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GEOL 104 Dinosaurs: A Natural History

Fall Semester 2018
Dragons of the Sea & Air: Pterosaurs & Mesozoic Marine Sauropsids


Detail from "Azhdarchid in Flight" by Mark Witton

Key Points:
•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:

Pterosaurs:

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:

First reptiles to return to an aquatic life were mesosaurs:

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:

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

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

Ichthyopterygia (ichthyosaurs):

Plesiosauria (plesiosaurs):

Mosasauridae (mosasaurs):

Marine turtles (Chelonioidea):

Recent work shows that the pelagic ichthyosaurs and plesiosaurs (and possibly the mosasaurs) had an elevated metabolism, more like endotherms than ectotherms.

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Last modified: 9 August 2018

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Diversity of Late Cretaceous Western Interior Seaway marine sauropsids (turtles, plesiosaurs, mosasaurs, hesperornithines) by James Kuether (2017)