Alexeyisaurus

{{Short description|Extinct genus of reptiles}}

{{Italic title}}

{{speciesbox

| name = Alexeyisaurus

| fossil_range = Late Triassic, {{Fossil range|210}}

| genus = Alexeyisaurus

| parent_authority = Sennikov & Arkhangelsky, 2010

| authority = Sennikov & Arkhangelsky, 2010

| species = karnoushenkoi

}}

Alexeyisaurus is an extinct genus of possible plesiosaur known from the upper Triassic (lower-middle Norian age) of Wilczek Formation, Wilczek Land, of Franz Josef Land, Russia.{{cite journal|author=A. G. Sennikov, M. S. Arkhangelsky |year=2010 |title=On a Typical Jurassic Sauropterygian from the Upper Triassic of Wilczek Land (Franz Josef Land, Arctic Russia)|journal=Paleontological Journal |volume=44 |number=5 |pages=567–572 |doi=10.1134/S0031030110050126|bibcode=2010PalJ...44..567S |s2cid=88505507 }} It was first named by A. G. Sennikov and M. S. Arkhangelsky in 2010 and the type species is Alexeyisaurus karnoushenkoi. While considered an elasmosaur in the initial publication, it has been described as a "partial, poorly preserved, and undiagnostic sauropterygian skeleton" in subsequent publications.{{Cite journal|last1=Wintrich|first1=Tanja|last2=Hayashi|first2=Shoji|last3=Houssaye|first3=Alexandra|last4=Nakajima|first4=Yasuhisa|last5=Sander|first5=P. Martin|date=2017-12-01|title=A Triassic plesiosaurian skeleton and bone histology inform on evolution of a unique body plan|journal=Science Advances|language=en|volume=3|issue=12|pages=e1701144|doi=10.1126/sciadv.1701144|pmid=29242826|pmc=5729018|bibcode=2017SciA....3E1144W|issn=2375-2548|doi-access=free}}