Rubeosaurus
| Rubeosaurus | ||||||||||||
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Artistic reconstruction of the head of Rubeosaurus ovatus . Illustration by Lukas Panzarin |
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| Medium Campanium | ||||||||||||
| 74 to 75 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Rubeosaurus | ||||||||||||
| McDonald & Horner , 2010 | ||||||||||||
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Rubeosaurus is a genus of ceratopsid dinosaurs from the Centrosaurinae group . The only known species of the so far monotypical genus is Rubeosaurus ovatus from the Two Medicine Formation (Middle Campanium ; approx. 74 to 75 million years ago) from Montana (USA).
Etymology and history of research
The generic name is made up of the Latin " rubeus " (literally "from the blackberry bush"; used here in the sense of "thorn bush") and the Latinized ancient Greek word σαῦρος " sauros " ("lizard", "salamander"). The name can be translated as "thorn bush lizard" and refers to the spiky extensions of the neck shield. The additional species " ovatus " ( Latin "egg-shaped", "oval") refers to the oval outline of these spinous processes.
The holotype (USNM 11869), a fragment of the part of the neck shield belonging to the parietal bone (parietal), was already recovered in the summer of 1928 by George F. Sternberg from the sediments of the Two Medicine Formation in Montana. It was first described in 1930 by Charles W. Gilmore , who interpreted the fossil as a new species of the genus Styracosaurus ( Styracosaurus ovatus ).
A fragmentary skull (MOR 492) that was discovered in approximately the same horizon in 1986 was assigned to the same species by Andrew T. McDonald and John R. Horner in 2010 . At the same time, the authors separated the fossils from the genus Styracosaurus and placed them in a separate genus Rubeosaurus . The second specimen (MOR 492) comprises parts of the two fused nasal bones including a bone cone for a nasal horn, a fragment of the left premaxilla , a fragment of the left postorbital including bone cones for an over-eye horn and an almost complete right parietal bone with two spiky epiparietals .
A year later, McDonald interpreted another fossil (USNM 14765) from the Two Medicine Formation as a subadult specimen of Rubeosaurus ovatus . USNM 14765 was found in 1935 and described by Gilmore in 1939 as an almost adult specimen of Brachyceratops montanensis . The validity of this taxon , which Gilmore had established in 1914, was however strongly questioned by later editors and Brachyceratops montanensis is now considered a noun dubium . The fossil material from USNM 14765 includes a nearly complete, but disarticulated (not anatomically related) skull and a few postcranial skeletal elements (a vertebra, a rib, the left shoulder blade, both femurs, and two phalanges).
features
(Description follows McDonald’s analysis, 2011 unless otherwise noted.)
Rubeosaurus differs from all other representatives of the Centrosaurinae by the inwardly inclined, spiky elongated epiparietals P3 ("LP3" and "RP3" in the figure on the right).
In addition, there are a number of characteristics that, taken individually , also occur in other genera of the Centrosaurinae, but in combination are unique for Rubeosaurus :
- A long, steeply erect bone plug for a nasal horn
- Short, dorsally aligned bone cones with a rounded tip for the ocular horns on the postorbital
- Spine-shaped elongated epiparietals P3, P4 and P5
- The epiparietal spines at position P3 are straight and not curved
- The P5 spines are significantly shorter than the spikes on positions P3 and P4
- The epiparietals P2, on the other hand, are small, rounded and also inclined inwards
- There is no epiparietalium at the median position P1
Gregory S. Paul mentions a length of 5 m and a body mass of 2 tons for Rubeosaurus , but does not give any information on how these data were determined.
Age classification of the finds
All previously known fossil records of Rubeosaurus come from various sites within the Two Medicine Formation. The locations are in the vicinity of Landslide Butte in the Blackfeet Nation area ( Glacier County , Montana) and occupy a similar stratigraphic position within the Two Medicine Formation, about 60 m below the hanging wall boundary to the overlying Bearpaw Formation . This stratigraphic position can be assigned an age of around 74–75 million years (Middle Campanium) on the basis of radiometric age data of two bentonite horizons.
Two other genera of the Centrosaurinae are known from the Two Medicine Formation. Their fossil evidence, however, comes from other stratigraphic levels of the formation about 45 m ( Einiosaurus ) and about 20 m ( Achelousaurus ) on the slope of the slope boundary to the Bearpaw Formation, and the two genera are therefore not necessarily to be rated as sympatric to Rubeosaurus .
