The cluster of taxa now lumped as Class Reptilia represents a difficult puzzle to unravel. Stem reptiles represented a major leap forward in evolutionary innovation and vitality, and as a result there is massive diversity in the group. Only a tiny sample of the fossil record is shown above. What remains unresolved at present is the exact boundaries for such groupings. The flying reptiles, pteranosaurs, are unlike their contemporary dinosaurs or any other Cretaceous reptiles.
Turtles are reptiles, sensu stricto.
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