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Fossil Friday: Sea Cows and the Abrupt Origin of Sirenia and Desmostylia

Günter Bechly
Photo: Pezosiren, Thesupermat via Wikimedia, CC BY-SA 3.0.

This Fossil Friday features the reconstructed skeleton of the “walking sea cow” Pezosiren from the Eocene of Jamaica, because today we look into the origins of the placental mammal order Sirenia, commonly known as sea cows. This order of herbivorous aquatic mammals includes only four living species of manatees and dugongs as well as the giant Steller’s sea cow, which was unfortunately exterminated by overhunting just a few decades after its discovery in the mid 18th century. Together with Proboscidea (elephants) and the extinct Desmostylia and Embrithopoda, the order Sirenia belongs to a subgroup of afrotherian mammals that is called Tethytheria (McKenna 1975, Gheerbrant et al. 2005, Nishihara et al. 2005Berta et al. 2006, Seiffert 2003, 2007Tabuce et al. 2008Domning et al. 2010O’Leary et al. 2013Self-Sullivan et al. 2014Domning 2018b), because they are thought to have evolved on the coast of the ancient Tethys Ocean (Heritage & Seiffert 2022).

The fossil record of sirenians is comparatively rich and even includes a lot of more or less complete skeletons. Domning et al. (1982: table 1)Domning (1994), and Self-Sullivan (2014)provided lists of all the ancient fossil sirenians known at that time. Diedrich (2013: fig. 1) and Springer et al. (2015: fig. 5) featured very good charts of the stratigraphic distribution of fossil sirenians, while Heritage & Seiffert (2022) provided the most comprehensive and up-to-date study or their phylogenetic relationships, ages or divergence, and paleobiogegraphic history. Based on molecular data, Sirenia are believed to have originated in the Earliest Paleocene about 65 million years ago (Springer et al. 2015: fig. 4), but when do sirenians first appear in the actual fossil record?

First Fossil Appearance

A putative fossil sirenian, Ishatherium subathuensiswas described by Sahni & Kumar (1980)and Sahni et al. (1980) from the early Eocene (Ypresian, 55.8-48.6 mya) Subhatu Formation in the Himalayas. It might represent the oldest known sirenian (Sereno 1982) but it could as well be an anthracobunid perissodactyl or a moeritheriid proboscidean (Wells & Gingerich 1983Domning et al. 1986Zalmout et al. 2003Cooper et al. 2014Rose et al. 2019). Domning et al. (1982) questioned the sirenian affinity as well as the dating. Two poorly preserved maxillary fragments from the Early Eocene (48.6-48.0 mya) Casamayoran Formation of Patagonia, which were named Florentinoameghinia mystica, were later attributed to Sirenia by Sereno (1982), but Domning (2001b) considered them as mammal of uncertain affinity.

The oldest unequivocal fossil sea cow is the quadrupedal prorastomid Prorastomus sirenoides from the Chapelton Formation (Yellow Limestone Group) in west-central Jamaica. It was first described by Richard Owen (1855), the famous enemy of Charles Darwin. Savage et al. (1994) re-described the holotype and described a second specimen. Even though Prorastomus is considered to be the most primitive known sirenian, it has some derived traits “that exclude it from the direct ancestry of other sirenians” (Savage et al. 1994). It is often stated to be of early Middle Eocene (48.6-40.4 mya) age, but according to Savage et al. (1994) the layers of the Stettin Member, where both known specimens were found, rather dates to the late Early Eocene (Ypresian) (Robinson 1988, Gold et al. 2018), thus about 49-50 million years ago.

About the same age of 48 million years (Late Ypresian / Early Lutetian), if not even slightly more ancient (Black 2013), is a petrosal bone from Chambi in Tunisia described by Benoit et al. (2013), which seems to be even more primitive than the Eocene prorastomids from Jamaica. 

Only slightly younger are the prorastomid Pezosiren portelli from Chapelton Formation in Jamaica (Domning 2001a), which is of early Middle Eocene (Lutetian 48.6-40.4 mya, but rather 47 mya) age (Donovan 2002), and an unnamed prorastomid from the Lutetian of Senegal (Hautier et al. 2012). The skeletal reconstruction of Pezosiren, which is featured in this Fossil Friday article and became quite popular as the “walking sea cow” (Berta 2012Prothero 2015), actually represents a composite of some hundred isolated bones collected from the same layers and believed to belong to the same species by Domning (2001a). The distal part of the tail and most of the feet bones were not found and added as “educated guesses.” This does not mean that the reconstruction is wrong, but at least some caution may be warranted.

From layers of the same Middle Eocene (Lutetian, 48.6-40.4 mya) age, several protosirenids have been found: Ashokia antiqua from the Harudi Formation in India (Bajpai et al. 2009), Libysiren sickenbergi from the Wadi Thamit Formation in Lybria (Domning et al. 2017), and Protosiren eothene from the early Lutetian Habib Rahi Formation in Pakistan, which is “virtually the same age as the prorastomids” according to Zalmout et al. 2003, early Lutetian). Furthermore, there are Sobrarsiren cardieli from the late middle Lutetian (SBZ15/C19r, 42 mya) Sobrarbe Formation in Spain (Díaz-Berenguer et al. 20182020), and a possible sirenian vertebra from the early Lutetian of Israel (Goodwin et al. 1998). All these protosirenid stem sea cows still had four legs and had an amphibic way of life (actually Sobrarsiren is not a genuine protosirenid but more closely related to the fully aquatic sirenians).

