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GEOL 240 The Dinosaurs: Marginocephalia

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Title: No Slide Title Author: Maribeth Price Last modified by: Art Chadwick Created Date: 1/6/1999 4:49:16 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: GEOL 240 The Dinosaurs: Marginocephalia


1
GEOL 240 The Dinosaurs Marginocephalia
2
Summary
  • Marginocephalia represent an important group of
    dinosaurs that became dominant in U. Cretaceous
  • Characterized by development of a marginal ridge
    of bone along the back of the skull
  • Ornithischian and herbivorous
  • Includes two taxa on the Ranch Triceratops and
    Pachycephalosauria

3
Marginocephalia
4
Marginocephalia
  • Name means "ridge head"
  • Characterized by a frill a shelf of bone
    extending back over occipital region of skull
  • Plant eating
  • Absent from fossil record until Middle
    Jurassic, and all known fossils except one are
    Cretaceous
  • Primitive forms are bipedal in one branch
    derived forms become very large and obligate
    quadrupeds
  • Marginocephalian skulls capture imagination
    with lots of suggestions as to functions, mainly
    display and/or combat

5
Marginocephalia
6
Marginocephalia
  • Except for a few fragmentary specimens, all
    marginocephalians known fall into one or the
    other of two clades the thick-skulled
    Pachycephalosauria or the deep-beaked and often
    frilled (and sometimes horned) Ceratopsia.

7
Marginocephalia
  • Oldest known ceratopsian fossil from the Middle
    Jurassic of China (Chaoyangosaurus)
  • Next oldest, and much better known, is Lower
    Cretaceous Psittacosaurus, the "parrot dinosaur"
  • Lowest fossil marginocephalians were bipeds
    (possibly facultative bipeds), with bodies like
    heavily build hypsilophodonts

8
Marginocephalia
  • Synapomorphies of Marginocephalia
  • Rostral bone, a bone unique to Ceratopsia
  • A single, non-paired bone attached in front of
    the premaxillae (and so it is a pre-premaxilla!)
  • Forms the upper part of the beak, mirror image of
    the predentary
  • Jugals form pointed "cheek bones"
  • Ceratopsians have very deep and powerful jaws,
    with strong shearing bite

9
Rostral bone of Triceratops
10
Ceratopsia
  • one of the most diverse groups of the Late
    Cretaceous
  • Two clades
  • Psittacosaurus
  • Neoceratopsia

11
Psittacosaurus
12
Psittacosaurus
  • parrot dinosaur
  • primitive Ceratopsia
  • rudimentary frill
  • short snout
  • high nostrils
  • tall rostrum
  • superficially resembles parrot beak

13
Psittacosaurus
14
Psittacosaurus
15
Psittacosaurus
16
Psittacosaurus
17
Neoceratopsia
  • In Upper Cretaceous, the first of the more
    advanced Neoceratopsia appears
  • Neoceratopsians characterized by a prominent
    frill
  • Frill formed by extensions of the parietal and
    squamosal
  • Served in part as increased surface attachment
    for jaw muscles
  • Could also have been used as a visual display or
    for cooling or for defense.

18
Neoceratopsia
  • Neoceratopsians also have enlarged heads (that
    is, their heads are 20 or more the length of the
    postcranium)
  • First fossil neoceratopsians, such as upper Lower
    Cretaceous Archaeoceratops may have been bipedal
  • Subsequent neoceratopsians had larger frills and
    heads, such that they were doubtless obligate
    quadrupeds
  • Protoceratops of the Upper Cretaceous of Mongolia
    and Leptoceratops of the Upper Cretaceous of
    western North America represent this class of
    neoceratopsians.

19
Neoceratopsia
  • extremely large head
  • broad and prominent frill
  • pointed and sharply keeled rostrum
  • obligate quadrupeds

20
Neoceratopsia
  • Two clades
  • Protoceratopsids and Ceratopsids

21
Neoceratopsia
22
Protoceratopsids
  • small (1.2 meters)
  • primitive group - intermediate between
    Pittscosaurus and ceratopsids
  • relatively larger skull but still small
  • more pronounced frill
  • fore and hind limbs equal length
  • massive limbs and big feet
  • no horns
  • small nostrils

23
Protoceratopsids
24
Protoceratopsids
25
Protoceratopsids
26
Ceratopsidae
  • moderately large 4 - 8 meters
  • habitual quadrupeds
  • very large skull (1 - 2.4 meters (!) long)
  • large nostrils
  • prominent frills
  • variety of horns

27
Ceratopsidae
  • two types
  • Pachyrhinosaurines (more primitive)
  • Ceratopsines

28
Ceratopsidae
29
Pachyrhinosaurines
  • relatively short high face
  • shorter frill
  • large nasal horns
  • smaller postorbital horns

30
Pachyrhinosaurines
31
Ceratopsines
  • long, low faces
  • long frills
  • large postorbital horns
  • small nasal horns
  • Triceratops the most common Upper Cretaceous
    form known only from North America
  • Found on the Hanson Ranch, second in abundance to
    Edmontosaurus

32
Ceratopsines
Triceratops horridus
33
Ceratopsines
34
Pachycephalosauridae
35
Pachycephalosauridae
  • Sometimes called boneheads or domeheads or
    buttheads
  • Except for a possible Lower Cretaceous form from
    Europe, are known only from the Late Cretaceous
    of Asia and western North America
  • Apparently were obligate bipeds (why?)
  • Postcranially resemble heavy hypsilophodonts

36
Pachycephalosauridae
  • Most obvious derived feature thickened bone on
    skull roof
  • In primitive forms, the skull is still
    relatively flat
  • In advanced forms, this thickened roof forms a
    dome
  • Suggested behavior uses for these domes
  • Used to butt theropod legs and bellies as defense
  • Used like the horns of bighorn sheep in dominance
    fights for females or territory, etc.

37
Pachycephalosauridae
  • Some indication of sexual dimorphism, with bigger
    domed males and smaller domed females
  • Pachycephalosaurs also have rows of small dermal
    ossifications around back of skull
  • Some indication of strengthened cervical and
    dorsal vertebrae (for absorbing impacts?)
  • Most were smaller than humans only last and
    largest (Pachycephalosaurus) was bigger than a
    human
  • Relatively unsophisticated jaws and teeth
  • Relatively rare as fossils several have been
    found on the Ranch

38
Pachycephalosauridae
39
Pachycephalosauridae
40
Pachycephalosauridae
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