NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 83 



with the proterotheriid Anisolambda which de Paula Couto (1952) 

 has shown includes Josepholeidya, and occurs in beds regarded as of 

 late Paleocene age in Brazil. Remarkably selenodont for so early a 

 form, nevertheless I note a somewhat different trend in the develop- 

 ment of the accessory cuspules of the upper molars. The proto- 

 conule, for example, is less crescentic and more closely connected 

 to the protocone, whereas the metaconule may be somewhat cres- 

 centic but shows little or no tendency to form a metaloph with the 

 hypocone. The lower molars are perhaps less easily distinguished 

 from those in Meniscotherium and show the metastylid crest as in 

 the latter, but I note that the trigonid is relatively a little shorter 

 anteroposteriorly and the labial wall of the protoconid perhaps more 

 acute. 



The litopterns are presumably of condylarthran affinity, as well as 

 the more bunodont didolodonts which are included within the latter 

 order, so that Meniscotherium may not be too distantly related to 

 such a form as Anisolambda; nevertheless, one was not derived from 

 the other as presently denned, and there is no evidence to show that 

 Meniscotherium represents a return to the Northern Hemisphere of a 

 South American condylarth. 



The possibility of a close relationship between Meniscotherium and 

 the hyracoids provoked considerable speculation during the earlier 

 history of investigation. I am inclined to believe, however, that the 

 relationship is decidedly remote. I suspect that much of the resem- 

 blance between them is adaptive in nature. There would appear to be 

 certain similarities in form and proportions but the details often seem 

 incompatible with any close affinity. There is, of course, a great 

 interval of time between the recent hyracoids and Meniscotherium, 

 as well as a wide geographic separation, and certain of the more 

 obvious differences in the skull may be attributed to its shortening 

 and the increase in the relative size of the brain. 



The shortening of the skull has resulted in the orbits being farther 

 forward with respect to the molar teeth, greatly affecting the orbital 

 plate of the maxilla, and with the convergence anteriorly of the 

 orbital margin of the frontals the possibility of binocular vision is 

 much better in the hyracoids than in the meniscotheres. Moreover, 

 the orbit is almost closed posteriorly by processes from the jugal and 

 parietal. The postorbital processes of the frontals only are well 

 developed in Meniscotherium. The parietals are not involved. 

 Another feature of interest in skull shortening is the more vertically 

 elongate and backward-facing pterygoid fossae, nearly as in man. 



