Alejandro G. Kramarz

NEW MIOCENE RODENTS FROM PATAGONIA (ARGENTINA) AND THEIR BEARING ON THE EARLY RADIATION OF THE OCTODONTOIDS (HYSTRICOGNATHI)

Abstract Three acaremyid rodents from the Miocene of Patagonia are described. Galileomys antelucanus, gen. et sp. nov. (Colhuehuapian SALMA, early Miocene) is the most plesiomorphic genus within the Acaremyidae. Galileomys? colloncurensis, sp. nov. is the first acaremyid recorded from the Colloncuran SALMA (middle Miocene). The generic referral is tentative because the known material does not display enough characters. Acaremys cf. murinus Ameghino, 1887 represents a second Colhuehuapian acaremyid. Cladistic analyses of dental and mandibular characters do not support previous hypotheses that Sciamys and Acaremys are the ancestors of the Octodontidae. On the contrary, these two genera and Galileomys constitute a monophyletic group united by the presence of a hypoflexus in P4, a well defined anterodorsal limit of mandibular masseteric fossa, and a figure-eight-shaped molar pattern. The inclusion of other genera in the Acaremyidae is not supported by cladistic analysis. A shared figure-eight-shaped dental pattern was the primary basis for a presumed close relationship between the Acaremyidae and Octodontidae, but this state evolved independently in the two taxa. The Acaremyidae is an extinct, early radiation of the Octodontoidea that persisted at least until the middle Miocene. The Octodontidae probably originated from an ancestor closer to the “echimyids” than to the Acaremyidae, with neither normal dental replacement nor mental foramen.

A New Early Miocene Chinchilloid Hystricognath Rodent; an Approach to the Understanding of the Early Chinchillid Dental Evolution

Chinchilloidea is an emblematical group of caviomorph rodents characterized by euhypsodont, laminated cheek teeth. Recent molecular analyses proposed that the extant Dinomys (and implicitly its fossil allies) is also part of this group. Their relationships with fossil caviomorphs with less derived dental features are still obscured by the deficiency of the fossil record documenting its early dental evolution. The new genus and species Garridomys curunuquem, from the early Miocene deposits of the Cerro Bandera Formation, northern Patagonia, is here described. It is represented by numerous mandible and maxillary remains with dentition. This species has protohypsodont cheek teeth with three transverse crests in all ontogenetic stages arranged in a transitory S-shaped pattern, resembling putative early dinomyids. Garridomys curunuquem is here interpreted as the sister group of the clade including the living and fossil chinchillids; both chinchillas and viscaccias would have diverged from a Garridomys-like ancestor and acquired hypsodonty independently. Garridomys and other chinchilloids would have diverged from the lineage leading to chinchillids in pre-Oligocene times, suggesting a very early, still poorly documented chinchilloid radiation.

A new early Miocene octodontoid rodent (Hystricognathi, Caviomorpha) from Patagonia (Argentina) and a reassessment of the early evolution of Octodontoidea

ABSTRACT A new caviomorph rodent, Dudumus ruigomezi, gen. et sp. nov., is described from the Sarmiento Formation, Trelew Member (early Miocene), of the Argentinian Patagonia. This new taxon is represented by upper and lower cheek teeth, mandible, and maxillary remains. It is characterized by retention of deciduous premolar, and low-crowned and terraced lower and upper cheek teeth with well-differentiated cusps, as in Caviocricetus lucasi; upper molariforms with the mesolophule and metacone fused with the posterior-most crest, as in C. lucasi; lower molars with lingual cusp enlarged and metalophulid II longer in m2 than in m1and m3, as in Prospaniomys priscus; and dp4 with metalophulid I separated from the metaconid and a spur projecting posterolingually from the posterior wall of metalophulid I, between the protoconid and anteroconid. The incisor enamel microstructure is derived, with the interprismatic matrix perpendicular (at a right angle) to the prisms, as in other octodontoids. A cladistic analysis corroborates that D. ruigomezi represents an octodontoid rodent with unusual tooth morphology. This analysis demonstrates that the early evolutionary history of Octodontoidea was characterized by the differentiation of successive lineages that survived until the early or middle Miocene, with no direct relationships with modern Octodontidae and Echimyidae. This analysis also suggests that fossil taxa previously classified as octodontoids are instead more closely related to the other caviomorph rodents.

