''Astroconodon'' is an extinct genus of mammal from the Cretaceous of North America. Part of

Eutriconodonta Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for t ...

, it was a small sized predator, either a terrestrial insectivore and

carnivore 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 so ...

, or a semi-aquatic piscivore. It is the first Cretaceous eutriconodont found.

Description

The type species is ''A. denisoni''. Known from the

Antlers Formation The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. ...

, its type specimen, ''FMNH PM 542'', was first described by

Bryan Patterson Bryan Patterson (born 10 March 1909 in London; died 1 December 1979 in Chicago) was an American paleontologist at the Field Museum of Natural History in Chicago. Life and career Bryan Patterson was the son of the soldier, engineer and aut ...

in 1951. It is a generally rather common species, known from a large quantity of isolated teeth, exhibiting a high degree of variability. Its molars are on average 0.59 to 2

millimeter 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter. The millimetre (American and British English spelling differences#-re, -er, ...

s long, and the

distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

ones see a marked increase in crown height. A second species, ''A. delicatus'', was later found in the

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain in northern Emery County, Utah, where Willia ...

. Its type locality is Mussentuchit (OMNH V239). It is smaller than ''A. denisoni'' by approximately 80%, and it differs from it, and most North American triconodontids, by lacking a lingual cingulid on the lower molars and premolars. A third species, currently unnamed, is known from the

Twin Mountains Formation The Twin Mountains Formation, also known as the Twin Mak Formation, is a sedimentary rock formation, within the Trinity Group, found in Texas of the United States of America. It is a terrestrial formation of Aptian age ( Lower Cretaceous), a ...

. Not much has been said about it.

Phylogeny

Always identified as a "

triconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for t ...

" mammal, recent studies have recovered it as a

triconodontid Triconodontidae is an extinct family of small, carnivorous mammals belonging to the order Eutriconodonta, endemic to what would become Asia, Europe, North America and probably also Africa and South America during the Jurassic through Cret ...

eutriconodont, as most closely related to '' Alticonodon'' and '' Corviconodon'' (these are in turn each other's sister taxa).Thomas Martin, Jesús Marugán-Lobón, Romain Vullo, Hugo Martín-Abad, Zhe-Xi Luo & Angela D. Buscalioni (2015). A Cretaceous eutriconodont and integument evolution in early mammals. Nature 526, 380–384.

Biology

Because of its abundance on lake and estuary deposits and particular association with fish-rich areas, it has been suggested that ''Astroconodon'' was an aquatic piscivore, an assertion reinforced by a perceived functional similarity between its molars and those of

cetaceans Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

and pinnipeds. Other researchers like

Zofia Kielan-Jaworowska Zofia Kielan-Jaworowska (25 April 1925 – 13 March 2015) was a Polish paleobiologist. In the mid-1960s, she led a series of Polish-Mongolian paleontological expeditions to the Gobi Desert. She was the first woman to serve on the executive commit ...

, however, were not convinced, noting that eutriconodont dentition cannot be easily compared to placental dentation, and that they generally have a shearing function as opposed to the non- occluding, grasping teeth of marine mammals. The prevalence on aquatic deposits, per her own words, "may well be real, but its significance is not clear", as like many other species found in fluvial deposits it may have simply been a terrestrial species whose remains were carried over by the waters, though she does cite Goldberg 2000 and recognises that there are stratifications of aquatic and terrestrial species to be noted. Terrestrial or aquatic, ''Astroconodon'', like most eutriconodonts, was almost certainly a predator. Like in most eutriconodonts, its triconodont molars were adapted for shearing, much ike the

carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified ...

s of therian carnivores.Zofia Kielan-Jaworowska, Richard L. Cifelli, Zhe-Xi Luo (2004). "Chapter 7: Eutriconodontans". Mammals from the Age of Dinosaurs: origins, evolution, and structure. New York: Columbia University Press. pp. 216–248. .

Palaeoecology

''Astroconodon'' occurs in several fossil formations, most depicting wetland and

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environments. In both the

and the

it occurs alongside iconic

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is the ...

such as ''

Tenontosaurus ''Tenontosaurus'' ( ; ) is a genus of medium- to large-sized ornithopod dinosaur. It was a relatively medium sized ornithopod, reaching in length and in body mass. It had an unusually long, broad tail, which like its back was stiffened with a n ...

'' and '' Deinonychus'', and in former it co-exists with a wide variety of other mammals including two other eutriconodonts, the considerably larger '' Jugulator amplissimus'' and closely related '' Corviconodon utahensis'', as well as many

multituberculate Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, ...

s and therians.

References

{{Taxonbar, from=Q12898868 Eutriconodonts Early Cretaceous mammals Mesozoic mammals of North America Cretaceous animals of North America Fossil taxa described in 1951 Taxa named by Bryan Patterson Prehistoric mammal genera