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Simbakubwa
Simbakubwa
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Simbakubwa
Temporal range: Early Miocene (Aquitanian) 23.0–22.0 Ma
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Reconstructed skull of
Simbakubwa kutokaafrika
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: †Hyaenodonta
Superfamily: †Hyainailouroidea
Family: †Hyainailouridae
Subfamily: †Hyainailourinae
Genus: †Simbakubwa
Borths & Stevens, 2019
Type species
†Simbakubwa kutokaafrika
Borths & Stevens, 2019

Simbakubwa ("great lion" in Swahili) is an extinct genus of hyaenodonts belonging to the family Hyainailouridae that lived in Kenya during the Early Miocene. It was discovered between 1978 and 1981 near Meswa Bridge in western Kenya, and its remains, consisting of a lower jaw, part of the snout, and some of the smaller limb bones, were originally believed to come from hyena. After re-examination by Matthew Borths and Nancy Stevens, it was named and assigned to the hyaenodont lineage in 2019. One species of Simbakubwa, S. kutokaafrika, has been described.

Body mass estimates for Simbakuba vary considerably based on which method is used, with the smallest being about 280 kg (620 lb), and the largest being 1,308 and 1,554 kg (2,884 and 3,426 lb), which would surpass modern polar bears. Based on body mass alone it is the second-largest known hyainailourid, behind Megistotherium. Due to the fact that the type skull has been heavily restored, not much is known about its shape. As with other hyaenodonts, Simbakubwa's molars bore so-called carnassial blades. These would have sharpened as the animal opened and closed its jaw, forming a perpetual cutting edge. Though little is known of the hindlimb anatomy of Simbakubwa, it appears to have had a semi-digitigrade gait, in which the heel was held off the ground, though not as strongly as in true digitigrades. A similar gait is seen in Hyainailouros, whereas Kerberos is an example of the ancestral plantigrade (with the heel planted on the ground) condition. A semi-digitigrade or digitigrade stance is an efficient means of conserving energy and is often associated with an open environment.

The enormous body size of Simbakubwa may be the result of its lineage evolving to specialise in large prey, such as proboscideans (elephants and their relatives) and rhinoceroses. Its extinction, along with that of other giant hyainailourines, may have been a consequence of this specialisation, as large herbivores tend to breed slowly and even a temporary population decrease would significantly impact a hyainailourine's prey base. Furthermore, as solitary animals, they may have been repelled from carcasses by more social carnivorans, further decreasing the resources available to them.

Taxonomy

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Early history

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The first fossils of Simbakubwa, consisting of a mandible (lower jaw), a right upper maxilla (one of the bones of the upper jaw), a calcaneus, and two unguals (bones that would have supported claws), were discovered by palaeontologists searching for the remains of early apes at the Meswa Bridge site in western Kenya,[1] between 1978 and 1981.[2][3] They were stored at the Nairobi National Museum in Kenya, where they were initially labelled as belonging to hyenas. In 2013, Matthew Borths, a palaeontologist working on a dissertation on hyaenodonts, became aware of the specimens,[3] and immediately recognised them as belonging to a member of that clade.[4] In 2019, Borths, alongside Nancy Stevens, published a paper in which they described a new species based on these remains, which they gave the binomial name Simbakubwa kutokaafrika. The generic name, Simbakubwa, comes from the Swahili language simba ("lion"), and kubwa ("big"); the specific name kutokaafrika comes from the Swahili for "from Africa".[5] An additional specimen, consisting of a third molar from the Nakwai locality in northern Kenya, was assigned to Simbakubwa in 2020.[6]

Taxonomy

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Simbakubwa belongs to the hyaenodont family Hyainailouridae, and occupies a derived position in the subfamily, Hyainailourinae. In their 2019 paper describing it, Borths and Stevens conducted a phylogenetic analysis which recovered Simbakubwa as the sister taxon to a clade which includes a paraphyletic Hyainailouros, Isohyaenodon, Sivapterodon, and an unnamed taxon listed as the Arrisdrift hyainailourine.[5]

