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New Cenomanian vertebrate tracksite at Tamajón in Spain



Ben Creisler
bcreisler@gmail.com


A new online paper:


Manuel Segura, Fernando Barroso-Barcenilla, Mélani Berrocal-Casero,
Diego Castanera, José F. García-Hidalgo & Vanda F. Santos (2015)
A new Cenomanian vertebrate tracksite at Tamajón (Guadalajara, Spain):
Palaeoichnology and palaeoenvironmental implications.
Cretaceous Research (advance online publication)
doi:10.1016/j.cretres.2015.04.011
http://www.sciencedirect.com/science/article/pii/S0195667115000634

A new Upper Cretaceous vertebrate tracksite has been discovered at
Tamajón (Iberian Ranges, Guadalajara, Spain). The track level is a
relatively smooth and slightly undulating sandy ferruginous crust,
corresponding to an erosive surface at the base of a small meandering
channel. It is incised into the underlying planar cross-bedded
sandstones of coastal bars located at the middle-upper part of the
Utrillas Formation (middle-upper Cenomanian). The site shows an
extraordinary concentration of vertebrate tracks, among which numerous
sets of two to five isolated digit impressions (“swim tracks”) and, at
least, two trackways referred to crocodyliforms, and a single
tridactyl footprint probably produced by a theropod dinosaur can be
recognized. There are also several long traces (epichnial grooves)
revealing sharp direction changes (up to 90°) which seem to be fish
fin traces (Undichna unisulca), although crocodyliforms (tail marks)
and/or fish invertebrates cannot be rejected as possible tracemakers.
Some crocodyliform tracks reveal a thin raised rim, due to the
displacement of the sediment by the pressure produced by the feet.
Several impressions are moderately deformed by small sediment slides,
only preserving their deepest part (claw marks). This is clearly
indicative of a soft substrate with a high degree of plasticity and
water content at the time of the track registration. Nevertheless, the
sediment was hard enough to preserve manus and pes print morphologies
and also possible crocodyliform tail and/or fish fin traces. Small
rhizoliths can also be recognized and may belong to herbaceous wetland
vegetation. The morphology of the palaeochannel, the sedimentary
context and the track preservation seem to indicate that the tracks
were impressed in a shallow channel located near the coast, under wet
conditions and in different moments of time. This discovery represents
the first occurrence of vertebrate ichnites in the Utrillas Formation,
a stratigraphic unit where osteological and ichnological remains are
relatively scarce, and it confirms that some crocodyliforms lived in
near coast channels during the deposition of this unit.