MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Delayed dental eruption is not a shared characteristic of Afrotherian mammals and South American Native Ungulates
Autor/es:
KRAMARZ, A.; GELFO J. N.; BOND M.; LOPEZ G. M.; LORENTE, M.; REGUERO, M.A.,
Lugar:
San Juan
Reunión:
Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011
Resumen:
In a recent paper, Agnolin and Chimento (2011) claimed that the endemic South American “ungulates” Notoungulata, Astrapotheria, and possibly Pyrotheria, are closely related to Afrotheria by sharing a late replacement of deciduous cheek teeth. This statement was based on: (1) the usual occurrence within these groups of individuals with deciduous and permanent teeth; (2) the impossibility of discriminating adults or senile individuals of these groups (with permanent premolars erupted) from juveniles (with deciduous premolars), when using the length/width ratio of cheek teeth to evaluate the total size of an individual; and (3) the retention of at least dP1–dP3 in adult or senile specimens of Parastrapotherium Ameghino 1895. More recently, Billet and Martin (2011) demonstrated categorically that there is no delayed dental eruption relative to skull growth in notoungulates, except in a few late-diverging lineages. Herein we critically examine the presumed existence of delayed dental eruption in astrapotheres, pyrotheres and xenungulates and the assumptions on which this was based. In most eutherians the DP4/4 is usually replaced before the eruption of M3/3, thus the coexistence of deciduous and permanent teeth (e.g. DP4/4 and M1/1) does not necessarily indicate that the permanent cheek teeth finished erupting after adult body size was reached. Among taxa where no juveniles are known, the eruption of P4/4 before the M3/3 can be inferred in adults when P4/4 is more worn than M3/3). The ontogenetic stage of astrapotheres, pyrotheres and xenungulates cannot be inferred though length/width ratio of molars because they are brachydont and their size is defined before eruption. In the only known specimen of the pyrothere Griphodon peruvianus Anthony 1924 with dp4, m1 and encrypted p3-4, the mesial part of alveolus of m2 is as deep as the p4, suggesting that both teeth would have erupted almost simultaneously, before the m3. In Astrapotherium magnum Burmeister 1879 (the only astrapothere in which the complete ontogenetic series is known) the p4 also erupted before m3. The timing of dental eruption relative to jaw growth in this species indicates that specimens with less than 90% adult jaw length have more than 60% of permanent cheek teeth, as seen in the YPM PU 15332, whereas afrotherian specimens of 95% adult jaw length have much less than 60% of permanent cheek teeth (Asher and Lehmann, 2008). In all known adult specimens of Parastrapotherium Ameghino the cheek teeth formula is unmistakably P3-4/3-4, M1-3/1-3 (Kramarz and Bond, 2008), and in no known astrapothere are the deciduous premolars retained in adult stages as was claimed by Agnolin and Chimento (2011). In the xenungulates Carodnia vieirai Paula Couto 1952 and Etayoa bacatensis Villaroel 1987, the P4/4 shows more wear than M3/3. Consequently, we conclude that there is no evidence of delayed dental replacement in astrapotheres, pyrotheres and xenungulates that could support afrotherian affinities for these mammals.