Brevirostres
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The Brevirostres are a large taxon of the crocodile crown group (Crocodylia), in which the real crocodiles (Crocodylidae) and the alligators (Alligatoridae) as a sister group of the Gavial (Gavialidae) are united. The results of relationship analyzes based on molecular data do not support the existence of such a group constellation.
etymology
The name “Brevirostres” is derived from the Latin words brevis (“short”) and rostrum (“beak”, “snout”) and means something like “short-snouted crocodile”. It was coined by the German paleontologist Karl Alfred von Zittel in a volume of his compendium Handbuch der Palaeontologie from 1890.
Taxonomic history and definition
Under the name “Brevirostres” in Zittel's phenetically oriented system, various recent and fossil groups of relatively short and broad-nosed crocodylomorphic archosaurs were subsumed. In addition to crocodylids and alligatorids, the group also included the atoposaurids and goniopholids from the Jurassic and the Cretaceous , which are now considered to be more distant relatives of modern crocodiles. The Brevirostres were compared to the "Longirostres", in which different groups of long and narrow-nosed crocodylomorphic archosaurs from the Mesozoic , u. a. the Metriorhynchids with which the Gavialids were united.
The taxon Brevirostres subsequently experienced little reception and was largely forgotten. It was not until 1997 that it was "revived" as part of a cladistic analysis of the relationships between fossil and recent crocodiles as the name for a clade that includes the crocodylids and alligatorids together with their closest relatives, excluding the gavialids. The exact, cladistic-knot-based redefinition of the taxon reads: " Last common ancestor of the Crocodylidae and Alligatoridae and all their descendants".
features
The characteristic that gives the Brevirostres their name is their relatively short and wide snout. Crocodiles with such a snout shape are generally called brevirostrin , regardless of their taxonomy . A prime example of brevirostrine crocodiles are the real alligators (Alligatorinae). However, the Brevirostres also include representatives with less broad and short ( mesorostrinen ), even with relatively long and narrow ( stenorostrinen ) snouts. In fact, for a crocodile taxon to belong to the Brevirostres, according to modern definition, it is not necessarily the formation of the snout, but other, less obvious features of the anatomy or bone structure (osteology) that are decisive. These relatively special unique selling points ( apomorphies ) include a. that the proximal end of the crista deltopectoralis , a bony outgrowth of the humerus, which serves as the attachment region for the chest and shoulder muscles, rises abruptly from the proximal end of the bone and is concave and that the rear edge of the suborbital window, the large opening in the bottom of the eye socket, has a notch.
Systematics
The taxon Brevirostres according to modern, cladistic definition comprises the majority of the crocodile crown group (Crocodylia), i. H. the majority of the group that goes back to the common ancestor of all recent crocodiles. Sister group of the Brevirostres are the Gaviale with their distinctly long and narrow-snouted (longirostrinen) recent representative, the Gharial ( Gavialis gangeticus ).
The Brevirostres are based exclusively on morphological (anatomical, osteological) features and although the Sundagavial Tomistoma schlegelii is a longirostrine species, due to the other morphological features it is part of the real crocodiles (Crocodylidae) and is therefore a representative of the Brevirostres. The following, simplified cladogram (after Brochu, 1997, 1999, 2003) shows this relationship hypothesis:
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The close relationship of the Sundagavial to the real crocodiles and the alligators was already a widespread belief before the redefinition of the Brevirostres. However, part of the research community has long favored a close relationship between the Sundagavial and the Gangesgavial and thus an assignment to the Gavialidae family. With the advent of molecular genetic methods for determining relationships in the 1980s, the evidence supporting the latter hypothesis increased. Meanwhile, a sister group relationship between Gangesgavial and Sundagavial within the recent crocodiles is considered relatively secure. In addition, the molecular data suggest that the gavials are not the sister group of a common clade of crocodylids and alligatorids, but that the gavialids are more closely related to the crocodylids than to the alligatorids.
The consequence of the latter aspect of this hypothesis presented in the cladogram below (according to Oaks, 2011) would be that the Brevirostres, according to the definition of the taxon, are a younger synonym of the Crocodylia and thus no longer have any meaning for the systematics of the crocodiles.
