Trionyx cf. priscus Leidy
cf. Bothremys barberi (Schmidt)
|Description: There are different types of scutes found from these turtles. These scutes have different shapes depending on where in the shell they came from. The carapace (top of the shell) is divided into the neurals (scutes along the spine), the costals (scutes fused to the ribs). The plastron is the bottom of the shell.
The neural scutes usually have a blocked chevron outline, a ridge in the middle and rarely fused verte-brae. The costal scutes have a rectangular outline and are flat with a slight curve. The rib is fused to the underside of the costal scute. The neural and the costal scutes have surface ornamentation composed of small irregular divots close to the neurals becoming ridges towards the ends. The peripherals are wedge shaped and when complete usually have a deep divot in the thick part of the wedge for the articulation of the ribs. Most of the time the costal scutes are broken in half after fossilization. The plastron scutes are thin and are usually flat.
Of the two types of aquatic turtles that occur, the easiest to identify are those of the soft-shelled Trionyx cf. priscus. Trionyx material possesses highly ornamental markings on their scutes making them identifiable even with isolated and scrappy remains. Their costal scutes are readily identified by the very shallow, irregular divots which have no distinct pattern (similar to a golf ball).
The other type of aquatic turtle is much more difficult to identify due to differences that are usually only noticeable with more complete scutes. The side-necked (Pleurodia) turtle, cf. Bothremys barberi is also known as the "Paving stone turtle" owing to the large, flat, and thick surfaces of its carapace scutes. The scutes are fairly smooth and look somewhat like the old time paving stones that were used for streets. They are thick, large, and dense for their size and may also have faint sulci.
Commonality: The side-necked and the soft-shelled turtles inhabited fresh to brackish waters and are consequently rare in the deeper water deposits of the Navesink but are slightly more common in the shallower water of the Mt. Laurel.
Similar fossils: Trionyx scutes can be confused with the scutes of the gavil-like "crocodile". The divots of Trionyx are shallower than "crocodile" scutes and are more circular. Trionyx scutes are also similar to Peritresius, but Trionyx lacks sulci and the deep patterned divots in their scutes.
Size: The soft-shelled turtle could reach about 1.5 meters (about 5 feet) in shell diameter. Presumably, the side-necked turtle could reach larger sizes.
Notes: Both the side-necked and the soft-shelled turtles inhabited fresh water but may have venured into brackish waters. As with the dinosaur material, most of the aquatic turtle material was washed into the sea from rivers during storm events. Both turtles, as their modern counter parts do today, inhabit lakes and rivers with fish as their main diet. These aquatic turtles were widespread worldwide during the Late Cretaceous and their decedents are still alive today.
|Trionyx costal scute showing
divots on the top side.
|Trionyx costal scute showing
fused rib on the bottom side.