Deseadan South American Land Mammal Research Articles

New late Oligocene caviomorph rodents from Mendoza Province, central-western Argentina

ABSTRACT Late Oligocene caviomorphs represent one of the most important early adaptive radiations of this group of rodents. They show a high taxonomic diversity and a wide geographic distribution, with those found in the upper Oligocene of Salla (Bolivia) and Patagonia (Argentina) being particularly diverse. However, caviomorphs from the Deseadan South American Land Mammal Age in other latitudes are still scarcely known. In this contribution, we describe new caviomorph rodents from the Deseadan levels of Quebrada Fiera locality (Mendoza Province; central-western Argentina) and evaluate their systematic and paleobiogeographic significance. The taxonomic composition of the caviomorphs from Quebrada Fiera reveals a complex biogeographic history, as we recognize one endemic Cavioidea (Asteromys puelche sp. nov.) and two Chinchilloidea: one with Patagonian affinities (Cephalomys sp.) and another with a wide distribution in South America (Incamys bolivianus). Asteromys puelche sp. nov., shows closer phylogenetic affinities with the Bolivian A. bolivianus than with the Patagonian A. punctus. These rodents, in common with the whole mammalian association from Quebrada Fiera, show a mix of endemic taxa and others shared with higher and lower latitudes.

A singular Hegetotheriinae (Notoungulata, Typotheria) from the late Oligocene-Early Miocene of the Subandean Region of Bolivia

Abstract Geological studies in the northern sector of the Chaco foreland Basin, Bolivia, yielded new fossils coming from late Oligocene-late Miocene of the Petaca Formation. Few fossil mammals were known from the Subandean Region of Bolivia. We report a partially complete mandible of a hegetotheriid Hegetotheriinae (Notoungulata, Typotheria) from Abapo (Rio Grande River). The specimen (YPFB-LIT-PAL-005) is very close in size and dental morphology to the late Oligocene (Deseadan South American Land Mammal Age, SALMA) — Santacrucian (early Miocene) Prohegetotherium schiaffinoi (Kraglievich 1932) from Fray Bentos (Uruguay and Argentina), Salla (Bolivia), Divisadero Largo-Potrerillos and Quebrada Fiera (Argentina). However, mandibular characteristics, as the shape with a marked change in height along its length, increasing towards the back, a prominent masseteric crest, a deep mandibular groove, and a remarkable thickening of the ventral rim of the mandible, indicate differences between this specimen and Prohegetotherium schiaffinoi and the other Hegetotheriinae. The affinity of YPFB-LIT-PAL-005 with P. schiaffinoi suggests a late Oligocene to early Miocene for the upper bearing horizon of the Petaca Formation (in Abapo), an older age than previously assigned to the top of this unit (late Miocene), and confirms the taxon distribution between ∼ 36 ° to ∼ 17 ° south latitude.

Macraucheniidae and Proterotheriidae (Mammalia, Litopterna) from Quebrada Fiera (Late Oligocene), Mendoza Province, Argentina

In this contribution we present new specimens of Litopterna recovered during the last decade in Quebrada Fiera (Mendoza Province, Argentina), whose fossiliferous sediments, currently recognized as the base of Agua de la Piedra Formation, are assignable to Late Oligocene (Deseadan South American Land Mammal Age). Two remains mentioned in the first publication on this locality were neither detailed nor described, and they have not been located in the corresponding repository. The new material consists of postcranial fragmentary remains (astragali, calcaneum, and metapodials) of Macraucheniidae (Cramaucheniinae) and an incomplete upper molar (M3) of Proterotheriidae (Proterotheriinae). These few remains of litopterns contrast with the abundance of notoungulates at Quebrada Fiera. A comparative study was carried out with material from Patagonia (Argentina) and taxa recorded in Bolivia and Peru for the same temporal interval. The specimens of Cramaucheniinae are assigned to Coniopternium andinum and the molar of Proterotheriinae to cf. Lambdaconus suinus. This contribution allows us to extend the geographical range of Coniopternium, filling the gap between the Patagonian and lower latitude localities (Bolivia and Peru) in which this genus was found. The record of L. suinus in Quebrada Fiera expands the geographical range of this species outside from Patagonia.

