''Ankalagon saurognathus'' is an extinct

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

of the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Mesonychidae Mesonychidae (meaning "middle claws") is an extinct family of small to large-sized omnivorous-carnivorous mammals. They were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene, and were the earliest group of la ...

, endemic to

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

during the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

epoch (63.3—60.2 mya), existing for approximately . Known from the

Nacimiento Formation The Nacimiento Formation is a sedimentary rock formation found in the San Juan Basin of western New Mexico (United States). It has an age of 61 to 65.7 million years, corresponding to the early and middle Paleocene. The formation has yielded an ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

, ''Ankalagon'' is the largest

mesonychid Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely ...

known from the Paleocene of

, and it provides the best evidence for

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

in mesonychids.

Description

The main feature that distinguishes ''A. saurognathus'' from the ancestral ''

Dissacus ''Dissacus'' is a genus of extinct carnivorous jackal to coyote-sized mammals within the family Mesonychidae, an early group of hoofed mammals that evolved into hunters and omnivores. Their fossils are found in Paleocene to Early Eocene aged stra ...

'' species is its size: ''Ankalagon'' grew to be as large as a bear,Paleocene mammals of the world
"Carnivores, creodonts and carnivorous ungulates: Mammals become predators" as compared to the coyote or jackal-sized species of ''Dissacus''. In fact, the only North American mesonychids that surpassed ''Ankalagon'' in size were the larger species of the Early Eocene genus, ''

Pachyaena ''Pachyaena'' (literally, "thick hyena") was a genus of heavily built, relatively short-legged mesonychids, early Cenozoic mammals that evolved before the origin of either modern hoofed animals or carnivores, and combined characteristics similar t ...

'', such as ''P. gigantea'' and ''P. ossifraga'', which, too, grew to the size of bears. Evidence of sexual dimorphism comes from an analysis of tooth and jaw size in two specimens of this genus, compared with unrelated, extant Carnivora (where the body size and sex of living individuals can be recorded and compared with their tooth size). Though the two ''Ankalagon'' jaws are of very different sizes, and one has much larger canines, the first two molars are close to the same size. As the size of the first two molars varies little in individuals of the same species even when body size is different, the study suggests two conclusions: first, that these two adult individuals are the same species, so ''Ankalagon'' had significant sexual dimorphism. Second, that size/weight estimates of ''Ankalagon'' and other fossil mammals with sexual dimorphism may not be trustworthy, since estimates are usually made with a formula based on the size of the first two molar teeth, and these teeth may be the same size in individuals of much different body sizes.

Ecology

The strong jaw musculature specialized for up-and-down biting rather than side-to-side grinding movement, and the triangular, laterally compressed premolars and molars with carnassial notches of ''Ankalagon'' are typical of mesonychids. Though no living group of animals has similar structures, these features suggest that ''A. saurognathus'' was carnivorous. Paleontologists believe that mesonychids would not have been able to slice meat as effectively as other carnivorous animals, but large genera like ''Ankalagon'' would have used their pointed teeth to grab a chunk of meat and their unusually strong jaw muscles to pull it free from a large carcass, perhaps bracing it with their front feet. Whether the genus was active hunters, scavengers, or both is unknown. The evidence of sexual dimorphism in ''Ankalagon'' suggests that they formed either permanent social groups (like a pride of lions) or temporary associations (like a lek of grouse) of one male and several females; all living species of Carnivora as well as Primates that show sexual dimorphism in canine size form mating groups of this type.

Etymology

The generic name refers to the dragon Ancalagon, who was mentioned in ''

The Silmarillion ''The Silmarillion'' () is a collection of myths and stories in varying styles by the English writer J. R. R. Tolkien. It was edited and published posthumously by his son Christopher Tolkien in 1977, assisted by the fantasy author Guy Gavriel ...

'' by

J. R. R. Tolkien John Ronald Reuel Tolkien (, ; 3 January 1892 – 2 September 1973) was an English writer and philologist. He was the author of the high fantasy works ''The Hobbit'' and ''The Lord of the Rings''. From 1925 to 1945, Tolkien was the Rawlins ...

. In ''The Silmarillion'', Ancalagon was described as being one of the more powerful servants of the malevolent being,

Morgoth Morgoth Bauglir (; originally Melkor ) is a character, one of the godlike Valar, from Tolkien's legendarium. He is the main antagonist of ''The Silmarillion'', ''The Children of Húrin'', ''Beren and Lúthien'' and ''The Fall of Gondolin''. ...

, having been bred to be the fiercest, mightiest, and largest dragon in all of Middle-earth. According to Tolkien, "Ancalagon" translates from

Sindarin Sindarin is one of the fictional languages devised by J. R. R. Tolkien for use in his fantasy stories set in Arda, primarily in Middle-earth. Sindarin is one of the many languages spoken by the Elves. The word is a Quenya word. Called in Eng ...

as being ''anc'' 'jaw', ''alag'' 'impetuous'. The species name, "''saurognathus''," translates as "lizard jaw."

Leigh Van Valen Leigh Van Valen (August 12, 1935 – October 16, 2010) was a U.S. evolutionary biologist. At the time of his death, he was professor emeritus in the Department of Ecology and Evolution at the University of Chicago. Research and interests Amongs ...

studied the New Mexico mesonychid ''Dissacus saurognathus'' and eventually came to the conclusion that ''D. saurognathus'' differed enough from the sympatric ''D. navajovius'', and from other members of the genus to merit its own genus. Van Valen attempted to erect the new genus "''Ancalagon''" for ''"Dissacus" saurognathus'' in 1978. However, he later found that the name was already occupied by '' Ancalagon minor'', a

Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...

priapulid Priapulida (priapulid worms, from Gr. πριάπος, ''priāpos'' 'Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility ...

worm described in 1977 by

Simon Conway Morris Simon Conway Morris (born 1951) is an English palaeontologist, evolutionary biologist, and astrobiologist known for his study of the fossils of the Burgess Shale and the Cambrian explosion. The results of these discoveries were celebrated in ...

. As a result, he renamed ''"Ancalagon" saurognathus'' to ''Ankalagon saurognathus'' in 1980.

References

{{Taxonbar, from1=Q102324, from2=Q16941704 Mesonychids Paleocene mammals of North America Fossil taxa described in 1980 Prehistoric placental genera Organisms named after Tolkien and his works