English: Silhouettes of Eocene sirenians, based on published remains and drawn to the same scale for size comparison with each other. Square pattern is in meters. From left to right, top to bottom:

• Pezosiren (Early Lutetian, 47 Mya (blue)),^[1][2] based on skeletal diagram put together by Domning from “isolated bones and associated partial skeletons” from three different bone-beds with “remains of several individuals commingled” within the Chapelton Formation of Jamaica.^[3] Domning concluded that all remains “represent a single taxon”.^[3]

• Protosiren (Lutetian-Priabonian, 46-37 Mya (pink),^[1] estimated to have diverged from a common ancestor with the larger protosirenid Libysiren around 48 Mya.^[2]). silhouette is based on the large species P. smithae (the specimens CGM 42292 (holotype) and UM 101224). Of the hind limbs, femur, tibia and fibula are known. Feet and distal part of the tail are still unknown.^[4][5] The restored fluke is speculative (it has been stated that it "probably had an at least incipient horizontal tail").^[6]

• Sobrarbesiren (Lutetian, 46-45 Mya (yellow)),^[1] size based on skeletal diagram from Díaz-Berenguer et.al., based on more than “300 disarticulated remains from at least six sirenian individuals, in different ontogenetic stages”.^[1] Because of this, the relative size of the hind limbs are uncertain.^[6]

• Eotheroides (Lutetian-Priabonian, 46-37 Mya (teal)),^[1] silhouette is based on the species E. sandersi (specimens UM 111558 and UM 97514). Of the hind limbs, only a the femur is known. Based on its morphology, it has been concluded that the lower leg would have been “very reduced if present at all”.^[5]

• Eosiren (Priabonian-Rupelian (purple)),^[5] primarily based on a specimen of the type species E. libyca (UM 101226).^[5]

• Prorastomus (previously dated to Ypresian-Lutetian, 49-46 Mya,^[1] subsequently re-dated to Early-Middle Lutetian, 47 Mya^[2] (orange)). Known from a skull (BMNH 44897) measuring 28 cm. long. head restoration is based on published drawings of the skull,^[7] while body shape and proportions are based on the skeletal restoration of Pezosiren published by Domning.^[3]

References

1. ↑ ^{a b c d e f} Díaz-Berenguer E, Badiola A, Moreno-Azanza. M & Canudo J.I. (2018). “First adequately-known quadrupedal sirenian from Eurasia (Eocene, Bay of Biscay, Huesca, northeastern Spain)”. Scientific Reports 8: 5127
2. ↑ ^{a b c} Heritage S & Seiffert E.S. (2022). "Total evidence time-scaled phylogenetic and biogeographic models for the evolution of sea cows (Sirenia, Afrotheria)". PeerJ 10:e13886
3. ↑ ^{a b c} Domning D.P. (2001). “The earliest known fully quadrupedal sirenian”, Nature 413(6856): p. 625-627
4. ↑ Domning D.P. & Gingerich P.D. (1994), “Protosiren smithae, New Species (Mammalia, Sirenia), from the Late Middle Eocene of Wadi Hitan, Egypt”, Contributions from the Museum of Paleontology 29(3): p. 69-87
5. ↑ ^{a b c d} Zalmout I.S. & Gingerich P.D. (2012), “Late Eocene sea cows (Mammalia, Sirenia) from Wadi al Hitan in the western desert of Fayum, Egypt”, University of Michigan Papers on Paleontology No. 37
6. ↑ ^{a b} Díaz-Berenguer E, Houssaye A, Badiola A & Canudo J.I. (2020). “The Hind Limbs of Sobrarbesiren cardieli (Eocene, Northeastern Spain) and New Insights into the Locomotion Capabilities of the Quadrupedal Sirenians”, Journal of Mammalian Evolution 27: p. 649–675
7. ↑ Savage R.J.G., Domning D.P. & Thewissen J.G.M. (1994). "Fossil Sirenia of the West Atlantic and Caribbean Region. V. the Most Primitive Known Sirenian, Prorastomus sirenoides Owen, 1855". Journal of Vertebrate Paleontology 14 (3): p. 427-449