Silvabestius
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Silvabestius is an extinct genus of marsupials from the group of Zygomaturinae within the Diprotodontoidea . The genus is occupied with at least two species from the late Oligocene of Australia .
Etymology and history of research
The generic name Silvabestius is derived from the Latin " silva " ("forest") and " bestia " ("animal", "wild animal", "beast") and can most easily be translated as "forest animal".
All previously known fossil record of the genus come from the Süßwasserkalken the Riversleigh - fossil deposit in northwest Queensland . As early as 1967, a fragment of the upper jaw from the Riversleigh site "Site D" was initially described as a representative of the Palorchestidae that could not be identified . The fossil was interpreted in 1993 on the basis of new comparative material as an ancient representative of the Zygomaturinae.
In 1989 two well-preserved skulls of an ancient representative of the Zygomaturinae were recovered from the Riversleigh discovery site "VIP Site" and in 1992 another well-preserved skull followed from the Riversleigh discovery site "Hiatus Site" with similar features. The new finds were described in 1997 by Black and Michael Archer as the new genus Silvabestius .
The two skulls of the VIP local fauna have been described as a type of the genus, Silvabestius johnnilandi . The Artzusatz " johnnilandi " honors John Niland , Vice-Chancellor of the University of New South Wales for his support of excavation in Riversleigh. The skull of the local hiatus fauna has been described in a separate species, Silvabestius michaelbirti . The additional species " michaelbirti " honors Michael Birt , Niland's predecessor as Vice-Chancellor of the University of New South Wales, who not only supported the excavation work in Riversleigh, but was also involved in it. The upper jaw fragment from "Site D" was also assigned to the new genus by the first descriptors , but not to a specific species ( Silvabestius sp. ).
features
The genus Silvabestius is characterized in particular by the special shape of the third upper premolar ( P 3 ) as a representative of the Zygomaturinae. The crown of this tooth shows an additional cusp (parastyle) in the anterior area and somewhat separated from the rest of the P 3 tooth crown. This characteristic, typical for all Zygomaturinae, is only weakly developed in Silvabestius .
Silvabestius differs from all other representatives of the Zygomaturinae, with the exception of Neohelos , by the presence of canine teeth in the upper jaw and some other features of the dentition that do not occur in this combination in any other genus of the Zygomaturinae.
species
Silvabestius johnnilandi Black & Archer , 1997 (type species)
The type species of the genus is documented by two specimens. The holotype (QMF30504) is the almost complete skull including the lower jaw of a young animal. The paratype (QMF30505) is also a largely complete skull of an adult specimen. The length of the skull of the paratype suggests that the adult animal was about the size of a sheep .
The alveoli of the upper canines are located just behind the suture between the premaxilla and maxilla . The premolar P 3 is four-humped with a small but distinct parastyle.
Silvabestius michaelbirti Black & Archer , 1997
The second described species of the genus is occupied by a single, relatively complete skull. S. michaelbirti became significantly smaller than S. johnnilandi .
The upper canines are right next to the suture between the premaxilla and maxilla. The premolar P 3 has three cusps and the poorly developed parastyle hardly stands out from the rest of the crown.
Systematics
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| Internal systematics of the Zygomaturinae according to Black & Mackness, 1999. |
The adjacent cladogram shows the systematic position of Silvabestius within the Zygomaturinae according to Black & Mackness , 1999.
The assignment of the genus Raemeotherium to the Zygomaturinae is not entirely certain, since the form of the decisive third upper premolar in this genus is still unknown. Accordingly, the species of the genus Silvabestius are considered to be the oldest and most primeval representatives of the Zygomaturinae
Paleecology
Like all representatives of the Zygomaturinae, Silvabestius was probably a leaf eater.
The fossil records of the genus Silvabestius come from three different sites of the Riversleigh fossil deposit, but all of which can be assigned to their "Faun Zone A". The "Faun Zone A" within the Riversleigh fossil deposit is assigned an Upper Oligocene age on the basis of faunal comparisons with better dated fossil sites. A lake in a tropical rainforest was originally assumed to be the depository for the freshwater limestone of “Faunezone A” (= “System A” of the older classification according to Archer et al. , 1989).
However, an analysis of the plant remains from another site (“Dunsinane Site”), which is also assigned to “Faunezone A”, paints a different picture. The plant fossils come from representatives of the silver tree family , casuarina family , myrtle family , soap tree family and possibly also the Australheide family . Leaf remnants from the site all show wide leaf shapes with serrated leaf margins and some wood remnants show clear growth rings. Both features are atypical for tropical rainforests. According to Guerin & Hill , 2006, the relatively low-species paleoflora speaks for open hardwood trees dominated by casuarina plants , interspersed with deciduous lianas and not for a tropical rainforest with a closed canopy.
