B R E XJ.n R A LIBRARY Miiseiiiii of Comparative Zoology JAI^Y 1974 ^^ us ISSN 0006-9698 HQ Cambridge, Mass. 28 December .l9|-% Number 419 PROTOPTYCHUS, A HYSTRIGOMORPHOUS RODENT FROM THE LATE EOCENE OF NORTH AMERICA John H. Wahlert^ Abstract. The North American late Eocene Protoptychus Scott possesses an enlarged infraorbital foramen, a depression on the side of the snout anterior to this foramen for the origin of the anterior part of the middle masseter, tetralophate P*-M^ an enlarged incisive foramen, a deep pterygoid fossa, and apparently no stapedial foramen or carotid canal. These char-acters also occin-in the Caviomorpha. With regard to the zygomasseteric structure and acquisition of an essentially molariform P^, Protoptychus is more advanced than both its possible North American ancestor, which may be either a paranlyid or Mysops, and Platypittamys, the most primitive Deseadan (Oligocene) caviomorph. The Protoptychidae, on present evi-dence, cannot be related closely to any rodents other than these. Pending further knowledge, the family is retained in the Protrogomorpha, but the possibility exists that it may be a specialized offshoot from the North American caviomorph ancestry. Introduction In the course of studying the cranial foramina of North American protrogomorphous and sciuromorphous rodents, I ex-amined the type skull of Protoptychus (Princeton University 11235) and a second, much damaged facial region (PU 11230). I was immediately struck by features that set this form com-pletely apart from all others I had at hand. These were the unusual shape and great posterior extent of the incisive foramen, the large size of the infraorbital foramen, the flatness of the sides ^American Museum of Natural History, Vertebrate Paleontology Depart-ment, Central Park West at 79th Street, New York, N.Y. 10024
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