María Teresa Dozo

New rodents (Mammalia) from the late Oligocene of Cabeza Blanca (Chubut) and the first rodent radiation in Patagonia

Caviomorph rodents, the New World Hystricognathi, are one of the most characteristic groups of South American mammals. Although they have been in the continent at least since the middle Eocene, those of the Deseadan Land mammal Age (early–late Oligocene) are the best source to understanding their early history due of their good record, large geographic distribution and good temporal calibration of many of the local faunas. Here, we describe the following new taxa from the classical locality of Cabeza Blanca: Octodontoidea Acaremyidae Galileomys baiosn. sp., Octodontoidea incertae sedis Ethelomys loomisin. gen.,n. comb., Acarechimys leucotheaen. sp., Protacaremys? adilosn. sp., Chinchilloidea incertae sedis Loncolicu tretosn. gen., n. sp., Incamys menniorumn. sp., Caviomorpha incertae sedis Llitun notucan. gen., n. sp., Leucokephalos zeffiaen. gen., n. sp. and Cephalomyidae Cephalomys ceciaen. sp. The DP4 of an ‘eocardiid’, Asteromys punctus? is described for the first time. These new taxa allow us to reinterpret the relationships of some of the previously known Deseadan species and genera. They show a great early diversification at least for extra Andean Patagonia, involving at least three of the main caviomorph lineages: octodontoids, chinchilloids and cavioids.

Neurocranial and Brain Anatomy of a Late Miocene Eagle (Aves, Accipitridae) from Patagonia

ABSTRACT The neurocranial fragment from the Late Miocene (Huayquerian SALMA, 9,0 to 6,8 Ma) of Estancia La Pastosa new locality, Puerto Madryn Formation, Patagonia, Argentina, is described. This is the first available fossil skull of Accipitridae in South America. Features as the elongated-triangular shape of the cranial roof, vast separation between the processus postorbitalis and between both fossae temporalis, and narrow and acuminate outline of the fossa temporalis allow to assign the fossil to Accipitridae Vieilloit, 1816. The well-preserved cavum cranii allowed construction of an endocast that partially reflects brain anatomy. The latter is very similar to those of extant and fossil species of Accipitridae. This fossil eagle is the only predator recorded at this new Miocene locality thus far.

First Skull and Associated Postcranial Bones of Macraucheniidae (Mammalia, Litopterna) from the Deseadan Salma (Late Oligocene) of Cabeza Blanca (Chubut, Argentina)

ABSTRACT The first skull associated with postcranial elements of Macraucheniidae (Litopterna) from the Sarmiento Formation in Cabeza Blanca (Chubut, Argentina) are described herein. The material consists of a nearly complete skull, nearly complete right humerus, left metacarpal IV, and three phalanges (proximal, intermediate, and distal of the same digit) of the same individual. It is compared with the Santacrucian genus Theosodon Ameghino, the Colhuehuapian Cramauchenia Ameghino, and the Deseadan species Coniopternium andinum and C. primitivum Soria and Hoffstetter. The comparative study leads us to recognize this specimen as Cramauchenia normalis. The presence of this species in Cabeza Blanca increases its biochronological distribution to Deseadan South American Land Mammal Age (SALMA) (late Oligocene).

First Digital Cranial Endocasts of late Oligocene Notohippidae (Notoungulata): Implications for Endemic South American Ungulates Brain Evolution