The oldest fully aquatic sea cows, with reduced hind legs and (likely) a fluke, are the Middle Eocene (Lutetian, 48.6-40.4 mya) “dugongids” Anisosiren pannonica from Hungary (Kordos 1979, 2002), Eosiren abeli from Egypt (Sickenberg 1934), Eotheroides sp. (Samonds et al. 2009), and Sirenavus hungaricus from Felsogalla in Hungary (Kretzoi 1941, Kordos 19812002). These advanced stem sirenians resembled modern dugongs, but crown group Sirenia first appear with genuine Dugongidae at the Eocene/Oligocene boundary about 33.9 million years ago (Heritage & Seiffert 2022).

Nevertheless, based on dental synapomorphies, Domning et al. (2010) had considered Eotheroides as a crown-group sirenian closer related to Dugongidae than to Trichechidae, which led to the use of this taxon as calibration data point for the age of crown group Sirenia by Benton et al. (2015, also see Fossil Calibration Database), who erratically also cited “Gheerbrant et al. (2005)” in support of this hypothesis even though these authors did not even mention Eotheroides. Such a crown group position was also suggested for Eotheroidesand Eosiren by the cladistic studies of Savage (1976)Springer et al. (2015)Vélez-Juarbe & Domning (2015), and Balaguer & Alba (2016)Domning et al. (2017) not only recovered Eotheroides as a crown group sirenian in Dugongidae, but even resolved the quadrupedal protosirenids AshokiaLibysiren, and Protosiren as crown group sirenians closer related to Trichechidae than to Dugongidae (compare Savage 1976). This would make fully aquatic sirenians diphyletic, as already indicated by Diedrich (2013). On the other hand, the studies by Domning (1994)de Buffrénil et al. 2010Díaz-Berenguer et al. (2018), and especially Heritage & Seiffert (2022) had the protosirenid genera as well as Eotheroides and Eosirenresolved well outside the crown group. I am sorry to say that phylogenetics turns out to be nothing but junk science when you look at the actual studies and their highly incongruent results and not just at the fancy polished text book figures. Darwin’s modern bulldogs like Richard Dawkins and Jerry Coyne are either totally ignorant or deliberately spreading falsehoods when they make their readers believe that there is one well-established tree of life. Nothing could be further from the truth. Phylogenetics is a mess!

Anyway, the sirenian fossil record, just like that of whales, is remarkable in featuring early representatives that still were quadrupedal and amphibic, which arguably supports common descent of sea cows from terrestrial ancestors and thus a secondary adaptation to a fully aquatic way of life (Sickenberg 1931Heal 1973Savage 1976Domning & Gingerich 1994Domning 198220002001a, 2001b, 2001c2018bBerta et al. 2006Uhen 2007de Buffrénil et al. 2010Berta 2012, 2017, Self-Sullivan et al. 2014Prothero 2015Díaz-Berenguer et al. 2020Heritage & Seiffert 2022, and Wikipedia).

Everything OK So Far?

So, is every thing OK with Darwinism after all? No so fast. Actually, there are some problems that do not square well with a Darwinian scenario:

  1. Sirenians appear abruptly in the fossil record at the onset of the Middle Eocene, together with other placental mammal orders, without a long transitional series establishing any kind or gradual development.
  2. There is a distinct morphological gap between the quadrupedal forms (Prorastomidae and Protosirenidae) and fully aquatic sea cows (Dugongidae and Trichechidae).
  3. Fully aquatic sirenians that looked like modern dugongs appear more or less around the same time as the primitive quadrupedal stem sirenians. Thus, sirenians immediately appear with a large diversity in the Middle Eocene.
  4. The origin of Trichechidae is totally in the dark, without any clear connection to the Dugongidae and their stem line.

Even though the fossil evidence in my view indeed supports common descent, it contradicts Darwinian expectations and does not at all support an unguided mechanism of evolution, which would imply slow and gradual transformations with small changes accumulating over long periods of time via numerous transitional species that only slightly differ from each other. The saltational pattern in the fossil record rather suggests very quick and dramatic changes within only a few transitional species, which arguably requires an infusion of new information from outside the system (also known as intelligent design).

Before we move on, I would like to share a little trivia that shows under what strange circumstances some important fossil finds were made: Voss et al. (2019) published one of the oldest fossil sea cows (Prototherium spec.) from Europe, which was found in Middle Eocene limestone from Spain that is dated to an Early Bartonian age of about 40 million years (also see Astibia et al. 2010). More precisely, the fossil was discovered in the paving stones of a shopping mall in the city of Girona in Catalonia, where thousands of people walked over this treasure for several years before its importance was recognized.

