Pablo E. Ortiz

A role for suppressed incisor cuspal morphogenesis in the evolution of mammalian heterodont dentition.

Changes in tooth shape have played a major role in vertebrate evolution with modification of dentition allowing an organism to adapt to new feeding strategies. The current view is that molar teeth evolved from simple conical teeth, similar to canines, by progressive addition of extra “cones” to form progressively complex multicuspid crowns. Mammalian incisors, however, are neither conical nor multicuspid, and their evolution is unclear. We show that hypomorphic mutation of a cell surface receptor, Lrp4, which modulates multiple signaling pathways, produces incisors with grooved enamel surfaces that exhibit the same molecular characteristics as the tips of molar cusps. Mice with a null mutation of Lrp4 develop extra cusps on molars and have incisors that exhibit clear molar-like cusp and root morphologies. Molecular analysis identifies misregulation of Shh and Bmp signaling in the mutant incisors and suggests an uncoupling of the processes of tooth shape determination and morphogenesis. Incisors thus possess a developmentally suppressed, cuspid crown-like morphogenesis program similar to that in molars that is revealed by loss of Lrp4 activity. Several mammalian species naturally possess multicuspid incisors, suggesting that mammals have the capacity to form multicuspid teeth regardless of location in the oral jaw. Localized loss of enamel may thus have been an intermediary step in the evolution of cusps, both of which use Lrp4-mediated signaling.

A NEW FOSSIL PHYLLOTINE (RODENTIA: MURIDAE) FROM NORTHWESTERN ARGENTINA AND RELATIONSHIPS OF THE REITHRODON GROUP

Abstract We describe an extinct murid, assigned to the tribe Phyllotini, from the late Pleistocene (Tafí del Valle Formation) of La Angostura (26°55′30″S, 65°41′50″W; 1,900 m elevation) in northwestern Tucumán Province, Argentina. The new genus is characterized by very hypsodont molars with flat crowns and simplified occlusal structure, upper incisors with a mediolateral groove, a straight premaxillary–maxillary suture, and high zygomatic plate with a small spine on its anterodorsal edge. Phylogenetic analyses including fossil and living members of the Reithrodon group show that the new genus is the sister taxon to the Reithrodon–Neotomys–Euneomys clade. The paleoenvironmental and paleogeographic significance of the new genus is discussed within the context of the climatic changes that occurred during the late Pleistocene in southern South America. The new phyllotine would have lived in high-elevation grasslands, which today occur >1,000 m higher under cold and dry climatic conditions than those of the last glacial maximum.

Distribution of sigmodontine rodents in Northwestern Argentina: main gaps in information and new records

Abstract Many uncertainties remain regarding our knowledge of sigmodontine rodent distributions in Northwestern Argentina. Most of the available information has never been critically evaluated. By reviewing the published literature and overlaying this information with other spatial layers (political, environmental, infrastructure, protected areas, and topographic layers), we identified information gaps and added new localities. The new records were obtained through field surveys, including captures and owl pellet samples. In the literature, we found 561 localities, most of them published in the past decade. These records come mainly from low-altitude areas in Salta province, as well as some higher-altitude belts in Yungas, and strongly associated with roads. Records from protected areas were scarce. Akodon, Calomys, Oligoryzomys, and Phyllotis were recorded for most of the localities. We add 18 new localities for 14 species, including the first records of Akodon dolores in Tucumán province, Necromys lasiurus in Santiago del Estero and Tucumán, and Calomys lepidus in Catamarca. We add records for poorly known species such as Andalgalomys olrogi in the Capital department (Catamarca) and Auliscomys sublimis and Neotomys ebriosus in Cochinoca (Jujuy) and La Poma (Salta). We emphasize the need for more surveys to obtain an adequate knowledge of the distribution of most sigmodontines.

