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
Comment: This was an important discovery because there has been much discussion on the origins of the Carettochelyidae and their relationships to the Trionychidae. Hence the placement of members of these groups through history is needed to understand these relationships. Scott Thomson (2004).
Introduction - The fossil forming the subject of the present note was discovered in October 1940, in a quarry on the road leading from the left bank of the Vailala River (Papua, Gulf Division) near the mouth of the Karlava Creek to the drilling site of Australian Petroleum Company's first exploration well in Papua. The fossil was sent to Port Moresby and handed to the writer by Dr. K. Washington Gray, chief geologist to Australian Petroleum Company. The quarry was situated 800 feet E. 7° S. from the mouth of the Karlava Creek. The writer visited the locality in May, 1941. No further vertebrate fossils were found, but mollusca, corals and foraminifera occur in the same beds the age of which is upper Miocene.
The fossil remains consisted of the external mould, in medium grained dark tuffaceous sandstone, of a single highly sculptured bone with a fragment of the bone, 1½ x 2 inches in size, still adhering to the matrix. About one-third of the mould was apparently lost in collecting, but it is likely that only this single detached bone was originally embedded in the rock.
Preliminary examination of the fossil made it clear that it was a fragment of the nuchal plate of a turtle, belonging apparently to the Trionychia but suggesting by its outline the presence of marginal plates in the species. Thus the fossil could not belong to the Trionychidae, but appeared to be related to the more primitive family Carettochelyidae. The only living representative of this family is the New Guinea Turtle, Carettochelys insculpta Ramsay ².
Description - A plaster cast of the mould was made (Plate X, Fig 1). It shows that the bone was irregularly pentagonal in outline, much wider than long, with a widely arched postero-lateral margin, a lateral angle of about 120°, shorter, slightly concave, antero-lateral margins and an almost straight long anterior margin which is very slightly concave in outline and about one-fourth of its length on either side of the median line. The preserved bone fragment (Plate X, Fig 2a, b) belongs to the posterior median part of the plate. On its well preserved sutural margin we recognise the small, rectangular, median excavation into which the anterior margin of the first neural plate must have been fitted. The arched posterio-lateral margins of the nuchal plate were joined to the anterior margins of the costal plates. The well-defined lateral angles and the antero-lateral margins of the costal plates. The well-defined lateral angles and antero-lateral margins indicate the presence of well-developed marginals.
The external surface of the bone is covered by Trionyx-like granulation consisting of isolated small rounded or elliptical mounds separated by narrower or equally wide anastomosing depressions. The general trend of the ornamentation is irregular or transversal about the central part of the plate, changing to radial arrangement near the posterior and postero-lateral margins and, to a lesser extent, near the anterior edge. There are no markings indicating the presence of horny plates on the bone.
On the internal surface of the bone two strong axially elongated projections are symmetrically arranged close to the posterior margin and to the median line. They rise gradually from the central part of the bone forming steeply inclined, elliptical, slightly saddle shaped, facets directed backward and downward. Reticulate impressions in front of these projections indicate attachment areas of muscles.
Measurements - Length of nuchal plate (reconstructed), 75mm.; width of nuchal plate (reconstructed), 130mm., width of anterior margin of nuchal plate, 104 mm., width of antero-lateral margin (nuchal-marginal suture), 40 mm.; suture joining nuchal and first neural plates, 11 mm.; angle between postero-lateral and antero-lateral margins, 120°; computed length of carapace (based on the proportions of Carettochelys insculpta Ramsay), 600 mm.