The first specimen of Hypsilophodon was recovered in 1849, when workers dug up the soon-called Mantell-Bowerbank block from an outcrop of the Wessex Formation, part of the Wealden Group, about one hundred yards west of Cowleaze Chine, on the south-west coast of Isle of Wight.
The larger half of the block (including seventeen vertebrae, parts of ribs and a coracoid, some of the pelvis, and assorted hindleg remains) was given to naturalist James Scott Bowerbank, and the remainder (including eleven caudal vertebrae and most of the rest of hindlegs) to Gideon Mantell.
After his death, Mantell's portion was acquired by the British Museum; Bowerbank's was acquired later, bringing both halves back together.
Richard Owen studied both halves and, in 1855, published a short article on the specimen, considering it to be a young Iguanodon rather than a new taxon.
This was unquestioned until 1867, when Thomas Henry Huxley compared the vertebrae and metatarsals of the specimen more closely to those of known Iguanodon, and concluded that it must be a different animal entirely.
The next year, he saw a fossil skull discovered by William Fox on exhibition at the Norwich Meeting of the British Associations.
Fox, who had also found his fossil in the Cowleaze Chine area, along with several other specimens, considered it to belong to a juvenile Iguanodon, or to represent a new, small species in the genus.
Huxley noticed its unique dentition and edentulous premaxilla, reminiscent of but obviously distinct from that of Iguanodon.
He concluded this specimen, too, represented a distinct animal from Iguanodon.
After losing track of the specimen for some months, Huxley requested Fox grant him permission to study the specimen to a more extensive degree.
The request was granted, and Huxley began work on his new species.

Huxley first announced the new species in 1869 in a lecture; the text of this, published the same year, forms the official naming article, because it contained a sufficient description.
The species was named Hypsilophodon foxii, and the holotype was the Fox skull (which today has the inventory number NHM R197).
The next year, Huxley published the expanded full description article.
Within the same block of stone as the Fox skull, the centrum of a dorsal vertebra had been preserved.
This allowed comparison with the Mantell-Bowerbank block, confirming it to belong to the same species.
Further supporting this, Fox had confirmed that the block was found in the same geological bed as his material.
As such, Huxley described this specimen in addition to the skull and centrum.
It would become the paratype; its two pieces are now registered in the Natural History Museum as specimen NHM 28707, 39560-1.
Later in the same year, Huxley classified Hypsilophodon taxonomically, considering it to belong to the family Iguanodontidae, related to Iguanodon and Hadrosaurus.
There would later be a persistent misunderstanding as to the meaning of the generic name, which is often translated directly from the Greek as "high-ridged tooth".
In reality Huxley, analogous to the way the name of the related genus Iguanodon ("iguana-tooth") had been formed, intended to name the animal after an extant herbivorous lizard, choosing for this role Hypsilophus and combining its name with Greek ὀδών, odon, "tooth".
Hypsilophodon thus means "Hypsilophus-tooth".
The Greek ὑψίλοφος, hypsilophos, means "high-crested" and refers to the back frill of the lizard, not to the teeth of Hypsilophodon itself, which are not high-ridged in any case.
The specific name foxii honours Fox.

Immediate reception to Huxley's proposal of a new genus, distinct from Iguanodon, was mixed.
The issue of distinctiveness was seen as important as more information on the form of Iguanodon was in demand, and the cranial anatomy in particular was of importance.
If the Cowleaze Chine material was a distinct genus, it ceased being useful in this respect.
William Boyd Dawkins saw the differences in the two genera (in particular focusing on a differing number of digits) as being as significant as those between
The first specimen of Hypsilophodon was recovered in 1849, when workers dug up the soon-called Mantell-Bowerbank block from an outcrop of the Wessex Formation, part of the Wealden Group, about one hundred yards west of Cowleaze Chine, on the south-west coast of Isle of Wight. The larger half of the block (including seventeen vertebrae, parts of ribs and a coracoid, some of the pelvis, and assorted hindleg remains) was given to naturalist James Scott Bowerbank, and the remainder (including eleven caudal vertebrae and most of the rest of hindlegs) to Gideon Mantell. After his death, Mantell's portion was acquired by the British Museum; Bowerbank's was acquired later, bringing both halves back together. Richard Owen studied both halves and, in 1855, published a short article on the specimen, considering it to be a young Iguanodon rather than a new taxon. This was unquestioned until 1867, when Thomas Henry Huxley compared the vertebrae and metatarsals of the specimen more closely to those of known Iguanodon, and concluded that it must be a different animal entirely. The next year, he saw a fossil skull discovered by William Fox on exhibition at the Norwich Meeting of the British Associations. Fox, who had also found his fossil in the Cowleaze Chine area, along with several other specimens, considered it to belong to a juvenile Iguanodon, or to represent a new, small species in the genus. Huxley noticed its unique dentition and edentulous premaxilla, reminiscent of but obviously distinct from that of Iguanodon. He concluded this specimen, too, represented a distinct animal from Iguanodon. After losing track of the specimen for some months, Huxley requested Fox grant him permission to study the specimen to a more extensive degree. The request was granted, and Huxley began work on his new species.
Huxley first announced the new species in 1869 in a lecture; the text of this, published the same year, forms the official naming article, because it contained a sufficient description. The species was named Hypsilophodon foxii, and the holotype was the Fox skull (which today has the inventory number NHM R197). The next year, Huxley published the expanded full description article. Within the same block of stone as the Fox skull, the centrum of a dorsal vertebra had been preserved. This allowed comparison with the Mantell-Bowerbank block, confirming it to belong to the same species. Further supporting this, Fox had confirmed that the block was found in the same geological bed as his material. As such, Huxley described this specimen in addition to the skull and centrum. It would become the paratype; its two pieces are now registered in the Natural History Museum as specimen NHM 28707, 39560-1. Later in the same year, Huxley classified Hypsilophodon taxonomically, considering it to belong to the family Iguanodontidae, related to Iguanodon and Hadrosaurus. There would later be a persistent misunderstanding as to the meaning of the generic name, which is often translated directly from the Greek as "high-ridged tooth". In reality Huxley, analogous to the way the name of the related genus Iguanodon ("iguana-tooth") had been formed, intended to name the animal after an extant herbivorous lizard, choosing for this role Hypsilophus and combining its name with Greek ὀδών, odon, "tooth". Hypsilophodon thus means "Hypsilophus-tooth". The Greek ὑψίλοφος, hypsilophos, means "high-crested" and refers to the back frill of the lizard, not to the teeth of Hypsilophodon itself, which are not high-ridged in any case. The specific name foxii honours Fox.
Immediate reception to Huxley's proposal of a new genus, distinct from Iguanodon, was mixed. The issue of distinctiveness was seen as important as more information on the form of Iguanodon was in demand, and the cranial anatomy in particular was of importance. If the Cowleaze Chine material was a distinct genus, it ceased being useful in this respect. William Boyd Dawkins saw the differences in the two genera (in particular focusing on a differing number of digits) as being as significant as those between 
Hypsilophodon