GEOL 104 Dinosaurs: A Natural History
Fall Semester 2006
Theropoda II, Coelurosauria: Tyrant Kings and Lesser Royals
Coelurosauria includes a wide diversity of forms, including omnivores,
herbivores, and birds!
Coelurosaurs are characterized by:
- Enlarged brain size compared to other dinosaurs
- Narrow, three-fingered hand
- "Boat-shaped" chevrons for extra tail stiffening
- Tall ascending process of astragalus to absorb stresses of running
- Long slender foot with compressed metatarsals
- "Protofeathers": filament-like structures covering much of the body
Coelurosaur interrelationships have been confusing, but there seems to be a growing consensus.
Compsognathidae (less than 1.5 m long) and 2 m long Ornitholestes represent small
basal coelurosaurs. The main clades of advanced coelurosaurs include Tyrannosauroidea,
Ornithomimosauria, and the diverse Maniraptora.
Tyrannosauroidea (tyrant dinosaurs):
- Characterized by:
- Large skull size
- Expanded area for jaw and neck muscle attachements
- Incisor-like premaxillary teeth for nipping or scraping
- Fused nasals
- Tyrannosauroids begin as small-to-medium-sized predators in the Jurassic and Early Cretaceous.
Best preserved so far is the recently discovered
Guanlong of the Late Jurassic of China. Also of interest is
Dilong of the Early Cretaceous of China (which has protofeathers preserved). Other examples inlcude
Early Cretaceous Eotyrannus of Europe: larger-sized than Guanlong and Dilong, but still with long grasping
three-armed hands. In the Late Cretaceous, become short-armed giants, including eastern North American Dryptosaurus and
the true Tyrannosauridae:
- Tyrannosaurids proper are characterized by:
- Gigantic size (9-13 m long)
- Maxillary and dentary teeth which are thick from side to side (not steak knife-
like, as in most theropods)
- Reduced forelimbs with only two fingers (digits I & II)
- Very long tibiae and metatarsi (also in ornithomimosaurs, troodontids, and
some alvarezsaurids and oviraptorosaurs)
- An arctometatarsus:
- Metatarsus where metatarsal III forms a wedge distally, but pinches out proximally
- Shown to be a good shock absorber for fast running
- Feet of closely related basal tyrannosauroids not completely known, so they may have had it, too
- Also found in some ornithomimosaurs, deinonychosaurs, alvareszaurids, and oviraptorosaurs
- Tyrannosaurids were the dominant predators of the Late Cretaceous of Asia and North America
Ornithomimosauria (name means "bird mimic dinosaurs", but often called
"ostrich mimics" or "ostrich dinosaurs" because of their general similarity to ostriches
in shape and size)
- Similar to tyrannosauroids from the hips back, but very different in
the front end!
- Characterized by:
- Very long necks and small heads
- Long snouts with small teeth (in at least the primitive forms)
- Long arms with metacarpals all the same length and hooking-and-clamping
(rather than grasping) hands
- Advanced clade of ornithomimosaurs: the Ornithomimidae:
- Toothless beaks
- Recent discovery of small jaw plates in ornithomimosaur beaks suggest some could dabble for
food like ducks!
- Were probably fast running omnivores, eating small vertebrates, invertebrates, and plants
- May have been the fastest Mesozoic dinosaurs
- Known from the Early Cretaceous of Europe and Asia, and (for Ornithomimidae) the
Late Cretaceous of Asia and western North America
- Most were about ostrich-sized or larger, but some were small and one (Deinocheirus) was as big as
Maniraptora ("hand snatchers") are characterized by:
Maniraptorans are very diverse. The major clades are:
- Enlarged sternal plates
- Increased forelimb length in most groups
- Large semilunate carpal blocks:
- Modified carpal bones with a pulley-like surface
- Allowed their large hands to be tucked against the body
- Shoulder joints that faced sideways rather than backwards (as in most dinosaurs)
- True broad feathers on arms and tail of at least the small forms
- Backwards-pointing pubis in many forms:
- Evolution of this character is complicated. Ovirpatorosaurs, the primitive therizinosauroid Falcarius,
and the advanced members of Troodontidae (a clade of deinonychosaurian eumaniraptorans) have a forward-pointing pubis;
all remaining maniraptorans have a backwards-pointing one.
- So there is definitely convergence, reversals, or both!
- In therizinosauroids, may have functioned as in ornithischians (to increase gut space for eating plants)
- In other maniraptorans, is more likley associated with changes in the arrangement of hindlimb muscles
between the tibia, femur, pelvis, and proximal caudals (all of which are modified in these groups)
Had short boxy skulls that are toothless in all but the most primitive forms
(which had either stout blunt pencil-shaped teeth and/or leaf-shaped teeth)
- Were probably omnivores, eating both small vertebrates and plants
- Found in many parts of the world in Cretaceous, but most common in Asia
- Most were smaller than humans
- Lots of varieties of oviraptorosaurs: some were short armed and long legged (often with
arctometatarsus); others were long armed and rather short legged.
- Sister group to Oviraptorosauria
- Had long necks, prosauropod-like heads with leaf-shaped teeth
- All but the most primitive genus Falcarius) had shortened tibiae and metatarsi
and backwards-pointing pubes
- Were almost certainly slow-moving herbivores, with big guts
- May have defended themselves with powerful claws
- Most were bigger than humans; one (Therizinosaurus) rivalled Tyrannosaurus in size and had 1 m
long manual claws!
- Had very short arms with very large manual digit I and very small
digits II and III
- Skull and small tooth shape resembles primitive ornithomimosaurs
- Pubis points strongly backwards and skull has joint in front of eyes as in avialians
- Advanced forms had arctometatarsus
- Known from South America, North America, Asia, Europe, and possibly Australia in the Cretaceous
- Most very small: 1-2 m long
- Diet uncertain: probably insect eaters. Their strong claw may have been used to pound into termite mounds.
- Eumaniraptora ("true maniraptorans"): subject of next lecture.
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Last modified: 14 July 2006