The Enigmatic Desmostylia

In the context of the fossil history of sirenians it is also necessary to discuss the extinct mammal order Desmostylia, because these semiaquatic herbivorous marine mammals were somewhat similar to early quadrupedal sirens and possibly closely related. Initially they were even erroneously considered to be sirenians (e.g., Hannibal 1922Simpson 1945). The degree of their aquatic adaptation is still a matter of scientific debate (Inuzuka et al. 1994, Domning 2002, Clementz et al. 2003Gingerich 2005Uhen 2007Hayashi et al. 2013). Desmostylia are only known from the Early Oligocene to Late Miocene of the North Pacific rim in 2-4 families and 10-12 genera with 13-14 species (Beatty 2009Domning 2018aMatsui & Tsuihiji 2019). Some relic species may have survived until the Pliocene (Kimura 1966). The most primitive and among the oldest representatives are the Behemotopsidae (Ray et al. 1994, Beatty & Cockburn 2015Domning 2018a), while the families Paleoparadoxiidae and Desmostylidae (= Cornwalliiidae) are more derived and usually younger. But if we look more closely into the data, the fossil record tells a somewhat different story:

According to PaleoDB all the earliest desmostylian fossils are of Chattian age (28.4-23.03 mya) and include:



  • Ashoroa laticosta from the Moravan Formation in Japan (Inuzuka 2000)
  • Cornwallius sookensis from the Sooke Formation on Vancouver Island, Yaquina Formation in Oregon, Unaslaska Formation in Alaska, and Baja California in Mexico

Many sources (including Wikipedia) still cite an Early Oligocene (Rupelian) age for Behemotops, which would make it to the oldest desmostylian. However, this appears to be based on an obsolete dating of the Pysht Formation in Washington (Domning et al. 1986Barnes & Goedert 2001), which has been re-dated as Late Oligocene / Chattian (Prothero et al. 2001, Beatty & Cockburn 2015). Actually, the layers where Behemotops proteus was found in the Pysht Formation (Chron C6Cr) have been more precisely dated to 24.8-24.1 million years ago (Prothero et al. 2008). A specimen of Behemotops from Hokkaido in Japan was initially believed to be older, but rather was more or less contemporaneous with the North American congeneric specimens (Saito et al. 1988).

In one of the more recent studies on Desmostylia the authors presented a diagram of the stratigraphic distribution (Matsui & Tsuihiji 2019: fig. 4), in which some of the more derived Desmostylidae not only appear together with the more primitive Behemotopsidae, but even predate them in the fossil record. The desmostylid Ashoroa laticosta is shown around the Rupelian/Chattian boundary about 29-27 mya and Cornwallius sookensis even from the middle Rupelian about 31 mya. The authors do not cite their sources for these more precise stratigraphic ranges, but they are congruent with the dating for all the localities of Cornwallius sookensis by Beatty (2002, 2006a2006b2009) to a Late Oligocene / Zemorrian (33.5-22 mya) age, which overlaps with the Rupelian and Chattian.

Finally, there is an isolated atlas vertebra from an undetermined putative desmostylian from the Lincoln Creek Formation in Washington, which dates to the Eocene/Oligocene boundary, about 37-36 million years ago (Prothero & Armentrout 1985), and arguably represents the oldest known fossil record of Desmostylia (Barnes & Goedert 2001).

Unlike Any Living Mammals

Desmostylians were quite unlike any living mammals, maybe resembling hippos, but their life reconstruction is still controversial even though complete skeletons are known (Inuzuka 1984, Halstead 1985, Domning 2002). The evolutionary origins of Desmostylia remain totally in the dark, and also their phylogenetic affinities are still hotly debated. Usually, they are considered as relatives of elephants and sea cows within Tethytheria (Reinhart 1953McKenna 1975Domning et al. 1986Novacek & Wyss 1987, McKenna & Bell 1997, Domning 2018a), but is unclear if they are closer related to elephants (Domning et al. 1986Clementz et al. 2003Berta et al. 2006Uhen 2007Beatty 2009Asher & Seiffert 2010) or to sea cows (Vélez-Juarbe & Domning 2015).

However, several new studies (Cooper et al. 2014Rose et al. 2019; also see Beatty & Cockburn 2015 and Heritage & Seiffert 2022) suggested that desmostylians are no tethytheres at all but rather odd-toed ungulates (Perissodactyla), thus not even members of the afrotherian clade. This would align with the fact that demostylians have “no African record whatsoever” (Asher et al. 2003). Gheerbrant et al. (2016) recovered desmostylians either as sister group of Paenungulata or as stem perissodactyls, but also found evidence for long-branch attraction between Desmostylia and Paenungulata (Tethytheria), suggesting possible convergent similarity. Therefore, Matsui (2017) and Matsui & Tsuihiji (2019) considered desmostylian affinities as controversial. If a perissodactyl relationship should be corroborated, then all the morphological similarities with Tethytheria would have to be reinterpreted as independently acquired convergences and thus not based on common ancestry. If you followed my previous articles in this series, this will hardly come as a surprise. I recently wrote a Fossil Friday article about the strange phenomenon of horizontal tooth displacement that independently originated three times within Tethytheria and confused scientists (Bechly 2022). As I said: phylogenetics is a mess and calling it science is misplaced and overselling this kind of fancy storytelling and educated guessing based on highly incongruent data!

Next Fossil Friday we will look into the final member of the Afrotheria, the order Proboscidea, which includes elephants and their fossil relatives.

