Mid-Cretaceous Cretoxyrhina (Elasmobranchii) from Mangyshlak, Kazakhstan and Texas, USA

Summary, in English

SIVERSON, M., WARD, D.J., LINDGREN, J. & KELLEY, L.S., iFirst article. Mid-Cretaceous Cretoxyrhina (Elasmobranchii) from Mangyshlak, Kazakhstan and Texas, USA. Alcheringa, 118. ISSN 0311-5518. The holotype of the nominal lamniform shark Pseudoisurus' vraconensis comprises an isolated tooth from a late Albian stratum at Besakty, Mangyshlak, Kazakhstan. Its stratigraphical provenance indicates that it is of Mortoniceras perinflatum Zone-age or somewhat older. It is indistinguishable at the species level from isolated teeth from the Mortoniceras rostratum Zone of the Pawpaw Shale in northeast Texas. Abundant teeth of P'. vraconensis-type from slightly younger strata close to the AlbianCenomanian boundary at Kolbay, eastern Mangyshlak, Kazakhstan, enabled the reconstruction of a dentition adhering to the dental blueprint of Cretoxyrhina, clarifying the generic identity of P'. vraconensis. In the Kolbay population, the distal lobe of the root on the three probable third upper anterior teeth at hand is not labiolingually compressed relative to the mesial lobe. Labiolingual flattening of the root lobe facing the mesial side of the intermediate bar is a characteristic feature of modern lamnids and may reflect limited accommodation space for a thick root lobe to form at the distal margin of the anterior hollow. An intermediate bar adds structural strength to the anterior part of the palatoquadrate while isolating the upper anterior teeth, facilitating deep penetration by their enlarged cusps. Individuals of Cretoxyrhina from the late Coniacian to earliest Campanian Smoky Hill Chalk in Kansas display a strongly disjunct heterodonty in the anterior half of the upper jaw dentition. This so-called lamnoid tooth pattern' is regarded by some researchers as a synapomorphy of the Lamniformes. The dwarfed teeth creating the lamnoid tooth pattern' in Smoky Hill Chalk individuals are seemingly matched by relatively larger, corresponding teeth in the 15 million years older C. vraconensis. The probable weakening of the disjunct upper jaw heterodonty in Cretoxyrhina with increasing geological age indicates that the lamnoid tooth pattern' might have evolved independently in two or more lamniform clades. ?????Pseudoisurus'vraconensis???????????, ?????Mangyshlak??Besakty??Albian????????????????Mortoniceras perinflatum????????????, ???????????Pawpaw??Mortoniceras rostratum??????????????Mangyshlak???Kolbay, ??Albian-Cenomanian??????????????? P'. vraconensis-???, ????Cretoxyrhina?????? 'P'. vraconensis ???????????Kolbay???, ????????????????????????????????????????????????????????????????????????????, ???????????????????????????????, ???????, ???????????????????Coniacian??Campanian?????Smoky Hill ????Cretoxyrhina???????????????????????lamnoid??????????????????????????????Smoky Hill ?????lamnoid?????, ???????15??????C. vraconensis ????????Cretoxyrhina???????????????????, ??lamnoid?????????????????????

• Författare: Mikael Siverson; David J. Ward; Johan Lindgren; L. Scott Kelley
• Avdelning/ar: Berggrundsgeologi
• Publiceringsår: 2013
• Språk: Engelska
• Sidor: 87-104
• Publikation/Tidskrift/Serie: Alcheringa
• Volym: 37
• Issue: 1
• Länkar: http://dx.doi.org/10.1080/03115518.2012.709440
• Dokumenttyp: Artikel i tidskrift
• Förlag: Taylor & Francis
• Ämne: Geology
• Nyckelord: Cretoxyrhina; vraconensis; Pseudoisurus; Cretaceous; Mangyshlak; sharks; dentition
• Aktiv: Published
• ISBN/ISSN/Övrigt: ISSN: 0311-5518