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First early Eocene tapiroid from India and its implication for the paleobiogeographic origin of perissodactyls
Published online: 9/8/15
Keywords:
Ceratomorpha; Helaletidae; Paléogène; Tapiromorpha; Vastan
https://doi.org/10.18563/pv.39.2.e5
Abstract
The presence of cambaytheres, the sister group of perissodactyls, in western India near or before the time of collision with Asia suggests that Perissodactyla may have originated on the Indian Plate during its final drift towards Asia. Herein we reinforce this hypothesis by reporting two teeth of the first early Eocene tapiromorph Perissodactyla from the Cambay Shale Formation of Vastan Lignite Mine (c. 54.5 Ma), Gujarat, western India, which we allocate to a new genus and species, Vastanolophus holbrooki. It presents plesiomorphic characters typical of the paraphyletic “Isectolophidae,” such as small size and weak lophodonty. However, the weaker hypoconulid and low paralophid, higher cusps, lower cristid obliqua, and the lingual opening of the talonid are found in Helaletidae, the most primitive tapiroid family. V. holbrooki, gen. et sp. nov., may be the oldest and the most primitive tapiroid, suggesting that at least tapiroid perissodactyls originated on India.
PV article infos
Published in Vol.39-2 (2015)
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Mode de vie et affinités de Paschatherium (Condylarthra, Hyopsopontidae) d'après ses os du tarse
Published online: 12/16/96
Keywords:
Astragalus; Calcaneum; Condylarthra; Eocene; Functional morphology; Paschatherium; PHYLOGENY
Abstract
Tarsals that can be confidently attributed to Paschatheríum dolloi from Dormaal (Belgium) are described. The astragalus is short; its broad neck is set at an angle of 30 degrees to the trochlea. The trochlea is pulley-shaped and proximally extended. There is no astragalar foramen. The medial tibial facet extends distally in a cup deeply excavated in the neck and buttressed. The sustentacular facet extends toward the navicular facet but is not fully confluent with it. The calcaneum bears a proximo-distally extended proximal facet for the astragalus. A relatively large peroneal tubercle projects from the body, and is situated distally. Functionally, the trochlea indicates extensive flexion-extension movements of the foot. Calcaneo-astragalar facets indicate sliding and rotation between the two tarsals. The inclination of the navicular facet suggests frequent foot inversion. The peroneal tubercle reflects good muscular capacities for foot rotation. Overall morphology is interpreted as a scansorial adaptation similar to that of sciurids.Comparisons are made with the tarsals of Macrocranion vandebroeki from Dormaal and Hyopsodus paulus from the Bridgerian of Wyoming. Some similarities between the astragali of Paschatherium and Macrocraníon (trochlea) are interpreted as convergences for rapid locomotion. However absence of mobility at the lower ankle and midtarsal joints in M. vandebroekzi suggests that this species was cursorial, as is known for M. tenerum from Messel. Similarities in the calcanea of Paschatherium and Hyopsodus are probably the result of close phylogenetic relations, and confirm the placement of Paschatherium in the hyopsodontids. The differences in the calcanea of Paschatherium and Macrocranion underline that Paschatherium is distinct from erinaceomorph insectivores. The differences in astragalar morphology between Paschatherium and Hyopsodus show that a marked adaptive divergence separates the two genera. We speculate about the common occurrence of a deep tibial cup (“cotylar fossa”) and a pulley-shaped trochlea in Paschatherium and hyracoids, suggesting that an adaptive scenario similar to that having led to Paschatherium (scansoriality) might explain the acquisition of the peculiar hyracoid tarsal characters; such a scenario contradicts the concept of Pantomesaxonia. Other peculiar characters of Hyopsodus suggest that hyopsodontids might be given more consideration in the search for hyracoid (and tethythere) origins.
PV article infos
Published in Vol. 25, Fasc. 2-4 (1996)
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