Abstracts

ARRATIA, Gloria & Alberto CIONE:
The Record of Fossil Fishes of Southern South America

The record of fossil fishes of southern South America is analyzed. Lists of taxa, their geographic occurrences, ages, and sources of literature are presented in appendices.

The fish diversity changes considerably from place to place and among geological periods. Records of Paleozoic fishes (e.g., primitive agnathans, chondrichthyans, placoderms, acanthodians, actinopterygians, and sarcopterygians) are almost exclusively restricted to Bolivian localities. Triassic fishes (e.g., primitive neopterygians) are mainly recorded from Argentina, but are poorly known because of incomplete preservation. In contrast, Jurassic fishes from Chile are represented by numerous well-preserved forms (e.g., mainly teleosts, a few pycnodontiforms, semionotiforms, pachycormiforms), they constitute the best known southern South American fossil fishes. The teleostean varasichthyid group (including the Chilean genera Bobbichthys, Domeykos, Protoclupea, and Varasichthys and the Cuban genus Luisichthys) is one of the few monophyletic groups among the Jurassic basal teleosts. The Cretaceous and Cenozoic fish faunas comprise chondrichthyans, few primitive actinopterygians, few halecostomes, numerous teleosts, and a few sarcopterygians.

During the Late Cretaceous-Paleocene southern South America was inhabited by forms (e.g., ceratodontid sarcopterygians and polypteriform and lepisosteiform actinopterygians) which do not occur today in the South American continent. Most Late Cretaceous-Paleocene freshwater forms become extinct during the Paleocene and were replaced by genera still living in South America today. Among them, the teleostean groups are the best represented.

BONAPARTE, José F.:
Cretaceous Tetrapods of Argentina

An annotated list of the Cretaceous tetrapods of Argentina and comments on the most significant paleobiogeographical and evolutionary issues of the South American and Gondwanian continental tetrapods are presented. In addition, a new and small theropod from Hauterivian beds of Patagonia is described and illustrated. It is named Ligabueino andesi n. gen. and n. sp., and interpreted as part of the Ceratosauria, possibly the Noasauridae. It is characterized by cervical neural arches provided with dorsal and lateral planes sharply defined. A new sauropod, Rayososaurus agrioensis n. gen. and n. sp. from Aptian beds of Patagonia is reported; it is characterized by an elongated triangular cross-section of the acromial process of the scapula; this form is possibly related to Rebbachisaurus from the Albian of Morocco. The concept of Titanosauria is reviewed to include titanosaurs of different degrees of derivation: (1) the Andesauridae provided with "normal" to very derived hyposphene-hypantrum structures, and amphyplatian caudals, and (2) the Titanosauridae without hyposphene-hypantrum, with procoelian caudals along the tail, and restricted to the Late Cretaceous.

The outstanding evolutionary pathways followed by the Cretaceous South American (and Gondwanian) continental tetrapods are emphasized. They produce different faunal assemblages and adaptative types to those known from Laurasia due to the long term biogeographic separation between Laurasia and Gondwana. New aspects of the evolutionary potentials of crocodiles, dinosaurs, and mammals from the Late Cretaceous of Argentina are discussed.

BÁEZ, Ana María & Néstor G. BASSO:
The earliest known frogs of the Jurassic of South America: Review and cladistic appraisal of their relationships

The earliest records of frogs in South America, which are also some of the oldest known occurrences of this group of amphibians, are from the Jurassic of the most southern part of this continent. The Liassic Vieraella herbstii REIG and the Callovian-Oxfordian Notobatrachus degiustoi REIG have been considered to be allied with the most primitive living anurans Ascaphus and Leiopelma; however, most of the characters that these taxa share are plesiomorphic. A reinterpretation of these fossil taxa, based on the study of high-fidelity casts of published, as well as recently collected, material is presented. Interesting features overlooked in previous studies include the presence of ten presacral vertebrae, the extensive posterior body of parasphenoid and the conspicuous vomers of Vieraella, and the presence of a parahyoid bone and the peculiar structure of the vertebrae of Notobatrachus. Based on this new information, a phylogenetic analysis was designed to address the problem of the cladistic relationships of both taxa. Cladistic analysis was performed using Hennig86 software, version 1.5. Fifty equally weighted characters, binary as well as multistate, and representing all of the major structural regions of the skeleton, were used. The living anuran taxa Alytes, Ascaphus, Bombina, Discoglossus, and Leiopelma were also included in the ingroup. Vieraella is the most basal known member of Salientia, except the Early Triassic Triadobatrachus from Madagascar, in the possession of a higher number of presacral vertebrae. However, several character states of Vieraella remain in doubt owing to the poor preservation of the single known representative; thus a high degree of uncertainty remains with respect to its phylogenetic position. The bizarre Notobatrachus is the sister taxon of the crown group Anura as it possesses the plesiomorphic state of several anuran synapomorphies. This study does not support neither a close relationship between these two fossil taxa nor their alliance with Ascaphus and/or Leiopelma, as proposed previously. Early vicariant events in salientian history might have been related to continental rifting, rather to actual break up of the Paleozoic-Early Mesozoic Pangaea.

