Mariano Bond

Main Pathways of Mammalian Diversification in South America

The most complete record of the continental mammal-bearing Cenozoic of South America comes from Argentina (Marshall et al., 1983a, 1984). This record, representing the southernmost part of the continent, became a unique example in which to study the evolutionary events affecting its mammal communities in relation to the outstanding climatic and environmental changes (Pascual, 1984). The main patterns of geological evolution in this southern part of the continent had a profound influence on its mammalian history. The chronostratigraphic diagrams (Figs. 1 and 2) show the geographical and chronological distribution of Cenozoic sedimentary and volcanic rocks in eastern and western Argentina. This lithostratigraphic distributional pattern makes evident the following historical facts:

Taxonomic revision and phylogeny of Paedotherium and Tremacyllus (Pachyrukhinae, Hegetotheriidae, Notoungulata) from the Late Miocene to the Pleistocene of Argentina

ABSTRACT Two genera of the subfamily Pachyrukhinae (Notoungulata, Hegetotheriidae), Paedotherium and Tremacyllus, are revised. The material comes from late Miocene (Chasicoan) to early Pleistocene (Marplatan) localities in Argentina and Bolivia. The genus Raulringueletia is here considered a synonym of Paedotherium. Three valid species of Paedotherium are recognized and re-characterized: P. bonaerense, P. typicum, and P. minor. Two species of Tremacyllus are recognized: T. impressus in the Pampean region, and T. incipiens in Catamarca Province. The presence of Tremacyllus sp. into the late Chasicoan extends its known temporal range. Pachyrukhos occurs slightly earlier within the Chasicoan, coexisting with Paedotherium. Paedotherium is dominant in frequency in the Pampean area (Buenos Aires and La Pampa) and extremely scarce in the Subandean region (Catamarca), while Tremacyllus has an opposite occurrence. Cladistic analysis of the subfamily shows Paedotherium as a monophyletic group, where P. bonaerense i...

Persistence of a Mesozoic, non-therian mammalian lineage (Gondwanatheria) in the mid-Paleogene of Patagonia

We describe two isolated molariforms recovered from early–middle Eocene (early Lutetian) levels of northwestern Patagonia, Argentina. Comparisons with major lineages of therian and non-therian mammals lead us to refer them to a new genus and species of Gondwanatheria (Allotheria). There is a single root supporting each tooth that is very short, wide, rounded, and covered by cementum; the steep sidewalls, lack of a neck between the crown and root, and the heavily worn stage in both molariforms suggest that they were of a protohypsodont type. Both teeth are strongly worn at their centers, all along their length, with the labial edge less worn than the lingual; they show strong transverse crests that alternate with lingual grooves. The protohypsodont aspect of the teeth, as well as the strong, transverse crests, are suggestive of sudamericid affinities; on the other hand, the thin enamel layer and the occlusal pattern formed by the crests and grooves shows more similarities to molariform teeth of the Ferugliotheriidae. The new taxon adds evidence regarding the (1) extensive radiation of the Gondwanatheria throughout the Southern Hemisphere, (2) persistence of several lineages well after the Cretaceous/Paleogene boundary, and (3) early evolution of hypsodont types among South American herbivorous mammals.

A New Xenungulata (Mammalia) from the Paleocene of Patagonia, Argentina

Abstract A new form of Xenungulata Paula Couto, 1952 from red levels of the Peñas Coloradas Formation in a locality near Puerto Visser (45°17′S, 67°01′W), Chubut province, Argentina, is represented by a fragmentary left jaw with the m3 (MPEF-PV 1871). Notoetayoa gargantuai n. gen. and n. sp. is the first ever found in direct association with Carodnia feruglioi Simpson, 1935a which characterizes the incompletely known homonymous zone of the late Paleocene of Patagonia. A preliminary phylogenetic analysis, including representatives of “Condylarthra,” Litopterna, Notoungulata, Pyrotheria, Xenungulata and Astrapotheria, plus the characters that could be scored in the new taxon, was performed using TNT software. A single most parsimonious tree was obtained. Notoetayoa gargantuai has a closer phylogenetic relationship with the Xenungulate Etayoa bacatensis Villarroel, 1987 from the ?middle Paleocene of Colombia than with any other Tertiary ungulate group of South America. Notoetayoa gargantuai fills an important gap in the knowledge of the mammalian faunas from the Paleocene of Patagonia, particularly of the poorly known pre-Itaborian times.

