# Astroconodon

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***Astroconodon*** is an extinct genus of mammal from the [Cretaceous](/source/Cretaceous) of [North America](/source/North_America). Part of [Eutriconodonta](/source/Eutriconodonta), it was a small sized [predator](/source/Predator), either a terrestrial [insectivore](/source/Insectivore) and [carnivore](/source/Carnivore), or a semi-aquatic [piscivore](/source/Piscivore).

It is the first [Cretaceous](/source/Cretaceous) eutriconodont found.[1][2]

## Description

The type species is *A. denisoni*. Known from the [Antlers Formation](/source/Antlers_Formation), its type specimen, ***FMNH PM 542***, was first described by [Bryan Patterson](/source/Bryan_Patterson) in 1951.[1] It is a generally rather common species, known from a large quantity of isolated teeth, exhibiting a high degree of variability.[3][2][4] Its molars are on average 0.59 to 2 [millimeters](/source/Millimeter) long, and the [distal](/source/Distal) ones see a marked increase in crown height.

A second species, *A. delicatus*, was later found in the [Cedar Mountain Formation](/source/Cedar_Mountain_Formation). Its [type locality](/source/Type_locality_(geology)) is [Mussentuchit](/source/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.[4]

A third species, currently unnamed, is known from the [Twin Mountains Formation](/source/Twin_Mountains_Formation). Not much has been said about it.[2][4]

## Phylogeny

Always identified as a "[triconodont](/source/Triconodont)" mammal,[1] recent studies have recovered it as a [triconodontid](/source/Triconodontid) [eutriconodont](/source/Eutriconodont), as most closely related to *[Alticonodon](/source/Alticonodon)* and *[Corviconodon](/source/Corviconodon)* (these are in turn each other's sister taxa).[5][6]

## Biology

Because of its abundance on [lake](/source/Lake) and [estuary](/source/Estuary) deposits and particular association with [fish](/source/Fish)-rich areas, it has been suggested that *Astroconodon* was an aquatic [piscivore](/source/Piscivore), an assertion reinforced by a perceived functional similarity between its molars and those of [cetaceans](/source/Cetaceans) and [pinnipeds](/source/Pinnipeds).[3] Other researchers like [Zofia Kielan-Jaworowska](/source/Zofia_Kielan-Jaworowska), however, were not convinced, noting that eutriconodont dentition cannot be easily compared to [placental](/source/Placental) dentation, and that they generally have a shearing function as opposed to the non-[occluding](/source/Occlusion_(dentistry)), 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](/source/Fluvial) deposits it may have simply been a terrestrial species whose remains were carried over by the waters, though she does cite Goldberg 2000[7] and recognises that there are stratifications of aquatic and terrestrial species to be noted.[2]

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 [carnassials](/source/Carnassial) of [therian](/source/Theria) carnivores.[2]

## Palaeoecology

*Astroconodon* occurs in several fossil formations, most depicting [wetland](/source/Wetland) and [delta](/source/River_delta) environments. In both the [Antlers Formation](/source/Antlers_Formation) and the [Cedar Mountain Formation](/source/Cedar_Mountain_Formation) it occurs alongside iconic [dinosaurs](/source/Dinosaurs) such as *[Tenontosaurus](/source/Tenontosaurus)* and *[Deinonychus](/source/Deinonychus)*, and in former it co-exists with a wide variety of other mammals including two other eutriconodonts, the considerably larger *[Jugulator amplissimus](/source/Jugulator_amplissimus)* and closely related *[Corviconodon utahensis](/source/Corviconodon_utahensis)*, as well as many [multituberculates](/source/Multituberculate) and [therians](/source/Theria).

## References

1. B. Patterson. 1951. Early Cretaceous mammals from northern Texas. American Journal of Science 249:31-46

1. 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. ISBN 0-231-11918-6.

1. [Bob H. Slaughter](/source/Bob_H._Slaughter), Astroconodon, the Cretaceous Triconodont, Journal of Mammalogy, Vol. 50, No. 1 (Feb., 1969), pp. 102-107

1. R. L. Cifelli and S. K. Madsen. 1998. Triconodont mammals from the medial Cretaceous of Utah. Journal of Vertebrate Paleontology 18(2):403-411

1. Jin Meng; Yuanqing Wang; Chuankui Li (2011). "Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont". *Nature*. **472** (7342): 181–185. [Bibcode:2011Natur.472..181M](https://ui.adsabs.harvard.edu/abs/2011Natur.472..181M). [doi:10.1038/nature09921](https://doi.org/10.1038/nature09921). [PMID 21490668](https://pubmed.ncbi.nlm.nih.gov/21490668). [S2CID 4428972](https://api.semanticscholar.org/CorpusID:4428972)

1. 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. [doi:10.1038/nature14905](https://doi.org/10.1038/nature14905)

1. Goldberg, Faunal composition, non-marine vertebrates, of the upper Cedar Mountain Formation (Cretaceous : Albian-Cenomanian), central Utah, Thesis (Ph. D.)--University of Oklahoma, 2000. Includes bibliographical references.

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