Systematics
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| Systematic position of Rubeosaurus according to Evans & Ryan , 2015. |
Rubeosaurus ovatus was originally described as a new species in the genus Styracosaurus .
The discovery of MOR 492 prompted McDonald & Horner to place the species in a separate genus within the Centrosaurinae in 2010. A first phylogenetic analysis showed Rubeosaurus to be a sister taxon of Einiosaurus and the two genera, together with Achelousaurus and Pachyrhinosaurus, formed their own partial clade within the Centrosaurinae. Styracosaurus , on the other hand, falls together with Centrosaurus into a second, separate clade.
A later analysis published in the context of the first description of Wendiceratops , however, showed Rubeosaurus as a sister taxon of Styracosaurus in a common partial clade with Coronosaurus , Centrosaurus and Spinops , apart from the partial clade with Einiosaurus , Achelousaurus and Pachyrhinosaurus . The results of this analysis are shown in simplified form in the cladogram opposite .
The family relationships within the Centrosaurinae have by no means been conclusively clarified and new evidence may at any time lead to changes in the systematic position of Rubeosaurus shown here .
Paleecology
Rubeosaurus was, like all representatives of the Ceratopsidae, a pure herbivore.
The North American continent was partially covered by a shallow epicontinental sea during the Middle and Upper Cretaceous Period . This Western Interior Seaway divided the continent into two land masses; the western Laramidia and the eastern Appalachia . The latter was temporarily split into a northern and a southern part by another inlet (Hudson Seaway). The sediments of the Two Medicine Formation were deposited as erosion material from the young Rocky Mountains on the east coast of Laramidia, i.e. in the direction of the Western Interior Seaway.
The upper Two Medicine Formation, from which the Rubeosaurus finds originate, was deposited in the area of shallow, anastomosing rivers or in the area of their alluvial plains . Sedimentological characteristics of the Two Medicine Formation suggest a deposit area that was characterized by a warm, semi-arid climate with pronounced dry seasons.
Individual evidence
- ↑ a b c d A. T. McDonald & JR Horner: New material of `` Styracosaurus '' ovatus from the Two Medicine Formation of Montana. In: MJ Ryan, BJ Chinnery-Allgeier & DA Eberth (Eds.): New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium , Indiana University Press, 2010, ISBN 978-0-253-35358-0 , p. 156 -168, ( reading sample ).
- ↑ a b c Ch. W. Gilmore: On dinosaurian reptiles from the Two Medicine Formation of Montana. In: Proceedings of the United States National Museum , Volume 77, 1930, pp. 1–39, ( digitized version )
- ↑ a b c d e f A. T. McDonald: A Subadult Specimen of Rubeosaurus ovatus (Dinosauria: Ceratopsidae), with Observations on Other Ceratopsids from the Two Medicine Formation. In: PLOS ONE , Volume 6, Number 8, 2011, e22710, doi : 10.1371 / journal.pone.0022710 .
- ^ Ch. W. Gilmore: Ceratopsian dinosaurs from the Two Medicine Formation, Upper Cretaceous of Montana. In: Proceedings of the United States National Museum , Volume 87, Number 3066, 1939, pp. 1-18, ( digitized ).
- ^ GS Paul: The Princeton Field Guide to Dinosaurs. 2nd edition, Princeton University Press, 2016, ISBN 978-0-691-16766-4 , p. 291, ( reading sample ).
- ^ RR Rogers, CC Swisher III & JR Horner: 40 Ar / 39 Ar age and correlation of the nonmarine Two Medicine Formation (Upper Cretaceous), northwestern Montana, USA In: Canadian Journal of Earth Sciences , Volume 30, 1993, p. 1066 -1075, ( digitized version ).
- ^ A b D.C. Evans & MJ Ryan: Cranial Anatomy of Wendiceratops pinhornensis gen. Et sp. nov., a Centrosaurine Ceratopsid (Dinosauria: Ornithischia) from the Oldman Formation (Campanian), Alberta, Canada, and the Evolution of Ceratopsid Nasal Ornamentation. In: PLOS ONE , Volume 10, Number 7, 2015, e0130007, doi : 10.1371 / journal.pone.0130007 .
- ^ RR Rogers: Taphonomy of Three Dinosaur Bone Beds in the Upper Cretaceous Two Medicine Formation of Northwestern Montana: Evidence for Drought-Related Mortality. In: Palaios , Volume 5, 1990, pp. 394-413, ( digitized version ).
