Barbourofelis

Barbourofelis is an extinct genus of large, predatory, from a subfamily of feliform carnivoran mammals of known as Barbourofelinae, which has recently been suggested to be part of Nimravidae family. Barbourofelis, along with Albanosmilus, was the last members barbourofelids, as well as the last nimravids. Barbourofelis lived North America and Eurasia during the Miocene epoch from 12 to 7 Ma.^[1][2][3]

Barbourofelis Temporal range: Middle to Late Miocene (Serravallian to Messinian), 12–7 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
B. loveorum, Florida Museum of Natural History Fossil Hall at the University of Florida
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Suborder:	Feliformia
Family:	†Barbourofelidae
Tribe:	†Barbourofelini
Genus:	†Barbourofelis Schultz, Schultz & Martin, 1970
Type species
†Barbourofelis fricki Schultz, Schultz & Martin, 1970
Other Species
†Barbourofelis loveorum †Barbourofelis morrisi †Barbourofelis oregonensis †Barbourofelis piveteaui

Five species are currently recognized within the genus: B. fricki, B. loveorum, B. morrisi, B. oregonensis, and B. piveteaui. B. morrisi likely evolved from Albanosmilus migrating into North America. With B. piveteaui evolving from reverse migration from North America into Eurasia. B. loveorum possibly evolved from B. morrisi, and may have evolved into B. fricki.

B. morrisi and B. piveteaui were the smallest species being about as large as a leopard. B. loveorum was the larger than B. morrisi and could’ve weighed anywhere from 70–128 kg (154–282 lb). B. fricki was the most recent and largest species of the genus, estimated to have been as large as lions, weighing around 328 kg (723 lb). B. oregonensis was described to being similar in morphology and size to B. fricki. It’s believed that Barbourofelis was an ambulatory, ambush predator that hunted within closed forested environments.

Taxonomy

Classification

Barbourofelis was named by Bertrand Schultz, Marian Schultz, and Larry Martin in 1970 in honor of Erwin Hinckley Barbour, who died a few days before the holotype was discovered. Its type species is Barbourofelis fricki and is the type genus of the subfamily Barbourofelinae.^[4] Originally, barbourofelids were considered members of the machairodont subfamily.^[5] However, this was called into question, and by the 1980s and 90s barbourofelids were considered to be nimravids instead of felids.^[6][7][8] In the 2000s, Morlo et al. (2004) argued that barbourofelids ranked as their own family, known as Barbourofelidae.^[9] This was also the prevailing view for barbourofelids during the 2010s,^[10][11][12] although some experts still considered them to be nimravids.^[2]

However, in the 2020s, majority of experts have begun reclassifying them as nimravids.^{[13][14][15][3][16][17]}

Evolution

Albanosmilus jourdani is believed to be the ancestor to the genus, which migrated into North America sometime during the Late Miocene.^[18] B. morrisi was the earliest species within the genus, probably from the result Albanosmilus migrating to North America and was likely ancestral to B. loveorum, which later evolved into B. fricki.^[2] The discovery B. piveteau suggests Barbourofelis reverse migrated back into Eurasia.^[19]

Description

Restoration of the head of B. fricki by Mauricio Antón

The type species, B. fricki, is thought to have been a lion-sized predator, having a weight comparable to an African lion, with limb bones indicating a muscular, robust body. Large individuals of B. fricki have been reconstructed with shoulder heights of around 90 cm (2 ft 11 in).^[20] In 2021, Barret estimated based on m1 length regression, B. fricki may have weighed up to 328 kg (723 lb), making it the largest nimravid.^[3] B. oregonensis was another large species, described to being similar in size and morphology to B. fricki, although it has some distinctions such as the absence of P4 and M1, as well as a more pronounced transverse.^[21]

However, B. morrisi was believed to have been closer to the size of a large leopard and 65 cm (2 ft 2 in), being intermediate in size between Sansanosmilus and B. fricki.^[22][20] B. loveorum was suggested to have been larger than B. morrisi.^[2] In a 2012 paper, Meachen estimated that B. loveorum may have weighed 70 kg (150 lb) on average.^[23] However, Orcutt and Calde estimated that based on articular width of the humerus, the species may have been larger, weighing between 87–128 kg (192–282 lb), with an average weight of 110 kg (240 lb).^[24] B. piveteaui is described to being similar in size to B. morrisi.^[19]

The genus had the longest canines of all the barbourofelids, which were also flattened, indicating a high degree of specialization to its diet. These canines had a longitudinal groove on the lateral surface that has been described as a means of allowing blood from a wound they have inflicted to flow away. This groove more likely was an adaptation to make the canines lighter while maintaining their strength. Other notable traits include the presence of a postorbital bar, the presence of a ventrally extended mental process (bony extensions on either side of the lower jaw), and the shortening of the skull behind the orbits, in addition to having a very robust constitution. The barbourofelids were probably very stocky in build, resembling a bear-like lion or lion-like bear. Based on its foot structure, species of Barbourofelis might have had a semi-plantigrade walking stance.^[20]

The most extensive selections of bones found for this genus come from B. loveorum and have allowed further inference to the proportions of other members of the genus.^[20]

