46006-G8
Vertebrate Paleontology of Upper Cretaceous Deposits of Jordan
Introduction: The paleobiogeographic relationships between Africa and neighboring landmasses during the Cretaceous remain a major question, in part because of the uneven distribution of fossiliferous sediments on southern landmasses. Southern South America is the only region of Gondwana with good representation of terrestrial vertebrates from both Lower and Upper Cretaceous sediments. Those of India, Antarctica, and Madagascar are only known from uppermost Cretaceous sediments, whereas those of Africa and Australia are only adequately known from Cenomanian and older horizons. This sampling discrepancy and conflicting paleogeographic reconstructions have led to competing scenarios to explain paleobiogeographic relationships between southern landmasses. Whilst Africa has relatively few latest Cretaceous vertebrate localities, the Arabian Peninsula has extensive Cretaceous exposures that have seen relatively little concerted collecting. Africa and Arabia maintained a broad geographic connection until rifting of the African and Arabian Plates and opening of the Red Sea ~34 mya and the relatively recent collision between the Arabian Peninsula and Eurasia ~10 mya. Jordan forms the northwestern part of the Arabian Peninsula, which was ringed by seas that received erosional products from the continent throughout the Phanerozoic. Latest Cretaceous deposits are abundant in central and southern Jordan and represent a coastal environment that preserves both terrestrial and aquatic animals.
Field Work: Field exploration in February–March 2008 by a joint National Resources Authority (Jordan) and University of Michigan team into uppermost Cretaceous sediments in central, southern, and western Jordan discovered and collected fossils from approximately 75 localities of varying richness. Lithological sections at 4 of the richest and most geographically separated localities will provide the stratigraphic context for interpreting the discoveries. New Jordanian fossil vertebrates as part of this research include two large marine turtles, the partial skull and skeleton of what will be Africa's most complete pterosaur (flying reptile), and the first diagnostic dinosaur from the Arabian Peninsula. The dinosaur is especially interesting because although it is a sauropod dinosaur - which include the largest land animals - it is relatively small (~9 m) and represents an evolutionarily dwarfed form that seems to have inhabited relatively restricted Tethyan coastal environments. Paleoenvironmental data indicate that this dinosaur lived in or near a coastal environment and likely fed on mangrove palms, which are abundant and well preserved. We collected several inflorescences (fruiting structures) that are among the earliest bona fide mangrove palm macrostructures known.
Results/Future Work: Very little is known of terrestrial vertebrates (such as dinosaurs) from the latest Cretaceous of Africa. The new dwarf sauropod is important because it offers an opportunity to reconstruct the phylogenetic links that may evidence a recent paleobiogeographic history between Africa and neighboring landmasses. Upcoming work will attempt to put the Jordanian dinosaur and pterosaur into a phylogenetic context. Preliminary data seems to suggest links between the Jordanian dwarf sauropod and a contemporaneous sauropod that lived on the northern margin of the Tethys in present day Spain. The Spanish dinosaur may also be an evolutionarily dwarfed form. Histological work on the Jordanian sauropod bones will also be performed in upcoming months to document, so far as possible, the adult status of this individual, which is presently suggested by sutural closure. Interpreting the phylogenetic position of the large pterosaur is more challenging, due to the paucity of diagnostic pterosaur bones known from Africa and the absence of pterosaurs from neighboring Gondwanan landmasses (i.e., Madagascar, India). Currently, the closest relative to our Jordanian pterosaur seems to be Quetzalcoatlus, from the Maastrichtian of North America. However, it is likely that this result will change as more pterosaurs become known from Africa are known and as more comparisons can be made to contemporaneous European and Asian pterosaurs and earlier-appearing Argentine pterosaurs.
