Both Hyphalosaurus species were aquatic, a lifestyle reflected by their long necks and tails and relatively small limbs.
Superficially, they resembled miniature plesiosaurs, though this resemblance arose convergently and does not reflect a close relationship.
Hyphalosaurus was among the most aquatically adapted choristoderans, with smoother, flatter scales than its relatives, a tall and flattened tail for swimming, a long neck and webbed feet.
Because the torso was fairly inflexible and the limbs were not particularly adapted for aquatic life, Hyphalosaurus probably swam using mainly its tall, flattened tail.
The chest was barrel-shaped and made up of thick, heavy rib bones which would have helped Hyphalosaurus stay submerged.

Hyphalosaurus appears to have exclusively inhabited deep-water lakes.
All specimens are preserved in silt characteristic of the deepest part of the lake environment, and are often preserved alongside deep-water fish and crustaceans.
Hyphalosaurus is also conspicuously absent from the aquatic sediments of the Jiufotang Formation, which preserved a more swampy, shallow-water ecosystem.

Hyphalosaurus is the most abundant tetrapod (four-limbed vertebrate) in the Yixian Formation, and probably played an important role in the aquatic food chain.
Its long and highly flexible neck and small, flattened skull indicates that it captured small prey animals like fish or arthropods using a sideways-strike, similar to modern aquatic predators with flattened skulls.
Unlike other choristoderans, Hyphalosaurus was likely an active predator, rather than one that used a "sit and wait" ambush strategy.
Its fossils are often found preserved alongside the small fish Lycoptera, which may have been a prey item, and at least one specimen preserved fish ribs as stomach contents.
However, the lack of preserved stomach contents among the thousands of known specimens may indicate that they ate mainly soft-bodied prey.
Both Hyphalosaurus species were aquatic, a lifestyle reflected by their long necks and tails and relatively small limbs. Superficially, they resembled miniature plesiosaurs, though this resemblance arose convergently and does not reflect a close relationship. Hyphalosaurus was among the most aquatically adapted choristoderans, with smoother, flatter scales than its relatives, a tall and flattened tail for swimming, a long neck and webbed feet. Because the torso was fairly inflexible and the limbs were not particularly adapted for aquatic life, Hyphalosaurus probably swam using mainly its tall, flattened tail. The chest was barrel-shaped and made up of thick, heavy rib bones which would have helped Hyphalosaurus stay submerged.
Hyphalosaurus appears to have exclusively inhabited deep-water lakes. All specimens are preserved in silt characteristic of the deepest part of the lake environment, and are often preserved alongside deep-water fish and crustaceans. Hyphalosaurus is also conspicuously absent from the aquatic sediments of the Jiufotang Formation, which preserved a more swampy, shallow-water ecosystem.
Hyphalosaurus is the most abundant tetrapod (four-limbed vertebrate) in the Yixian Formation, and probably played an important role in the aquatic food chain. Its long and highly flexible neck and small, flattened skull indicates that it captured small prey animals like fish or arthropods using a sideways-strike, similar to modern aquatic predators with flattened skulls. Unlike other choristoderans, Hyphalosaurus was likely an active predator, rather than one that used a "sit and wait" ambush strategy. Its fossils are often found preserved alongside the small fish Lycoptera, which may have been a prey item, and at least one specimen preserved fish ribs as stomach contents. However, the lack of preserved stomach contents among the thousands of known specimens may indicate that they ate mainly soft-bodied prey.
Hyphalosaurus