EPS SCI 17 Lecture Notes - Lecture 15: Squamata, Crurotarsi, Synapomorphy
26 May 2018
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Lec 15: Seas and Skies
May 24
WHAT ARE PTEROSAURS?
● pterosaurs are part of the avemetatarsalia
(which also includes dinosaurs)
○ the other branch originating from archosaurs is crurotarsi (crocodile-like)
○ pterosaurs = cousins of
● pterosaurs
: the earliest vertebrates known to have evolved powered flight (pppp from
mid-Triassic through late Cretaceous
○ has long 4th finger from which the wing membrane is attached
○ no good transitional fossils → difficult to place on evolutionary tree, since it does
not look much like other reptiles
● Pterosaur Evolution: late Triassic (3 ft) → early Cretaceous (14 ft)
○ started off many small teeth → over time, develop toothless beaks (way to lighten
skeleton for flight)
○ smaller tails
○ larger bodies
■ possible increase in size, due to competition with early birds (ex.
Archaeopteryx
)
○ crests
PTERASAUR FLIGHT
● Pterosaur Takeoff Forces
● wings (the evolution of flight) in pterosaurs, bats, and birds occurred convergently
○ bone structure in arms / hands are all from the same common ancestor
(homologous
)
○ however, wings are analogous
● Bird Adaptations for Flight:
○ toothless beak (to lighten weight)
○ fusion of carpals and metacarpals in digits 1-3
○pneumatic
(hollow) bones
■ hollow bones evolved in dinosaurs, before in birds → good pre-adaptation
or exaptation
for flight (ancestral trait in birds)
○ asymmetrical flight feathers
○keel
bone for flight muscles
● Pterosaur Adaptations to Flight
○ toothless beak
■ Rhamphorhynchus
(primitive pterosaur) - had long pointed teeth that was
likely for tearing into fish
■ Pteranodon
(advanced pterosaur) - had toothless beak
○ elongation of digit 4
○ pneumatic
(hollow) bones)
○ rather than feathers for lift, pterosaurs have instead a membrane of skin, blood,
muscle, and tightly-organized connective tissue
○ keel bone for flight muscles
○ strong forelimbs
■ walked around on the ground on all 4 legs → used flight muscles to vault
themselves forward to gain lift
○ high metabolism
■ many reconstructions of pterosaurs show them with fur
■ fossils have pycnofibres
(hair-like structures that are coming off the
body)
● pycnofibres have far different structures, than that of mammals
● independently evolved fur-like coverings (convergent evolution)
○ vertebrae are fused together → stiff skeleton helps keep body rigid for flight
○ brain → need to take in a lot of sensory information very quickly
■ CT scans of 2 pterosaur brains showed that they had larger relative size
size than non-avian reptiles, smaller than birds
■ enlarged semicirculuar canals (equilibrium) → balance
■ enlarged cerebellar floccular lobes (neurosensory integration) →
integrate sensory data
○ crests (?) - over time, develop elaborate crests (large crest not found in juveniles)
■ cooling & thermoregulation
■ steering - reduce drag and move forward
■ counterbalance - to stabilize the head and keep it looking forward during
flight
■ also may serve a purpose in mutual sexual selection
(identifying
members of the same species) - where both sexes have different, but
elaborate crests
● females like the crest in the males → mate with them to pass that
trait onto the next generation
● crests attract mates
PTEROSAUR DIVERSITY
Document Summary
Pterosaurs are part of the avemetatarsalia (which also includes dinosaurs) The other branch originating from archosaurs is crurotarsi (crocodile-like) Pterosaurs : the earliest vertebrates known to have evolved powered flight (pppp from mid-triassic through late cretaceous. Has long 4th finger from which the wing membrane is attached. No good transitional fossils difficult to place on evolutionary tree, since it does not look much like other reptiles. Pterosaur evolution : late triassic (3 ft) early cretaceous (14 ft) Started off many small teeth over time, develop toothless beaks (way to lighten skeleton for flight) Possible increase in size, due to competition with early birds (ex. Wings (the evolution of flight) in pterosaurs, bats, and birds occurred convergently. Bone structure in arms / hands are all from the same common ancestor ( homologous ) Fusion of carpals and metacarpals in digits 1-3. Hollow bones evolved in dinosaurs, before in birds good pre-adaptation or exaptation for flight (ancestral trait in birds)
