Petralca
| Petralca | ||||||||
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Petralca austriaca (Holotype NHMW 1980/0025 / 0001a) |
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| Temporal occurrence | ||||||||
| Lower Miocene ( Aquitanium ) | ||||||||
| approx. 22 million years | ||||||||
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Petralca | ||||||||
| Mlíkovský , 1987 | ||||||||
| Art | ||||||||
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Petralca is an extinct genus of birds from the order of the loons-like (Gaviiformes). The only known species of the so far monotypical genus is Petralca austriaca from the Ebelsberg Formation ( Aquitanium - Lower Miocene , about 20.44 to 23.03 million years ago) from Pucking in Upper Austria .
Etymology and history of research
The generic name is a suitcase word from the Latin " petra " (after the ancient Greek πέτρα - "rock") and the generic name " Alca " for the recent razorbill ( Alca torda ). The additional species “ austriaca ” refers to the place where it was found in Austria. The species name can be roughly translated as "Austrian rock alk".
The so far only fossil record of Petralca was found in 1980 in the course of a fossil excavation by the Natural History Museum Vienna and the Upper Austrian State Museum in what was then the construction site of the Traun-Pucking power plant. The first description of the genus and type species was carried out in 1987 by Jiri Mlíkovský .
Mlíkovský interpreted the fossil in his first description as a representative of the alkenvogel (Alcidae), which also explains his choice of the generic name. However, since he had also recognized some striking differences in the skeletal morphology, he placed Petralca in its own subfamily (Petralcinae) within the family of Alcidae. According to his information, the strata in which the fossil was found had an Upper Oligocene age. Petralca was not only a rather unusual, but also the oldest known representative of the alkenbird.
In 2009, doubts were raised about the systematic classification of the fossil. Both Gerald Mayr and Erik Wijnker and Storrs L. Olson assumed, independently of one another, a position for Petralca in the order of the loons-like (Gaviiformes). The stratigraphic classification was also revised in 2009 and 2010. The find horizon was no longer placed in the Upper Oligocene ( Chattian ), but in the Lower Miocene (Aquitanium) and could be dated relatively precisely to an age of about 22 million years.
In 2017 Ursula B. Göhlich and Gerald Mayr finally published a complete new description of the holotype in which they were able to confirm the already suspected assignment to the Gaviiformes. After Gavia schultzi from the Middle Miocene of Sankt Margarethen in Burgenland , Petralca was the second fossil representative from the order of loons in Austria.
Fossil record
The holotype and the only fossil evidence for the genus and type species is a relatively poorly preserved partial skeleton from the Ebelsberg Formation. The original fossil is available as a plate and counter plate and is kept at the Natural History Museum Vienna under the inventory number NHMW 1980/0025 / 0001a + b. The skeletal remains essentially comprise parts of the shoulder girdle (both raven bones and fragments of both shoulder blades ) and both wings . There are also some vertebrae and ribs that have been preserved in fragments , as well as a single, isolated phalanx . Many of the bones are damaged or only preserved as an impression .
features
Petralca austriaca has numerous skeletal features that confirm an assignment to the loons-like species. In particular the os carpi radiale , the carpal bones of the spoke and carpometacarpus , shows with a deep, centrally located notch for the tendon of the ulnometacarpalis ventralis, a feature that is only known in this form from representatives of the Gaviiformes. The thick-walled shaft of the humerus is round in cross-section, as in the loons and not craniocaudally flattened, as in the alken birds. The shape of the raven bones also corresponds to the conditions of the loons and differs clearly from the raven bones of the alken birds.
All in all , the remains are strongly reminiscent of Colymboides , a genus of loons that existed in Europe from the Upper Eocene to the Lower Miocene with several species. However, in their new description from 2017, Göhlich and Mayr also point to differences between the two fossil genera and rate Petralca as more closely related to today's loons ( Gavia ) than Colymboides .
Petralca is described in terms of size as lying between Colymboides anglicus and Colymboides minutus . C. anglicus was significantly smaller than the recent red-throated diver ( Gavia stellata ), the smallest living member of the genus Gavia , and C. minutus was only about half the size of a red-throated diver.
Paleecology
The fossil-rich horizon of the Ebelsberg Formation, which was briefly exposed during the construction of the Traun-Pucking power plant, can be characterized as a conservation deposit. The sandy to clayey silts of the find horizon were deposited in the area of the northern Alpine Molasse Basin on the northern edge of the Central Paratethys . The fossil record indicates a marine deposit area with a water depth of more than 100 m. The coastline of the Bohemian Massif was 10–20 km away in a north to north-easterly direction.
