Cranial Morphology of Some Oligocene Artiodactyla · PDF file CRANIAL MORPHOLOGY OF SOME OLIGOCENE ARTIODACTYLA By FRANK C. WHITMOKB, JR. ABSTRACT A study of the cranial morphology

Cranial Morphology

of Some Oligocene /

Artiodactyla GEOLOGICAL SURVEY PROFESSIONAL PAPER 243-H

Cranial Morphology

of Some Oligocene

Artiodactyla By FRANK C. WHITMORE, JR.

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 1952, PAGES 117-160

GEOLOGICAL SURVEY PROFESSIONAL PAPER 243-H

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1953

UNITED STATES DEPARTMENT OF THE INTERIOR

Douglas McKay, Secretary

GEOLOGICAL SURVEY

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 35 cents (paper cover)

CONTENTS Page

Abstract_--_-------___________-__________________ 117 Introduction _______________________________________ 117

Acknowledgments_ ____________________________ 117 Cranial morphology of some Oligocene Artiodactyla____- 118

Cranial morphology of Merycoidodon ______________ 118 Bones of the skull___.__________________ 118

Occipital.__________________________ 118 Basisphenoid_ ________________________ 120 Alisphenoid_ __________________________ 123 Presphenoid_ _________________________ 123 Orbitosphenoid— _ ______________________ 124 Ethmoid and turbinals________________ 124 Vomer__________________________ 126 Preinterparietal and interparietal— _______ 126 Parietal.. ______________________ 126 Frontal—_____________________ 126 SquamosaL ____________________________ 127

Tympanic region. __________________________ 131 Pars petrosa of the periotic bone________ 131 Middle ear and surrounding structures- - _ _ 132 External auditory meatus______________ 135 Pars mastoidea of the periotic bone _______ 135

Pneumatic sinuses__________________________ 136 Circulatory system of the skull-______________ 137

Arteries _______________________________ 137 Veins and venous sinuses._______________ 138

Dorsal sinus system_________________ 138 Basilar sinus system_______________ 139 Subsphenoid veins and sinus venosus

ossis sphenoidalis_________________ 140 Nerves of the skull region__________________ 141

Cranial morphology of Poebrotherium______________ 141 Bones of the skull_________________________ 141 Tympanic region.__________________________ 144

Pars petrosa of the periotic bone________ 144 Middle ear and surrounding structures. _ _ _ 145 External auditory meatus______________ 146 Pars mastoidea of the periotic bone _______ 146

Pneumatic sinuses__________________________ 146 Circulatory system of the skull— _____________ 147

Arteries.,_____________________________ 147

Cranial morphology of some Oligocene Artiodactyla—Con. Cranial morphology of Poebrotherium—Continued

Circulatory system of the skull—Continued Veins and venous sinuses____----___---_-

Dorsal sinus system_______-___-_-.__ Basilar sinus system——____________ Sinus venosus ossis sphenoidalis- _

Nerves of the skull region.— ____-----------_ Cranial morphology of Leptomeryx. _______________

Bones of the skull_________________________ Tympanic region____________--_------_--_--

Pars petrosa of the periotic bone_____.__._ Middle ear and surrounding structures External auditory meatus— _____________ Pars mastoidea of the periotic bone.______

Pneumatic sinuses__________________________ Circulatory system of the skull____---____-_--

Arteries ______________-____---___------ Veins____________________---___----__

Dorsal sinus system_________________ Basilar sinus system———____________ Sinus venosus ossis sphenoidalis-_____

Morphological conclusions______-_____---_---_----_-- Bones of the skull_____________________________

Primitive characteristics_____________________ Characteristics of doubtful significance__ ______

Tympanic region. ______________________________ Primitive characteristics_____________________ Characteristics of doubtful significance. _______

Pneumatic sinuses._____________________________ Primitive characteristics.____________________

Arteries.-________--_____-----_--------------_- Primitive characteristics _____________________

Veins and venous sinuses--__-_--_-------_------- Primitive characteristics.____________________

Anatomical peculiarities indicating habits, evolution- ary trends, relationships.----------------------

Phylogenetic conclusions___________________________ Tylopoda._______________________-_--_--__--- Mery coidodontidae. _____________ _______________ Leptomerycinae. ______________---___-----_----_ Summary of phylogenetic conclusions _____________

Selected bibliography.-________-_---_---------_-----_ Index.______________________---___------_--_-----_

ILLUSTRATIONS

FIGURE 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.

