| Eucercosaurus | |
|---|---|
 | |
| Sacral vertebrae CAMSM 55614-16 from the holotype | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Clade: | †Iguanodontia |
| Genus: | †Eucercosaurus Seeley,1879[1] |
| Species: | †E. tanyspondylus |
| Binomial name | |
| †Eucercosaurus tanyspondylus Seeley, 1879 | |
| Synonyms | |
| |
Eucercosaurus (meaning "good-tailed lizard"[3]) is the name given to agenus ofornithopoddinosaur from theAlbian stage of theEarly Cretaceous. It was anornithopod discovered in theCambridge Greensand ofEngland and is known from 19 centra, 3 sacrals, 4 dorsals and 12 caudals, and aneural arch found nearTrumpington, Cambridgeshire.[4] Thetype species,E. tanyspondylus, was described by BritishpaleontologistHarry Seeley in 1879.
It is considered adubious name, and was once considered anankylosaur.[5] According to a 2020 study,Eucercosaurus andSyngonosaurus were basaliguanodontians.
Throughout the 1860s and 1870s, large collections of fossil vertebrate remains were made from theCambridge Greensand for theWoodwardian Museum ofSedgwick Museum of Earth Sciences inCambridge, first being described by British palaeontologistHarry Govier Seeley. Many of the 500 bones collected were found in association, allowing Seeley to establish which bones belonged to which individual, though much of the material was limited tovertebrae. One such associated series of vertebrae, found atTrumpington, was chosen by Seeley to represent a new taxon he described in1879, given the nameEucercosaurus tanyspondylus. The specimen included 18 vertebral centra and one partialneural arch, with generally poor preservation andphosphate encrustations, as well as some wear and damage from picks used during excavation. The anatomy ofEucercosaurus, in particular the hexagonal cross-section of the vertebrae, was believed by Seeley to be unique toEucercosaurus, and its general anatomy was found most similar toiguanodonts.[1]
The mid-Cretaceous age of the Cambridge Greensand fossils is significant due to the rarity of deposits of that age in Europe, consisting of about 22% of the mid-Cretaceous tetrapod fossils in the world. The Cambridge Greensand is a member of theWest Melbury Marly Chalk Formation, with the quarries being historic and now largely inaccessible.Eucercosaurus was collected from an unknown quarry near Trumpington as multiple were being worked at the time of its discovery by local quarrymen as they sieved and washed the phosphate nodules they were quarrying for. There are no maps or other records to verify the presence ofEucercosaurus as a single individual, but the consistency in preservation, size, and morphology supports their identification as such. Theholotype ofEucercosaurus has since been designated as CAMSM B55610-29, with a unique number in the series for each of the 19 partial vertebrae. While the Cambridge Greensand sediments themselves are from theCenomanian, the vertebrate remains includingEucercosaurus werereworked from the lateAlbianGault Formation.
While Seeley consideredEucercosaurus to be an iguanodontian, he noted its similarities toHylaeosaurus, leading to later discussion about a possiblyankylosaur identity. In 1969, British palaeontologist Rodney Steel opted to referEucercosaurus to the genusAnoplosaurus from the same deposits, creating thenew combinationAnoplosaurus tanyspondylus. Steel also referredSyngonosaurus, also from the Cambridge Greensand, toAnoplosaurus, uniting all Greensand ornithischians under one genus.[2] While Steel consideredAnoplosaurus to be an iguanodont, it has since been identified more confidently as an ankylosaur. Following this,Eucercosaurus has been considered distinct, an undiagnosticnomen dubium, or a synonym of the ankylosaurAcanthopholis, as either an ankylosaur or an iguanodontian. The status ofEucercosaurus was revisited in 2020 by British palaeontologists Paul Barrett and Joseph Bonsor, who found that its anatomy matched that of an iguanodontian, with its elongate, hexagonal vertebrae, and a ridge on the side, differing subtly from all other iguanodontians, but not enough to consider the taxon valid.[6]