Aetosaurus

{{Short description|Extinct genus of reptiles}} {{Automatic taxobox | fossil_range = [[Late Triassic]], {{fossilrange|Carnian|Norian}} | image = Aetosaurus ferratus.JPG | image_caption = Assemblage of fossil ''A. ferratus'' | taxon = Aetosaurus | authority = Fraas, [[1877 in paleontology|1877]] | subdivision_ranks = Species | subdivision = * {{extinct}}''A. arcuatus'' (Marsh, 1896) * {{extinct}}''A. crassicauda'' Fraas, 1907 * {{extinct}}''A. ferratus'' Fraas, 1877 ([[Type species|type]]) | synonyms = * ''Stegomus arcuatus'' [[Othniel Charles Marsh|Marsh]], 1896 }}

'''''Aetosaurus''''' is an extinct [[genus]] of [[pseudosuchian]] [[reptile]] belonging to the [[order (biology)|order]] [[Aetosauria]]. It is generally considered to be the most primitive aetosaur.<ref name="HL99">{{cite journal|last=Heckert|first=A.B.|author2=Lucas, S.G.|year=1999|title=A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs|url=https://www.researchgate.net/publication/254314124|journal=Journal of Vertebrate Paleontology|volume=19|issue=1|pages=50–68|citeseerx=10.1.1.563.9516|doi=10.1080/02724634.1999.10011122|bibcode=1999JVPal..19...50H }}</ref> Three species are currently recognized: ''A. ferratus'', the [[type species]] from [[Germany]] and [[Italy]];<ref name=FO77>{{cite journal |last=Fraas |first=O. |year=1877 |title=''Aetosaurus ferratus'' Fr. Die gepanzerte Vogel-Echse aus dem Stubensandstein bei Stuttgar |journal=Festschrift zur Feier des 400jährigen Jubiläums der Eberhard-Karls-Universät zu Tübingen, Wurttembergische Naturwissenschaftliche Jahreshefte |volume=33 |issue=3 |pages=1–22}}</ref> ''A. crassicauda'' from Germany;<ref name=FE07>{{cite journal |last=Fraas |first=E. |year=1907 |title=''Aëtosaurus crassicauda'' n. sp., nebst Beobachtungen tiber das Becken der Aëtosaurier |journal=Jahreshefte des Vereins für Vaterländische Naturkunde Württemberg |volume=42 |pages=101–109}}</ref> and ''A. arcuatus'' from eastern [[North America]].<ref name="LHH98" /> Additional specimens referred to ''Aetosaurus'' have been found in the [[Chinle Group]] of the southwestern [[United States]],<ref name="HL98">{{cite journal |last=Heckert |first=A.B. |author2=Lucas, S.G. |year=1998 |title=First occurrence of ''Aetosaurus'' (Reptilia: Archosauria) in the Upper Triassic Chinle Group (USA) and its biochronological significance |journal=Neues Jahrbuch für Geologie und Paläontologie |volume=1998 |issue=10 |pages=604–612|doi=10.1127/njgpm/1998/1998/604 }}</ref><ref name="SBJ98">{{cite journal |last=Small |first=B.J. |year=1998 |title=The occurrence of ''Aetosaurus'' in the Chinle Formation (Late Triassic, USA) and its biostratigraphic significance |journal=Neues Jahrbuch für Geologie und Paläontologie |volume=1998 |issue=3 |pages=289–300}}</ref> and the [[Fleming Fjord Formation]] of [[Greenland]].<ref name=Jetal94>{{cite journal |last=Jenkins |first=F.A. Jr. |author2=Shubin, N.H.|author3=Amaral, W.W.|author4=Gatesy, S.M.|author5=Schaff, C.R.|author6=Clemmensen, L.B.|author7=Downs, W.R.|author8=Davidson, A.R.|author9=Bonde, N.|author10= Osbaeck, F.F. |year=1994 |title=Late Triassic continental vertebrates and depositional environments of the Fleming Fjord Formation, Jameson Land, East Greenland |journal=Meddelelser om Grønland, Geoscience |volume=32 |pages=1–25}}</ref> Specimens of ''Aetosaurus'' occur in [[Norian]]-age strata.

