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|The most successful group of archosaurs is the group Ornithodira which includes Scleromochlus, pterosaurs, and dinosaurs. While there are a number of traits which unite Scleromochlus and pterosaurs (including shoulder, pelvis, leg,a nd foot characteristics), there are also several which unite Scleromochlus with dinosaurs. Scleromochlus is close to the base of Ornithodira and perhaps is an early member of the branch which produced the pterosaurs. Scleromochlus measured 18 cm from snout to tip of tail (Benton, 1999; Sereno, 1991a).|
|Pterosaurs were the first major group of vertebrates to evolve powered flight, although a few gliding reptiles are known from the Paleozoic. Pterosaurs possessed membranous wings that are supported by elongated 4th finger and the impressions of wings have been left in many fossils.|
| Pterosaur skull bones tended to fuse and
there was a broad sternum for the attachment of flight muscles. They differed from birds in that there was no
clavicle in the pectoral girdle, only the scapula and coracoid. Primitive pterosaurs have 5-6 wrist bones; in
later genera these bones fused, creating one large joint between the forearm
bones and the hand. There was no
trace of a fifth finger. Pterosaurs
had a unique wrist bone called the pteroid which supported the membrane
that stretched from the wrist to neck. They still retained the primitive
puboischiadic plate in the pelvis and the hip socket was located more dorsally
than in other archosaurs. Some genera also possessed membranes between
toes which might have been used in swimming.
There were narrow fibers (perhaps made of cartilage or collagen)
which supported the wing. Like birds
and theropod dinosaurs, pterosaurs possessed openings in many
of their bones. In birds, these openings
allow extensions of the lungs to extend into the bones support a higher
metabolic rate. The presence of these openings in pterosaur bones suggests
that they possessed a higher metabolic rate than seen in other archosaurs
Pterosaur brains were larger than those
of comparably sized reptiles and approach the sizes observed in birds. The optic lobes of the brain were large, suggesting
a developed sense of vision, and the olfactory lobes were reduced.
The cerebellum (the region of the brain which is enlarged in birds
for the control of flight muscles) was larger and some parts of the cerebellum
were larger than seen in birds. These features suggest that pterosaurs were
capable of active, flapping flight (
There were two suborders of pterosaurs:
1) The primitive rhamporhynchoids existed from the Triassic through the Jurassic. They had a long tail, a short neck, and a short face. They were smaller pterosaurs which would have depended on a flapping style of flight.
2) Pterodactyloids existed from the Jurassic through the Late Cretaceous. They possessed a short tail a longer neck, skull, and metacarpals. They were larger pterosaurs which would have depended more on the use of air currents to soar.
| Three early species are known from the Upper
Triassic. Eudimorphodon was typical of pterosaurs but unlike the others, it
had ossified tendons in its tail. Eudimorphodon still
retained the primitive condition of teeth in its palatal bones. Peteinosaurus also from Upper Triassic
but more primitive because its wings were only 2/3 length of other pterosaurs
that size. Preondactylus
was the most primitive pterosaur but its remains are incomplete. Its femur was longer than its humerus and the
scapula and coracoid were not yet fused as in later species (
|Rhamphorynchoids were most diverse in the Jurassic Period and none are known from the Cretaceous. The known varieties include Dimorphodon (4 ft wingspan), Anurognathus (whose peglike teeth suggest that it fed on insects), and Rhamphorynchus (whose teeth and the remains of fish in the stomach indicate that it fed on fish).|
Rhamphorynchoids were most diverse in the Jurassic Period and none are known from the Cretaceous. The known varieties include Dimorphodon (4 ft wingspan), Anurognathus (whose peglike teeth suggest that it fed on insects), and Rhamphorynchus (whose teeth and the remains of fish in the stomach indicate that it fed on fish).
In the Cretaceous, derived pterodactyls replaced the earlier, more primitive group of archaeopterodactyloids. Apparently, competition with birds had driven pterodactyls to be most common along the coast than inland (Wang, 2005).
Although pterodactyls became extinct at the end of the Cretaceous, only a few species are known to have existed at that time (Pteranodon, Nyctosaurus, and Quetzalcoatlus). Therefore, they did not undergo a mass extinction. The rhamphorynchoids had become extinct earlier, perhaps because of competition from birds.
The mouths and teeth of pterosaurs show a number of adaptations for feeding on insects and fish. Some of the pterosaurs had very fine teeth for filtering water.