Tylopoda

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Tylopoda
Temporal range: Middle Eocene-Holocene
07. Camel Profile, near Silverton, NSW, 07.07.2007.jpg
A dromedary camel
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Suborder: Tylopoda
Illiger, 1811
Families

Camelidae
and numerous prehistoric families (see text)

Contents

Tylopoda (meaning "calloused foot") [1] is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels are introduced. The group has a long fossil history in North America and Eurasia. Tylopoda appeared during the Eocene around 46.2 million years ago. [2]

Tylopoda has only one extant family, Camelidae, which includes camels, llamas, guanacos, alpacas and vicuñas. This group was much more diverse in the past, containing a number of extinct families in addition to the ancestors of living camelids (see below).

Tylopods are not ruminants. [3]

Taxonomy and systematics

Tylopoda was named by Illiger (1811) and considered monophyletic by Matthew (1908). It was treated as an unranked clade by Matthew (1908) and as a suborder by Carroll (1988), Ursing et al. (2000) and Whistler and Webb (2005). It was assigned to Ruminantia by Matthew (1908); to Artiodactyla by Flower (1883) and Carroll (1988); to Neoselenodontia by Whistler and Webb (2005); and to Cetartiodactyla by Ursing et al. (2000) and by Agnarsson and May-Collado (2008). [4] [5] [6]

The main problem with circumscription of Tylopoda is that the extensive fossil record of camel-like mammals has not yet been thoroughly examined from a cladistic standpoint. Tylopoda is a highly distinctive lineage among the artiodactyls, but its exact relationships are somewhat elusive because the six living species are all closely related and can be considered "living fossils", the sole surviving lineage of a prehistorically wildly successful radiation. More recent studies suggest that tylopods are not as closely related to ruminants as traditionally believed, expressed in cladogram form as: [7] [8] [9] [10] [11] [12]

Artiodactyla  

Tylopoda (camels) Cladogram of Cetacea within Artiodactyla (Camelus bactrianus).png

  Artiofabula  

  Suina (pigs) Recherches pour servir a l'histoire naturelle des mammiferes (Pl. 80) (white background).jpg

  Cetruminantia  

  Ruminantia (ruminants) Walia ibex illustration white background.png  

  Cetancodonta/Whippomorpha  

  Hippopotamidae (hippopotamuses) Voyage en Abyssinie Plate 2 (white background).jpg

  Cetacea (whales) Bowhead-Whale1 (16273933365).jpg

Tylopoda are extremely conservative in their lifestyle and (like ruminants) seem to have occupied the same ecological niche since their origin over 40 million years ago. Thus, it seems that the previous assumption of a close relationship between Tylopoda and ruminants is simply because all other close relatives (whales, pigs etc.) are so divergent in their adaptations as to have obscured most indications of relationship, or at least those visible to phenetic analyses. However, the rather basal position that Tylopoda appears to have among the even-toed ungulates and relatives means that the oldest members of this lineage are still morphologically very primitive and hard to distinguish from the ancestors of related lineages. The first major modern and comprehensive analysis of the problem (in 2009) supported this; while some taxa traditionally considered Tylopoda could be confirmed to belong to this suborder (and a few refuted), the delimitation of this group is still very much disputed despite (or because of) an extensive fossil record. [7]

Life restoration of Agriochoerus antiquus Agriochoerus.jpg
Life restoration of Agriochoerus antiquus

The taxa currently assigned (with some reliability) to Tylopoda are: [7]

Basal and incertae sedis

Superfamily †Anoplotherioidea

Superfamily Cameloidea

Superfamily †Merycoidodontoidea (=Oreodontoidea)

Superfamily †Xiphodontoidea

Life restoration of the primitive artiodactyl Diacodexis pakistanensis (foreground) being stalked by Pakicetus Diacodexis pakistanensis e.jpg
Life restoration of the primitive artiodactyl Diacodexis pakistanensis (foreground) being stalked by Pakicetus

Disputed Tylopoda

Several additional prehistoric (cet)artiodactyl taxa are sometimes assigned to the Tylopoda, but other authors consider them incertae sedis or basal lineages among the (Cet)artiodactyla:

The Cebochoeridae and Protoceratidae, on the other hand, are prehistoric families that were occasionally placed within Tylopoda in the past, but are now considered more closely related to cetaceans and ruminants respectively than to camels.

