polycotylidae

{{Short description|Extinct family of reptiles}}

{{Automatic taxobox

| name = Polycotylids

| fossil_range = Early - Late Cretaceous, {{fossil range|113|72}}

| image = Martinectes transparent background.png

| image_upright = 1.15

| image_caption = Martinectes in the Rocky Mountain Dinosaur Resource Center

| taxon = Polycotylidae

| authority = Williston, 1909

| subdivision_ranks = Genera

| subdivision =

• {{extinct}}Edgarosaurus
• {{extinct}}Manemergus
• {{extinct}}Mauriciosaurus
• {{extinct}}Piratosaurus?
• {{extinct}}Rarosaurus?
• {{extinct}}Thililua
• {{extinct}}Occultonectia{{cite journal |author1=V. Fischer |author2=R. B. J. Benson |author3=P. S. Druckenmiller |author4=H. F. Ketchum |author5=N. Bardet |year=2018 |title=The evolutionary history of polycotylid plesiosaurians |journal=Royal Society Open Science |volume=5 |issue=3 |pages=172177 |doi=10.1098/rsos.172177 |pmid=29657811 |pmc=5882735 |bibcode=2018RSOS....572177F }}
• {{extinct}}Plesiopleurodon
• {{extinct}}Sulcusuchus
• {{extinct}}Palmulasaurinae
• {{extinct}}Pahasapasaurus
• {{extinct}}Palmulasaurus
• {{extinct}}Polycotylinae
• {{extinct}}Eopolycotylus
• {{extinct}}Georgiasaurus
• {{extinct}}Polycotylus
• {{extinct}}Scalamagnus
• {{extinct}}Serpentisuchops
• {{extinct}}Trinacromerum
• {{extinct}}Dolichorhynchia{{Cite journal |last1=Clark |first1=Robert O. |last2=O’Keefe |first2=F. Robin |last3=Slack |first3=Sara E. |date=2023-12-24 |title=A new genus of small polycotylid plesiosaur from the Upper Cretaceous of the Western Interior Seaway and a clarification of the genus Dolichorhynchops |url=https://www.sciencedirect.com/science/article/pii/S0195667123003403 |journal=Cretaceous Research |volume=157 |pages=105812 |doi=10.1016/j.cretres.2023.105812 |issn=0195-6671|url-access=subscription }}
• {{extinct}}Dolichorhynchops
• {{extinct}}Martinectes
• {{extinct}}Unktaheela

}}

Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceous. Several species survived into the final stage of the Cretaceous, the early Maastrichtian around {{Ma|72}}.{{Cite journal|last1=Fischer|first1=V.|last2=Benson|first2=R. B. J.|last3=Druckenmiller|first3=P. S.|last4=Ketchum|first4=H. F.|last5=Bardet|first5=N.|date=March 2018|title=The evolutionary history of polycotylid plesiosaurians|url= |journal=Royal Society Open Science|language=en|volume=5|issue=3|pages=172177|doi=10.1098/rsos.172177|issn=2054-5703|pmc=5882735|pmid=29657811|bibcode=2018RSOS....572177F }} The possible latest surviving member Rarosaurus from the late Maastrichtian is more likely a crocodylomorph.{{Cite journal |last1=Alhalabi |first1=W. A. |last2=Bardet |first2=N. |last3=Sachs |first3=S. |last4=Kear |first4=B. P. |last5=Joude |first5=I. B. |last6=Yazbek |first6=M. K. |last7=Godoy |first7=P. L. |last8=Langer |first8=M. C. |year=2024 |title=Recovering lost time in Syria: New Late Cretaceous (Coniacian-Santonian) elasmosaurid remains from the Palmyrides mountain chain |journal=Cretaceous Research |volume=159 |at=105871 |doi=10.1016/j.cretres.2024.105871 |bibcode=2024CrRes.15905871A }}

With their short necks and large elongated heads, they resemble the pliosaurs, but closer phylogenetic studies indicate that they share many common features with the Leptocleididae and Elasmosauridae. They have been found worldwide, with specimens reported from New Zealand, Australia, Japan, Morocco, the US, Canada, Eastern Europe, and South America.{{Cite journal |author1=Druckenmiller, Patrick S. |author2=Russell, Anthony P. |name-list-style=amp |year=2009 |title=Earliest North American Occurrence Of Polycotylidae (Sauropterygia: Plesiosauria) From The Lower Cretaceous (Albian) Clearwater Formation, Alberta, Canada |url=http://www.bio.ucalgary.ca/contact/faculty/pdf/russell/335.pdf |journal=Journal of Paleontology |volume=83 |issue=6 |pages=361–392 |doi=10.1666/09-014.1 |bibcode=2009JPal...83..981D |s2cid=130695434 |url-status=dead |archive-url=https://web.archive.org/web/20110706211048/http://www.bio.ucalgary.ca/contact/faculty/pdf/russell/335.pdf |archive-date=2011-07-06 }}