In the summer of 1832, during blasting at a quarry near Tilgate ( West Sussex , England), about 50 bone fragments belonging to the early Cretaceous period were discovered [4] . These bones were acquired by the British paleontologist Gideon Mantell , known by this time as the discoverer of the iguanodon and the author of an essay on The Era of Reptiles, dedicated to the giant fossil reptiles [5] .
Bones of the Gileosaur
holotype from the quarry in Tilgate Forest
Investigating the remains, Mantell concluded that they all belong to the same individual, forming a relatively well-preserved skeleton [4] . They were allocated a partially preserved cranium, cervical and dorsal vertebrae, scapulae and coracoids (in reptiles, connecting the scapula to the sternum ), as well as very large spikes [6] . Initially, Mantell regarded the Sussk discovery as a new copy of his iguanodon, but his friend, the curator of the Royal College of Surgeons, William Clift, managed to make him doubt this, indicating that the spikes appear to be part of the outer shell that the iguanodon did not have, and that speech, Obviously, it is about a new, not previously described, form of lizards [4] .
By the autumn of 1832, Mantell was already convinced that he had discovered a new species, and by the end of November gave him the name Hylaeosaurus [6] (“forest lizard”, in honor of Tilgate Forest - the area where it was discovered). Mantell announced the discovery of the Gileozavr at the meeting of the Geological Society on December 5, 1832 [7] . He planned to publish the report in the form of an article in a journal, but was refused because of its excessive length. As a result, in 1833, the text of the report on December 5 was included as a separate chapter in the book Mantell "Geology of South-East England" [8] . There also appeared a new species name of the find, given in accordance with the recently adopted binomial nomenclature , Hylaeosaurus armatus [4] .
At that time, the taxonomic affiliation of the Gileozavra remained a mystery - if the vertebrae, the bones of the shoulder and the ribs vaguely resembled crocodiles, then the sternum and the coracoid were not similar to anything known, including the previously described megalosaurus [6] . In 1841, the Hiloosaurus, along with the iguanodon and megalosaurus, was included by Richard Owen in a new taxon - “ tribe or suborder ” - which he called Dinosauria , or “terrible lizards”. According to Owen, all representatives of this taxon possessed teeth of the same type as the thecodonts , a large sacrum formed from five accrete vertebrae, two-headed ribs, complex coracoids, long, partially hollow limbs and feet, arranged like in “large thick-skinned” mammals [9 ] (at the same time, Owen himself conducted a revision of the previous works of Mantell, attributing a previously unidentified sacrum and several teeth, which were previously attributed to the Mantell Iguanodon [10] , to the gileosaurus). Subsequently, new paleontological discoveries made it possible to form an idea of the infrakryad ankylosaurus - armored dinosaurs, which also included the hyleosaur. However, in view of the small number of known remains (two partial skeletons and an incomplete skull from England and probable fragmentary bones from West Germany and Romania), the exact phylogenetic place of the hyleosaur among ankylosaurs remains a subject of controversy. Different authors placed him in one of the two recognized families of ankylosaurs - Nodosauridae (for which he would be the basal genus ) [11] - or in the unrecognized clade Polacanthidae [12] . In addition, although various paleontologists have discovered the discovery of new species of hyleosaurs, by the beginning of the 21st century only one was considered a valid species name - Hylaeosaurus armatus [4] .
Gileosaurus was a relatively small dinosaur. The "Princeton Dinosaur Identifier" estimates its total length at 5 m and body weight at 2 tons [13] , paleontologist Stephen Brusatte assesses body length at 5-6 meters, height 0.8-1 m , and weight 1.4-1 2.4 tons [14] .
The back and tail of the Gileozavr were covered with armor (the skull, as far as can be assessed by fragmentary remains, was not protected), while along the tail, on the sides of the body above the thighs and around the neck were long and sharp spikes, and along the back - rows of bone plates [ 14] . Gileosaurus is the only European ankylosaurus with preserved elements of armor from the pre-sacral and caudal areas of the body (armor from the sacral area is known from another European ankylosaurus, ) [12] . Chevrons of caudal vertebrae are not soldered to the vertebral body; the same trait is characteristic of the Polacanthus genus, distinguishing them from such Upper Cretaceous nodosaurids such as Edmontonia and [15] .
From the skull, the left square bone , arched to the side, is well preserved, as in the ankylosaurus (known from the findings of the Jurassic period in America); along the lateral edge, at the junction with the square-zygomatic bone, apparently, during the life of the groove passed, but its length can not be estimated due to damage. The square-zygomatic bone itself is short ( 1.4 cm long and 2.4 cm high), like most ankylosaurs; its high position relative to the square bone is characteristic of the primitive representatives of the infraorder - nodezavridov and polakantidov. The device of the muscular knot in the region of the occipital bone indicates that the square bone could be soldered to it. A partially damaged post-orbit spike on the right side has survived, resembling the ones known from the remains of the Gargoyleosaurus and the early Cretaceous ankilosaurus Gastonia [16] . The blades are powerful, elongated, with a thick, rounded upper end and a thinner lower end; on the outer lateral surface near the upper edge of the scapula, there is a transverse, spike-like protrusion, characteristic of other ankylosaurs, but less pointed [15] .
Gileosaurus remains the most ancient of the known European ankylosaurs - its remains belong to the Valanginian age of the Lower Cretaceous , an earlier period than any other European genus (it is not reliably established whether the bones from the even earlier Berriasian century belong to Guileosaurus in Romania) [12] .
Apparently, like other ankylosaurs, the Hylaeosaurus was a herbivorous lizard moving on four legs [14] . For the region of Great Britain known as Wilde ( English Weald ), in which remains of hyleosaurs were found, in the Valanginian tier there are ferns (including genus ), cycloids and conifers ( Pinites , Sewardia , Sphenolepides ) [17] .
