Microcleidus is an extinct genus of sauropterygian reptile belonging to the Plesiosauroidea. It was about the size of a medium-sized dolphin, reaching a length of 3 metres (9.8 ft).[citation needed] The species has 40 neck vertebrae and a short tail of 28 vertebrae. Fossils of the genus have been found in France, the Posidonia Shale in Germany and Luxembourg, and the Alum Shale Formation of England.

Temporal range: Toarcian
~182–175 Ma
Fossil M. homalospondylus
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Family: Microcleididae
Genus: Microcleidus
Watson, 1909
Type species
Plesiosaurus homalospondylus
(Owen, 1865)
Other species
  • M. macropterus (Seeley, 1865)
  • M. tournemirensis (Sciau et al., 1990)
  • M. melusinae Vincent et al., 2019

M. macropteus

  • Plesiosaurus macropteus Seeley, 1865

M. tournemirensis

  • Plesiosaurus tournemirensis Sciau et al., 1990
  • Occitanosaurus tournemirensis
    Bardet et al., 1999


Fossil M. homalospondylus
Fossils of Microcleidus tournemirensis

Species include: Microcleidus homalospondylus (Owen 1865) and Microcleidus macropterus (Seeley 1865).

Occitanosaurus tournemirensis (originally "Plesiosaurus" tournemirensis), was named by Sciau et al. in 1990, based on a nearly complete skeleton of an animal approximately 4 meters (13 ft) long.[1] It was later found to be a species of Microcleidus.

The following cladogram follows an analysis by Ketchum & Benson, 2011.[2]


"Pistosaurus postcranium"

Augustasaurus hagdorni

Bobosaurus forojuliensis


Yunguisaurus liae


Thalassiodracon hawkinsii

Hauffiosaurus spp.

Attenborosaurus conybeari

advanced pliosaurids


NHMUK 49202 [now Anningasaura lymense]

advanced rhomaleosaurids

"Plesiosaurus" macrocephalus

Archaeonectrus rostratus

Macroplata tenuiceps


OUMNH J.10337 [now Stratesaurus taylori]


Seeleyosaurus guilelmiimperatoris

OUMNH J.28585

Plesiosaurus dolichodeirus

Elasmosauridae and Cryptoclidia

Microcleidus homalospondylus

Hydrorion brachypterygius

Occitanosaurus tournemiensis

See alsoEdit


  1. ^ Ketchum HF, Benson RBJ. Global interrelationships of Plesiosaur (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses. Biological Reviews
  2. ^ Hilary F. Ketchum and Roger B. J. Benson (2011). "A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay Formation (Middle Jurassic, Callovian) of England: evidence for a gracile, longirostrine grade of Early-Middle Jurassic pliosaurids". Special Papers in Palaeontology. 86: 109–129.{{cite journal}}: CS1 maint: uses authors parameter (link)