New caviomorph rodents from the late Oligocene of Salla, Bolivia: taxonomic, chronological, and biogeographic implications for the Deseadan faunas of South America

Caviomorph rodents have been an important component of South American mammal faunas at least since the Oligocene. Those from the Deseadan South American Land Mammal Age (SALMA; late Oligocene) have been exhaustively studied because they are considered key to understanding the evolution of South American rodents. Deseadan faunas are widely distributed from northern Peru to central Patagonia, with those from Salla (Bolivia) and Cabeza Blanca (Argentinean Patagonia) being the most diverse. Recent studies of Deseadan rodents at some localities in high (Cabeza Blanca, Punta Nava, Scarritt Pocket) and low (Contamana) latitudes revealed greater taxonomic diversity. However, at middle latitudes, Salla has not received the same attention, despite being exceptional in terms of the abundance and high-quality preservation of specimens. The aim of this work is to report new caviomorph rodents from Salla, and to discuss their systematic and palaeobiogeographical implications in the context of the South American Deseadan caviomorph assemblages. We describe two new genera (†Lapazomys gen. nov. and †Cholamys gen. nov.) and five new species (†Migraveramus lavocati sp. nov., †Sallamys woodi sp. nov., †Lapazomys hartenbergeri sp. nov., †Protosteiromys pattersoni sp. nov. and †Cholamys tetralophodonta sp. nov.). These include the first erethizontids and the oldest Cavioidea sensu stricto for middle and low latitudes. The increase in the number of species corroborates the existence of an important rodent diversification already evidenced in the late early/early late Oligocene. In addition, the new rodents lessen the degree of endemism of the Salla rodent fauna proposed in previous papers. We interpret that the differences among Deseadan assemblages from low, middle and high latitudes are due essentially to climatic, historical and local environmental conditions, whereas diachronism seems less important in the modelling of faunas.http://zoobank.org/urn:lsid:zoobank.org:pub:A8A04332-12E1-4966-9807-47B66554718E

Late Oligocene caviomorph rodents from Contamana, Peruvian Amazonia

AbstractThe Deseadan South American Land Mammal Age (late Early Oligocene – Late Oligocene) attests to a time of great diversification in the caviomorph rodent fossil record. Nevertheless, Deseadan rodent‐bearing localities in Neotropical lowlands are few and poorly known. Here we describe the rodent assemblages from two Late Oligocene localities, near Contamana, Loreto, Peru. Seven taxa are new to science: Palaeosteiromys amazonensis gen. et sp. nov., Plesiosteiromys newelli gen. et sp. nov., Loretomys minutus gen. et sp. nov., Scleromys praecursor sp. nov, Ucayalimys crassidens gen. et sp. nov., Chambiramys sylvaticus gen. et sp. nov. and Chambiramys shipiborum gen. et sp. nov. These rodent faunas show that caviomorphs were relatively diverse in Peruvian Amazonia during the Late Oligocene, with the co‐occurrence of at least three extant superfamilies: Erethizontoidea, Octodontoidea and Chinchilloidea. Additionally, they mark the earliest known occurrences of Scleromys, of a small erethizontid closely related to Microsteiromys and of an adelphomyine closely reminiscent of Ricardomys (all taxa previously restricted to Miocene localities thus far). They also document a form potentially related to Eosallamys (previously known from around the Eocene–Oligocene transition at Santa Rosa in Peruvian Amazonia). Finally, the geographical range of Adelphomyinae and of Deseadomys is widely expanded to the lower latitudes of South America for the Deseadan interval. The latter elements, in addition to the record of a very primitive species of Scleromys, suggest the absence of palaeogeographical and palaeoenvironmental barriers within the southern cone of South America before the Oligocene–Miocene transition.

Palaeothentid Marsupials of the Salla Beds of Bolivia (Late Oligocene): Two New Species and Insights into the Post-Eocene Radiation of Palaeothentoids

We report the finding of new remains of palaeothentid marsupials (Paucituberculata: Marsupialia) from the late Oligocene of Salla, Bolivia (Deseadan South American Land Mammal Age). These fossils represent two new taxa, Antawallathentes illimani and Antawallathentes quimsacruza, increasing the known number of Deseadan palaeothentoid species to 11. Antawallathentes illimani is represented by two incomplete skulls and A. quimsacruza is known only from the holotype, a partial mandible with p3 - m4. Our phylogenetic analysis, based on a data matrix modified from that of Abello, suggests that the two new Salla species are members of the Palaeothentidae (sensu stricto) and are more closely related to each other than they are to other known palaeothentids. Although these new taxa inidicate a greater diversity of Deseadan palaeothentoids than previously appreciated, nowhere in the Deseadan are palaeothentoids abundant, as they are in later Colhuehuapian and Santacrucian faunas. Thus, Deseadan palaeothentoid species richness, coupled with the observation that these palaeothentoids are numerically few in Deseadan faunas, permits the development of a general outline of the post-Eocene palaeothentoid radiation. This may be summarized as follows: 1) EOB Pulse that began near the Eocene/Oligocene Boundary; 2) Deseadan Diversification, increased species richness without large population sizes; and 3) Early Miocene Diversification, increased species richness with local abundances. This Colhuehuapian to Santacrucian diversity with local abundences declined after the Santacrucian. Palaeothentoids are unknown after the Laventan SALMA.

