A plesiosauroid skull from the Toarcian (Lower Jurassic) of Alhadas, Portugal

Adam Stuart Smith, Ricardo Araújo, Octávio Mateus

Research output: Contribution to conferencePosterpeer-review


During the early days of geological exploration in Portugal, a plesiosauroid skull was discovered in the marine beds of the Toarcian age São Gião Formation in the Lusitanian Basin, Alhadas. The specimen (MG33) was studied by H.E. Sauvage who referred it to Plesiosaurus sp. This fossil has since been stored in the Geological Museum, Lisbon, where it hasbeen largely forgotten by paleontologists for over a century. It consists of a partial isolatedcranium with the premaxillary, suspensorium, and basicranium regions missing. The dorsalsurface of the skull is highly abraided so few sutures are visible. The palate on the otherhand is well preserved. There are presently four valid plesiosauroid genera known from theToarcian stage: Seeleyosaurus, Occitanosaurus, Hydrorion, and Microcleidus. To assess thephylogenetic position of MG33, we coded it as an additional operational taxonomic unit inan existing data matrix and reran the cladistic analysis. In the resulting strict consensus of15 equally parsimonious trees, MG33 forms an unresolved polytomy with Hydrorion, Occitanosaurus and Microcleidus. Further comparison of MG33 with these taxa indicates greatersimilarity to Hydrorion. MG33 has a flatparasphenoid between the posterior interpterygoid vacuities, whereas the parasphenoid in Microcleidus and Occitanosaurus is keeled. MG33 isa rare example of a plesiosaurian from Portugal and represents the westernmost occurence ofany European plesiosaurian.
Original languageEnglish
Publication statusPublished - Oct 2010
EventAnnual Meeting of the Society of Vertebrate Paleontology -
Duration: 1 Jan 2010 → …


ConferenceAnnual Meeting of the Society of Vertebrate Paleontology
Period1/01/10 → …


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