•Pterosauria represents a clade of ornithodiran archosaurs that achieved flight in the Late Triassic and survived until the very end of the Cretaceous.
•Pterosaurs were ecologically diverse; metabolically they seem to have been tachymetabolic homeothermic endotherms.
•There is no compelling evidence that they were ecologically competing with Mesozoic birds, occupying a different set of niches than birds before the K/Pg extinction.
•Diverse groups of sauropsids (reptiles) invaded the sea during the Mesozoic.
•While many Mesozoic marine sauropsids lived in near-shore environments, several were pelagic (adapted for life in the open seas). These include the superficially-dolphin-like ichthyosaurs; the diverse plesiosaurs; the marine true lizards the mosasaurs; marine crocodiliforms; marine turtles; and hesperornithine birds. (Only the hesperornithines were actually dinosaurs!)
•Many marine reptiles gave birth live directly in the water, allowing them to evolve away from any particular land-moving adaptations.
PTEROSAURS: DRAGONS OF THE AIR
Not all reptiles of the Mesozoic were dinosaurs. There was a diversity of reptiles on land, and also in the sea and in the air.
A number of Permian & Triassic gliding reptiles, but only two powered flying groups:
Avialians (i.e., birds, a type of theropod dinosaur)
Pterosauria (pterosaurs, probably the sister group to
Dinosauromorpha within Ornithodira, but some consider them more primitive archosauriforms)
First appear in Late Triassic; died out at very end of Cretaceous
Had simple hinge-like ankle and S-shaped neck of other ornithodirans, but perhaps not parasaggital stance
Skin stretched between finger and body, between legs, and from arm to neck
Wings reinforced by special internal fibres attached to muscles: could control shape of wing
Body covered with hair-like structures
Some used to think they walked bipedally, but most evidence suggests quadrupedal (almost gorilla-like), at least for the derived groups. (Primitive forms may not have been able to do much walking at all.)
Active powered fliers with large muscle attachments
Quite probably warm-blooded (insulated; very fast growth rates; active fliers)
Babies seem to have been able to fly right after hatching!
Earlier forms relatively small, short metacarpi, and long tails; later forms (Pterodactyloidea, the true pterodactyls) could be very large, had long metacarpi, and short tails and were better adapted at walking
Variety of diets: insectivores, fish eaters, fruit eaters, etc.
No evidence of direct competition between birds and pterosaurs.
DRAGONS OF THE SEA: MESOZOIC MARINE REPTILES
Throughout Earth History, many reptiles (and other amniotes) have returned to the sea:
However, aquatic amniotes have to deal with:
Breathing (remain air-breathers)
Feeding (small fish, large fish & amniotes, shellfish, vegetation, etc.)
Locomotion (flippers, fins, etc.)
Reproduction (come out of water to lay eggs or some form of internalized reproduction)
First reptiles to return to an aquatic life were
Early Permian of Gondwana
Members of the primitive reptile group Parareptilia
Long needle-like teeth for catching small fish
Big (webbed?) hands and feet for paddling, tall deep tail for swimming
Could probably crawl on land, although probably not too well
Now known to have retained eggs (or young) in the body until they were developed enough to swim
Probably did not travel far from shore
Most primitive relatives of Mesozoic marine sauropsids were similar in general form (long needle-like teeth, webbed hands and feet, deep tail, some terrestrial ability, probably shore-dwelling or fresh-water) to mesosaurs, but later forms become more specialized for life in the sea.
Many different clades of Mesozoic marine sauropsids, from almost every clade:
Testudines (marine turtles)
Lepidosauria, both Rhynchocephalia (pleurosaurs) and Squamata (mosasauroids)
Remains show that even primitive euryapsids retained young inside body
until birth, thus allowing them to live their entire life in the water. This allowed for the extreme specializations of the two
highly derived pelagic (open seas) euryapsid groups: ichthyosaurs and plesiosaurs
First appear in latest Triassic; die out at the end of the Cretaceous
Fore- and hindlimbs turned into large flippers for swimming; tail generally short
Two general body types:
Small head, needle-like teeth, long neck: small fish or squid eaters
Large head, big cone-shaped teeth, shorter neck: large fish or marine reptile eater
The large-headed forms appear to evolve a number of times from the long-necks
Include the largest known marine reptiles of all (bigger than all theropods, and in
fact bigger than all dinosaurs other than sauropods!)
A newly-described fossil shows that at least some plesiosaurs gave birth live to a
single large-bodied baby (more like whales than the many small babies found in ichthyosaurs, mosasaurs, and sea snakes). This may in fact
suggest extended parental care for at least the derived plesiosaurs.