''Utaherpeton'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

lepospondyl Lepospondyli is a diverse taxon of early tetrapods. With the exception of one late-surviving lepospondyl from the Late Permian of Morocco (''Diplocaulus minumus''), lepospondyls lived from the Early Carboniferous ( Mississippian) to the Early Per ...

amphibian from the

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

. It is one of the oldest and possibly one of the most basal ("primitive") known lepospondyls. The genus is

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

, including only the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Utaherpeton franklini''. ''Utaherpeton'' was named in 1991 from the Manning Canyon Shale Formation, which dates to the Mississippian- Pennsylvanian boundary. It was originally classified within

Microsauria Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considere ...

, a group of superficially lizard- and salamander-like lepospondyls that is now no longer considered to be a valid

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

or evolutionary grouping, but rather an

evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Definition An evolutionary grade is a group of ...

consisting of the most basal lepospondyls. ''Utaherpeton'' has been proposed as both the most basal lepospondyl and the oldest "microsaur", although more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

lepospondyls are known from earlier in the Carboniferous. However, its position within Lepospondyli remains uncertain due to the incomplete preservation of the only known specimen. The inclusion of ''Utaherpeton'' in various

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses has resulted in multiple

phylogenies A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

(hypotheses of evolutionary relationships) that are very different from one another, making it a significant

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

in terms of understanding the interrelationships of lepospondyls.

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 . 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 The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

bones at the front of the skull.

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 ''Microbrachis'' is an extinct genus of lepospondyl amphibian from the Carboniferous Kladno Formation of the Czech Republic. Description ''Microbrachis'' was an elongated, salamander-like creature, about long, with over 40 vertebrae ins ...

''. A 2001

analysis found ''Utaherpeton'' to be the most basal lepospondyl, followed by the "microsaur" ''

Hyloplesion ''Hyloplesion'' is an extinct genus of microbrachomorph microsaur. It is the type and only genus within the family Hyloplesiontidae. Fossils have been found from the Czech Republic near the towns of Plzeň, Nýřany, and Třemošná, and da ...

'', 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

nectridea Nectridea is the name of an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including animals such as ''Diplocaulus''. In appearance, they would have resembled modern newts or aquatic salamanders, although they ...

ns and

aïstopod Aistopoda (Greek for " avingnot-visible feet") is an order of highly specialised snake-like stegocephalians known from the Carboniferous and Early Permian of Europe and North America, ranging from tiny forms only , to nearly in length. They fir ...

s 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 In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

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 In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

group, but ''Utaherpeton'' was found to be the most basal member of a separate clade that included all other lepospondyls.

References

{{Taxonbar, from=Q3764833 Carboniferous amphibians Carboniferous amphibians of North America Fossil taxa described in 1991 Prehistoric amphibian genera