Coelurosauria includes a wide diversity of forms, including omnivores, herbivores, and birds!

Coelurosaurs are characterized by:

• Narrow, three-fingered hand
• "Boat-shaped" chevrons for extra tail stiffening
• Tall ascending process of astragalus to absorb stresses of running
• "Protofeathers": filament-like structures covering much of the body

Compsognathidae (less than 1.5 m long) and 2 m long Ornitholestes represent small basal coelurosaurs. However, 8 m long Dryptosaurus was also a primitive coelurosaur.

The more advanced coelurosaurs form a clade Maniraptoriformes, characterized by:

• Enlarged brain size compared to other dinosaurs
• Bony secondary palate (roof of mouth), to absorb additional stresses

Maniraptoriformes is divided into two main clades, Arctometatarsalia and Manraptora. Arctometatarsalians are characterized by:

• Incisor-like premaxillary teeth for nipping
• Very long tibiae and metatari (also in 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
  • Also found in troodontids and some alvareszaurids and oviraptorosaurs

There are two main clades of arctometatarsalians, with very similar hindquarters but very different front ends:

• Ornithomimosauria (name means "bird mimic dinosaurs", but often called "ostrich mimics" because of their general similarity to ostriches in shape and size)
  • Characterized by:
    • Long necks and small heads
    • Long snouts which are toothless in the advanced forms (although primitive ornithomimosaurs had lots of teeth)
    • Long arms with metacarpals all the same length and hooking-and-clamping (rather than grasping) hands
  • 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 the Late Cretaceous of Asia and western North America
  • Most were about ostrich-sized or larger, but some were small and one was as big as Tyrannosaurus
• Tyrannosauridae ("tyrant dinosaurs")
  • Characterized by:
    • Large skull size
    • Expanded area for jaw and neck muscle attachements
    • 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)
  • Were probably fast running carnivores, eating large dinosaurs
  • Known from the Early Cretaceous of Asia and the Late Cretaceous of Asia and western North America
  • Began fairly small (5 m or so), but in Late Cretaceous reached giant size

Maniraptora ("hand snatchers") are characterized by:

• Enlarged sternal plates
• Increased forelimb length
• Enlarged semilunate carpals, perhaps to compensate for enlarged forelimb and hand
• Shoulder joints that faced sideways rather than backwards (as in most dinosaurs)

• Oviraptorosauria, with short boxy skulls that are toothless in all but the most primitive form
  • 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
• Therizinosauroidea, with long necks, prosauropod-like heads with leaf-shaped teeth, 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 rivalled Tyrannosaurus in size and had 1 m long manual claws!
• Eumaniraptora ("true maniraptorans")
  • Characterized by:
    • Backwards-pointing pubis (in this case, associated with change in leg muscles)
    • Tails which were very mobile proximally but very stiff distally
    • Retractable pedal digit II, often tipped with a big sickle claw
  • Eumaniraptorans include Avialae (subject of next lecture) and Dromaeosauridae
    • Dromaeosaurids, or "raptors", were carnivorous, had tails stiffened by long rods and extremely large sickle claws
    • Dromaeosaurids seem to have shorter, stockier legs than a lot of other predator theropods: may have been more cat-like (agile ambush predators) than dog-like (fast pursuit predators)
    • Range throughout Cretaceous (some possible teeth from Middle Jurassic)
    • Best known from 4 m long Deinonychus of the late Early Cretaceous of North America and 2 m long (at most) Velociraptor of the Late Cretaceous of Mongolia
    • Dromaeosaurids may have hunted in groups

Two particularly problematic groups:

• Troodontids:
  • Had short arms, like primitive coelurosaurs
  • Had arctometatarsi, long legs, and a specialized expanded pocket in the braincase like ornithomimosaurs
  • Had leaf-shaped teeth like therizinosauroids
  • Had tails which were very mobile at the base and retractable pedal digit II with sickle claws like in eumaniraptorans
  • Famous for large brain size, but other maniraptoriforms seem comparably brainy
  • Known from Middle Jurassic teeth, but best known from Cretaceous of Asia and North America
  • Smaller than humans
  • Seem to have been omnivorous, eating small vertebrates (including baby dinosaurs), but also plants
• Alvarezsaurids:
  • Had very short arms with only manual digit I, unlike all other theropods
  • Skull and small tooth shape resembles primitive ornithomimosaurs
  • Pubis points backwards and skull has joint in front of eyes as in avialians
  • Known from South America, North America, Asia, and possibly Australia in the Cretaceous
  • Very small: 1-2 m long
  • Diet uncertain: maybe insect eaters

More work still needs to be done to sort the relationships of these dinosaurs out. Nevertheless, it is within the coelurosaurs that the birds arose.

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