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I. PACHYCEPHALOSAURS A. Shared, Derived Characters of the M

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I. PACHYCEPHALOSAURS A. Shared, Derived Characters of the M CLASS 7: PACHYCEPHALOSAURS AND HOW TO GIVE A DINOSAUR AN IQ (EQ) I. PACHYCEPHALOSAURS A. Shared, derived characters of the main groups Reminder: Pachycephalosaurs are ornithischian, genasaurian, but on a different evolutionary branch than stegosaurs and ankylosaurs (thyreophoran eurypods). Derived characters of Cerapoda 5 or fewer teeth on premaxilla Diastema between teeth on premaxilla and those on maxilla Finger-like projection (trochanter) on the femur Derived characters of Marginocephalians Shelf of bone at back of skull made of thickened, expanded squamosal and parietal bones Reduced pubis Derived characters of Pachycephalosauria Shared derived traits: Thickened skull roof, Ultimately lose temporal fenestra Expanded cheek bones Forward rotation of the occipital region, Expanded occipital region V-shaped notch on cervical vertebrae (nuchal ligament) Ossified tendons in tail Double ridge and groove articulation on dorsal vertebrae Expanded ribs in sacrum, Very reduced pubis General traits: Moderate brain size, most with expanded nerves for olfaction (sense of smell) Short arms (1/4 leg length), Obligate bipeds A who's who of: Flat-heads: Basal Homalocephaloidea: short canines, pitted skull roof, smaller Fat-heads: Pachycephalosauridae: extreme doming, smooth skull roof, larger B. When did pachycephalosaurs evolve? Early Cretaceous first appearance, Late Cretaceous dominance (up to 10% of fauna) C. Where did pachycephalosaurs live? Primitive taxa: Europe - why did they fail here? Flat heads: Asia Fat heads: North America, Asia D. Pachycephalosaur Lifestyles 1. HABITAT Poor preservation may be strongly biasing record North American specimens may largely be transported from upland regions (or not). Preferred inland vs. coastal settings? Do occur in desert and rich basin settings in Asia. Seem to be forest adapted animals 1 2. MOVEMENT No well established trackways known, so speed is a mystery 3. FOOD AND EATING Herbivorous browsers (probably restricted to vegetation 2 m high or lower) Peg-like teeth in front, triangular, leaf-shedding teeth in back Expanded posterior gut for fermentation 4. BRAINS Encephalization quotients moderately low, like ceratopsians Large olfactory lobe 5. INTRASPECIFIC COMBAT AND DEFENSE Head butting Pros: Thick skulls with many scars, unique head-neck arrangement (head down, strong nuchal ligament, rotated occiput), skull bone texture with bony columns are optimum for absorbing shock, strong development of tendon ossification, tongue-groove articulation along spine Sexual Dimorphism: are we sure? Cons: Skulls lack air pockets and stabilizing horns of modern head-butters; narrow contact on domes would be hard targets, body columns are most pronounced in young, not older, individuals, dome bones are highly vascularized (vulnerable to bleed out). Alternate Hypotheses for Domes Flank butting? Head pushing? Species recognition? II. CERATOPSIANS (PART I) GENERAL COMMENTS First really recognized in 1880's First named genus was Triceratops Mostly North American Excellent fossil record, suggesting that they existed in large numbers and in suitable habitats for good preservation One of most diverse groups of plant-eating dinosaurs of Late Cretaceous CERATOPSIAN SHARED DERIVED TRAITS rostral bone at tip of narrow snout flared cheeks (jugal bones) highly vaulted palate nares high on skull MAJOR CLADES IN CERATOPSIA Psittacosaurus most species-rich, genus-poor dino clade (7 species) widespread and common in Asia in Early Cretaceous 2 Shared derived traits short snout, nares very high on skull, 3 long fingers, 1 reduced finger General traits bipedal broad wear surfaces on cheek teeth, but teeth did not occlude precisely less than 2 m long back and hip ossified tendons in some specimens skin with large and small scales bristles extending vertically from tail!!! Neoceratopsians all over North American in the Late Cretaceous best fossil record of any dino group Shared derived traits sharply keeled rostral & predentary bones very large head & prominent frill obligate quadrupeds fusion of first 3 cervical vertebrae Protoceratopsidae All Late Cretacous Shared derived traits Sinus in maxilla, small-bodied (1 - 2.5 m) Small frills, but no horns General Features Jaw muscles expand from coronoid process onto frill Clustered skeletons indicate gregariousness Sexual dimorphism Ceratopsidae Shared derived traits Enormous skulls (>6 feet) (largest of any land animal EVER) with big frill Enlarged nostrils Reduced temporal openings Horns (probably with sheaths) Large: 4 - 8 m long Up to 10 sacral vertebrae First neck vertebrae fused (4 in Triceratops) Complex dental battery (adjacent teeth locked together in longitudinal rows and vertical columns); as teeth along cutting edge wore out, they were lost and replaced by new teeth from below General Features Ossified tendons in hip region Quadrupedal 5 fingers, 4 toes 3 Short-frilled Ceratopids Large nasal horn, short brow horns More primitive Short high face, short frill Long-frilled Ceratopsids Enlarged rostral bone, long supraorbital horns, short nasal horn, some sinuses on skull Long, low faces, include largest of all ceratopsids (Torosaurus, Triceratops, Pentaceratops) Long frill supported large, jaw-moving muscles Bone of horns and frills bore grooves and channels for blood vessels WHERE AND WHEN Psittacosaurus: ~100 Ma in Early Cret. of Asia (only) Protoceratops: Late Cret. of Asia and North America (migration about 75 Ma?) Ceratopsids: all Late Cret. of North Amercia They were around for the final curtain call! ***originated in Asia and spread to North America 4 .
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