In Depth
The first description of Paleoparadoxia remains was published in 1939 by Tokunaga as Cornwallius tabatai. The genus Paleoparadoxia was not named until 1959 when R. H. Reinhart published a review of the Sirenia and Desmostylia. Paleoparadoxia was a large quadrupedal mammal that has been identified as a member of the Desmostylia (type genus Desmostylus). Like other members, the large bulk of the body of Paleoparadoxia meant that it would have been fairly cumbersome on land, but like its relatives, Paleoparadoxia would have actually ventured into the water to feed upon submerged aquatic plants.
When in the water, the large body and resulting body weight would have been supported by the water. This means that while swimming Paleoparadoxia might have been quite graceful in the same way that hippos are quite nimble when they are submerged in the water. The lack of specialised aquatic features such as limbs modified into flippers, means that even though Paleoparadoxia swam in the sea, it probably restricted itself to the shallows. Relatively shallow water environments would have also had the greatest abundance of plant growth since the shallows would have had a greater concentration of sunlight as well. The mouth of Paleoparadoxia is broad and bucket shaped which means it was likely capable of scooping up large quantities of plant matter with a single bite.
Because Paleoparadoxia still had functioning legs and feet, it of course would have returned to the land. It is impossible to say if mating and birth took place on land or in the water where buoyancy could have supported the individuals, though other large mammals are known to be capable of not needing to enter the water. Paleoparadoxia however almost certainly rested and slept on land however, and by being able to walk, it may have been able to enter bodies of water such as lagoons rather than just relying upon the sea.
Paleoparadoxia certainly did swim in coastal regions of the sea since its remains have been discovered in Japan and the Western coasts of the USA and Mexico. Rather than swim across several thousand miles of open and deep water with nothing to eat, Paleoparadoxia were likely spread across the entire Northern rim of the Pacific Ocean, from what is now known as mainland Asia, Beringia (better known as the Bering land bridge but is now submerged), to Canada and the Upper United States. By hugging the coastlines, Paleoparadoxia would have had both access to food and areas to rest, and future fossil discoveries, especially from Miocene age rock, may one day reveal a more complete distribution of this genus.
Further Reading
- A review of the Sirenia and Desmostylia, R. H. Reinhart - 1959. - The Stanford Skeleton of Paleoparadoxia (Mammalia: Desmostylia), N. Inuzuka - 2005. - A new early Miocene species of Paleoparadoxia (Mammalia: Desmostylia) from California, J. M. Clark - 1991. - An outline of the Miocene cetotheres of Japan, T. Kimura and Y. Hasegawa - 2004. - Desmostylian fossils from the Yatsuo Group in Toyama Prefecture, Central Japan and their paleoenvironments, K. Kaneko and N. Inuzuka - 1992. - Miocene marine vertebtates from San Clemente Island, California, E. D. W. Mitchell and J. H. Lipps - 1964. - A partial skeleton of Paleoparadoxia from San-yama, Ogano-cho, Saitama Prefecture, central Japan, H. Saegusa - 2002. - A smaller manus of the Paleoparadoxia (Mammalia: Desmostylia) from the Haratajino Formation, Tomioka Group, Gunma, Japan, H. Yoshikazu, K. Toshiyuki & M. Ryosuke - 2006. - Desmostylian tooth remains from the Miocene Tokigawa Group at Kuzubukuro, Saitama, Japan, K. Shimada & N. Inuzuka - 1994. - Paleoparadoxia tabatai from Yanagawa-machi, Fukushima Prefecture, Northeastern Japan, Y. Hasegawa and Y. Taketani - 1994. – A new name for the ‘Stanford Skeleton’ of Paleoparadoxia (Mammalia, Desmostylia). – Journal of Vertebrate Paleontology. 27 (3): 748–751. – D. P. Domning & L. G. Barnes – 2007. – Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria). – PLOS ONE. 8 (4): e59146. – Shoji Hayashi, Alexandra Houssaye, Yasuhisa Nakajima, Kentaro Chiba, Tatsuro Ando, Hiroshi Sawamura, Norihisa Inuzuka, Naotomo Kaneko, & Tomohiro Osaki – 2013.