Notohippidae were middle-sized toxodonts recorded from the Eocene to the early Miocene. We provide the first description of the cranial endocasts of Rhynchippus equinus and Eurygenium latirostris based on three-dimensional reconstructions extracted from high-resolution X-ray computed tomography imagery. The endocasts of R. equinus and E. latirostris indicate that they were similar in size, proportions of the encephalic components, and neocortical design. The endocranial morphology of these notohippids is very close to that of toxodontids Adinotherium and Nesodon and differs markedly from both other Toxodontia and Typotheria. Notohippids, together with toxodontids, show the most complex neocortical surface among notoungulates. On the other hand, the neuromorphology of notohippids is in contrast to the neocortical morphological pattern described for Tertiary euungulates (Perissodactyla and Artiodactyla) from the Northern Hemisphere and litoptern Protetotheriidae, South American native euungulates. The relative brain size of R. equinus and E. latirostris compared with coeval holarctic euungulates from the late Oligocene are significantly below Perissodactyla and near the values obtained for Artiodactyla. Regarding the location of some functional neocortical areas, the expansion of the frontal lobe in Notohippidae may reflect the acquisition of heightened tactile sensitivity in the front of the snout, as recorded in the somatic sensory cortex of living euungulates. The bulging temporal lobe may reflect expansion of the auditory cortex, likely related to the marked enlargement of the middle ear chamber. Both neuromorphological and quantitative data suggest that during the late Paleogene, notohippids developed as complex and encephalized brains as those of the coeval Artiodactyla of northern continents.

SKULL ANATOMY AND NEUROMORPHOLOGY OF HYPSOSTEIROMYS, A COLHUEHUAPIAN ERETHIZONTID RODENT FROM ARGENTINA

Abstract A relatively complete skull of Hypsosteiromys with a well-preserved natural cranial endocast was recovered from the Colhuehuapi Member, Sarmiento Formation (lower Miocene) at Gran Barranca, Chubut Province, Argentina. The only known skull of this genus, it differs from those of other erethizontids because it is continuously very low, the ascending ramus of the premaxillae extends behind the posterior margins of the nasals, and the external auditory meatus has a ventral furrow. Comparison of the endocast with the brains of extant Erethizontidae demonstrates remarkable neuromorphological homogeneity, despite differences in size. Erethizontid brains have rounded, telencephalic hemispheres with prominent frontal lobes and small olfactory bulbs, and lack temporal lobes and neocortical sulci. Thus, the Gran Barranca skull shows that the external neuromorphology of erethizontids has not changed substantially since at least the early Miocene.

A Late Miocene Potential Neobalaenine Mandible from Argentina Sheds Light on the Origins of the Living Pygmy Right Whale

The origins and evolutionary relationships of the pygmy right whale (Caperea marginata), the only living member of the Neobalaeninae, have been the subject of a long-standing debate. This phylogenetic uncertainty is compounded by a limited neobalaenine fossil record. Here, we report a Late Miocene mysticete mandible from Patagonia, Argentina, and provisionally refer it to Neobalaeninae, gen. et sp. indet. The new material represents only the third report of a fossil neobalaenine, and the first fossil occurrence of this lineage in the southwestern Atlantic. It is also the oldest specimen so far reported, thus corroborating the idea of an early divergence time for neobalaenines.

Cranial Morphology of the Late Oligocene Patagonian Notohippid Rhynchippus equinus Ameghino, 1897 (Mammalia, Notoungulata) with Emphases in Basicranial and Auditory Region.

“Notohippidae” is a probably paraphyletic family of medium sized notoungulates with complete dentition and early tendency to hypsodonty. They have been recorded from early Eocene to early Miocene, being particularly diverse by the late Oligocene. Although Rhynchippus equinus Ameghino is one of the most frequent notohippids in the fossil record, there are scarce data about cranial osteology other than the classical descriptions which date back to the early last century. In this context, we describe the exceptionally preserved specimen MPEF PV 695 (based on CT scanning technique and 3D reconstruction) with the aim of improving our knowledge of the species, especially regarding auditory region (petrosal, tympanic and surrounding elements), sphenoidal and occipital complexes. Besides a modular description of the whole skull, osteological correlates identified on the basicranium are used to infer some soft-tissue elements, especially those associated with vessels that supply the head, mainly intracranially. One of the most informative elements was the petrosal bone, whose general morphology matches that expected for a toxodont. The endocranial surface, together with the surrounding parietal, basisphenoid, occipital, and squamosal, enabled us to propose the location and communication of main venous sinuses of the lateral head wall (temporal, inferior and sigmoid sinuses), whereas the tympanic aspect and the identification of a posterior carotid artery canal provided strong evidence in support of an intratympanic course of the internal carotid artery, a controversial issue among notoungulates. Regarding the arrangement of tympanic and paratympanic spaces, the preservation of the specimen allowed us to appreciate the three connected spaces that constitute a heavily pneumatized middle ear; the epitympanic sinus, the tympanic cavity itself, and the ventral expansion of the tympanic cavity through the notably inflated bullae. We hope this study stimulates further inquires and provides potentially informative data for future research involving other representatives of the order.

