''Horshamosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of herbivorous

ankylosaurian Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the Early Cretaceous of England. It lived during the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is precede ...

of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

and the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

is ''Horshamosaurus rudgwickensis''.

Discovery

In 1985, at the marl quarry of the Rudgwick Brickworks Company near

Rudgwick Rudgwick is a village and Civil parishes in England, civil parish in the Horsham (district), Horsham District of West Sussex, England. The village is west from Horsham on the north side of the A281 road. The parish's northern boundary forms par ...

West Sussex West Sussex is a county in South East England on the English Channel coast. The ceremonial county comprises the shire districts of Adur, Arun, Chichester, Horsham, and Mid Sussex, and the boroughs of Crawley and Worthing. Covering an ...

, fossils were dug up of dinosaurs by John Underhill. These were secured by two volunteers of the

Horsham Museum Horsham Museum is a museum at Horsham, West Sussex, in South East England. It was founded in August 1893 by volunteers of the Free Christian (now Unitarian) Church and became part of Horsham District Council in 1974. It is a fully accredited ...

: Morris Zdzalek and Sylvia Standing. After 1988, the finds were exhibited in the museum as ''

Iguanodon ''Iguanodon'' ( ; meaning ' iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. While many species have been classified in the genus ''Iguanodon'', dating from the late Jurassic Period to the early Cretaceous Period of Asia, ...

'' bones. Subsequently, neurologist William T. Blows, an amateur paleontologist who already had extensively published on the subject of armoured dinosaurs, determined that the bones were not iguanodontian but instead represented ankylosaurian remains. In 1996, on basis of the finds, a new species of the genus ''

Polacanthus ''Polacanthus'', deriving its name from the Ancient Greek polys-/πολύς- "many" and akantha/ἄκανθα "thorn" or "prickle", is an early armoured, spiked, plant-eating ankylosaurian dinosaur from the early Cretaceous period of England. In ...

'', ''Polacanthus rudgwickensis'', was named and described by Blows. The specific name refers to the provenance from Rudgwick.Blows W.T. (1996) "A new species of ''Polacanthus'' (Ornithischia; Ankylosauria) from the Lower Cretaceous of Sussex, England". ''Geological Magazine'', 133 (6): 671–682 The material,

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

HORSM 1988.1546, was found in a layer of gray-green marl beds of the lower

Weald Clay Weald Clay or the Weald Clay Formation is a Lower Cretaceous sedimentary rock unit underlying areas of South East England, between the North and South Downs, in an area called the Weald Basin. It is the uppermost unit of the Wealden Group of ro ...

dating from the

age, over 125 million years old. It is fragmentary and includes two incomplete dorsal

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

, part of a front tail vertebra, bone fragments of other vertebrae, a partial left scapulocoracoid of the shoulder girdle, the distal end of a humerus, a nearly complete right

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

, rib fragments, and two

osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amphi ...

. In 2015, Blows made it a separate genus ''Horshamosaurus'', the generic name referring to Horsham. Its

is ''Polacanthus rudgwickensis''. The '' combinatio nova'' is ''Horshamosaurus rudgwickensis''. In 2020, ''Horshamosaurus'' was determined to be dubious, and not diagnosable beyond

Nodosauridae Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia. Description Nodosaurids, like their close relatives the ankylosaurids, we ...

. The presumed tibia would be an ischium.Raven, T. J., P. M. Barrett, S. B. Pond, and S. C. R. Maidment. 2020. Osteology and taxonomy of British Wealden Supergroup (Berriasian–Aptian) ankylosaurs (Ornithischia, Ankylosauria). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2020.1826956

Description

''Horshamosaurus'' seems, at roughly five metres length, to have been about 30% longer than the type species of ''Polacanthus'', ''Polacanthus foxii'' and differs from it in numerous characters of the vertebrae and

dermal The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided ...

armour. Apart from the greater length, in 1996 several traits were established, distinguishing ''Horshamosaurus'' from ''Polacanthus''. The centrum facets of the back and tail vertebrae have a round instead of a heart-shaped profile. The transverse processes of the vertebrae each have two ridges at their undersides delimiting a depression and gradually merging with the vertebral body. The transverse processes of the front tail vertebrae have a distinctive top ridge, running from the front to the rear, merging with the

neural arch The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

at the base of the process, while sloping downwards at its inner side. The "pseudoacromion" is located close to the front edge of the shoulder blade. The rear ribs are large and tall instead of rather slender. The shinbone is relatively longer. The osteoderm spikes on the back have a circular base of which the front underside is excavated but the rear underside solid, instead of an oval base with a uniformly concave underside. One of the osteoderms seems to have been part of the back armour and is large and flat with a concave underside; plates of such a type have not been discovered with ''Polacanthus foxii''. In 2015, three traits were added. The shoulder blade is robust and large, fused with the coracoid. The vertebral centra of the front tail vertebrae are shorter and especially taller. With the tail vertebrae, the base of the side process covers the top half of the centrum, seen from the front or from behind, instead of a quarter of the height.

Phylogeny

''Horshamosaurus'' was in

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

analyses not recovered as a

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of ''Polacanthus''. In 2015, Blows did not place ''Horsamosaurus'' in a Polacanthidae but in a more derived position in the

Ankylosauria Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

. He suggested it was a member of the

References

{{Taxonbar, from=Q21011926 Nodosaurids Barremian life Early Cretaceous dinosaurs of Europe Cretaceous England Fossils of England Fossil taxa described in 2015 Nomina dubia Ornithischian genera