Micropholis (amphibian)

Last updated

Contents

Micropholis
Temporal range: Early Triassic
Micropholis stowi.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: Temnospondyli
Family: Micropholidae
Genus: Micropholis
Huxley, 1859
Species
  • M. stowiHuxley, 1859 (type)
Synonyms
  • Petrophryne Owen, 1876

Micropholis (Greek 'mikros' = small and 'pholis' = scale) is an extinct genus of dissorophoid temnospondyl. Fossils have been found from the Lystrosaurus Assemblage Zone of the Karoo Basin in South Africa and are dated to the Induan (Early Triassic). Fossils have also been found from the lower Fremouw of Antarctica. [1] Micropholis is the only post-Permian dissorophoid and the only dissorophoid in what is presently the southern hemisphere and what would have been termed Gondwana during the amalgamation of Pangea.

History of study

FMNH PR 5105, cast of skull of M. stowi in the Field Museum of Natural History. Micropholis stowi skull.jpg
FMNH PR 5105, cast of skull of M. stowi in the Field Museum of Natural History.

Micropholis was one of the first dissorophoids to be named by English paleontologist Thomas Huxley in 1859 based on a partial skull. [2] Micropholis stowii (properly Micropholis stowi), the type species, is named for George William Stow, the South African geologist and ethnologist who discovered the specimen and who proposed that it represented some extinct amphibian. English paleontologist Richard Owen later named a new genus and species, Petrophryne granulata, for a better-known skull, also from the Karoo Basin, that he suggested might be the same animal as M. stowi; [3] this synonymy was eventually accepted by other workers. Additional description was furnished by German paleontologists Ferdinand Broili and Joachim Schröder in 1937. [4] The taxon was most recently revised by German paleontologist Jürgen Boy in 1985 [5] and again in 2005 by German paleontologist Rainer Schoch and South African paleontologist Bruce Rubidge. [6] Micropholis has been repeatedly incorporated in phylogenetic analyses of temnospondyls and dissorophoids. In 2015, American paleontologist Julia McHugh published a description of histological patterns in Micropholis [7] .

Description

Practically the entire skeleton of Micropholis is now known. Many specimens have been found, a number of which are on blocks preserving partial to complete skeletons of multiple individuals in close association, [4] and two distinct morphotypes are evident, differing in skull width and palatal dentition. [5] [6]

The "slender-headed" morph is defined by corresponding narrowing of many features and cranial elements, differences in dentition on the vomer, and possibly by smaller and more numerous maxillary teeth when compared with the "broad-headed" morph. Additionally, a wide size range of individuals are known, ranging from skull lengths around 20 mm to over 40 mm. There remains some uncertainty about whether the slender-headed morph is an advanced ontogenetic stage, as the largest individuals all exhibit this skull morphology. Schoch & Milner (2014)[ full citation needed ] identified 10 features in the diagnosis of Micropholis:

(1) dermal ornament, with irregularly spaced pustules;
(2) accessory fangs on the vomer;
(3) unpaired anterior palatal fenestra (sometimes 'fontanelle');
(4) palatine and ectopterygoid reduces to struts along medial maxillary margin;
(5) short basipterygoid ramus of pterygoid;
(6) basal plate with prominent posterolateral horns;
(7) hyobranchial skeleton well ossified;
(8) short tail;
(9) elongate skull table (plesiomorphy); and
(10) postparietal much longer than tabular (plesiomorphy).

Phylogenetic relationships

When it was first described, Micropholis was recognized as a 'labyrinthodont,' an outdated term used to refer to extinct 'amphibians' in a broad sense. However, Huxley remarked that it did not show close affinities with any of the known Triassic labyrinthodonts of the time. Its uncertain affinities continued to plague paleontologists who remarked that "no types really closely allied to it have been found". [8] As a result, it was placed within its own family, Micropholidae, [9] and sometimes within its own superfamily, Micropholoidea. [10] Although it was suggested in the 1930s that Micropholis might be allied with dissorophoids by comparison with the dissorophid Broiliellus , [11] this idea was not widely adopted [10] until the 1960s. [12] Subsequent discovery of amphibamiforms, either referred to monotaxic families such as Doleserpetontidae [13] or to Dissorophidae, has further strengthened the placement of Micropholis among dissorophoids, which has since been maintained by computer-assisted phylogenetic analyses. [14] Micropholis now belongs to the recently resurrected family Micropholidae, [15] which is included in what was historically termed Amphibamidae (now Amphibamiformes). However, its placement has long been perplexing because it retains numerous plesiomorphies and is usually recovered as one of the earlier diverging amphibamiforms despite being tens of millions of years younger than all other dissorophoids.