==Description== ''Aetosaurus'' was a small, primitive aetosaur. Unlike more [[Synapomorphy|derived]] aetosaurs such as ''[[Desmatosuchus]]'' or ''[[Typothorax]]'', the [[carapace]] was long and narrow and lacked spikes. The paramedian [[scute]]s that covered the back (with one row on each side of the vertebrae) are considerably wider than they are long. The lateral scutes, which are beneath the paramedian and formed a row on either side of the animal, do not bear any spikes or other projections.<ref name=LHH98>{{cite journal|last=Lucas |first=S.G. |author2=Heckert, A.B. |author3=Huber, P. |year=1998 |title=''Aetosaurus'' (Archosauromorpha) from the Upper Triassic of the Newark Supergroup, eastern United States, and its biochronological significance |journal=Palaeontology |volume=41 |issue=6 |pages=1215–1230 |url=http://palaeontology.palass-pubs.org/pdf/Vol%2041/Pages%201215-1230.pdf |url-status=usurped |archive-url=https://web.archive.org/web/20120309062222/http://palaeontology.palass-pubs.org/pdf/Vol%2041/Pages%201215-1230.pdf |archive-date=2012-03-09 }}</ref>

==Behaviour== A 2023 study based on a fossil assemblage found in [[Kaltental]], suggested that juvenile ''A. ferratus'' were likely [[gregarious]] animals, possibly to increase their chances of survival and to deter predators.<ref>{{Cite journal |last1=Teschner |first1=Elżbieta M. |last2=Konietzko-Meier |first2=Dorota |last3=Desojo |first3=Julia B. |last4=Schoch |first4=Rainer R. |last5=Klein |first5=Nicole |date=2023-02-12 |title=Triassic Nursery? Evidence of gregarious behavior in juvenile pseudosuchian archosaurs as inferred by humeral histology of Aetosaurus ferratus (Norian; southern Germany) |journal=Journal of Vertebrate Paleontology |volume=42 |issue=2 |article-number=e2168196 |doi=10.1080/02724634.2023.2168196 |s2cid=256864004 |issn=0272-4634}}</ref><ref>{{Cite web |last=Lazaro |first=Enrico de |date=2023-02-13 |title=Aetosaurs Were Gregarious, Paleontologists Say {{!}} Sci.News |url=https://www.sci.news/paleontology/gregarious-aetosaurus-ferratus-11649.html |access-date=2023-02-14 |website=Sci.News: Breaking Science News |language=en-US}}</ref>

==Species== [[File:Aetosaurus ferratus skull.png|thumb|left|Reconstructed skull of ''A. ferratus'']] ''Aetosaurus'' was first named, with the description of the type species ''A. ferratus'', in 1877 by German [[paleontologist]] [[Oscar Fraas]]. At the time, ''Aetosaurus'' was known from 22 articulated skeletons that had been found in the [[Lower Stubensandtein]] of Germany.<ref name=FO77/> Thirty years later, Fraas' son [[Eberhard Fraas|Eberhard]] described a second species, ''A. crassicauda'', also from Germany.<ref name=FE07/> ''A. crassicauda'' can be distinguished from ''A. ferratus'' by its larger size; ''A. crassicauda'' reached a maximum length of {{convert|150|cm|in}} while ''A. ferratus'' reached a length of up to {{convert|90|cm|in}}.<ref name=HL99/>

In addition to the Stubensandtein in Germany, ''A. ferratus'' is also known from the [[Zorzino Limestone|Calcare di Zorzino Formation]] in [[Cene, Lombardy|Cene]], Italy.<ref name="WR89">{{cite journal|last=Wild|first=R.|year=1989|title=''Aëtosaurus'' (Reptilia:Thecodontia) from the Upper Triassic (Norian) of Cene near Bergamo, Italy, with a revision of the genus|url=https://www.museoscienzebergamo.it/web/images/stories/museo/Rivista_museo/14_volume/riv_14_wild.pdf|journal=Revista del Museo Civico di Scienze Naturali "Enrico Caffi"|volume=14|pages=1–24}}</ref> Specimens of ''Aetosaurus'' that have been recovered from the Fleming Fjord Formation in Greenland likely represent ''A. ferratus''.<ref name=Jetal94/> Some material from the Chinle Group in the southwestern United States probably represent ''A. ferratus'', as well.<ref name=HL98/><ref name=SBJ98/>