Paleobiology

B. fricki skull

Growth and development

A 1988 study found that based on the analysis of the skulls and maxillary materials, Barbourofelis had delayed eruptions of deciduous upper canines, which suggests that Barbourofelis practiced a long period of parental care.^[7] Additionally, skeletons of juvenile Barbourofelis have been found, and examination of their skeletons indicates that the cubs would reach near-adult size before their milk sabers would begin to erupt. This indicates that they were dependent on their mother or potential family group until well into their second year, similar to that of modern lions. Such a long period of dependence would have likely led to situations in which near-adult cubs would have likely helped to restrain prey while their mother made the kill.^[20][25]

Social behavior

Barbourofelis was found to have large carnassial teeth, meant it was for efficiently processing a carcass and ate at a fast and competitive manner. This indicated it either lived in a highly competitive ecosystem or that it was social, or even a combination of both scenarios.^[26] In addition, experts argued due to the delayed eruption of their upper canines may have been further evidence of gregariousness in Barbourofelis.^[7][26][25] Although, some authors have suggested that Barbourofelis was a solitary ambush predator.^[27]

Predatory behavior

Forelimb analysis from a 2021 found that B. loveorum may have less constrained forelimb movement compared to the contemporary machairodont Nimravides galiani and extant felids. The increased mobility in the forelimbs suggests it relied on grappling prey and subduing prey, as an ambulatory ambush predator, that walked and trotted around the forest floor similar to ursids, wolverines, and badgers. It would’ve been opportunistic and attacked prey upon reach, and could’ve engaged in scavenging similar to wolverines due to their large carnassial teeth. In addition to possibly being able to climb, although it wouldn’t have been arboreal.^[28] A 2005 study found that the leopard-sized B. morrisi had a similar crural index to the lion-sized Smilodon fatalis, but had a lower brachial index than the machairodont and ambush predators, having an index score closer to that of ambulators. This suggests B. morrisi had the same leverage as Smilodon. In addition, B. loveroum and B. fricki were found to have even lower brachial and crural indexes than Smilodon, suggesting that barbourofelids possibly had a greater power output of the limbs than Smilodon.^[29] The robustness of the humerus suggests it could’ve taken on prey larger than itself.^[30]

B. loveorum mounted as if attacking Teleoceras

Previously, it has been suggested by Naples and Martin that B. fricki had a jaw gape of 115 degrees or greater.^[27] However, Lautenschlager et al. (2020) suggests a lower jaw gape for Barbourofelis. Their analysis suggests jaw gapes of 89.13°, 85.29°, and 65.68° for B. fricki, B. loveorum, and B. morrisi respectively.^{[31] Including supplementary materials}

Figueirido et al. (2024) study on the cranial biomechanics of B. fricki found based on m. masseter pars profunda, this species would’ve had a maximum jaw gape of 73 degrees and found little evidence to support jaw gapes of over 90 degrees. They also found that Barbourofelis skull was less stressed when it came to bilateral canine biting compared to Smilodon fatalis. When it came to stabbing, the skull of Barbourofelis were not as evenly distributed as Smilodon, with regional stresses mainly present in occipital and parietal bones, as well as the upper canines. With pulling-back, stress in Smilodon skull was more evenly distributed than Barbourofelis, with the stress of Barbourofelis being concentrated in the premaxilla, parietal-occipital region, postorbital bar, and canines. Despite having a stress resistant skull, the canines were found to be very weak when extrinsic forces are applied due to its sharp and flattened canines, so it would’ve been able to penetrate more easily than Smilodon. The authors argued, since Barbourofelis skull experiences less stress than Smilodon, it may have been more generalist in prey killing than Smilodon.^[32]

Brain anatomy

Despite its derived craniodental adaptations, Barbourofelis brain was similar to that of Oligocene nimravids.^[33] Compared to living felids, its brain its anterior lobes were more narrow and the highest point of the cerebrum was situated more caudally.^[34]

Paleoecology

B. loveorum's environment in the Love Bone Beds deposits (of Clarendonian Age) was a mixture of grassland, riverine forest, and marshes, in which it would have shared territory with herbivorous animals like the amphibious rhinoceros Teleoceras, the protoceratid Synthetoceras, the camel Aepycamelus, horses like Neohipparion and Nannippus, and carnivores like Nimravides, in addition to borophaginae canids such as Epicyon and Borophagus, and the bear Agriotherium.^[35] Forelimb morphology suggests B. loveorum and N. galiani weren’t competing with one another, but instead niche partitioned by preferring different habitats. The robust forelimbs of Barbourofelis suggests it preferred forested environments, while Nimravides preferred more open habitats. This is further supported by forest dwelling fauna such as tapirs, Prosthennops, Aepycamelus, and B. loveorum itself being unusually abundant in Love Bone Beds compared to Late Miocene sites. In addition, the shorter metacarpals of Barbourofelis suggested it hunted smaller prey than Nimravides.^[28]

During the following stage, the Hemphillian, B. fricki shared territory with the machairodont species Amphimachairodus coloradensis. Both genera of machairodont, as well as the bear Agriotherium and the dogs Epicyon and Borophagus would have presented competition to the barbourofelid, while any and all of the large animals present were potential prey species.^[35][36]

The extinction of Barbourofelis, is thought to have been due to faunal overturn in the Late Miocene, not competition with machairodonts.^[3][37]