P.S.: You can download a very nice and instructive booklet, “Sirenians & Sirens” (Godfrey 2002), on sea cows and their origins as a free PDF by the Calvert Marine Museum.


  • Asher RJ & Seiffert ER 2010. Systematics of Endemic African Mammals. Chapter 46, pp. 911–928 in: Werdelin L & Sanders WJ (eds). Cenozoic Mammals of Africa. University of California Press, Berkeley (CA), 1008 pp. DOI: https://doi.org/10.1525/california/9780520257214.003.0046
  • Asher RJ, Novacek MJ & Geisher JH 2003. Relationships of Endemic African Mammals and Their Fossil Relatives Based on Morphological and Molecular Evidence. Journal of Mammalian Evolution 10(1/2), 131–194. DOI: https://doi.org/10.1023/A:1025504124129
  • Astibia H, Bardet N, Pereda-Suberbiola X, Payros A, de Buffrénil V, Elorza J, Tosquella J, Berreteaga A & Badiola A 2010. New fossils of Sirenia from the Middle Eocene of Navarre (Western Pyrenees): the oldest West European sea cow record. Geological Magazine147(5), 665–673. DOI: https://doi.org/10.1017/S0016756810000130
  • Bajpai S, Domning DP, Das DP & Mishra VP 2009. A new middle Eocene sirenian (Mammalia, Protosirenidae) from India. Neues Jahrbuch für Mineralogie, Geologie und Palaeontologie 252(3), 257–267. DOI: https://doi.org/10.1127/0077-7749/2009/0252-0257
  • Balaguer J & Alba DM 2016. A new dugong species (Sirenia, Dugongidae) from the Eocene of Catalonia (NE Iberian Peninsula). Comptes Rendus Palevol 15(5), 489–500. DOI: https://doi.org/10.1016/j.crpv.2015.10.002
  • Barnes LG & Goedert JL. 2001. Stratigraphy and paleoecology of Oligocene desmostylian occurrences in western Washington State, USA. Bulletin of Ashoro Museum of Paleontology 2, 7–22. https://www.researchgate.net/publication/291771756
  • Beatty BL 2002. Cornwallius sookensis (Desmostylia, Mammalia): A Re-evaluation of a Late Oligocene Desmostylian from the Eastern North Pacific Coast. Journal of Vertebrate Paleontology 22(Suppl.3), 35A.
  • Beatty BL 2006a. Specimens of Cornwallius sookensis (Desmostylia, Mammalia) from Unalaska Island, Alaska. Journal of Vertebrate Paleontology 26(3), 785–787. DOI: https://doi.org/10.1671/0272-4634(2006)26[785:SOCSDM]2.0.CO;2
  • Beatty BL 2006b. Rediscovered specimens of Cornwallius (Mammalia, Desmostylia) from Vancouver Island, British Columbia, Canada. www.PalArch.nl Vertebrate Palaeontology Series 1(1), 1–6. https://www.researchgate.net/publication/231549565
  • Beatty BL 2009. New material of Cornwallius sookensis (Mammalia: desmostylia) from the Yaquina Formation of Oregon. Journal of Vertebrate Paleontology 29(3), 894–909. DOI: https://doi.org/10.1671/039.029.0320
  • Beatty BL & Cockburn TC 2015. New insights on the most primitive desmostylian from a partial skeleton of Behemotops (Desmostylia, Mammalia) from Vancouver Island, British Columbia. Journal of Vertebrate Paleontology 35(5):e979939, 1–15. DOI: https://doi.org/10.1080/02724634.2015.979939
  • Bechly G 2002. Fossil Friday: Desmostylia, and the Problem of Horizontal Tooth Displacement. Evolution News November 4, 2022. https://evolutionnews.org/2022/11/fossil-friday-desmostylia-and-the-problem-of-horizontal-tooth-displacement/
  • Benoit J, Adnet S, El Mabrouk E, Khayati H, Ben Haj Ali M, Marivaux L, Merzeraud G, Merigeaud S, Vianey-Liaud M & Tabuce R 2013. Cranial Remain from Tunisia Provides New Clues for the Origin and Evolution of Sirenia (Mammalia, Afrotheria) in Africa. PLoS ONE 8(1):e54307, 1–9. DOI: https://doi.org/10.1371/journal.pone.0054307
  • Benton MJ, Donoghue PCJ, Asher RA, Friedman M, Near TJ & Vinther J 2015. Constraints on the timescale of animal evolutionary history. Palaeontologia Electronica 18.1.1FC. DOI: https://doi.org/10.26879/424
  • Berta A 2012. Diversity, Evolution, and Adaptations to Sirenians and Other Marine Mammals. Chapter 5, pp. 127–150 in: Berta A & Sumich JL. Return to the Sea: The Life and Evolutionary Times of Marine Mammals. University of California, Berkeley (CA), 205 pp. DOI: https://doi.org/10.1525/california/9780520270572.003.0005 [Google Books]
  • Berta A 2017. The Rise of Marine Mammals: 50 Million Years of Evolution. John Hopkins University Press, Baltimore (MD), 216 pp.
  • Berta A, Sumich JL, Kovacs KM, Folkens PA & Adam PJ 2006. Sirenian and Other Marine Mammals. Marine Mammals. Chapter 5, pp. 89–110 in: Berta A, Sumich J & Kovacs K (eds). Marine Mammals (Second Edition). Academic Press, San Diego (CA), x+547. DOI: https://doi.org/10.1016/b978-012088552-7/50006-0
