Two specimens of Hyphalosaurus have been described with clear impressions of the skin.
One specimen represents H. lingyuanensis, and the other (with clearer impressions) cannot be assigned to a species because part of the neck (the length of which is a key indicator of species) was destroyed when fossil dealers grafted a skull from a different specimen onto the slab.
However, both specimens show nearly identical patterns of scales.

Hyphalosaurus was covered mostly in small, irregularly patterned polygonal scales, though these varied across the body.
The scales of the hind legs were smaller, finer and more irregular than those of the torso, while the scales of the tail were nearly square and arranged in more regular rows.
In addition to the small scales, two rows of large, round scutes with shallow keels ran along the animals sides.
One row ran directly along the flank, with the other either slightly higher or lower and composed of scutes only 1/4 the size of the flank scutes.
The flank row of larger scutes extended all the way to the base of the tail, and remained uniform in size across the entire row.

The tail itself has preserved soft tissue extending well beyond the margins of the skeleton.
This, combined with the already flattened appearance of the tail vertebrae, suggests that a ridge of skin may have extended from the top and bottom of the tail creating a small fin.
The feet and hands also appear to have been webbed.
Two specimens of Hyphalosaurus have been described with clear impressions of the skin. One specimen represents H. lingyuanensis, and the other (with clearer impressions) cannot be assigned to a species because part of the neck (the length of which is a key indicator of species) was destroyed when fossil dealers grafted a skull from a different specimen onto the slab. However, both specimens show nearly identical patterns of scales.
Hyphalosaurus was covered mostly in small, irregularly patterned polygonal scales, though these varied across the body. The scales of the hind legs were smaller, finer and more irregular than those of the torso, while the scales of the tail were nearly square and arranged in more regular rows. In addition to the small scales, two rows of large, round scutes with shallow keels ran along the animals sides. One row ran directly along the flank, with the other either slightly higher or lower and composed of scutes only 1/4 the size of the flank scutes. The flank row of larger scutes extended all the way to the base of the tail, and remained uniform in size across the entire row.
The tail itself has preserved soft tissue extending well beyond the margins of the skeleton. This, combined with the already flattened appearance of the tail vertebrae, suggests that a ridge of skin may have extended from the top and bottom of the tail creating a small fin. The feet and hands also appear to have been webbed.
Hyphalosaurus