Hemicyon spp.

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Hemicyon spp.


Reconstruction of H. sansaniensis. © @ Maurico Antón

Temporal range: Middle Miocene (Langhian-Serravallia; ~15.97-12.75Ma[1])

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Clade: Eutheriodonta
Suborder: Cynodontia
Clade: Epicynodontia
Infraorder: Eucynodontia
Parvorder: Probainognathia
Superfamily: Chiniquodontoidea
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
(unranked): Pegasoferae
(unranked): Zooamata
Clade: Holotheria
Superlegion: Trechnotheria
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Boreoeutheria
Superorder: Laurasiatheria
(unranked): Ferae
(unranked): Carnivoramorpha
Order: Carnivora
Suborder: Caniformia
Infraorder: Arctoidea
Family: Ursidae or †Hemicyonidae
Subfamily: †Hemicyoninae (if part of Ursidae)
Genus: †Hemicyon
Species: †H. barbouri
†H. sansaniensis
†H. ursinus
†H. goeriachensis
†H. grivensis
†H. minor
†H. statzlingii

Hemicyon ("half dog") is an extinct genus of carnivoran that lived in Eurasia and North America during the middle Miocene from 15.97-12.75 million years ago.[1] It contained multiple species. It and its relatives are known as the "dog bears".

Taxonomy:
Hemicyon and co. are either referred to as a subfamily of Ursidae (Hemicyoninae) or a separate family altogether (Hemicyonidae).[2]

Description & ecomorphology:
H. sansaniensis weighed as much as a small brown bear.[2]

Hemicyon resembled the grey wolf (C. lupus) in that it had a narrow rostrum and a well-developed carnassial shear. The relative development of the talonid (RGA) of the lower dentition of a close relative, Phoberocyon johnhenryi, was greater than that of the grey wolf and other exclusively carnivorous extant canids but within the range of primarily carnivorous extant canids. This suggests that the animal, and by inference its relatives (including Hemicyon) was primarily carnivorous. Hemicyon would also still have included plant matter in its diet. Evidence for this comes in the form of substantial flat wear facets on the protocone of the fourth premolar (P4), as well as on the buccal and lingual cusps on the upper molars. This is the same condition observed in Agriotherium sp., Arctodus simus, and Ursus arctos gyas and suggests that Hemicyon used its posterior teeth to crush and grind plant matter, as well as to shear meat. Furthermore, a premasseteric fossa was present on the mandible in Hemicyon, providing further evidence of plants in its diet.[3]

The postcranial skeleton reveals the predator behavior of Hemicyon. Like the short faced bears Arctodus and Agriotherium, the deltoid and pectoral ridges ended more proximally on the humerus and the supinator ridge and medial epicondyle was reduced compared to those of U. arctos. The radius was nearly as long relative to the humerus as in the grey wolf and the feet were digitigrade. The lumbar vertebrae were longer than they were tall, had ample space between them, and had cranially angled spines with ventrally projecting transverse processes. Such vertebral morphology would have increased stride length, allowing for rapid acceleration and high maximal running speed.

Thus, the skeleton of Hemicyon indicates that it was an active cursorial predator, although apparently less specialized than the living grey wolf.[3] The related Plithocyon was more cursorial than Hemicyon.[4]

Evolutionary history & extinction:
Early in its evolutionary history, Hemicyon was restricted to Eurasia, but subsequently became very successful and spread to North America.[5]

The extinction of the hemicyonines/hemicyonids has been linked to the radiation of the Agriotheriinae, an unequivocal subfamily of bears. Alternatively, competition with large felids may have contributed to their extinction.[5]

References:

[1] Fossilworks page on Hemicyon barbouri
[2] Denizens of Madrid’s Miocene Woods: The “Dog-Bears”
[3] Sorkin, B. (2006). Ecomorphology of the giant short-faced bears Agriotherium and Arctodus. ResearchGate. doi: 10.1080/08912960500476366
[4] Agusti, J., Antón, M. (2013). Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution (p. 119). Columbia University Press.
[5] Mclellan, B. (1994). A Review of Bear Evolution. Bears Their Biology and Management. doi: 10.2307/3872687

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Figueirido (2014)->

For example, on the one hand, a slender anatomy for humerus, radius and ulna is present in most canine canids (with the manned wolf, Chrysocyon brachyurus, as the most extreme example), hyaenids, the cheetah (Acinonyx jubatus), the bobcat (Lynx rufus) and the serval (Leptailurus serval) among the felids, the extinct ‘‘dog-like’’ bear Hemicyon among the ursids, and the racoon (Procyon lotor) among the procyonids. A slender condition has been usually interpreted as an adaptation of long bones to reduce the energetic costs of terrestrial locomotion by decreasing the moment of inertia of limbs and by increasing stride length[13,32,112]. Therefore, to have slender long bones allows the animal to travel longer distances on the ground (by increasing stamina) and/or to run faster. In other words, this adaptation is related with cursoriality.

Andersson & Werdelin (2003)->

The results for 31 early–middle Miocene (23.8–11.2 Myr ago) carnivores show overall similarities in pattern to the Oligocene and Recent carnivores, but also some notable differences (figure 2b). The overall pattern, with an axis of moderately large, cursorial species and an axis of non-cursorial species of increasing size, remains. However, the whole pattern is shifted to the right, with the result that in the Miocene there were larger taxa with an intermediate elbow-joint morphology than in either the Oligocene or Recent. The best examples of such intermediate taxa are the amphicyonid Pliocyon sp. (123 kg reconstructed body mass) and the ursid Hemicyon ursinus (122 kg). This is in strong contrast to the Recent or the Oligocene, where no carnivore above ca. 20 kg body mass takes such an intermediate position. We suggest that this difference is a reflection of the extraordinary species richness of browsing ungulates in the early Miocene of North America (Janis et al. 2000). Such an increase in prey spectrum in a mixed environment would create a unique situation, in which large carnivores need not commit to a cursorial habitus to fill their nutritional requirements. Among individual taxa, the position of Barbourofelis whitfordi among cursorial taxa is in marked contrast to the nimravids of the Oligocene, which retain full supinatory ability (figure 2a).

So judging from the information above:

1) Hemicyon possessed slender forelimbs bones, as seen in mostly cursorial carnivoran taxa.

2) It had intermediate ability to supinate its forelimbs.


What I think we're looking at is a predator that was fairly cursorial, though not as specialized as modern canids and hyaenids. It seems like grappling with prey to some extent is possible, but it was not as specialized as dedicated grapplers either.