Historical Papers
Glaessner, M.F. (1942). The occurrence of the New Guinea turtle (Carettochelys) in the Miocene of Papua. Rec. Aust. Mus. 21:106-109. ¹
Comparison - The peculiar surface of the bone points to the Trionychia as the only group of turtles in which this type of ornamentation combined with the absence of horny plates is a general distinctive feature. The presence of marginal plates is clearly indicated by the outline of the nuchal plate here described. In the Trionychidae proper, in which the marginal plates are absent, the nuchal plate has no distinctive antero-lateral margin and the lateral angle is acute or split into a number of projecting spines. A detailed comparison of the newly discovered bone with the nuchal plate of Carettochelys insculpta Ramsay reveals almost complete identity. Walther³ describes the nuchal plate of this species as follows: The nuchal plate of Carettochelys is wide in its central part and narrower in its posterior part. It is firmly connected with the surrounding elements of the carapace. The well-expressed granulations of its surface resemble more the sculpture of the marginal than of the costal plates, being circular in outline as in the former. On the posterior part of the internal surface of the nuchal plate there are two strong protuberances serving as condyli for the eighth cervical vertebra. Together with the strongly raised anterior articular processes of the first pectoral vertebra they form a deep socket in which the peculiar roll of the last cervical vertebra is inserted, articulating with the protuberances. These form some kind of locking device preventing the last cervical vertebra from moving beyond a certain point. Such protuberances are not found in the Trionyx, but are known in Anosteira. In front of these projections we see two depressions with rough surfaces representing areas of attachment for the cervical muscles. They contain on each side a foramen for nerves or blood vessels. The deep depressions extending across to the costal plates in Trionyx and according to Ogushi serving as a socket for the scapulae are not clearly developed in Carettochelys. Figures published by Walther and Hummel4 show the angle between costal and marginal sutures on the nuchal plate of Carettochelys to be approximately 120° (Figure 1). The width of the first neural plate equals about one-twelfth of the width of the nuchal plate in the recent species as well as in the fossil specimen. |
 Figure 1. Dorsal View. One-fourth natural size. After Hummel. N = Nuchal Plate |
These comparisons reveal almost complete identity between the observable features of the fossil specimen and the characters of the corrosponding plate of the living Carettochelys insculpta Ramsay. While this appears to prove at least generic identity, no other known turtle having a nuchal plate of the same shape and dimensions, specific identification can obviously not be based on the examination of a single bone. Until further remains are discovered the fossil form should therefore be known as Carettochelys sp.
Relationships and History of Carettochelys insculpta - Carettochelys insculpta was discovered in 1885 by the Everill Expedition of the Royal Geographical Society of Australasia on the Strickland River in Western Papua, probably 100-150 miles above its junction with the Fly River.5 Another specimen was caught about 150 miles further south in the Morehead River,6 and the species is also known from Netherlands New Guinea,7 from the Lorentz River, Merauke, Setakwa River, and Lake Jamur. As far as recent forms are concerned, these are the only occurances of the species, genus, and family.
Beginning shortly after its discovery and continuing up to recent years, there has been a considerable amount of discussion on the relations of this family to other living and fossil turtles. The question was lately reviewed by Hummel in his comprehensive study of the fossil Trionychia. The family Carettochelyidae includes the Eocene genus Anosteira Leidy. According to Hummel, Pseudotrionyx Dollo and possibly several other incompletely known Eocene forms belong to Anosteira. Morphologically the Carettochelyidae are more primitive than the Trionychidae which are known already from the upper Cretaceous and appear to provide a link between them and the typical Cryptodira.