Merycoidodon culbertsonii. Lateral view of skull__-____________________-_---_____---_-_- M. culbertsonii. Ventral view of basis cranii.__________________________________________ M. culbertsonii. Internal view of basis cranii, from above________________-_-___-__------ M. culbertsonii. Ventral view of basis cranii, with restoration of blood vessels..____________ Frontal sections of the skulls of M. culbertsonii and Dicotyles labiatus... ______-_____--__-_- M. culbertsonii. Thick section of skull, viewed posteriorly into cerebellar fossa.____________

Thick section of skull in region of auditory bulla___________.______--_--- Thick section of skull at level of post-glenoid processes._._________---_--- Thick section of skull, looking anteriorly into olfactory lobes_______--__-_- Thick section of skull, looking anteriorly through nasal cavity___________ Same as figure 1, with nasal cavity and pneumatic sinuses outlined.. ______-

Poebrotherium wilsoni. Lateral view of skull____________________-___-_____-_______-_--- P. wilsoni. Ventral view of basis cranii.______________________________________________ P. wilsoni. Thick section of skull, looking posteriorly from level of vagina processus hyoidei. P. wilsoni. Thick section of skull, looking anteriorly into olfactory lobes__________________ Leptomeryx evansi. Lateral view of skull_________________________-__-_-______-___-_-_- L. evansi. Ventral view of basis cranii______________________________._________________ L. evansi. Thick section of skull, looking anteriorly from region of bulla._____-___-__-_-__-

M. culbertsonii. M. culbertsonii. M. culbertsonii. M. culbertsonii. M. culbertsonii.

Page

147 147 147 147 147 148 148 149 149 150- 150 150 150 150 150 151 151 151 151 151 151 151 151 152 152 152 152 152 152 152 153 153

153 154 154 154 155 155 155 159

Page 118 119 120 121 124 128 128 129 129 130 136 141 142 143 145 148 149 140

CRANIAL MORPHOLOGY OF SOME OLIGOCENE ARTIODACTYLA

By FRANK C. WHITMOKB, JR.

ABSTRACT

A study of the cranial morphology of three Oligocene Artio- dactyla (Merycoidodon, Poebrotherium, and Leptomeryx), based largely on serial sections, reveals many cranial charac- teristics found only in the most primitive Recent mammals.

The Oligocene genera had several cranial veins which indicate that these artiodactyls were not far removed from a primitive insectivore-like ancestor. They had a well-developed internal carotid artery in contrast to the Recent Artiodactyla, very few of which retain this structure. The cranial circulation pattern of the Oligocene forms shows an evolutionary tendency in the Artiodactyla to abandon endocranial for extra-cranial paths.

Other primitive characteristics are the lateral partitions of the pituitary fossa (representing the primitive side wall of the skull) and large temporal venous sinus in Merycoidodon, and the simple pneumatic sinus system in all three genera.

The selenodont Artiodactyla exhibit an evolutioaary trend toward the amastoid skull pattern now found only in bunodont families.

The subarcuate fossa of the pars petrosa of the periotic bone in the Tylopoda has a peculiar shape, constant in the suborder and differing from the condition in other selenodont Artio- dactyla. This is added evidence that the Tylopoda must have separated from other artiodactyl lines of evolution no later than the middle Eocene. The simpler subarcuate fossa of Merycoido- don and Leptomeryx indicates their alliaace with the suborder Pecora.

On the basis of cranial structure, the family Hypertragulidae is divided into the subfamilies Hypertragulinae and Leptomery- cinae, both of which existed from the early Oligocene through the early Miocene.

INTRODUCTION

The Artiodactyla, or "even-toed ungulates", form one of the largest and most varied of the orders of mam- mals. They are today near the acme of their develop- ment ; their distribution is world-wide and they include in their numbers the pigs, peccaries, hippopotami, camels, deer, giraffes, cattle, sheep, goats, antelope and the tiny chevrotains of Asia and Africa.

An examination of the Artiodactyla reveals several characteristics in common: hoofs, a more or less herbiv- orous diet, and a tendency toward a foot structure in which the weight rests mainly upon two toes of each foot. This mesaxonic type of foot, whose axis runs between the third and fourth toes, has given rise to the name of the order. Two other morphological peculiari- ties possessed by all the Artiodactyla are not externally visible but are very important. The first of these is the absence of the third trochanter of the femur, an

eminence on the posterior side of the bone which selves as a muscle attachment in some mammals. The second and even mor