What shared novelties unite the dinosaurs? • Dinosaur means "Terrible lizards" • Dinosaurs were mostly large, bipedal or quadrupedal diapsid reptiles with an upright posture. • Most of the traits that characterize dinosaurs are related to their upright posture and locomotion.
Features inherited from near relatives • 90° angle between shaft and head of the upper leg bone (femur). • The ball-shaped femur head fits into a socket in the hip. • A crest on the hip bone holds the leg in place. • The knee is in a straight line between hip and foot. • Advanced ankle structure: the ankle bones are welded to the lower leg. • When these animals walked, only their toes touched the ground, not their heels. Dinosaur Hip Bones
New features • The middle toe in the foot supports most of the animal's weight, other toes are reduced. • Open hip socket. • Opposable digits
Comparing Dinosaur Hip Bones Ornithischia:The bone on the bottom of the pelvis has a large projection that points toward the back of the animal. Saurischia:The bone on the bottom of the pelvis has a large process pointing toward the front of the animal. Scientists divide dinosaurs into two groups--ornithischians and saurischians--according to the structure of the hips. Ornithischians, such as Corythosaurus, had a birdlike hip structure. Saurischians, such as Allosaurus, had hips like those of lizards. The two groups differed in the three bones that made up the hipbone--the ilium, ischium, and pubis.
What did the first dinosaurs look like? • The earliest dinosaurs are known from the mid-to-late Triassic, ~230 Mya. • To date, the best fossils from this time period have come from Argentina, though recent reports suggest that very early dinosaurs were present in Madagascar as well. • Three early dinosaurs from Argentina: Herrerasaurus, Eoraptor, and Pisanosaurus
Herrerasaurus was large, over 4 m long. • Herrerasaurus had all but a few of the characters which define the dinosaurs, lacking only certain features of the hip and leg bones. • Slashing teeth and three finger on their hands with slashing nails. • The pelvic structure is similar to saurichian dinosaurs, which had previously led to Herrerasuarus being classified in that group. • This arrangement of hip bones, however, is ancestral in the archosaurs and not uniquely derived. • Systematic relationships of Herrerasaurus and its relatives are far from certain. • While some analyses suggest they are sister to the dinosaurs, others consider them Saurischian or even theropods. • The importance of this group is that they give us some idea of the time at which dinosaurs evolved (towards the end of the Triassic) and what the earliest dinosaurs would have looked like.
Eoraptorwas tiny, only ~1 m long. • It also had slashing teeth and three finger on their hands with slashing nails. • One of the earliest known dinosaurs and a contemporary of Herrerasaurus, its already bipedal stance and short, specialized forelimbs suggest an affinity with theropod dinosaurs. • Eoraptor lends support to the hypothesis that dinosaurs diverged rapidly and at small body sizes from a common ancestor, and that the main herbivorous and carnivorous lineages were already present by the Middle Carnian. • The general picture: Active, bipedal carnivores. • They were both lizard-hipped dinosaurs that were closely related to the theropods.
Pisanosauruswas a small (>1 m), bipedal dinosaur with serrated, shearing teeth. • It was an herbivorous bird-hipped dinosaur.
Saurischian dinosaurs:"Lizard-hipped" dinosaurs • The saurischian, like all other tetrapods, had pelves (hips) composed of three elements: the ilium, ischium, and pubis. • What distinguishes saurischians (among other major characteristics; including a grasping hand, asymmetrical fingers, and a long, mobile neck) is the pubis that points downward and forward at an angle to the ischium • In addition, the pinkie toe in the foot is small, and the index finger (the one next to the thumb that you use for pointing) in the hand is longest. • The oldest known dinosaurs, from the middle Triassic of South America, were saurischians. • The saurischians are often divided into three major groups: Sauropoda, Therapoda, and Prosauropoda
Sauropoda "Lizard foot" Jurassic-Cretaceous: quadrupedal herbivores, largest land animals, up to 35 m long, 12 m tall, 80,000 kg (or more), small heads, broad snout with peg-like teeth (and gastroliths in gut), very long necks and tails, massive pillar-like limbs, short broad hands and feet with claws, large lightweight vertebrae. e.g., Diplodocus. The Sauropoda were large herbivores such as Apatosaurus and Diplodocus
Diplodocus • A Late Jurassic SAUROPOD with a long, snaky neck, a long, whip-like tail, and front legs shorter than the hind legs. . • It is the longest dinosaur skeleton ever found; 90 feet (27 m) long, and has a 26-foot (8-m) neck and a 45-foot (13.7-m) tail; stood 13 feet (4 m) tall at the hips and probably weighed 25 tons (22.7 metric tons). • The elephant-like feet and legs of this four-legged plant eater indicate that it was a land or swamp dweller. • Because its nostrils were on top of its head, scientists once thought that it lived on the bottom of lakes with only the top of its head above the water, because the pressure of the water would have been too great.
Diplodocus cont. • Diplodocus may have used its tail as a weapon. • The Y-shaped SPINES on the tail vertebrae could have provided extra places of attachment for muscles that made it possible to move the tail from side to side. • Its long neck enabled the animal to lift its head to see and approaching enemy from a long distance. • Diplodocus may have lived into Early Cretaceous times.
