{{Short description|Geological formation in Antarctica}} {{Infobox rockunit | name = Fremouw Formation | image = | caption = | type = [[Geological formation]] | age = latest [[Permian]]-early [[Late Triassic]]{{fossilrange|252|235}} | period = Triassic | prilithology = [[Sandstone]], [[siltstone]], [[mudstone]] | otherlithology = | namedfor = [[Fremouw Peak]], [[Queen Alexandra Range]], Antarctica.<ref name="Barrett1969a"/> | namedby = P. J. Barrett<ref name="Barrett1969a">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 .</ref> | region = [[Transantarctic Mountains]] of [[Antarctica]] | country = [[Ross Dependency]] | coordinates = {{coord|84.0000|S|165.0000|E|source:wikidata|display=inline,title}} | paleocoordinates = {{coord|81.8|S|69.8|E|display=inline}} | unitof = [[Beacon Supergroup]] | subunits = Lower, middle, upper | underlies = [[Falla Formation]] | overlies = [[Buckley Formation]] | thickness = up to {{convert|1000|m|ft|abbr=on}} | extent = | area = | map = {{Location map+ | Antarctica | relief = 1 | width = 250 | float = center | places = {{Location map~ | Antarctica | lat_deg = -84.0 | lon_deg = 165.0 | mark = Pink ff0080 pog.svg | marksize = 12 }} }} | map_caption = }}
The '''Fremouw Formation''' is a [[Triassic]]-age [[Formation (stratigraphy)|rock formation]] in the [[Transantarctic Mountains]] of the [[Ross Dependency]] 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.
== 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.<ref name=Eetal70>{{cite journal |last=Elliot |first=D.H. |author2=Colbert, E.H.|author3= Breed, W.J.|author4= Jensen, J.A.|author5= Powell, J.S. |year=1970 |title=Triassic tetrapods from Antarctica: evidence for continental drift |journal=Science |volume=169 |issue=3951 |pages=1197–1201 |doi=10.1126/science.169.3951.1197|bibcode = 1970Sci...169.1197E |pmid=17815934|s2cid=10995542 }}</ref> It overlies the Permian [[Buckley Formation]], which consists of coal and ''[[Glossopteris]]'' fossils.<ref name=BBC68>{{cite journal |last=Barrett |first=P.J. |author2=Baillie, R.J.|author3= Colbert, E.H. |year=1968 |title=Triassic amphibian from Antarctica |journal=Science |volume=161 |issue=3840 |pages=460–462 |doi=10.1126/science.161.3840.460|pmid=5659679 |bibcode = 1968Sci...161..460B |s2cid=28006253 }}</ref> 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 [[siltstone]]s and [[mudstone]]s, coarse-grained channel sandstones, and [[Conglomerate (geology)|conglomerate]]s.<ref name=TVPPB>{{cite web |url=http://www.antarcticvp.com/background.html |title=Background |year=2008 |work=Transantarctic Vertebrate Paleontology Project |publisher=Augustana College |access-date=13 July 2011 |archive-url=https://web.archive.org/web/20110707145930/http://www.antarcticvp.com/background.html |archive-date=7 July 2011 }}</ref>
