If the tendency to gigantism was represented by Erythosuchus, then the
opposite, tendency towards the small light agile bird-like form was expressed
by its cat-sized relative Euparkeria, which at 65 centimetres (26 inches)
from snout to tail-tip was only an eighth the linear dimensions.
This was a small, long-legged, and agile, with a more erect stance, and
capable of bipedal gait. Euparkeria in turn gave rise, to two evolutionary
branches - the Psuedosuchians and crocodiles on the one hand, and ornithosuchians
and dinosaurs on the other. Both began as small agile forms, but
the Psuedosuchians quickly reverted to the standard lizard-like form, although
these were lizards of great size - e.g. the parasuchia, aetosauria, and
crocodilia, all of which reached 3 metres or more in length. Most
interesting of all were the great Rauisuchians, which although roughly
lizard/crocodile-like in form had a fully erect dinosaurian and mammalian
posture.
Euparkeria
, image by Richard Hammond
Palaeos Page (incorporates some of this material, plus a lot of additional material)
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