Borhyaena

Borhyaena is an extinct genus of South American metatherian known as borhyaenaid, a family of mammalian predators part of the now extinct order, Sparassodonta. The genus lived from 21 to 15.5 million years ago from the Early to Middle Miocene.^[2]

Borhyaena Temporal range: Early-Middle Miocene (Colhuehuapian-Friasian) ~21.0–15.5 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
B. tuberata skull
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Sparassodonta
Family:	†Borhyaenidae
Genus:	†Borhyaena Ameghino 1887
Species
B. macrodonta (Ameghino 1902) B. tuberata (Ameghino 1887)
Synonyms
Conodonictis Ameghino 1891 Dinamictis Ameghino 1891 Pseudoborhyaena Ameghino 1902

Description

Borhyaena was a predator and had a large head and a long, powerful neck similar to living hyenas. Its legs were cursorial, albeit less specialized than those of wolves or the marsupial thylacine. The most complete specimen is estimated to have weighted 23 kilograms (51 lb) and stood 50 centimetres (1.6 ft) at the shoulders.^[3] It was believed that Borhyaena may have had digitgrade locomotion,^[4] although this has been questioned by some experts.^[5]

Paleobiology

Predatory behavior

While having some adaptations of cursoriality, Borhyaena wasn’t a true cursorial predator due to the generalized morphology of the autopodials, femur, and tibia, instead it may have been a long distance traveler but not a fast runner.^[6] It’s estimated that B. tuberata had an estimated bite force of 538 N or 121 lbf, with a BFQ of 165. Its BFQ is similar to that of thylacine and American black bear.^[7]

Brain anatomy and senses

A 2025 study found that B. tuberata had an encephalization quotient score of 0.21 to 0.24. From dorsal view, cerebrum of B. tuberata is slightly gyrencephalic and ovoid in shape.^[8] Compared to early sparassodonts, later diverging sparassodonts such as Borhyaena and Thylacosmilus had lower hearing ranges of frequency compared to other metatherians in the study.^[9]

Paleoecology

Restoration of Theosodon garretorum and Borhyaena tuberata

The genus has been found in Patagonia, Argentina (Santa Cruz and Sarmiento Formations) and Chile (Río Frias Formation).^[10] Santa Cruz Formation had a heterogeneous environment with patches forests, semi-arid forests, and open areas. Within this formation, B. tuberata coexisted with other sparassodonts. This included fellow borhyaenoids such as Acrocyon sectorius, Artodictis munizi, Lycopsis torresi, and Prothylacynus patagonicus. Hathliacynids were also present including Acyon tricuspidatus, Cladosictis patagoncia, Pseudonotictis pusillus, Perathereutes pungens, and Sipalocyon. Because of its large size, it would’ve been capable of displacing Acrocyon and Cladosictis. Borhyaena also coexisted with birds such as Brontornis, cariamid Cariama santacrucensis, the terror birds Patagornis marshi, Phorusrhacos, and Psilopterus bachmanni. Terror birds and sparassodonts likely niche partitioned due to locomotive differences. Herbivores present in Santa Cruz Formation included litoperns Diadiaphorus, Theosodon, and Tetramerorhinus, sloths Eucholoeops and Hapalops, and notoungulate toxodontid Adinotherium. Borhyaena may have typically preyed on animals that weighed 17–48 kilograms (37–106 lb), such as Hapalops.^[11]