Historical Papers
Baur, G. (1891). On the Relations of Carettochelys, Ramsay. American Naturalist. 1891:631-639.
Pseudotrionyx is placed by Dollo, Zittel, and Lydekker among the Chelydridae. A skull originally rerferred by Sir R. Owen to Platemys is considered by Lydekker (8) as beloning to Pseudotrionyx. It is stated that it agrees essentially with that of Macrochelys ; and that this reference is confirmed by the total absence of the impression of horny shields, indicating that the skull, as in the Trionychidæ, was merely covered with skin. I think it is at least doubtful wetheer this skull belongs to Pseudotrionyx.
We have now to consider the relations of Carettochelys. Its nearest relative is, as I have shown, Pseudotrionyx. There is no idenceev from the present material that Pseudotrionyx belongs to a different family from Carettochelys. I do not hesitate, therefore, to place both genera in one family, Carettochelyidæ Boulenger, 1887, which name has the priority before Pseudotrionychidæ Boulenger, a family established in the Encyclopedia Britannica, (Vol. XXIII.), P. 457, to contain Pseudotrionyx Dollo and Anostira Leidy.
This family may be charachterized in the following way :
CARETTOCHELYIDAE
Shell without epidermal shields. Plastron composed of eleven elements, two small mesoplastora being present, which are separated from each other. Only ten peripherals on each side, besides the single nuchal and pygal. (Carettochelys, Pseudotrionyx.)
Upper surface of skull covered with small, round ; raised rugosities exactly as the shell, with three posteria processses, as in Trionychia ; skull resembling in shape that of the Cinosternidæ, but snout more projecting. Limbs paddle-shaped ; digits much elongate, only the two inner clawed. (Carettochelys.)
How far Pseudotrionyx agrees with Carettochelys in the latter charachters, new finds have yet to determine.
The question now is, To which group of tortoises does this family belong ? In a former paper I distinguished four groups of tortoises : the Amphichelydia, Cryptodira, Pleurodira, and Trionychia. Of one thing we are sure : it does not belong to the Pleurodira. Unfortunately we do not know the structure of the crevicals, which is so charachteristic of the three remaining groups. From all that is at present known, it appears to me that the Charettochelyidæ are nearest to the Trionychia, but show at the same time charachters of a group of Cryptodira, composed of the families Staurotypidæ and Cinosternidæ. I expressed a few years ago the opinion that the Trionychia did come from forms which had the peripherals complete, and carapace and plastron closed ; that the Trionychia are not an original, but a highly specialized group. Carettochelys shows structurs of the skull, especially of the posterior portion, Trionychian affinity. I believe that the ancestors of the Trionychia consisted of forms which in structure of carapace and plastron were very much like Carettechelys. On the other hand, there seem to be connections through Anostira with the groups of Cryptodira named above. These affinities are shown in the same shape of the skull and plastron, and the peculiar number of perpherals. Until the cervicals and pelves are known, I think it is impossible to determine the correct systematic position of the Carettochelyidæ. The most probable view seems to be this : the Carettochelyidae came from a group of tortoises related to the stock from which Staurotypidae and Cinosternidæ developed. It is probable that the Carettochelyidæ are very close to the ancestors of the Trionychia, of which thay are only survivals. For the ancestors of the Trionychia we have to look at the Jurassic and Lower Cretaceous ; for I have shown in another paper that the Trionychia of the Upper Cretaceous (Laramie) are typical forms, in which the periphernalia had already entirely reduced. I have little doubt that these started from the Amphichelydia.
There are some points which could be made out by examination of the uniqu type specimen of Carettochelys ; the entire structure of the skull, for instance, the condition of the first dorsal, which is probably preserved. It would be very important to know wether the premaxillary is small and single, as in the Trionychia, or wether it is developed, as in the Staurotypidæ, for instance. It would be interesting to know wether the anterior part of the centrum of the first dorsal vertebra is modified as in the Trionychidæ or not.
I can only hope that new specimens will be collected soon in New Guinea. They doubtless exist there in great numbers, and I think that the time will not be far away when we will know the whole anatomy of this most interesting tortoise.
Clarke University, Worcester, Mass, April 5th, 1891.
AUTHORITIES CITED.
1. RAMSAY, E.P.---On new genus and species of fresh-water tortoise, from the Fly river, New Guinea. Proc. Linn. Soc., New South Wales, second series, Vol. I., MMay 25th, 1886, PP. 158-162, Pls. III.-VI.
2. BOULENGER, G.A.---On a New Family of Pleurodiran turtles. Ann. Mag. Nat. Hist., Vol. XIX. March, 1887, PP. 170, 171. Encyclopedia Britannica, Vol. XXIII., P. 457. Catal. of the Chelonians in the Brit. Mus., London, 1889, P. 236.
3. GILL, Theodore.---- A remarkable Tortoise. Annual Report of the Board of Regents of the Smithsonian Inst. for the year ending June 30th, 1887, Part I., Washington, 1889, PP. 509-511.
4. LYDEKKER, R.----Eocene Chelonians from the salt-range. Mem. Geol. Survey India. Paleontology India, series X., Vol. IV. Calcutta, 1887, PP. 61-63, Pl.XII ; also Lydekker Nicholson Manual of Pal., Vol. II., P. 1101, 1889.
5. BAUR, G.-----Note on Carettochelys Ramsay. Amer. Nat., Nov. 1889 P 1017 (Published 1890)
6. Mem de l'Acad. Imp. des Sciences V. St. Petersbourg, VII. C. Serie Tome XXXVIII., No. 2, St. Petersbourg, 1890, Decembre.
7. DOLLO, L.----Premiere note sur les Cheloniens du Bruxellien (Eocene moyen) de la Belgiqu. Bull. Mus. Roy. Hist. Nat., Belg., Tome, IV.,1886.
8. LYDEKKER, R.----Quart. Journ. Geol. Soc., Vol. XIV., P.242. Catal. foss. Rept., Part III., PP. 145, 146. Paleontology, P. 1195.
Plates: Plate XIV Plate XV Plate XVI