| Ceratosuchus | |
|---|---|
 | |
| Ceratosuchus burdoshi | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Order: | Crocodilia |
| Family: | Alligatoridae |
| Subfamily: | Alligatorinae |
| Genus: | †Ceratosuchus Schmidt, 1938 |
| Type species | |
| †Ceratosuchus burdoshi Schmidt, 1938 | |
Ceratosuchus ("horned crocodile") is anextinctgenus ofalligatorinecrocodylian from latestPaleocene rocks ofColorado'sPiceance Basin and earliestEocene rocks ofWyoming'sBighorn Basin inNorth America, a slice of time known as theClarkforkianNorth American Land Mammal Age. Like its modern relatives,Ceratosuchus was a swamp-dwelling predator. It is named for the pair of flattened, triangularbony plates that extend from the back of its head.
Thetype species isC. burdoshi, a name chosen by the Field Museum after Theodore Burdosh discovered a nearly complete skull on an expedition to Western Colorado in 1937.
"Fortunately, a knob of bone projecting from an otherwise undistinguished piece of rock had caught the eye of Mr. Burdosh, and the block had been broughtto the Museum. When the rock was chipped away, the insignificant external lump proved to belong to a fairly complete skull of a fossil crocodilian allied to the alligators; and on one posterior corner it bore a triangualr horn-like knob which proved to be identical with the mysterious separate fragments."[2]
Ceratosuchus was named in 1938 by K. P. Schmidt for a skull from Colorado. Further remains, including additional skulls,mandibles, andcervicalarmor, was recovered from Wyoming byUniversity of Michigan paleontologists and described by William Bartels in 1984. The skull, of a moderately-size alligatorine, is most notable for its horns, formed by expansion of the bones (squamosals) that formed the rear corners of the skull roof. These horns were bulbous and pointed up. There were five teeth in both of the bones that made up the tip of the snout (premaxilla), fifteen in the pairedmaxillae that formed the sides of the upper jaw, and twenty in bothdentaries of the lower jaw. The front of the lower jaw had a flattened shape, and the teeth located here pointed partially forward, with aspade-like form. The teeth hadvariable shapes; the first thirteen teeth in the lower jaw were pointed, while the last seven graded from aspatulate shape to a large globular shape. Aside from the horns, the skull and particularly the lower jaw ofCeratosuchus were very similar to that of its contemporaryAllognathosuchus. The neck armor had blade-like keels that may have been aligned with the skull horns.[3]
AlthoughCeratosuchus is the only known horned alligatorine, horns are not unknown incrocodilians; similar structures are known on two other species:Voay robustus andCrocodylus rhombifer. Bartels proposed that the horns' small size and bluntness made them unlikely weapons, and their small size also made use in a threat display unlikely. Instead, he favored their use as signals for species recognition: in this case, the horns would allowCeratosuchus and species ofAllognathosuchus to tell each other apart.[3]
Ceratosuchus is known from overbankmudstone deposits. It so far has been a rare find compared toAllognathosuchus from the same rocks. Bartels reported that only 5% of Clarkforkian crocodilians collected by the University of Michigan can be certainly assigned toCeratosuchus (although this may be partially artificial because fragmentary specimens ofCeratosuchus could be confused withAllognathosuchus).Ceratosuchus may have beenecologically restricted in comparison toAllognathosuchus.[3]
Although the blunt posterior teeth ofAllognathosuchus andCeratosuchus have been traditionally interpreted as for feeding onmollusks orturtles, Bartels noted that these crocodilians were too small to feed on large bivalves or non-juvenile turtles, and that modern crocodilians usually swallowsnails whole. Instead, he proposed that skullmorphology and tooth wear better fit generalizedpredation on a variety of invertebrates and vertebrates.[3]
The precise placement ofCeratosuchus withinAlligatoroidea is disputed. Some studies have shown it as abasal member ofAlligatoridae, within thestem groupAlligatorinae,[4][5] as shown in thecladogram below.[5]
Alternatively, other studies have recoveredCeratosuchus outside ofAlligatoridae andAlligatorinae, as abasal member ofAlligatoroidea within thecladeGlobidonta, as shown in thecladogram below.[6]
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