  • Black R 2013. Walking with Sea Cows. National Geographic January 16, 2013. https://www.nationalgeographic.com/science/article/sea-cow
  • Clementz MT, Hoppe KA & Koch PL 2003. A paleoecological paradox: the habitat and dietary preferences of the extinct tethythere Desmostylus, inferred from stable isotope analysis. Paleobiology 29(4), 506–519. https://www.jstor.org/stable/4096970
  • Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST & Thewissen JGM 2014. Anthracobunids from the Middle Eocene of India and Pakistan are stem perissodactyls. PLoS ONE 9(10):e109232, 1–15. DOI: https://doi.org/10.1371/journal.pone.0109232
  • De Buffrénil V, Canoville A, D’Anastasio R & Domning DP 2010. Evolution of Sirenian Pachyosteosclerosis, a Model-case for the Study of Bone Structure in Aquatic Tetrapods. Journal of Mammalian Evolution 17(2), 101–120. DOI: https://doi.org/10.1007/s10914-010-9130-1
  • Díaz-Berenguer E, Badiola A, Moreno-Azanza M & Canudo JI 2018. First adequately-known quadrupedal sirenian from Eurasia (Eocene, Bay of Biscay, Huesca, northeastern Spain). Scientific Reports 8(1):5127, 1–13. DOI: https://doi.org/10.1038/s41598-018-23355-w
  • Díaz-Berenguer E, Houssaye A, Badiola A & Canudo JI 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, 649–675. DOI: https://doi.org/10.1007/s10914-019-09482-9
  • Diedrich CG 2013. The most northerly record of the sirenian Protosiren and the possible polyphyletic evolution of manatees and dugongs. Natural Science 5(11), 1154–1164. DOI: https://doi.org/10.4236/ns.2013.511142
  • Domning DP 1982. Evolution of Manatees: A Speculative History. Journal of Paleontology56(3), 599–619. https://www.jstor.org/stable/1304394
  • Domning DP 1994. A Phylogenetic Analysis of the Sirenia. Proceedings of the San Diego Society of Natural History 29, 177–189. https://www.biodiversitylibrary.org/part/149304
  • Domning DP 1996. Bibliography and Index of the Sirenia and Desmostylia. Smithsonian Contributions to Paleobiology 80, 1–611. DOI: https://doi.org/10.5479/si.00810266.80.1
  • Domning DP 2000. The readaptation of Eocene sirenians to life in water. Historical Biology14(1-2), 115–119. DOI: https://doi.org/10.1080/10292380009380559
  • Domning DP 2001a. The earliest known fully quadrupedal sirenian. Nature 413(6856), 625–627. DOI: https://doi.org/10.1038/35098072
  • Domning DP 2001b. Evolution of the Sirenia and Desmostylia. pp. 151–168 in: Mazin J-M & de Buffrenil V (eds). Secondary Adaptation of Tetrapods to Life in Water. Proceedings of the international meeting, Poitiers, 1996. Verlag Dr. Friederich Pfeil, Munich (DE).
  • Domning DP 2001c. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 166(1-2), 27–50. DOI: https://doi.org/10.1016/s0031-0182(00)00200-5
  • Domning DP 2002. The Terrestrial Posture of Desmostylians. Smithsonian Contributions to Paleobiology 93, 99–111.
  • Domning DP 2018a. Desmostylia. pp. 250–253 in: Würsig B, Thewissen JGM & Kovacs KM (eds). Encyclopedia of Marine Mammals (Third Edition). Academic Press, London (UK), xxxi+1157 pp. DOI: https://doi.org/10.1016/B978-0-12-804327-1.00103-5
  • Domning DP 2018b. Sirenian Evolution. pp. 856–859 in: Würsig B, Thewissen JGM & Kovacs KM (eds). Encyclopedia of Marine Mammals (Third Edition). Academic Press, London (UK), xxxi+1157 pp. DOI: https://doi.org/10.1016/B978-0-12-804327-1.00229-6
  • Domning DP & Gingerich PD 1994. Protosiren smithae, New Species (Mammalia, Sirenia), from the Late Middle Eocene of Wadi Hitan, Egypt. Contributions from the Museum of Paleontology (The University of Michigan) 29(3), 69–87. https://hdl.handle.net/2027.42/48642
  • Domning DP, Morgan GS & Ray CE 1982. North American Eocene Sea Cows (Mammalia: Sirenia). Smithsonian Contributions to Paleobiology 52, 1–69. DOI: https://doi.org/10.5479/si.00810266.52.1
  • Domning DP, Ray CE & McKenna MC. 1986. Two New Oligocene Desmostylians and a Discussion of Tethytherian Systematics. Smithsonian Contributions to Paleobiology 59, 1–56. DOI: https://doi.org/10.5479/si.00810266.59.1
  • Domning DP, Zalmout IS & Gingerich PD 2010. Sirenia. Chapter 14, pp. 147–160 in: Werdelin L & Sanders WJ (eds). Cenozoic Mammals of Africa. University of California Press, Berkeley (CA), 1008 pp. DOI: https://doi.org/10.1525/california/9780520257214.003.0014
