{{Short description|Geological formation in Madagascar}} {{Infobox rockunit|name=Lower Sakamena Formation|thickness_ts=|map={{Location map+ | Madagascar | relief = 1 | width = 250 | float = center | places = {{Location map~ | Madagascar | lat_deg =-22.5476111 | lon_deg = 45.423666 | mark = Red pog.svg | marksize = 10 }} }}|area=|location=|paleocoordinates=|coordinates={{coord|22.5476111|S|45.423666|E|display=inline,title}}|region=|country=Madagascar|extent=Morondava Basin|namedfor=|namedby=|year_ts=|prilithology=|age=Lopingian<br />~{{fossil range|259|252}}|otherlithology=Sandstone, conglomerate, Mudstone|unitof=Sakamena Group|subunits=|underlies=Middle Sakamena Formation|overlies=Sakoa Formation|thickness=|image=|imagesize=|caption=|type=Geological formation|period=Lopingian|map_caption=}}
The '''Lower Sakamena Formation''' is a geological formation found in the Morondava Basin on the southern part of the island of Madagascar. It is widely regarded as dating to the Late Permian period, around 259-252 million years ago. It is well known for largely complete, articulated fossils of fish and reptiles that are found in concretions, along with more fragmentary therapsid and amphibian remains.
== Geology and setting == The Lower Sakamena Formation is generally thought to be Late Permian in age. The formation forms the lowest part of the 4000 m thick Sakamena Group (which is sometimes considered part of the Karoo Supergroup) within the Morondava Basin of southern Madagascar, of consists of predominantly coarse fluvial and lacustrine derived sediments, including sandstone and conglomerate as well as mudstone,<ref>{{Cite journal |last1=Wescott |first1=William A. |last2=Diggens |first2=John N. |date=October 1998 |title=Depositional history and stratigraphical evolution of the Sakamena group (Middle Karoo Supergroup) in the southern Morondava Basin, Madagascar |url=https://linkinghub.elsevier.com/retrieve/pii/S0899536298000736 |journal=Journal of African Earth Sciences |language=en |volume=27 |issue=3–4 |pages=461–479 |doi=10.1016/S0899-5362(98)00073-6 |bibcode=1998JAfES..27..461W |url-access=subscription }}</ref> deposited within a rift valley system with rift lakes. Articulated remains of vertebrates (which are sometimes preserved as moulds) are primarily found in concretions concentrated within certain horizons, though disarticulated vertebrate remains are also sometimes found separately from concretions.<ref name=":0">Smith, R. M. H. 2000. Sedimentology and taphonomy of Late Permian vertebrate fossil localities in Southwestern Madagascar. Paleontologia Africana 36:25–41</ref>
== Paleoenvironment == [[File:Thadeosaurus colcanapi (life restoration).jpg|left|thumb|Life restoration of ''Thadeosaurus'' in the lakeshore environment of the Lower Sakamena Formation, with ''Glossopteris'' leaves in the foreground]] The environment of the formation is thought to have been warm and humid with a temperate climate, with rainfall likely being seasonal and possibly monsoonal, with the immediate area surrounding the lakes likely being a riparian forest in which ''Glossopteris'' trees were likely a prominent component. The lower waters of the lakes within the rift system are likely to have been cold and anoxic (oxygen depleted), which helped to preserve animal remains by slowing decay. The articulated animal remains are suggested to largely have originated from mass mortality events when during heavily rain and floods, the anoxic waters in the lower part of the lakes became mixed with those in the upper part, killing aquatic animals as a result of oxygen deprivation in the case of fish or thermal shock. Articulated remains of terrestrial vertebrates were probably were washed in postmortem rather than being killed by the anoxic water.<ref name=":0" /><ref>{{Cite journal |last1=Buffa |first1=Valentin |last2=Jalil |first2=Nour-Eddine |last3=Falconnet |first3=Jocelyn |last4=Vincent |first4=Peggy |date=March 2025 |title=The neodiapsid Thadeosaurus colcanapi from the upper Permian of Madagascar |url=https://onlinelibrary.wiley.com/doi/10.1002/spp2.70008 |journal=Papers in Palaeontology |language=en |volume=11 |issue=2 |article-number=e70008 |doi=10.1002/spp2.70008 |bibcode=2025PPal...11E0008B |issn=2056-2799|doi-access=free }}</ref>
== Paleobiota == After Smith (2000):<ref name=":0" />
=== Vertebrates === {| class="wikitable" style="margin:auto; width:100%;" ! colspan="3" style="text-align:center;" |Vertebrates of the Lower Sakamena Formation |- !Genus !Note !Images |- |''Claudiosaurus'' |A probably aquatic neodiapsid reptile |center|frameless |- |''Hovasaurus'' |An aquatic tangasaurid neodiapsid reptile |center|frameless |- |''Barasaurus'' |An owenettid procolophonian non-diapsid reptile |center|frameless |- |''Coelurosauravus'' |A gliding weigeltisaurid neodiapsid reptile |center|frameless |- |''Thadeosaurus'' |A probably terrestrial tangasaurid neodiapsid reptile |center|frameless |- |''Acerosodontosaurus'' |A probably aquatic tangasaurid neodiapsid reptile |center|frameless |- |''Oudenodon'' |A dicynodont therapsid known from a skull. Other indeterminate postcranial dicynodont remains are also known from the formation |center|thumb|Skull of the related ''Oudenodon latirostris'' |- |''Atherstonia'' |A "palaeoniscoid"-grade ray-finned fish | |- |Rhinesuchidae indet |Temnospondyl amphibians known from fragmentary remains |[[File:Rhinesuchus1DB.jpg|center|thumb|Life restoration of the related rhinesuchid ''Rhinesuchus'']] |- |Theriodontia indet |An indeterminate therapsid known from a lower jaw | |}
=== Flora === {| class="wikitable" style="margin:auto; width:100%;" ! colspan="3" style="text-align:center;" |Flora of the Lower Sakamena Formation |- !Genus !Note !Images |- |''Glossopteris'' |A glossopterid seed-bearing tree known from leaves | |- |''Lepidopteris'' |A peltasperm seed fern known from stems | |- |''Schizoneura'' |An equisetalean related to modern horsetails known from stems | |}
== References == {{Reflist}} Category:Geologic formations of Madagascar Category:Permian Madagascar