Genus of dinosaurs
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Eousdryosaurus ("eastern "Dryosaurus"") is a genus of basal iguanodontian dinosaur known from a partial skeleton discovered in Upper Jurassic rocks in western Portugal. The type, and only species, is Eousdryosaurus nanohallucis, named and described in 2014.
Discovery and naming.
"Eousdryosaurus" is based on SHN(JJS)-170, kept in the Sociedade de História Natural in Torres Vedras, Portugal. The articulated and well-preserved specimen includes a hip vertebra and eight vertebrae from the proximal part of the tail, their chevrons, the left ilium, the entire left leg, and the right thigh bone (femur). These bones were discovered in sandstone of the late Kimmeridgian-age (late Jurassic, approximately 152 million years old) Praia da Amoreira-Porto Novo Member of the Lourinhã Formation in Porto das Barcas, Lourinhã, Portugal. The genus name is a reference to "Eousdryosaurus" being a relative of "Dryosaurus" on the east side of the Atlantic Ocean. The type and only species is "E. nanohallucis", meaning "small hallux", in reference to the small size of that toe. "Eousdryosaurus" was named in 2014 by Fernando Escaso and colleagues, after having been described briefly in 2000.
Description.
The only known individual of "Eousdryosaurus" was a small dryosaurid, estimated at in length, comparable to immature individuals of "Dryosaurus" and "Dysalotosaurus". The right femur measures long and the left shin bone (tibia) measures long.
It is differentiated from other dryosaurids by various details of the vertebrae, hip, and hind limb. The foot is unique among ornithopods in that the first digit (the hallux or big toe) includes a single phalanx bone; most basal ornithopods had two phalanges, and most derived ornithopods, including hadrosaurs ("duckbills"), lost this digit.
Classification.
Escaso et al. performed a phylogenetic analysis and found "Eousdryosaurus" to be a basal dryosaurid within the Dryomorpha, a type of small bipedal herbivore near the base of Iguanodontia.
On the other hand, Dieudonné et al. (2020) found "Eousdryosaurus" to be a sister taxon to the Elasmaria.
In their 2024 description of the contemporary "Hesperonyx", Rotatori et al. found support for a dryosaurid position of "Eousdryosaurus" in both their parsimony and Bayesian analyses, contrasting with the suggestions of Dieudonné et al. (2020). Their results are displayed in the cladogram below:
References.
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