Friday, 6 June 2014

Theropod remains from the earliest Jurassic of Luxembourg.

Terrestrial faunas of the Triassic comprised a wide variety of large Vertebrates, including Synapsids and both Dinosaurian and non-Dinosaurian Archosaurs. At the end of the Triassic a major extinction event wiped out or greatly reduced most of these groups, with the Dinosaurs rapidly rising to dominate terrestrial faunas for the remainder of the Jurassic and Cretaceous. However at the beginning of the Jurassic is a period of 3.1 million years, known as the Hettangian, in which Dinosaur remains are virtually unknown; the global total currently comprising one specimen from England, another from Arizona, and three more specimens that may originate from the Hettangian from Zimbabwe, France and Antarctica. This gap is considered particularly puzzling as Dinosaur trackways from this era are widespread and abundant across the globe, suggesting that Dinosaurs were present but have failed to be preserved.

In a paper published in the journal Geologica Belgica in 2014, Dominique Delsate of the Centre de Recherche Scientifique, Paléontologie at the Musée national d’histoire naturelle de Luxembourg and Martin Ezcurra of the School of Geography, Earth and Environmental Sciences, at the University of Birmingham and GeoBio-Center at Ludwig-Maximilian-Universität München describe two fragmentary, isolated Theropod Dinosaur specimens from the Late Hettangian of the Luxembourg Sandstone Formation (Grès de Luxembourg) at the Feidt Quarry at Reckingerwald, near Brouch. These deposits are considered to be marine in origin, and have previously produced a variety of marine invertebrates, plus Marine Reptile, Shark and Myriacanthid Fish remains. However the site is also thought to have been close to the eastern tip of the London-Brabant-Ardennes Landmass at the time of deposition, so terrestrial Dinosaur remains are not completely surprising.

(A) Map of Luxembourg showing the provenance (black bone) of the specimens described here. (B) Palaeogeographical reconstruction of part of western Europe during earliest Jurassic times. Exposed landmasses during the earliest Jurassic are indicated in grey and the position of the Luxembourg area is indicated by a black bone in (B). Delsate & Eczurra (2014).

The material described comprises an isolated partial pedal phalanx (foot-bone) attributed to a Neotheropod Dinosaur (Ceratosauria and Tetanurae; i.e. all but the earliest and most primitive Theropods) and a partial tooth, which is compressed and curved backwards and which lacks ornamentation, which suggests that it almost certainly originated from a Theropod Dinosaur (some early Crocodilomophs also produced teeth similar to this, but this specimen would be exceptionally large for such a tooth, making a Theropod origin the more likely explanation.

Pedal phalanges of the Feidt Quarry Neotheropod (A,C,E) and Dilophosaurus wetherilli (B, D, F). (A-B) Lateral; (C-D) dorsal and (E-F) proximal views. Abbreviations: cp = collateral pit, dat = distal articular trochlea, ef = extensor fossa, lvf = lateroventral flange, paf = proximal articular facet. Scale bars equal 2 cm. Delsate & Eczurra (2014).

Tooth crown of the Feidt Quarry Theropod (A,C,E) and Dilophosaurus wetherilli (B, D). (A-B) Labial; (C-D) distal and (E) basal views. Abbreviations: cr = crown-root boundary, dd = distal denticles, md = mesial denticles, wd = weathered distal carena. Scale bars equal 1 cm. Delsate & Eczurra (2014).

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