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Individual evidence
- ^ A b Karl Alfred von Zittel: Handbuch der Palaeontologie. I. Department: Palaeozoology , III. Volume: Vertebrata (Pisces, Amphibia, Reptilia, Aves) , published by R. Oldenbourg, Munich and Leipzig 1890, doi : 10.5962 / bhl.title.61419 , p. 633 ff.
- ^ A b Christopher A. Brochu: A review of " Leidyosuchus " (Crocodyliformes, Eusuchia) from the Cretaceous through Eocene of North America. Journal of Vertebrate Paleontology. Vol. 17, No. 4, 1997, pp. 679-697, doi : 10.1080 / 02724634.1997.10011017 (alternatively: JSTOR 4523857 )
- ↑ a b c d Christopher A. Brochu: Phylogenetics, Taxonomy, and Historical Biogeography of Alligatoroidea. Society of Vertebrate Paleontology Memoir. Vol. 6 (Journal of Vertebrate Paleontology, Vol. 19, Supplementum No. 2), 1999, pp. 9-100, doi : 10.1080 / 02724634.1999.10011201
- ↑ Christopher A. Brochu: Phylogenetic Approaches Toward Crocodylian History. Annual Review of Earth and Planetary Sciences. Vol. 31, 2003, pp. 357-397, doi : 10.1146 / annurev.earth.31.100901.141308
- ↑ For a brief overview, see Ralph E. Molnar: Biogeography and Phylogeny of the Crocodylia . In: CG Glasby, GJB Ross, PL Beesley (Eds.): Fauna of Australia. Volume 2A: Amphibia and Reptilia. AGPS Canberra, 1993, PDF
- ↑ Llewellyn D. Densmore III, Robert D. Owen: Molecular Systematics of the Order Crocodilia. American Zoologist. Vol. 29, No. 3, 1989, pp. 831-841, doi : 10.1093 / icb / 29.3.831
- ↑ John Gatesy, George D. Amato: Sequence Similarity of 12S Ribosomal Segment of Mitochondrial DNAs of Gharial and False Gharial. Copeia. Jhrg. 1992, No. 1, 1992, pp. 241-243, doi : 10.2307 / 1446560
- ↑ RK Aggarwal, KC Majumdar, JW Lang, L. Singh: Generic affinities among crocodilians as revealed by DNA fingerprinting with a Bkm-derived probe. PNAS. Vol. 91, No. 22, 1994, pp. 10601-10605, PMC 45069 (free full text)
- ↑ John Harshman, Christopher J. Huddleston, Jonathan P. Bollback, Thomas J. Parsons, Michael J. Braun: True and false gharials: a nuclear gene phylogeny of crocodylia. Systematic Biology. Vol. 52, No. 3, 2003, pp. 386-402, doi : 10.1080 / 10635150390197028
- ↑ Axel Janke, Anette Gullberg, Sandrine Hughes, Ramesh K. Aggarwal, Ulfur Arnason: Mitogenomic Analyzes Place the Gharial ( Gavialis gangeticus ) on the Crocodile Tree and Provide Pre-K / T Divergence Times for Most Crocodilians. Journal of Molecular Evolution. Vol. 61, No. 5, 2005, pp. 620–626, doi : 10.1007 / s00239-004-0336-9 (free full text: Researchgate )
- ↑ Ray E. Willis, L. Rex McAliley, Erika D. Neeley, Llewellyn D. Densmore III: Evidence for placing the false gharial ( Tomistoma schlegelii ) into the family Gavialidae: Inferences from nuclear gene sequences. Molecular Phylogenetics and Evolution. Vol. 43, No. 3, 2007, pp. 787-794, doi : 10.1016 / j.ympev.2007.02.005
- ↑ Ray E. Willis: Transthyretin Gene (TTR) Intron One Elucidates Crocodylian Relationships. Molecular Phylogenetics and Evolution. Vol. 53, No. 3, 2009, pp. 1049-1054, PMC 2787865 (free full text)
- ↑ a b c Jamie R. Oaks: A time-calibrated species tree of Crocodylia reveals a recent radiation of the true crocodiles. Evolution. Vol. 65, No. 11, 2011, pp. 3285-3297, doi : 10.1111 / j.1558-5646.2011.01373.x