== Paleoenvironment == [[File:Bowenia Spectabilis in Prague Botanical Garden DSC 0083.jpg|thumb|Cycads from the Fremouw Formation are similar to the living ''[[Bowenia]]'' from [[Australia]]|left]] Well-preserved plants are common in the Fremouw Formation. Logs have been found in channel deposits, and roots and stems have been found in [[Permineralization|permineralized]] soil. Smaller fossils on Fremouw Peak include [[cycad]]s, [[horsetail]]s, [[seed fern]]s, [[Osmundaceae]] ferns, and even [[fungi]]. One cycad called ''[[Antarcticycas]]'' is similar in appearance to the living ''[[Bowenia]]'' of [[Australia]].<ref name="TT93">{{cite book|last=Taylor|first=E.L.|title=The Nonmarine Triassic|author2=Taylor, T.N.|publisher=The New Mexico Museum of Natural History and Science Bulletin|year=1993|editor=Lucas, S.G.|location=Albuquerque|pages=453–455|chapter=Fossil tree rings and paleoclimate from the Triassic of Antarctica|editor2=Morales, M.|chapter-url=http://work.geobiology.cn/ebook/%E8%8B%B1%E6%96%87%E6%96%87%E7%8C%AE/The%20Nonmarine%20Triassic/80%20Fossil%20Tree%20Rings%20and%20Paleoclimate%20from%20the%20Triassic%20of%20Antarctica.pdf|access-date=2011-07-13|archive-date=2012-03-23|archive-url=https://web.archive.org/web/20120323185839/http://work.geobiology.cn/ebook/%E8%8B%B1%E6%96%87%E6%96%87%E7%8C%AE/The%20Nonmarine%20Triassic/80%20Fossil%20Tree%20Rings%20and%20Paleoclimate%20from%20the%20Triassic%20of%20Antarctica.pdf}}</ref> 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.<ref name="CTTK03">{{cite journal|last=Cúneo|first=N.R.|author2=Taylor, E.L.|author3=Taylor, T.N.|author4=Krings, M.|year=2003|title=In situ fossil forest from the upper Fremouw Formation (Triassic) of Antarctica: paleoenvironmental setting and paleoclimate analysis|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=197|issue=3–4|pages=239–261|bibcode=2003PPP...197..239C|doi=10.1016/s0031-0182(03)00468-1}}</ref> 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.<ref name="TT93" />
The Fremouw Formation preserves many tetrapod fossils that span the [[Permian–Triassic extinction event|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 lineage]]s 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 (population biology)|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.<ref name="FAS10" />
== 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.<ref name=BBC68/> The bone was found the previous year by a researcher from [[Ohio State University]] who was studying the geology of the Transantarctic Mountains.<ref name=CC74>{{cite journal |last=Colbert |first=E.H. |author2=Cosgriff, J.W. |year=1974 |title=Labyrinthodont amphibians from Antarctica |journal=American Museum Novitates |issue=2552 |pages=1–30|hdl=2246/2750 }}</ref> The animal was later named ''[[Austrobrachyops|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, [[therapsid]]s, and [[archosauriform]] reptiles have all been found in the formation.<ref name=SSD07>{{cite journal |last=Sidor |first=C.A. |author2=Steyer, J.S.|author3= Damiani, R. |year=2007 |title=Parotosuchus (Temnospondyli: Mastodonsauridae) from the Triassic of Antarctica |journal=Journal of Vertebrate Paleontology |volume=27 |issue=1 |pages=232–235 |doi=10.1671/0272-4634(2007)27[232:PTMFTT]2.0.CO;2}}</ref> These fossils are found around the [[Shackleton Glacier|Shackleton]] and Beardmore glaciers, in places such as [[Gordon Valley]] and [[Fremouw Peak]].
