Ostarriraja
| Ostarriraja | ||||||||||||
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Ostarriraja parva , holotype NHMW 2005z0283 / 0097a |
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| Temporal occurrence | ||||||||||||
| Lower Miocene (Middle Burdigalium ) | ||||||||||||
| approx. 18 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Ostarriraja | ||||||||||||
| Marramá , Schultz & Kriwet , 2018 | ||||||||||||
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Ostarriraja is an extinct genus of rays from the order of the Rajiformes . The only known species of the so far monotypical genus is Ostarriraja parva from the Middle Burdigalium (Lower Miocene , Ottnangian according to the regional stratigraphy of the Central Paratethys , about 18 million years ago) from Rainbach im Innkreis in Upper Austria . Ostarriraja is one of the oldest and most basal representatives of the Rajiformes, of which more than just a few individual teeth are known.
Etymology and history of research
The generic name is made up of " Ostarri- ", after " Ostarrîchi ", the oldest documented name for Austria and the Latin " raja " ("ray"). The additional species “ parva ” (Latin; feminine of “ parvus ”: “small”) refers to the small size of the holotype . The species name can accordingly be translated roughly as "Little Austria ray".
The holotype and so far the only fossil record is an almost complete and articulated (anatomically related) skeleton from marine deposits of the northern Alpine Molasse Basin . The original fossil is available as a plate and a counter plate and is kept at the Natural History Museum Vienna under the inventory number NHMW 2005z0283 / 0097a + b.
The fossil was already described in 1973 by Ortwin Schultz as a possible representative of the genus Dasyatis ( Dasyatis (?) Sp. ) Within the family of stingrays (Dasyatidae). As Dasyatis sp. the fossil is also listed and mapped in the Catalogus Fossilium Austriae .
In 2018, Giuseppe Marramá , Ortwin Schultz and Jürgen Kriwet re-described the fossil. This description, based on more modern research methods , led to a reassessment of the fossil and the establishment of the genus Ostarriraja . In particular, morphological investigations of the fossil under UV light , which enables a clearer differentiation between fossil and rock matrix , and scanning electron microscopic analyzes of the dentition were used. According to the results, the fossil was no longer interpreted as a stingray (Dasyatidae), but as a primitive representative of the Rajiformes.
Fossil record
The holotype shows a very small individual who was probably only 12-14 cm long during his lifetime. The specimen copy lies with the back (dorsal) embedded in the rock and the ventral side (ventral) exposed. Indications of Klaspern are not recognizable despite the good state of preservation. The morphology of the teeth and the still incomplete calcification of individual elements of the cartilage skeleton are further indications that it is probably the remains of a juvenile to maximally subadult female.
The tip of the snout and the distal radialia of the pectoral fins are not preserved, so that the exact shape of the body disc consisting of the skull, trunk and pectoral fins can no longer be reconstructed. The tip of the tail is also missing and accordingly no information is available about the number and shape of the dorsal fins.
features
(Abbreviations in brackets used in the text refer to the figures on the right)
The re-analysis of the fossil by Marramá et al. has shown some anatomical features that rule out belonging to the stingray-like (Myliobatiformes). A sawtooth reinforced spike is missing in the tail area. A synarcual (“syn”), a section of the spine in which the individual vertebral bodies are fused together by a tubular cartilage capsule , is present in the area between the neurocranium and beyond the shoulder girdle (“cervicothoracic synarcual”), a second synarcual in the The transition area between thoracic and lumbar vertebrae ("thoracolumbar synarcuale") is missing. The arrangement of the three large basal pieces of cartilage of the pectoral fin, Propterygium (“pro”), Mesopterygium (“mes”) and Metapterygium (“met”) also differs from that of the stingray-like. The distance between the joint attachment points on the shoulder girdle ("scapulocoracoid"; "sca") for Pro- and Mesopterygium is shorter than that between the attachment points for Meso- and Metapterygium; in the case of the stingray, the situation is reversed. The suprascapular appears to be fused dorsally with the synarcual ("pa").
