Bonisicyon
Bonisicyon | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Family: | †Amphicyonidae |
Subfamily: | †Amphicyoninae |
Genus: | †Bonisicyon Werdelin and Simpson, 2009 |
Type species | |
†Bonisicyon illacabo Werdelin and Simpson, 2009
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Bonisicyon is an extinct genus of carnivoran mammals, belonging to the family Amphicyonidae ("bear dogs"). It is the last-surviving member of its family, living in East Africa during the end of the Miocene epoch. Known only from a damaged mandible and isolated teeth from the Nawata Formation, and possibly also the Lukeino Formation, its closer taxonomic affinities are unclear. It is notable for both its small size, and its unique dentition.[1]
History and naming
The first published material belonging to this genus includes a broken mandibular ramus with a damaged m1 and alveoli for m2 and m3, as well as roots for p4, from the Upper Nawata Formation in Lothagam, Kenya.[2] Bonisicyon was described on basis of material found at Gona, Ethiopia, with a right m1 (HMD1/P11) serving as holotype. Other described material includes an isolated left m2 and a damaged right M2. A M1 from Lemudong’o, Kenya, originally referred to the ailurid Simocyon, has also been tentatively attributed to the genus.[1] A P4 discovered at the Kenyan Lukeino Formation has also been proposed to belong to an amphicyonid, as both its age and dimensions are similar to Bonisicyon.[3]
The genus is named in honour of Dr Louis de Bonis, whereas illacabo is the Afar word for (as in "the end of the story").[1]
Description
Bonisicyon is a rather small amphicyonid. Its body mass has been estimated at 33 kg based on tooth size, though this is likely an overestimation. The relatively slender mandible, and similarities in tooth size to a coyote, suggest that its mass was closer to 20 kg than 30 kg.[4]
The robust m1 is relatively wide at the base of its crown, and possesses an entirely mesiodistal carnassial shear. The tall hypoconid is formed into an elongated crest, and is effectively part of the carnassial shear, only separated from the trigonid by a narrow postvallid notch, which is morphologically similar to the carnassial notch. The trigonid consists of a well-developed paraconid and protoconid, and a reduced metaconid, which is only evidenced as a bulge on the lingual side of the protoconid. The almost entirely mesiodistal carnassial shear only has a very slight angle between paraconid and protoconid. All these features suggest that Bonisicyon was a hypercarnivore. However, it lacks several features usually associated with such a diet, such as taller trigonid cuspids and a shortened talonid. Indeed, the trigonid is relatively short and its cuspids blunt. Therefore, its dentition possesses a peculiar mix of hypercarnivorous and mesocarnivorous features, although the narrowness of the tooth means it lacks a proper crushing basin, therefore pointing towards hypercarnivory.[1][4]
Other notable features include the paraconid, which is much lower and mesodistally shorter than the tall
The m1 of Bonisicyon shares several features with that of Afrocyon, such as the relatively short talonid and reduced metaconid. However, Afrocyon differs in its very tall and relatively transversely thin mandibular ramus and elongated m2. Bonisicyon lacks the peculiar m1 of Myacyon dojambir, and numerous features differentiate it from the similarly sized ?M. peignei. Among these are its taller, more bulbous, but less trenchant paraconid, lower and blunter protoconid and reduced metaconid. In both size and shape, it is most similar to Cynelos/Hecubides euryodon. Their M1 is almost indistinguishable, and their m2 are very similar, although C. euryodon has a less developed metaconid and a more cusp-like hypoconid. Their m1 too shares many similarities, although most of these are shared, primitive characteristics. In comparison, Bonisicyon possesses a much more developed hypoconid and paraconid, a reduced metaconid and a distinct, sharp notch between protoconid and hypoconid.
Classification
By the Late Miocene, the diversity of the Amphicyonidae was decreasing, likely as a result of the
Palaeoecology
The Upper Nawata, where the first fossils of Bonisicyon were found, was likely covered by a mixed, although rather open, environment.[1] During this time period, a dry interval led to floodplain vegetation changing from tree savanna to dry or thornbush savanna.[12] As all localities where remains of Bonisicyon were discovered were covered by such habitat, it has been suggested that may have successfully adapted to these new environments, unlike its larger relatives. If that was the case, competition with Eucyon (a medium-sized canid arriving in Africa around this time in Africa), which was better adapted to these environments, may have resulted in the extinction of this amphicyonid. However, more evidence, and especially postcranial remains, are needed to confirm this speculation.[1]
At Lothagam, Bonisicyon shared its habitat with several other carnivorans, such as the machairodontines Lokotunjailurus and Dinofelis, the mustelid Erokomellivora and the hyaena Ictitherium, with which it may have competed for food.[4] Among the small to medium-sized mammals on which it may have preyed are primates, like Parapapio, the aardvark Leptorycteropus, the tiny suid Cainochoerus as well as various rodents. Larger herbivores are represented by various proboscidean, among them Stegotetrabelodon, Anancus and Deinotherium, the hippopotamus Hexaprotodon, rhinos such as Brachypotherium and Ceratotherium, the equid Eurygnathohippus, the giraffe Palaeotragus, the suid Nyanzochoerus and a variety of bovids, including Aepyceros, Tragoportax, Kobus and Hippotragus.[12]
References
- ^ S2CID 73677723.
- ISBN 978-0-231-50760-8, retrieved 2023-02-27
- ^ ISSN 1698-6180.
- ^ a b c Otto, Oksanen (2017). Feeding ecology of Lothagam and Koobi Fora fossil carnivorans (Thesis). University of Helsinki.
- ISSN 0016-6995.
- ^ Hunt, Robert (1998-01-01). "Amphicyonidae". Mammalogy Papers: University of Nebraska State Museum.
- ISSN 0031-0182.
- ^ Morales, J.; Brewer, P.; Pickford, M. (March 2010). "Carnivores (Creodonta and Carnivora) from the basal middle Miocene of Gebel Zelten, Libya, with a note on a large amphicyonid from the middle Miocene of Ngorora, Kenya". Bulletin of the Tethys Geological Society. 5: 43–54 – via ResearchGate.
- S2CID 134929306.
- S2CID 253346978.
- S2CID 128757418.
- ^ ISBN 978-0-231-11870-5.
- PMID 35726261.
- ^ Morales, Jorge; Pickford, Martin (2022). "The taxonomic status of "Ysengrinia" ginsburgi Morales et al. 1998 (Amphicyonidae, Carnivora) from the basal middle Miocene of Arrisdrift, Namibia" (PDF). Communications of the Geological Survey of Namibia. 24: 1–16 – via Google Scholar.