Below is a phylogeny from Schoch (2018) [15] showing the position of Micropholis.

Related Research Articles

<span class="mw-page-title-main">Dissorophoidea</span> Extinct superfamily of amphibians

Dissorophoidea is a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the skull, and many species seem to have been well adapted for life on land.

<span class="mw-page-title-main">Temnospondyli</span> Ancestors of modern amphibians adapted to life on land

Temnospondyli or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the larval stage, metamorphosis and maturity. Most temnospondyls were semiaquatic, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are amphibians, many had characteristics such as scales and armour-like bony plates that distinguish them from the modern soft-bodied lissamphibians.

<i>Cynognathus</i> Assemblage Zone Biozone which correlates to the Burgersdorp Formation of the Beaufort Group

The Cynognathus Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossiliferous and geologically important Karoo Supergroup. The Cynognathus Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late Early Triassic (Olenekian) to early Middle Triassic (Anisian) in age. The name of the biozone refers to Cynognathus crateronotus, a large and carnivorous cynodont therapsid which occurs throughout the entire biozone.

The Fremouw Formation is a Triassic-age rock formation in the Transantarctic Mountains of Antarctica. It contains the oldest known fossils of tetrapods from Antarctica, including synapsids, reptiles and amphibians. Fossilized trees have also been found. The formation's beds were deposited along the banks of rivers and on floodplains. During the Triassic, the area would have been a riparian forest at 70–75°S latitude.

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

Eryosuchus is an extinct genus of capitosauroid temnospondyl from the Middle Triassic of northern Russia. It was a very large predator: the largest specimen known could reach up to 3.5 m (11.5 ft) in length, with a skull over 1 m long.

<span class="mw-page-title-main">Brachyopoidea</span> Extinct superfamily of temnospondyls

Brachyopoidea is a superfamily of temnospondyls that lived during the Mesozoic. It contains the families Brachyopidae and Chigutisauridae. The earliest records of brachyopids are from the Lower Triassic in Australia. The latest-surviving member of the superfamily is the chigutisaurid Koolasuchus from the Early Cretaceous of Australia.

<span class="mw-page-title-main">Lydekkerinidae</span> Extinct family of temnospondyls

Lydekkerinidae is a family of stereospondyl temnospondyls that lived in the Early Triassic period. During this time period, lydekkerinids were widely distributed, with putative remains reported from Russia, Greenland, India, South Africa, Madagascar, Australia, and Antarctica. In contrast to most other stereospondyls, lydekkerinids were relatively small-bodied. The type genus is Lydekkerina, the namesake of the family and the best-known lydekkerinid.

<span class="mw-page-title-main">Trematopidae</span> Extinct family of temnospondyls

Trematopidae is a family of dissorophoid temnospondyls spanning the late Carboniferous to the early Permian. Together with Dissorophidae, the family forms Olsoniformes, a clade comprising the medium-large terrestrial dissorophoids. Trematopids are known from numerous localities in North America, primarily in New Mexico, Oklahoma, and Texas, and from the Bromacker quarry in Germany.

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

Acroplous is an extinct genus of dvinosaurian Temnospondyli within the family Eobrachyopidae.

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

Bothriceps is an extinct genus of stereospondyl temnospondyl. It is a member of the infraorder Trematosauria and is the most basal brachyopomorph known. It may be the only brachyopomorph that lies outside the superfamily Brachyopoidea, which includes the families Brachyopidae and Chigutisauridae. It shares several similarities to Keratobrachyops, another basal brachyopomorph, and may be closely related to or even synonymous with it.

