GEOL 104 Dinosaurs: A Natural History
Fall Semester 2000
Dragons of the Sea and Air: Marine reptiles and pterosaurs
Not all reptiles of the Mesozoic were dinosaurs.
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
First reptiles (or maybe non-reptilian sauropsids, the sister group to Reptilia) were
- Early Permian of Gondwana
- 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)
- Pseudosuchia (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.
Euryapsida: the sister group to archosaurs and their relatives (Archosauriformes).
Euryapsida + Archosauriformes together are called Archosauromorpha.
- First appear in Early Triassic
- Most primitive members have webbed fingers and could likely crawl around on land
- Early euryapsids (and most later ones) seem to have been fish eaters, with needle- or
- A variety of smallish Triassic forms: thallatosaurs, huphesuchians, pachypleurosaurs,
nothosaurs, and placodonts (the latter with big crushing teeth, probably mollusk eaters)
Two highly specialized aquatic euryapsid groups: ichthyosaurs and plesiosaurs.
- 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
- Remains show that they retained young inside body until birth
- 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!)
- Might have been able to crawl up onto land to lay eggs, like sea turtles
- 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
- A couple of different closely-related families of marine turtles
- First groups are Late Cretaceous; some died out in Early Cenozoic, others survive to
- 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
A number of Permian & Triassic gliding reptiles, but only two powered flying groups:
- Avialae (birds, a type of theropod dinosaur)
- Pterosauria (pterosaurs, possibly the sister group to Dinosauriformes within
Ornithodira, but may be more primitive archosauriforms)
- First appear in Late Triassic; died out at very end of Cretaceous
- Had long hindlimbs and S-shaped neck.
- 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
- Body covered with hair-like structures
- Some think they walked bipedally, but most evidence suggests quadrupedal (almost
- Active powered fliers with large muscle attachments
- Possibly warm-blooded
- Ranged from 15 cm to 12-14 m wingspan!
- 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
- Variety of diets: insectivores, fish eaters, fruit eaters, etc.
No evidence of direct competition between birds and pterosaurs.
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