The cladogram below is based on the results recovered by Borths and Stevens:[5]

Hyainailourinae

Falcatodon schlosseri

Simbakubwa kutokaafrika

Hyainailouros sulzeri

Arrisdrift hyainailourine

Hyainailouros napakensis

Isohyaenodon andrewsi

Sivapterodon

Hyainailouros bugtiensis

Description

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Size

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Size comparison between S. kutokaafrika and a human

Different regression models produce a wide range of body mass estimates for Simbakubwa kutokaafrika. All of the ones implemented used the length of the third lower molar, though used different formulas for the corresponding body size calculations. The lowest estimate, was 280 kg (620 lb), based on an equation derived from the length of the third lower premolar in various mid-sized and large carnivorans; this would be comparable to the largest lions. The higher estimates, based on comparisons between the third molar lengths in hyaenodonts and felids, were 1,308 and 1,554 kg (2,884 and 3,426 lb), which would surpass the modern polar bear in size.[7] Hyainailourids possessed very large heads in proportion to their body size, and postcranial remains indicate that the similar sized Hyainailouros was about the size of a tiger, whereas the larger Megistotherium has been estimated to have reached a maximum weight of 500 kilograms (1,100 lb).[8] The Simbakubwa study, however, estimated the body mass of Megistotherium as having a lower estimate of 317 kg (699 lb), and higher estimates of 1,794–3,002 kg (3,955–6,618 lb). Whichever estimate is adopted, S. kutokaafrica eclipses every Palaeogene hyaenodont in body size.[5] Hyaenodonts did increase in size over the course of their evolution, though later taxa such as Simbakubwa took this to its greatest extent.[9]

Skull and dentition

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The skull of Simbakubwa is known from a partial maxilla and a left mandible. Much of what is known has been at least partly restored, making certain aspects of its morphology difficult to discern. Due to the relative incompleteness of Simbakubwa's mandible, and the fact that the distal (front, away from the midline) portion is reconstructed, it is not certain how long the mandibular symphysis was. The coronoid process appears to begin distally to the third molar, to be low and rounded, and to slightly recurve along the posterior (rear) edge, although the restoration of the fossil makes it difficult to determine whether this is actually the case. The masseteric fossa of the mandible to which the masseter muscle would have attached is bordered anteriorly (towards the front) by a thick coronoid ridge, and inferiorly (at the bottom) by a poorly defined ridge. The insertion points for the pterygoid muscles are well-defined.[5]

The left mandible known from Simbakubwa preserves three teeth: a canine, the fourth lower premolar, and the third lower molar. The lower canines were strongly compressed laterally (from side-to-side), more so than in Hemipsalodon, Kerberos, Orienspterodon, and Pterodon. The fourth premolar of Simbakubwa was relatively short, was more laterally compressed than that of Hyainailouros, and its talonid region bore a single laterally compressed cusp. All of Simbakubwa's molars had protocones which projected lingually (the inner side, towards the tongue), rather than mesially (towards the midline of the skull). The metastyles of the first and second upper molars were fairly gracile. The second upper molar bore multiple cusps on its parastyle. Unlike in Megistotherium, the trigonids of the fourth lower premolar and the third lower molar were strongly laterally compressed relative to their mesiodistal length. The molar protocones project lingually (inwards), rather than mesially (upwards). The parastyle of the second molar has multiple cusps, unlike in Hyainailouros. As with other large hyainailourids, Simbakubwa's molars bear so-called carnassial notches. The carnassial blades were rotated lingually, and would have been sharpened whenever it closed its jaw, thus ensuring a perpetual shearing edge.[5]

Postcranial skeleton

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Little is known of Simbakubwa's postcranial skeleton, besides a calcaneum and two ungual phalanges, the bones which would have sported claws in life. Based on what is known, Simbakubwa likely walked with a semi-digitigrade posture, walking primarily but not entirely on its digits. A digitigrade stance conserves energy and often correlates to an open habitat, and the stance of Simbakubwa, shared with Hyainailouros, would have been more efficient than the plantigrade stance of the related Kerberos.[5]

