Sea Turtles
Osteophyis ernarginatus Cope   cf. Toxochelys atlantica Zangeri
Peritresius ornatus (Leidy)                     Ctenochelys sp.
Description: There are four main families of turtles found at this locality. They are Cheloniidae, Toxochelyinae, Trionychidae (see Aquatic Turtle), and the side-necked Pelomedusidae (see Aquatic Turtle). The two most common types are marine turtles. They are represented mostly by their scutes or bony plates that made up the shell. There are different types of scutes from the shell and 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), and the peripherals (scutes along the edge). The plastron is the bottom of the shell. Other skeletal material such as, skull, limb bones and vertebrae are very rarely found.

The neural scutes usually have a blocked chevron to hexagonal outline and a ridge in the middle that are fused to the tops of the vertebrae. The costal scutes have a rectangular outline and are fairly flat with a slight curve. The rib is fused to the underside of the costal scute and extends out to articulate into the divots of the peripherals. The neural and the costal scutes may have surface ornamentation. 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. There are two peripherals on each side near the shoulder region on every type of sea turtle found here that lack rib articulations. Most of the time the costal scutes are broken in half after fossilization. The plastron scutes are thin and are usually flat in comparison to the scutes of the carapace.

The most common marine turtle find is that of
Osteophyis emarginatus. It belongs to the family Cheloniidae that is interestingly the family of most modem day sea turtles. The scutes are not as diagnostically ornamented as that of Trionyx and Peritresius. The Osteophyis carapace scutes are fairly smooth with only shallow irregular divots displaying no particular patterns. In this case, it is not a good practice to utilize these markings to make a positive identification, especially with stream worn specimens.

There has been some material that has been found has been tentatively identified as cf.
Toxochelys atlantica. These specimens are fairly smooth and lack the faint markings of Osteophyis. The neural and the costal scutes of this Toxochelid turtle have a rectangular outline with a somewhat smooth upper surface and a raised rounded rib on the under side. The upper surface may have sulci (the shallow groves that mark the boundary of the chitinous scutes). Most neural and the costal scutes from the carapace are 3 to 4 cm (about 1.25 to 1.5 in) long and about 6 to 10 mm (about .25 in) thick. The peripherals are probably the most diagnostic with a radial starburst pattern of shallow groves in the scute. They are usually 5 cm (about 2 in) long, about 25 mm (about 1 in) thick, and about 2 cm (about .75 in) wide. The plastron scutes are fairly thin and posses the star burst pattern as well. These remains would seem to be either from Toxochelys or Ctenochelys. These interesting remains may even represent more than one species of Toxochelid turtle.

The easiest locality marine turtle to identify is the Toxochelid
Peritresius ornatus. This turtle has highly ornamental markings on its scutes making it identifiable even with isolated and scrappy remains. Their peripheral scutes are readily identified by the very prominent, deep, elongated divots which radiates out from a central point. The only difficulty in its identification is differentiating it from the other ornamented turtle, Trionyx. Trionyx has irregular divots that are shallower and they have no distinct pattern. Also they lack the sulci that the hard-shelled types possess.

There might be evidence of another Toxochelid turtle besides
Toxochelys atlantica and Peritresius ornatus. A skull section (left parietal) has been tentatively identified as Ctenochelys sp. This would be the first reported occurrence of this Toxochelid turtle at Big Brook. Even more interesting is the fact that the carapaces of Ctenochelys and Toxochelys are very similar.

Commonality: Marine turtles are one of the most common reptile remains at this and other similar Atlantic Coastal Plain localities. Most often the fragmented carapace or plastron bones turn up while shattered limb bones and vertebra are found very uncommonly. As with any other animal in this type of marine deposit, skull material is rare. Most of the identifiable scutes and other material come from either Ctenochelys or Toxochelys. Fragments of scutes from Osteophyis are fairly common but the complete scutes are less common. Peritresius scutes are very uncommon.

Similar fossils: Isolated remains from Cheloniidae turtles and Toxochelid turtles are similar and are difficult to distinguish between them. Trionyx scutes are also similar to Peritresius, but Trionyx lacks sulci and the deep patterned divots in their scutes.


Size: The sea turtles commonly ranged from 1 to 2.5 meters (about 3 to 8.25 feet) shell length.

Notes: Among the myriad of scrappy and isolated reptile bones that are recovered from Big Brook, there are the scattered remains of several different types of marine turtles. This type of preservation makes it very hard to segregate between the four main groups of turtles. It is also uncertain exactly how many species are represented at Big Brook. Acknowledging this important point, it is probably best to identify these fossils to the family level and offer comparisons and possibilities. The sea turtles were a large group of large marine reptiles that roamed the open surface waters of the sea feeding on the abundant schools of fish. These sea turtles were widespread during the Late Cretaceous and their decedents are still alive today.
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Osteophyis ernarginatus Cope
Diagram of the sulci of
cf.
Toxochelys (Dollochelys) atlantica Zangeri
Diagram of the neural (n), costal (c), and peripheral (p) scutes of
cf.
Toxochelys (Dollochelys) atlantica Zangeri
Costal Scute
O. emarginatus
a. Top  b. Bottom
Peripheral scutes of
cf.
T. atlantica Zangeri
Costal Scute
P. ornatus
a. Top  b. Bottom
Bottom part of Limb Bone
Unknown Sp.
Skull of
cf.
T. atlantica
Skull of
Ctenochelys sp.
Skull of
O. emarginatus