# Fremouw Formation

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Geological formation in Antarctica

Fremouw Formation Stratigraphic range: latest Permian-early Late Triassic252–235 Ma PreꞒ Ꞓ O S D C P T J K Pg N Type Geological formation Unit of Beacon Supergroup Sub-units Lower, middle, upper Underlies Falla Formation Overlies Buckley Formation Thickness up to 1,000 m (3,300 ft) Lithology Primary Sandstone, siltstone, mudstone Location Coordinates 84°00′00″S 165°00′00″E / 84.0000°S 165.0000°E / -84.0000; 165.0000 Approximate paleocoordinates 81°48′S 69°48′E / 81.8°S 69.8°E / -81.8; 69.8 Region Transantarctic Mountains of Antarctica Country Ross Dependency Type section Named for Fremouw Peak, Queen Alexandra Range, Antarctica.[1] Named by P. J. Barrett[1] Fremouw Formation (Antarctica)

The **Fremouw Formation** is a [Triassic](/source/Triassic)-age [rock formation](/source/Formation_(stratigraphy)) in the [Transantarctic Mountains](/source/Transantarctic_Mountains) of the [Ross Dependency](/source/Ross_Dependency) of [Antarctica](/source/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](/source/Riparian) forest at 70–75°S latitude.

## Stratigraphy

The Fremouw Formation is mostly Triassic in age, with the oldest rocks dating back to the latest [Permian](/source/Permian). Much of the formation is [quartzose sandstone](/source/Quartzose_sandstone) that was deposited in stream beds.[2] It overlies the Permian [Buckley Formation](https://en.wikipedia.org/w/index.php?title=Buckley_Formation&action=edit&redlink=1), which consists of coal and *[Glossopteris](/source/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](/source/Siltstone) and [mudstones](/source/Mudstone), coarse-grained channel sandstones, and [conglomerates](/source/Conglomerate_(geology)).[4]

## Paleoenvironment

Cycads from the Fremouw Formation are similar to the living *[Bowenia](/source/Bowenia)* from [Australia](/source/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](/source/Permineralization) soil. Smaller fossils on Fremouw Peak include [cycads](/source/Cycad), [horsetails](/source/Horsetail), [seed ferns](/source/Seed_fern), [Osmundaceae](/source/Osmundaceae) ferns, and even [fungi](/source/Fungi). One cycad called *[Antarcticycas](https://en.wikipedia.org/w/index.php?title=Antarcticycas&action=edit&redlink=1)* is similar in appearance to the living *[Bowenia](/source/Bowenia)* of [Australia](/source/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](/source/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](/source/Permian%E2%80%93Triassic_extinction_event), 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](/source/Early_Triassic) rocks, implying a major decline in diversity after the extinction. The presence of many of these groups in [Middle Triassic](/source/Middle_Triassic) strata indicates that long [ghost lineages](/source/Ghost_lineage) 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](/source/Refugium_(population_biology)) for these animals. During the extinction, global temperatures rose and the supercontinent [Pangea](/source/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](/source/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](/source/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](/source/Mandible) of a [temnospondyl](/source/Temnospondyl) amphibian.[3] The bone was found the previous year by a researcher from [Ohio State University](/source/Ohio_State_University) who was studying the geology of the Transantarctic Mountains.[8] The animal was later named *[Austrobrachyops Jenseni](https://en.wikipedia.org/w/index.php?title=Austrobrachyops&action=edit&redlink=1)*. After its discovery, paleontological expeditions were launched to the area around the [Beardmore Glacier](/source/Beardmore_Glacier) to uncover more fossils. Since then, fragmentary remains of temnospondyls, [therapsids](/source/Therapsid), and [archosauriform](/source/Archosauriform) reptiles have all been found in the formation.[9] These fossils are found around the [Shackleton](/source/Shackleton_Glacier) and Beardmore glaciers, in places such as [Gordon Valley](/source/Gordon_Valley) and [Fremouw Peak](/source/Fremouw_Peak).

### Tetrapods

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

#### Temnospondyls

Taxon Species Member Material Notes Images 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 Kryostega K. collinsoni[10] Upper Fremouw Large snout fragment A stereospondyl temnospondyl Micropholis M. stowi[11] Lower Fremouw A block containing the skeletons of 4 individuals of the taxon, accounting for much of the skeletons. A Euskelian temnopodyl Parotosuchus P. sp.[9] Upper Fremouw Fragment of the right side of the snout. A temnospondyl Rhigerpeton R. isbelli[12] Lower Fremouw Partial skull A lapillopsid temnospondyl Rhytidosteidae R. indet.[4] Lower Fremouw A temnospondyl

#### Reptiles

Taxon Species Member Material Notes Images 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 Prolacerta P. broomi[14] Lower Fremouw A prolacertiform reptile

#### Synapsids

#### Cynodonts

Taxon Species Member Material Notes Images Cynognathus Cynognathus sp.[15] Upper Fremouw A cynodont Impidens I. hancoxi[16] Upper Fremouw Partial snout A cynodont, originally described as Diademodontidae indet.[15] Thrinaxodon T. liorhinus[17] Lower Fremouw A cynodont

#### Dicynodonts

Taxon Species Member Material Notes Images 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 Myosaurus Myosaurus gracilis[4] Lower Fremouw A dicynodont

#### Therocephalians

Taxon Species Member Material Notes Images Ericiolacerta E. parva[19] Lower Fremouw A therocephalian Notictoides N. absens [20] A therocephalian Pedaeosaurus P. parvus[19] Lower Fremouw A therocephalian Rhigosaurus R. glacialis[19] Lower Fremouw A therocephalian

### See also

- [List of fossiliferous stratigraphic units in Antarctica](/source/List_of_fossiliferous_stratigraphic_units_in_Antarctica)

## References

1. ^ [***a***](#cite_ref-Barrett1969a_1-0) [***b***](#cite_ref-Barrett1969a_1-1) Barrett, P.J., 1969, *Stratigraphy and petrology of the mainly fluviatile Permian and Triassic Beacon rocks, Beardmore Glacier area, Antarctica.* *Ohio State University Institute of Polar Studies Report* 34, pp1-132 .

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Adapted from the Wikipedia article [Fremouw Formation](https://en.wikipedia.org/wiki/Fremouw_Formation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Fremouw_Formation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.