Palaeobiology

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In their paper describing Simbakubwa, Borths and Stevens suggested a correlation between large body size in hyainailourines and an increase in prey size. With the habitat changes brought on by the onset of the Miocene, there was an increase in the number of large herbivore taxa. Carnivorous mammals with a body mass above 25 kg (55 lb) frequently hunt prey with a mass equal to or greater than their own, and giant hyainailourines such as Simbakubwa were close in size to some of the anthracotheres, rhinocerotids and proboscideans which they shared their environment with. As such, the evolution of a large body size in hyainailurine (which appears to have evolved repeatedly, as both Simbakubwa and Megistotherium's closest relatives are far smaller)[9] may correlate with the exploitation of a niche which was otherwise unoccupied, that being the hunting and scavenging of large megafaunal herbivores.[5] Megistotherium, for example, was found by Robert J. G. Savage to have a large enough gape to engulf the limbs of certain proboscideans.[5][10] Being reliant on large mammalian prey presented issues, however, particularly in that they tend to have long generation times. As a result, even a slight drop in population size would have affected large, solitary hyainailourines disproportionately in relation to the smaller and more social carnivorans which they coexisted with. Despite them being able to fall back on scavenging (including osteophagy),[5][11] this behavioural dichotomy may have effected hyainailourines in other regards, as carnivorans that hunted in packs would have found it easier to steal kills. This, in turn, may have led to the former's extinction.[5]

References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Simbakubwa

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from Grokipedia
Simbakubwa is an extinct of gigantic hyaenodont in the Hyainailourinae, known from the early of and representing one of the largest terrestrial carnivores in mammalian history. The , Simbakubwa kutokaafrika, meaning "big from " in , lived approximately 22 million years ago and is estimated to have reached a body mass ranging from 280 to 1,500 kg (620–3,300 lb) depending on estimation method, potentially surpassing the size of modern . Fossils, including portions of the , , and postcranial , were discovered between 1978 and 1981 from the Meswa Formation at Meswa Bridge, identified in 2013, and formally described in 2019. As a , Simbakubwa featured specialized with deep notches, tall paracones fused to shorter metacones, lingually oriented molar protocones, gracile metastyles, and compressed canines, enabling it to slice through flesh efficiently like modern lions or , though it was unrelated to them. Its robust build suggests it was an in a forested , preying on large herbivores amid the ecological transition from to faunas in Afro-Arabia. Phylogenetically, Simbakubwa is the sister taxon to a clade including Hyainailouros and Megistotherium, supporting an origin of hyainailourines in Afro-Arabia followed by dispersal to Eurasia during the early Miocene. The genus provides critical insights into the evolution of large-bodied carnivorans before the rise of modern Carnivora families, highlighting how environmental shifts and prey instability contributed to the decline of such hyaenodonts by the late Miocene.

Taxonomy and Naming

Classification

Simbakubwa is classified within the extinct order , family Hyainailouridae, and subfamily Hyainailourinae, as an early representative from . This placement follows cladistic analyses that elevated Hyainailourinae to familial status within , distinguishing it from other hyaenodontid subfamilies based on shared derived cranial and dental traits. Key diagnostic features of Simbakubwa include robust (m1 and m2) with lingually oriented protocones and gracile metastyles, enlarged and buccolingually compressed canines suited for piercing, and sectorial premolars (particularly p4) with a shearing talonid adapted for processing flesh and bone. These characteristics align it closely with other hyainailourines while differentiating it from smaller or more generalized hyaenodonts through its emphasis on hypercarnivory. In evolutionary context, Simbakubwa represents part of the African radiation of hyaenodonts that originated in Afro-Arabia during the late early , diverging from earlier forms amid ecological shifts to drier habitats and larger faunas. Phylogenetic analyses recover Simbakubwa as the sister to a clade of large-bodied hyainailourines, including genera such as Megistotherium and , supporting an Afro-Arabian cradle for the subfamily before dispersals to . Prior to its formal description, some researchers suggested referring the material to napakensis, but the 2019 analysis established Simbakubwa as a distinct based on unique dental morphology.

