Fig 1.- Lexovisaurus durobrivensis (= Loricatosaurus priscus)
Compared to the
Stegosaurs of North America, restricted to the sole Morrison Formation and represented only by 1 or 2 genera and a handful of species, all from the Kimmeridgian-Tithonian age of the Late Jurassic, the plated dinosaurs from England appear comparatively more diversified with up to 6 genera spanning from the Middle Jurassic to the Early Cretaceous. Unfortunately, the fossils there are for the most part quite scrappy, consisting of teeth, bits of plates and other bones, making their identification difficult or even dubious. Susannah Maidment and colleagues in their 2008 general revision of the Stegosauria, have recognized only 2 valid species to the United Kingdom,
Dacentrurus armatus and the newly erected
Loricatosaurus priscus, but this is certainly an underestimation. Let’s make a quick overview of stegosaurian materials found in England.
Middle Jurassic Stegosaurs
The most ancient British stegosaurs date from the Bathonian stage (165-168 MYA) of the Middle Jurassic and consist of a few isolated bones, including a massive right femur of a juvenile individual from the Cornbrah formation of Oxfordshire (Upper Batthonian), two incomplete vertebrae from the Sharp’s Hill Formation of Oxfordshire and two large dermal plates from the Chipping Norton Formation of Gloucestershire. These bones were all referred to
“Lexovisaurus” vetustus (=
“Omosaurus” vetustus). All that can be said is that they are the oldest recorded Stegosaurids in the world (the family to which all the most derived stegosaurs such as Stegosaurus and Kentrosaurus belong) and that a least one large species was present in Europe at that time.
Next, from the Middle Callovian (161-165 MYA) Oxford Clay Formation came
Lexovisaurus durobrivensis, known from two partial skeletons. Maidment et al, 2008 have invalidated the name
Lexovisaurus, on the basis that no unique character could be found in the holotype specimen. In its stead, a new genus,
Loricatosaurus, was erected for the second partial skeleton that includes vertebrae, various pelvic and limb elements, and a piece of dermal armor, and folded into the species
Loricatosaurus priscus. A large dermal plate named
‘Omosaurus leedsi’ from the same locality may be from the same animal. A third partial skeleton from a contemporary formation in Normandy, France is also referred to
Loricatosaurus priscus. However there is no real indication that
Lexovisaurus durobrivensis and
Loricatosaurus priscus represent different taxa and the two might well be the same.
Loricatosaurus probably measured about 5-6 meters in length. It is characterized by relatively short limbs and narrow plates and spines on the back. Shoulder spines may or may not have been present (A previously reported shoulder spine in the skeleton turns out to be a tail spine instead).
Upper Jurassic Stegosaurs
Fig 2.- Dacentrurus armatus.
From the Coralline Oolite Formation, Yorkshire, of Middle Oxfordian age (156-161 MYA), came a poorly preserved femur of a juvenile individual that has been named ‘Omosaurus phillipsi’ (= ‘Dacentrurus phillipsi’). There is no real indication that it was a stegosaur at all and the name is considered a nomen dubium (dubious name).
From the Kimmeridge Clay Formation of Wiltshire, of Lower Kimmeridgian age (151-156 MYA), came Dacentrurus armatus, a partial skeleton preserved in a large slab on exhibit at the Natural History Museum of London. Some fragmentary materials from France, Spain and Portugal were also referred to Dacentrurus. It was a large stegosaur with an estimated length of some 8 meters. Its aspect is not well known, but it probably resembled the African Kentrosaurus. From the Kimmeridge Clay also came a few dermal spines named “Omosaurus hastiger” that might belong to the same animal than Dacentrurus.
Fig 3.- Dacentrurus armatus holotype on display at the Natural History Museum in London (Credit: Emőke Dénes, via Wikipedia)
Early Cretaceous Stegosaurs
From the Lower Cretaceous Wealden Beds, Sussex of Valanginian age (136-140 MYA), came a partial right mandible, Regnosaurus northamptoni, that was variously attributed to the Ornithopod Iguanodon (Mantell, 1841), the ankylosaur Hylaeosaurus (Owen, 1858), a scelidosaur (Lydekker, 1888), and even a sauropod (Ostrom, 1970) until it was discarded as a nomen dubium (Coombs, 1971). However, more recently, Barrett & Upchurch, 1995, resuscitated Regnosaurus as a stegosaur and found it to be a relict of the old stegosaurian lineage that included the Chinese Huayangosaurus. The dubious Craterosaurus pottonensis, known from a single incomplete and poorly preserved dorsal vertebra, has been described as a stegosaur, but that is probably more wishful thinking. Interestingly Craterosaurus from Bedfordshire is probably also of Valanginian age.
Fig 4.- Regnosaurus northamtoni was a close relative of Huayangosaurus taibaii.
This concludes our tour of the stegosaurian remains of England.
Original artworks on Paleoexhibit are copyrighted to Nobu Tamura. Do not use without permission (Email: nobu dot tamura at yahoo dot com)
References:
P. M. Barret & P. Upchurch. 1995. Regnosaurus northamptoni, a stegosaurian dinosaur from the Lower Cretaceous of Southern England. Geological Magazine 132: 213–222.
P. M. Galton and H.P. Powell, H. P. 1983. Stegosaurian dinosaurs from the Bathonian (Middle Jurassic) of England, the earliest record of the Family Stegosauridae. Geobios 16: 219-229.
P. M. Galton. 1985. British plated dinosaurs (Ornithischia, Stegosauridae). Journal of Vertebrate Paleontology 5(3):211-254.
S. C. R. Maidment, D. B. Norman, P. M. Barrett and P. Upchurch. 2008. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6(4):367-407.
