a unique set of adaptive characteristics among crocodilia in the context of the first great expansion of the size and number of mammalian species.

Fossil specimens of “Allognathosuchus” teeth are commonly found, especially in Early and Middle Eocene rocks. These are small to large blunt button-like teeth with low rounded crowns and enamel crenulations running from the enamel-root boundary to the apex of the crown.

References Cited

Brochu, C.A. (2004). Alligatorine phylogeny and the status of Allognathosuchus mook, 1921. Journal of Vertebrate Paleontology, 24, 4, 857-873.

Mook, C.C. (1921). Allognathosuchus, a new genus of Eocene crocodilians. Bulletin of the American Museum of Natural History, 44, 105-110.

Simpson, G.G. (1930). Allognathosuchus mooki, a new crocodile from the Puerco Formation. American Museum Novitates, 445, 1-16.

By Elena K. O’Bryan

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