Sauropsids: True Reptiles

The group Sauropsida, also called the Sauropsids, is the first major recognized split in the fossil record for reptiles. The ancestral reptiles which were creatures such as Hylonomus split into two main groups: the mammal-like reptiles (Synapsids) and the reptile-like reptiles. This sounds a bit funny but that's what the name Sauropsida means.

This group does not point to any particular species or fossil remains, but rather is simply a broad division of all living land dwelling vertebrates. The main ways of separating species into either side of this divide are either on physical characteristics (if it's a reptile with scaly skin and cold blood, it's in the reptile group) or fossil remains.

The split between the two big groups of reptiles happened at almost the same time as the development of the first reptiles, so we can assume that this split in the evolutionary lines took place some time between 310 and 320 million years ago.

At the time of their split with the mammal-like reptiles, it is assumed that these animals were small and lizard-like, as in the case of the basal reptile Hylonomus. We can assume this because both the anapsids and the eureptilia that evolved from them started out as small, lizard-like forms.

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