6533b870fe1ef96bd12d0514

RESEARCH PRODUCT

Ammonite dating of latest Cretaceous mosasaurid reptiles (Squamata, Mosasauroidea) from Jordan—preliminary observations

subject

description

Newly collected ammonoid material from the uppermost Cretaceous portion of the Muwaqqar Chalk Marl Formation exposed some 30 km southeast of the Qasr Al’Harrana area (east-central Jordan) includes medium-sized baculitids (Baculites ovatus auctorum, non Say), the sphenodiscid Libycoceras acutodorsatus (Noetling) and the pachydiscids Menuites fresvillensis (Seunes) and Pachydiscus (Pachydiscus) dossantosi (Maury). Of the two last named taxa, the former is a good marker species for the upper Maastrichtian, with records from Europe, central Chile, South India, Baluchistan (Pakistan), Australia, Madagascar and South Africa. The latter is known from the United Arab Emirates/Oman border area, from strata of (late) early to early late Maastrichtian age, as well as from more poorly constrained Maastrichtian levels in Brazil and Nigeria. A comparison with ammonoid assemblages from the Maastrichtian type area (southeast Netherlands/northeast Belgium) suggests correlation of the Muwaqqar Chalk Marl Formation with the middle/upper Maastricht Formation (Emael and Nekum members, ca 66.5–66.1 Ma) and the upper part of the coeval Kunrade Formation. However, associated ‘tegulated’ inoceramids of the Tenuipteria argentea group from the Muwaqqar Chalk Marl Formation favour equivalence with a higher level of the Maastrichtian type area, i.e., the Meerssen Member. From the upper Maastricht Formation and the equivalent upper part of the Kunrade Formation, the following mosasaur genera are currently known: Mosasaurus, Prognathodon, Plioplatecarpus and Carinodens. Interestingly, coeval strata of the Muwaqqar Chalk Marl Formation in east-central Jordan have yielded remains of a largely comparable suite comprising Prognathodon, Mosasaurus, Carinodens and an unnamed, highly derived plioplatecarpine.