In 1998, the genus ''Stegomus'' was synonymized with ''Aetosaurus''.<ref name=LHH98/> In 1896, paleontologist [[Othniel Charles Marsh]] named ''Stegomus arcuatus'' from a [[Fossil#Casts and molds|cast]] of an aetosaur known as [[Peabody Museum of Natural History|YPM]] 1647 from the [[New Haven Formation]] in the [[Fair Haven Heights neighborhood]] of New Haven.<ref name=MOC96>{{cite journal |last=Marsh |first=O.C. |year=1896 |title=A new belodont reptile (''Stegomus'') from the Connecticut River Sandstone |journal=American Journal of Science |volume=2 |issue=7 |pages=59–62 |doi=10.2475/ajs.s4-2.7.59|bibcode=1896AmJS....2...59M |url=https://zenodo.org/record/1450162 }}</ref> This cast consisted of the dorsal carapace. Several other casts preserving the surface of the skull and tail have been found in the [[Passaic Formation]] of [[Hunterdon County, New Jersey|Hunterdon]] and [[Somerset County, New Jersey|Somerset counties]], [[New Jersey]]<ref name="JGL48">{{cite journal |last=Jepsen |first=G.L. |year=1948 |title=A Triassic armored reptile from New Jersey |journal=State of New Jersey Department of Conservation Miscellaneous Geological Paper |pages=1–20}}</ref><ref name="BD86">{{cite journal |last=Baird |first=D. |year=1986 |title=Some Upper Triassic reptiles, footprints and an amphibian from New Jersey |journal=The Mosasaur |volume=3 |pages=125–135}}</ref> and an outcrop of the Lower [[Sanford Formation]] at the [[Triangle Brick Co. Quarry]] in [[Durham County, North Carolina]].<ref name=PJM66>{{cite journal |last=Parker |first=J.M. |year=1966 |title=Triassic reptilian fossil from Wake County, North Carolina |journal=Journal of the Elisha Mitchell Society |volume=82 |page=92}}</ref> ''Stegomus arcuatus'' was found to be synonymous with ''Aetosaurus'' on the basis of several similarities, including a lack of spikes and a distinctive radial pattern of grooves on some of the caudal scutes.<ref name=LHH98/> [[File:Stegomus arcuatus Marsh.JPG|thumb|right|Photograph of YPM 1647, a specimen of ''A. arcuatus'']] [[File:Aetosaurus.jpg|thumb|right|Skeletal drawing of ''A. ferratus'' by Marsh]] ''A. arcuatus'' has paramedian scutes that are much wider than they are long, even in comparison to other species of ''Aetosaurus''. There is very little pitting on the surface of the scutes, although the porosity of the sandstone that makes up the casts has been mistaken for pitting.<ref name=LRS53>{{cite journal |last=Lull |first=R.S. |year=1953 |title=Triassic life of the Connecticut Valley revised |journal=Bulletin of the Connecticut Geologic and Natural History Survey |volume=81 |pages=1–336}}</ref> The tail narrows significantly past the base. The carapace is "waisted", meaning that it narrows in front of the [[pelvis]].<ref name=LHH98/>

The following [[cladogram]] is simplified after an analysis presented by Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat (2012).<ref name=Aetobarbakinoides>{{cite journal |author=Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat |year=2012 |title=A new aetosaur genus (Archosauria: Pseudosuchia) from the early Late Triassic of southern Brazil |journal=Zootaxa |volume=3166 |pages=1–33 |issn=1175-5334 |url=https://www.mapress.com/zootaxa/2012/f/z03166p033f.pdf |doi=10.11646/zootaxa.3166.1.1 }}</ref>

{{clade| style=font-size:90%;line-height:85% |label1='''Aetosauria''' |1={{clade |1=''[[Aetosauroides scagliai]]'' |label2=[[Stagonolepididae]] |2={{clade |1='''''Aetosaurus ferratus''''' |2=''[[Coahomasuchus kahleorum]]'' |3={{clade |1=''[[Neoaetosauroides engaeus]]'' |2={{clade |1=''[[Calyptosuchus wellesi]]'' |2=''[[Stagonolepis robertsoni]]'' |3={{clade |1=''[[Aetobarbakinoides brasiliensis]]'' |2={{clade |label1=[[Typothoracisinae]] |1={{clade |1={{clade |1=''[[Typothorax]]'' |2=''[[Redondasuchus]]'' }} |label2=[[Paratypothoracisini]] |2={{clade |1=''[[Tecovasuchus chatterjeei]]'' |2={{clade |1=''[[Rioarribasuchus chamaensis]]'' |2=''[[Paratypothorax andressorum]]'' }} }} }} |label2=[[Desmatosuchinae]] |2={{clade |1=''[[Sierritasuchus macalpini]]'' |2={{clade |1=''[[Longosuchus meadei]]'' |2={{clade |1=''[[Lucasuchus hunti]]'' |2={{clade |1=''[[Acaenasuchus geoffreyi]]'' |label2=''[[Desmatosuchus]]'' |2={{clade |1=''[[Desmatosuchus haplocerus]]'' |2=''[[Desmatosuchus smalli]]'' }} }} }} }} }} }} }} }} }} }} }} }}

==References== {{Reflist}}

==External links== *[https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=38269 ''Aetosaurus''] in the [[Paleobiology Database]]

[[Category:Late Triassic reptiles of Europe]] [[Category:Aetosauria]] [[Category:Late Triassic reptiles of Africa]] [[Category:Aetosaurs of North America]] [[Category:Late Triassic pseudosuchians]] [[Category:Prehistoric pseudosuchian genera]] [[Category:Fossil taxa described in 1877]]