First record of Abrothrix jelskii (Thomas, 1894) (Mammalia: Rodentia: Cricetidae) in Salta province, northwestern Argentina: filling gaps and distribution map

Abrothrix jelskii is one of the lesser-known species in the genus Abrothrix , and it has only been recorded in a few localities in highland environments along the central Andean range. In Argentina, existing records are restricted to just one locality in Jujuy province. We have recently recorded this species in Salta Province, extending its known distribution 150 km northward in northwestern Argentina and 175 km further to the southeast compared to existing records from localities in southern Bolivia. Ten other rodent species were also recorded in the same area, with some of these records, such as those for Auliscomys sublimis , Akodon boliviensis , and Phyllotis sp., being noteworthy as well.

A New fossil phyllotine (Rodentia, Sigmodontinae) from the late Pliocene in the Andes of northern Argentina

ABSTRACT †Pardinamys humahuaquensis, a new genus and species of Phyllotini (Rodentia, Cricetidae), is described on the basis of 111 cranial, mandibular, and dental remains belonging to at least 29 individuals. The fossils were recovered from a microvertebrate assemblage found in late Pliocene deposits (between 3 and 2.5 Ma ago) from the Uquía Formation, central Jujuy Province, northwestern Argentina. †Pardinamys is morphologically intermediate between the extant genera Eligmodontia and Calomys and can be differentiated from these taxa by the combination of several traits, including short masseteric crest, with upper and lower ramus similarly developed; coronoid process well developed; anteromedian flexus in M1 only present in very young individuals, without any trace of anteromedian style; M1 and M2 with developed second minor fold; large M2 and M3; and metaflexus, paracone, and metacone of M3 well developed. The morphologic characteristics of the new genus and the other sigmodontines found in the Uquian assemblage (at least three extinct genera) suggest an important radiation before the establishment of the modern communities in the central Andean region and indicate the need for a reevaluation of the divergence-age estimates for the group. The recovered taxa indicate the presence of open environments during depositional times, within arid or semiarid conditions, unlike previous reconstructions for this geologic unit. The finding reveals the need for improving the fossil record of sigmodontines in the central Andean region and its importance to understanding the radiation of this group in a more inclusive South American context.

Integration of morphological, ecological, and genetic evidence suggests that the genus Andinomys (Rodentia, Cricetidae) is monospecific

Two subspecies of Andinomys edax are currently recognized. Andinomys e. edax ranges from southern Perú to northernmost northwestern Argentina and A. e. lineicaudatus is mainly distributed in southern northwestern Argentina. However, some workers have recognized both taxa as distinct species, stating that A. edax is restricted to Puna and Prepuna habitats between 2,000 and 4,800 m elevation, whereas A. lineicaudatus occurs in Yungas forest below 2,500 m. We assessed the taxonomic status of both forms through an integrative approach including morphological (discrete skin and skull characters), morphometric (univariate and multivariate), geographicenvironmental niche modeling (Mahalanobis Typicalities), and molecular (Bayesian analysis of cytochrome-b gene sequences) analyses. We did not find characters that consistently differentiated skins and skulls of the 2 forms. The morphometric analysis indicated that lineicaudatus is, on average, larger than edax for some measurements, but only 2 (alveolar width and occipital condyle width) differed significantly between forms. No group of specimens was clearly segregated in the PCA morphospace. Distribution models obtained separately for each taxon do not offer a better fit to the known distribution than models based on the combined data sets. We documented coincident environmental variables as relevant in the model building of edax and lineicaudatus, noting some segregation in elevation, but similar habitat suitability for the remainder of the environmental variables. The geographic continuity between niche models of edax and lineicaudatus was clear but specimens morphologically assignable to each of the nominal forms were not found in areas of overlap. The phylogenetic analyses recovered a polytomy of 4 allopatric and genetically divergent clades, which also failed to support the taxonomic hypothesis of 2 species. Based on all available evidence, we conclude that Andinomys consists of a single species. Nevertheless, observed genetic divergences among clades and their geographic distribution indicate that past events probably fragmented populations of A. edax.