The pectoral fins are supported by about 86 radials ("rad"). Of these, 33 originate from the Propterygium, 10 from the Mesopterygium and 32 from the Metapterygium. About 11 radialia are directly connected to the scapulocoracoid between the meso- and metapterygium; a characteristic that typically occurs in the Rajiformes, the saw ray genus Pristis , the genus Zanobatus and the guitar rays. The nasal capsules ("nc") are wide and oval. The antorbital cartilage ("ac") is massive, arched and unbranched. It creates a direct connection between the nasal capsule and the propterygium (“pro”).
The clasp-shaped pelvic girdle (“pub”) has two long, spike-shaped appendages (“prp”) anteriorly . The long basipterygia ("bas") articulate posteriorly and externally on the pelvic girdle. The pelvic fins are supported by about 20-21 radials ("rad") and are clearly bilobed. The anterior area is supported by a rod of fused radials (“cr”) and the foremost 3–4 radials which are attached directly to the pelvic girdle. The rod-shaped fused radials are connected in series with the distal segments of the individual radials. The posterior area is supported by individual radials extending from the basipterygium. However, there does not appear to be a gap between the two lobes of the pelvic fins.
The number of predorsal (in front of the first dorsal fin) vertebrae can only be estimated due to the lack of the tip of the tail, but at 65–70 it should be rather low. There are no ribs. The long and strong tail itself shows at least three longitudinal rows of placoid scales dorsally transformed into cross-shaped thorns . The body disc, on the other hand, does not seem to have any placoid scales, at least on the abdomen.
Dentition
Ostarriraja's teeth are small and arranged in several rows. The dental crowns show an occlusal view of a semi-oval outline having a maximum diameter of about 0.4-0.5 mm. The labial edge of the crown is evenly curved, while the lingual edge has a small, hump-like projection in the center. The labial and lingual sides of the tooth crown are separated by a distinct, curved cutting edge that runs over a slightly pronounced, approximately centrally located, conical tip. There is no additional cutting edge on the labial side of the crown.
The teeth are holaulacorhizid, which means that the vascular supply occurs through numerous small openings (foramina) that are concentrated in a median pit of the tooth root. The tooth roots themselves are divided into two unequal lobes by the median pit and reach approximately the width of the crown. The teeth of Ostarriraja are more suited to crushing food than to fix a prey animal ("crushing teeth", "crushing-type dentition").
Systematics
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| Systematic position of Ostarriraja within the Rajiformes, according to Marramá et al. , 2018. |
The internal systematics of the rays (Batoidea) has by no means been conclusively clarified. This applies in particular to their fossil representatives, for which naturally only morphological but no molecular genetic data are available. In addition, due to the largely cartilaginous skeleton, fossil evidence is mostly limited to individual teeth or placoid scales. Fossil finds of almost complete skeletons, as in the case of Ostarriraja , are rare and accordingly provide valuable information on the tribal history of the rays.
Marramá and co-authors identify several features in Ostarriraja that justify assignment to the Rajiformes; in particular the wide and oval nasal capsules, the suprascapular fused with the synarcual and the connection between the rod-shaped fused radials with the distal segments of the individual radials of the anterior lobe of the pelvic fins. In the opinion of the authors, however, the totality of the characteristics does not allow an assignment to a specific clade of the Rajiformes and Ostarriraja is interpreted as a basic representative with an unclear systematic position ( incertae sedis ) within the order.
As part of the first description of the genus Ostarriraja , two further, almost completely preserved fossil taxa , Rajorhina and Cyclobatis , were re-evaluated. Both genera come from the fossil deposits of Haqel and Hjoula from the Upper Cretaceous ( Cenomanian ) of Lebanon and are therefore much older than Ostarriraja . Both Rajorhina and Cyclobatis are often assigned to the Rajiformes, although the assignment is not undisputed.
For Rajorhina , the authors refer, among other things, to the deviating structure of the pelvic fins (no division into two fin flaps, no contact of the rod-shaped fused radials with the distal segments of the individual radials, absence of individual radials that start directly on the pelvic girdle and not only on the basipterygia) The absence of long, spiky projections on the pelvic girdle, the different blueprint of the tooth roots and the clear presence of ribs to put the genus in the order of the Rhinopristiformes .
The genus Cyclobatis is known to have several species and some well-preserved fossil records . Although it shows the typical division of the pelvic fins and also clear spike-shaped appendages on the pelvic girdle, it also shows striking differences in the area of the skull and shoulder girdle. There is no antorbital cartilage and the nasal capsules are in direct contact with the propterygium. In addition, the suprascapular is not connected to the synarcual, as in the Rajiformes, but to the neural arches of the vertebrae behind the synarcual. The latter characteristic suggests a relationship with the saw rays (Pristidae) or the electric ray-like (Torpediniformes).
