Maria B. Aguirre-Urreta

The ammonites Karakaschiceras and Neohoploceras (Valanginian Neocomitidae) from the Neuquen Basin, west-central Argentina

Three species of Karakaschiceras, K. attenuatus (Behrendsen, 1892), K. neumayri (Behrendsen, 1892), and K. lycoris (Leanza and Giovine, 1949), and one species of Neohoploceras, N. arnoldi (Pictet and Campiche, 1860), are described and figured from the Valanginian strata of the Neuquen basin in west-central Argentina. The large collection of fossils available for study shows wide intraspecific variation regarding ornament and whorl section in Karakaschiceras neumayri and Neohoploceras arnoldi, casting some doubts on the current systematics applied to species of these genera. The biostratigraphic position of the four species in the Neuquen basin corresponds to the Karakaschiceras attenuatus Subzone of the Olcostephanus atherstoni Zone. This subzone is correlated with the Mediterranean Karakaschiceras inostranzewi and Saynoceras verrucosum zones of Europe at the base of upper Valanginian sections.

Lower Cretaceous ammonites from the Neuquén Basin, Argentina: the Hauterivian genus Holcoptychites

Holcoptychites is known only from the Neuquen Basin, Argentina, but appears close to the more widespread genera Jeanthieuloyites and Spitidiscus. Thus it is placed in the subfamily Spitidiscinae (Family Holcodiscidae). Previously described Holcoptychites species are revised and their taxonomy clarified, while one new species is left under open nomenclature. The sequence of forms allows two subzones to be recognized. These are correlated provisionally with the lowest Hauterivian Acanthodiscus radiatus Zone of the Mediterranean region.

Tertiary Freshwater Decapoda (Crustacea: Parastacidae) from the Ñirihuau Basin, Patagonia, Argentina

Very well preserved specimens of a macruran decapod from the Lower (Lacustrine) Member of the Nirihuau Formation, northwestern Patagonia, Argentina, permitted description of Lammuastacus longirostris , a new genus and species of Parastacidae. The sedimentological and paleontological evidences provided by the faunal assemblage indicate a freshwater environment. This is the first certain record of a fossil Parastacidae from Tertiary deposits, most probably Oligocene. The fossil material shows similarities with Geocharax , the extant Australian genus considered to retain many primitive characters, and other related genera from New Zealand and Chile.

Stratigraphic Position of Valanginites, Lissonia, and Acantholissonia in the Lower Valanginian (Lower Cretaceous) Ammonite Sequence of the Neuquen Basin, Argentina

Valanginites, previously known from Argentina by a single specimen (holotype of V. argentinicus Leanza & Wiedmann), is recorded from two localities in the Neuquen Basin, each of which has yielded six specimens. It occurs just beneath a widely distributed Lissonia/Acantholissonia fauna that forms a distinctive level, here separated as the Lissonia riveroi Zone, in the top part of the Vaca Muerta Formation and its equivalents. Both these faunas occur well below a basal Upper Valanginian Karakaschiceras fauna. Hence Valanginites appears considerably earlier in Argentina than in Europe.

On the Pterosaur Remains from the Río Belgrano Formation(Barremian), Patagonian Andes of Argentina

Pterosaur remains from the Río Belgrano Formation, Santa Cruz Province, Argentina, were found close to the Estancia Río Roble, along with several ammonoids that indicate a Barremian age for those strata. The specimens (MACN-SC 3617) consist of one ulna and one element tentatively identified as a portion of a wing metacarpal. The ulna shows morphological affinities with the Pteranodontoidea (sensu Kellner 1996), particularly with the members of the Anhangueridae by having a well developed ventral crest close to the proximal articulation, and is tentatively referred to this pterosaur clade. The oldest record of the Anhangueridae, previously limited to the Aptian/Albian, is therefore extended to the Barremian. The Argentinean material is preserved in three dimensions, an unusual condition for pterosaur fossils from that country, indicating that the site situated near the Estancia Río Roble has a great potential for new and well preserved specimens.

A Cretaceous hermit crab from Antarctica: predatory activities and bryozoan symbiosis

A hermit crab assigned to Paguristes sp. is described from James Ross Island, Antarctica. The fossil was obtained from the Gamma Member of the Santa Marta Formation of late Campanian age. The specimen is associated with an external mould of the gastropod Taioma , that was encrusted by a colony of ascophoran bryozoans. Another specimen of Taioma shows typical predatory marks in the outer lip that are attributed to the action of pagurids. It is concluded that the particular dwelling habits of the hermit crabs, their symbiosis with bryozoan, and their predatory activities were already established by the end of the Cretaceous.

First Polychelidae (Crustacea, Palinura) from the Jurassic of Antarctica

A new fossil genus of decapod Crustacea, belonging to the family Polychelidae is described from James Ross Island, Antarctic Peninsula. The specimen was obtained from a block of reworked Jurassic tuffaceous black shale belonging to the Ameghino (= Nordenskjold) Formation in the Lower Cretaceous Kotick Point Formation. This is the first report of fossil Polychelidae in the Southern Hemisphere.

Cretaceous Evolution of the Magallanes Basin

This work presents a summary of the evolution of the Magallanes basin in the Patagonian Andes, between 45°S and 54°S latitude, during the Cretaceous. A brief description is given of the pre-Mesozoic basement and the Jurassic volcanic sequences which underlie the Tithonian- Cretaceous deposits.

A new tube-builder hydractinian, symbiotic with hermit crabs, from the Cretaceous of Antarctica

An Upper Cretaceous (early Maastrichtian) tube-building hydractinian ( Psammoactinia antarctica n. gen. and sp.) from Sanctuary Cliffs, Snow Hill Island, believed to live in association with hermit crabs, is described for the first time from Antarctica. Psammoactinia forms thick, concentric, globular colonies that encrust gastropod shells and extend the shell aperture by forming an open spiral tube. The colony consists of concentric layers with chambers and pillars made of silt and very fine sand grains agglutinated by collophane, which is interpreted as a diagenetic modification of an original chitinous phosphatic material. On the basis of the additional finding of isolated claws of pagurid crabs, assigned to Paguristes sp., the functional analysis of the hydractinian structure, and a comparison with modern and fossil analogous structures it is concluded that the peculiar hydractinian tube is a carcinoecium that housed a symbiotic hermit crab. Paleoenvironmental and paleoecological inferences suggest that the Psammoactinia–Paguristes association is mainly controlled by a fine-grained substrate and by a lack of abundant gastropod shells of different sizes. These factors do not necessarily correlate with absolute water depth, and favorable environments could include either offshore, relatively deep water or shallow restricted depositional settings.

A new Eocene crab (Crustacea, Decapoda) from Seymour Island, Antarctica

A new xanthid crab, Tumidocarcinus foersteri n. sp. is described from the La Meseta Formation on Seymour Island, Antarctica. The fossils were obtained from the Allomember Submeseta of Late Eocene age. As other representatives of the genus Tumidocarcinus were only known from New Zedand and Australia, this finding provides new insights on the palaeobiogeography of high latitude faunas during the Early Tertiary.