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A reappraisal of the Middle Triassic Chirotherium ibericus from Spain

The definitive pdf of this already announced paper:

Ignacio Díaz-Martínez, Diego Castanera, J.M. Gasca, J.I. Canudo. 2015.
A reappraisal of the Middle Triassic chirotheriid Chirotherium
ibericus Navás, 1906 (Iberian Range NE Spain), with comments on the
Triassic tetrapod track biochronology of the Iberian Peninsula. PeerJ,
3: e1044.


Abstract: Triassic vertebrate tracks are known from the beginning of
the 19th century and have a worldwide distribution. Several Triassic
track ichnoassemblages and ichnotaxa have a restricted stratigraphic
range and are useful in biochronology and biostratigraphy. The record
of Triassic tracks in the Iberian Peninsula has gone almost unnoticed
although more than 25 localities have been described since 1897. In
one of these localities, the naturalist Longinos Navás described the
ichnotaxon Chirotherium ibericus in 1906.The vertebrate tracks are in
two sandy slabs from the Anisian (Middle Triassic) of the Moncayo
massif (Zaragoza, Spain). In a recent revision, new, previously
undescribed vertebrate tracks have been identified. The tracks
considered to be C. ibericus as well as other tracks with the same
morphology from both slabs have been classified as Chirotherium
barthii. The rest of the tracks have been assigned to Chirotheriidae
indet.,Rhynchosauroides isp. and undetermined material. This new
identification ofC. barthii at the Navás site adds new data to the
Iberian record of this ichnotaxon, which is characterized by the small
size of the tracks when compared with the main occurrences of this
ichnotaxon elsewhere. As at the Navás tracksite, the Anisian C.
barthii-Rhynchosauroides ichnoassemblage has been found in other
coeval localities in Iberia and worldwide. This ichnoassemblage
belongs to the upper Olenekian-lower Anisian interval according to
previous biochronological proposals. Analysis of the Triassic Iberian
record of tetrapod tracks is uneven in terms of abundance over time.
>From the earliest Triassic to the latest Lower Triassic the record is
very scarce, with Rhynchosauroides being the only known
ichnotaxon.Rhynchosauroides covers a wide temporal range and gives
poor information for biochronology. The record from the uppermost
Lower Triassic to the Middle Triassic is abundant. The highest
ichnodiversity has been reported for the Anisian with an assemblage
composed of Dicynodontipus,Procolophonichnium, Rhynchosauroides,
Rotodactylus, Chirotherium,Isochirotherium, Coelurosaurichnus and
Paratrisauropus. The Iberian track record from the Anisian is coherent
with the global biochronology proposed for Triassic tetrapod tracks.
Nevertheless, the scarcity of track occurrences during the late
Olenekian and Ladinian prevents analysis of the corresponding
biochrons. Finally, although the Iberian record for the Upper Triassic
is not abundant, the presence of Eubrontes, Anchisauripus and probably
Brachychirotherium is coherent with the global track biochronology as
well. Thus, the Triassic track record in the Iberian Peninsula matches
the expected record for this age on the basis of a global
biochronological approach, supporting the idea that vertebrate
Triassic tracks are a useful tool in biochronology.

Jose Ignacio Ruiz-Omenaca
Owner at Geol-Deco, mineral, rock and fossil shop