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.

Many reptiles (and other amniotes) have returned to the sea:

• Abundant food
• Equitable temperatures
• Easy migrations

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 mesosaurs:

• Early Permian of Gondwana
• Members of the primitive reptile group Proganosauria ("Anapsida" to some)
• 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, and probably laid eggs on land
• Probably did not travel far from shore

Most primitive relatives of Mesozoic marine reptiles 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 reptiles, from almost every clade:

• Testudines (marine turtles)
• Lepidosauria, both Rhynchocephalia (pleurosaurs) and Squamata (mosasauroids)
• Crurotarsi (various marine crocs)
• Even Dinosauria (hesperornithiform birds)

We will cover the most diverse and highly specialized forms: euryapsids (esp. ichthyosaurs and plesiosaurs), mosasaurs, and marine turtles.

A reminder of amniote phylogeny:
:

Euryapsida: more closely related to Archosauria than to Lepidosauria, so part of the larger clade of Archosauromorpha. Euryapsids:

• First appear in Early Triassic
• Most primitive members have webbed fingers and may have crawlled around on shore
• Early euryapsids (and most later ones) seem to have been fish eaters, with needle- or cone-shaped teeth.
• A variety of smallish Triassic forms: thallatosaurs, huphesuchians, pachypleurosaurs, nothosaurs, and placodonts (the latter with big crushing teeth, probably mollusk eaters)
• Recent discovery shows that even
• 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 euryapsid groups: ichthyosaurs and plesiosaurs

Ichthyopterygia (ichthyosaurs):

• First appear in Early Triassic; die out in the earliest part of Late Cretaceous
• Range from 1.5 to 15 m long
• Most of long snouts and cone-shaped teeth: fish or squid eaters
• Fore- and hindlimbs turned into flippers (for steering)
• Carbonized impressions show big tail fin and dorsal fin: very dolphin- or tuna-like
• VERY large eyes in some species: probably dove to deep water hunting squid
• HIGHLY transformed anatomy: probably very fast swimmers but incapable of surviving on land

Plesiosauria (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!)

Mosasauridae (mosasaurs):

• Late Cretaceous only; survived until very end of Cretaceous
• True lizards
  • Mosasauroidea includes Mosasauridae and some non-oceanic semi-aquatic forms
  • Close relatives of monitor lizards and sister group to snakes
• Forelimbs powerful webbed flippers; hindlimbs reduced
• Tail powerful and deep
• Most mosasaurs with large cone-shaped teeth: fish, squid, ammonoid, and marine reptile eaters; a few have crushing teeth for feeding on shellfish
• Remains show that they retained young inside the body until hatching

Marine turtles:

• A couple of different closely-related families of marine turtles
• First groups are Late Cretaceous; some died out in Early Cenozoic, others survive to today
• Fore- and hindlimbs turned to flippers, forelimbs provide must of the thrust
• Feed on shellfish, fish, jellyfish, vegetation, etc.
• Shells are typically thinner than land-living turtles
• Crawl onto beach to lay eggs, but otherwise fully marine

Just as several different groups of reptiles went back to the sea, some others took to 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)

Pterosaurs:

• 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
• Flew using extended manual digit IV (ring finger)
• 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 think they walked bipedally, but most evidence suggests quadrupedal (almost gorilla-like)
• Active powered fliers with large muscle attachments
• Possibly warm-blooded
• Ranged from 15 cm to 12-14 m wingspan!
• 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.

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Last modified: 21 November 2007