NO. 7 TERTIARY APHELISCUS AND PHENACODAPTES — GAZIN 5 



The mental foramen, the position of which, as Simpson (1937a, 

 p. 120) notes, has been unduly emphasized, may warrant comment. 

 It exhibits a comparatively small posterior opening somewhat farther 

 forward in the Apheliscinae than in Pentacodontinae or Pantolestinae. 

 It is variable in Phenacodaptes and is observed in positions beneath 

 the anterior part of P 4 to the posterior part of P 3 . A larger opening 

 is noted beneath P x or P 2 . In a specimen of Apheliscus (U.S.N.M. 

 No. 1 9162), these foramina were noted beneath posterior portion of 

 P 3 and beneath P^ In Aphronorus the posterior foramen may be 

 small and varies in position from beneath Mx to the posterior part of 

 P 4 . An equally large or larger anterior opening is seen below P 2 . In 

 Bessoecetor foramina were noted beneath the posterior part of both 

 M x and P 2 , and in one specimen, U.S.N.M. No. 9442, anterior fora- 

 mina were observed below the posterior portions of both P 2 and P 3 . 

 In Bridger Pantolcstes I have seen only the well-developed foramen 

 beneath M 1# 



Among the Insectivores outside of the Pantolestidae I find a rather 

 more remote relationship to the mixodectids indicated. There would 

 appear to be rather less to suggest affinities with other orders. Among 

 these, however, perhaps the condylarths should be considered. The 

 relatively low trigonids of the lower molars seem indicative of a pos- 

 sible condylarthran relationship, and a form such as Choeroclaenus 

 among the mioclaenine hyopsodonts is not too different from Phenaco- 

 daptes but there is, nevertheless, a more inflated appearance to the 

 molar cusps and the premolars would appear to have little or nothing 

 to recommend them. The possibility that the Phenacodaptes- Aphelis- 

 cus line represents condylarth development rather paralleling that of 

 pentacodonts cannot be entirely disregarded, but the same reasoning 

 might apply equally well were they to be regarded as belonging to such 

 other orders as primates, creodonts, or artiodactyls. Comparison with 

 Pentacodon and Aphronorus appears rather more pertinent and better 

 accounts for a number of minor details of similarity not easily 

 dismissed. 



REFERENCES 



Cope, Edward D. 



1874. Report upon the vertebrate fossils discovered in New Mexico with 



descriptions of new species. Geogr. Expl. and Surv. West of 100th 

 Meridian (Wheeler), Appendix FF, Ann. Rep. Chief of Engineers, 

 1874, pp. 1 -18. 



1875. Systematic catalogue of Vertebrata of the Eocene of New Mexico, 



collected in 1874. Geogr. Expl. and Surv. West of 100th Meridian 

 (Wheeler), pp. 1-37. 