GASPARINI, Zulma:
Biogeographic Evolution of the South American Crocodilians

The record of South American crocodilians comprises their whole chronological history: from the Late Triassic to the Present. A correlation between the geotectonic macroevents and the geographic distribution of these reptiles is observed. The close phylogenetic relationship of Hemiprotosuchus, from the Late Triassic of Argentina, and Protosuchus from the Late Triassic-Early Jurassic of North America and Africa is consistent with the proximity of Laurasia and Gondwana by that time. The only Jurassic crocodilians in South America are the marine Thalattosuchia from the Pacific edge. While the scarce Liassic remains present doubtful biogeographic relationships, those of Dogger (Metriorhynchus) and Malm (e.g., Metriorhynchus, Geosaurus, Dakosaurus) are closely linked with those of the European Tethys. The passage of these excellent swimmers through the Hispanic Corridor during the Middle Jurassic, and through this corridor and other new ways that opened in the Late Jurassic are the most admissible explanations. In the Early Cretaceous (up to the Aptian-Albian) South America-Africa share vicariant groups such as Araripesuchus, Sarcosuchus and a group of notosuchians with multicuspidated teeth. Nevertheless, in the Late Cretaceous, and as a consequence of the virtual isolation of South America, strong endemisms are observed (e.g., Notosuchus, Uruguaysuchus, Comahuesuchus, Baurusuchidae, Peirosauridae, and Dolichochampsidae). The broad distribution of the Maastrichtian dirosaurids (in both Americas, Africa and part of Asia) coincides with their marine-estuarine habits.

During the Tertiary, the familiar composition changes and a direct concordance between the habitat alteration and the local or final extintion of each family is observed. Except for the dirosaurids which cross the K-T boundary, in the Paleogene new autochthonous families (Sebecidae, Bretesuchidae) occur with other alochthonous ones (Crocodylidae, Alligatoridae). In the Neogene the diversity increases and, with the exception of the already extinct dirosaurids, the Nettosuchidae (autochthonous) and the Gavialidae (alochthonous) occurred too. During the Pleistocene the crocodilians were reduced to a few records of living forms, and a slight increase of the present diversity is recognized.

ALBINO, Adriana M.:
The South American Fossil Squamata (Reptilia: Lepidosauria)

The record of South American fossil Squamata extends from the Cretaceous to the Holocene. It includes families and species with living and extinct representatives from Argentina, Brazil, Bolivia, Chile, Peru, Ecuador, Colombia, and Venezuela. The recorded groups are Amphisbaenia, Aniliidae, Boidae, Colubridae, Gekkonidae, Iguania, ?Scincidae, Teiidae, Tropidopheidae, and Viperidae. Among the groups that inhabit South America at present, the Anguidae, Anomalepididae, Elapidae, Gymnophthalmidae, Leptotyphlopidae, and Typhlopidae do not have fossil representatives. Dinilysiidae from the Late Cretaceous, Madtsoiidae from the Late Cretaceous to early Eocene, and Palaeopheidae from the late Eocene are the only known extinct recorded families. Madtsoiidae is referred to the Alethinophidia as a separate family, probably close to their origin. The distribution of Squamata during the Cretaceous and most of the Tertiary was apparently more extensive than at present, due to more generalized subtropical climatic-environmental conditions. The geological events during the Cenozoic would have caused climatic and environmental changes that would have favored the appearance of new adaptative forms and the restriction in the geographic distribution of many species.

CHIAPPE, Luis M.:
Late Cretaceous Birds of Southern South America: Anatomy and Systematics of Enantiornithes and Patagopteryx deferrariisi

The finding of abundant material of Cretaceous birds in Argentinian territory significantly improves available information about the early evolutionary history of birds. In the present paper, the most outstanding anatomical aspects of the main groups of birds recorded in the Late Cretaceous of Argentina, the Enantiornithes and Patagopteryx deferrariisi are summarized.

The Enantiornithes comprise a diverse group of flying birds worldwide distributed during the Cretaceous. Numerous characters diagnose this clade. Among the most outstanding are: the presence of dorsal vertebral bodies with strong lateral grooves; a broad, deep fossa on the dorsal surface of the coracoid; and a well-developed posterior trochanter on the proximal end of the femur.

