Short Notes

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 66. PP. P39-240 FEBRUARY 1955

OCCURRENCE OF CHIROTHERIUM IN SOUTH AMERICA

BY FRANK E. PEABODY

The discovery of the pseudosuchian foot- C. barthi of Arizona occurs near the top of print of the genus Chirotherium in Mendoza, the type Moenkopi, a horizon currently con- Argentina, by Carlos Rusconi (1951) is im- sidered uppermost Lower or lowest Middle portant for our understanding of land con- . The marked similarity amounting to nections between and South specific identity of the Argentine footprint America in the early Mesozoic era. The foot- indicates that the Argentine stratum producing print occurs in the red, sandy shales of the the footprint and referred to the Upper Higueras formation, currently considered is a general correlative of the Moenkopi. This Upper Permian. Rusconi's clear photograph of practical identity of highly characteristic the chirothere pes leaves no doubt that his pseudosuchian footprints also suggests a species Chirotherium higuerensis is nearly if not definite land connection between North actually identical with the variety of C. barthi America and South America during a period occurring in the Holbrook member of the when faunal relations in the Middle Triassic of Arizona. The latter of East Africa and Brazil were, as pointed out species is slightly but not specifically different by Romer (1952), close enough to suggest some from the 'type of C. barthi of the German sort of direct continuity between the two Bunter. The species is among the most if not southern continents. Discovery of identical the most distinctive and most clearly recorded species of chirothere footprints in North of known tetrapod footprints. America and South America make it necessary The pes described by Rusconi is identical to explain why cynodont therapsids and with that of C. barthi of Arizona (cf. Peabody, rhynchocephalians, which are assumed by 1948, PL 40) in such diagnostic details as size, some to have reached South America directly claw shape, proportions of digit length, dis- from Africa, did not subsequently reach North position and shape of digital pads, and scale America from the south. Romer thinks that the pattern. The seemingly double heel mark of Moenkopi does not contain evidence of therap- the pes is in reality the tip of digit V strongly sids or rhynchocephalians, and that this fact recurved upon the heel and obviously showing minimizes the significance of the available a skid mark leading to the definitive impression evidence for relating South American pseudo- of the digit from behind. In chirotheres the tip suchians with those of North America (the of digit V may have the position shown by latter indicated largely by their footprints). Rusconi's reconstruction but, as is really the However, there are some trackways in the case with his specimen, is often greatly re- Moenkopi suggesting rhynchocephalians (Pea- curved. A manus impression found 50 cm from body, 1948, PL 29) and also some which pos- the pes (hence not belonging with the set of sibly represent therapsids (PL 45) as well as prints represented by the pes) is compared the clear indication of a rich pseudosuchian with the manus of several Moenkopi species assemblage. Lack of positive proof of the clearly different from C. barthi. The manus as presence in North America of rhynchoceph- described appears more than alians and cynodonts may well be a result of reptilian and, if chirothere, is definitely too the vagaries of preservation. Much upland small to be associated with the described pes. country in the province of erosion existed to 239

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the south, east, and north of the Moenkopi proposition that chirotheres entered South province of deposition. Within the Moenkopi, America from via Africa is perhaps skeletal material of any including the possible but not probable in our present state patently abundant pseudosuchians is exceed- of knowledge. Yet another alternate proposi- ingly rare; and even the extensive fauna re- tion that chirotheres and other pseudosuchians corded on the many mudflats represents mostly originated in the southern hemisphere and a single environment (riparian). In general dispersed northward is not likely, but if true support of the contention that the record of would not affect the premise that a definite North American of Middle through land connection existed between North America Late Permian and Triassic times is markedly and South America in Triassic time. biased, we may note recent osteological dis- In summary, the occurrence of the chirothere coveries of a large carnivorous therapsid footprint, Chirotherium barthi, in Argentina (Dimacrodon hottoni) in the Middle Permian of taken with slowly growing correlative evidence Texas and of typical tritylodont therapsids in increases the possibility of explaining the the latest Triassic (or early ) of North- dispersal of early terrestrial reptiles in terms ern Arizona. These discoveries supplement the of the Matthew-Simpson principles of mam- isolated and seemingly anomalous occurrence malian dispersal. of the dicynodont Placerias in the Late Triassic of Arizona. Thus, evidence is accumulating REFERENCES CITED that makes increasingly possible the thesis Peabody, F. E., 1948, Reptile and amphibian that a Holarctic distribution of early reptiles trackways from the Lower Triassic Moenkopi with southward dispersals could account for formation of Arizona and Utah: Univ. Calif. the composition of South American reptile Pub., Bull. Dept. Geol. Sci., v. 27, p. 295- 468, 40 figs., 23 pis. faunas particularly during the Triassic. In any Romer, A. S., 1952, [Discussion of, "The Mesozoic case, it is clear that typical chirotheres of wide Tetrapods of South America" by E. H. Col- distribution in the Triassic of Europe and bert.] Am. Mus. Nat. Hist. Bull., v. 99, no. 3, p. 250-254. North America were able to reach South Rusconi, Carlos, 1951, Rastros de patas de reptiles America probably via a Central American Permicos de Mendoza: Rev. Soc. Hist. Geog. route. Evidence of paleogeography (Woodring, Cuyo, v. 3, no. 3, p. 1-14, 2 figs., 1 pi. Woodring, W. P., 1954, Caribbean land and sea 1954) strongly suggests that the concept of a through the ages: Geol. Soc. America, Bull., Tethys sea forming a major barrier between v. 65, p. 719-732, 3 figs., 1 pi. the two continents at least during Early and DEPT. ZOOLOGY, UNIV. OF KANSAS, LAWRENCE, Middle Triassic is untenable. An alternate KANSAS

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