| Microcleidids | |
|---|---|
 | |
| Microcleidus homalospondylus skeleton (NHMUK PV OR 36184) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Plesiosauria |
| Superfamily: | †Plesiosauroidea |
| Family: | †Microcleididae Benson, Evans & Druckenmiller,2012 |
| Genera | |
Microcleididae is anextinctfamily ofbasalplesiosauroidplesiosaurs from theEarly Jurassic (middleSinemurian to lateToarcian stages) ofFrance,Germany,Portugal and theUnited Kingdom. Currently, the oldest and the most known microcleidid isEretmosaurus from the middle Sinemurian of the United Kingdom. Microcleididae was formally named and described by Roger B. J. Benson, Mark Evans and Patrick S. Druckenmiller in 2012.[1][2]
Großman (2007) referred informally to "microcleididelasmosaurs", a clade comprising the three taxa referred to the Microcleididae by Bensonet al. (2012). Ketchum and Benson (2010) found the traditional "microcleidid" genera to nest within a monophyletic Plesiosauridae, in a close position toPlesiosaurus.[3] However, Ketchum and Benson (2011) performed a phylogenetic analysis which found a monospecific Plesiosauridae, and a monophyletic Microcleididae.[4] Smithet al. (in press) described a new "microcleidid"Lusonectes, and obtained similar results in a different phylogenetic analysis.[2] However, the family has not formally been erected until Bensonet al. (2012) also found the same results in their analysis.[1]
To avoid further confusion between Plesiosauridae and Microcleididae, Bensonet al. (2012) proposed astem-based definition for this taxon, utilizingPlesiosaurus as an external specifier. Microcleididae was defined as "Microcleidus homalospondylus and all taxa more closely related to it than toPlesiosaurus dolichodeirus,Cryptoclidus eurymerus,Elasmosaurus platyurus,Leptocleidus superstes,Pliosaurus brachydeirus orPolycotylus latipinnis." Bensonet al. (2012) found strong support for Microcleididae, however their diagnosis focused on unambiguouspostcranialsynapomorphies since cranial material of basal microcleidids is unknown. The synapomorphies are: widely separated posteriorcervical rib facets, posteriormost dorsal rib facets split betweencentrum andneural arch, medial surface of the iliac blade anteroposteriorly concave and a prominent flange extends anteriorly from the proximal half of the radius. This analysis focused on basal plesiosaurs and therefore only one derived pliosaurid and onecryptoclidian were included whileelasmosaurids weren't included at all. Thecladogram below follows the topology from Bensonet al. (2012) analysis.[1]
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