Lecture 6: Saurischia and Theropoda
Saurischia
Term coined by Seeley (an employee of the Cambridge Museum) in 1887
Name is based on the anteriorlly-oriented pubis of most (but not all saurischians).
This is not a shared derived trait; it is a primitive trait from deep in Reptilia
Shared derived characters of Saurischia:
Twisted thumb (digit 1)
Reduced pinky (digit 5)
New articulation points in dorsal vertebrae (hyposphene-hypantrum articulation)
Elongation of forward neck (cervical) vertebrae
Controversy over placement of earliest, carnivorous dinosaurs (Eoraptor,
Herrerasaurus, etc.).
1) Basal Dinosaur
2) Basal Theropod (this is what I told you in class)
3) Basal Saurischian
OUTLINE OF THEROPOD LECTURE
1. Defining characteristics of clades
2. Distribution in time and place
3. Lifestyle issues
Theropods
1. Defining characteristics of clades
Theropoda (‘beast foot’, really bird-footed)
General characters: bipedal, carnivores (more or less), less abundant than
herbivorous dinosaurs (only ½ to 1/11 as numerous), less diverse than herbivores
(only 40%), classification nightmares, ranged in size from <2 feet/10 lbs. to 50
feet or more and 5-7 tons.
Shared derived characters: big eyes, extra antorbital fenestra, broad lachrymal
(“tear-duct”) bone, 3 elongate fingers (vestigal 4th and 5th digits) with grasping
capability, narrow hind foot with three functional digits, hollow bones, bowed
femur, sacrum with at least 5 vertebrae, pubic “boot”, tails stiff distally used as
counterbalances, loosely-jointed kinetic skulls
Long bones are hollow - have an outer layer of dense, compact bone that is far
thicker than that of other dinosaurs; spongy bone confined to the articulation zones
and edge of the marrow cavity.
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Ceratosauria
Shared derived characters: Reduction and fusion of skeleton, specifically the
upper ankle bones and the sacral ribs with the ilium, ridges around hip socket
for support, in most - notch between maxilla and premaxilla on upper jaw to
accept large lower tooth
Representative genera: Ceratosaurus (7 m), Coelophysis (2-3 m), Syntarsus,
Dilophosaurus
Ceratosaurs existed from the Late Triassic through the Late Jurassic, global
distribution
Tetanurae
Shared derived characters: Overall, more bird-like than ceratosaurs: Large
portions of the tail stiffened by extended bony struts (zygopophyses); tooth
row doesn’t extend behind antorbital opening)
Spinosauroidea
Shared derived characters: Large snouts, strong shoulders, long arms and
clawed hands; probable fish eaters
Representative genera: Afrovenator (10 m), Megalosaurus (10 m), Spinosaurus
(~18 m), Baryonyx (7 m) + see below, and including Masiakasaurus
knopfleri (2 m spinosauroid from Madagascar named after Dire Straits
guitarist Mark Knopfler)
Late Jurassic – Early Cretaceous, global distribution
*Note: Spinosaurus was first discovered in Egypt in 1915; specimens in Munich
were destroyed during the allied bombing in WW II. More remains from the
Bahariya oasis have recently been found by grad students from Penn
Carnosauria
Shared derived characters: Big nostrils with elaborate sinuses, big heads, all
more than 5 m long
Representative genera: Allosaurus, Gigantosaurus
Late Jurassic – Early Cretaceous, global distribution
Coelurosauria
Shared derived characters: Big brains, elongate forelimb, arctometatarsal ankle,
very bird-like
Tyrannosauroidea
Shared derived characters: Very reduced forelimbs with only 2 functional
fingers, 14-15 m long
Ornithomimosauria
Shared derived characters: Small, lightly built skulls with very large orbits, no
upper teeth, few lower teeth, long arms
Very ostrich-like
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Oviraptosauria
Shared derived characters: Short skulls with many fenestrae, no teeth,
wishbone
Therizinosauroidea “The giant claw”
Shared derived characters: very long claws, teeth adapted for plant-eating
Troodontidae
Shared derived characters: Huge front-facing eyes, very large brain
Dromaeosauridae
Shared derived characters: Enlarged claw on 2nd toe, rear-facing pubis
One spectacular fossil of Velociraptor captures it in a struggle with a Protoceratops
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2. Distribution in time and place
Ceratosauria: Late Triassic through the Late Jurassic, global distribution
Spinosauroidea: Late Jurassic – Early Cretaceous, global distribution
Carnosauria: Late Jurassic – Early Cretaceous, global distribution
Coelurosauria: Early - Late Cretaceous, largely Northern Hemisphere
3. Lifestyle issues
a. Habitats
Theropods lived in all habitats!
