Alejandro G. Kramarz, Mariano Bond and Analia M. Forasiepi
Astraponotus Ameghino, 1901, the only valid Mustersan (late Eocene) astrapothere, typifies the Ameghino’s ‘‘Capas Astraponotenses’’. This taxon is traditionally interpreted as structurally ancestral to all the Oligocene– Miocene astrapotheriids. However, it was imperfectly known: only isolated teeth and very partial mandibles have hitherto been described. In this contribution we provide the first description of the skull, mandible, and complete dentition of Astraponotus based on new materials from the Gran Hondonada and other Mustersan localities in central Patagonia, Argentina. The features observed in the dentition of Astraponotus are intermediate between the Casamayoran (middle Eocene) and the Oligocene–Miocene astrapotheres in the degree of hypsodonty, reduction of the dental formula, and development of accessory occlusal elements. Concordantly, the skull retains some plesiomorphies, also observed in Trigonostylops, whereas the auditory region and the basicranium are much closer to those of Parastrapotherium, Astrapotherium, and Granastrapotherium. On the other hand, the skull of Astraponotus differs from all known astrapotheres by the disproportioned height and narrowness of the braincase, the extreme reduction of the nasals and the premaxillaries, the absence of anteorbital rim, and the reduction of the frontal region. Some of these features represent cranial specializations exactly opposite to that of Astrapotherium. These characters look astonishingly derived for an Eocene astrapothere, suggesting that extreme cranial specializations occurred independently during the evolution of the order, and that Astraponotus represents a distinctive lineage from that of Astrapotherium and other Miocene forms.
Kramarz, A. G., Bond M. and Forasiepi, A. M., 2010. New remains of Astraponotus (Mammalia, Astrapotheria) and considerations on Astrapothere cranial evolution. Paläontol Z. DOI 10.1007/s12542-010-0087-4.
0 comentarios Publicado por Leonardo Filippi en 6:25
Paula Muzzopappa and Laura Nicoli
Two fossil tadpoles collected in the Deseadan levels (Oligocene) at the Scarritt Pocket locality of central Patagonia are studied herein. These specimens, which show different degrees of skeletal development, have been assigned to the neobatrachian Calyptocephalella canqueli based on the morphology of the frontoparietals and the presence of adult spec− imens of this fossil species at the same locality. The concurrent analysis of three developmental stages (Gosner Stages 35/36 and 38/39, and adult) has provided significant data about the ontogeny of this species, including the change of the pattern of exostosis of the frontoparietals, from a pitted to a tuberculated pattern, and the corroboration of the inclusion of two neural arches in the formation of the urostyle. This evidence will shed light on developmental mechanisms that might be involved in the evolution of the genus Callyptocephalella.
Muzzopappa, P. and Nicoli, L. 2010. A glimpse at the ontogeny of the fossil neobatrachian frog Calyptocephalella canqueli from the Deseadan (Oligocene) of Patagonia, Argentina. Acta Palaeontologica Polonica 55 (4): 645–654.