Fremouw Formation

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Fremouw Formation
Stratigraphic range: latest Permian-early Late Triassic 252–235  Ma
Type Geological formation
Unit of Beacon Supergroup
Sub-unitsLower, middle, upper
Underlies Falla Formation
Overlies Buckley Formation
Thicknessup to 1,000 m (3,300 ft)
Lithology
Primary Sandstone, siltstone, mudstone
Location
Coordinates 84°00′00″S165°00′00″E / 84.0000°S 165.0000°E / -84.0000; 165.0000
Approximate paleocoordinates 81°48′S69°48′E / 81.8°S 69.8°E / -81.8; 69.8
Region Transantarctic Mountains of Antarctica
Type section
Named for Fremouw Peak, Queen Alexandra Range, Antarctica. [1]
Named byP. J. Barrett [1]
Antarctica relief location map.jpg
Pink ff0080 pog.svg
Fremouw Formation (Antarctica)

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.

Contents

Stratigraphy

The Fremouw Formation is mostly Triassic in age, with the oldest rocks dating back to the latest Permian. Much of the formation is quartzose sandstone that was deposited in stream beds. [2] It overlies the Permian Buckley Formation, which consists of coal and Glossopteris fossils. [3] The formation is informally divided into lower, middle, and upper units. Most fossils are found in the Lower Fremouw Formation. Here, bones are preserved in fine-grained siltstones and mudstones, coarse-grained channel sandstones, and conglomerates. [4]

Paleoenvironment

Cycads from the Fremouw Formation are similar to the living Bowenia from Australia Bowenia Spectabilis in Prague Botanical Garden DSC 0083.jpg
Cycads from the Fremouw Formation are similar to the living Bowenia from Australia

Well-preserved plants are common in the Fremouw Formation. Logs have been found in channel deposits, and roots and stems have been found in permineralized soil. Smaller fossils on Fremouw Peak include cycads, horsetails, seed ferns, Osmundaceae ferns, and even fungi. One cycad called Antarcticycas is similar in appearance to the living Bowenia of Australia. [5] In 2003, 99 fossilized tree trunks were described from Gordon Valley. These trunks comprise an intact fossilized forest, allowing for an estimation of the distribution of plants and tree cover. Dicroidium fossils are present around the conifer-like stumps, suggesting that they were the leaves of these large trees. [6] Based on the geology of the area, the trees grew alongside riverbanks and on floodplains. The structure of the plants shows no adaptation towards cold tolerance, suggesting that the climate was much warmer in the Triassic. [5]

The Fremouw Formation preserves many tetrapod fossils that span the Permo-Triassic boundary, which marks the Permo-Triassic mass extinction. Around the world, the fossil record of many tetrapod groups is absent or very limited in Early Triassic rocks, implying a major decline in diversity after the extinction. The presence of many of these groups in Middle Triassic strata indicates that long ghost lineages must have extended back into the Early Triassic. Tetrapods such as temnospondyl amphibians, diapsid reptiles, and dicynodont therapsids were common in the Late Permian and seemed to have recovered by the Middle Triassic, but there is little record of their presence in the Early Triassic. All of these tetrapods are present in Early Triassic strata of the Fremouw Formation, suggesting that Antarctica served as a refugium for these animals. During the extinction, global temperatures rose and the supercontinent Pangea moved northward, putting pressure on populations that could not adapt to the warming climate. Antarctica, while much warmer in the Early Triassic than it is today, was cooler than other parts of Gondwana and may have been more hospitable to tetrapod populations. Antarctica's milder climate allowed many groups to take refuge in the region while other populations experienced decline. In the Early Triassic, many Fremouw Formation tetrapods had smaller body sizes than their Permian ancestors, and many were adapted for burrowing. Both of these characteristics are seen as adaptations to Antarctica's greater seasonal variability and protracted day-night cycles. [7]

Biota

The first tetrapod, or land-living vertebrate, from Antarctica was found in the Fremouw Formation and described in 1968. It was represented by a small bone fragment that is probably part of the left mandible of a temnospondyl amphibian. [3] The bone was found the previous year by a researcher from Ohio State University who was studying the geology of the Transantarctic Mountains. [8] The animal was later named Austrobrachyops Jenseni . After its discovery, paleontological expeditions were launched to the area around the Beardmore Glacier to uncover more fossils. Since then, fragmentary remains of temnospondyls, therapsids, and archosauriform reptiles have all been found in the formation. [9] These fossils are found around the Shackleton and Beardmore glaciers, in places such as Gordon Valley and Fremouw Peak.

