Merriamosauria

{{Short description|Extinct clade of reptiles}}

{{more citations needed|date=March 2017}}

{{Automatic taxobox

| taxon = Merriamosauria

| fossil_range = Middle Triassic - Late Cretaceous

| image = Shastasaurus pacificus.jpg

| image_caption = A partial skull of Shastasaurus pacificus, a species which defines the clade Merriamosauria

| authority = Motani, 1999

| subdivision_ranks = Subgroups

| subdivision = * {{extinct}}Besanosaurus

• {{extinct}}Pessopteryx
• {{extinct}}Pessosaurus
• {{extinct}}Thalattoarchon
• {{extinct}}Shastasauridae
• {{extinct}}Euichthyosauria
• {{extinct}}Californosaurus
• {{extinct}}Callawayia
• {{extinct}}Guizhouichthyosaurus
• {{extinct}}Parvipelvia

}}

Merriamosauria is an extinct clade of ichthyosaurs. It was named by Ryosuke Motani in his 1999 analysis of the relationships of ichthyopterygian marine reptiles and was defined in phylogenetic terms as a stem-based taxon including "the last common ancestor of Shastasaurus pacificus and Ichthyosaurus communis, and all of its descendants." The name honours John Campbell Merriam.{{Cite journal | last1 = Motani | first1 = R. | title = Phylogeny of the Ichthyopterygia | doi = 10.1080/02724634.1999.10011160 | journal = Journal of Vertebrate Paleontology | volume = 19 | issue = 3 | pages = 473–496 | year = 1999 | bibcode = 1999JVPal..19..473M }} Based on this definition, Merriamosauria includes most ichthyosaurs except for several Triassic groups such as the clade Mixosauria, the family Cymbospondylidae, and perhaps the family Toretocnemidae. Merriamosaurs are characterized by features in their pectoral girdles and limb bones, including an extensive connection between the scapula and the coracoid bone, the absence of the first metacarpal and the absence of a pisiform bone.

In addition to Shastasaurus, this clade includes Shonisaurus, Guizhouichthyosaurus, an unnamed Norian taxon from Alaska, and many other genera.{{Cite journal|last1=Druckenmiller|first1=Patrick S.|last2=Kelley|first2=Neil|last3=Whalen|first3=Michael T.|last4=Mcroberts|first4=Christopher|last5=Carter|first5=Joseph G.|date=2014-09-19|title=An Upper Triassic (Norian) ichthyosaur (Reptilia, Ichthyopterygia) from northern Alaska and dietary insight based on gut contents|journal=Journal of Vertebrate Paleontology|volume=34|issue=6|pages=1460–1465|doi=10.1080/02724634.2014.866573|bibcode=2014JVPal..34.1460D |s2cid=129908740|issn=0272-4634|url=https://figshare.com/articles/journal_contribution/1228040 }}