The fossil content of the deposit is not evenly distributed. Different taxa are enriched in certain combinations in layers:
- Monodominant (one single taxon dominates) mass occurrences of planktonic gastropods of the genera Limacina or Clio together with accumulations of calcareous nannoplankton occur several times and indicate a regular oversupply of nutrients, triggered by upwelling or increased nutrient input from the coastal areas.
- In several layers there are accumulations of shells of the nautiloid Aturia together with remains of the brown alga Cystoseirites altoaustriacus . The combination of pelagic cephalopods and plants from the littoral is interpreted as the material of a former flushing rim that was washed out into the open sea again by storms or floods. The latter is also single dominant accumulations of fish from the family of pipefish suspected (Syngnathidae), which also prefer shallow coastal waters.
- A fish-rich horizon with remains of various taxa forms the third type of deposit and represents the necton of the deposit area. The fish fauna is dominated by representatives of the hake (Merlucciidae), herring (Clupeidae) and mackerel (Scombridae). More rarely there are representatives of the sawfish (Serranidae), jackfish (Carangidae) and boarfish (Caproidae) as well as isolated teeth of the nail shark Echinorhinus pollerspoecki and of comb tooth sharks of the genus Heptranchias . For this horizon and the holotype of stem Petralca austriaca and other spectacular finds such as the giant sunfish Austromola angerhoferi or a nearly complete skeleton of a yet unnamed, dolphin-like Zahnwals.
Relatively common, but largely uniformly distributed in the sediment is found fossilized driftwood with traces of wood-boring barnacles and marine growth of bryozoans , Vielborstern and barnacles . Macro benthos , on the other hand, occurs only sporadically and with a few species. The Shell Megaxinus bellardianus , a representative of with sulfur bacteria in symbiosis living lucinidae (Lucinidae) is perpendicular sticking to the layering in the sediment found in living position. The occurrence of the mussel and geochemical parameters of the sediment itself indicate an oxygen deficit in the area of the deposition area close to the ground, which also explains the good conservation status of the vertebrate fossils.
Way of life
Recent loons, as the common name suggests, are excellent divers who primarily hunt for fish underwater. The thick-walled shaft of the humerus found in Petralca can be interpreted as an adaptation to a diving lifestyle; the feature also occurs in recent loons. Whether Petralca , like his recent relatives, ate mainly piscivor has not been established. A corresponding fossil record is available for ? Colymboides metzleri from the Oligocene in southern Germany, which indicates that representatives of the loon-like species were already adapted to this diet in the Palaeogene .
Individual evidence
- ^ A b c J. Mlíkovský & J. Kovar: A new species of alken (Aves: Alcidae) from the Upper Oligocene of Austria. In: Annals of the Natural History Museum in Vienna. Series A for Mineralogy and Petrography, Geology and Paleontology, Anthropology and Prehistory, Volume 88, 1987, pp. 131-147 ( digitized version ).
- ↑ G. Mayr: Paleogene Fossil Birds. Springer Verlag, Berlin / Heidelberg 2009, ISBN 978-3-540-89627-2 , p. 88 ( reading sample ).
- ↑ E. Wijnker & SL Olson: A revision of the genus Fossil Miocepphus and other Miocene Alcidae (Aves: Charadriiformes) of the Western North Atlantic Ocean. In: Journal of Systematic Palaeontology , Volume 7, Number 4, 2009, pp. 471-487 ( digitized ).
- ^ R. Gregorova, O. Schultz, M. Harzhauser, A. Kroh & St. Ćorić: A Giant Early Miocene Sunfish from the North Alpine Foreland Basin (Austria) and its Implication for Molid Phylogeny. In: Journal of Vertebrate Paleontology , Volume 29, Number 2, 2009, pp. 359-371 ( digitized version ).
- ↑ a b c d P. Grunert, M. Harzhauser, F. Rögl, R. Sachsenhofer, R. Gratzer, A. Soliman & WE Piller: Oceanographic conditions as a trigger for the formation of an Early Miocene (Aquitanian) conservation deposit in the Central Paratethys Sea. In: Palaeogeography, Palaeoclimatology, Palaeoecology , Volume 292, Number 3–4, 2010, pp. 425–442 ( digitized version )
- ↑ a b c d e f g U. B. Göhlich & G. Mayr: The alleged early Miocene Auk Petralca austriaca is a Loon (Aves, Gaviiformes): restudy of a controversial fossil bird. In: Historical Biology , Volume 30, Number 8, 2017, pp. 1076-1083 doi : 10.1080 / 08912963.2017.1333610 ( digitized version ).
- ↑ a b c G. Mayr: Paleogene Fossil Birds. Springer Verlag, Berlin / Heidelberg 2009, ISBN 978-3-540-89627-2 , pp. 75-76 ( reading sample )
