Dinosaurs » A-Z Dinosaurs List » Hylaeosaurus Dinosaur
Hylaeosaurus (hi-LAY-ee-oh-SORE-us) is the most difficult to understand
of the three animals used by Sir Richard Owen to first define the new
group Dinosauria, in 1842. The original specimen, improved by Gideon Mantell
in 1832 from the Tilgate Forest in the south of England in 1832, now resides
in the Natural History Museum of London, where it is still covered in
the limestone block in which it was found. Despite never having been prepared,
it is still the best specimen that exists of this prehistoric, armored
Description and environment
Description and environment
Hylaeosaurus lived about 135 million years ago, in the Valanginian to Berriasian ages of the near the beginning Cretaceous. Gideon Mantell originally estimated that the Hylaeosaurus was about 25 feet (7.5 meters) long, or about half the size of the other two original dinosaurs, the Iguanodon and the Megalosaurus. New estimates range from 3 to 6 meters (10 to 20 feet) in length.
It is a fairly typical unbreakable dinosaur, with three long spines on its shoulder, two at the hips, and three rows of armor running down its back. It may also have had a row of plates down its tail. It has a long head, extra like the head of a Nodosaurus than an Ankylosaurus; and a beak, which it probably used to crop low-lying vegetation.
Hylaeosaurus armatus was first named by Gideon Mantell in 1833, and is
at present considered the only species in the genera. It is known from
only two partial skeletons, some horny (dermal) spines, armor, and a variety
of other minor pieces. The best specimen (the original) is self-possessed
of the front end of a skeleton minus most of the head, though only the
parts on the face of the stone block are easily studied.
Polacanthoides ponderosus, Hylaeosaurus conybearei, and Hylaeosaurus
oweni have all been measured distinct dinosaurs in the past, but are now
measured to be alternate names for this species (junior synonyms), along
with Hyaelosaurus. It has also been recommended that Polacanthus is same
species, but there are a number of differences in their bone structure
Hylaeosaurus is traditionally measured to be a primitive nodosaurid,
in the Polcanthinae subfamily, like Gastonia and Polcanthus. In the 1990s,
the polcanthines were reclassified as prehistoric ankylosaurids, because
they were mistakenly believed to have small tail-clubs; they are almost
certainly primitive ankylosaurids, but as a whole the polcanthines are
poorly known. The group peaked in the Barremian age in North America and
Europe, and then vanished soon after, replaced by more advanced ankylosaurians.
The first Hylaeosaurus fossils were exposed in Sussex. Additional remains
have been discovered on the Isle of Wight (also part of Great Britain),
and in Ardennes, France, though the leftovers from France may actually
belong to a Polacanthus. Mantell published a lithograph of his find in
The Geology of the South-east of England in 1833; and another sketch in
the fourth edition of The Wonders of Geology, in 1840.
Gideon Mantell at first claimed the name Hylaeosaurus meant "forest
lizard", after the Tilgate Forest in which it was discovered. Later,
he claimed that it meant "Wealden lizard" ("wealden"
being another word for forest), in orientation to the Wealden Group, the
name for the early Cretaceous geological formation in which the dinosaur
was first establish.
In any case, the species epithet armatus, or "armored", was
selected by Mantell because there"Appears every reason to end that either its back was armed with
a formidable row of spines, constituting a dermal fringe, or that its
tail obsessed the same appendage".