Sauropod Saurichians Diplodocus
Theropoda Bird-like, bipedal carnivores. The hand has three or four fingers withclaws. They had a long bony tail. They reduced their toes until just 3 touch the ground. The Theropoda were bipedal carnivores (meat eaters), ranging from the chicken-sized Compsognathus and the fearsome Deinonychus and……….
Therapod Saurichians • 30 very sharp, curved teeth in a long, flat snout, an s-shaped neck; long thin legs; arms with three-fingered clawed hands and four-toed clawed feet Velociraptor
Therapod Saurichians cont. The most unusual feature of this theropod is the pair of ridges along the top of the skull Dilophosaurus did not have a neck frill (it had standard neck ribs) nor did it spit venom (it lacks hollow fangs through which snakes expel venom). Dilophosaurus
Therapod Saurichians cont. A group of large carnivorous dinosaurs that roamed North America and Asia during the last part of the Cretaceous, 85 to 65 million years ago. The most famous tyrannosaur, of course, is Tyrannosaurus rex, one of the last non-avian dinosaurs to walk the earth before the great extinction. It stood approximately 15 feet high and was about 40 feet in length, roughly six tons in weight. In its large mouth were six-inch long, sharp, serrated teeth. Tyrannosaurus rex
T. rex: Scavenger or Predator? • Paleontologist Jack Horner has proposed that T. rex could not have been a predator. • His arguments against predation include its small eyes (needed to see prey), small arms (needed to hold prey), huge legs (meaning slow speed) and that there is no evidence for predation — bones have been found with tyrannosaur teeth embedded in them or scratched by them, but so far no study has shown that tyrannosaurs killed other dinosaurs for food (a bone showing tyrannosaur tooth marks that had healed would be strong evidence for predation). • His evidence supporting scavenging include its large olfactory lobes (part of the brain used for smell), and that its legs were built for walking long distances (the thigh was about the size of the calf, as in humans). • There are arguments against scavenging: most large living predators do scavenge meat happily when it is available, but most do prefer fresh meat.
Note: • Living birds had common ancestors on the theropod lineage. • Oddly, birds are derived from the "lizard-hipped" dinosaurs and not from the "bird-hipped" ornithischian dinosaurs. • The "bird-hipped" condition of a pubis pointing toward the back of the animal occurred twice independently, once in the ornithischians and once in the lineage leading to birds, an example of convergent evolution. • Thus "ornithischia," taken literally, is a misnomer, since the ornithischians have ornithischian-like pelves, not bird-like. Only birds (and their immediate ancestors) have bird-like pelves.
Prosauropoda "Before lizard foot": • Triassic-Jurassic: Bipedal to quadrupedal, small to large herbivores, up to 10 m long, small head, long neck, bulky body, long tail, 5 toes and 5 fingers, thumb claw for grasping veggies, massive hind limbs, slimmer front limbs. • Ridged spoon-shaped teeth. Gastroliths.
Prosauropod Saurichians • Unearthed all over western Europe. • Like most of its kind, the Plateosaur was heavy, sturdy limbed, and its tail made up half its length. • Its head was stronger and deeper than most prosauropods. It walked on all four legs, rearing up on its hind legs to search at higher levels or gain access to higher foilage. Plateosaurus
Ornithischia: Bird-hipped dinosaurs • Have an extra lip bone and the middle finger on hand is longest. • Eurypoda: have plates on their backs • Stegosaurs "Roof lizards": • Jurassic-Cretaceous: 3 to 9 m long, 300 to 6500 kg. Quadrupedal with two rows of plates along spine, shoulder and tail spikes, small head, pointy snout, short neck, bulk body, hind limbs longer than front limbs. No evidence of gastroliths. Plates for protection and perhaps thermoregulation.
Ornithischia cont. Ankylosaurs: "Fused lizards": Jur-Cret: 5 to 9 m long. Quadrupedal with heavy flexible armor of fused plates, studs, and spikes. Broad shielded skull, short massive limbs, sturdy tail with club.
Ornithischia cont. Ceratopsians: "Horned faces": Cret: bipedal and quadrupedal, small to large (1 to 9 m long), triangular skull often with bony frill, tall narrow snout with parrot-like beak, battery of shearing teeth, horns. Evidence for herding. Triceratops
Ornithischia cont. Pachycephalosaurs:"Thick-headed lizards": Jur-Cret: bipedal, small to large (0.5 to 5 m long), thick domed or flattened heads (Head butting) with bumbs, strong hips and legs, short arms, stiffened tail, spine horizontal.
Ornithischia cont. Ornithopods: "Bird-foot": Tri-Cret: diverse and abundant herbivorous group, bipedal quadrupedal, small to very large (1 to 15 m long), legs longer than arms, fingers with claws or hooves (5th one reduced), toes with hoof-like nails (5th toe reduced), long stiff tail held off ground for balance, large head with cropping beak and battery of self- sharpening cheek teeth, cheek pouches.