Temporal range: Late Cretaceous
Dalla Vecchia, 2009
The genus was named and described by Italian paleontologist Fabio Marco Dalla Vecchia in 2009. Its only and type species is Tethyshadros insularis. The genus name refers to the Tethys Ocean and the Hadrosauroidea. The specific name means "insular" or "of the island" in Latin, a reference to the fact that the location of the find was at the time part of the Adriatic-Dinaric Island, one of the larger islands of the European Archipelago.
Tethyshadros is based on holotype SC 57021, a mostly complete but crushed skeleton, that previously had been nicknamed "Antonio". The growth lines of the bones indicate that the specimen was perhaps five to six years old. It was found in the Villaggio del Pescatore site in the Province of Trieste, near Duino-Aurisina. This site was in the eighties discovered by Alceo Tarlao en Giorgio Rimoli in an old quarry near the sea. Here layers are exposed from the Liburnia Formation, from the Campanian-Maastrichtian, 71-70 million years old. In them a chalkstone lens was present, containing fossils, ten metres thick and seventy metres in diameter. In 1994 student Tiziana Brazzatti in it discovered the hand bones of a larger skeleton. A company dealing in fossils, Stoneage, was given the commission to retrieve any remains, for which an overburden of three hundred tons had to be removed. Later paleontologist Dalla Vecchia was brought in to provide professional guidance. In April 1999 "Antonio" was removed from the quarry, being slightly damaged by the process. Until December 2000 this specimen was during 2800 hours further prepared by spraying it with formic acid to dissolve the chalk matrix and protecting the gradually exposed bone with resin. Another six specimins of Tethyshadros were discovered, one of them a skeleton that fell apart during the removal, another a skeleton of which only the forelimbs were recovered. All fossils are kept at the Civico Museo di Storia Naturale di Trieste but are property of the Italian State: "SC" stands for "State Collection".
With a length of about 4 metres (13 ft) and a weight of 350 kilograms (770 lb), Tethyshadros is a relatively small species, which has been explained by Dalla Vecchia as an instance of insular dwarfism. The skull is relatively long, the neck and tail short, the legs, especially the shin bones, again long. These proportions, together with a reduction of the number of fingers, are seen as cursorial adaptations for bipedal running.
Tethyshadros shows a mix of basal and derived traits. A cladistic analysis indicated that it was closely related to the Hadrosauridae sensu Sereno and Telmatosaurus. According to Dalla Vecchia, the presence of Tethyshadros on a European island is caused by a radiation of basal hadrosauroids, island-hopping from Asia. He rejects the possibility that the species is a relict of isolated evolution from earlier European hadrosauroids or descended from American hadrosaurs.
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