The name Simbakubwa is derived from the words simba, meaning "," and kubwa, meaning "big," translating to "big " and reflecting the animal's status as an in early Miocene . The species epithet kutokaafrika also draws from , combining kutoka ("from") and Afrika (""), to honor the fossil's discovery in and emphasize its African origins. This nomenclature was proposed by paleontologists Matthew R. Borths and Nancy J. Stevens in their 2019 description of the . By incorporating Swahili, a of , the name evokes the region's rich wildlife heritage and celebrates the continent's paleontological contributions, while clarifying that Simbakubwa—a hyaenodont rather than a true felid—bears no close relation to modern lions despite the evocative terminology.

Discovery and Description

Fossil Evidence

The fossils of Simbakubwa kutokaafrika were first discovered during field expeditions in the late 1970s and early 1980s at the Meswa Bridge locality in western , near . These specimens were collected by teams including local Kenyans and international researchers focused primarily on early hominoid , leading to their placement in the collections of the in without immediate study. For nearly four decades, the material languished undescribed in museum drawers, initially overlooked due to misidentification as remains of a smaller hyaenodont species rather than a gigantic form. In 2013, paleontologist Matthew R. Borths examined the specimens during research for his dissertation on hyaenodonts at the , recognizing their significance as belonging to a large hyaenodont. Collaborating with Nancy J. Stevens, they formally described Simbakubwa kutokaafrika as a new and in the Journal of Vertebrate Paleontology. The , KNM-ME 20A, consists of a fragmentary left dentary preserving the canine, p4, m3, and alveoli for p3, m1, and m2, while referred material includes KNM-ME 20B, a right with P3–M2, alongside isolated teeth and dentary fragments such as KNM-ME 12 (right lower canine) and KNM-ME 13 (partial left dentary with m2). These remains represent a single individual, likely a , and provide the primary evidence for the . The fossils originate from early Miocene sediments at Meswa Bridge, correlated to the stage and dated to approximately 23–22 million years ago based on faunal associations and regional . This locality, part of the valley system, yields a diverse assemblage of early Miocene vertebrates, though the Simbakubwa material was preserved in fluvial sandstones indicative of a wooded . An additional isolated molar from the Nakwai Locality 1 in West Turkana, in the Nakwai Formation and similarly dated to the early Miocene, was later referred to Simbakubwa in 2020, extending the known geographic range.

Physical Characteristics

Simbakubwa exhibited a robust cranial structure with an elongated estimated at approximately 60 cm in length, characterized by a deep measuring about 40 cm. The upper canines were particularly massive, reaching lengths of up to 10 cm, providing formidable piercing capabilities, while the lower canines measured around 4.3 cm in mesiodistal length and 2.8 cm buccolingually. The teeth, including the upper fourth (P4) and lower first molar (m1), featured blade-like shearing edges with deep notches, adapted for slicing flesh and crushing bone. The comprised 44 teeth in a primitive placental arrangement, including three incisors, one canine, three premolars, and three molars per quadrant, reflecting a hypercarnivorous specialization. The molars were low-crowned and robust, with upper molars displaying lingually oriented protocones and gracile metastyles, and lower molars featuring reduced talonids lacking metaconids. Enamel thickness was notable, exhibiting crenulation on buccal and lingual surfaces along with zigzag Hunter-Schreger bands, structural features indicative of durophagous feeding involving bone processing. Body mass estimates for Simbakubwa derive primarily from regressions applied to tooth dimensions. The 2019 description reported values of 1,308 kg using Morlo's (1999) equation for average molar length and 1,554 kg based on Van Valkenburgh's (1990) felid-specific model for the lower third molar (m3), suggesting a gigantic predator comparable to or exceeding the . An alternative regression from Van Valkenburgh (1990) for carnivorans over 100 kg yielded a lower 280 kg, highlighting methodological variability; the higher figures were favored given the fossil's scale. Limited postcranial fossils, including a wedge-shaped calcaneum with a short and rounded sustentacular facet, along with broad, bifurcated ungual phalanges, suggest a robust, terrestrial build akin to large ursids but with adaptations for semidigitigrade locomotion and powerful leaps. These features imply an overall body length of 3–4 m and shoulder height of 1.2–1.5 m, supported by a relatively longer tail than in modern bears.

