Lect 15 Flashcards
Theropoda phylogeny
• therion = “wild beast” + pous = “foot”
• Dinosauria
• Saurischia
• Theropoda “beast foot”
• Maniraptora
• Aviale
• Aves
Theropod characters
• Bipedal
• Three-toed foot
(In contact with ground, 4th tow could be present, reduced and/or doesn’t touch ground)
• Furcula
(in shoulder girdle)
• Pneumatized vertebrae: air spaces inside bones
• Air sacs around body
Some bones connected to air sacs, some thought had air sacs around body that connect to lungs
• Ziphodont teeth (not only seen in theropods, some in mammals and extinct reptiles)
- Knifelike
- Laterally compressed
- Serrated (notches up teeth)
- Grow in sockets (in the jaw = extra strength)
- Very efficient for puncturing and pulling through flesh
De-Oliveira and Pinheiro, 2017
Theropod diversity
• Theropoda was very diverse
- Range of body sizes
- Range of habitats
- Range of diets
Theropod diversity
• Allosauroidea, Ceratosauria, Tyrannosauroidea
Groups of apex predators
• All exhibited gigantism (but not all members will be large)
• Hypercarnivores (mostly eat meat with little plant matter entering diet)
• Possible pack behaviour (som kind of social structure)
Theropod diversity
• Therizinosaurs (”scythe lizards”)
• Long claws on forelimbs
• Four functional toes in hindfeet
• Wide body cavity (evi from chest cavity)
• Non-ziphodont teeth
• Considered to be herbivorous
Theropod diversity
• Spinosaurus – semi-aquatic
• Crocodile-like skull
• Short limbs
• Laterally-compressed tail
• Dense bones
• Piscivorous
Mosaic evolution
different parts of the body (or behaviours) evolve separately and at different rates
• Evolution is not directional
Exaptation
an already existing trait is used for a new function
• Evolution works on existing traits
Maniraptoran-like ancestor
Ancestral state from which birds arose
• Downy and pennaceous (vaned) feathers
• Enlarged brain
• Pubis (pelvic bone) directed
anteriorly
• Bony tail
• Gastralia (2nd set of ribs across body)
• Discrete wrist/hand and ankle/foot bones
• Flexible wrist joint
• Two functional ovaries
Mosaic evolution
Archaeopteryx
Clade in this evo transition, prob not direct lineage to birds but parallel
• Pubis directed posteriorly (closer to flight feathers (vane and outside)
• Wings with primary feathers
• Retained gastralia (in comparison to Dino ancestors)
• Retained long bony tai
Mosaic evolution
• Confuciusornis
• Caudal vertebrae reduced (bony tail), remaining caudals fused to form pygostyle (modern birds have, provide support to tail feathers)
• Sternum with keel (increased depth of sternum and area for muscles to attach to)
• Wings with primary feathers, but shoulder still primitive (still likely cannot fly but do flapping flight for very long periods)
• Retained gastralia
Mosaic evolution
• Enantiornithes: enantios = “opposite” + ornithes = birds
• Sternum with well-developed keel
• Derived (but unique) shoulder morphology
- Differs from derived state in extant birds (1 joint in wing)
• Some fusion of hand bones
Modern birds come from most likely close relative, parallel evolution
Mosaic evolution
• Aves
• Pygostyle further shortened
• Gastralia lost
• Derived shoulder morphology
• Teeth lost
• Synsacrum develops
Evolution of powered flight
Re-purposing exaptations
• The combination of the numerous previously derived traits made flight possible
• Small, light skeletons – less mass to get airborne
• Keeled sternum, flexible wrist, modified shoulder – able to move the arms to flap
• Feathers – form airfoil that produces thrust and lift
Evolution of powered flight
Ground-up models
Jump and swat
• Originally hypothesized as a prey- capture strategy
• Suggested that feathers served to catch insects
Counterarguments
• No birds do this today
• Would have swatted insect away
• Feathers significantly predate flight
Wing-assisted incline running
• Some extant galliforms flap their wings while the run up steep surfaces
• Transition from this behaviour to flapping to get off the ground
Counterarguments
• The shoulder structure of avialians would not have allowed this range of motion
