Ichthyolestes

Last updated

Ichthyolestes
Temporal range: Early Eocene, circa 50  Ma
Ꞓ
O
S
D
C
P
T
J
K
Pg
N
↓
Ichthyolestes BW.jpg
Ichthyolestes life restoration, pencil drawing.
Scientific classification OOjs UI icon edit-ltr.svg
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]

Contents

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

Size of Ichthyolestes compared to a human. Ichthyolestes.png
Size of Ichthyolestes compared to a human.

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 Kuldana Formation, Pakistan, from the early-middle Eocene, [8] [6] [9] [2] and from the Subathu sediments of Jammu and Kashmir, India. [10]

Description

Ichthyolestes is the smallest pakicetid, approximately 29% smaller than Pakicetus, and has been considered “fox-sized.” [9] They retain many features typical of terrestrial Eocene artiodactyls, including long and gracile limb bones, a fused sacrum, small mandibular foramen, and no cranial telescoping. [9] [11] The body plan of Ichthyolestes is generally similar to Pakicetus , but smaller and more gracile. [2] [4] Therefore, locomotion is also thought to be reliant on quadrupedal paddling. [4]

Teeth

Ichthyolestes exhibits heterodont and diphyodont dentition with cusped cheek teeth. [4] The upper second molar has pointed cusps with a high narrow paracone and a lower connate metacone behind it. [8] [10] The molars are also relatively labio-lingually compressed with serrated crests along the labial cusps. [8] [10]

Braincase and orbital region an Ichthyolestes pinfoldi skull (HGSP 98134) Ichthyolesties pinfoldi.jpg
Braincase and orbital region an Ichthyolestes pinfoldi skull (HGSP 98134)

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, [11] but likely used bone conducting mechanisms when hearing underwater. The tympanic bulla also differs between pakicetid taxa. [3] The absolute size of Ichthyolestes tympanic bulla is smaller than either Pakicetus or Nalacetus; but when compared relative to their body size, the tympanic bulla of Ichthyolestes is proportionally larger than that of Pakicetus. [3]

The semicircular canal system of the vestibular apparatus in the inner ear, which is involved in neural control of locomotion, is similar in size to that of Eocene artiodactyls. [12] They do not show the size reduction as seen in other pakicetids and Eocene cetaceans like Remingtonocetus , Indocetus , and Dorudon , which have canal sizes within the upper range of modern cetaceans. [12] This suggests that Ichthyolestes had not fully invaded aquatic ecosystems and still remained somewhat terrestrial. [12]

Postcranial

Although Ichthyolestes is the smallest pakicetid, some features are larger or more robust than Nalacetus, such as the astragalus, calcaneus, and pelvis. Ichthyolestes also has proportionally longer lumbar and caudal vertebrae relative to its shorter limb segments. [2]

Ichthyolestes also has long digits and strong post-thoracic vertebrae. [2] The sacrum is composed of four elongate vertebrae with complete fusion, except for the spinous processes of S2 to S4 which are columnar with smooth ventral faces. [2] The lumbar vertebrae are narrower and shallower to Pakicetus and Nalacetus. [2] Although still relatively large compared to other related taxa, the atlas vertebrae of Ichthyolestes is smaller and more gracile than Pakicetus or Nalacetus, and the neural canal is disproportionately large. [2]

Terrestrial or semi-aquatic locomotion

The astragalus bone, which is present in the ankle of artiodactyls and archaic whales that retained feet, has similar dimensions in both Eocene artiodactyls and Ichthyolestes. [5] In addition to lending evidence to the theory of a direct relationship between artiodactyls and cetaceans, [11] this knowledge has led to two competing hypotheses about the locomotion of Ichthyolestes and other pakicetids. The first states that Ichthyolestes and Pakicetus were terrestrial and cursorial, implying that aquatic locomotor adaptation occurred after the origin of Cetacea. [9] [13] The second states that Ichthyolestes and Pakicetus were already semi-aquatic and cetaceans originated from an earlier unknown Eocene artiodactyl, such as Elomeryx [14] [15] or Indohyus, [16] [17] implying that aquatic locomotor adaptations occurred before or during the origin of Cetacea. [5]

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. [18] Their fossils are usually found around river channel deposits, not marine deposits or fauna. [4] The regions around northern Pakistan and northwest India, where fossils have been recovered, are thought to have been an arid environment with ephemeral streams and moderately developed floodplains. [19] Ichthyolestes, therefore, had an affinity for water and were either terrestrial or semi-aquatic. [4] The fluvial facies of the lower Kuldana Formation represent shallow tropical riverine complexes and were likely habitats for the initial stages of transition into water. [5] [2]

See also

Related Research Articles

<i>Rodhocetus</i> Genus of mammals

Rodhocetus is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. The best-known protocetid, Rodhocetus is known from two partial skeletons that taken together give a complete image of an Eocene whale that had short limbs with long hands and feet that were probably webbed and a sacrum that was immobile with four partially fused sacral vertebrae. It is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.

