Ornithopods
-bipedal or facultatively quadrupedal, ornithischian dinosaurs
-no body armor
-1st appeared during early Jurassic
-among last dinosaurs to disappear
-5 families
Major evolutionary novelties found in skull
-ventrally offset premaxillary tooth row
(with respect to maxillary and lower tooth rows)
-elongate lateral process of the premaxillary
-lower jaw joint located well below the level of the maxillary and lower tooth rows
Family Heterodontosauridae
-different toothed lizard"
-known only from lower Jurassic of southern Africa
-small (1-1.5 meters long)
-uniquely shaped cheek teeth:
a) chisel-shaped with cusps (denticles) restricted to apex of crown
b) canine-like teeth (tusks) in front of mouth which had very different shape from cheek teeth.
-some lack tusks (sexual dimorphism?)
-cheek teeth form dental battery set in massive lower jaw
- short fore-limbs and long hind limbs
- long tail and short neck typical of primitive ornithischians
-ossified tendons only in back region
-fusion of the tibia and fibula and both fused to tarsals (stabilized the lower leg and ankle)
-stout and flexible hands
Family Hypsilophodontidae
-small to medium sized (2 - 4 meters)
-bipedal
-Middle Jurassic to Upper Cretaceous of North America, Europe, Asia, Australia
-distal segments of hind limbs, especially ankle, were elongate
-long tail, stiffened by calcified tendons (counterbalance while running)
-skull resembles Heterodontosaurus but lacks tusks
-eyes large
-narrow horny besk at tip of both upper and lower jaws
-massive jaws supported dental battery of interlocking cheek teeth that wore down to produce a continuous inclined cutting edge
-hinge in skull from front of tooth row to nearly the jaw joint or posterior corner of skull allowed the jaw to move from side to side as dinosaur chewed
Evolutionary Links between hypsilophodontids and large Iguanodontids
-Tenontosaurus (1.5 to 7.5 meters long)
-lacks premaxillary teeth
-3 instead of 4 phalanges in 3rd finger of hand
-Family Dryosauridae
-includes Dryosaurus and Valdosaurus both of which also lack premaxillary teeth
Family Iguanodontidae
-most bipedal or facultative quadrupedal
-mainly late Jurassic to late Cretaceous
-relatively large (up to 10meters)
-heavily built
-heavy shoulder and forelimbs
-massive hindlimbs
-feet broad with hoof-like tips on their toes
-spike-like "thumb" is an evolutionary novelty
-large heads with horse-like snout
-broad toothless beak
Examples:
1)Camptosaurus
-upper Jurassic and lower Cretaceous
-relatively small (5 - 7 meters)
-no fully developed "thumb" spike
-small hooves on tips of toes
-facultative quadruped
-fused wrist bones
-relatively long neck
-small but otherwise basically iguanodontid skull
2) Iguanodon
-lower Cretaceous of Belgium
-long forelimbs (70 - 80% of hindlimb length)
-wrist bones fused
-three central digits of hands ended in hooves
-large conical "thumb" =defensive weapon?
-large head with long snout
-long neck and tail
-ossified tendons from back of shoulder region to tail
-teeth leaf shaped with long ridges on sides and small cusps on cutting edges
-teeth resemble thos of iguana, hence name which means "iguana tooth"
Odd Iguanodont - Ouranosaurus from middle Cretaceous of Niger
-long neural spines = small fin on back?
Family Hadrosauridae
-"duck-billed" dinosaurs
-appear in middle Cretaceous
-generally large ornithopods (7 to 10 m)
-broad toothless beaks
-intricate dental batteries including 3 or more replacement teeth for each tooth position
-loss of first digit (thumb) on hands
-deep, long jaws
Two types based on skull morphology:
a)Hadrosaurines
-more primitive subfamily with rather flat skull roofs
-Ex: Edmontosaurus
b)Lambeosaurines
-"crested" skull roof
-also elongated neural spines and robust limbs