THE CRANIAL FORAMINA OF PROTROGOMORPHOUS RODENTS; AN ANATOMICAL AND PHYLOGENETIC STUDY JOHN H. WAHLERr Dedicated to Katherine Alexander and James Carol and Daniel CONTENTS LIST OF FIGURES 363 ABSTRACT 363 INTRODUCTION 364 CRANIAL FORAMINA OF RODENTS WITH SPECIAL REFERENCE TO MARMOTA 366 Systems: Cranial nerves 367 Arteries . 368 Veins 369 Foramina of the rodent skull 369 PARAMYIDAE Param ys 374 Leptotomus 379 Reithroparannjs 380 Ischyrotumus 381 Fseudotomus 383 Manitsha 384 SCIURAVIDAE .-... 385 ISCHYROMYIDAE 388 CYLINDRODONTIDAE 393 PROSCIURIDAE 397 APLODONTOIDEA 400 CONCLUSIONS 405 REFERENCES 408 LIST OF FIGURES 1. Marmota monax 370 2. Paramys copei _ _ 375 3. Paramys delicattis 376 4. Auditory and pterygoid regions of Paramys copei 377 ^ American Museum of Natural History, Verte-brate Paleontology Department, Central Park West at 79th Street, New York, N. Y. 10024. 5. 6. 9. 10. 11a. lib. 12. 13. Reithroparamys delicatissimus 380 Auditory and pterygoid regions of Ischyrotomus oweni 382 Sciiiraviis nitidus .__. 385 Auditory region of Sciuravus nitidus 387 Ischyromys typus 389 Ardyitomys occidentalis 394 Prosciurus sp. 398 Prosciurus aff. saskatchewaensis 398 Allomys nitens 400 Mijlugauhis laevis 401 Abstract. The cranial foramina and the blood vessels and nerves passing through them are de-scribed in detail for the sciurid genus Marmota; this data serves as the basis for understanding structures seen in the fossils. The cranial foramina are described and compared in North American specimens of the protrogomorphous rodent families Paramyidae, Sciuravidae, Ischyromyidae, Cylindro-dontidae, Prosciuridae, Aplodontidae, and Myla-gaulidae. The least variable foramina are those that transmit nerves; the most variable, veins. Presence or absence, relative position, number, and relative size of foramina are useful characters in determining relationships. Within the Para-myidae differences indicate an early radiation of lineages. Paramyids and sciuravids ha\'e man\' primitive features in common, but differ in several details; of especial interest in these families are the pathways of the internal carotid artery and its branches. Peculiarities common to the foramina of ischyromyids and cylindrodontids suggest that the two groups can be made subfamilies of the family Ischyromyidae. The Prosciuridae are included like-wise with the Aplodontidae and Mylagaulidae in the Aplodontoidea. Bull. Mus. Comp. Zool., 146(8) : 363-410, December, 1974 363
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