Megalocephalus

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Megalocephalus
Temporal range: Late Carboniferous, Westphalian A-C
Megalocephalus skull diagram.png
Skull diagram of Megalocephalus pachycephalus in dorsal view (left) and ventral view (right)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Sarcopterygii
Clade: Tetrapodomorpha
Family: Baphetidae
Subfamily: Loxommatinae
Genus: Megalocephalus
Barkas, 1873
Type species
Orthosaurus pachycephalus
Barkas, 1873
Species
  • Megalocephalus pachycephalus(Barkas, 1873)
  • Megalocephalus lineolatus(Cope, 1877)
Synonyms
Synonyms of M. pachycephalus
  • Pteroplax brevicornis
    Thomas & Young, 1870
  • Orthosaurus pachycephalus
    Barkas, 1873
  • Megalocephalus macromma
    Barkas, 1873
  • Orthosauriscus pachycephalus
    (Kuhn, 1933)
  • Megalocephalus brevicornis
    (Romer, 1947)
Synonyms of M. lineolatus
  • Leptophractus lineolatus
    Cope, 1877
  • AnisodexisCope, 1882

Megalocephalus (meaning "big head") is an extinct genus of baphetid tetrapodomorph from the late Carboniferous (Westphalian A-C) of the British Isles and the United States (Ohio). [1] It contains two species, M. pachycephalus and M. lineolatus. [2]

Contents

History

Megalocephalus pachycephalus

Skull of Megalocephalus pachycephalus Megalocephalus sp.JPG
Skull of Megalocephalus pachycephalus

Megalocephalus pachycephalus is one of the most common large tetrapodomorphs from the Carboniferous of Britain, and is known from several sites in England, Scotland, and Ireland. The first known fossils of the genus were cranial fragments which were misattributed to Rhizodus jaw bones upon their discovery in 1864. These fragments, and many subsequent discoveries, were recovered from a quarry near Newsham, Northumberland. Other Megalocephalus fossils found in the 1860s had been referred to other large amphibians, namely Pteroplax and Anthracosaurus . Two well-preserved skulls and associated jaw bones were found in Newsham in 1870 and 1871, though these were also mistakenly referred to a pre-existing genus, Loxomma . In 1873, Thomas P. Barkas named a pair of new genera for two more Newsham skulls. One was described as a supposed new reptile, Orthosaurus pachycephalus, while the other was given the name Megalocephalus macromma. [3]

Megalocephalus fossils continued to be collected in the coming decades, though most were initially referred to Loxomma. "Orthosaurus" was re-established as a distinct genus of loxommatid amphibian by D.M.S. Watson in 1926. However, it was later determined to be a preoccupied name, and the name Orthosauriscus pachycephalus was invented and used for the rest of the early 20th century. In 1947, Alfred Romer decided to rename Orthosauriscus pachycephalus to Megalocephalus brevicornis, combining Barkas' 1873 genus with "Pteroplax" brevicornis, a species named for Megalocephalus fossils in 1870. However, the "Pteroplax" brevicornis fossils were poorly described and probably destroyed by a 1909 fire, so few subsequent paleontologists use Romer's combination. The modern combination Megalocephalus pachycephalus was popularized by Eileen H. Beamont's 1977 redescription of available "loxommatid" fossils. [3]

Megalocephalus lineolatus

The second apparently valid species in the genus is Megalocephalus lineolatus. This species is from the fossiliferous coal mine of Linton, Ohio, and was originally named as "Leptophractus" lineolatus by E.D. Cope in 1877. In the 1920s, Watson placed the species within "Orthosaurus", based on both Cope's specimens and new loxommatid fossils from Linton. Romer referred all Linton loxommatid material to Macrerpeton huxleyi . However, later investigation revealed that Romer's conception of Macrerpeton was chimeric, including an edopoid temnospondyl (Macrerpeton), a loxommatid (referred to Baphetes ), and possibly several more species of loxommatids. Another skull described in 1957 demonstrated that "Leptophractus" lineolatus was a species of Megalocephalus, as it showed several diagnostic traits of the genus. [3] Megalocephalus lineolatus has also been mentioned under the name "Megalocephalus enchodus", based on a belief that the lineolatus species name should instead be assigned to the Baphetes material. [4]

Description

Restoration MegalocephalusDB.jpg
Restoration

Megalocephalus was an amphibian, measuring 1.5 metres (4.9 ft) from head to tail. [1]

Skull

It is only known from its skull, like most other baphetids. The skull of Megalocephalus was 30 centimetres (12 in) long. The teeth of Megalocephalus were long and pointed. Baphetids had a small elongation of their eye sockets, the current use of which is not certain. It has been suggested that the elongation was housing for a salt gland to get rid of excess salt, or an extra region for jaw muscle attachments, to allow a harder bite force. [1]

