Borhyaena spp.

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Borhyaena spp.


Life reconstruction of Borhyaena tuberata. © @ Roman Yevseyev

Temporal range: Early Miocene (20-15 Ma; Burdhigalian-Langhian)

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Phylum: Chordata
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Suborder: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Infraclass: Metatheria
Order: †Sparassodonta
Family: †Borhyaenidae
Genus: †Borhyaena
Species: †Borhyaena tuberata
†Borhyaena macrodonta

Borhyaena is an extinct genus of predatory metatherian that lived in South America during the Miocene epoch.

Description and functional anatomy:
Borhyaena was estimated to weigh between 19-29 kilograms by Argot (2003), with 23 kilograms as the mean weight. Weight estimates based off of skull length give Borhyaena an inflated mass of 74 kilograms, failing to take Borhyaena’s proportions into account.[1]

Borhyaena had a very massive skull with large zygomatic arches. This means that it had powerful jaw muscles. This is akin to the wide zygomatic arches seen in hyenas, and Borhyaena’s skull proportions are comparable to those of the striped hyena. The cervical vertebrae point to strong development of the neck muscles. The development of the ventral processes of the cervical vertebrae indicate that the neck flexors could exert a high amount of force, suggesting the predatory habits of Borhyaena. The neural process of the axis was posteriorly expanded, suggesting that Borhyaena could violently shake its head after prey apprehension in the jaws, just like some extant predators. The cervical vertebrae’s long cervical neural processes show that the neck extensors were well developed, and this was related to the weight of the skull. Therefore, the powerful jaw muscles of Borhyaena and the long, powerful neck prove that it could lift and carry heavy loads, particularly large prey.[1]


The powerful skull of B. tuberata. © @ DeviantArt user thylobscene

Not only did Borhyaena have powerful jaw muscles, but it also had robust teeth with bulbous roots and robust, deep, and sometimes even fused dentaries. This suggests that Borhyaena was specialized for bone-cracking to some extent, although it was probably less specialized for it than extant hyenas.[2]

The postcranial skeleton of Borhyaena give insights into its lifestyle. The distal portion of Borhyaena’s humerus suggests that the forearm was restricted to the parasagittal plane. Moreover, the radius’ morphology suggests a reduced capacity for pronation and supination. Borhyaena’s manus was semi- or fully-digitigrade. The bone cores of the claws were comparatively rounded in cross section and not particularly deep; the tips had clefts and were not sharp (this suggests that the jaws were the only weapon that Borhyaena had to its disposal). Lastly, the distal limb segments were lightened with the muscle mass more concentrated in the proximal regions. All of these are adaptations for a cursorial lifestyle, although Borhyaena was less specialized for such a lifestyle than Canis or Thylacinus (e.g. the lumbar vertebrae had relatively reduced flexibility).[1]


References:

[1] Argot, C. (2003). Functional Adaptations of the Postcranial Skeleton of Two Miocene Borhyaenoids (Mammalia, Metatheria), Borhyaena and Prothylacinus, from South America.
[2] Kay, R.F., Bargo, M.S. (2012). Early Miocene Paleobiology in Patagonia: High-Latitude Paleocommunities of the Santa Cruz Formation p. 180. Cambridge University Press.

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I found a website with better pictures of Borhyaena's skull (link).





My suspicions were confirmed. This animal really did have quite wide zygomatic arches. For a skull that looks to be ~19 cm long or so (and for an animal weighing at most <30 kilograms), the width at the zygomatic arches seems to be >10 cm.

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I found a paper on borhyaenoid bite mechanics, which includes Borhyaena tuberata.

Estimated body mass was 21.40 kg, a value taken from Wroe et al. (2004). The bite force estimation method was the dry skull method, and under this it was found to have a canine bite force of 538 N, and a bite force quotient of 165. Read below to see how it compares to other mammalian carnivores, and the functional implications.

Borhyaena tuberata has an estimated BF similar to Ursus americanus (m=105.2 kg; BF=541N; BFQ=64) and Hyaena hyaena (m=40.8 kg; BF=545N; BFQ=113). The BFQ value is very similar to that of the powerful extinct predator Canis dirus. It is close to the values of all other living and fossil predatory marsupials (see Table 3), mainly to Thylacinus cynocephalus and the extant Dasyurus maculatus (m=3.0 kg; BF=153N; BFQ=179).

Borhyaena tuberata has an estimated BFQ value very close to that of the powerful extinct predator Canis dirus. The mandibular strength at the canine and between M₁ and P₃ is very similar to the values of Canis dirus, reinforcing the similarity between BFQ values. Several authors have suggested that Canis dirus was a canid adapted for hunting larger mammals than living wolves (Wang et al. 2008). The BFQ of B. tuberata is similar to those of other predatory marsupials (see Table 3) such as Thylacinus cynocephalus and the extant Dasyurus maculatus. The MFP also indicates a very powerful bite. The extremely high BFQ is inferior only to some values in fossil marsupials such as Thylacoleo carnifex (see Table 3). The MFP also suggests a large bite force at the canines, slightly greater than Panthera nebulosa and Canis lupus but smaller than Panthera leo and Crocuta crocuta. The MFP shows that bite force at the molars does not increase as much as in Crocuta or bears (Ursidae) (Christiansen 2007). This pattern suggests that it probably was able to kill large prey but it was not good at breaking bones, as previously suggested from its dentition (Argot 2004 and references therein). It probably had the capacity to kill or feed on large prey such as protherotediids [sic] and macraucheniids.

This same source also makes note that, although Borhyaena was much less suited for cursorial running than modern pursuit predators, it bones were relatively more robust and heavier in exchange.

It was relatively short-legged and its bones were relatively more robust and heavier than modern pursuit predators.

Blanco et al. (2010)