Prorastomus sirenoides is an extinct species of primitive sirenian that lived during the Eocene Epoch 40 million years ago in Jamaica.

In 1892, naturalist Richard Lydekker respelled it as Prorastoma with a feminine ending, however this was unjustified as stomus is masculine in Latin.

However, the modern understanding of Afrotheria as a clade that originally diversified in Africa overturns this idea.

Another specimen was found in 1989 in the same formation, USNM 437769, comprising the frontal bone, a tusk, vertebrae fragments, and ribs.

[1] While modern sirenians are fully aquatic, the 1.5-metre (5 ft) Prorastomus was predominantly terrestrial, judging from the structure of its skull.