A basal thunnosaurian from Iraq reveals disparate phylogenetic origins for Cretaceous ichthyosaurs

A new thunnosaurian from the Kurdistan region of Iraq represents the first post-Triassic ichthyosaur from the Middle East. The specimen is an articulated partial skeleton that includes a partial skull, complete left forefin, partial ribcage and anterior section of the vertebral column. Associated palynomorphs uncontroversially date the specimen (preserved on a loose slab of matrix) to the late Hauterivian- Barremian interval of the Early Cretaceous. A posterior projection on the humerus, short and trapezoidal humerus, enlarged intermedium, and trapezoidal cervical and anterior dorsal neural spines represent autapomorphies. Forefin morphology is archaic: the carpals, metacarpals and phalanges form a mosaic similar to that of Triassic-Early Jurassic parvipelvians, accessory digits are absent, and notching is present on the leading edge of the first digit. These and other characters indicate exclusion of the Iraq ichthyosaur from Ophthalmosauridae, the only ichthyosaur clade currently known from the Cretaceous. A phylogenetic analysis of Parvipelvia – the largest yet produced – recovers the new taxon as the sister- taxon of Ichthyosaurus communis, thereby invoking a ghost-lineage of over 60 million years. Inclusion of the new taxon in analyses produced by other authors also resulted in exclusion from Ophthalmosauridae, though relationships with other neoichthyosaurians are less resolved than in our analysis. We conclude that the new taxon represents a highly conservative relict – a member of the Ichthyosaurus lineage – that retained an ‘Early Jurassic’ grade of pectoral anatomy into the Cretaceous. Ophthalmosauridae and members of the Ichthyosaurus lineage therefore both persisted beyond the Jurassic. Clearly, both have highly contrasting evolutionary histories and Cretaceous ichthyosaurs do not all represent members of the same evolutionary radiation. The Iraq ichthyosaur is one of several new taxa originally worked on by the late Robert M. Appleby. An inability to resolve conflicting views on the age of the specimen, combined with other issues, derailed his plans to publish on this specimen during the 1970s.