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

Cryobatrachus is an extinct genus of temnospondyl amphibian from the Early Triassic of Antarctica. The type species is Cryobatrachus kitchingi. It is known from a partial skull and an imprint of the skull roof, both found in the Fremouw Formation of the Transantarctic Mountains at about 85° south latitude and described in 1974. Many small bone fragments have also been identified, although they cannot be attributed with certainty to C. kitchingi. Cryobatrachus has been classified in the family Lydekkerinidae, as it is similar in appearance to the genus Lydekkerina from South Africa. Because only a small number of features distinguish it from other lydekkerinids, Cryobatrachus kitchingi has more recently been considered a nomen dubium, meaning that its distinction from other better-known species may be unwarranted.

<i>Lydekkerina</i> Extinct genus of temnospondyls from the Early Triassic

Lydekkerina is an extinct genus of stereospondyl temnospondyl. It is the type genus of the family Lydekkerinidae. Fossils have been collected from Early Triassic deposits in South Africa and Australia. The type species is L. huxleyi, first described in 1889. While most other stereospondyls were semiaquatic, Lydekkerina was exclusively terrestrial.

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

Lapillopsis is an extinct genus of stereospondyl temnospondyl within the family Lapillopsidae. Fossils belonging to the genus have been found in the Arcadia Formation of Queensland, Australia.

Tersomius is an extinct genus of dissorophoid temnospondyl within the family Micropholidae. It is known from the early Permian of North America.

<span class="mw-page-title-main">Amphibamidae</span> Extinct family of temnospondyls

The Amphibamidae are an ancient family of dissorophoid temnospondyls known from Late Carboniferous-Early Permian strata in the United States.

Pasawioops is an extinct genus of early Permian dissorophoid temnospondyl within the clade Amphibamiformes.

Plemmyradytes is an extinct genus of dissorophoid temnospondyl from the early Permian. It is an amphibamiform from the Eskridge Formation exposures of Nebraska. The type species is Plemmyradytes shintoni. The genus name derives from the Greek plemmyris and dytes ('diver'), while the specific name honors John Shinton, a fossil preparator at the Denver Museum of Natural History where all known specimens of this taxon are reposited following collection in the late 20th century.

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

Eolydekkerina is an extinct genus of temnospondyl from the Early Triassic of South Africa. It belongs to the family Lydekkerinidae, along with the closely related genus Lydekkerina. It is known from a single type species, Eolydekkerina magna, which was named in 1996 from a part of the Beaufort Group called the Lystrosaurus Assemblage Zone.

The Micropholidae are an extinct family of dissorophoid temnospondyls known from Late Carboniferous to Early Triassic strata in the United States and South Africa.

<span class="mw-page-title-main">Amphibamiformes</span> Extinct clade of temnospondyls

Amphibamiformes is an unranked clade with Dissorophoidea created by Schoch (2018). It encompasses all of the taxa traditionally considered to be "amphibamids", branchiosaurids, and hypothetically lissamphibians under the traditional temnospondyl hypothesis of lissamphibian origins. These taxa are typically small-bodied dissorophoids and form the sister group to Olsoniformes, which comprises dissorophids and trematopids.