<span class="mw-page-title-main">Pakicetidae</span> Family of mammals

Pakicetidae is an extinct family of Archaeoceti that lived during the Early Eocene in Pakistan. A 2013 publication presents the emergence of cetacea in the Paleogene as starting with the pakicetids.

<span class="mw-page-title-main">Evolution of cetaceans</span>

The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene, the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. Being mammals, they surface to breathe air; they have five finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.

<i>Ambulocetus</i> Genus of extinct mammals of the order Cetacea

Ambulocetus is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, Ambulocetus natans, known solely from a near-complete skeleton. Ambulocetus is among the best-studied of Eocene cetaceans, and serves as an instrumental find in the study of cetacean evolution and their transition from land to sea, as it was the first cetacean discovered to preserve a suite of adaptations consistent with an amphibious lifestyle. Ambulocetus is classified in the group Archaeoceti—the ancient forerunners of modern cetaceans whose members span the transition from land to sea—and in the family Ambulocetidae, which includes Himalayacetus and Gandakasia.

<i>Basilosaurus</i> Prehistoric cetacean genus from the Late Eocene epoch

Basilosaurus is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistoric whale known to science. Fossils attributed to the type species B. cetoides were discovered in the United States. They were originally thought to be of a giant reptile, hence the suffix "-saurus", Ancient Greek for "lizard". The animal was later found to be an early marine mammal, prompting attempts at renaming the creature, which failed as the rules of zoological nomenclature dictate using the original name given. Fossils were later found of the second species, B. isis, in 1904 in Egypt, Western Sahara, Morocco, Jordan, Tunisia, and Pakistan. Fossils have also been unearthed in the southeastern United States and Peru.

<i>Pakicetus</i> Genus of ancient whales

Pakicetus is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Pakistan during the Ypresian period, roughly 50 million years ago. It was a wolf-like mammal, about 1 metre to 2 metres long, and lived in and around water where it ate fish and other animals. The vast majority of paleontologists regard it as the most basal whale, representing a transitional stage between land mammals and whales. It belongs to the even-toed ungulates with the closest living non-cetacean relative being the hippopotamus.

<span class="mw-page-title-main">Archaeoceti</span> Paraphyletic group of primitive cetaceans from Early Eocene to Late Oligocene

Archaeoceti, or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene. Representing the earliest cetacean radiation, they include the initial amphibious stages in cetacean evolution, thus are the ancestors of both modern cetacean suborders, Mysticeti and Odontoceti. This initial diversification occurred in the shallow waters that separated India and Asia 53 to 45 mya, resulting in some 30 species adapted to a fully oceanic life. Echolocation and filter-feeding evolved during a second radiation 36 to 35 mya.

<i>Protocetus</i> Species of mammal (fossil)

Protocetus atavus is an extinct species of primitive cetacean from Egypt. It lived during the middle Eocene period 45 million years ago. The first discovered protocetid, Protocetus atavus was described by Fraas 1904 based on a cranium and a number of associated vertebrae and ribs found in middle Lutetian Tethyan marine limestone from Gebel Mokattam near Cairo, Egypt.

Himalayacetus is an extinct genus of carnivorous aquatic mammal of the family Ambulocetidae. The holotype was found in Himachal Pradesh, India, in what was the remnants of the ancient Tethys Ocean during the Early Eocene. This makes Himalayacetus the oldest archaeocete known, extending the fossil record of whales some 3.5 million years.

Nalacetus is an extinct pakicetid early whale, fossils of which have been found in Lutetian red beds in Punjab, Pakistan. Nalacetus lived in a fresh water environment, was amphibious, and carnivorous. It was considered monophyletic by Cooper, Thewissen & Hussain 2009. It was said to be wolf-sized and one of the earliest forms of the order Cetacea.

Gandakasia is an extinct genus of ambulocetid from Pakistan, that lived in the Eocene epoch. It probably caught its prey near rivers or streams.

<i>Kutchicetus</i> Genus of mammals (fossil)

Kutchicetus is an extinct genus of early whale of the family Remingtonocetidae that lived during Early-Middle Eocene in what is now the coastal border of Pakistan and India. It is closely related to Andrewsiphius with which it was synonymized by Gingerich et al. 2001. Thewissen & Bajpai 2009 proposed a new clade, Andrewsiphiinae, for the two species. Later authors, however, still accept both as separate genera.

<i>Remingtonocetus</i> Genus of mammals

Remingtonocetus is an extinct genus of early cetacean freshwater aquatic mammals of the family Remingtonocetidae endemic to the coastline of the ancient Tethys Ocean during the Eocene. It was named after naturalist Remington Kellogg.

<span class="mw-page-title-main">Remingtonocetidae</span> Family of mammals

Remingtonocetidae is a diverse family of early aquatic mammals of the order Cetacea. The family is named after paleocetologist Remington Kellogg.

<i>Dalanistes</i> Species of mammal (fossil)

Dalanistes is an extinct genus of remingtonocetid early whale known from the late early Eocene of Kutch, India and Punjab and Balochistan, Pakistan. Dalanistes is closely related to Remingtonocetus, but also shares several features with Ambulocetus, and, with its combination of terrestrial and amphibious adaptations, Dalanistes apparently is an intermediate form between these two groups. Isotopic evidence suggest that Dalanistes had a marine diet.

