Temporal range: Late Miocene – Late Pliocene (Huayquerian–Uquian) ~7–3 Ma
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S
D
C
P
T
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Pg
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[1]
T. natans skeleton in its hypothesized swimming pose, Muséum national d'histoire naturelle, Paris
Scientific classification
Domain:
Eukaryota
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Pilosa
Family:
†Nothrotheriidae
Subfamily:
†Thalassocninae
Genus:
†Thalassocnus de Muizon & McDonald, 1995
Type species
†Thalassocnus natans
de Muizon & McDonald, 1995
Other species
†T. antiquus de Muizon et al., 2003
†T. carolomartini McDonald & Muizon, 2002
†T. littoralis McDonald & Muizon, 2002
†T. yuacensis de Muizon et al., 2004
Thalassocnus is an extinct genus of semiaquatic ground sloths from the Miocene and Pliocene of the Pacific South American coast. It is monotypic within the subfamily Thalassocninae. The five species—T. antiquus, T. natans, T. littoralis, T. carolomartini, and T. yuacensis—represent a chronospecies, a population gradually adapting to marine life in one direct lineage. They are the only known aquatic sloths, but they may have also been adapted to a terrestrial lifestyle. They have been found in the Pisco Formation of Peru, the Tafna Formation of Argentina,[2] and the Bahía Inglesa, Coquimbo, and Horcón formations of Chile. Thalassocninae has been placed in both the families Megatheriidae[3] and Nothrotheriidae.[4]
Thalassocnus evolved several marine adaptations over 4 million years, such as dense and heavy bones to counteract buoyancy, the internal nostrils migrating farther into the head to help with breathing while completely submerged, the snout becoming wider and more elongated to consume aquatic plants better, and the head angling farther and farther downwards to aid in bottom feeding. The long tail was probably used for diving and balance similar to the modern day beaver (Castor spp.) and platypus (Ornithorhynchus anatinus).
Thalassocnus probably walked across the seafloor and dug up food with its claws. They probably could not do high-powered swimming, relying on paddling if necessary. Early Thalassocnus were probably generalist grazers eating seaweed and seagrasses close to shore, whereas later species specialized on seagrasses farther off the coast. They were probably preyed upon by sharks and macroraptorial sperm whales such as Acrophyseter. Thalassocnus were found in formations with large marine mammal and shark assemblages.
^Thalassocnus. Fossilworks. Retrieved 25 August 2018
^Quiñones, Sofía I.; Zurita, Alfredo E.; Miño-Boilini, Ángel R.; Candela, Adriana M.; Luna, Carlos A. (2022-09-15). "Unexpected record of the aquatic sloth Thalassocnus (Mammalia, Xenarthra, Folivora) in the upper Neogene of the Puna (Jujuy, Argentina)". Journal of Vertebrate Paleontology. 42 (1): e2109973. Bibcode:2022JVPal..42E9973Q. doi:10.1080/02724634.2022.2109973. ISSN 0272-4634. S2CID 252327107.
^Cite error: The named reference Amson2017 was invoked but never defined (see the help page).
^Cite error: The named reference Varela2019 was invoked but never defined (see the help page).
whales such as Acrophyseter. Thalassocnus were found in formations with large marine mammal and shark assemblages. Thalassocnus were ground sloths that lived...
to 11,000 years ago. As well as ground sloths, this family included Thalassocnus, a genus of either semiaquatic or fully aquatic sloths. Superfamily Mylodontoidea...
genus Thalassocnus of the west coast of South America became adapted to a shallow-water marine lifestyle. However, the family placement of Thalassocnus has...
; Urbina, M. (June 2004). "The Youngest Species of the Aquatic Sloth Thalassocnus and a Reassessment of the Relationships of the Nothrothere Sloths (Mammalia:...
include the giant raptorial sperm whale Livyatan, the aquatic sloth Thalassocnus, the sperm whale Acrophyseter, and the walrus-like dolphin Odobenocetops...
and functional morphology of the axial postcranium of the marine sloth Thalassocnus (Mammalia, Tardigrada) with paleobiological implications". Journal of...
"Osteology and Functional Morphology of the Forelimb of the Marine Sloth Thalassocnus (Mammalia, Tardigrada)" (PDF). Journal of Mammalian Evolution. 22 (2):...
with a number of ground sloth genera migrating northwards. One genus, Thalassocnus, even adapted for marine life along the Pacific coast of South America...
; Urbina, M. (June 2004). "The Youngest Species of the Aquatic Sloth Thalassocnus and a Reassessment of the Relationships of the Nothrothere Sloths (Mammalia:...
large ground-living herbivores (and possibly omnivores) Aquatic sloths: Thalassocnus, a medium-sized herbivore, is the only known aquatic sloth Xenarthrans...
vertebrates. In aquatic animals, such as seacows (manatees and dugongs), Thalassocnus, and plesiosaurs, pachyostosis in the thoracic region provides (or provided)...
comprising mostly marine vertebrate species like Otodus, Pelagornis, Thalassocnus, among others. Gutstein, C. S.; Toro, A. V.; Pereira (2018). Sánchez...
among other genera, Nothrotherium, Nothrotheriops, and the semiaquatic Thalassocnus are placed, are regarded as a separate family, which forms the sister...
Odobenocetops have been yielded. Other marine mammals include the marine sloth Thalassocnus and pinnipeds like Acrophoca. At least 28 different species of sharks...
(June 2004). "The evolution of feeding adaptations of the aquatic sloth Thalassocnus". Journal of Vertebrate Paleontology. 24 (2): 398–410. Bibcode:2004JVPal...
and functional morphology of the axial postcranium of the marine sloth Thalassocnus (Mammalia, Tardigrada) with paleobiological implications". Journal of...
swordfish, aquatic sloths (not a group as such, but rather the genus Thalassocnus) and invertebrate trace fossils. The unusual concentration of cetacean...
is suggested to have been a mixed feeder (both browsing and grazing). Thalassocnus "Ahytherium in the Paleobiology Database". Fossilworks. Retrieved 17...
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