EPS SCI 17 Lecture Notes - Lecture 14: Stokesosaurus, Dinosaur Renaissance, Deinonychus
26 May 2018
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Lec 14: The Cretaceous - Carnivores & the
Evolutionary Ratchet
May 22
BIG QUESTION: How did the evolutionary ratchet shape Cretaceous theropods?
●niche partitioning
: over time, different species partition the environment & ecological
niches → kept from directly competing with one another and can coexist
○ Review: from Lecture 12, in the Jurassic (with sauropods)
○ niche partitioning in carnivores encourages specialization in specific prey
■Stokesosaurus
- more specialized for smaller prey
■Allosaurus
- has sharp, serrated teeth and wide jaw → takes large chunk out
of prey and then backs off until it bleeds to death
■
● carnivore evolutionary ratchet
: pervasive selection for large body size leads to the
evolution of hypercarnivore
(a diet of large prey)
○ predators that require large amounts of food (lot of energy needed) will have
smaller population sizes
○ small population sizes and specialized diets reduce evolutionary versatility
→
increasing the chance of extinction (if environment changes)
● 3 case studies:
○ Spinosaurus
○ Velociraptor
○ Tyrannosaurus rex
THERAPODS
●theropod
: (“flesh-eating dinosaurs”) carnivorous
dinosaurs that are members are typically bipedal and
range from small and delicately built to very large
○ also includes maniraptors, and living birds
● Theropod Traits:
○ generally bipedal, with claw facing backwards
○ vastly meat-eaters (with sharp, serrated teeth)
○ elongated stiffened tail (with ossified tendons)
○ further reduced digits
■ loss of IV & V
■ III is reduced / lost
○ more pneumatized
- full of holes
■ keeps bones & skeletons light → allows for development of such a heavy
gigantic head
○ pubic foot serves as attachment site for muscles
○ cannot pronate (swivel) their hands → wrists are locked to the side
● Therapod Phylogeny: one lineage becomes ornithischia and other becomes saurischia
→ composed of:
○ sauropods
○ theropods
■ Coelophysis
■ Carnosauria
SPINOSAURUS: found in Africa (mostly in Egypt) → where there were shallow seas in the
Cretaceous time period
● not many bones from the Spinosaurus
○ housed in Munich
○ destroyed during Allied bombing raids on Munich (April 1944)
● elongated dorsal processes, along the spine
● evolving image of Spinosaurus
(based off other theropod’s skeletons)
○ 1936-1990s: imagined as being similar to Tyrannosaurus
or Allosaurus
○ 1983-1998: has long jaw with numerous peg-like teeth, that was very similar to
Baryonyx
→ image still looks a lot like other therapods
■Baryonyx
- has long low skull and lots of small teeth, much like a
crocodile (adapted to fishing, due to presence of its large hand claw)
● fish scales found in the stomach region
■ much longer arms than T. rex
■ the skeleton was incomplete, but based on the proportions of other
theropods, was thought to be the largest of all
○ 2016: tiny hind legs that are almost same size as forelimbs
■ might be the 1st discovered therapod that moved on 4 legs
■ strange forelimb positioning - may have walked on all fours or walked with
legs splayed out
● filled a different ecological niche that other theropods did not fill → Spinosaurus
was a
giant predator that evolved to eat many of these giant prehistoric fish
○ hyper-specialized to feed on fish, to the point where it probably had a difficult
time walking on land
● What were the spines used for? → Theories:
○ thermoregulation - sail could help with cooling or heat storage
○ display
○ support - could really be all muscle
Document Summary
Lec 14: the cretaceous - carnivores & the. Niche partitioning : over time, different species partition the environment & ecological niches kept from directly competing with one another and can coexist. Review : from lecture 12, in the jurassic (with sauropods) Niche partitioning in carnivores encourages specialization in specific prey. Stokesosaurus - more specialized for smaller prey. Allosaurus - has sharp, serrated teeth and wide jaw takes large chunk out of prey and then backs off until it bleeds to death. Carnivore evolutionary ratchet : pervasive selection for large body size leads to the. Predators that require large amounts of food (lot of energy needed) will have evolution of hypercarnivore (a diet of large prey) smaller population sizes. Small population sizes and specialized diets reduce evolutionary versatility increasing the chance of extinction (if environment changes) Theropod : ( flesh-eating dinosaurs ) carnivorous dinosaurs that are members are typically bipedal and range from small and delicately built to very large.