In 2009, Travouillon and co-authors came to a similar finding when evaluating the cenograms of the individual fauna zones of Riversleigh. In a cenogram, the estimated maximum body mass of all mammal species in a biotope is plotted logarithmically against the number of mammal species in the biotope, in descending order of magnitude. Conclusions about the character of the living space can be drawn from the resulting distribution pattern. The cenograms of the Upper Oligocene "Faunezone A" are also interpreted as an indication of open forests without a closed canopy.
The holotype of Silvabestius johnnilandi (QMF30504) shows some signs that the young was still suckled by its mother. The paratype (QMF30505) comes from the same site and was found less than 1 m from the holotype. The left upper incisor LI 3 of the paratype was found immediately next to the tip of the snout of the young animal. The circumstances of the find are interpreted as meaning that a mother and the young she suckled, practically lying face to face, perished.
literature
- JA Long, M. Archer, T. Flannery & S. Hand: Prehistoric Mammals of Australia and New Guinea, one hundred million years of evolution . Johns Hopkins University Press, Baltimore / London 2002, ISBN 0-8018-7223-5 .
Individual evidence
- ↑ a b c d e f g h i j k l K. Black & M. Archer: Silvabestius gen. Nov., A primitive zygomaturine (marsupialia, diprotodontidae) from Riversleigh, Northwestern Queensland. In: Memoirs of theQueens / and Museum , Volume 41, Number 2, 1997, pp. 193-208, ( digitized ).
- ^ JA Long, M. Archer, T. Flannery & S. Hand: Prehistoric Mammals of Australia and New Guinea, one hundred million years of evolution. Johns Hopkins University Press, Baltimore / London 2002, ISBN 0-8018-7223-5 , p. 97, ( reading sample ).
- ^ A b K. Black & B. Mackness: Diversity and Relationships of Diprotodontoid Marsupials. In: Australian Mammalogy , Volume 21, 1999, pp. 20-21, ( digitized )
- ^ JA Long, M. Archer, T. Flannery & S. Hand: Prehistoric Mammals of Australia and New Guinea, one hundred million years of evolution. Johns Hopkins University Press, Baltimore / London 2002, ISBN 0-8018-7223-5 , p. 91, ( reading sample ).
- ↑ KJ Travouillon, M. Archer, SJ Hand & H. Godthelp: Multivariate analyzes of Cenozoic mammalian faunas from Riversleigh, northwestern Queensland. In: Alcheringa , Special Issue 1, 2006, pp. 323-349, ( digitized ).
- ^ KH Black, M. Archer, SJ Hand & H. Godthelp: The Rise of Australian Marsupials: A Synopsis of Biostratigraphic, Phylogenetic, Palaeoecologic and Palaeobiogeographic Understanding. In: JA Talent (Ed.): Earth and Life: Global Biodiversity, Extinction Intervals and Biogeographic Perturbations Through Time. Springer, Dordrecht, 2012, ISBN 978-90-481-3427-4 , pp. 983-1078, ( digitized version ).
- ↑ M. Archer, H. Godthelp, SJ Hand & D. Megirian: Fossil Mammals of Rivensleigh, Northwestern Queensland: Preliminary Overview of Biostratigraphy, Correlation and Environmental Change. In: Australian Zoologist , Volume 25, Number 2, 1989, pp. 29-66, ( digitized ).
- ^ A b D. A. Arena: The palaeontology and geology of Dunsinane Site, Riversleigh. In: Memoirs of the Queensland Museum , Volume 41, Number 2, 1997, pp. 171-179, ( digitized ).
- ^ A b G. R. Guerin & RS Hill: Plant macrofossil evidence for the environment associated with the Riversleigh fauna. In: Australian Journal of Botany , Volume 54, 2006, pp. 717-731, ( digitized version )
- ^ A b K.J. Travouillon, S. Legendre, M. Archer & SJ Hand: Palaeoecological analyzes of Riversleigh's Oligo-Miocene sites: Implications for Oligo-Miocene climate change in Australia. In: Palaeogeography, Palaeoclimatology, Palaeoecology , Volume 276, 2009, pp. 24-37, ( digitized version ).
- ^ S. Legendre: Analysis of Mammalian communities from the late Eocene and Oligocène of southern France. In: Palaeovertebrata , Volume 16, Number 4, 1986, pp. 191-212, ( digitized version ).