Editing Archelon (section)

==Paleoecology==
[[File:Archelon BW.jpg|thumb|left|Restoration in environment|alt=A green turtle with white spots, underwater, swimming downwards]]
''Archelon'' inhabited the shallow [[Western Interior Seaway]];<ref name=hoganson/> the muddy, oxygen-depleted seafloor was probably, on average, no more than {{cvt|600|ft|m|order=flip}} below the surface,<ref name=fossilmuseum/> and average water temperature may have been {{cvt|17|C|F}} in the Campanian.<ref name=Petersen2016>{{cite journal|first1=S. V.|last1=Petersen|first2=C.|last2=Tabor|first3=K. C.|last3=Lohmann|first4=C. J.|last4=Poulsen|last5=Meyer|first5=K. W.|last6=Carpenter|first6=S. J.|last7=Erickson|first7=J. M.|last8=Matsunaga|first8=K. K. S.|last9=Smith|first9=S. Y.|last10=Sheldon|first10=N. D.|year=2016|title=Temperature and salinity of the Late Cretaceous Western Interior Seaway|journal=Geology|volume=44|issue=11|pages=903–906|doi=10.1130/G38311.1|bibcode=2016Geo....44..903P|url=https://www.researchgate.net/publication/308036435}}</ref> The Late Cretaceous Dakotas were submerged in the Northern Inland Subprovince, an area characterized by moderate to cool temperatures, with an abundance of [[plesiosaur]]s, [[hesperornithiform]] seabirds, and mosasaurs, particularly ''[[Platecarpus]]''. There is no fossil evidence for vertebrate migration between the northern and southern provinces. Though sharks were generally more common in the southern province,<ref>{{cite journal|first1=E. L.|last1=Nicholls|first2=A. P.|last2=Russell|year=1990|title=Paleobiogeography of the Cretaceous Western Interior Seaway of North America: the Vertebrate Evidence|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=79|issue=1–2|pages=162–166|doi=10.1016/0031-0182(90)90110-S|bibcode=1990PPP....79..149N}}</ref> several sharks are known from the Pierre Shale, including ''[[Squalus]]'', ''[[Squalicorax]]'', ''[[Pseudocorax]]'', and ''[[Cretolamna]]''.<ref name=hoganson/> Other large predatory fish include [[Ichthyodectidae|ichthyodectid]]s such as ''Xiphactinus''.<ref name=fossilmuseum/> The Pierre Shale's invertebrate assemblage includes a variety of mollusks, namely [[ammonite]]s–from the Pierre Shale ''[[Placenticeras|Placenticeras placenta]]'', ''[[Scaphites|Scaphites nodosus]]'', ''[[Didymoceras]]'', and ''[[Baculites|Baculites ovatus]]''–bivalves–such as the giant ''[[Inoceramus]]''–<ref>{{cite thesis|url=https://commons.und.edu/cgi/viewcontent.cgi?article=1037&context=theses|first=K. F.|last=Brinster|year=1970|title=Molluscan Paleontology of the Pierre Shale (Upper Cretaceous), Bowman County, North Dakota|publisher=University of North Dakota|type=MS}}</ref> the squid-like [[Belemnitida|belemnites]],<ref name=fossilmuseum>{{cite web|url=http://www.fossilmuseum.net/fossil-art/maps/seaway/seaway100mya.htm|title=Western Interior Seaway|website=The Virtual Fossil Museum|access-date=25 December 2018}}</ref> and [[nautilus]].<ref name=wendell/>

As the seaway progressively migrated southward, it is possible ''Archelon'' was unable to migrate with it. The increasing threat of egg or hatchling predation by new marine or mammalian species may have led to the extinction of ''Archelon'', and the disappearance of gigantic protostegids seems to have coincided with the increasing size of dermochelyids.<ref name=wieland1909/> Protostegidae is more-or-less absent in [[Maastrichtian]] deposits, the latest Cretaceous, and probably died off due to a cooling trend<ref name=weems>{{cite journal|first=R. E.|last=Weems|year=1988|title=Paleocene turtles from the Aquia and Brightseat Formations, with a Discussion of their Bearing on Sea Turtle Evolution and Phylogeny|journal=Proceedings of the Biological Society of Washington|volume=101|issue=1|page=144|url=https://www.researchgate.net/publication/236103438}}</ref> which other turtles were able to survive due to some [[thermoregulatory]] capabilities.<ref>{{cite journal|first1=A. D.|last1=Gentry|first2=J. F.|last2=Parham|first3=D. J.|last3=Ehret|first4=J. A.|last4=Ebersole|year=2018|title=A New Species of ''Peritresius'' Leidy, 1856 (Testudines: Pan-Cheloniidae) from the Late Cretaceous (Campanian) of Alabama, USA, and the Occurrence of the Genus within the Mississippi Embayment of North America|journal=PLOS ONE|volume=13|issue=4|page=e0195651|pmc=5906092|pmid=29668704|doi=10.1371/journal.pone.0195651|bibcode=2018PLoSO..1395651G|doi-access=free}}</ref> Average water temperature may have decreased to {{cvt|7|or|12|C|F}} depending on estimated CO<sub>2</sub> levels.<ref name=Petersen2016/> However, some Maastrichtian-age Kansas Pierre Shale fossils may have been eroded millions of years ago, and it is possible ''Archelon'' survived well into the Maastrichtian.<ref name=everhart/>