Taxonomy of the Phyllotis osilae species group in Argentina; the status of the “Rata de los nogales” ( Phyllotis nogalaris Thomas, 1921; Rodentia: Cricetidae)

The taxonomic status of populations of the genus Phyllotis from northwestern Argentina (NWA) has undergone recent changes, with the addition of two species (P. alisosiensis and P. anitae) to the traditionally recognized forms (P. caprinus, P. xanthopygus, and P. osilae). Three of these species (P. anitae, P. osilae, and P. alisosiensis) were included within the Phyllotis osilae species group. Most authors recognized three subspecies of P. osilae for NWA: P. osilae osilae, P. o. nogalaris, and P. o. tucumanus. Morphological, morphometric, and molecular studies based on recently collected specimens suggest that current classification does not reflect the diversity of this group in NWA, revealing the need of some taxonomic reallocations and new distributional delimitations. Here we propose that P. nogalaris must be recognized as a valid species and the restriction of P. osilae to southern Peru and central Bolivia. Following our results, we expect an outstanding improvement in the taxonomic knowledge of the Phyllotis osilae species group in the coming years.

The Quaternary record of Reithrodon auritus (Rodentia: Cricetidae) in northwestern Argentina and its paleoenvironmental meaning

Abstract Reithrodon auritus is a living sigmodontine with one of the broader temporal records, from the lower Pliocene of Argentina. Its populations in northwestern Argentina are today found patchily and restricted to five high-elevation and isolated localities in open areas of highland grasslands vegetation (at >3000 m). During the Pleistocene and early Holocene, R. auritus would have had a broader range, reaching lower altitudes everywhere and being one of the dominant small mammal species in some fossil localities. In this note, we summarize the known Pleistocene and early Holocene fossil record of R. auritus in northwestern Argentina, provide new paleontological sites for the species, and make comments concerning the paleoenvironmental implications of its presence at such lower altitudes. The paleontological evidence indicates that during the Pleistocene and early Holocene, R. auritus inhabited around 1000 m below their current altitudinal distribution in the eastern Andean ranges, with populations clearly more abundant than today. The fossils of R. auritus are indicative of colder and perhaps more xeric paleoenvironmental conditions, characterized by open areas with sparse grassy vegetation as those developed today around 3000 m elevation.

Notes on the distribution of the genus Andalgalomys (Rodentia, Cricetidae), with the first record of A. pearsoni (Myers 1978) from Argentina

Abstract We documented the first record of Andalgalomys pearsoni (Myers 1978) in Argentina, based on one individual caught at Cerro Colorado (Metán department, Salta province, Argentina). This new record enlarges the distribution of this species, to date only known from Bolivia and Paraguay, ca. 530 km SW and fills a gap without records for Andalgalomys of approximately 850 km between Paraguay and NW Argentina. The finding of this mouse, caught more than 50 years ago, highlights the importance that biological collections have in our understanding of biological diversity.

A new genus of Sigmodontinae (Mammalia, Rodentia, Cricetidae) from the Pliocene of central Argentina

ABSTRACT Chukimys favaloroi, new genus and species, is added to the past diversity of sigmodontine rodents, the largest subfamily of Neotropical mammals. It is based on a maxillary with the entire tooth row and both first and second lower molars collected in sediments of the Brochero Formation (Late Pliocene) that crop out in Córdoba Province, Argentina. The new genus represents a small rodent (about 40 g) and has a unique combination of traits, including a zygomatic plate with deeply excavated anterior border and conspicuous zygomatic spine, incisive foramen reaching the level of the protocone of the first upper molar, palate narrow and flat, molars moderately hypsodont, and the first lower molar four-rooted. The new sigmodontine shows similarities with several extant members of the tribes Phyllotini and Reithrodontini, as well as with the extinct Dankomys vorohuensis from the Pliocene of Buenos Aires, Argentina. The comparisons performed suggest that Chukimys has anatomical features related to omnivory and the incorporation of hard material in its diet. Chukimys is the first fossil genus of sigmodontine described from central Argentina and probably represents a new member of the currently monotypic tribe Reithrodontini.