Patagopteryx deferrariisi is a flightless bird only known from the Late Cretaceous of Neuquén. P. deferrariisi exhibits characters previously unknown within birds, such as the quadrato-pterygoid fusion, the presence of transversely reniform and procoelous posterior dorsals, and a metacarpal minor that is more robust than the metacarpal major.

To establish the phylogenetic relationships of these two taxa, 67 cranial and postcranial characters and their distribution in the main avian clades were analyzed. This analysis indicates that Patagopteryx deferrariisi is the sister group of the Ornithurae (defined as the common ancestor of Hesperornithiformes and modern birds plus all its descendants), and that Enantiornithes is the sister group of the clade formed by P. deferrariisi + Ornithurae.

TAMBUSSI, Claudia & Jorge NORIEGA:
Summary of the Avian Fossil Record from Southern South America

The present contribution summarizes the Cenozoic (with emphasis on the Tertiary) avian fossil record from the Southern South America and West Antarctica. Also included are a few Mesozoic records of ornithurine birds. The analysis comprises all the known orders of Aves, with the exception of the oceanic sphenisciform and procellariform birds. Birds are valuable indicators of paleobiogeographic and paleoenvironmental conditions. Discussed are the late Miocene avifauna of the Mesopotamian region of Argentina and the early-middle Pliocene one of Buenos Aires Province: birds belonging to extant families has proven to be better in some cases than several South American extinct mammals which do not have analogue descendants. Regarding the faunal interchange between North and South America during the late Tertiary, it is noted that some groups of birds completely flightless or poor fliers evolved in a complete isolation. Likewise, some good flying birds did not participate in the interchange until the definitive connection was established. In contrast, other families developed an important interchange before the Pliocene.

PASCUAL, Rosendo, Edgardo ORTIZ JAUREGUIZAR & José Luis PRADO:
Land Mammals: Paradigm of Cenozoic South American Geobiotic Evolution

Cenozoic South American land mammals demonstrated to be the richest and most eloquent known testimonies to infer the geobiotic evolution of the continent throughout this geological span. The concept and practice followed to recognize by them the South American Land Mammal Ages (SALMAs) are explained. Likewise, it is explained the analytical method used to recognize four hierarchical ranks of organization of the 16 SALMAs, which are distinguished as "faunistic cycles" (from higher to lower, Megacycles, Supercycles, Cycles, and Subcycles). Each of these cycles is defined by an unique association of mammal families, and on the whole are apparently correlated to a hierarchy of world-wide and regional changes in environmental conditions. The Faunistic Cycles are used as "standard units" because they appear to be more closely related to physical and biological regional phenomena. The long-standing autochthonism showed by the South American Late Cretaceous-Cenozoic mammals, as well as the peculiar South American biogeographical history, is briefly analyzed as associated to the climatic shifts related to eustatic falls and geodynamic processes. The successive Late Cretaceous-Cenozoic range pattern and facies of land mammal-bearing deposits is also analized in association to eustatic falls and geodinamic processes. Finally, using this background, and as base for the seven Faunistic Cycles so far recognized, the general pattern of evolution of land mammals is chronologically and synthetically analyzed, and particularly, the trends and features of each of the Faunistic Cycles.

COZZUOL, Mario:
The Record of the Aquatic Mammals in Southern South America

Fossil aquatic mammals in southern South America have been known for more than a century. Despite this fact, they have received little attention compared with the unique South American land mammals. During recent years the interest increased and several new species and reviews of old ones have been published. The South American aquatic mammals include late Eocene, late Oligocene-early Miocene, middle Miocene, Pliocene, and Quaternary records. Between the Cetacea all the three orders, the Archaeoceti, Mysticeti, and Odontoceti are represented with the families Basilosauridae, Llanocetidae, Cetotheriidae, Balaenidae, Balaenopteridae, Physeteridae, Ziphidae, Squalodelphidae, Squalodontidae, Eurhinodelphidae, Iniidae, Pontoporiidae, Kentriodontidae, Phocoenidae, Odobenocetopsidae, Delphinidae, and Phocoenidae. The Pinnipedia are represented by the families Otariidae and Phocidae, with records starting in the middle Miocene. Both living families of the Sirenia (Trichechidae and Dugongidae) are recorded. A summary of the aquatic mammals known up to date is given here, with comments on the most significant ones. This review includes a complete list of species based on the literature and unpublished data. Two case studies are included. The phylogeny of the family Iniidae is discussed proposing a new subfamilial arrangement and introducing the new subfamily Ischyrorhynchinae. The auditory region of the problematic odontocete Phoberodon arctirostris CABRERA 1926 is described by the first time and its relationship with the family Squalodontidae is discussed considering that Phoberodon should probably be excluded of this family.