References

  1. Gee, Bryan M.; Sidor, Christian A. (2021-05-21). "First record of the amphibamiform Micropholis stowi from the lower Fremouw Formation (Lower Triassic) of Antarctica". Journal of Vertebrate Paleontology. 41: e1904251. doi: 10.1080/02724634.2021.1904251 . ISSN   0272-4634.
  2. Huxley, T. H. (1859-01-01). "On some Amphibian and Reptilian Remains from South Africa and Australia". Quarterly Journal of the Geological Society. 15 (1–2): 642–658. doi:10.1144/gsl.jgs.1859.015.01-02.71. ISSN   0370-291X. S2CID   129159449.
  3. Owen, Richard (1876). "On Petrophryne granulata Ow., a labyrinthodont reptile from the Trias of South Africa, with special comparison of the skull with that of Rhinosaurus jasikovii". Bulletin Société Sciences Naturelles Moscou. 50: 147–153.
  4. 1 2 Broili, Ferdinand; Schröder, Joachim (1937). "Beobachtungen an Wirbeltieren der Karrooformation. XXV. Uber Micropholis Huxley". Sitzungsberichte der Bayrischen Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Abteilung. 1937: 19–38.
  5. 1 2 Boy, Jürgen A. (1985-01-29). "Micropholis the last surviving dissorophoid (Amphibia, Temnospondyli; Lower Triassic)". Neues Jahrbuch für Geologie und Paläontologie - Monatshefte. 1985 (1): 29–45. doi:10.1127/njgpm/1985/1985/29. ISSN   0028-3630.
  6. 1 2 Schoch, Rainer R.; Rubidge, Bruce S. (2005-09-30). "The amphibamid Micropholis from the Lystrosaurus Assemblage Zone of South africa". Journal of Vertebrate Paleontology. 25 (3): 502–522. doi:10.1671/0272-4634(2005)025[0502:TAMFTL]2.0.CO;2. ISSN   0272-4634. S2CID   85979872.
  7. Mchugh, Julia B. (2015-01-02). "Paleohistology of Micropholis stowi (Dissorophoidea) and Lydekkerina huxleyi (Lydekkerinidae) humeri from the Karoo Basin of South Africa, and implications for bone microstructure evolution in temnospondyl amphibians". Journal of Vertebrate Paleontology. 35 (1): e902845. doi:10.1080/02724634.2014.902845. ISSN   0272-4634. S2CID   86106336.
  8. Watson, D.M.S. (August 1913). "II. — Micropholis stowi, Huxley, a temnospondylous amphibian from South Africa". Geological Magazine. 10 (8): 340–346. Bibcode:1913GeoM...10..340W. doi:10.1017/S0016756800127001. ISSN   1469-5081.
  9. "I. The structure, evolution and origin of the amphibia. - The "orders' rachitomi and stereospondyli". Philosophical Transactions of the Royal Society of London. Series B, Containing Papers of a Biological Character. 209 (360–371): 1–73. January 1920. doi: 10.1098/rstb.1920.0001 . ISSN   0264-3960.
  10. 1 2 Romer, Alfred Sherwood (1947). Review of the Labyrinthodontia. Museum of Comparative Zoology. OCLC   12898383.
  11. Säve-Söderbergh, G. (1935). "[Presumed Danish title not cited]" [On the dermal bones of the head in labyrinthodont stegocephalians and primitive reptilia, with special reference to eo-triassic stegocephalians from east Greenland]. Meddelelser om Grønland [Communications on Greenland] (in Danish). 98 (3). Copenhagen, DK: 1–211, plates 1–15;[ full citation needed ]
    [reviewer not cited] (April 1935). "Reviews – Stegocephalians and primitive reptiles". Geological Magazine. 72 (4): 190–191. Bibcode:1935GeoM...72..190.. doi:10.1017/s001675680009261x. ISSN   0016-7568;
    Double-citation needs to be checked: The first ref., to Meddelelser om Grønland is embedded inside the second citation, to Geological Magazine, where the first article is reviewed. It is displayed that way in the original text in the front-page of the review article in Geological Magazine.
  12. Romer, Alfred Sherwood. Vertebrate Paleontology (Third ed.). Chicago, IL. ISBN   0-226-72488-3. OCLC   174202.
  13. Bolt, J.R. (1969-11-14). "Lissamphibian origins: Possible protolissamphibian from the Lower Permian of Oklahoma". Science. 166 (3907): 888–891. Bibcode:1969Sci...166..888B. doi:10.1126/science.166.3907.888. ISSN   0036-8075. PMID   17815754. S2CID   10813454.
  14. Boy, Jürgen A. (1972). Die Branchiosaurier <Amphibia> des saarpfälzischen Rotliegenden <Perm, SW-Deutschland>. OCLC   163720370.
  15. 1 2 Schoch, Rainer R. (2018-11-05). "The putative lissamphibian stem-group: Phylogeny and evolution of the dissorophoid temnospondyls". Journal of Paleontology. 93 (1): 137–156. doi: 10.1017/jpa.2018.67 . ISSN   0022-3360.