Shell Shock: Coprolite with a Hatchling Turtle

[piranha]

Godfrey, S.J., Weems, R.E., & Palmer, B. 2018

Turtle Shell Impression in a Coprolite from South Carolina, USA.

Ichnos, (ahead-of-print publication) 8 pp.

 

ABSTRACT
Coprolites (fossilized feces) can preserve a wide range of biogenic components.  A mold of a hatchling turtle partial shell (carapace) referable to Taphrosphys sulcatus is here identified within a coprolite from Clapp Creek in Kingstree, Williamsburg County, South Carolina, USA.  The specimen is the first-known coprolite to preserve a vertebrate body impression.  The small size of the turtle shell coupled with the fact that it shows signs of breakage indicates that the turtle was ingested and that the impression was made while the feces were still within the body of the predator.  The detailed impression could only have survived the act of defecation if the section of bony carapace was voided concurrently and remained bonded with the feces until the latter lithified.  Exceptionally, the surface texture of the scutes is preserved, including its finely pitted embryonic texture and a narrow perimeter of hatchling scute texture. The very small size of the shell represented by the impression makes it a suitable size for swallowing by any one of several large predators known from this locality.  The coprolite was collected from a lag deposit containing a temporally mixed vertebrate assemblage (Cretaceous, Paleocene and Plio-Pleistocene).  The genus Taphrosphys is known from both sides of the Cretaceous–Paleogene (K–Pg) boundary so, based on the size of the coprolite and the locally-known predators, the juvenile turtle could have been ingested by a mosasaur, a crocodylian, or a theropod dinosaur.  Unlike mosasaurs and theropod dinosaurs, crocodylian
stomachs have extremely high acid content that almost always dissolves bone.  Therefore, the likely predator of this turtle was a mosasaur or a (non-avian or avian) theropod dinosaur.

 

selected quotes:

 

Until now, no coprolite was known to preserve a vertebrate body impression.  Here a single coprolite (Calvert Marine Museum Vertebrate collection, CMM-V-4524, Fig. 1) from Clapp Creek in Kingstree, Williamsburg County, South Carolina, USA is documented to preserve a natural mold of a partial turtle shell (carapace and scutes) referable to Taphrosphys sulcatus (Bothremydidae, Testudines).  This occurrence provides another example of how coprolites can preserve evidence of trophic interactions that cannot be known solely from the study of body fossils.

 

Among the twelve turtle taxa known from the Paleocene in South Carolina (Hutchison and Weems, 1998), and the nine or ten taxa known from the Late Cretaceous (Weems, 2015), only Taphrosphys has all of these characteristics (Fig. 5).  While Adocus is similar in that it also has an elongate first neural and first costals, it differs in that it had a square-shaped second neural (Meylan and Gaffney, 1989) quite unlike the hexagonal second neural seen in the CMM-V-4524 carapace impression.  Based on this identification, the stratigraphic origin of this specimen can be restricted either to the Late Cretaceous or early Paleocene (Danian), because Taphrosphys has never been reported from the Williamsburg Formation (Thanetian, upper Paleocene).  It is notable that “Taphrosphys leslianus,” now considered a junior synonym of T. sulcatus, has relatively wider vertebral scutes than are found in adult specimens.  This suggests that, as T. sulcatus grew, its vertebral scutes became relatively narrower and its pleural scutes relatively wider.  Carrying this trend back to hatchling size implies that hatchlings of T. sulcatus probably had very wide vertebral scutes as seen in CMM-V-4524 (Fig. 5).  Identification of this specimen as T. sulcatus greatly expands our knowledge of the growth and developmental stages of this turtle from hatching to maturity.  Based on the paleoenvironments in which specimens of T. sulcatus are found, this turtle probably was an inhabitant of both estuaries and shallow marine environments.  Based on the hatchling or near-hatchling size of the specimen described here, it was probably living in an estuarine environment at the time it was eaten.

 

In addition to a mosasaur, the predator may have been a theropod dinosaur (including avian theropods).  The tyrannosauroids Appalachiosaurus montgomeriensis (Carr, Williamson and Schwimmer, 2005) and Dryptosaurus aquilunguis (Carpenter et al., 1997) are among the known Late Cretaceous theropod dinosaurs from eastern North America that would have been large enough to produce coprolites of this size (Weishampel, 1990), so one of these animals could have been the predator if the coprolite is of Late Cretaceous age.  If the coprolite is of Paleocene age, however, then it most likely was produced by a large bird.  Although poorly known, there were a number of species of Late Cretaceous and Paleocene birds large enough to produce coprolites of this size, including a Paleocene pelagornithid (relevant literature summarized in Mayr, 2007).  Bird predation is a major factor limiting turtle hatchling survival today (e.g., Janzen, Tucker and Paukstis, 2000), so it is likely that a similar pattern existed in the Late Cretaceous and early Paleocene.

 

The small (i.e., young post-hatchling) size of the turtle shell and the fact that the shell shows signs of breakage both indicate that the turtle was ingested and that the shell impression was made while the feces were still within the body of the predator.  The way in which the feces tapers immediately beyond the turtle shell impression (Fig. 1B) suggests that as the shell was voided, the cloacal aperture was stretched more than it might ordinarily have been.  CMM-V-4524 is the first-known coprolite to preserve a largely complete body impression; though turtle vertebrae have been reported from Late Cretaceous shark coprolites (Anagnostakis, 2013, fig. 9J; Schwimmer, Weems and Sanders, 2015).  This specimen also represents the first-known record of embryonic and early post-hatchling turtle scute texture preserved in the fossil record.

 

[Fruitbat]

Wow!  Fascinating stuff!  Thanks for sharing!

 

-Joe

[Tidgy's Dad]

DON'T LOOK, TIDGY ! ! ! !

[Miocene_Mason]

Very interesting, thanks for sharing!

[old bones]

Very interesting!  @GeschWhat Lori, check this out!

[Gizmo]

Sad news, Billy Palmer one of the authors of this paper passed away several weeks ago.