Miocene Marine Transgressions: Paleoenvironments and Paleobiodiversity

Two major marine transgressions covered part of Patagonia during the Miocene and both are recorded in the Peninsula Valdes region. The older (early Miocene) is represented by the volumetrically scarce outcrops of the Gaiman Formation, composed by shelf mudstones and fine sandstones. The late Miocene transgression is represented by the Puerto Madryn Formation, widely distributed in Peninsula Valdes and composed of mudstones, sandstones and shell beds, being the focus of this work. Sediments of this unit were deposited in inner shelf, nearshore, tidal channel and tidal flat environments. Fossil content is abundant and diverse, including palynomorphs, foraminifers, marine invertebrates (dominated by molluscs), cetaceans, pinnipeds, marine fishes and birds, as well as continental mammals, birds, and fishes. Isotopic and biostratigraphical data suggest a late Miocene age for the Puerto Madryn Formation, although some middle Miocene biostratigraphical indicators are present. Paleoenvironmental information suggests oceanic and continental temperatures warmer than present day, evidenced by the Caribbean molluscan association and the continental vertebrate and palinological associations, respectively. Instead, cetaceans, dinoflagellates, and some marine fishes, suggest colder oceanic temperatures. Precipitations were also higher than present, evidenced by the presence of freshwater mammals, birds, fishes, and plants. This work highlighted some gaps in the geological and paleontological knowledge including geochronology, stratigraphic control of paleontological studies and the knowledge of poorly known fossil groups, which should be the focus of future investigations.

First Confirmed Record of Incamys Bolivianus (Caviomorpha, Chinchilloidea) in the Deseadan of Patagonia (Argentina)

Here we describe the first record of Incamys bolivianus for Patagonia, in the Late Oligocene locality of Cabeza Blanca (Sarmiento Formation; Chubut Province, Patagonia, Argentina). This specimen documented by a partial mandible, clearly confirms the presence of the species in southern South America, since only some doubful reports were available so far. Incamys bolivianus is the first shared species between Salla-Luribay (Bolivia) and Patagonia (Argentina) fauna.

A New Cramaucheniinae (Litopterna, Macraucheniidae) from the Early Miocene of Patagonia, Argentina

ABSTRACT A new litoptern Cramaucheniinae species, Pternoconius bondi, sp. nov., from Colhuehuapian levels of the Sarmiento Formation in Bajada del Diablo (Chubut, Argentina) is described herein. The specimen belongs to an adult animal and preserves the anterior portion of the skull with the maxillary region, some fragments of nasal bones, a small portion of the left zygomatic process, and most of the upper dentition (i.e., left P2–M3, right C, and right P1–M3). It is compared with the Deseadan species ?Coniopternium primitivum Cifelli and Soria 1983 and Pternoconius polymorphoides Cifelli and Soria 1983, and also with the Colhuehuapian species Cramauchenia normalis Ameghino and Theosodon lydekkeri Ameghino. Although the hypocone and precingulum development, the paracone and metacone heights, and the connection between paraconule and protocone are singular features, the main characters that diagnose this new species are lack of a mesostyle pillar, soft labial bending of the ectoloph, absence of the metaconule in molars, and the smaller size with respect to other species of the genus. Comparative study leads us to recognize this specimen as a new species that increases the diversity of the Macraucheniidae in the early Miocene of Patagonia.