According to Marramá et al. is Ostarriraja making it possible to demonstrate an association with the Rajiformes the previously oldest fossil evidence of the based on a nearly complete skeleton. Finds of single teeth indicate, however, that the tribal history of the order can be traced back at least to Maastrichtium .
Paleecology
The marine sediments of the Ottnangium von Rainbach im Innkreis were deposited in the area of the north Alpine Molasse Basin on the northern edge of the Central Paratethys . At this time the Eastern Paratethys Basin was already isolated and the connection between the Mediterranean and the Indian Ocean was cut off. However, there were still straits of the sea that made a connection between Central Paratethys and the Mediterranean Sea. The Mediterranean itself was already in contact with the Atlantic. The north alpine Molasse Basin was part of one of these sea routes that connected the central Paratethys via the Rhone Basin with the western Mediterranean (“Burdigalian Seaway”).
Micropalaeontological and isotope geochemical parameters indicate that the deposit area was strongly characterized by rising, cold and nutrient-rich deep waters. The water temperature at the sea surface was only 10–14 ° C on average. This upwelling , which is rather untypical for a relatively narrow strait like the northern Molasse Basin, was triggered by prevailing wind directions and tidal currents and favored the steeply sloping coastline of the Bohemian Massif , which is characterized by tectonic disturbances . The overall situation can be compared with the recent conditions in the Santa Barbara Canal off the coast of California .
The nutrient-rich deep waters were the basis for the fossil-proven abundance of fish in the habitat of Ostarriraja
Individual evidence
- ↑ a b c d e f g h i j k l m n o p q r s t G. Marramá, O. Schultz & J. Kriwet: A new Miocene skate from the Central Paratethys (Upper Austria): the first unambiguous skeletal record for the Rajiformes (Chondrichthyes: Batomorphii). In: Journal of Systematic Palaeontology , 2018, 24 pp. Doi: 10.1080 / 14772019.2018.1486336
- ^ R. Brzobohatý & O. Schultz: The fish fauna of the Innviertel layer group and the Rzehakia formation. In: A. Papp, F. Rögl & J. Senes (eds.): M2 Ottnangien. The Innviertel, Salgótarjáner, Bántapusztaer strata group and the Rzehakia formation. Chronostratigraphy and neostratotypes, Miocene of the Central Paratethys. Publishing House of the Slovak Academy of Sciences, Bratislava, 1973, pp. 652–693.
- ↑ O. Schultz: Pisces. In: Catalogus Fossilium Austriae , Volume 3, Verlag der Österreichischen Akademie der Wissenschaften, Vienna, 2013, ISBN 978-3-7001-7238-3 , p. 103 and plate 30. ( digitized version )
- ↑ W. Westheide & G. Rieger (Eds.): Special Zoology. Part 2: vertebrates or skulls. 2nd edition, Spektrum Akademischer Verlag, Heidelberg, 2010, ISBN 978-3-8274-2039-8 , pp. 222-223, ( reading sample ).
- ↑ J. Herman, M. Hovestadt-Euler, DC Hovestadt & M. Stehmann: Contributions to the study of the comparative morphology of teeth and other relevant ichthyodorulites in living supra-specific taxa of Chondrichthyan fishes - Part B: Batomorphii No. 1a: Order Rajiformes - Suborder Rajoidei - Family: Rajidae - Genera and Subgenera: Anacanthobatis (Schroederobatis), Anacanthobatis (Springeria), Breviraja, Dactylobatus, Gurgesiella (Gurgesiella), Gurgesiella (Fenestraja), Malacoraja, Neoraja and Pavoraja. In: Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Biologie , Volume 64, 1994, pp. 165-207, ( digitized version ).
- ^ A b P. Grunert, A. Soliman, M. Harzhauser, St. Müllegger, WE Piller, R. Roetzel & F. Rögl: Upwelling conditions in the Early Miocene Central Paratethys Sea. In: Geologica Carpathica , Volume 61, Number 2, 2010, pp. 129-145, ( digitized ).