Kretzoiarctos beatrix
| Kretzoiarctos beatrix | ||||||||||||
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Right lower jaw (left) as well as upper premolar and molar of Kretzoiarctos beatrix |
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| Temporal occurrence | ||||||||||||
| Miocene ( Aragonium , MN 8 ) | ||||||||||||
| 11.8 to 11.2 million years | ||||||||||||
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| Scientific name of the genus | ||||||||||||
| Kretzoiarctos | ||||||||||||
| Abella , Alba , Robles , Valenciano , Rotgers , Carmona , Montoya , Morales , 2012 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Kretzoiarctos beatrix | ||||||||||||
| (Abella, Montoya, Morales, 2011) | ||||||||||||
Kretzoiarctos beatrix is an extinct species of bear (Ursidae) thatlivedin the northeast of the Iberian Peninsula during the Middle Miocene . The only member of the genus Kretzoiarctos was a comparatively small bear, which found its habitat in the vicinity of shallow lakes and probably ate a large part of vegetable food. Its appearance in the fossil record coincides with a period of increased humidity in southwest Europe.
After the fossil remains of the animals were long attributed to other species and genera, they were placed in their own species in 2011 and a year later in their own genus. Phylogenetic studies identified Kretzoiarctos as a member of the subfamily Ailuropodinae , the only representative of which is the giant panda today. His remains represent the earliest find of this group and suggest a European origin of the lineage.
features
Compared to recent bears, Kretzoiarctos beatrix was rather small, not quite the size of a sloth bear ( Melursus ursinus ). Based on the findings, reliable statements can only be made about the skulls and teeth of the animals. The lower jaw was built short and robust. The teeth of the animals were characterized by long lower premolars , which had a high, dune-shaped central hump and a rudimentary front and rear hump; they were not separated by a diastema . The lower molar m1 had a deep crown , had meta- and protoconids of about the same height, a long and flat talonid pelvis, but no cusps in the paraconid-hypoconid valley. The molar m2 was long and had wide, flat talonid and trigonid basins. The canines of the lower jaw were deeply crowned and curved backwards. The approximately triangular premolar P4 was characterized by a rounded protocon that clearly stood out from the parastyle. The molar M4 was roughly square in outline and provided with a pyramid-shaped paracon, which just protruded above the approximately equally large metacon. The parastyle stood out clearly but was small, while the metastyle was very large.
Site, fossil material and stratigraphy
The first finds of Kretzoiarctos come from the Calatayud-Daroca Basin , a sedimentary formation in the southwest of Aragon . It is a premolar and a molar from the upper jaw, which were found in the Nombrevilla 2 deposit near Zaragoza in the late 1990s . In 2011, the right part of a lower jaw was recovered from the Catalan Vallès-Penedès basin near Els Hostalets de Pierola , which had complete dentition from canine to molar. Its found layer, the Abocador-de-Can-Mata layer sequence , lies in the Vallès-Penedès basin and, at 11.8–11.2 mya , is similar in age to Nombrevilla 2. They come from the late Aragonium , a regional stage of the Miocene. In the ELMMZ Neogen it corresponds to the MN-8 zone.
ecology
The dentition of Kretzoiarctos beatrix shows a shift in the omnivorous diet of the early bears towards more plant-based foods. The species continued to be omnivorous, but probably ate more plant material than the Ursavus bears or most of the species in the genus Ursus . The sites of Kretzoiarctos during his lifetime were flat, spacious lake plateaus. The animals shared their habitat with species such as the pigs Listriodon splendens , Albanohyus steinheimensis and Paracleuastochoerus castellensis or the mice Hispanomys aguirrei and H. lavocati . The species occurs at the same time as there is a shift in the Iberian Peninsula towards a more humid climate.
Systematics and taxonomy
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| Systematic position of Kretzoiarctos according to Abella et al. (2012). The genus is part of the Ailuropodini and is one of its most derived representatives. |
Due to the lack of material, the fossils of Kretzoiarctos beatrix could only be compared and related to other bears to a limited extent. The original shape of the upper molars and premolars prompted a group of paleontologists around Susana Fraile in 1997 to assign the teeth to the early bear Ursavus depereti . Six years later, a study led by María Ángeles Álvarez Sierra came to the conclusion that it was rather the older species Ursavus primaevus . A closer examination of the tooth material and a comparison with extinct bears from the family of the giant panda by Juan Abella , Plinio Montoya and Jorge Morales finally transferred them to the genus Agriarctos and described them as Agriarctos beatrix . The specific epithet honors the paleontologist Beatriz Azanza for her research on the paleontology of Aragon.
With the discovery of the lower jaw fragment in Catalonia, it was possible to classify the species phylogenetically based on tooth features. The analysis performed by Abella and colleagues in 2012 found that while the bear was indeed a close relative of Agriarctos , it showed differences in many traits. Because it also appeared earlier than Agriarctos , the researchers put it in its own genus. The name Kretzoiarctos is made up of the ancient Greek "arktos" for the great bear and the surname Miklós Kretzois . Kretzoiarctos forms the sister clade to Agriarctos and stands opposite Ailurarctos together with this genus . The most basic branch of this group is the genus Ailuropoda , to which the panda also belongs. Kretzoiarctos is the earliest known representative of the subfamily Ailuropodinae , which is particularly noteworthy with regard to their distribution. Both the panda and most of the extinct species are found in eastern Asia. The fact that a strongly derived representative of the group occurred in Europe before the later species emerged leads to the conclusion that the strongly herbivorous panda relatives developed from an Ursavus ancestor in Europe instead of in East Asia .
swell
literature
- Juan Abella, Plinio Montoya, Jorge Morales: A New species of Agriarctos (Ailuropodinae, Ursidae, Carnivora) in the locality of Nombrevilla 2 (Zaragoza, Spain). In: Estudios Geológicos 67 (2), 2011. doi : 10.3989 / egeol.40714.182 , pp. 187-191.
- Juan Abella, David M. Alba, Josep M. Robles, Alberto Valenciano, Cheyenn Rotgers, Raul Carmona, Plinio Montoya, Jorge Morales: Kretzoiarctos gen. Nov., The Oldest Member of the Giant Panda Clade. In: Plos One 7 (11), 2012. e48985, doi : 10.1371 / journal.pone.0048985 , pp. 1-7.
