''Solenodonsaurus'' ("single-tooth lizard") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

reptiliomorph Reptiliomorpha (meaning reptile-shaped; in PhyloCode known as ''Pan-Amniota'') is a clade containing the amniotes and those tetrapods that share a more recent common ancestor with amniotes than with living amphibians (lissamphibians). It was de ...

s that lived in what is now

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. Th ...

, during the Westphalian stage.

Description

''Solenondosaurus'' had snout-vent length with a skull length . ''Solenodonsaurus'' shows a curious mix of characters making it difficult to place phylogenetically. The teeth lack

labyrinthodont "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally conside ...

folding of the enamel, and it skull has a much smaller

otic notch Otic notches are invaginations in the posterior margin of the skull roof, one behind each orbit. Otic notches are one of the features lost in the evolution of amniotes from their tetrapod ancestors. The notches have been interpreted as part of an ...

than seen in other reptiliomorph amphibians. Yet general build ties it in with the

Diadectomorpha Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs (transitional ...

. Laurin, M. and Rize R.R. (1999): A new study of ''Solenodonsaurus janenschi'', and a reconsideration of amniote origins and stegocephalian evolution. ''Canadian Journal of Earth Science'', no 36 (8): pp 1239–1255 (1999)

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Paleobiology

''Solenodonsaurus'' was likely best adapted to life on land, as opposed to living in an aquatic environment like many other early tetrapods. The limbs and pelvis are incomplete in all known specimens of ''Solenodonsaurus'', making it difficult to infer how the animal may have moved. One feature that suggests a terrestrial lifestyle is the 90° rotation of the ends of the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, which orients the forelimb forward rather than out to the side. Several presumably terrestrial groups of Paleozoic tetrapods, including amphibamid temnospondyls, microsaurs, and the first amniotes, have a similar degree of rotation in their humeri. The short, triangular shape of the skull of ''Solenodonsaurus'' distinguishes it from most aquatic forms, which have either long and narrow or broad and parabolic heads. ''Solenodonsaurus'' was once believed to have had an

impedance matching In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize si ...

hearing system like those of modern tetrapods, with an eardrum-like membrane called a tympanum that covered a notch in the

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

at the back of the skull. Evidence for a tympanum is seen in a ridge that runs along the squamosal notch, which may have been an attachment point for the membrane. However, since the otic notch is very small, the presence of a tympanum is now considered unlikely.

Phylogeny

''Solenodonsaurus'' is traditionally classified as a close relative of amniotes (vertebrates that lay eggs on land). However, a 2012 phylogenetic analysis of ''Solenodonsaurus'' and other early

tetrapod Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...

s (four-limbed vertebrates) found that it was more closely related to the amphibian group

Lepospondyli 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 ...

. Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

from that analysis: The phylogeny of early tetrapods is poorly understood.Laurin, M. (1996)
Phylogeny of Stegocephalians
from the

Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site ...

References

External links

An overview of ''Selenodonsaurus'' at the Tree of Life web project, authored by Michel Laurin
{{Taxonbar, from=Q589089 Fossils of the Czech Republic Reptiliomorphs Carboniferous reptiliomorphs Transitional fossils