=== Tetrapods === {{paleobiota-key-compact}}
==== Temnospondyls ==== {| class="wikitable sortable" align="center" |- ! Taxon ! Species ! Member ! class="unsortable" | Material ! class="unsortable" | Notes ! class="unsortable" | Images |- |style="background:#E6E6E6;"| ''[[Austrobrachyops]]'' |style="background:#E6E6E6;" | ''[[Austrobrachyops|A. jenseni]]''<ref name=CC74/> |style="background:#E6E6E6;" | Lower Fremouw |style="background:#E6E6E6;" | Jaw fragment, [[pterygoid bone]], and other small fragments |style="background:#E6E6E6;" | A ''[[nomen dubium]]'' based on a combination of material from [[Brachyopidae|brachyopid]] temnospondyls, a [[dicynodont]], and other animals<ref name=SSD07/> |style="background:#E6E6E6;" | |- |''[[Antarctosuchus]]'' | ''[[Antarctosuchus|A. polyodon]]'' | Upper Fremouw | A mostly complete skull | A [[capitosaur]] temnospondyl | |- | ''[[Cryobatrachus]]'' | ''[[Cryobatrachus|C. kitchingi]]''<ref name=CC74/> | Lower Fremouw | A partial skull and other bone fragments | A [[lydekkerinid]] temnospondyl | [[Image:Cryobatrachus kitchingi.jpg|150px]] |- | ''[[Kryostega]]'' | ''[[Kryostega|K. collinsoni]]''<ref name=SDH08>{{cite journal |last=Sidor |first=C.A. |author2=Damiani, R.|author3= Hammer, W.R. |year=2008 |title=A new Triassic temnospondyl from Antarctica and a review of Fremouw Formation biostratigraphy |journal=Journal of Vertebrate Paleontology |volume=28 |issue=3 |pages=656–663 |doi=10.1671/0272-4634(2008)28[656:ANTTFA]2.0.CO;2}}</ref> | Upper Fremouw | Large snout fragment | A [[stereospondyl]] temnospondyl | [[File:KryostegaDB16.jpg|150px]] |- | ''[[Micropholis (amphibian)|Micropholis]]'' |''[[Micropholis (amphibian)|M. stowi]]''<ref>{{Cite journal|last1=Gee|first1=Bryan M.|last2=Sidor|first2=Christian A.|date=2021-05-21|title=First record of the amphibamiform Micropholis stowi from the lower Fremouw Formation (Lower Triassic) of Antarctica|journal=Journal of Vertebrate Paleontology|volume=41|issue=1 |article-number=e1904251|doi=10.1080/02724634.2021.1904251|issn=0272-4634|doi-access=|bibcode=2021JVPal..41E4251G }}</ref> |Lower Fremouw |A block containing the skeletons of 4 individuals of the taxon, accounting for much of the skeletons. |A [[Euskelia|Euskelian]] temnopodyl |[[File:Micropholis stowi.jpg|center|150px]] |- | ''[[Parotosuchus]]'' | ''P. sp.''<ref name=SSD07/> | Upper Fremouw | Fragment of the right side of the snout. | A temnospondyl | [[Image:Parotosuchus BW.jpg|150px]] |- |''[[Rhigerpeton]]'' |''[[Rhigerpeton|R. isbelli]]''<ref>{{Cite journal |last1=Gee |first1=Bryan M. |last2=Beightol |first2=Charles V. |last3=Sidor |first3=Christian A. |date=2023-06-28 |title=A new lapillopsid from Antarctica and a reappraisal of the phylogenetic relationships of early diverging stereospondyls |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2023.2216260 |journal=Journal of Vertebrate Paleontology |language=en |doi=10.1080/02724634.2023.2216260 |issn=0272-4634|url-access=subscription }}</ref> |Lower Fremouw |Partial skull |A [[Lapillopsidae|lapillopsid]] temnospondyl | |- | [[Rhytidosteidae]] | R. indet.<ref name=TVPPB/> | Lower Fremouw | | A temnospondyl | |- |}
