힐라 에 오 사우루스 의 화석 이미지 ( 위 ) Shoulder girdle of Hylaeosaurus showing the characteristic flange - like acromion of polacanthids . ( 위 ) 힐라 에 오 사우루스 의 이미지 ( 위 , 아래 ) 위키피디아 Hylaeosaurus ( pronouncedhye - LEE - oh - SAWR - us ) , from the Greek words hylē / υλη “ forest ” and saurus / σαυρος “ lizard ” , is the most obscure of the three animals used by Sir Richard Owen tofirst define the new group Dinosauria , in 1842 . The original specimen , recovered by Gideon Mantell from the Tilgate Forest in the south of England in 1832 , now resides in the Natural History Museum of London , where it is stillencased in the limestone block in which it was found . Despite never having beenprepared , it is still the best specimen that exists of this genus of primitive , armored ankylosaurian dinosaur . Description and environmentHylaeosaurus lived about 135 million years ago , in the Valanginian to Berriasian ages of theearly Cretaceous Period . GideonMantell originally estimated that the Hylaeosaurus was about 25 feet ( 7 . 5 meters ) long , or about half the size of the other two original dinosaurs , theIguanodon and the Megalosaurus . Modern estimates range from 3 to 6 meters ( 10 to 20 feet ) in length . It is a fairly typical armoreddinosaur , with three long spines on its shoulder , two at the hips , and threerows of armor running down its back . It may also have had a row of plates downits tail . It has a long head , more like the head of a Nodosaurus than anAnkylosaurus , and a beak , which it probably used to crop low - lying vegetation . C lassificationHylaeosaurus armatus was firstnamed by Gideon Mantell in 1833 , and is currently considered the only speciesin the genus . It is known from only two partial skeletons , some horny ( dermal ) spines , armor , and various other minor pieces . The best specimen ( the original ) is composed of the front end of a skeleton minus most of the head , though onlythe parts on the face of the stone block are easily studied . Polacanthoides ponderosus , Hylaeosaurus conybearei , and Hylaeosaurus oweni have all been considereddistinct dinosaurs in the past , but are now considered to be alternate namesfor this species ( junior synonyms ) , along with Hylaeosaurus . It has also beensuggested that Polacanthus is same species , but there are a number ofdifferences in their bone structure ( osteology ) . Hylaeosaurus is traditionally consideredto be a primitive nodosaurid , in the Polocanthinae subfamily , like Gastonia andPolocanthus . In the 1990 s , the polocanthines were reclassified as primitiveankylosaurids , because they were mistakenly believed to have small tail - clubs ; they are probably primitive ankylosaurids , but as a whole the polacanthines arepoorly known . The group peaked in the Barremian age in North America andEurope , and then vanished shortly after , replaced by more advancedankylosaurians . HistoryThe first Hylaeosaurus fossilswere discovered in Sussex . Additional remains have been discovered on the Isleof Wight ( also part of Great Britain ) , and in Ardennes , France , though theremains from France may actually belong to a Polacanthus . Mantell published alithograph of his find in The Geology of the South - east of England in 1833 ; andanother drawing in the fourth edition of The Wonders of Geology , in 1840 . Gideon Mantell originally claimedthe name Hylaeosaurus meant “ forest lizard ” , after the Tilgate Forest in whichit was discovered . Later , he claimed that it meant “ Wealden lizard ” ( “ wealden ” being another word for forest ) , in reference to the Wealden Group , the name forthe early Cretaceous geological formation in which the dinosaur was firstfound . In any case , the species epithetarmatus , or “ armored ” , was chosen by Mantell because there “ appears every reason to concludethat either its back was armed with a formidable row of spines , constituting adermal fringe , or that its tail possessed the same appendage ” .