Ichthyolestes
Ichthyolestes | |
---|---|
Ichthyolestes life restoration, pencil drawing. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Infraorder: | Cetacea |
Family: | †Pakicetidae |
Genus: | †Ichthyolestes Dehm & Oettingen-Spielberg 1958 |
Type species | |
†Ichthyolestes pinfoldi |
Ichthyolestes ("fish thief") is an extinct genus of archaic cetacean that was endemic to Indo-Pakistan during the Lutetian stage.[1] To date, this monotypic genus is only represented by Ichthyolestes pinfoldi.[1]
Like other members of the family Pakicetidae, which are considered the earliest and least specialized of the archaic cetaceans,[2] Ichthyolestes represents an early quadrupedal phase of the land-to-sea transition which occurs in the cetacean lineage.[3][4]
Discovery and classification
Ichthyolestes pinfoldi was initially known only from teeth, which were found in the Eocene locality Ganda Kas, Pakistan.[1][5] Upon their discovery, I. pinfoldi was placed within the family Mesonychidae,[1][3] a group of terrestrial mammals from which cetaceans were previously thought to have evolved.[6] Due to morphological distinctions from other mesonychids, I. pinfoldi was later acknowledged and described as an archaeocete,[7][8] making it the first pakicetid to be described.[4]
Cranial and postcranial material of I. pinfoldi have also been found in the
Description
Ichthyolestes is the smallest pakicetid, approximately 29% smaller than Pakicetus, and has been considered “fox-sized.”
Teeth
Ichthyolestes exhibits
Cranial
Ichthyolestes has dorsally oriented eyes and a narrow skull, which is smaller than the skulls of both Pakicetus and Nalacetus.[3] Like other pakicetids, Ichthyolestes lacks a supraorbital shield; however, there is some variation in supraorbital morphology between the three genera. The supraorbital region of Ichthyolestes and Pakicetus is cup-like and cradles the dorsal portion of the eye. Ichthyolestes also has a weaker incisure on the dorsal side of the supraorbital region compared to Pakicetus.[3]
All three pakicetid taxa largely retained the peripheral ear morphology of terrestrial mammals,
The
Postcranial
Although Ichthyolestes is the smallest pakicetid, some features are larger or more robust than Nalacetus, such as the
Ichthyolestes also has long digits and strong post-thoracic vertebrae.
Terrestrial or semi-aquatic locomotion
The
Although the postcranial anatomy of Ichthyolestes is similar to that of Eocene artiodactyls and implies cursoriality,[2][5] the assessment of bone morphology and microstructure indicate that they, and other pakicetids, were semi-aquatic like protocetids.[2] Hypermineralization occurs in all regions of the skeleton; in particular, the long bones and ribs had small or absent marrow cavities due to the thick cortices which developed.[2] Hypermineralization of load-bearing skeletal elements put Ichthyolestes at an increased risk of fractures during prolonged terrestrial loading and this risk increased with velocity, implying that terrestriality was limited.[2] Additionally, the dense skeletons may have allowed bottom-walking or wading in shallow pools as it would counteract buoyancy created by inflated lungs and fur-trapped air.[2] Therefore, the retention of an artiodactyl-like astragalus does not signify full terrestriality or cursoriality in Ichthyolestes.[2][5]
Paleoenvironment
Fossil findings indicate Ichthyolestes shared habitat with its relatives Pakicetus and Nalacetus.
See also
References
- ^ a b c d Dehm, R.; zu Oettingen-Spielberg, T. (1958). Paläontologische und geologische Untersuchungen im Tertiär von Pakistan. 2. Die mitteleocänen Säugetiere von Ganda Kas bei Basal in Nordwest-Pakistan (PDF). Bayerische Akademie der Wissenschaften, Mathematisch-naturwissenschaftliche Klasse, Abhandlungen, Neue Folge. Vol. 91. Munich: C. Beck’sche Verlagsbuchhandlung.
- ^ a b c d e f g h i j k l m n o Madar, S. (2007). "The postcranial skeleton of early Eocene Pakicetid cetaceans". Journal of Paleontology. 81 (1): 176–200.
- ^ a b c d e f Nummela, S.; Hussain, S. T.; Thewissen, J. G. M. (2006). "Cranial anatomy of Pakicetidae (Cetacea, Mammalia)". Journal of Vertebrate Paleontology. 26 (3): 746–759.
- ^ a b c d e f g Thewissen, J. G. M.; Williams, E. M. (2002). "The early radiation of Cetacea (Mammalia): Evolutionary pattern and development correlations". Annual Review of Ecology and Systematics. 33: 73–90.