Nuevos restos de toxodonte (Mamalia, Notoungulata) en estratos de la Formación Chucal, Mioceno, Altiplano de Arica, norte de Chile

espanolSe describen tres piezas dentarias de un mamifero notoungulado, encontradas en estratos de la parte superior de la Formacion Chucal, Altiplano de Arica, norte de Chile (18-19°S). Los caracteres morfologicos permiten referir el material disponible a un Toxodontidae, relacionado con especimenes generalizados de Haplodontheriinae presentes en Argentina, tales como Palyeidodon (= Prototrigodon). Estos ultimos, morfologicamente mas avanzados que aquellos de Edad Mamifero Santacrucense (Mioceno Inferior), proveen evidencias suficientes para asignar al Colloncurense (Mioceno Medio temprano) la edad maxima de los depositos portadores. EnglishThree dental pieces of a notoungulate mammal, found in the strata of the upper part of the Chucal Formation, Altiplano of Arica, northern Chile (18-19°S) are described. The morphological characters allow to refer the available material to a Toxodontidae, related to generalised specimens of Haplodontheriinae as Palyeidodon (= Prototrigodon), which are present in Argentina. These specimens, morphologically more advanced than those of Santacrucian Mammal Age (Lower Miocene), give sufficient evidence to assign to Colloncuran (Early Middle Miocene) the maximum age of the deposits where they are present.

Estratigrafía y vertebrados (Aves y Mammalia) de la Formación Cerro Bandera, Mioceno Temprano de la Provincia del Neuquén, Argentina

La Formacion Cerro Bandera comprende una serie de pequenos afloramientos aislados, que conforman los relictos de un antiguo relleno aluvial desarrollado sobre pequenos valles locales. Se compone de una sucesion de depositos piroclasticos reelaborados con intercalaciones de piroclastitas primarias y escasos niveles de areniscas. Estos depositos fueron originalmente reconocidos en el extremo nordeste de la Barda Negra, sur de Cerro Bandera y noroeste de Sierra del Portezuelo; nuevos afloramientos son reconocidos aqui en la vertiente noroeste del cerro Bayo Mesa, Provincia del Neuquen, Argentina. Los restos fosiles exhumados corresponden a aves (Falconidae) y mamiferos (17 familias), entre los que se destacan Cramauchenia normalis Ameghino, Proadinotherium cf. P. muensteri Ameghino, Eosteiromys sp. y Caviocricetus lucasi Vucetich y Verzi, junto con una especie de Protypotherium con dentadura mas primitiva que las conocidas para la Edad Santacrucense. Esta asociacion confirma una Edad Mamifero Colhuehuapense (Mioceno Temprano) para esta unidad. La fauna exhibe marcadas diferencias con la registrada en la seccion inferior de la Formacion Chichinales, Provincia de Rio Negro. El grado de diferenciacion faunistica entre estas dos unidades posiblemente sincronicas podria obedecer a diferencias en los factores paleoambientales locales.

The youngest record of fossil land mammals from Antarctica; its significance on the evolution of the terrestrial environment of the Antarctic Peninsula during the late Eocene

The record of fossil land mammals from Antarctica has been restricted previously to the middle levels of the Eocene-?early Oligocene La Meseta Formation in Seymour Island, Antarctic Peninsula. This mostly shallow-marine sequence was divided informally into seven subunits (Tertiary Eocene La Meseta or TELM 1 to 7) by Sadler (1988). Land mammals, representing South American lineages of marsupials, edentates, and ungulates were recovered from TELM 3, 4, and 5 (Marenssi et al., 1994; Vizcaino et al., 1994). The purpose of the present note is to report the discovery of a well-preserved ungulate tooth from the uppermost level of the La Meseta Formation (TELM 7) and to discuss its paleoenvironmental implications.

