UPPER CRETACEOUS INSECTIVORA 



137 



Crown 



tops apparently belongs either in the Zalambalestidae or in the Leptictidae, but any 

 attempt to refer the other two genera definitely to some known family would probably 

 be premature. 



Gypsonictops Simpson 1 927 

 1927. Gypsonictops, Simpson, Amer. Mus. Novitates, No. 267, p. 6. 



Definition. — Typical upper molars of leptictid type, short, transverse, with 

 crescentic protocone, laterally compressed paracone and metacone, small para- and 

 metaconules, narrow, sharp external cingulum, a small heel posterior to the protocone, 

 and a feeble anterior cingulum. Referred last molar oblique, metacone reduced, para- 

 style large and prominent. Referred last premolar with paracone and metacone closely 

 approximated, the former the larger, protocone a small low heel directly internal to 

 the metacone, with small posterointernal cingulum but no anterointernal cingulum. 



Type. — G. hypoconus Simpson. 



Distribution. — Lance and equivalents, Wyoming and Montana. 



Last upper premolars and typical 

 upper molars of this type were known to 

 Marsh, who referred them to Telacodon 

 laevis and Batodon tenuis (1892 a, PI. 

 IX, fig. 2, PI. XI, figs. 1-2). Since the 

 types of the latter genera and species 

 have no parts directly comparable with 

 these upper teeth, such association is not 

 open to proof. It may eventually prove 

 that Gypsonictops is the upper dentition 

 of one or the other of these two genera, 

 but the association would indicate an 

 animal quite diflFerent from those which 

 Gypsonictops seems most closely to re- 

 semble in the upper cheek teeth and in 

 any event this important type, the only 

 definite American pre-Paleocene placental, should have an applicable name. 



In molar structure Gypsonictops stands very close to the Paleocene to Oligocene 

 Leptictidae. If P* is correctly identified it is distinguished from that of any later 

 leptictid by being somewhat less molariform, a primitive feature. If, as is possible, this 

 tooth is really P', then it is somewhat more advanced than in the later forms, which is 

 improbable. There is also a close resemblance to Zalambdalestes of the Mongolian 

 Cretaceous, although Gypsonictops is more advanced in the possession of a definite 

 hypocone. Reference to one or the other of the closely related families Leptictidae and 

 Zalambdalestidae would depend chiefly on the specializations shown by the more 

 anterior teeth, as yet unknown in association. For the present provisional reference to 

 the Leptictidae is possible, and in any event relationship to this division of the Insec- 

 tivora is clearly indicated. 



LcLat. PrcTTtotar 



Sxtemal 



Posterior 



Fig. 53. Gypsonictops hypoconus. Upp)er cheek teeth. 

 Eight times natural size. 