b. Preservation and taphonomy
Theropod fossils are relatively rare (delicate bones), however some spectacular
nearly complete fossils have been found and there are at least two theropod bone
beds: the Coelophysis quarry at Ghost Ranch (where 5-10,000 skeletons and partial
skeletons of the dinosaur Coelophysis bauri have been found) and the Cleveland-Lloyd
quarry in Utah where the remains of at least 44 Allosaurus have been found.
It is unusual for large numbers of carnivores to amass, so the sites above must be
anomalous.
c. Diet
i. The "Great" Tyrannosaurus Debate: was T. rex a predator (using a chasing or ‘land
shark’ ambush approach) or a scavenger?
Evidence for predation
Evidence for scavenging
May have had pockets on teeth that
Had rounded (crushing) rather than
housed bacteria (for poisoning victims; flattened (slicing) teeth
Komodo dragons have these too)
Analysis of Triceratops bone with bite
Teeth typically found in mass death
marks indicates a very strong bite
deposits
potential (13,000 newtons, like that of
an alligator)
Arms too small to hold on to struggling
prey
Skull analysis shows that tyrannosaur
Large olfactory lobes in brains (for
had vertically oriented orbits, like other detecting rotting meat)
carnivores with very strong bites
T. rex couldn’t run fast enough to catch
prey
**The Truth? T. rex probably did both
Tyrannosaurs were clearly alpha carnivores (bone-filled coprolites are direct
evidence).
ii. Oviraptors – used tough beaks for eating shellfish, seeds, or eggs?
iii. Spinosauroids – fish eaters? (narrow snouts, long claws)
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iv. Ornithomimids – some are found with gastroliths and one species has a mouth full
of baleen – they were almost certainly not carnivores
d. Senses
Smell: tyrannosaurs had huge olfactory lobes
Vision: based on the positions of their orbits, tyrannosaurs also had excellent
stereoscopic vision (over a 50° range) and depth perception; the troodon
Saurornithoides had an even larger range of stereoscopic view (~130°, the same as
modern cats), but many theropods had a much more restricted range for excellent
depth perception (e.g. Carcharadontosaurus = 20°)
Hearing: Theropods all had large auditory canals, which probably equated to
excellent hearing; troodons had an extra feature: an aural canal that connected the
two ears and allowed for outstanding sound location
e. Living arrangements
Several fossil sites contains groups of one theropod species (e.g. Albertosaurus),
suggesting that theropods, like many modern carnivores, lived and hunted in packs or
prides
f. Nesting
Little evidence of theropod parental skills or strategies. However, one exceptional
nest in Mongolia preserves an Oviraptor brooding its eggs and an Albertasaurus site in
Canada includes both adults and sub-adults. These suggest significant parental care.
g. Moving around
All theropods were obligate bipeds (very long legs, trackways always narrow).
Estimates based on trackways, leg lengths and leg proportions suggest that large
theropods like T. rex might have been able to run as fast as 50 km/h or more
Functional analysis of the T. rex skeleton suggest that it couldn’t run faster than about
30 km/h because of the unrealistic amount of muscle mass needed to move
faster and because of potential damage to the skull if it fell
Tails would have been important counterbalances in large running theropods!
Ornithomimids could probably run fast – up to 80 km/hr (based on leg length, leg
proportions, trackway evidence)
h. Brains and behavior
Theropods had the largest EQ’s of any dinosaur clade, and the EQ of troodontids and
dromaeosaurs was well above that of any living reptile, and very much like that of
some modern birds and mammals.
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