Gaviacetus is an extinct archaeocete whale that lived approximately 45 million years ago. Gaviacetus was named for its characteristic narrow rostrum and the fast pursuit predation suggested by its unfused sacral vertebrae.

Babiacetus is an extinct genus of early cetacean that lived during the late Lutetian middle Eocene of India . It was named after its type locality, the Harudi Formation in the Babia Hills, Kutch District, Gujarat, India.

<i>Indocetus</i> Genus of mammals

Indocetus is a protocetid early whale known from the late early Eocene Harudi Formation in Kutch, India.

<span class="mw-page-title-main">Hans Thewissen</span> Dutch/American paleontologist

Johannes Gerardus Marie (Hans) Thewissen is a Dutch-American paleontologist known for his significant contributions to the field of whale evolution. Thewissen's fieldwork has led to the discovery of key fossils that have shed light on the transition of whales from land to water, including the discovery of Ambulocetus, Pakicetus, Indohyus, and Kutchicetus. In addition to his work on fossil discoveries, Thewissen also studies modern bowhead and beluga whales in Alaska, focusing on their biology and the implications of this knowledge for management and conservation efforts. His research has been instrumental in deepening our understanding of cetacean evolution and the adaptations that allowed these mammals to transition from terrestrial to fully aquatic lifestyles.

The Kuldana Formation is a fossil-bearing geological formation of Lutetian age which crops out in northern Pakistan. The abundant fossil remains were deposited by rivers and estuaries crossing an arid to semi-arid environment, between several marine transgressions. Its fossil fauna is best known for the early cetaceans Indohyus, Pakicetus and Ambulocetus, that helped to shed a new light on the evolution of whales, but it also features a large number of early ungulates, rodents and primates.

References

  1. 1 2 3 4 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.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Madar, S. (2007). "The postcranial skeleton of early Eocene Pakicetid cetaceans". Journal of Paleontology. 81 (1): 176–200. doi:10.1666/0022-3360(2007)81[176:TPSOEE]2.0.CO;2.
  3. 1 2 3 4 5 6 Nummela, S.; Hussain, S. T.; Thewissen, J. G. M. (2006). "Cranial anatomy of Pakicetidae (Cetacea, Mammalia)". Journal of Vertebrate Paleontology. 26 (3): 746–759. doi:10.1671/0272-4634(2006)26[746:CAOPCM]2.0.CO;2.
  4. 1 2 3 4 5 6 7 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. doi:10.1146/annurev.ecolsys.33.020602.095426.
  5. 1 2 3 4 5 6 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 (4): 601–627. Bibcode:2017PalZ...91..601G. doi:10.1007/s12542-017-0362-8.
  6. 1 2 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. doi:10.1126/science.220.4595.403. PMID   17831411.
  7. ↑ 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.
  8. 1 2 3 4 West, R. M. (1980). "Middle Eocene large mammal assemblage with Tethyan affinities, Ganda Kas Region, Pakistan". Journal of Paleontology. 54: 508–533.
  9. 1 2 3 4 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 (6853): 277–281. Bibcode:2001Natur.413..277T. doi:10.1038/35095005. PMID   11565023.
  10. 1 2 3 Kumar, K.; Sahni, A. (1985). "Eocene mammals from the Upper Subathu group, Kashmir Himalaya, India". Journal of Vertebrate Paleontology. 5 (2): 153–168. Bibcode:1985JVPal...5..153K. doi:10.1080/02724634.1985.10011853.
  11. 1 2 3 Marx, F. G.; Lambert, O.; Uhen, M. D. (2016). Cetacean Paleobiology. Chichester, UK; Hoboken, NJ: John Wiley & Sons Ltd. Bibcode:2016cepa.book.....M.
  12. 1 2 3 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 (6885): 163–166. Bibcode:2002Natur.417..163S. doi:10.1038/417163a. PMID   12000957.
  13. ↑ Fish, F. E. (2016). "Secondary evolution of aquatic propulsion in higher vertebrates: Validation and prospect". Integrative and Comparative Biology. 56 (6): 1285–1297. doi:10.1093/icb/icw123. PMID   27697779.
  14. ↑ 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 (5538): 2239–2242. Bibcode:2001Sci...293.2239G. doi:10.1126/science.1063902. PMID   11567134.
  15. ↑ 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 (3): 429–454. Bibcode:2003Pbio...29..429G. doi:10.1666/0094-8373(2003)029<0429:LTIEWE>2.0.CO;2.
  16. ↑ 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 (7173): 1190–1195. Bibcode:2007Natur.450.1190T. doi:10.1038/nature06343. PMID   18097400.
  17. ↑ 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.
  18. ↑ 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 Paleontology29(4): p. 746-759. [[doi:10.1671/0272-4634(2006)26[746:CAOPCM]2.0.CO;2]]
  19. ↑ 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

External Sources

Ichthyolestes in the Paleobiology Database. Retrieved June 2013.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.