- ^ a b c d e f Gingerich, P. D.; Heissig, K.; Bebej, R. M.; von Koenigswald, W. (2017). "Astragali of Pakicetidae and other early-to-middle Eocene archaeocetes (Mammalia, Cetacea) of Pakistan: Locomotion and habitat in the initial stages of whale evolution". PalZ. 91: 601–627.
- ^ a b Gingerich, P. D.; Wells, N. A.; Russell, D. E.; Ibrahim Shah, S. M. (1983). "Origin of whales in epicontinental seas: New evidence from the early Eocene of Pakistan". Science. 220 (4595): 403–406.
- ^ Gingerich, P. D.; Russell, D. E.; Sigogneau-Russell, D.; Hartenberger, J. -L.; Ibrahim Shah, S. M.; Hassan, M.; Rose, K. D.; Ardrey, R. H. (1979). "Reconnaissance survey and vertebrate paleontology of some Paleocene and Eocene formations in Pakistan". Contributions from the Museum of Paleontology University of Michigan. 25 (5): 105–116.
- ^ a b c d West, R. M. (1980). "Middle Eocene large mammal assemblage with Tethyan affinities, Ganda Kas Region, Pakistan". Journal of Paleontology. 54: 508–533.
- ^ a b c d Thewissen, J. G. M.; Williams, E. M.; Roe, L. J.; Hussain, S. T. (2001). "Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls". Nature. 413: 277–281.
- ^ a b c Kumar, K.; Sahni, A. (1985). "Eocene mammals from the Upper Subathu group, Kashmir Himalaya, India". Journal of Vertebrate Paleontology. 5 (2): 153–168.
- ^ a b c Marx, F. G.; Lambert, O.; Uhen, M. D. (2016). Cetacean Paleobiology. Chichester, UK; Hoboken, NJ: John Wiley & Sons Ltd.
- ^ a b c Spoor, F.; Bajpai, S.; Hussain, S. T.; Kumar, K.; Thewissen, J. G. M. (2002). "Vestibular evidence for the evolution of aquatic behaviour in early cetaceans". Nature. 417: 163–166.
- ^ Fish, F. E. (2016). "Secondary evolution of aquatic propulsion in higher vertebrates: Validation and prospect". Integrative and Comparative Biology. 56: 1285–1297.
- ^ Gingerich, P. D.; Haq, M.; Zalmout, I. S.; Khan, I. H.; Malkani, M. S. (2001). "Origin of whales from early artiodactyls: Hands and feet of Eocene Protocetidae from Pakistan". Science. 293: 2239–2242.
- ^ Gingerich, P. D. (2003). "Land-to-sea transition of early whales: Evolution of Eocene Archaeoceti (Cetacea) in relation to skeletal proportions and locomotion of living semiaquatic mammals". Paleobiology. 29: 429–454.
- ^ Thewissen, J. G. M.; Cooper, L. N.; Clementz, M. T.; Bajpai, S.; Tiwari, B. N. (2007). "Whales originated from aquatic artiodactyls in the Eocene epoch of India". Nature. 450: 1190–1195.
- ^ Cooper, L. N.; Thewissen, J. G. M.; Bajpai, S.; Tiwari, B. N. (2011). "Postcranial morphology and locomotion of the Eocene raoellid Indohyus (Artiodactyla: Mammalia)". Historical Biology. 24: 279–310.
- ^ Cooper L.N., Thewissen J.G.M. & Hussain S.T. (2009). "New middle Eocene archaeocetes (Cetacea: Mammalia) from the Kuldana Formation of northern Pakistan". Journal of Vertebrate Paleontology 29(4): p. 746-759. [[doi:10.1671/0272-4634(2006)26[746:CAOPCM]2.0.CO;2]]
- ^ Aslan, A.; Thewissen, J. G. M. (1996). "Preliminary evaluation of paleosols and implications for interpreting vertebrate fossil assemblages, Kuldana Formation, northern Pakistan". Palaeovertebrata. 25 (2–4): 261–277.
Works cited
- Dehm, Richard; Oettingen-Spielberg, Therese zu (1958). Paläontologische und geologische Untersuchungen im Tertiär von Pakistan. 2. Die mitteleocänen Säugetiere von Ganda Kas bei Basal in Nordwest-Pakistan. Abhandlungen / Neue Folge, 91. Munich: Beck. OCLC 163296508.
External Sources
Ichthyolestes in the Paleobiology Database. Retrieved June 2013.