o^ 



GEOLOGICAL SERIES 



OF 

 FIELD MUSEUM OF NATURAL HISTORY 



Volume VI Chicago, December 31, 1934 No. 5 



THE AUDITORY REGION OF AN UPPER 

 PLIOCENE TYPOTHERID 



By Bryan Patterson 



Assistant in Paleontology 



Results of the First Marshall Field Paleontological Expedition 

 TO Argentina and Bolivia, 1922-24 



A thorough account of the otic region of Tijpotherium cristatum 

 (Serres) has been given by Van Kampen in his classic work "Die 

 Tympanelgegend des Saugetier-schadels" (1905, pp. 610-613). A 

 few new features are brought out in the present study and certain 

 of Van Kampen's homologies are re-interpreted. The auditory 

 region of Pseudotypotherium, as here understood, agrees in essentials 

 with that of other notoungulates previously described by me (1932). 

 The description given below has been taken from American Museum 

 No. 14509 and has been written to serve as a basis of comparison in 

 connection with the study of the Typotheria from the Deseado and 

 Colhue-Huapi beds of Patagonia collected by the First Marshall 

 Field Expedition of Field Museum (1922-24) and by the Scarritt 

 Patagonian Expedition of the American Museum (1930-31). 



I wish to express my thanks to the authorities of the American 

 Museum for their kindness in permitting study of this and other 

 specimens, and to Mr. Carl F. Gronemann, Staff Illustrator, Field 

 Museum, for his painstaking work on the figures. 



Pseudotypotherium pseudopachygnathum^ (Ameghino). 



Horizon. — Monte Hermoso beds, upper Pliocene. 



The auditory bulla in the Typotheria has hitherto been regarded 

 as simple and hollow; Van Kampen, in describing the bulla of 

 T. cristatum, states that it is wahrscheinlich hohl. Recently con- 

 ducted investigations on the internal structure of typotherian bullae, 



1 For synonymy see Kraglievich (1934, pp. 35-36, and references'). Pseudo- 

 typotherium is very close to Typotherimn, the principal distinction being that in the 

 Monte Hermoso genus the palatal constriction at the anterior end of the maxillaries 

 is very slight, whereas in the Pampean genus it is pronounced. 



No. 331 



