EVOLUTION OF THE SKULL AND DENTITION OF OLIGOCENE TITANOTHERES 481 



Measurements of sJculls and jaws associated with or referred to the Brontops phylum, in millimeters 



SYSTEMATIC DESCRIPTIONS OF GENERA AND SPECIES IN 

 THE BRONTOPS-DIPLOCLONUS PHYLUM 



Teleodus Marsh 



Plate XIX, D>, D^; text figures 188, 204, 409, 413 

 [For original description and type references see p. 227] 



Generic characters. — Related to or identical with the 

 lower Oligocene Brontops. Three lower incisors in 

 each jaw, instead of two as in other Oligocene titano- 

 theres; i2 the largest of the series; rounded or non- 

 cingulate incisor crowns. 



Species. — Teleodus avus Marsh, Teleodus primitivus 

 (Lambe). As the most primitive Oligocene genus 

 known Teleodus should be distinguished from the most 

 progressive upper Eocene species, Profitanotherium 

 superhum, P. emarginafum, and other Eocene types. 

 Teleodus is distinguished from Protitanotherium by 

 three characters — (1) incisors smaller, round topped, 

 not flat topped; (2) canines erect, more slender; (3) 

 premolars more advanced in evolution. 



Teleodus avus Marsh 



{" Megacerops avus" Osborn, 1902) 

 Plate XIX, D; text figures 188, 409 



[For original description and type references see p. 228J 



Type locality and geologic horizon. — Chadron forma- 

 tion, lower Titanotherium zone. Exact locality not 

 published. 



Specific characters. — Dental formula I-j, Cx, P-j, 

 M^. Of the three lower incisors in place on each 

 side the middle one is the largest; there is a short 

 diastema behind the lower canine, but no first pre- 

 molar. P^-p* 106 millimeters; molars incomplete. 

 Type, Yale Mus. 10321. 



As already indicated, this species is known only 

 from the type lower jaw in the Yale Museum collec- 

 tion and is of exceptional interest because it retains, 

 either as a reversional or as a fixed generic or specific 

 character, the full number (6) of lower incisor teeth, 

 as in all the Eocene titanotheres, the formula thus 

 being I^ as against I^qj- 



Consistent with this primitive morphologic condi- 

 tion the type jaw was found by Hatcher near the 

 base of the lower Titanotherium zone, and if the 

 structural indications are supported by other speci- 

 mens it may well remain as the type of a distinct 

 genus, Teleodus Marsh; yet other structural characters 

 relate it closely to Brontops and point rather to affinity 

 to this genus. 



Dentition. — The summits of the incisors are ob- 

 tusely rounded and noncingulate, as in Brontops; the 

 lateral pair (I3) is so much reduced and crowded as 

 to furnish conclusive evidence that it is the lateral 

 incisors (I3) which first disappear in all the bron- 

 topine titanotheres. The second incisors (I2) are 

 relatively large — larger, in fact, than the median pair. 



