New early Jurassic decapod crustacean from Patagonia (Chubut province), Argentina

Abstract

A well-preserved decapod specimen was found in early Toarcian deposits cropping out on the western slope of Meseta Catreleo, central Chubut province, Argentina. It is a nearly complete exoskeleton preserved in lateral view, slightly crushed, in fine-grained sandstones. The skeleton is mostly articulated, though some pieces are disarticulated or missing. Taphonomic features indicate a relatively rapid burial after death, with little or no transport. This specimen is here described as a new species of the genus Mecochirus Germar (Decapoda: Glypheoidea). Mecochirus robbianoi n. sp. is characterized by a very long, achelate, first pair of pereiopods with a narrow, long, straight dactylus, a thin carapace ornamented by low tubercules, with a slightly oblique cervical groove and a short acute rostrum. The family Mecochiridae arose in the Triassic, but the group diversified during the Early Jurassic. Mecochirus had a wide geographical distribution and is known for sure from Lower Jurassic to Upper Cretaceous deposits. The new record from Chubut is one of the oldest for the genus, the oldest for South America, and the first for Argentina, thus considerably extending the known distribution of the genus during the Early Jurassic.Kurzfassung Ein gut erhaltener Decapode wurde in Ablagerungen des unteren Toarciums auf der Westseite der Meseta Catreleo im Zentrum der Provinz Chubut (Argentinien) gefunden. Es handelt sich um ein fast komplett erhaltenes Exoskelett, welches in einem feinkörnigem Sandstein leicht verdrück in Seitenlage eingebettet ist. Die taphonomische Analyse deutet auf eine rasche Einbettung nach dem Tod, mit nur geringem oder fehlendem Transport. Das hier beschriebene Exemplar wird als neue Art der Gattung Mecochirus Germar (Decapoda: Glypheoidea), M. robbianoi n. sp., beschrieben. Sie zeichnet sich durch ein sehr langes, achelates Paar der ersten Pereiopoden mit schmalen, langem, geradem Daktylus, einem mit flachen Tuberkeln verzierten Carpax mit leicht gerundeter Cervicalfurche und ein kurzes, spitzes Rostrum aus. Die Familie Mecochiridae erschien in der Trias; im Unterjura kam es zu einer Diversifikation. Mecochirus hatte eine weite paläo-geographische Verbreitung und ist vom Unterjura bis in die Oberkreide mit Sicherheit bekannt. Die neue Art ist eine der ältesten der Gattung, die älteste aus Südamerika und zugleich der erstnachweis aus Argentinien. Dies weist auf eine viel größere Verbreitung im Unterjura hin als bisher angenommen.Schlü sselwörter Decapoda Á Glypheoidea Á Mecochirus Á Unter Jura Á Patagonia Á Chubut Á Argentina

Una nueva localidad marina de edad jurásica temprana en la cuenca sudoccidental del Chubut, Argentina.

“…Preliminary biostratigraphic analyses carried out in the southern and west-central Chubut Province (Pagani et al, 2012;Ferrari, 2013Ferrari, , 2014a indicated a late Pliensbachian-early Toarcian age for these deposits. Moreover, Damborenea and Ferrari (2008), Ferrari (2009Ferrari ( , 2011aFerrari ( , b, 2012Ferrari ( , 2013Ferrari ( , 2014a, Ferrari et al (2014) and Pagani et al (2011Pagani et al ( , 2012 recently carried out new studies on the taxonomic composition of the faunas in the Early Jurassic of south-western and central Chubut Province, including the investigation of new fossil localities and the collection of Early Jurassic material.…”

“…The stratigraphy of these deposits has been established by several studies. An updated and detailed historical chronology of the Jurassic stratigraphic sequence of this region in Patagonia was recently provided by Ferrari (2009Ferrari ( , 2011aFerrari ( , b, 2013Ferrari ( , 2014a and Pagani et al (2011).…”

“…According to Damborenea (2002a), the genera Kolymonectes and Agerchlamys show a bipolar distribution, restricted to high latitudes and present in both hemispheres but absent from low latitudes. In the Jurassic of Argentina, species of Kolymonectes are distributed from southern Mendoza Province to the Piedra Pintada region at southern Neuquén, having their southernmost occurrence at the Chubut Province (Damborenea, 2002b;Pagani et al, 2011). Species of Agerchlamys are also found in the Andean region of Argentina, at the late Pliensbachian (Fanninoceras Zone) of Mendoza and Neuquén provinces, and some specimens have been recovered at the Chubut Basin in the Pampa de Agnia area (Damborenea, 2002b).…”

“…naxensis (Gemmellaro) at Lomas de Betancourt, indicates a latest Pliensbachian age (Fanninoceras disciforme Zone, see local zonation of Riccardi, 2008) for this association. marine sediments crop out in the Pampa de Agnia region at Puesto Currumil locality (Ferrari, 2009;Pagani et al, 2011) (Fig. 4B.…”

“…Bivalves, gastropods, cephalopods, brachiopods and corals were reported by these authors from several localities in the area, including Lomas Occidentales, Cerro La Trampa, Piedra Shotle and Lomas de Betancourt, which have yielded the most important Jurassic fossiliferous beds from the marine Mulanguiñeu Formation (Chubut Province). Another important marine locality was reported at the Early Jurassic of the Osta Arena Formation from the Pampa de Agnia region (central Chubut Province), known as Puesto Currumil (Ferrari, 2009(Ferrari, , 2012(Ferrari, , 2013Pagani et al, 2012). Preliminary biostratigraphic analyses carried out in the southern and west-central Chubut Province (Pagani et al, 2012;Ferrari, 2013Ferrari, , 2014a indicated a late Pliensbachian-early Toarcian age for these deposits.…”