  • Domning DP, Heal GJ & Sorbi S 2017. Libysiren sickenbergi, gen. et sp. nov.: a new sirenian (Mammalia, Protosirenidae) from the middle Eocene of Libya. Journal of Vertebrate Paleontology 37(2):e1299158, 1–19. DOI: https://doi.org/10.1080/02724634.2017.1299158
  • Donovan SK 2002. Field guide to the geology of the Eocene Chapelton Formation (Yellow Limestone Group), western Central Inlier. Caribbean Journal of Earth Science 36, 39–47. http://caribjes.com/CJESpdf/CJES%2036-4-Donovan%20Chap%20Fieldtrip.pdf
  • Fischer MS & Tassy P 1993. The interrelation between Proboscidea, Sirenia, Hyracoidea, and Mesaxonia: the morphological evidence. pp. 217–234 in: Szalay FS, Novacek MJ & McKenna MC (eds). Mammal Phylogeny, Vol. 2: Placentals. Springer, New York (NY), 332 pp.
  • Gheerbrant E, Domning DP & Tassy P 2005. Paenungulata (Sirenia, Proboscidea, Hyracoidea, and relatives). Chapter 7, pp. 84–105 in: Rose KD & Archibald JD (eds). The Rise of Placental Mammals: Origins and Relationships of the Major Extant Clades. John Hopkins University Press, Baltimore (MD), 280 pp.
  •  Gheerbrant E, Filippo A & Schmitt A 2016. Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco. PLoS ONE 11(7):e0157556, 1–35. DOI: https://doi.org/10.1371/journal.pone.0157556
  • Gingerich PD 2005. Aquatic Adaptation and Swimming Mode Inferred from Skeletal Proportions in the Miocene Desmostylian I. Journal of Mammalian Evolution 12(1-2), 183–194. DOI: https://doi.org/10.1007/s10914-005-5719-1
  • Gold DP, Fenton JPG, Casas-Gallego M, Novak V, Pérez-Rodríguez I, Cetean C, Price R, Nembhard N & Thompson H 2018. The biostratigraphic record of Cretaceous to Paleogene tectono-eustatic relative sea-level change in Jamaica. Journal of South American Earth Sciences 86, 140–161. DOI: https://doi.org/10.1016/j.jsames.2018.06.011
  • Goodwin MB, Domning DP, Lipps JH & Benjamini C 1998. The first record of an Eocene (Lutetian) marine mammal from Israel. Journal of Vertebrate Paleontology 18(4), 813–815. DOI: https://doi.org/10.1080/02724634.1998.10011110
  • Halstead LB 1985. On the Posture of Desmostylians: A Discussion of Inuzuka’s “Herpetiform Mammals”. Memoirs of the Faculty of Science, Kyoto University, Series of Biology NS 10(2), 137–144.
  • Hannibal H 1922. Notes on Tertiary sirenians of the genus Desmostylus. Journal of Mammalogy 3(4), 238–242. DOI: https://doi.org/10.2307/1373255
  • Hautier L, Sarr R, Tabuce R, Lihoreau F, Adnet S, Domning DP, Samb M & Hameh PM 2012. First Prorastomid Sirenian from Senegal (Western Africa) and the Old World Origin of Sea Cows. Journal of Vertebrate Paleontology 32(5), 1218–1222. DOI: https://doi.org/10.1080/02724634.2012.687421
  • Hayashi S, Houssaye A, Nakajima Y, Chiba K, Ando T, Sawamura H, Inuzuka N, Kaneko N & Osaki T (2013). Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria). PLoS ONE 8(4):e59146, 1–20. DOI: https://doi.org/10.1371/journal.pone.0059146
  • Heal GJ 1973. Contributions to the Study of Sirenian Evolution. PhD thesis, University of Bristol, 245 pp. https://research-information.bris.ac.uk/en/studentTheses/contributions-to-the-study-of-sirenian-evolution
  • Heritage S & Seiffert ER. 2022. Total evidence time-scaled phylogenetic and biogeographic models for the evolution of sea cows (Sirenia, Afrotheria). PeerJ 10:e13886, 1–52. DOI: https://doi.org/10.7717/peerj.13886
  • Inuzuka N 1984. Skeletal restoration of the Desmostylians: Herpetiform Mammals. Memoirs of the Faculty of Science, Kyoto University, Series of Biology NS 9, 157–253.
  • Inuzuka N 1987. Primitive Desmostylians, Behemotops and the Evolutionary Pattern of the Order Desmostylia. Professor Masaru Matsui Memorial Volume 5, 13–25.
  • Inuzuka N 2000. Primitive late Oligocene desmostylians from Japan and Phylogeny of the Desmostylia. Bulletin of the Ashoro Museum of Paleontology 1, 91–123.
  • Inuzuka N, Domning DP & Ray CE 1994. Summary of taxa and morphological adaptations of the Desmostylia. The Island Arc 3(4), 522–537. DOI: https://doi.org/10.1111/j.1440-1738.1994.tb00131.x
  • Kimura M 1966. [Discovery of a molar tooth of Desmostylus in the Nawan conglomerate sandstone layer near Honbetsu-cho, Nakagawa-gun, Hokkaido]. Earth Science 31(4), 167–170 [In Japanese]. DOI: https://doi.org/10.15080/agcjchikyukagaku.31.4_167
