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
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.
|Osteophyis ernarginatus Cope
|Diagram of the sulci of
cf. Toxochelys (Dollochelys)
|Diagram of the neural (n), costal (c),
and peripheral (p) scutes of
cf. Toxochelys (Dollochelys)
a. Top b. Bottom
|Peripheral scutes of
cf. T. atlantica Zangeri
a. Top b. Bottom
|Bottom part of Limb Bone