A mitogenomic timetree for Darwin’s enigmatic South American mammal Macrauchenia patachonica

The unusual mix of morphological traits displayed by extinct South American native ungulates (SANUs) confounded both Charles Darwin, who first discovered them, and Richard Owen, who tried to resolve their relationships. Here we report an almost complete mitochondrial genome for the litoptern Macrauchenia. Our dated phylogenetic tree places Macrauchenia as sister to Perissodactyla, but close to the radiation of major lineages within Laurasiatheria. This position is consistent with a divergence estimate of ∼66 Ma (95% credibility interval, 56.64–77.83 Ma) obtained for the split between Macrauchenia and other Panperissodactyla. Combined with their morphological distinctiveness, this evidence supports the positioning of Litopterna (possibly in company with other SANU groups) as a separate order within Laurasiatheria. We also show that, when using strict criteria, extinct taxa marked by deep divergence times and a lack of close living relatives may still be amenable to palaeogenomic analysis through iterative mapping against more distant relatives.

A new oligocene astrapothere (mammalia, meridiungulata) from patagonia and a new appraisal of astrapothere there phylogeny

Synopsis The new genus and species Maddenia lapidaria from pre‐Deseadan (Oligocene) deposits at the southern cliff of Lake Colhue Huapí (Chubut Province, Argentina) is described. This small Oligocene astrapothere represents an adaptive type that is distinct from the usual one proposed for post‐Casamayoran (Eocene) forms. Because of its small body size and dental characters, preliminarily interpreted as primitive, this genus was originally considered to be a member of the Albertogaudryinae surviving into the Oligocene and coexisting with more derived species. However, a phylogenetic analysis based on dental and mandibular characters indicates that Maddenia lapidaria is, rather, the sister group of the giant Deseadan and later astrapotheriids by sharing with them a well developed upper molar crista and crochet, P4 lingual valley, p2 absent and superficial premolar and molar hypoflexid. Maddenia lapidaria has highly molarised upper premolars, representing the top‐most expression of the evolutionary trend of increasing premolar complexity in the Astrapotheria. Asubsequent evolutionary turnover resulted in a reduction of the size and number of premolars and secondary occlusal simplification, coinciding with an abrupt increase in hypsodonty and body size that characterise the more advanced astrapotheriids. This interpretation challenges the progressive acquisition of astrapotheriid characters traditionally accepted for the group. The moderately deep premolar and molar hypoflexid seen in Maddenia lapidaria is interpreted as the ancestral condition for the younger astrapotheres, which, on the one hand, would have evolved into the complete reduction of this structure in the Uruguaytheriinae and, on the other hand, the development of a deep labial vertical cleft in the Astrapotheriinae (Astrapotherium and Astrapothericulus).

A New Astrapothere (Mammalia, Meridiungulata) from La Meseta Formation, Seymour (Marambio) Island, and a Reassessment of Previous Records of Antarctic Astrapotheres

ABSTRACT During the past quarter century, the uplifted nearshore sediments comprising the Eocene La Meseta Formation (LMF) of Seymour (Marambio) Island have produced a diverse assemblage of terrestrial mammals that closely, but not exactly, resembles late Early Eocene faunas from southern Patagonia. This assemblage includes the only astrapothere and litoptern fossils known from outside South America. The occurrence of astrapotheres in LMF was originally indicated by fragmentary dental remains tentatively referred to family Trigonostylopidae on the basis of their general resemblance to the Patagonian genus Trigonostylops Ameghino. In this contribution we describe a new astrapothere specimen from LMF; unlike specimens collected previously, this one is a complete and excellently preserved lower cheek tooth, providing a basis for a review of all previous records of Astrapotheria from this formation. This tooth (probably p4 rather than m1) is sufficiently distinct from all other known astrapothere cheek teeth to warrant assignment to a new genus and species, Antarctodon sobrali. It has a transversally elongated entoconid, resembling that observed in at least one specimen of the Mustersan genus Astraponotus, but the tooth as a whole is much lower crowned and less lophodont than in the latter. Phylogenetic analysis suggests that Antarctodon is closer to genera classified by previous authors as astrapotheriids (e.g., Albertogaudrya and Tetragonostylops) than it is to Trigonostylops. Reexamination of other LMF specimens previously referred to Trigonostylopidae reveals that some specimens are attributable to this new taxon and others either are not astrapotheres at all or lack distinctive features. Consequently, at present the record of order Astrapotheria in Antarctica should be considered as restricted to non-trigonostylopids.