Hyenadon

''Hyaenodon'' (" hyena-tooth") is an extinct genus of carnivorous hyaenodont mammals from tribe Hyaenodontini, within subfamily Hyaenodontinae in family Hyaenodontidae,Malcolm C. McKenna, Susan K. Bell (1997.
"Classification of Mammals: Above the Species Level"
Columbia University Press, New York, 631 pages. that lived in Eurasia and North America during the middle Eocene to early Miocene, existing for about 25.1 million years.

Description

Typical of early carnivorous mammals, individuals of ''Hyaenodon'' had a very massive skull, but only a small brain. The skull is long with a narrow snout - much larger in relation to the length of the skull than in canine carnivores, for instance. The neck was shorter than the skull, while the body was long and robust and terminated in a long tail. Compared to the generally larger (but not closely related) ''Hyainailouros'', the dentition of ''Hyaenodon'' was geared more towards shearing meat and less towards bone crushing.

Some species of this genus were among the largest terrestrial carnivorous mammals of their time; others were only of the size of a marten. Remains of many species are known from North America, Europe, and Asia.X. Wang, Z. Qiu and B. Wang (2005.
"Hyaenodonts and carnivorans from the early Oligocene to early Miocene of the Xianshuihe Formation, Lanzhou Basin, Gansu Province, China."
Palaeontologia Electronica 8(1):1-14 The average weight of adult or subadult ''H. horridus'', the largest North American species, is estimated to about and may not have exceeded . ''H. gigas'', the largest ''Hyaenodon'' species, was much larger, being and around . ''H. crucians'' from the early Oligocene of North America is estimated to only . ''H. microdon'' and ''H. mustelinus'' from the late Eocene of North America were even smaller and weighed probably about .

Tooth eruption

Studies on juvenile ''Hyaenodon'' specimens show that the animal had a very unusual system of tooth replacement. Juveniles took about 3–4 years to complete the final stage of eruption, implying a long adolescent phase. In North American forms, the first upper premolar erupts before the first upper molar, while European forms show an earlier eruption of the first upper molar.

Paleoecology

The various species of ''Hyaenodon'' competed with each other and with other hyaenodont genera (including ''Sinopa'', ''Dissopsalis'', and ''Hyainailurus''), and played important roles as predators in ecological communities as late as the Miocene in Asia and preyed on a variety of prey species such as primitive horses like ''Mesohippus'', Brontotheres, early camels, oreodonts and even primitive rhinos. Species of ''Hyaenodon'' have been shown to have successfully preyed on other large carnivores of their time, including a nimravid ("false sabertooth cat"), according to analysis of tooth puncture marks on a fossil ''Dinictis'' skull found in North Dakota.

In North America the last ''Hyaenodon'', in the form of ''H. brevirostrus'', disappeared in the late Oligocene. In Europe, they had already vanished earlier in the Oligocene.

Classification and phylogeny

Taxonomy

* Tribe: †Hyaenodontini
** Genus: †''Hyaenodon''
*** †''Hyaenodon brachyrhynchus''
*** †''Hyaenodon chunkhtensis''
*** †''Hyaenodon dubius''
*** †''Hyaenodon eminus''
*** †''Hyaenodon exiguus''
*** †''Hyaenodon filholi''
*** †''Hyaenodon gervaisi''
*** †''Hyaenodon heberti'' (Europe, 41-33.9 mya)
*** †''Hyaenodon leptorhynchus''
*** †''Hyaenodon minor''
*** †''Hyaenodon pervagus''
*** †''Hyaenodon pumilus''
*** †''Hyaenodon requieni''
*** †''Hyaenodon rossignoli''
*** †''Hyaenodon weilini'' (China, 23-16,9 mya)
*** †''Hyaenodon yuanchuensis''
*** Subgenus: †'' Neohyaenodon'' ^{( paraphyletic subgenus)}
**** †''Hyaenodon gigas''
**** †''Hyaenodon horridus''
**** †''Hyaenodon incertus''
**** †''Hyaenodon macrocephalus''
**** †''Hyaenodon megaloides''
**** †''Hyaenodon milvinus''
**** †''Hyaenodon mongoliensis''
**** †''Hyaenodon montanus''
**** †''Hyaenodon vetus''
*** Subgenus: †'' Protohyaenodon'' ^{( paraphyletic subgenus)}
**** †''Hyaenodon brevirostrus''
**** †''Hyaenodon crucians''
**** †''Hyaenodon microdon''
**** †''Hyaenodon mustelinus'' (North America, 38-30 mya)
**** †''Hyaenodon raineyi'' E. P. Gustafson (1986.
"Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas."
Texas Memorial Museum Bulletin 33:1-66
**** †''Hyaenodon venturae''

Phylogeny

The phylogenetic relationships of genus ''Hyaenodon'' are shown in the following cladogram

References

{{Taxonbar, from=Q131465

Hyaenodonts
Eocene mammals
Oligocene mammals
Miocene mammals
Miocene genus extinctions
Cenozoic mammals of Asia
Cenozoic mammals of North America
Cenozoic mammals of Europe
White River Fauna
Eocene genus first appearances
Prehistoric placental genera
Fossil taxa described in 1838