Paleobiology and Paleoecology

Diet and Predatory Behavior

Simbakubwa kutokaafrika exhibited a hypercarnivorous diet, characterized by dental adaptations specialized for processing large quantities of flesh from prey. Its featured buccolingually compressed canines and deep notches on the molars, enabling efficient shearing and slicing of , with reduced talonids and absent metaconids further emphasizing a reliance on animal tissue over matter. This morphology suggests it primarily targeted large herbivores, such as anthracotheres (early relatives of ) and small proboscideans, which were among the biggest available prey in its ecosystem around 22 million years ago. As an in early Afro-Arabian landscapes, Simbakubwa likely employed both active hunting and scavenging strategies to exploit its niche, leveraging its massive body size—estimated at up to 1,500 kg—to overpower or access carcasses of herbivores that smaller could not handle. Its robust and elongated metastyles on the upper molars indicate capabilities for piercing and tearing, though the relatively gracile build of its suggests it was less specialized for extensive bone-crushing compared to later hyainailourines. This predatory role positioned it as the dominant , potentially competing with giant crocodylians for access to large vertebrate remains in fragmented forest environments. While direct ontogenetic data are limited, the ' size and solitary suggest adults operated as dominant individuals, possibly shifting from more opportunistic scavenging in juveniles to targeted predation in maturity, though evidence remains indirect from fossil morphology. Contemporaneous such as anthracotheres and Phiomia likely formed part of its prey base, underscoring its role atop the .

Habitat and Contemporaries

Simbakubwa kutokaafrika inhabited the proto-East African landscape during the earliest , approximately 22 million years ago, in what is now western . The Tonde Bridge locality (formerly known as Meswa Bridge), where its fossils were found, is situated within the Muhoroni Agglomerate Formation, preserving evidence of fluvio-lacustrine environments that supported heterogeneous habitats ranging from dense forests to wooded savannas and riparian woodlands. This subtropical setting featured seasonal rainfall patterns, with pollen and faunal assemblages indicating a mix of closed-canopy forests along watercourses and more open, grassy woodlands influenced by the emerging System, which promoted drier conditions over time. In this environment, Simbakubwa coexisted with a diverse assemblage of early mammals, including basal proboscideans such as Phiomia, semi-aquatic anthracotheres, and smaller mesocarnivores like early viverrid carnivorans, as well as (e.g., ) and macroscelideans. These contemporaries reflect an Afro-Arabian fauna adapted to mixed woodland settings, with herbivores like Phiomia and anthracotheres providing potential prey in and niches, while smaller carnivores occupied lower trophic levels without direct competition for apex predation. Giant crocodylians may have posed indirect competition in aquatic habitats, preying on similar large herbivores near rivers and lakes. As the largest known of its time in Africa, with an estimated body mass exceeding 1,300 kg, Simbakubwa occupied the top predator niche, filling a role later dominated by radiating felids in the middle ; its size likely minimized overlap with smaller carnivorans. This positioning highlights its adaptation to exploit large-bodied herbivores in a landscape undergoing and habitat mosaicking. Simbakubwa's occurrence aligns with the "Proboscidean Event," an early faunal turnover marked by the radiation and dispersal of proboscideans from to around 19–17.5 million years ago, which influenced broader diversification by altering communities and dynamics across Afro-Arabia. This event contributed to the temporary dominance of gigantic hyaenodonts like Simbakubwa before the rise of modern families in African ecosystems.
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