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Embolomeri

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Embolomeres
Temporal range: Mississippian - Wuchiapingian
Restoration of Archeria from the Lower Permian of Texas.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Sarcopterygii
Clade: Tetrapodomorpha
Clade: Elpistostegalia
Clade: Stegocephali
Order: †Embolomeri
Cope, 1885
Genera

See text.

Embolomeri is an order of tetrapods or stem-tetrapods, possibly members of Reptiliomorpha. Embolomeres first evolved in the Early Carboniferous (Mississippian) Period and were the largest and most successful predatory tetrapods of the Late Carboniferous (Pennsylvanian) Period. They were specialized semiaquatic predators with long bodies for eel-like undulatory swimming. Embolomeres are characterized by their vertebral centra, which are formed by two cylindrical segments, the pleurocentrum at the rear and intercentrum at the front. These segments are equal in size. Most other tetrapods have pleurocentra and intercentra which are drastically different in size and shape.[1]

Embolomeres were among the earliest large carnivorous tetrapods, with members such as the crocodilian-like Proterogyrinus appearing in the Visean stage of the Carboniferous. They declined in diversity during the Permian period, though at least one representative (Archeria) was common in the Early Permian.[2] Embolomeres went extinct shortly before the end of the Permian.[3]

Classification

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Vertebrae from several different tetrapods, with those of "Cricotus" (Archeria) in A-C, showing the large, cylindrical intercentra (I) and pleurocentra (P)

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]

Tetrapoda

Genera

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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 Mississippian-Pennsylvanian (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

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  1. ^ Panchen, A. L. (10 February 1972). "The skull and skeleton of Eogyrinus attheyi Watson (Amphibia: Labyrinthodontia)". Phil. Trans. R. Soc. Lond. B. 263 (851): 279–326. Bibcode:1972RSPTB.263..279P. doi:10.1098/rstb.1972.0002. ISSN 0080-4622.
  2. ^ a b Romer, Alfred Sherwood (11 January 1957). "The Appendicular Skeleton of the Permian Embolomerous Amphibian Archeria" (PDF). Contributions from the Museum of Paleontology. 13 (5): 105–159.
  3. ^ Chen, Jianye; Liu, Jun (2020-12-01). "The youngest occurrence of embolomeres (Tetrapoda: Anthracosauria) from the Sunjiagou Formation (Lopingian, Permian) of North China". Fossil Record. 23 (2): 205–213. doi:10.5194/fr-23-205-2020. ISSN 2193-0066.
  4. ^ Cope, E.D. (January 1884). "The Batrachia of the Permian Period of North America". The American Naturalist. 18: 26–39. doi:10.1086/273563. S2CID 84133633.
  5. ^ Laurin, Michel (1998). "The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I. Systematics, middle ear evolution and jaw suspension". Annales des Sciences Naturelles - Zoologie et Biologie Animale. 19 (1): 1–42. doi:10.1016/S0003-4339(98)80132-9.
  6. ^ Chen, Jianye; Liu, Jun (2020-12-01). "The youngest occurrence of embolomeres (Tetrapoda: Anthracosauria) from the Sunjiagou Formation (Lopingian, Permian) of North China". Fossil Record. 23 (2): 205–213. doi:10.5194/fr-23-205-2020. ISSN 2193-0066.
  7. ^ Klembara, Jozef; Clack, Jennifer A.; Čerňanský, Andrej (2010-09-16). "The anatomy of palate of Chroniosaurus dongusensis (Chroniosuchia, Chroniosuchidae) from the Upper Permian of Russia". Palaeontology. 53 (5): 1147–1153. doi:10.1111/j.1475-4983.2010.00999.x. ISSN 0031-0239.
  8. ^ Carroll, Robert L. (2012-10-18). "The Importance of Recognizing Our Limited Knowledge of the Fossil Record in the Analysis of Phylogenetic Relationships among Early Tetrapods". Fieldiana Life and Earth Sciences. 5: 5–16. doi:10.3158/2158-5520-5.1.5. ISSN 2158-5520. S2CID 85114894.
  9. ^ Sookias, Roland B.; Böhmer, Christine; Clack, Jennifer A. (2014-10-07). "Redescription and Phylogenetic Analysis of the Mandible of an Enigmatic Pennsylvanian (Late Carboniferous) Tetrapod from Nova Scotia, and the Lability of Meckelian Jaw Ossification". PLOS ONE. 9 (10): e109717. Bibcode:2014PLoSO...9j9717S. doi:10.1371/journal.pone.0109717. ISSN 1932-6203. PMC 4188710. PMID 25290449.
  10. ^ Laurin, M.; Reisz, R.R. (1999). "A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution". Canadian Journal of Earth Sciences. 36 (8): 1239–1255. doi:10.1139/e99-036.
  11. ^ a b Marcello Ruta, Michael I. Coates and Donald L. J. Quicke (2003). "Early tetrapod relationships revisited" (PDF). Biological Reviews. 78 (2): 251–345. doi:10.1017/S1464793102006103. PMID 12803423. S2CID 31298396. Archived from the original (PDF) on 2008-05-22. Retrieved 2012-05-26.
  12. ^ Clack, J. A. (July 2002). "An early tetrapod from 'Romer's Gap'". Nature. 418 (6893): 72–76. doi:10.1038/nature00824. ISSN 0028-0836. PMID 12097908. S2CID 741732.
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