Indohyus Explained

Indohyus (Meaning "India's pig" from the Greek words Indos, "from India" and hûs, "pig") is an extinct genus of digitigrade even-toed ungulates known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is one of the earliest known non-cetacean ancestors of whales.[1]

Discovery

The fossils were discovered among rocks that had been collected in 1971 in Kashmir by the Indian geologist A. Ranga Rao who found a few teeth and parts of a jawbone;[2] when he died, however, many rocks had yet to be broken open. Ranga Rao's widow gave the rocks to Hans Thewissen, who was working on them. When his technician accidentally broke one of the skulls they had found, Thewissen recognised the ear structure of the auditory bulla, formed from the ectotympanic bone in a shape which is highly distinctive, found only in the skulls of cetaceans both living and extinct, including Pakicetus.

Paleobiology

About the size of a raccoon or domestic cat, this omnivorous pig-like creature shared some of the traits of whales, and showed signs of adaptations to aquatic life. Their bones were similar to the bones of modern creatures such as the hippopotamus, and helped reduce buoyancy so that they could stay underwater.[3] This suggests a survival strategy similar to that of the African mousedeer or water chevrotain which, when threatened by a bird of prey, dives into water and hides beneath the surface for up to four minutes.[4] [5]

From isotopes and the structure of the bones in the fossils Indohyus had heavy bones. Heavy bones help reduce the buoyancy of living aquatic mammals so that they do not float up to the surface of the water.[6]

Classification

Raoellids may be the "missing link" sister group to whales (Cetacea).[7] All other Artiodactyla are "cousins" of these two groups. Oxygen-18 values and osteosclerotic bones indicate that the raccoon-like or chevrotain-like Indohyus was habitually aquatic, but 13C values suggest that it rarely fed in the water. The authors suggest this documents an intermediate step in the transition back to water completed by the whales, and suggests a new understanding of the evolution of cetaceans.[8] [9]

Notes and References

  1. Bajpai . S . Thewissen . JG . Hans Thewissen . Sahni . A . and . November 2009 . The origin and early evolution of whales: macroevolution documented on the Indian subcontinent . dead . J Biosci . 34 . 5 . 673–86 . 10.1007/s12038-009-0060-0 . 565869881 . 20009264 . 28232300 . https://web.archive.org/web/20170504142727/https://www.ias.ac.in/article/fulltext/jbsc/034/05/0673-0686 . 2017-05-04.
  2. Ranga . A. Rao . 1971 . New mammals from Murree (Kalakot Zone) of the Himalayan foot hills near Kalakot, Jammu and Kashmir state, India . Journal of the Geological Society of India . 12 . 2 . 124–134.
  3. Web site: Zimmer . Carl . Carl Zimmer . Whales: From So Humble A Beginning... . December 19, 2007 . . dead . https://web.archive.org/web/20120214135236/http://scienceblogs.com:80/loom/2007/12/19/whales_from_so_humble_a_beginn.php . February 14, 2012.
  4. News: Sample . Ian . 19 December 2007 . How Bambi evolved into Moby-Dick . 12 July 2024 . The Guardian.
  5. Web site: Myers . PZ . PZ Myers . Indohyus . 19 December 2007 . . . dead . https://web.archive.org/web/20071220115757/http://scienceblogs.com/pharyngula/2007/12/indohyus.php . 20 December 2007 .
  6. Web site: Zimmer . Carl . Carl Zimmer . 2007-12-19 . Whales: From So Humble A Beginning... . dead . https://web.archive.org/web/20181202070600/https://www.nationalgeographic.com/science/phenomena/2007/12/19/whales-from-so-humble-a-beginning/ . December 2, 2018 . December 1, 2018 . National Geographic.
  7. Thewissen . J. G. M. . Hans Thewissen . Cooper . Lisa Noelle . Clementz . Mark T. . Bajpai . Sunil . Tiwari . B. N. . amp . 2007 . Whales originated from aquatic artiodactyls in the Eocene epoch of India . dead . Nature . 450 . 7173 . 1190–4 . 2007Natur.450.1190T . 10.1038/nature06343 . 18097400 . 4416444 . https://web.archive.org/web/20160304082613/http://www.masonposner.com/media/evolution/thewissen2007.pdf . 2016-03-04.
  8. Web site: Holmes . Bob . A life spent chasing down how whales evolved . New Scientist . December 2, 2018.
  9. Book: Marx . Felix . Cetacean Paleobiology (TOPA Topics in Paleobiology) . Lambert . Oliver . Uhen . Mark . 2016 . Wiley-Blackwell . 978-1118561270 . 1st.

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