Baru huberi
| "Baru" huberi Temporal range: Late Oligocene,
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| The holotype skull of "Baru" huberi | |
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| Species: | "Baru" huberi Willis, 1997
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"Baru" huberi is a species of mekosuchine Crocodilian from the Miocene of Australia. Although initially named as a member of the genus Baru, both phylogenetic analysis and additional discoveries of related forms have shown that this species belonged to a distinct mekosuchine lineage more closely related to Mekosuchus and Trilophosuchus. Consequently, several researchers have argued that it should be placed in its own genus, which has yet to be named.
"Baru" huberi was a broad-headed semi-aquatic crocodilian resembling true species of Baru. In addition to some more subtle anatomical features, it was much smaller than either Baru darrowi or Baru wickeni.
History and naming
All remains of "Baru" huberi have been collected from the White Hunter Site of the Riversleigh World Heritage Area, which dates to the Late Oligocene.[1] The fossil material includes an incomplete rostrum (holotype QM F31060), as well as several other isolated skull and lower jaw remains. The material was first described by Paul Willis in 1997, who named the species alongside Baru wickeni as well as new species of Quinkana and Mekosuchus.[2] Although Willis described it as a species of Baru, later research has increasingly shown that the two were not related. This includes both the genus revision of Baru published by Adam M. Yates in 2017[3] as well as multiple phylogenetic analysis conducted in 2018,[4] 2021[5] and 2023.[6] Although the distinctive nature of "Baru" huberi is now well recognized, it is yet to be given its own genus name.
"Baru" huberi was named for a Professor Huber, who was employed as rector at the University of Bonn, Germany.[2]
Description
Like Baru, the skull of "Baru" huberi was flat and broad, although Willis notes that it was not nearly as broad as in either Baru darrowi or Baru wickeni. Juvenile "Baru" huberi began life with five teeth in each premaxilla, however, as the animal ages the second tooth becomes gradually reduced until it is lost in adult individuals. The maxillae contain 14 teeth on each side, which is one pair more than in true species of Baru. The teeth are laterally compressed and have smooth cutting edges, carinae, which lack serrations, an ancestral trait shared by Baru wickeni, but not Baru darrowi. Similarly, in both "Baru" huberi and Baru wickeni, the paired nasal bones reach until the external opening of the nares, whereas in Baru darrowi this is not the case.[2]
Dentary material of "Baru" huberi is assigned to this species on a variety of factors. The dentaries described by Willis do not fit any of the other crocodilians from the White Hunter Site, but their size and proportions would be a match for "Baru" huberi. Furthermore, Willis notes that one dentary in particular is a perfect fit for the holotype rostrum. The first teeth of the lower jaw neatly slide into a pair of occlusal pits located in the underside of the premaxilla, however, while these pits are deep they do not pierce the upper surface of the skull. As in many crocodilians, the fourth teeth of the lower jaw are notably enlarged and slide into the notches located near the contact between premaxilla and maxilla. The mandibular symphysis, the region where the two halves of the dentary meet to form the front of the lower jaw, is shorter than in Baru, only extending until the 5th dentary tooth.[2]
"Baru" huberi was much smaller than the other two species typically included in Baru,[3][2] with estimates indicating a length of around 1.5 m (4 ft 11 in).[7]
Phylogeny
Phylogenetic analysis have repeatedly shown that "Baru" huberi does not group with the other species of Baru, those being B. darrowi and B. wickeni. In Lee and Yates (2017), "Baru" huberi was recovered as being closely related to the Bullock Creek taxon, with which it forms a clade that sits at the base of the group including traditionally terrestrial forms like Trilophosuchus, Quinkana and Mekosuchus. The other Baru species meanwhile occupy a different branch within Mekosuchinae, with Lee and Yates finding them to be allied to Pallimnarchus (now Paludirex) and Kalthifrons, both of which are considered to have been more semi-aquatic forms. A later study from 2023 found similar results, showing derived mekosuchines split into two lineages. One containing Paludirex, the accepted species of Baru and Quinkana, whereas the other contains "Baru" huberi and the many dwarf and island forms.[4][6]
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These results confirm Yates' suggestion that "Baru" huberi should be treated as a distinct genus, as otherwise Baru would be a polyphyletic genus within Mekosuchinae.
Paleobiology
"Baru" huberi was found at the Whitehunter Site in the Riversleigh World Heritage Area. The White Hunter Site is well known for its diverse crocodilian fauna, which besides "Baru" huberi also included Mekosuchus whitehunterensis, Quinkana meboldi and Baru wickeni. While Mekosuchus and Quinkana are two possibly terrestrial animals and thus not in competition with the more semi-aquatic forms, "Baru" huberi and Baru wickeni are thought to have been much more similar in niche. Both are believed to have been semi-aquatic generalists due to their broad, platyrostral skulls. One possible explanation for the two morphologically similar species being able to coexist is the great difference in size, with the smaller "Baru" huberi evading the larger crocodilians of its ecosystem. Although the idea that the fossils of the White Hunter Site only came together due to transportation after death (thanatocoenosis) has been suggested, the local mammal fauna seems to suggest that the animals of the site were in fact truly sympatric.[2]
References
- ^ a b "†Baru huberi Willis 1997 (crocodile)". Fossilworks.
- ^ a b c d e f Willis, P.M.A. (1997). "New crocodilians from the late Oligocene White Hunter Site, Riversleigh, northwestern Queensland". Memoirs of the Queensland Museum. 41: 423–438. ISSN 0079-8835.
- ^ a b Yates, A.M. (2017). "The biochronology and palaeobiogeography of Baru (Crocodylia: Mekosuchinae) based on new specimens from the Northern Territory and Queensland, Australia". PeerJ. 5.
- ^ a b Michael S. Y. Lee; Adam M. Yates (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". Proceedings of the Royal Society B. 285 (1881). doi:10.1098/rspb.2018.1071. PMC 6030529. PMID 30051855.
- ^ Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ. 9: e12094. doi:10.7717/peerj.12094. PMC 8428266. PMID 34567843.
- ^ a b Ristevski, J.; Willis, P.M.A.; Yates, A.M.; White, M.A.; Hart, L.J.; Stein, M.D.; Price, G.J.; Salisbury, S.W. (2023). "Migrations, diversifications and extinctions: the evolutionary history of crocodyliforms in Australasia". Alcheringa: An Australasian Journal of Palaeontology: 1–46. doi:10.1080/03115518.2023.2201319. S2CID 258878554.
- ^ Wroe, S. (2002). "A review of terrestrial mammalian and reptilian carnivore ecology in Australian fossil faunas, and factors influencing their diversity: the myth of reptilian domination and its broader ramifications". Australian Journal of Zoology. 50 (1). doi:10.1071/zo01053.