Preliminary analisys of crown formation time and life history variables in archaic ungulates from South America

GELFO J. N.; RAMIREZ ROZZI, F.

San Juan

Congreso; Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Museo de Ciencias Naturales Universidad Nacional de San Juan

The pattern of tooth growth and eruption among mammals were considered as useful tools for phylogenetic analysis and identification of life history traits. Several studies in primates indicated that there is a high correlation among crown formation times (CFT) and several life history traits, particularly body mass and brain size (Macho, 2001). Among archaic ungulates, CFT are known for the Paleocene and Eocene laurasic archaic ungulates Meniscotherium Cope, 1874 and two species of Phenacodus Cope, 1873 (Dirks et al., 2009), but at present no information is available from bunodont South American native ungulates. Here we analyzed an histological enamel section of the paracone of one right upper molar of Ernestokokenia nitida Ameghino, 1901 (Mammalia, Didolodontidae) from the Paleocene and Eocene of Patagonia, Argentina, and compared the results with the available information of CFT of bunodont mammals. The timing of crown formation was inferred considering the periodicity (P), which is the number of cross-striations, and indicates enamel daily growth increments; and striae of Retzius (SR) which account for longer increment periods. Depending whether the SR contact or not the enamel surface, the paracone section was divided in a lateral and cuspal part respectively. The daily secretion rate (DSR) was determined as the average distance between cross-striations. In the cuspal part DSR was obtained for the inner, middle and outer section, and the CFT was determined by dividing the prism length by DSR. The CFT of the lateral part was calculated by multiplying number of SR by P. The preliminary results indicate for E. nitida a P of 3, DSR of 3.8 (outer) and 3.0 (middle) and a CFT of 0.75 years. A mean value for E. nitida body mass was inferred in 4.74 kg using several dental measures following the equations of Scarano et al. (2011). Compared with primates of similar body mass E. nitida shows a faster time to form and grow their molars. This CFT values is similar to the observed in taxa with similar ecological roles, represented by Laurasic archaic ungulates, which in contrast, are five times larger (i.e. Phenacodus intermedius Granger, 1915 and Phenacodus trilobatus Cope, 1882). This analysis raises questions about the relationships between CFT, body mass, and ecological roles in basal ungulates, which seem not to follow those suggested for primates.