aN N a ls o f c a r N e g i e M u s e u M vol. 79, nuMbeR 2, PP. 91–123 15 FebRuaRy 2011 New MioceNe DecapoDa (ThalassiNiDea; Brachyura) froM Tierra Del fuego, argeNTiNa: paleoBiogeographic iMplicaTioNs Rodney M. FeldMann [Research associate, section of invertebrate paleontology, carnegie Museum of Natural history] Department of geology, Kent state university, Kent, ohio 44242 [email protected] CaRRie e. SChweitzeR [Research associate, section of invertebrate paleontology, carnegie Museum of Natural history] Department of geology, Kent state university at stark, 6000 frank avenue Nw, North canton, ohio 44720 [email protected] Silvio CaSadío instituto de investigación en paleobiología y geología universidad Nacional de río Negro, 8332 roca, río Negro, argentina [email protected] Miguel gRiFFin división paleozoología invertebrados, facultad de ciencias Naturales y Museo, universidad Nacional de la plata, la plata, Buenos aires, argentina [email protected] aBsTracT a decapod crustacean fauna of Tierra del fuego, argentina, is documented from the middle Miocene carmen silva formation and the early? Miocene cerro Águila conglomerate of the cabo Domingo group. Three new genera and five new species are named: Asthenognathus australen- sis, new species; Miotymolus quadratus, new genus and species; Mursia fuegiana, new species; Pharkidodes agele, new genus and species; and Tierrapilumnus edseli, new genus and species. compilation of all described species of decapods from late oligocene to early pliocene exposures in 18 general localities in patagonia, southern argentina, and chile documents two paleobiogeographic provinces, argentine and chilean. coupled with evidence from the biogeographic patterns of associated mollusks, the faunas from Tierra del fuego have been assigned to the argentine paleobiogeographic province. comparison of the distribution of Miocene decapods with that of extant decapods (Boschi 2000) leads to the con- clusion that the thermal separation of south atlantic and south pacific water in the Miocene was more pronounced than today, so that there is no evidence of a discrete Magellanic Biogeographic province characterizing the high southern latitude region during the Miocene. Key woRdS: anomura, argentina, Brachyura, Decapoda, Miocene, paleobiogeography, Thalassinidea iNTroDucTioN paleobiogeographic distribution of species in southern south america. Decapod crustaceans have been known from Tierra del fuego, argentina, since steinman and wilckens (1908) noted the presence of Geryon peruvianus (d’orbigny, geological seTTiNg 1842), in the cliffs of sierra de carmen silva. subse- quently, aguirre-urreta (1987) made note of this record The geological evolution of the austral (or Magallanes) in a study of geryonidae from southern argentina. other Basin involves three tectonic phases: rift, sag, and foreland than those published accounts referring to decapods from stages that were initiated during the Jurassic and ended in the area, the only collecting of decapods from Tierra del the Neogene. By the late cretaceous, the uplift of the fuego has been anecdotal until recently. in 2007, two of fuegian andes (olivero et al. 2003) preceded the subse- us (sc and Mg) studied the exposures of cenozoic rocks quent origination of the foreland austral Basin (Biddle et in the area and identified several localities that contained al. 1986). decapod material (fig. 1). in the following year, three of The northern propagation of the deformation initiated us (rMf, Mg, and ces) visited these localities and made four clastic successions of late cretaceous–Danian, late large collections of fossils from several of them. in 2009, paleocene–early eocene, late middle eocene–late eocene, two of us (sc and Mg) returned to the localities to make and oligocene–middle Miocene ages; they are thicker to- more detailed stratigraphic analyses of the sections. The ward the fold and thrust belt to the west and south, and material from these recent field excursions forms the basis thinner with internal truncations toward the foreland in the for the present study. east and north (olivero and Malumián 2002, 2008; ponce The purposes of the study are to describe the geologi- et al. 2008). cal setting in which fossil decapods occur in Tierra del The late oligocene–Miocene succession of the austral fuego, to describe the decapods, and to summarize the Basin in Tierra del fuego island, southern patagonia, lies 92 AnnalS oF CaRnegie MuSeuM vol. 79 fig. 1.