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.

EOCARDIIDS (RODENTIA, HYSTRICOGNATHI) FROM THE PINTURAS FORMATION, LATE EARLY MIOCENE OF PATAGONIA, ARGENTINA

Abstract Eocardiid rodents from the late early Miocene Pinturas Formation (Ameghinos “Piso Astrapothericu-lense”) of Patagonia are here studied. Three species are recognized: Luantus propheticus Ameghino and Luantus toldensis sp. nov. are recorded exclusively from the Pinturas Formation; Phanomys mixtus Ameghino is also known from the Santa Cruz Formation (Santacrucian SALMA). The dentition of Luantus propheticus has rudiments of accessory prisms in M3 and p4, and the cheek teeth exhibit a bilobated occlusal pattern with interlobular cement and discontinuous enamel covering in senile stages. Luantus toldensis has more hypsodont cheek teeth than L. propheticus, even more developed M3 and p4 accessory prisms, and a bilobated pattern that is attained in earlier stages of wear. Luantus propheticus, L. toldensis, and Phanomys mixtus represent an evolutionary series that leads to the hypselodont pattern of Eocardia; thus, the traditional dichotomy between “Luantinae” and “Eocardiinae” is not supported. Luantus propheticus occurs in the lower and middle sequences of the Pinturas Formation, whereas the more derived species are recorded in localities interpreted as corresponding to the upper sequence. This distribution agrees with that of other faunal components recorded at the Pinturas Formation.

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.

New early Miocene primate fossils from northern Patagonia, Argentina

Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’ e CONICET, Av. Angel Gallardo 470, 1405 Ciudad de Buenos Aires, Argentina Centro Nacional Patagónico e CONICET, Boulevard Alte. Brown 2915, 9120 Puerto Madryn, Provincia de Chubut, Argentina Museo de Historia Natural de San Rafael e CONICET, Parque Mariano Moreno s/nro, 5600 San Rafael, Provincia de Mendoza, Argentina Museo Provincial de Ciencias Naturales ‘Prof. Dr. Juan A. Olsacher’, Dirección Provincial de Minería, Zapala, Provincia de Neuquén, Argentina

The first Eocardiidae (Rodentia) in the Colhuehuapian (early Miocene) of Bryn Gwyn (northern Chubut, Argentina) and the early evolution of the peculiar cavioid rodents

ABSTRACT Caviidae and Hydrochoeridae (extant Cavioidea s.s.), probably the most peculiar among rodents, are characterized by their evergrowing double-heart-shaped cheekteeth. They have classically been rooted in Eocardiidae, which ranges from Deseadan to ‘Colloncuran’ (late Oligocene-middle Miocene) in Patagonia, although in the Deseadan and Colhuehuapian (early Miocene) remains are very scanty. For the Colhuehuapian, only one species coming from the southern cliff of the Colhué Huapi Lake (Gran Barranca, Chubut, Argentina) was known so far. In this paper, the first Colhuehuapian eocardiids from outside Gran Barranca are reported: Luantus minor, sp. nov., and Chubutomys leucoreios, sp. nov. They are represented by two fragmentary mandibles and a few isolated cheek teeth, from the Trelew Member of the Sarmiento Formation at Bryn Gwyn, lower valley of the Chubut River, Chubut. The new species enlarge the knowledge of eocardiid diversity, and reinforce the hypothesis of a basal dichotomy for the group. L. minor represents one of the smallest species of the series Asteromys + Luantus + Phanomys + Eocardia, which likely gave rise to modern Cavioidea s.s. C. leucoreios pertains to a group of species with precocious hypsodonty and apparently low diversity, but without modern descendant.