Tetrapods

Color key
Taxon Reclassified taxonTaxon falsely reported as presentDubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Temnospondyls

TaxonSpeciesMemberMaterialNotesImages

Austrobrachyops

A. jenseni [8]

Lower Fremouw

Jaw fragment, pterygoid bone, and other small fragments

A nomen dubium based on a combination of material from brachyopid temnospondyls, a dicynodont, and other animals [9]

Antarctosuchus

A. polyodon

Upper Fremouw

A mostly complete skull

A capitosaur temnospondyl

Cryobatrachus

C. kitchingi [8]

Lower Fremouw

A partial skull and other bone fragments

A lydekkerinid temnospondyl

Cryobatrachus kitchingi.jpg

Kryostega

K. collinsoni [10]

Upper Fremouw

Large snout fragment

A stereospondyl temnospondyl

KryostegaDB16.jpg

Micropholis M. stowi [11] Lowe FremouwA block containing the skeletons of 4 individuals of the taxon, accounting for much of the skeletons.A Euskelian temnopodyl
Micropholis stowi.jpg
Parotosuchus

P. sp. [9]

Upper Fremouw

Fragment of the right side of the snout.

A temnospondyl

Parotosuchus BW.jpg

Rhigerpeton R. isbelli [12] Lower FremouwPartial skullA lapillopsid temnospondyl
Rhytidosteidae

R. indet. [4]

Lower Fremouw

A temnospondyl

Reptiles

TaxonSpeciesMemberMaterialNotesImages
Antarctanax

A. shackletoni [13]

Lower Fremouw

Eight presacral vertebrae, left humerus, ribs, feet

Medium-sized archosauriform

Archosauriformes Indeterminate. [14]

Lower Fremouw

Partial presacral vertebra and left humerus

A large-bodied archosauriform reptile

Palacrodon

P. browni [14]

Lower Fremouw

An enigmatic diapsid reptile; initially named Fremouwsaurus geludens

Procolophon

P. trigoniceps [14]

Lower Fremouw

A procolophonid reptile

Procolophon BW.jpg

Prolacerta

P. broomi [14]

Lower Fremouw

A prolacertiform reptile

Prolacerta broomi.jpg

Synapsids

TaxonSpeciesMemberMaterialNotesImages
Cynognathus

Cynognathus sp. [15]

Upper Fremouw

A cynodont

Cynognathus NT small.jpg

Impidens

I. hancoxi [16]

Upper Fremouw

Partial snout

A cynodont, originally described as Diademodontidae indet. [15]

Impidens.jpg
Ericiolacerta

E. parva [17]

Lower Fremouw

A therocephalian

Ericiolacerta BW.jpg

Kannemeyeriidae Indeterminate. [15]

Upper Fremouw

A dicynodont

Kombuisia K. antarctica [7]

Lower Fremouw

A dicynodont

Lystrosaurus

L. curvatus [18]

Lower Fremouw

A dicynodont

L. murrayi [18]

Lower Fremouw

A dicynodont

Lystrosaurus BW.jpg

Myosaurus

Myosaurus gracilis [4]

Lower Fremouw

A dicynodont

Myosaurus.jpg

Notictoides N. absens [19] A therocephalian
Pedaeosaurus

P. parvus [17]

Lower Fremouw

A therocephalian

Rhigosaurus

R. glacialis [17]

Lower Fremouw

A therocephalian

Thrinaxodon

T. liorhinus [20]

Lower Fremouw

A cynodont

Thrinaxodon BW.jpg

See also

Related Research Articles

<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>Ericiolacerta</i> Extinct genus of therapsid from the #REDIRECT early Triassic

Ericiolacerta is an extinct genus of small therocephalian therapsids from the early Triassic of South Africa and Antarctica. Ericiolacerta, meaning "hedgehog lizard", was named by D.M.S. Watson in 1931. The species E. parva is known from the holotype specimen which consists of a nearly complete skeleton found in the Lystrosaurus Assemblage Zone within the Katberg Formation of the Beaufort Group in South Africa, and from a partial jaw found in the Lower Triassic Fremouw Formation in Antarctica. Ericiolacerta was around 20 centimetres (7.9 in) in length, with long limbs and relatively small teeth. It probably ate insects and other small invertebrates. The therocephalians – therapsids with mammal-like heads – were abundant in Permian times, but only a few made it into the Triassic. Ericiolacerta was one of those. It is possible that they gave rise to the cynodonts, the only therapsid group to survive into post-Triassic times. Cynodonts gave rise to mammals.

<i>Hovasaurus</i> Extinct genus of reptiles

Hovasaurus is an extinct genus of basal diapsid reptile. It lived in what is now Madagascar during the Late Permian and Early Triassic, being a survivor of the Permian–Triassic extinction event and the paleontologically youngest member of the Tangasauridae. Fossils have been found in the Permian Lower and Triassic Middle Sakamena Formations of the Sakamena Group, where it is amongst the commonest fossils. Its morphology suggests an aquatic ecology.