  • Kordos L 1979. Major finds of scattered fossils in the palaeovertebrate collection of the Hungarian Geological Institute. Relationes Annuae Instituti Geologici Publici Hungarici1977, 313–326.
  • Kordos L 1981. Some complements to the knowledge of a Middle Eocene Sirenia, Sirenavus hungaricus Kretzoi, 1941. Fragmenta Mineraologica et Palaeontologica 10, 75–78. https://www.researchgate.net/publication/345804381
  • Kordos L 2002. Eocene sea cows (Sirenia, Mammalia) from Hungary. Fragmenta Palaeontologica Hungarica 20, 43–48. http://publication.nhmus.hu/fragpaleo/cikkreszletes.php?idhoz=3276
  • Kretzoi M 1941. Sirenavus hungaricus n. g. n. sp., ein neuer Prorastomide aus dem Mitteleozän (Lutetium) von Felsogallia in Ungarn. Annales Musei Nationalis Hungaricic Pars Mineralogica, Geologica et Palaeontologica 34, 146–156.
  • Matsui K 2017. How can we reliably identify a taxon based on humeral morphology? Comparative morphology of desmostylian humeri. PeerJ 5:e4011, 1–20. DOI: https://doi.org/10.7717/peerj.4011
  • Matsui K & Tsuihiji T 2019. The phylogeny of desmostylians revisited: proposal of new clades based on robust phylogenetic hypotheses. PeerJ 7:e7430, 1–17. DOI: https://doi.org/10.7717/peerj.7430
  • McKenna MC 1975. Toward a Phylogenetic Classification of the Mammalia. pp. 21–46 in: Luckett WP & Szalay FS (eds.). Phylogeny of the primates: a multidisciplinary approach. Proceedings of WennerGren Symposium no. 61, Burg Wartenstein, Austria, July 6–14, 1974. Plenum Press, New York (NY). DOI: https://doi.org/10.1007/978-1-4684-2166-8_2
  • McKenna MC & Bell SK 1997. Classification of Mammals Above the Species Level. Colombia University Press, New York (NY), xii+631 pp.
  • Nishihara H, Satta Y, Nikaido M, Thewissen JG, Stanhope MJ & Okada N 2005. A retroposon analysis of Afrotherian phylogeny. Molecular Biology and Evolution 22(9), 1823–1833. DOI: https://doi.org/10.1093/molbev/msi179
  • Novacek M & Wyss AR 1987. Selected Features of the Desmostylian Skeleton and Their Phylogenetic Implications. American Museum Novitates 2870, 1–8. http://hdl.handle.net/2246/5190
  • O’Leary MA, Bloch JI, Flynn JJ et al. 2013. The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals. Science 339 (6120), 662–667. DOI: https://doi.org/10.1126/science.1229237
  • Owen Professor 1855. On the Fossil Skull of a Mammal (Prorastomus Sirenoïdes, Owen), from the Island of Jamaica. Quarterly Journal of the Geological Society 11, 541–554. DOI: https://doi.org/10.1144/GSL.JGS.1855.011.01-02.58
  • Prothero DR 2015. Walking Manatees – The Origin of Sirenians – Pezosiren. Chapter 21, pp. 285–299 in: The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonders of Evolution. Columbia University Press, New York (NY), xi+389 pp. DOI: https://doi.org/10.7312/prot17190-022
  • Prothero DR & Armentrout JM 1985. Magnetostratigraphic correlation of the Lincoln Creek Formation, Washington: Implications for the age of the Eocene/Oligocene boundary. Geology 13(3), 208–211. DOI: https://doi.org/10.1130/0091-7613(1985)13<208:MCOTLC>2.0.CO;2
  • Prothero DR, Streig A & Burns A 2001. Magnetic stratigraphy and tectonic rotation of the upper Oligocene Pysht Formation, Clallam County, Washington. pp. 224–233 in: Prothero DR (ed.). Magnetic Stratigraphy of the Pacific Coast Cenozoic. The Pacific Section. Society for Sedimentary Geology, Santa Fe Springs (CA).
  • Prothero DR, Draus E, Cockburn TC & Nesbitt EA 2008. Paleomagnetism and counterclockwise tectonic rotation of the Upper Oligocene Sooke Formation, southern Vancouver island, British Columbia. Canadian Journal of Earth Sciences 45(4), 499–507. DOI: https://doi.org/10.1139/E08-012
  • Ray CE, Domning DP & McKenna MC 1994. A New Specimen of Behemotops proteus (Order Desmostylia) from the Marine Oligocene of Washington. pp. 205–222 in: Berta A & Deméré TA (eds). Contributions in Marine Mammal Paleontology Honoring Frank C. Whitmore. San Diego Society of Natural History, San Diego (CA).
  • Reinhart R 1953. Diagnosis of the New Mammalian Order, Desmostylia. The Journal of Geology 61(2), 187. DOI: https://doi.org/10.1086/626067
  • Robinson E 1988. Late Cretaceous and early Tertiary sedimentary rocks of the Central Inlier, Jamaica. Journal of the Geological Society of Jamaica 24, 49–67.
