SUBORDER D 



ASTRAPOTHERIOIDEA 



243 



Suborder D. ASTEAPOTHERIOIDEA Ameghino.i 



{Amblypoda Ameghino.) 



Medium-sized to large herbivores with hrachyodont dentition, spatulate incisors 

 and tush-like canine. Premolars, at times also the incisors, partly atrophied, and 

 smaller than molars. Upper molars, as a rule, longer than broad, with a parastyle, 

 and often also with a crest on the ectoloph, with slightly curved protoloph and a short 

 metaloph. Loiver molars loith two unequally long crescents and two inner cusps, of 

 which the first is inwardly connected with the posterior extremity of the first crescent, 

 and the second later becomes fused with the anterior end of the second crescent. 

 Astragalus with flat articulation for the tibia. 



The Astrapotherioidea are closely allied to the Entelonychia. They are 

 distinguished from the latter principally by the tusk-like canine and usually 

 by the form of the molars, which are somewhat like those of the rhinoceros. 

 There is no inflation of the squamosal region, at least not in Astrapotherium. 

 The Trigonostylopidae are most nearly related to the Entelonychia, and differ 

 from them only in the shape of the incisors and canines, in the very 

 brachyodont and simple molars. The astragalus, at first convex, becomes 

 flattened as the weight of the animal increases, and loses almost entirely its 

 mobility. 



n.4.3. 



Family 1. Trigonostylopidae Ameghino. 



Incisors small, canines well developed. There is a long diastema 



in front of and behind the conical first premolar. Upper premolars and molars with 

 rounded triangular or quadrangular shape, very simple, with a parastyle, ectoloph, 

 protoloph, and rudiment of a metaloph. 

 Lower premolars and molars composed of 

 a short oblique transverse ridge and one 

 crescent, at the posterior end of which there 

 is a small inner cusp. Astragalus with a 

 rather long neck. 



TrigoTwstylops ivortmani Ameghino. Upper Eocene 

 (Notostylops beds), Patagonia. A, Upper fourth 

 premolar. B, Upper molar. C, Lower third molar. 



l/l. 



It becomes practically 

 Upper molars 



The Trigonostylopidae have the 

 simplest and lowest molars of all 

 South American mammals of the 

 Tertiary. Descendants of this family are unknown 

 extinct in the Oligocene. 



Trigonostylops (Fig. 329), Pleurystylops Ameghino, 

 triangular. Eocene ; Notostylops beds. 



Pseudostylops, Edvardocopeia Ameghino. Upper molars quadrangular. 

 Oligocene ; Astraponotus beds. 



^ Ameghino, Florentino, Sur les ongules fossiles de I'Argentine. Revista del Jardin zoologico 

 Buenos Aires, 1894. — Notices preliminaires sur des ongules nouveaux des terrains cretaces. Bol. 

 Acad. Nacion. de Cienc. de Cordoba, vol. xvi., 1901. — Gaudry, A., Mem. Soc. Geol. France. 

 Paleont. vol. xii., 1904. Annales de Paleontologie, 1906. — Lydekker, R., Anales del Museo 

 de La Plata. Paleontologia, vol. ii., 1892. 



