Thalassodraco etchesi

Holotype specimen of Thalassodraco etchesi（圖片來源：Megan L. J., David M. M. (2020).，採用 CC BY 4.0 授權）

Age

Jurassic（Tithonian）

149 Ma

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Taxonomy

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ichthyosauria

Family: Ophthalmosauridae

Genus: Thalassodraco

Species: Thalassodraco etchesi

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Morphological description

Thalassodraco etchesi is a medium-sized ophthalmosaurid ichthyosaur with an estimated total body length of about 2.25 meters. The skull is estimated to have measured approximately 52 centimeters in total length. Within the orbit, the sclerotic ring consists of at least fourteen trapezoidal plates. These plates average about 1.77 centimeters in length, forming an inner circular margin with a diameter of approximately 4.2 centimeters and an outer margin with a diameter of about 9.8 centimeters.

Skeletal reconstruction of Thalassodraco etchesi, with known elements shown in gray（圖片來源：Megan L. J., David M. M. (2020).，採用 CC BY 4.0 授權）

The preserved portion of the premaxilla contains twenty-eight teeth, the preserved maxilla holds twenty teeth, and the preserved portion of the dentary contains thirty-five teeth. The teeth from all three regions share a similar morphology. Their crowns are slender and conical, the roots are expanded, and the tips are rounded.

A total of thirty-three vertebrae are preserved. The first ten vertebrae articulate through interlocking joints, and the neural arches are not fused to the centra. The pectoral girdle is completely preserved. In the pelvis, the ischium and pubis are fused proximally and together form a flattened structure. The ischium is broader than the pubis, with a distal margin that expands into a flared shape, whereas the pubis is elongated and rod-like.

The phalanges are rounded, relatively few in number, and become rapidly narrower toward the distal end. The entire forelimb is estimated to have been about 26 centimeters long, making it relatively small compared with the body.

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Etymology

The genus name Thalassodraco combines the Greek word thalasso, meaning "sea," with the Latin word draco, meaning "dragon."

The species name honors Steve Etches, who discovered the fossil and carefully prepared it after its discovery.

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Biological description

Thalassodraco etchesi was discovered in 2009 by Steve Etches in Dorset, southwestern England. The holotype specimen is MJML K1885, and two additional specimens, MJML K1886 and MJML K1174, are also known. These fossils were originally part of a private collection until 2016, when Steve Etches placed them on public display in his personal museum.

Phylogenetic analysis indicates that Thalassodraco etchesi belongs to the subfamily Ophthalmosaurinae and forms a sister-group relationship with the genus Nannopterygius.

Thalassodraco etchesi represents the fifth ichthyosaur species named from this local stratigraphic unit. Steve Etches' fossil collection also contains numerous undescribed ichthyosaur specimens. Continued research on this collection is expected to further expand our understanding of ichthyosaur diversity, ecology, and distribution in Late Jurassic Britain.

（Author: Bai Leng）

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Reference

Megan L. J., David M. M. (2020). A new ophthalmosaurid ichthyosaur from the Upper Jurassic (Early Tithonian) Kimmeridge Clay of Dorset, UK, with implications for Late Jurassic ichthyosaur diversity. PLOS ONE.

+50.735, -2.607

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