Thoracosaurus neocesariensis (DeKay)
|Description: The gavial-like "crocodile" is represented at Big Brook by teeth, dermal scutes, vertebrae, other scrap bone, and coprolites.
Teeth from this "crocodile" are generally conical, curved, and more often than not lacking distinctive carinae (the cutting edges on the teeth). Leidy originally described these teeth as possessing low sharp carinae. No doubt only the best teeth not worn by the stream display this distinctive characteristic. Their teeth are coated with enamel and are usually smooth but can sometimes have small vertical ridges on the lower half of the tooth. Crocodile teeth have steep conical indents in the bottom of their roots, which fit into the socket of the jaw. They are only about 1 to 2 cm (about .5 to.75 in) long.
The scutes (the bony plates along the back that float in the skin) are somewhat uncommon but can be found with some diligent searching. Most of the time these scutes are recovered fragmented. When relatively complete, they have a roughly rectangular to square outline and are about 9 cm (about 3.5 in) long and about 5 cm (about 2 in) wide. The underside of the scute is smooth while the top has many irregular shaped divots, looking something like the surface of a golf ball magnified.
Vertebrae are found uncommonly and somewhat resemble mosasaur vertebrae. The centrum, or the main part of the vertebrae, is usually the only part that is recovered. They are more than likely lacking any of the other structures of the vertebrae because they are easily broken. The centrum is slightly conical and one end is convexed while the other is concave.
The coprolites from this "crocodile" are similar in shape to shark coprolites. These are round to ovate in cross section with a general shape not unlike the stream worn gravel except that the top is rounded and the bottom is somewhat pointed. Most coprolites do not exceed 4 cm (about 1.5 in) in length and 1.5 to 2 cm (about .5 to .75 in) in diameter. They may be confused with shark coprolites except that they lack the spiral patterning that is characteristic of shark coprolites and are mostly smooth. Also, the pointed end is usually not symmetrical as it is in shark coprolites.
Other "crocodile" bones are not easily distinguishable and are usually very scrappy. The scrappy reptilian bone of mosasaurs, sea turtles, "crocodiles", and plesiosaurs are similar and are all found at this locality. Unless the bones are complete, it is difficult to attribute them to the "crocodile".
Commonality: Teeth are uncommon while vertebrae and coprolites are very uncommon.
Similar fossils: The teeth of the "crocodile" can be confused with the teeth of the mosasaurs and plesiosaurs. Both mosasaur and plesiosaur teeth are larger and plesiosaur teeth are more slender. The scutes of the "crocodile" can be confused with the scutes of Trionyx but the divots in "crocodile" scutes are deeper than Trionyx and are more irregular.
"Crocodile" vertebrae are distinguishable from mosasaur vertebrae by the general conical shape, instead of the cylindrical shape of the vertebrae of the mosasaur. The vertebrae of Halisaurus are rare and most of the vertebrae that display this shape are usually "crocodile". "Crocodile" vertebrae also have divots in the convexed faces that Halisaurus and other mosasaur vertebrae lack.
Size: The fossil "crocodiles" reached from 2 to 3 meters (about 6 to 9 feet) long.
Notes: These "crocodiles" would seem best suited for roaming the surface of the sea hunting for the abundant schools of fish because of their elongated and narrow jaws. These "crocodiles", according to fossil evidence, were probably more closer related to the gavial found in the rivers of India, than to true modern crocodiles. The gavial is not a true crocodile but is a close relative. The large group of crocodilians were common world wide and their relatives are still around today.
|Complete Crocodile Vertebra
a. Top b. Back c. Side
a. Drawing b. Picture