DEPARTMENT. OF THE INTERIOR FRANKLIN K. LANE, Secretary UNITED STATES GEOLOGICAL SURVEY· GEORGE OTIS SMITH, Director Professional Paper 103 I BRACI-IYCERATOPS A CERATOPSIAN DINOSAUR. FROM THE TWO MEDIClNE FORMATION.OF MONTANA WITH NOTES ON ASSOCIATED FOSSIL REPTILES BY CHAHLES W. GILMORE WASHINGTON GOVERNMENT PRINTING OFFICE 1917 ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 10 CENTS PER COPY A CONTENTS. Page. Introduction ...................................................................... _...................... 1 Stratigraphy of the Two Medicine formation, by Eugene Stebinger .-. 1 Fauna of tho Two Medicine and related formations ...... ~. 3 Ceratopsidae............................................................................................. 7 Brachyceratops montanensis . ............................. , . 7 Osteology of Brachyceratops. 8 The skull .............................................. -. 8 General features.. 8 Nasals...................................................................................... 9 Prefrontals.................................................................................. 9 Post£rontals ..................-. 10 Postorbital... 11 Dermosupraoccipital ................................................................ ~....... 11 Lachrymal ................. .- . 12 Alisphenoid .....................•.... : ................................................· . 13 Exocci pi tal. 14 Premaxillarios ..................... -......................................................... 14 Maxillaries............ 15 Rostral ..............._ .... •................................ ·.................................. 15 Predentary .................... ·. 15 Dentary.................................................................................... 16 Teeth...................................................................................... 16 Supratemporal fossae ........................ ·..... .-. 16 Measurements of the skull.................................................................... 18 The vertebral column .......................................................................... __ 19 General features ........................................................................... _- 19 Cervicals. 19 Dorsals ..............................~. 19 Sacrum ........................................................................-.............. 21 Caudal vertebrae ..............................................................· ....... -....... 23 'fhe ribs .................................................................... , . 25 'l'he chevrons..................................................................................... 2? Ossified tendons ............. ~ . .. 26 The shoulder girdle and fore limb... .. 26 Scapula...................................................................................... 26 Ulna........................................................................................ 27 Radius...................................................................................... 27 li'ore foot..... .. 27 The pelvic girdle and hind limb ....................................· ............................. - 28 Ilium....................................................................................... 28 Pubis ................................................................ :...................... 29 Ischium.................................................................................... 29 Femur ............................. :....................................................... 30 Tibia ..........................................................................·.............. 31 Fibula ............................................................. ·........................ 31 The hind foot......... 31 The specimens.................................................................................. 31 Tarsus ........................................... ·.......................................... 33 ~fetatarsus.................................................................................. 33 Phalanges ................................................................................ : . 34 Restoration of Brachyceratops. 35 Relations of Brachyceratops.. 36 III IV CONTENTS. Page. Trachodontidae ..........· ...................... ~ . 38· Hypacrosaurus altispinus? Brown. : ........ -.............................•. 38. Stephanosaurus marginatus? (Lambe) ............... ~ ...........................·....................... 41 Trachodpnt gen. and sp. undet................... 41 Trachodont gen. and sp. undet......... 43. Ankylosauridae......... • . 43 Europlocephalus sp ... : . .. ~ .............·. 43. Chelonia ...........................· ................. ·r··.................................................. 44 Basilemys sp ............................................ ·..... " .........................·.............. 44 ILLUSTRATIONS. Page. PLATE I. Life restoration of Brachyceratops montanensis ...................•......................•..•.•.•... II. A, Badlands on :Milk River about 30 miles northwest of Cut Bank, Mont.; B; Two Medicine forma­ tion as exposed on Two Medicine River, Mont.; C, Two Medicine formation as exposed on Milk River, Mont .................................. ~............................................... 2 Ill. A, Articulated caudal vertebrae of Brachyceratops montanensis; B, Sacrum of Brachyceratops rnf;>nta- nensis; C, Sacral centra of Brachyceratops montanensis. 20 IV. Skeletal restoration of Brachyceratops montanensis. • . 34 FIGURE l. Gimeralized section of the formations of the Montana group (Upper Cretaceous) in northwestern Montana ............................................... ~..................................... z· · 2. Skull of Brachyceratops niontanensis, lateral view .......·........................................ S 3. Skull of Brachyceratops montanensis, superior view ................................... _. _....... 9 4. Nasals and nasal horn cores of Brachyceratops montanensis ................................ _....... 10• 5. Right prefrontal of Brachyceratops montanensis. .................. : . .......·..................... ll 6. Postfrontals and prefrontals of Brachyceratops montanensis........................................ 11 7. Right postorbital of Brachyaratops montanensis....................................... 12· 8. Cross section of dermosupraoccipital of Brachyceratops rnontanensis .................... _.. 12 9. Dermosupraoccipital of Brachyceratops rnontanen~is. .. 13 10. Derniosupraoccipital of Monoclonius crassus. 14 11. Left exoccipital of Brachyceratops rnontanensis................................................... 14 12. Left premaxillary of Brachyceratops montanensis ..................................... :........... 14 13. Left maxillary of Brachyceratops rnontanensis.................................................... 15 14. Rostral of Brachyceratops rnontanensi~.......................................................... 16 15. Predentary of Brachyceratops rnontanensis...................................................... 16 16. Dentary of Brachyceratops rnontanensis .............. ·......................................... 17 17. Dentary of Brachyceratops rnontanensis......................................................... 17 18. Third upper tooth of Brachyceratops rnontanensis .......................... : . 18 19. Unworn lower tooth of Brachyceratops rnontanensis ............... ·............................... 18 20. Detached tooth of Brachyceratops rnontanensis .............. ~ .. :................................. 18 21. Posterior cervical process of Brachyceratops rnontanensis. 19 22. Anterior dorsal vertebra of Brachyceratops rnontanensis........................................... 20 ' 23. Median dorsal vertebra of Brachyceratops rnontanensis . ....... ; . ... 20 24. Posterior dorsal vertebra of Brachyceratops rnontanensis........................................... 20 25. Centrum of dorsal vertebra of Brachyceratops rnontanensis . ................................. : . 20 26. Sacrum of Brachyceratops rnontanensis with ilia in position....................................... 21 27. Sacrum of Triceratops prorsus with ilia in position............................................... 22 28. Anterior caudal vertebra of Brachyceratops rnontanensis. 24 29. Median caudal vertebra 'of Brachyceratops rnontanen5is........................................... 24 30. Distal caudal vertebrae of Brachyceratops rnontanensis... 24 31. Dorsal ribs of Brachyceratops rnontanensis. 25 32. Posterior dorsal rib of Brachycerat9ps rnontanensis . ...................... : . 26 33. Chevron o~ Brachyceratops rnontanensis .................................. ·....................... 26 34. Left scapula of Brachyceratops rnontanensis. 27 35. Left ulna of Brachyceratops montanensis. 27 36. Proximal and distal portions of the radius of Brachyceratops rnontanensis ................ :......... 28 37. Bones provisionally identified as pertaining to the forefoot of Brachyceratops montanen~is. 28 38. Left ilium of Brachyceratops montanensis. .. 29 39. Left ilium ofBrachyceratops rnontanensis........................................................ 29 CON~ENTS. V Page. FmuRE 40. Right ilium of Triceratops flabellatus Marsh ..................... ~............................... 30 41. Left pubis of Brachyceratops 11wntanensis. ~ ................................................. ,..