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Indohyus

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Indohyus
Temporal range: Middle Eocene
Indohyus major
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Artiodactyla
Family:
Raoellidae
Genus:
Indohyus

Species

I. indirae
I. major

Indohyus ("India's pig") is a genus of extinct artiodactyl known from Eocene fossils in Asia. This small deer-like animal found in the Himalayas is a close relative of whales.[1]

Description

Two Indohyus
File:Indohyus.JPG
Indohyus reconstruction in Museo di storia naturale e del territorio dell'Università di Pisa

The fossils were discovered among rocks that had been collected more than 30 years ago in Kashmir by the Indian geologist A Ranga Rao who found a few teeth and parts of a jawbone,[2] but when he died many rocks had yet to be broken open. Ranga Rao's widow gave the rocks to Professor Thewissen, who was working on them when his technician accidentally broke one of the skulls they had found and 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.[3]

About the size of a raccoon or domestic cat, this herbivorous deer-like creature shared some of the traits of whales, and showed signs of adaptations to aquatic life, including a thick and heavy outer coating to bones which is similar to the bones of modern creatures such the hippopotamus, and reduces buoyancy so that they can stay underwater.[4] This suggests a similar survival strategy to 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.[3][4][5]

Taxonomy

A December 2007 article in Nature by Thewissen et al. used an exceptionally complete skeleton of Indohyus from Kashmir to indicate that raoellids may be the "missing link" sister group to whales (Cetacea).[6][7] All other Artiodactyla are "cousins" of these two groups. δ18O values and osteosclerotic bones indicate that the raccoon-like or chevrotain-like Indohyus was habitually aquatic, but δ13C 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.

However, not all paleontologists are firmly persuaded that Indohyus is the transitional fossil that cetacean-origin experts were looking for. O'Leary & Gatesy 2008[8] postulates an extinct group of carnivorous mammals called "mesonychids" as more closely related to cetaceans. Additionally, ScienceNOW, a daily news feature of the journal Science, notes that "cetaceans are so different from any other creature that researchers haven’t been able to agree which fossil relatives best represent their nearest ancestors."[9]

Two species have been described.

  • Genus Indohyus
    • I. indira
    • I. major

Notes

  1. ^ Bajpai, Thewissen & Sahni 2009
  2. ^ Rao 1971
  3. ^ a b Sample 2007
  4. ^ a b Zimmer 2007
  5. ^ Myers 2007
  6. ^ Thewissen et al. 2007
  7. ^ Minkel 2007
  8. ^ O'Leary & Gatesy 2008, Conclusions, p. 421
  9. ^ Stokstad 2007

References

  • Bajpai, S; Thewissen, JG; Sahni, A (2009). "The origin and early evolution of whales: macroevolution documented on the Indian subcontinent". J Biosci. 34 (5): 673–86. doi:10.1007/s12038-009-0060-0. OCLC 565869881. PMID 20009264. {{cite journal}}: Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
  • Minkel, JR (2007). "Closest Whale Cousin — A Fox-Size Deer? Researchers split on closest evolutionary kin to whales and dolphins". Scientific American. {{cite web}}: Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
  • Myers, PZ (2007). "Indohyus". Pharyngula. ScienceBlogs. Retrieved December 2007. {{cite web}}: Check date values in: |accessdate= (help); Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
  • O'Leary, Maureen A; Gatesy, John (2008). "Impact of increased character sampling on the phylogeny of Cetartiodactyla (Mammalia): combined analysis including fossils" (PDF). Cladistics. 24 (4): 397–442. doi:10.1111/j.1096-0031.2007.00187.x. Retrieved February 2013. {{cite journal}}: Check date values in: |accessdate= (help); Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
  • Rao, A Ranga (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): 124–34. {{cite journal}}: Invalid |ref=harv (help)
  • Sample, Ian (2007). "Whales may be descended from a small deer-like animal". London: Guardian. Retrieved December 2007. {{cite news}}: Check date values in: |accessdate= (help); Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
  • Thewissen, JGM; Cooper, LN; Clementz, MT; Bajpai, S (2007). "Whales originated from aquatic artiodactyls in the Eocene epoch of India". Nature. 450 (7173): 1190–4. Bibcode:2007Natur.450.1190T. doi:10.1038/nature06343. PMID 18097400. {{cite journal}}: Invalid |ref=harv (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • Stokstad, Erik (2007). "Long-Lost Relative of Whales Found?". Science NOW Daily News. Retrieved December 2007. {{cite web}}: Check date values in: |accessdate= (help); Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
  • Zimmer, Carl (2007). "Whales: From So Humble A Beginning..." The Loom, ScienceBlogs. Retrieved December 2007. {{cite web}}: Check date values in: |accessdate= (help); Invalid |ref=harv (help); Unknown parameter |month= ignored (help)
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