Pezosiren portelli

Overview

Pezosiren portelli was an early sea cow with four legs. Its hind limbs stand out when compared with modern dugongs or manatees. It invites exploration of the starting form of mammalian bodies that moved into the water.^[1]

Key facts

The spine, as well as the legs, reveals a relationship to terrestrial life. Pezosiren had a terrestrial-type spine and a joint connecting it to the pelvis. Examining the center of the body together with the limbs helps us understand changes in sea cows.^[1]

Time and place

It is associated with the end of the early Eocene to the beginning of the middle Eocene, around 50 million years ago. Fossils came from the Chapelton Formation in the Seven Rivers area of present-day Jamaica. They show that the Caribbean region was important in early sea cow evolution.^[1]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The four legs, pelvis, and several vertebral regions have been studied. A 2026 study virtually connected vertebrae from multiple specimens to compare their form. The relationship of the body axis through the back to the pelvis can be examined.^[1]

An early composite skeletal reconstruction estimated a total body length of about 2.1 m. It also reconstructed regions with insufficient fossil evidence, such as the tail tip and feet.^[4]

Habitat and reproduction

Pezosiren allows comparison between a body used on land and that of aquatic sea cows. Researchers examine connections among the spine, pelvis, and legs to study how it used water and land. Limbs unlike those of living sea cows reveal a starting point of change.^[1]

Fossil discovery

Following early research, a virtual reconstruction study reassembled and compared the spine. The 2026 study analyzed the forms of several bones to examine an ancient sea cow’s body axis. New comparative methods connect scattered bones to questions about a single body.^[1]

References

1. Pérez-Ramos et al.2026 — Virtual reconstruction and morphological analysis of Pezosiren vertebrae
2. Díaz-Berenguer et al.2018 — First adequately-known quadrupedal sirenian from Eurasia
3. Pérez-Ramos et al.2026 — Virtual reconstruction and morphometric analysis of the vertebral column of Pezosiren portelli
4. Domning (2001) — An early sea cow that walked on four legs

Research questions

Did the back and legs change together as sea cows adapted to aquatic life? Terrestrial-type vertebrae are compared with those of aquatic sea cows. Changes in the central axis of movement matter as well as limb reduction.^[1]

Observation

After examining the four legs, follow the spine toward the pelvis. Looking at the connection between the body’s center and its limbs makes differences from living sea cows clearer.^[1]