Related Research Articles

Ungulate Group of animals that use the tips of their toes or hooves to walk on

Ungulates are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, camels, sheep, deer, and hippopotamuses. Cetaceans such as whales, dolphins, and porpoises are also classified as even-toed ungulates, although they do not have hooves. Most terrestrial ungulates use the hoofed tips of their toes to support their body weight while standing or moving.

Even-toed ungulate Order of mammals

The even-toed ungulates are ungulates—hoofed animals—which bear weight equally on two of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, odd-toed ungulates bear weight on an odd number of the five toes. Another difference between the two with the exception of Suina many other even-toed ungulates digest plant cellulose in one or more stomach chambers rather than in their intestine as the odd-toed ungulates do.

Hippopotamidae Family of mammals

Hippopotamids are stout, naked-skinned, and semiaquatic artiodactyl mammals, possessing three-chambered stomachs and walking on four toes on each foot. While they resemble pigs physiologically, their closest living relatives are the cetaceans. Hippopotamids constitute the family Hippopotamidae.

Placentalia Infraclass of mammals in the clade Eutheria

The infraclass Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals. Placentals are partly distinguished from other mammals in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young who are then kept for a period in the mother's pouch.

Ruminant Hoofed herbivorous grazing or browsing mammals

Ruminants are large hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. The word "ruminant" comes from the Latin ruminare, which means "to chew over again".

Camelidae Family of mammals belonging to even-toed ungulates

Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The 7 extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, and guanacos. Camelids are even-toed ungulates classified in the order Cetartiodactyla, along with species like whales, pigs, deer, cattle, and antelopes.

Suina Lineage of omnivorous, non-ruminant artiodactyl mammals that includes the pigs and peccaries

Suina is a suborder of omnivorous, non-ruminant artiodactyl mammals that includes the pigs and peccaries. A member of this clade is known as a suine. Suina includes the family Suidae, termed suids, known in English as pigs or swine, as well as the family Tayassuidae, termed tayassuids or peccaries. Suines are largely native to Africa, South America, and Southeast Asia, with the exception of the wild boar, which is additionally native to Europe and Asia and introduced to North America and Australasia, including widespread use in farming of the domestic pig subspecies. Suines range in size from the 55 cm (22 in) long pygmy hog to the 210 cm (83 in) long giant forest hog, and are primarily found in forest, shrubland, and grassland biomes, though some can be found in deserts, wetlands, or coastal regions. Most species do not have population estimates, though approximately two billion domestic pigs are used in farming, while several species are considered endangered or critically endangered with populations as low as 100. One species, Heude's pig, is considered by the International Union for Conservation of Nature to have gone extinct in the 20th century.

Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Cetartiodactyla, being composed thus of several unrelated lineages.

Mammal classification

Mammalia is a class of animal within the phylum Chordata. Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums. Many earlier ideas from Linnaeus et al. have been completely abandoned by modern taxonomists, among these are the idea that bats are related to birds or that humans represent a group outside of other living things. Competing ideas about the relationships of mammal orders do persist and are currently in development. Most significantly in recent years, cladistic thinking has led to an effort to ensure that all taxonomic designations represent monophyletic groups. The field has also seen a recent surge in interest and modification due to the results of molecular phylogenetics.

Ferae A clade of mammals consisting of Carnivores and Pholidotes

Ferae is a clade of mammals, consisting of the orders Carnivora and Pholidota. Another name, Ostentoria, has also been proposed for a grouping of the Carnivora and Pholidota. The last common ancestor of extant Ferae is supposed to have diversified c. 78.9 million years ago. Several extinct orders such as creodonts are members of Ferae as well.

Pecora Infraorder of mammals

Pecora is an infraorder of even-toed hoofed mammals with ruminant digestion. Most members of Pecora have cranial appendages projecting from their frontal bones; only two extant genera lack them, Hydropotes and Moschus. The name “Pecora” comes from the Latin word pecus, which means “horned livestock”. Although most pecorans have cranial appendages, only some of these are properly called “horns”, and many scientists agree that these appendages did not arise from a common ancestor, but instead evolved independently on at least two occasions. Likewise, while Pecora as a group is supported by both molecular and morphological studies, morphological support for interrelationships between pecoran families is disputed.

