Utaherpeton
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Through Basal (phylogenetics), Phylogenetics and Phylogenetic tree
Description
Like many other lepospondyls, Utaherpeton is salamander-like in appearance. It has an elongated body made up of 26 presacral (neck and back) vertebrae. The total body length excluding the tail is about 4 centimetres (1.6 in). The forelimbs are markedly smaller than the hind limbs and the hind feet are unusual in that they are larger than the rest of the hind limbs. A unique anatomical feature that distinguishes Utaherpeton from other "microsaur" lepospondyls is a connection between the prefrontal and premaxilla bones at the front of the skull.
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Classification
When Utaherpeton was first described in 1991, it was tentatively classified within a group of "microsaurs" called Microbrachomorpha, which included the better-known Microbrachis. A 2001 phylogenetic analysis found Utaherpeton to be the most basal lepospondyl, followed by the "microsaur" Hyloplesion, which has also been considered a microbrachomorph. However, Microbrachomorpha was not recognized as a true clade because Microbrachis was found to be more deeply nested within Lepospondyli, more closely related to derived lepospondyls like nectrideans and aïstopods than to other "microsaurs". A 2004 analysis including Utaherpeton produced a very different phylogeny for lepospondyls, placing aïstopods and nectrideans as the most basal lepospondyls, followed by a paraphyletic assemblage of "microsaurs". Utaherpeton was still recovered as one of the most basal "microsaurs", but not as the most basal lepospondyl. Tentative support for a close relationship between Utaherpeton and Microbrachis was also found. In a 2010 analysis, all "microsaurs" except Utaherpeton were recovered within a monophyletic group, but Utaherpeton was found to be the most basal member of a separate clade that included all other lepospondyls.