Milwaukee Public Museum: Third Planet
The Mesozoic Era: The breakup of the late Paleozoic world...A flowering of plants... and a radiation of reptiles until the great dying, 225 to 65 million years ago.
Reptiles dominated the Mesozoic world. By the Jurassic and Cretaceous periods, they had invaded almost every habitat Earth had to offer. Giant dinosaurs and their smaller kin dominated the land, while gliding reptiles, some sparrow-sized and some with wingspans of up to 50 feet, rode on offshore air currents in search of surfacing fish. Some reptiles (ichthyosaurs, plesiosaurs, and mosasaurs) moved into open oceans and evolved fish-eating ways of life. And of the commonplace reptiles (commonplace only because they survived the trials of time and change, and are with us still), there were the crocodiles, tortoises and turtles, and lizards and snakes in that ancient world.
Coelophysis
Coelophysis was one of the earliest saurischian dinosaurs. It was a cannibal, and the remains of a young Coelophysis are in the stomach region. This is a reproduction of a fossil collected in New Mexico.
From Little Thecodonts, Mighty Dinosaurs Evolved.
A diverse group of small Triassic reptiles, the thecodonts, gave rise to the first dinosaurs and gradually displaced the mammal-like reptiles. Some particularly agile, fine-boned thecodonts achieved a two-legged stance that permitted them to maneuver with a swift, ostrich-like running gait. While hind legs increased in length and power, the front legs became shorter and weaker, and a large mouth with pointed teeth developed for grasping prey. These thecodonts were the forerunners of the two great orders of dinosaurs, of
gliding reptiles, of crocodiles, and of birds, surviving descendants of dinosaurs.
The Hip-Bone Connection
A handy key to identifying the two orders of dinosaurs:
The pelvis of both the lizard-hipped (saurischian) and bird-hipped (ornithischian) dinosaurs were composed of three bones. Above the hip joint, the ilium attached the pelvis to the backbone. Below this joint, in the saurischian, the pubis was in front, and the ischium faced back. Some dinosaurs of this order were gigantic two-footed meat-eaters like Allosaurus. Others were four-footed plant-eaters, some of which, like Brachiosaurus, were among the largest animals ever to have lived on land.
The bird-hipped or ornithischian dinosaurs were virtually all plant-eaters. In their pelvis, the pubis was parallel to the ischium. An additional bony appendage from the pubis supported the dinosaur's belly muscles. Many ornithischian dinosaurs were four-footed with hind legs conspicuously larger than front legs, as in Stegosaurus. This characteristic presumably was retained from their ancestors, most of which walked erect on powerful hind legs.
Milwaukee Public Museum: Third Planet
The Mesozoic Era: The breakup of the late Paleozoic world...A flowering of plants... and a radiation of reptiles until the great dying, 225 to 65 million years ago.
Reptiles dominated the Mesozoic world. By the Jurassic and Cretaceous periods, they had invaded almost every habitat Earth had to offer. Giant dinosaurs and their smaller kin dominated the land, while gliding reptiles, some sparrow-sized and some with wingspans of up to 50 feet, rode on offshore air currents in search of surfacing fish. Some reptiles (ichthyosaurs, plesiosaurs, and mosasaurs) moved into open oceans and evolved fish-eating ways of life. And of the commonplace reptiles (commonplace only because they survived the trials of time and change, and are with us still), there were the crocodiles, tortoises and turtles, and lizards and snakes in that ancient world.
Coelophysis
Coelophysis was one of the earliest saurischian dinosaurs. It was a cannibal, and the remains of a young Coelophysis are in the stomach region. This is a reproduction of a fossil collected in New Mexico.
From Little Thecodonts, Mighty Dinosaurs Evolved.
A diverse group of small Triassic reptiles, the thecodonts, gave rise to the first dinosaurs and gradually displaced the mammal-like reptiles. Some particularly agile, fine-boned thecodonts achieved a two-legged stance that permitted them to maneuver with a swift, ostrich-like running gait. While hind legs increased in length and power, the front legs became shorter and weaker, and a large mouth with pointed teeth developed for grasping prey. These thecodonts were the forerunners of the two great orders of dinosaurs, of
gliding reptiles, of crocodiles, and of birds, surviving descendants of dinosaurs.
The Hip-Bone Connection
A handy key to identifying the two orders of dinosaurs:
The pelvis of both the lizard-hipped (saurischian) and bird-hipped (ornithischian) dinosaurs were composed of three bones. Above the hip joint, the ilium attached the pelvis to the backbone. Below this joint, in the saurischian, the pubis was in front, and the ischium faced back. Some dinosaurs of this order were gigantic two-footed meat-eaters like Allosaurus. Others were four-footed plant-eaters, some of which, like Brachiosaurus, were among the largest animals ever to have lived on land.
The bird-hipped or ornithischian dinosaurs were virtually all plant-eaters. In their pelvis, the pubis was parallel to the ischium. An additional bony appendage from the pubis supported the dinosaur's belly muscles. Many ornithischian dinosaurs were four-footed with hind legs conspicuously larger than front legs, as in Stegosaurus. This characteristic presumably was retained from their ancestors, most of which walked erect on powerful hind legs.