Merycoidodontoidea Extinct superfamily of mammals

Merycoidodontoidea, sometimes called "oreodonts" or "ruminating hogs", is an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were generally hog-like, and the group has traditionally been placed within the Suina, though some recent work suggests they may have been more closely related to camels. "Oreodont" means "mountain teeth", referring to the appearance of the molars. Most oreodonts were sheep-sized, though some genera grew to the size of cattle. They were heavy-bodied, with short four-toed hooves and comparatively long tails.

Carnivoramorpha Extinct clade of carnivores

Carnivoramorpha ("carnivora-shaped") is a clade of placental mammals that includes the modern order Carnivora and its extinct stem-relatives.

Whippomorpha Suborder of mammals

Whippomorpha or Cetancodonta is a group of animals that contains all living cetaceans and hippopotamuses, as well as their extinct relatives, I.E Entelodonts, Andrewsarchus. All Whippomorphs are descendants of the last common ancestor of Hippopotamus amphibius and Tursiops truncatus. This makes it a crown group. Whippomorpha is a suborder within the order Artiodactyla. The placement of Whippomorpha within Artiodactyla is a matter of some contention, as hippopotamuses were previously considered to be more closely related to Suidae (pigs) and Tayassuidae (peccaries). Most contemporary scientific phylogenetic and morphological research studies link hippopotamuses with cetaceans, and genetic evidence has overwhelmingly supported an evolutionary relationship between Hippopotamidae and Cetacea. Modern Whippomorphs all share a number of behavioural and physiological traits; such as a dense layer of subcutaneous fat and largely hairless bodies. They exhibit amphibious and aquatic behaviors and possess similar auditory structures.

Cetruminantia Taxonomic clade

The Cetruminantia are a clade made up of the Cetancodontamorpha and their closest living relatives, the Ruminantia.

Oromerycidae Extinct family of mammals

Oromerycidae is a small, extinct family of artiodactyls closely related to living camels, known from the early to late Eocene of western North America.

<i>Paracamelus</i> Extinct genus of mammals

Paracamelus is an extinct genus of camel in the family Camelidae. It originated in North America during the Middle Miocene but crossed the Beringian land bridge into Eurasia during the Late Miocene, approximately 7.5–6.5 million years ago (Ma); its later range spanned from Spain and Italy to Chad and Shanxi Province, China. It is ancestral to living camels of the genus Camelus. A population remained in northern North America, which became the high Arctic camel, which survived until the Middle Pleistocene approximately 1 Ma.

Artiofabula Clade of mammals comprising pigs, cows, hippos, and whales, among others

Artiofabula is a clade made up of the Suina and the Cetruminantia. The clade was found in molecular phylogenetic analyses and contradicted traditional relationships based on morphological analyses.

Tragulina Infraorder of ungulates

Tragulina is an infraorder of even-toed ungulates. Only the chevrotains survive to the present, including the genera Tragulus and Hyemoschus, all within the family Tragulidae.

Cetancodontamorpha Clade of tetrapods

Cetancodontamorpha is a total clade of artiodactyls defined, according to Spaulding et al., as Whippomorpha "plus all extinct taxa more closely related to extant members of Whippomorpha than to any other living species". Attempts have been made to rename the clade Whippomorpha to Cetancodonta, but the former maintains precedent.

References

  1. Donnegan, James (1834). "A New Greek and English Lexicon"
  2. PaleoBiology Database: Priscocamelus, basic info
  3. Fowler, M.E. (2010). "Medicine and Surgery of Camelids", Ames, Iowa: Wiley-Blackwell. Chapter 1, General Biology and Evolution, addresses the fact that camelids (including llamas and camels) are not ruminants, pseudoruminants, or modified ruminants.
  4. Matthew, W. D. (1908). "Osteology of Blastomeryx; and phylogeny of the American Cervidae". Bulletin of the American Museum of Natural History. 24 (27): 535–562. hdl:2246/1442.
  5. R. L. Carroll. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Company, New York 1-698
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