Rodhocetus

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Rodhocetus
Temporal range: Eocene (Lutetian), 47–46  Ma
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Rodhocetus FMNH.jpg
Skull of Rodhocetus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Protocetidae
Subfamily: Protocetinae
Genus: Rodhocetus
Gingerich et al. 1994
Species

Rodhocetus (from Rodho, the geological anticline at the type locality, and cetus, Latin for whale) [1] is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. [2] 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. [3] It is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.

Contents

Description

An artist's rendering of Rodhocetus Rodhocetus.jpg
An artist's rendering of Rodhocetus
Size of Rodhocetus relative to a human. Rodhocetus size.png
Size of Rodhocetus relative to a human.
Pelvis, vertebrae, and hind limb of Rodhocetus. Rodhocetus sp pelvis hind limb.jpg
Pelvis, vertebrae, and hind limb of Rodhocetus.

Rodhocetus was a small whale measuring 2–3 m (6.6–9.8 ft) long. [4] Throughout the 1990s, a close relationship between cetaceans and mesonychians, an extinct group of cursorial, wolf-like ungulates, was generally accepted based on morphological analyses. In the late 1990s, however, cladistic analyses based on molecular data clearly placed Cetacea within the Artiodactyla near the hippopotamus. One of the diagnostic characteristics of artiodactyls is the double-pulley astragalus (heel bone), and palaeontologists, unconvinced by the data from the labs, set themselves out to find archaeocete single-pulley heel bones. Hind legs from three archaeocete species were recovered within a few years, among them those of Rodhocetus balochistanensis, and all three had double-pulley heel bones, thus settling the cladistic controversy. [5]

Through a principal components analysis Gingerich 2003 demonstrated that Rodhocetus had trunk and limb proportions similar to the Russian desman, a foot-powered swimmer using its tail mainly as a rudder. From this Gingerich concluded that Rodhocetus was swimming mostly at the surface by alternate strokes of its hind feet, and that it was insulated by fur rather than blubber, as are Dorudon and modern cetaceans, which made it buoyant and incapable of deep diving. [6]

R. kasrani

The holotype of R. kasrani, GSP-UM  3012 found in 1992, was described by Gingerich et al. 1994: a cranium with two dentaries, most of the vertebral column as far as the anterior tail (C2–C7; T1–13; L1–6, S1–4, Ca1–4), most ribs, parts of the sternum, both hip bones, and a left femur. Gingerich et al. 1994 referred a specimen collected in 1981, GSP-UM 1852 two dentaries with teeth, to R. kasrani. [1] The body mass of the holotype has been estimated between 340 and 590 kg (750 and 1,300 lb) based on different techniques. [7]

Derived traits in R. kasrani, relative to older archaeocetes such as Pakicetus, include high-crowned cheek teeth, larger auditory bullae, larger mandibular foramen, and mandibular canals. The higher neural spines and shorter femur (60–70%) distinguish Rodhocetus from the more primitive Ambulocetus. The convex posterior surface of the exoccipital, shorter cervical vertebrae, and unfused sacral vertebrae distinguishes R. kasrani from Indocetus. In contrast to later archaeocetes such as Protocetus and later cetaceans, Rodhocetus retains external nares above upper canines, high neural spines on anterior thoracic vertebrae, and four sacral vertebrae with sacroiliac joints similar to those in land-mammals (suggesting a hip joint that could support the body weight.) [8]

Several cranial features identifies R. kasrani as an archaeocete: both the premaxillae and the dentaries are elongated, the frontal shield is wide, and the nuchal crest is high. The auditory bullae are large and dense but, there are no associated pterygoid fossae or air sinuses. The mandibular foramina are large with a pan bone 90 mm (3.5 in) long and 65 mm (2.6 in) high. [8]

The specific name kasrani comes from Qaisrani, the Baloch tribe inhabiting the type locality. [1] The protocetid Qaisracetus is also named after them.