  • Rose KD, Holbrook LT, Kumar K, Rana RS, Ahrens HE, Dunn RH, Folie A, Jones KE & Smith T 2019. Anatomy, Relationships, and Paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the lower Eocene of western India. Journal of Vertebrate Paleontology 39(Sup.1), 1–147. DOI: http://doi.org/10.1080/02724634.2020.1761370
  • Sahni A & Kumar K 1980. Lower Eocene Sirenia, Ishatherium subathuensis, gen. et. sp. nov. from the type area, Subathu Formation, Subathu, Simla Himalayas, H. P. Journal of the Palaeontological Society of India 23-24, 132–135. https://www.researchgate.net/publication/256092090
  • Sahni A, Kumar K & Tiwari BN 1980. Lower Eocene marine mammal (Sirenia) from Dharampur, Simla Himalayas, H. P. Current Science 49, 270–271.
  • Saito T, Barron JA & Sakamoto M 1988. An early Late Oligocene age indicated by diatoms for a primitive desmostylian mammal Behemotops from eastern Hokkaido, Japan. Proceedings of the Japan Academy Series B 64(9), 269–273. DOI: https://doi.org/10.2183/pjab.64.269
  • Samonds KE, Zalmout IS, Irwin MT, Krause DW, Rogers RR & Raharivony LL 2009. Eotheroides lambondrano, new middle Eocene seacow (Mammalia, Sirenia) from the Mahajanga Basin, northwestern Madagascar. Journal of Vertebrate Paleontology 29(4), 1233–1243. DOI: https://doi.org/10.1671/039.029.0417
  • Savage RJG 1976. Review of Early Sirenia. Systematic Zoology 25(4), 344–351. DOI: https://doi.org/10.2307/2412509
  • Savage RJG, Domning DP & Thewissen JGM 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), 427–449. https://www.jstor.org/stable/4523580
  • Seiffert ER 2003. A phylogenetic analysis of living and extinct afrotherian mammals. Unpublished PhD dissertation, Duke University.
  • Seiffert ER 2007. A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological, and fossil evidence. BMC Evolutionary Biology 7(1):224, 1–13. DOI: https://doi.org/10.1186/1471-2148-7-224
  • Self-Sullivan C, Domning DP & Velez-Juarbe J 2014. Evolution of the Sirenia: An Outline. 10 pp.
  • Sereno PC 1982. An Early Eocene Sirenian from Patagonia (Mammalia, Sirenia). American Museum Novitates 2729, 1-10. http://hdl.handle.net/2246/5341
  • Sickenberg O 1931. Morphologie und Stammesgeschichte der Sirenen. Palaeobiologica 4, 405-444. https://www.zobodat.at/pdf/Palaeobiologica_4_0405-0444.pdf
  • Sickenberg O 1934. Beiträge zur Kenntnis Tertiärer Sirenen. Memoires de Musée Royal d’Histoire Naturelle de Belgique 63, 3–352.
  • Simpson GG 1945. The Principles of Classification and a Classification of the Mammals. Bulletin American Museum of Natural History 85, ix+350 pp. http://hdl.handle.net/2246/1104
  • Springer MS, Signore AV, Paijmans JLA et al. 2015. Interordinal gene capture, the phylogenetic position of Steller’s sea cow based on molecular and morphological data, and the macroevolutionary history of Sirenia. Molecular Phylogenetics and Evolution 91, 178–193. DOI: https://doi.org/10.1016/j.ympev.2015.05.022
  • Tabuce R, Asher RJ & Lehmann T 2008. Afrotherian mammals: a review of current data. Mammalia 72(1), 2–14. DOI: https://doi.org/10.1515/MAMM.2008.004
  • Uhen MD 2007. Evolution of Marine Mammals: Back to the Sea After 300 Million Years. The Anatomical Record 290(6), 514–522. DOI: https://doi.org/10.1002/ar.20545
  • Vélez-Juarbe J & Domning DP 2015. Fossil Sirenia of the West Atlantic and Caribbean region. XI. Callistosiren boriquensis, gen. et sp. nov., Journal of Vertebrate Paleontology 35(1):e885034, 1–16. DOI: https://doi.org/10.1080/02724634.2014.885034
  • Voss M, Hampe O, Mata Lleonart R & Ferrer Lopez J 2019. Fossil Sea Cow Remains (Mammalia: Sirenia) on Paving Stones in the City of Girona (Catalonia, Spain). Geoheritage 11, 1981–1987. DOI: https://doi.org/10.1007/s12371-019-00419-5
  • Wells NA & Gingerich PD 1983. Review of Eocene Anthracobunidae (Mammalia, Proboscidea) with a new genus and species, Jozaria palustris, from the Kuldana Formation of Kohat (Pakistan). Contributions from the Museum of Paleontology (The University of Michigan) 26(7). 117–139. https://hdl.handle.net/2027.42/48515
  • Zalmout IS, Ul-Haq M & Gingerich PD 2003. New Species of Protosiren (Mammalia, Sirenia) from the Early Middle Eocene of Balochistan (Pakistan). Contributions from the Museum of Paleontology (The University of Michigan) 31(3), 79–87. https://hdl.handle.net/2027.42/41257