==== Reptiles ==== {| class="wikitable sortable" align="center" |- ! Taxon ! Species ! Member ! class="unsortable" | Material ! class="unsortable" | Notes ! class="unsortable" | Images |- | ''[[Antarctanax]]'' | ''[[Antarctanax|A. shackletoni]]''<ref>{{Cite journal|last1=Peecook|first1=Brandon R.|last2=Smith|first2=Roger M. H.|last3=Sidor|first3=Christian |date=2019|title=A novel archosauromorph from Antarctica and an updated review of a high-latitude vertebrate assemblage in the wake of the end-Permian mass |journal=Journal of Vertebrate Paleontology|language=en|pages=1–16|doi=10.1080/02724634.2018.1536664|s2cid=92116260|issn=0272-4634}}</ref> | Lower Fremouw | Eight presacral vertebrae, left humerus, ribs, feet | Medium-sized archosauriform | |- | [[Archosauriformes]] |Indeterminate.<ref name=Cetal11>{{cite journal |last=Smith |first=N.D. |author2=Crandall, J.R.|author3= Hellert, S.M.|author4= Hammer, W.R.|author5= Makovicky, P.J. |year=2011 |title=Anatomy and affinities of large archosauromorphs from the lower Fremouw Formation (Early Triassic) of Antarctica |journal=Journal of Vertebrate Paleontology |volume=31 |issue=4 |pages=784–797 |doi=10.1080/02724634.2011.586662|bibcode=2011JVPal..31..784S |s2cid=129231144 |url=https://pubs.usgs.gov/of/2007/1047/ea/of2007-1047ea047.pdf }}</ref> | Lower Fremouw | Partial presacral [[vertebra]] and left [[humerus]] | A large-bodied archosauriform reptile | |- | ''[[Palacrodon]]'' | ''[[Palacrodon|P. browni]]''<ref name=Cetal11/> | Lower Fremouw | | An enigmatic [[diapsid]] reptile; initially named ''Fremouwsaurus geludens'' | |- | ''[[Procolophon]]'' | ''[[Procolophon|P. trigoniceps]]''<ref name=Cetal11/> | Lower Fremouw | | A [[procolophonid]] reptile | [[File:Procolophon BW.jpg|150px]] |- |''[[Prolacerta]]'' | ''[[Prolacerta|P. broomi]]''<ref name=Cetal11/> | Lower Fremouw | | A [[prolacertiform]] reptile | [[File:Prolacerta broomi.jpg|150px]] |- |}
==== Synapsids ==== ===== Cynodonts ===== {| class="wikitable sortable" align="center" |- ! Taxon ! Species ! Member ! class="unsortable" | Material ! class="unsortable" | Notes ! class="unsortable" | Images |- |''[[Cynognathus]]'' | ''Cynognathus sp.''<ref name=HWR95>{{cite journal |last=Hammer |first=W.R. |year=1995 |title=New therapsids from the Upper Fremouw Formation (Triassic) of Antarctica |journal=Journal of Vertebrate Paleontology |volume=15 |issue=1 |pages=105–112 |doi=10.1080/02724634.1995.10011210|bibcode=1995JVPal..15..105H }}</ref> | Upper Fremouw | | A [[cynodont]] | [[File:Cynognathus NT small.jpg|150px]] |- |''[[Impidens]]'' | ''[[Impidens|I. hancoxi]]''<ref name="Tolchard2021"/> | Upper Fremouw | Partial snout | A cynodont, originally described as [[Diademodontidae|Diademodontidae indet.]]<ref name=HWR95/> | [[File:Impidens.jpg|center|150px]] |- |''[[Thrinaxodon]]'' | ''[[Thrinaxodon|T. liorhinus]]''<ref name=CK77>{{cite journal |last=Colbert |first=E.H. |author2=Kitching, J.W. |year=1977 |title=Triassic cynodont reptiles from Antarctica |journal=American Museum Novitates |issue=2611 |pages=1–30|hdl=2246/2011 }}</ref> | Lower Fremouw | | A cynodont | [[File:Thrinaxodon BW.jpg|150px]] |}
===== Dicynodonts ===== {| class="wikitable sortable" align="center" |- ! Taxon ! Species ! Member ! class="unsortable" | Material ! class="unsortable" | Notes ! class="unsortable" | Images |- | [[Kannemeyeriidae]] | Indeterminate.<ref name=HWR95/> | Upper Fremouw | | A [[dicynodont]] | |- |''[[Kombuisia]]'' |''[[Kombuisia|K. antarctica]]''<ref name=FAS10>{{cite journal |last=Fröbisch |first=J. |author2=Angielczyk, K.D.