Embolomeri

The order Embolomeri was first named by Edward Drinker Cope in 1884 during his revision of "batrachian" (amphibian) evolution. Embolomeri was differentiated from several other newly named amphibian orders, such as "Rachitomi", by the presence of intercentra and pleurocentra of the same size and shape, that being large cylinders. At the time, embolomere fossils were uncommon, so Cope could only identify "cricotids" such as Cricotus as possessing embolomerous vertebrae.^[4] The genus name "Cricotus" is dubious, as it has been used by Cope to refer to embolomere fossils spanning anywhere between mid-Pennsylvanian deposits of Illinois and the Permian red beds of Texas. Most paleontologists now refer the red bed "Cricotus" specimens to the genus Archeria.^[2]

Michel Laurin (1998) formally defined Embolomeri as "the last common ancestor of Proterogyrinus and Archeria and all of its descendants."^[5] This definition excludes Eoherpeton, which is almost always considered a close ally of the group. Some authors place Silvanerpeton or chroniosuchians as close relatives as well, though they are generally agreed to lie outside Embolomeri proper.^[6][7][8][9]

The poorly-defined group Anthracosauria is sometimes considered synonymous with Embolomeri, and the group's namesake, Anthracosaurus, is an embolomere. However, other authors use the term "Anthracosauria" in reference to a broader group which includes embolomeres in combination with various other reptile-like amphibians (reptiliomorphs). Reptiliomorphs are all tetrapods more closely related to living reptiles and synapsids (mammals and their ancestors), rather than living amphibians. Despite this, reptiliomorphs likely had amphibian-like biological traits, such as water-based reproduction.

Many studies conducted since the 1990s have also placed the group Lepospondyli as closer to amniotes than embolomeres were. Lepospondyls are a particularly unusual group of tetrapods, with some members (i.e. brachystelechids) very similar to lissamphibians and others (i.e. tuditanids) very similar to amniotes. If lepospondyls are both close relatives of amniotes and the ancestors of modern amphibians, then that means that crown-Tetrapoda (descendants of the common ancestor to all living tetrapods) is a much more restricted group than previously assumed. In this situation, various traditional orders of Tetrapoda such as Embolomeri and Temnospondyli actually would qualify as stem-tetrapods due to having evolved prior to the split between modern amphibians and amniotes.^[10]

However, most authors consider temnospondyls to be the ancestors of modern amphibians. This would suggest that embolomeres are likely reptiliomorphs (closer to reptiles) and within the clade Tetrapoda.^[11] However, even this classification is not stable, as some analyses have found embolomeres to be more basal than temnospondyls.^[12]

Below is a cladogram from Ruta et al. (2003):^[11]

Genera

List of genera
Name	Year	Age	Location	Notes	Images
Anthracosaurus	1863	Pennsylvanian (Westphalian A-B)	United Kingdom ( Scotland)	The namesake of Anthracosauria, possessed a small number of large fangs compared to other embolomeres
Archeria	1918	Early Permian	United States ( Texas)	A common, late-surviving member of the group, sometimes considered a species of Cricotus
Aversor	1985	Early Permian (Ufimian)	Russia	Supposedly the latest surviving eogyrinid, but very poorly known
Calligenethlon	1934	Pennsylvanian (Bashkirian)	Canada ( Nova Scotia)	The largest named tetrapod preserved inside lycopod tree stumps in the Joggins Fossil Cliffs
Cricotus	1875	Pennsylvanian	United States ( Illinois)	Responsible for the identification of Embolomeri as a unique order of tetrapods, although its history is convoluted and its taxonomic validity is questionable
Carbonoherpeton	1985	Pennsylvanian (Westphalian D)	Canada ( Nova Scotia)	A lightly built member of the group with characteristics of both archeriids and eogyrinids
Diplovertebron	1879	Pennsylvanian (Moscovian)	Czech Republic	A small member of the group sometimes confused with Gephyrostegus
Eobaphetes	1916	Pennsylvanian	United States ( Kansas)	A possible relative of Anthracosaurus, originally named "Erpetosuchus" until it was determined that the name was preoccupied by a Triassic reptile.
Eogyrinus	1926	Pennsylvanian (Westphalian B)	United Kingdom ( England)	One of the largest and most well-known of the eogyrinids, although sometimes synonymized with Pholiderpeton
Eoherpeton	1975	Visean-Bashkirian )	United Kingdom ( Scotland)	One of the oldest and most basal members of the group (if it even counts as part of it), without vertebrae that were not fully embolomerous
Leptophractus	1873	Pennsylvanian (Westphalian D)	United States ( Ohio)	Known from a skull found at the Linton Diamond Mine
Neopteroplax	1963	Pennsylvanian	United States ( Ohio)	One of the largest Carboniferous limbed vertebrates known from North America
Palaeoherpeton	1970	Pennsylvanian (Westphalian A-B)	United Kingdom ( Scotland)	An eogyrinid known as Palaeogyrinus from 1926 to 1970, until it was determined that this name was occupied by a genus of beetles
Papposaurus	1914	Mississippian-Pennsylvanian (Namurian)	United Kingdom ( Scotland)	Known from a femur, may have been a relative of Proterogyrinus
Pholiderpeton	1869	Pennsylvanian (Westphalian A-B)	United Kingdom ( England,  Scotland)	An eogyrinid similar to Eogyrinus which would take priority if the two were synonymized
Proterogyrinus	1970	Mississippian (Serpukhovian)	United States ( West Virginia),  United Kingdom ( Scotland)	An early member of the group possessing robust limbs but lacking certain adaptations of later members of the group
Pteroplax	1868	Pennsylvanian (Westphalian B)	United Kingdom ( England)	Poorly known despite being among the first embolomeres to be described
Seroherpeton	2020	Late Permian (Wuchiapingian )	China	The youngest known embolomere
Spondylerpeton	1912	Pennsylvanian	United States ( Illinois)	A close relative of Cricotus known from vertebrae found at the Mazon Creek fossil beds

References