Plesiohadros
| Plesiohadros | ||||||||||
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| Temporal occurrence | ||||||||||
| Upper chalk (? Upper Campanium ) | ||||||||||
| ? 76.4 to 72 million years | ||||||||||
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Plesiohadros | ||||||||||
| Tsogtbaatar et al., 2014 | ||||||||||
| Art | ||||||||||
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Plesiohadros is a genus from the group of Hadrosauroidea . The only known species of the so far monotypical genus is Plesiohadros djadokhtaensis , whichlivedin what is now Mongolia during the Upper Campanian (approx. 76–72 million years ago).
Etymology, fossil evidence, and history of research
The generic name is made up of the ancient Greek πλησίος ( plēsíos = "near", "almost") and the name " hadros " as an abbreviation for a representative of the Hadrosauridae , which is intended to illustrate the close relationship to this group. The additional species " djadokhtaensis " refers to the formation in which the fossils were found. The name can be roughly translated as "almost hadrosauride from the Djadokhta formation".
The fossil remains come from the Djadokhta formation at the Alag Teeg site in Aimag Ömnö-Gobi in southern Mongolia. The holotype (MPC-D100 / 745) comprises an almost completely preserved skull with a lower jaw, a hyoid bone , some cervical vertebrae as well as metacarpal and finger bones . Other fossil material (MPC-D100 / 751) includes the tibia and fibula as well as other metacarpal and finger bones.
The fossil deposit at Alag Teeg was discovered as early as 1969 by one of the numerous “Soviet-Mongolian Paleontological Expeditions” and has since been explored more or less regularly as part of excavation campaigns. The remains of Plesiohadros were also recovered as part of one such campaign . After the first finds of unidentifiable bone remnants of newly hatched Hadrosauroidea became known as early as 1983, Plesiohadros djadokhtaensis is the first ornithopod from the Djadokhta formation that can be assigned to the genus and species level . The first description of the genus and type species was carried out in 2014 by Tsogtbaatar , Weishampel , Evans and Watabe .
features
Plesiohadros djadokhtaensis was a tall representative of the Hadrosauroidea. The reconstructed skull length is estimated to be 82 cm. The entire animal should have reached a body length of> 10 m and a body mass of at least 2 tons.
Plesiohadros differs from all other representatives of the Hadrosauroidea in particular through a peculiarity of the Os praefrontale . This bone of the facial skull forms the anterior, upper ( rostrodorsal ) border of the eye socket . In Plesiohadros , this edge of the eye socket is widened laterally and upwards ( dorsolateral ) to form a wrinkled, wing-like process. This special feature is so far only known from Plesiohadros ( autapomorphy ).
In addition, Plesiohadros has a number of other characteristics that, in combination with one another, are unique for the genus:
The teeth of the dental show lingual to only one or two additional strips, the mesial and distal to the main cutting edge ( " Carina are arranged"). The diastema , the toothless area of the dental between the predentals and the foremost teeth of the lower jaw, is extremely long and measures about ⅓ the length of the row of teeth. The rear end of the row of teeth in the lower jaw does not extend beyond the tip of the coronoid process ( coronoid process ).
The front edge of the premaxilla has a clearly recurved edge and the beak-shaped premaxilla tapers sharply immediately behind the broad, arched front edge. An indentation on the border between quadratum and quadratojugale is only indistinctly formed. The postorbital clasp and the main body of the zygomatic bone form an acute angle to delimit the infratemporal window .
With regard to the postcranial skeleton, a special feature is emphasized that the proximal end of metacarpus III lies on the same line with those of metacarpus II and IV.
Systematics
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| Systematic position of Plesiohadros ; simplified from Tsogtbaatar et al., 2014 |
The cladogram shown on the right illustrates the systematic position of Plesiohadros within the Hadrosauroidea and in relation to the Hadrosauridae.
Plesiohadros occupies a position as the sister taxon of that clade , which includes the group of Hadrosauridae and the genus Lophorhothon . This assignment is supported by 8 common characteristic features ( synapomorphies ) of the cranial skeleton. However, it is not a representative of the Hadrosauridae, but is classified by the authors of the first description as "non-hadrosaurid hadrosauroid" ("non-hadrosaurid hadrosauroid").
Paleoecology
Plesiohadros was, like all representatives of the Hadrosauroidea, a pure herbivore.
The sediments of the Djadokhta Formation are usually built up from Aeolian sandstones, into which locally (e.g. Bajandsag ) lacustrine sediments can be incorporated. The composition of the Djadokhta formation at the Alag Teeg site differs from this general structure. Aeolian sandstones also occur here, but the lying parts of the formation in particular are dominated by the sediments of alluvial fans and alluvial plains . The combination of Erg -like dune fields with lakes and river oases is compared by Jerzykiewicz in 1998 with the situation in today's Okavango Delta in the north of the Kalahari .
The vertebrate fauna of the Djadokhta Formation is dominated by the small- stature ceratopsian Protoceratops and a number of small theropods such as Oviraptor or Velociraptor . Plesiohadros was next to the ankylosaur Pinacosaurus and an unspecified representative of the Tyrannosauridae the largest representative of the Djadokhta fauna.
Web links
- Artistic reconstruction of Plesiohadros djadokhtaensis in his living space The painting by the Canadian “Paleoart” artist Julius T. Csotonyi served as the front cover for the book in which the first description was made.
Individual evidence
- ↑ a b c d e f g h i j k l m K. Tsogtbaatar, DB Weishampel, DC Evans & M. Watabe: A New Hadrosauroid (Plesiohadros djadokhtaensis) from the Late Cretaceous Djadokhtan Fauna of Southern Mongolia . In: DA Eberth & DC Evans (Eds.): Hadrosaurs: Proceedings of the International Hadrosaur Symposium , pp. 108-135, Indiana University Press, 2014. ISBN 978-0-253-01385-9 (reading sample)
- ↑ Ph. J. Currie, D. Badamgarav, EB Koppelhus, R. Sissons & MK Vickaryous: Hands, feet, and behavior in Pinacosaurus (Dinosauria: Ankylosauridae) . In: Acta Palaeontologica Polonica , Vol. 56, Issue 3, pp. 489–504, 2011. (digitized version )
- ^ R. Barsbold & A. Perle: On taphonomy of a joint burial of juvenile dinosaurs and some aspects of their ecology . In: The Joint Soviet-Mongolian Paleontological Expedition Transaction, Nauka, Vol. 24, pp. 121-125, 1983.
- ↑ T. Jerzykiewicz: Okavango Oasis, Kalahari Desert: A Contemporary Analogue for the Late Cretaceous Vertebrate Habitat of the Gobi Basin, Mongolia. In: Geoscience Canada , Vol. 25, No. 1, pp. 15–26, 1998. (digitized version)