Like Kyrinion , the lacrimal is excluded from the nares (nostrils) and the dentary has large fangs. [5] A 2009 phylogenetic analysis suggests that Megalocephalus is paraphyletic relative to Kyrinion, with M. pachycephalus closer to K. martilli than to M. lineolatus. Likewise, Loxomma forms a paraphyletic grade ancestral to Megalocephalus. [6]

Related Research Articles

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<i>Ichthyostega</i> Extinct genus of tetrapodomorphs

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<span class="mw-page-title-main">Labyrinthodontia</span> Paraphyletic group of tetrapodomorphs

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<i>Pholiderpeton</i> Extinct genus of tetrapodomorphs

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<i>Diplovertebron</i> Extinct genus of tetrapodomorphs

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<i>Anthracosaurus</i> Extinct genus of tetrapodomorphs

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<i>Pederpes</i> Extinct genus of tetrapods

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<span class="mw-page-title-main">Colosteidae</span> Extinct family of tetrapodomorphs

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<i>Spathicephalus</i> Extinct genus of tetrapods

Spathicephalus is an extinct genus of stem tetrapods that lived during the middle of the Carboniferous Period. The genus includes two species: the type species S. mirus from Scotland, which is known from two mostly complete skulls and other cranial material, and the species S. pereger from Nova Scotia, which is known from a single fragment of the skull table. Based on the S. mirus material, the appearance of Spathicephalus is unlike that of any other early tetrapod, with a flattened, square-shaped skull and jaws lined with hundreds of very small chisel-like teeth. However, Spathicephalus shares several anatomical features with a family of stem tetrapods called Baphetidae, leading most paleontologists who have studied the genus to place it within a larger group called Baphetoidea, often as part of its own monotypic family Spathicephalidae. Spathicephalus is thought to have fed on aquatic invertebrates through a combination of suction feeding and filter feeding.

<i>Loxomma</i> Extinct genus of amphibians

Loxomma is an extinct genus of Loxommatinae and one of the first Carboniferous tetrapods. They were first described in 1862 and further described in 1870 when two more craniums were found. It is mostly associated with the area of the United Kingdom. They share features with modern reptiles as well as with fish. They had 4 paddle-like limbs that they used to swim in lakes, but they breathed air. Their diet consisted mostly of live fish. They are of the family Baphetidae which are distinguished by their keyhole shaped orbits, while Loxomma themselves are distinguished by the unique texture on their skulls, said to be honeycomb-like.

<span class="mw-page-title-main">Allegheny Group</span> Pennsylvanian-age geological unit

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Kyrinion is an extinct genus of baphetid tetrapodomorph from the Late Carboniferous of England. It is known from a skull that was found in Tyne and Wear county dating back to the Westphalian stage. Along with the skull is part of the lower jaw, an arch of the atlas bone and a rib possibly belonging to a cervical (neck) vertebra. The type species K. martilli was named from this material in 2003.

<i>Adamanterpeton</i> Extinct genus of temnospondyls

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References

  1. 1 2 3 Benson, R.; Anderson, J.; Brusatte, S.; Clack, J.; Dennis-Bryan, K.; Duffin, C.; Hone, D.; Naish, D.; Xu, X.; Prothero, D.; Parsons, K.; Milner, A.; Johanson, Z. (2012). Prehistoric Life. London: Dorling Kindersley. p. 165. ISBN   978-0-7566-9910-9.
  2. "Confirmation of Romer's Gap as a low oxygen interval constraining the timing of initial arthropod and vertebrate terrestrialization". Ward et al. National Academy of Sciences. 2008. Retrieved 2008-08-15.
  3. 1 2 3 Beaumont, Eileen H. (1977). "Cranial morphology of the Loxommatidae (Amphibia: Labyrinthodontia)". Philosophical Transactions of the Royal Society of London. B, Biological Sciences. 280 (971): 29–101. doi:10.1098/rstb.1977.0099. ISSN   0080-4622.
  4. Hook, Robert W.; Baird, Donald (1986-06-19). "The Diamond Coal Mine of Linton, Ohio, and its Pennsylvanian-age vertebrates". Journal of Vertebrate Paleontology. 6 (2): 174–190. doi:10.1080/02724634.1986.10011609. ISSN   0272-4634.
  5. Clack, J A (2003-04-01). "A new baphetid (stem tetrapod) from the Upper Carboniferous of Tyne and Wear, U.K., and the evolution of the tetrapod occiput". Canadian Journal of Earth Sciences. 40 (4): 483–498. doi:10.1139/e02-065. ISSN   0008-4077.
  6. Milner, Angela C.; Milner, Andrew R.; Walsh, Stig A. (2009). "A new specimen of Baphetes from Nýřany, Czech Republic and the intrinsic relationships of the Baphetidae". Acta Zoologica. 90: 318–334. doi:10.1111/j.1463-6395.2008.00340.x.