|author3= Sidor, C.A. |year=2010 |title=The Triassic dicynodont ''Kombuisia'' (Synapsida, Anomodontia) from Antarctica, a refuge from the terrestrial Permian-Triassic mass extinction |journal=Naturwissenschaften |volume=97 |issue=2 |pages=187–196 |doi=10.1007/s00114-009-0626-6 |pmid=19956920|bibcode = 2010NW.....97..187F |s2cid=20557454 }}</ref> | Lower Fremouw | | A dicynodont | |- |rowspan = "2"| ''[[Lystrosaurus]]'' | ''[[Lystrosaurus|L. curvatus]]''<ref name=CEH74>{{cite journal |last=Colbert |first=E.H. |year=1974 |title=''Lystrosaurus'' from Antarctica |url=http://digitallibrary.amnh.org/dspace/bitstream/handle/2246/5462//v2/dspace/ingest/pdfSource/nov/N2535.pdf?sequence=1 |journal=American Museum Novitates |issue=2535 |pages=1–44}}</ref> | Lower Fremouw | | A dicynodont | |- | ''[[Lystrosaurus|L. murrayi]]''<ref name="CEH74"/> | Lower Fremouw | | A dicynodont | [[Image:Lystrosaurus BW.jpg|150px]] |- |''[[Myosaurus]]'' | ''[[Myosaurus|Myosaurus gracilis]]''<ref name=TVPPB/> | Lower Fremouw | | A dicynodont | [[Image:Myosaurus.jpg|150px]] |}
===== Therocephalians ===== {| class="wikitable sortable" align="center" |- ! Taxon ! Species ! Member ! class="unsortable" | Material ! class="unsortable" | Notes ! class="unsortable" | Images |- |''[[Ericiolacerta]]'' | ''[[Ericiolacerta|E. parva]]''<ref name=CK81>{{cite journal |last=Colbert |first=E.H. |author2=Kitching, J.W. |year=1981 |title=Scaloposaurian reptiles from the Triassic of Antarctica |journal=American Museum Novitates |issue=2709 |pages=1–22|hdl=2246/5362 }}</ref> | Lower Fremouw | | A [[therocephalia]]n | [[File:Ericiolacerta BW.jpg|150px]] |- |''[[Notictoides]]'' |'' N. absens ''<ref>{{Cite journal |last1=Sidor |first1=Christian A. |last2=Kulik |first2=Zoe T. |last3=Huttenlocker |first3=Adam K. |date=2021-10-01 |title=A new bauriamorph therocephalian adds a novel component to the Lower Triassic tetrapod assemblage of the Fremouw Formation (Transantarctic Basin) of Antarctica |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2021.2081510 |journal=Journal of Vertebrate Paleontology |language=en |volume=41 |issue=6 |article-number=e2081510 |doi=10.1080/02724634.2021.2081510 |bibcode=2021JVPal..41E1510S |issn=0272-4634|url-access=subscription }}</ref> | | |A therocephalian | |- |''[[Pedaeosaurus]]'' | ''[[Pedaeosaurus|P. parvus]]''<ref name=CK81/> | Lower Fremouw | | A therocephalian | |- |''[[Rhigosaurus]]'' | ''[[Rhigosaurus|R. glacialis]]''<ref name=CK81/> | Lower Fremouw | | A therocephalian | |- |}
=== See also === * [[List of fossiliferous stratigraphic units in Antarctica]]
== References == <references>
<ref name="Tolchard2021">{{Cite journal| doi = 10.1080/02724634.2021.1929265| issn = 0272-4634| article-number = e1929265| last1 = Tolchard| first1 = Frederick| last2 = Kammerer| first2 = Christian F.| last3 = Butler| first3 = Richard J.| last4 = Hendrickx| first4 = Christophe| last5 = Benoit| first5 = Julien| last6 = Abdala| first6 = Fernando| last7 = Choiniere| first7 = Jonah N.| title = A new large gomphodont from the Triassic of South Africa and its implications for Gondwanan biostratigraphy| journal = Journal of Vertebrate Paleontology| date = 2021-07-26| volume = 41| issue = 2| bibcode = 2021JVPal..41E9265T| s2cid = 237517965| hdl = 11336/147732| hdl-access = free}}</ref>
</references>
[[Category:Geologic formations of Antarctica]] [[Category:Triassic Antarctica]]<!--re: fossil biota list--> [[Category:Permian System of Antarctica]] [[Category:Triassic System of Antarctica]] [[Category:Sandstone formations]] [[Category:Siltstone formations]] [[Category:Mudstone formations]] [[Category:Fluvial deposits]] [[Category:Paleontology in Antarctica]] [[Category:Permian south paleopolar deposits]] [[Category:Dufek Coast]]