Latest Cretaceous mosasaurs and lamniform sharks from Labirinta cave, Vratsa District (northwest Bulgaria): A preliminary note

Abstract

Preliminary descriptions are given of selected specimens from an assemblage of >65 isolated vertebrate remains, collected in 1985 at the Labirinta cave situated between the villages of Drashan and Breste, east of Cherven Briag (Vratsa district, northwest Bulgaria), from strata of late Maastrichtian age (Kajl?ka Formation). Recorded are a fragmentary lower jaw of a mosasaurine squamate, Mosasaurus cf. hoffmanni (MANTELL, 1829), with two teeth preserved in situ, as well as two isolated teeth of lamniform sharks, assigned to Squalicorax pristodontus (AGASSIZ, 1843) and Anomotodon sp. Other vertebrate remains in this assemblage include rather poorly preserved fragments of skull and appendicular skeleton of mosasaurs, but it cannot be ruled out that other vertebrate groups (elasmosaurid plesiosaurs) are represented as well. To establish this, the additional material needs to be studied in detail and compared with existing collections; it will be described in full at a later date. A partial phragmocone of a scaphitid ammonite, found associated, is here assigned to Hoploscaphites constrictus (J. SOWERBY, 1817) and briefly described as well. This record dates the Labirinta cave sequence as Maastrichtian, as does the echinoid Hemipneustes striatoradiatus (LESKE 1778); tooth morphology of Squalicorax pristodontus and a find of the pachydiscid ammonite Anapachydiscus (Menuites) cf. terminus WARD and KENNEDY 1993 from correlative strata nearby narrow this down to late, or even latest Maastrichtian. Finally, some remarks on mosasaur and plesiosaur distribution during the Campanian-Maastrichtian across Europe are added.Daju se prethodni opisi primeraka odabranih iz asocijacije od preko 65 izdvojenih ostataka kicmenjaka, sakupljenih 1985. godine u pecini Labirinta izmedju sela Drasan i Breste istocno od Cervenog Briaga (Vracanski kraj severozapadna Bugarska) iz slojeva gornjomastrihtske starosti (formacija Kajlaka). Registrovan je deo donje vilice kraljustastog mozazaura, Mosasaurus cf. hoffmanni (MANTELL, 1829), sa dva ocuvana zuba in situ, kao i dva posebna zuba lamniformnih ajkula, koji se pripisuju Squalicorax pristodontus (AGASSIZ, 1843) i Anomotodon sp. Medju ostalim ostacima kicmenjaka u ovoj asocijaciji nalaze se dosta slabo ocuvani fragmenti lobanje i pripadajuceg skeleta mozazaura, ali se ne iskljucuje prisustvo i drugih grupa kicmenjaka (elasmozauridski pleziozauri). Da bi se to utvrdilo, potrebno je detaljno prouciti dopunski materijal i uporediti ga sa postojecim kolekcijama. Potpuniji opis ce biti naknadno uradjen. Delimicni fragmakon skafitidnog amonita, nadjen u asocijaciji, pripisuje se Hoploscaphites constrictus (J. SOWERBY, 1817) i ukratko se opisuje. Prema ovom nalazu, kao i na osnovu jeza Hemipneustes striatoradiatus (LESKE, 1778); sekvenca pecine Labirinta odredjuje se kao mastrihtska; morfologija zuba Squalicorax pristodontus i nalazak pahidiscidnog amonita Anapachydiscus (Menuites) cf. terminus WARD and KENNEDY, 1993 iz obliznjeg izdanka formacije Kajlaka omogucava precizniju odredbu starosti kao kasni mastriht, ili cak najkasniji mastriht. Bliza odredba na gornji mastriht zasniva se na morfologiji zuba. Na kraju, daju se i neka zapazanja u vezi rasprostranjenosti mozazaura i pleziozaura za vreme kampan-mastrihta sirom Evrope.