136 BULLETIN 16 9, UZS^ITED STATES NATIONAL MUSEUM 



Ml that Douglass mistook for a complete tooth. The type species 

 are synonymous. 



Douglass referred Picrodus questionably to the Epanorthidae 

 (=Caenolestidae) and Alegopterna questionably to the Insectivora, 

 without family reference. The resemblance to caenolestids is con- 

 fined to a vague adaptive similarity to some fossil forms with enlarged 

 Ml and is not indicative of affinity. Picrodus is almost certainly a 

 placental mammal. Among placentals, however, I am not acquainted 

 with any genus with which close and direct comparison is possible. 

 There is, indeed, a vague resemblance to certain liighly speciahzed 

 recent bats, but this does not extend to structural details, is contra- 

 dicted by the quite different arrangement of the anterior dentition, 

 and is more likely to be misleading than not. 



There is one known genus, Zanycteris, with which Picrodus is almost 

 certainly closely related, although direct comparison is impossible 

 since in Picrodus only lower and in Zanycteris only upper teeth are 

 known. As I have elsewhere noted (Simpson, 1935a), Zanycteris 

 (like Picrodus) resembles some recent bats, particularly the phyllo- 

 stomatids, in adaptive characters of the cheek teeth but is different 

 in details probably of more importance as indices of affinity and in 

 the structure of the anterior dentition, as far as it is known. The 

 great probabihty of affinity between Picrodus and Zanycteris is inde- 

 pendent of the possibility that they are related to the Chiroptera. 

 In Zanycteris the reduction and complete lack of molarization of the 

 premolars, the enlargement of M^ and reduction of M^, and the peculiar 

 papillated coronal enamel are all unusual specializations analogously 

 developed in the lower dentition of Picrodus. Furthermore, even in 

 detail the shapes of M^"^ in Zanycteris adapt them perfectlj^ for occlu- 

 sion with lower teeth like those of Picrodus. Zanycteris paleocena 

 will not occlude with Picrodus silhejiingi, being a smaller species, but 

 probably a dentition structurally the same as that of Zanycteris but of 

 different size would occlude with Picrodus silherlingi. Zanycteris is 

 known only from one specimen found in the Tiffany, Upper Paleocene, 

 of southwestern Colorado. Its type is certainly not the same species 

 as that of Picrodus, and the genera are probably distinct, but not 

 surely. Knowledge of their exact affinities must await discovery of 

 upper teeth of Picrodus or lower teeth of Zanycteris. 



PICRODUS SILBERLINGI Douglass 



Figure 28 



Picrodus silherlingi Douglass, 1908, p. 17. 

 Megopterna minuta Douglass, 1908, p. 18. 



Tyjpe. — Carnegie Mus. no. 1670, right lower jaw with P4-M1. 

 Collected by A. C. Silberling. 