R. balochistanensis

The fossil remains of R. balochistanensis were found in eastern Balochistan, Pakistan in 2001 by Philip Gingerich. Dating from about 47 million years ago, they are one of a series of recent discoveries, including the pakicetids, which have thrown considerable light on the previously mysterious evolutionary origin of whales. [9]

The holotype of Rodhocetus balochistanensis, GSP-UM 3485, is: [10] [11]

The five-fingered hand of R. balochistanensis is mesaxonic (i.e. has a central digit) with three weight-bearing central digits equipped with nail-like hooves, flanked by two more slender digits lacking hooves (distal phalanges preserved on first, second, and fourth digits). The four-toed foot is paraxonic (i.e. central axis passes between the two central digits), with all four digits ending in pointed nails (distal phalanges preserved on second and third digits). [12]

With an estimated body weight of 450 kg (990 lb), R. balochistanensis was 13% smaller than R. kasrani (590 kg (1,300 lb)), but its femur is larger. [10]

See also

Related Research Articles

<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.

<i>Ichthyolestes</i> Genus of mammals

Ichthyolestes is an extinct genus of archaic cetacean that was endemic to Indo-Pakistan during the Lutetian stage. To date, this monotypic genus is only represented by Ichthyolestes pinfoldi.

<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.

<i>Artiocetus</i> Genus of mammals

Artiocetus is an extinct genus of early whales belonging to the family Protocetidae. It was a close relative to Rodhocetus and its tarsals indicate it resembled an artiodactyl.

<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.

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.

Ancalecetus is an extinct genus of early whale known from the Late Eocene Birket Qarun Formation in Wadi Al-Hitan, Egypt. The species is named after anthropologist and primate researcher Elwyn L. Simons who discovered the type specimen in 1985.

Protocetidae, the protocetids, form a diverse and heterogeneous group of extinct cetaceans known from Asia, Europe, Africa, South America, and North America.

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>Qaisracetus</i> Genus of mammals

Qaisracetus is an extinct protocetid early whale known from the Eocene of Baluchistan, Pakistan.

Carolinacetus is an extinct protocetid early whale found in the Bartonian Tupelo Bay Formation in Berkeley County, South Carolina.

<i>Indocetus</i> Genus of mammals

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

Eocetus is an extinct protocetid early whale known from the early-late Eocene Giushi Formation in Gebel Mokattam, outside Cairo, Egypt. The specimen was first named by Fraas as Mesocetus schweinfurthi. However, the name Mesocetus was previously used causing a change to the species name to Eocetus schweinfurthi. Since the genus was first described in the early 20th century, several other specimens, mostly isolated vertebrae, have been attributed to Eocetus, but the taxonomic status of these widely distributed specimens remain disputed.

References

Notes

  1. 1 2 3 Gingerich et al. 1994 , p. 844
  2. Rhodocetus in the Paleobiology Database. Retrieved September 2013.
  3. Thewissen & Williams 2002 , p. 81
  4. Gingerich PD, Ul-Haq M, von Koenigswald W, Sanders WJ, Smith BH, Zalmout IS (2009). "New protocetid whale from the middle eocene of pakistan: birth on land, precocial development, and sexual dimorphism". PLOS ONE. 4 (2): e4366. Bibcode:2009PLoSO...4.4366G. doi: 10.1371/journal.pone.0004366 . PMC   2629576 . PMID   19194487.
  5. Rice 2008 , p. 236
  6. Gingerich 2003 , pp. 448, 449
  7. Waugh, D.A.; Thewissen, J.G.M. (2021). "The pattern of brain-size change in the early evolution of cetaceans". PLOS ONE. 16 (9). e0257803. Bibcode:2021PLoSO..1657803W. doi: 10.1371/journal.pone.0257803 . PMC   8478358 . PMID   34582492.
  8. 1 2 Gingerich et al. 1994 , pp. 846, 847
  9. Gingerich, Philip D. "Research on the Origin and Early Evolution of Whales (Cetacea)" . Retrieved 26 January 2013.
  10. 1 2 Gingerich et al. 2001 , pp. 2240–2241; Note 35
  11. Gingerich et al. 2001 , Suppl. mat.: Description of GSP-UM 3485, holotype of Rodhocetus balochistanensis; Supplemental Figure 4
  12. Gingerich et al. 2001 , Fig. 2

Sources