—locality map of a part of eastern Tierra del fuego showing the sites from which fossil decapods were collected. in front of the fold and thrust belt, and primarily represents sequences are constructed of three main architectural ele- the infilling of the youngest foredeep of the foreland basin ments: hyperpycnal lobe complexes, hyperpycnal channel (fig. 1). The best outcrops of this sequence are on the cliffs complexes, and associated hyperpycnal levee complexes, along the atlantic coast of the island. which were interpreted by ponce et al. (2008) as deposi- since the early Miocene, sedimentation was repre- tional slope clinoform systems in a mainly deep marine sented by primarily unfolded strata developed after the environment. hyperpycnal flows and their deposits are compressive deformation (Malumián and olivero 2006). a formal part of the walker (1978) classification of deep This youngest succession of marine and fluvial deposits water deposits. Mulder and syvitski (1995) and Mulder et is mostly included in the upper part of the cabo Domingo al. (2003) differentiate turbidity currents that are generated group (Malumián 1999). This group is partially correlated by the transformation of a submarine slide into a turbulent with shelf deposits of the marine Monte león and centine- flow from flows that are generated by processes, such as la formations in the northern part of the austral Basin, and from hyperpycnal discharge of a river during floods. with the overlying continental deposits of the santa cruz formation (Malumián 1999; Malumián and olivero 2006; olivero and Malumián 2008). The cabo Domingo group collecTiNg localiTies reflects the typical geometry of a foreland basin fill with thicker packages and a more complete stratigraphic record San Julio Section.—Middle Miocene carmen silva near the fold and thrust belt, and a less wide-ranging re- formation on cerro castillo, estancia san Julio, lat. cord toward the foreland. 53°39’47.7”s, long. 68°26’49.3”w, Tierra del fuego, ar- ponce et al. (2008) recognized five depositional se- gentina, our waypoint 173 (fig. 2). quences within the late oligocene–Miocene clastic suc- The carmen silva formation of the cabo Domingo cession along the atlantic coast of Tierra del fuego. The group at the san Julio section consists of mudstones, 2010 FeldMann et al.—new MioCene deCaPoda 93 fig. 2.—stratigraphic section exposed in the san Julio section. photographs a–e are referred to in the text. M = mud, FS = fine sand, MS = medium sand, CS = coarse sand, G = gravel. sandstones, and conglomerates that, according to the fos- of the section records deposition in a distal prodelta en- sil content, are middle Miocene in age (codignotto and vironment. The middle part of the section is composed of Malumián 1981). The lower part of the san Julio section sandstones and minor conglomerates. The latter consists is comprised of seven meters of laminated mudstones of more than 80% pebbles with sandy matrix. conglom- and fine-grained sandstones that crop out in small scarps. erates include intraformational clasts of laminated mud- These beds pass upwards into tuffaceous sandstones with stone, igneous rocks, common reworked trace fossils and gently undulating, low angle cross-lamination. This part well-preserved corals, Flabellum cf. F. cuneiforme wailesi 94 AnnalS oF CaRnegie MuSeuM vol. 79 conrad, 1855; mollusks, Nucula (Leionucula) grandis of the mudstones. Based upon the fossil content and the Malumián, camacho, and gorroño, 1978; Neilo doello- lithology, codignotto and Malumián (1981) proposed that juradoi Malumián, camacho, and gorroño, 1978; Glycy- this part of the section records deposition in a distal pro- meris cuevensis (ihering, 1897); Cucullaea fueguensis delta environment. overlying the mudstones are up to 15 Malumián, camacho, and gorroño, 1978; unnamed spe- m of interbedded, chaotic, mostly sandy, matrix-supported cies of Swiftopecten Bernardi, 1858; Modiolus ameghinoi conglomerates and sandstones. conglomerates form cha- ihering, 1897; Pteromyrtea crucialis (ihering, 1907); Fas- otic meter-thick beds and are poorly sorted, with sub-an- ciculicardia freti (ihering, 1907); Pleuromeris sylva (iher- gular to sub-rounded intraformational clasts of laminated ing, 1907); Retrotapes fuegoensis del río, 1997; Turritella mudstones (fig. 3c). pumicite pebbles and mollusk shells sylva (ihering, 1907); unnamed species of Penion fischer, are commonly dispersed in the beds (fig. 3D). among the 1884; unnamed species of Calyptraea lamarck, 1799; species identified areNeilo cf. N. ornata, Arca (Neonavic- Calyptraea merriami (ortmann, 1899); Struthiochenopus ula) cf. N. patagonica (ihering, 1897), Glycymeris cueven- santacruzensis (ihering, 1907); Perissodonta fuegensis sis (ihering, 1897), unnamed species of Ostrea (linnae- (ihering, 1907); new species of Polinices Montfort, 1810; us, 1758), Zygochlamys geminata (sowerby, in Darwin, Polinices santacruzensis ihering, 1907; Falsilunatia pun- 1846), Pleuromeris elegantoides (ortmann, 1902), Tur- tarenasensis (ihering, 1907); Buccinanops