<i>Cistecephalus</i> Assemblage Zone

The Cistecephalus Assemblage Zone is a tetrapod assemblage zone or biozone found in the Adelaide Subgroup of the Beaufort Group, a majorly fossiliferous and geologically important geological group of the Karoo Supergroup in South Africa. This biozone has outcrops located in the Teekloof Formation north-west of Beaufort West in the Western Cape, in the upper Middleton and lower Balfour Formations respectively from Colesberg of the Northern Cape to east of Graaff-Reinet in the Eastern Cape. The Cistecephalus Assemblage Zone is one of eight biozones found in the Beaufort Group, and is considered to be Late Permian in age.

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

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<i>Procolophon</i> Extinct genus of reptiles

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

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.

Pedaeosaurus is an extinct genus of therocephalian therapsids. Fossils have been found from the Fremouw Formation in the southern Transantarctic Mountains of Antarctica. Pedaeosaurus has traditionally been classified as a scaloposaurid and more recently as an ericiolacertid closely related to Ericiolacerta.

Rhigosaurus glacialis is a species of therocephalian therapsid. Its fossilized remains have been found in the Fremouw Formation of Antarctica. Part of a juvenile skull was found near Mount Kenyon, Antarctica. The holotype of the partial skull shows evidence of promiment upper and lower canine teeth.

<i>Micropholis</i> (amphibian) Extinct genus of amphibian from the early Triassic of South Africa

Micropholis 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. Fossils have also been found from the lower Fremouw of Antarctica.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.

Christian Alfred Sidor is an American vertebrate paleontologist. He is currently a Professor in the Department of Biology, University of Washington in Seattle, as well as Curator of Vertebrate Paleontology and Associate Director for Research and Collections at the Burke Museum of Natural History and Culture. His research focuses on Permian and Triassic tetrapod evolution, especially on therapsids.

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<span class="mw-page-title-main">Abrahamskraal Formation</span> Geological formation of the Beaufort Group in South Africa

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<span class="mw-page-title-main">Diademodontidae</span> Family of gomphodontian cynodonts

Diademodontidae is an extinct family of Triassic gomphodonts. The best-known genus is Diademodon from South Africa. Titanogomphodon from Namibia may also be a member of Diademodontidae. The Chinese genera Hazhenia and Ordosiodon have also been included in the family, but were more recently identified as baurioid therocephalians. Remains of a diademodontid were reported in the Early-Middle Triassic Fremouw Formation in Antarctica, but that specimen was later referred to the trirachodontid Impidens

<i>Bunostegos</i> Genus of reptiles (fossil)

Bunostegos is an extinct genus of pareiasaur parareptile from the Late Permian of the Agadez Region in Niger. The type species, Bunostegos akokanensis, was named from the Moradi Formation in 2003. It was a cow-sized animal with a distinctive skull that had large bony knobs, similar in form to those of other pareiasaurs but far larger. The species appears to have lived in a desert in the centre of the supercontinent of Pangaea.

Titanogomphodon is an extinct genus of diademodontid cynodonts from the Middle Triassic Omingonde Formation of Namibia. It is known from a single partial skull that was described in 1973 from the Omingonde Formation. The type and only species is Titanogomphodon crassus. At about 40 centimetres (16 in), the skull of Titanogomphodon was significantly larger than that of its closest relative, Diademodon. Its teeth are similar to those of another group of cynodonts called Traversodontidae, but the similarities are likely the result of convergent evolution. Aside from its larger size, Titanogomphodon differs from Diademodon in having a bony projection on the postorbital bar behind the eye socket.

Antarctanax is a genus of basal archosauriform that during the Triassic lived in Antarctica. The type species is Antarctanax shackletoni. It was a reptile around the size of an iguana.

<span class="mw-page-title-main">Richards Spur</span>

Richards Spur is a Permian fossil locality located at the Dolese Brothers Limestone Quarry north of Lawton, Oklahoma. The locality preserves clay and mudstone fissure fills of a karst system eroded out of Ordovician limestone and dolomite, with the infilling dating to the Artinskian stage of the early Permian (Cisuralian), around 289 to 286 million years ago. Fossils of terrestrial animals are abundant and well-preserved, representing one of the most diverse Paleozoic tetrapod communities known. A common historical name for the site is Fort Sill, in reference to the nearby military base. Fossils were first reported at the quarry by workers in 1932, spurring a wave of collecting by local and international geologists. Early taxa of interest included the abundant reptile Captorhinus and microsaurs such as Cardiocephalus and Euryodus. Later notable discoveries include Doleserpeton, the most diverse assortment of parareptiles in the Early Permian, and the rare early diapsid Orovenator.

<i>Impidens</i> Extinct genus of cynodonts

Impidens is an extinct genus of large omnivorous cynodont from the Triassic of South Africa and Antarctica. Its type and only species is Impidens hancoxi. Impidens inhabited high-latitude environments of southern Gondwana during the Middle Triassic, where it was probably the apex predator.

References

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