First record of squamate reptiles from the Oligocene of South America

Squamata are known from South America since the Cretaceous, but their fossil record has an occurrence gap between the late Eocene and early Miocene. Fossils recovered from the Sarmiento Formation (Deseadan South American Land Mammal Age, late Oligocene) at Cabeza Blanca (45°S) partially fill this interval. The squamates recovered from Cabeza Blanca include both lizards (an indeterminate Iguanidae and a probable Iguaninae) and snakes (Madtsoiidae). If these taxonomic assignments are correct, the presence of an Iguaninae at such a latitude is unexpected because these lizards are presently absent from Argentine territory. The madtsoiid, here referred to Madtsoia, would extend the Cenozoic record of this genus back to around 16 Ma. The squamate fauna from Cabeza Blanca is compatible with warm and humid environments inferred for the Patagonian Deseadan.

A new species of Chubutomys (Rodentia, Hystricognathi) from the late Oligocene of Patagonia and its implications on the early evolutionary history of Cavioidea sensu stricto

Cavioidea is represented today by Dasyproctidae (agouties), Cuniculidae (pacas), and Caviidae (cavies or “guinea pigs”, maras, mocos, and capybaras). Cavioidea sensu stricto (Cavioidea s.s.) clusters the extant and extinct Caviidae together with a diverse assemblage of extinct taxa grouped in the family Eocardiidae. Recent phylogenetic analyses of this group based on morphological characters corroborated the monophyly of Cavioidea s.s., but retrieved a paraphyletic arrangement of “eocardiids” as successive sister taxa of the crown-group Caviidae. The late Oligocene (Deseadan South American Land Mammal Age, SALMA) record of Cavioidea s.s. is relevant because it represents the oldest occurrence of the group, represented only by very scarce materials of Asteromys punctus and Chubutomys simpsoni. New materials of Deseadan cavioids are of prime importance to understand the early evolution of this group. The locality of Punta Nava (northeastern Santa Cruz Province, Patagonia, Argentina) has yielded a fauna assigned to the Deseadan SALMA, but no rodent remains were known so far. A recent fieldwork in this locality provided the first findings of fossil caviomorphs, including remains of Cavioidea, Octodontoidea, Chinchilloidea, and Erethizontoidea. A new species of Cavioidea s.s. from this locality is here described, and its phylogenetic affinities are evaluated. This new cavioid from the Deseadan SALMA, and the reinterpretation of the morphology of Chubutomys simpsoni, provide new insights into the early diversification of Cavioidea s.s. The new species from the late Oligocene, and the high position of Chubutomys in the phylogeny, draw back the origin of all protohypsodont lineages of Cavioidea s.s. to the Deseadan SALMA. Furthermore, this suggests that the early evolution of Cavioidea s.s. occurred through a major diversification pulse larger than previously proposed.

New Leontiniid Notoungulata (Mammalia) from Chile and Argentina: Comparative Anatomy, Character Analysis, and Phylogenetic Hypotheses

Herein we describe and name two new species of leontiniid notoungulates, one being the first known from Chile, the other from the Deseadan South American Land Mammal Age (SALMA) of Patagonia, Argentina. The Chilean leontiniid is from the lower horizons of the Cura-Mallín Formation (Tcm1) at Laguna del Laja in the Andean Main Range of central Chile. This new species, Colpodon antucoensis, is distinguishable from Patagonian species of Colpodon by way of its smaller I2; larger I3 and P1; sharper, V-shaped snout; and squarer upper premolars. The holotype came from a horizon that is constrained below and above by 40Ar/39Ar ages of 19.53 ± 0.60 and 19.25 ± 1.22, respectively, suggesting an age of roughly 19.5 Ma, or a little older (∼19.8 Ma) when corrected for a revised age of the Fish Canyon Tuff standard. Either age is slightly younger than ages reported for the Colhuehuapian SALMA fauna at the Gran Barranca. Taxa from the locality of the holotype of C. antucoensis are few, but they (e.g., the mylodontid sloth, Nematherium, and a lagostomine chinchillid) also suggest a post-Colhuehuapian faunal age. The second leontiniid named in this paper has been known in the literature for over 75 years as Leontinia sp. Several specimens referable to this species were discovered at Pico Truncado (Deseadan SALMA) during the Field Museums first Marshall Field Expedition, led by Elmer Riggs in 1924. This “new” taxon, Elmerriggsia fieldia, is a small-bodied leontiniid, possessing grooved premolar protocones that lack intermediate lingual cingulae, but have well-developed labial cingulids on their lower molars. This new taxon is fairly common at Pico Truncado, in Santa Cruz, Argentina, but we have not encountered it at other localities.The character-taxon matrix that we constructed for this analysis differs from those previously developed for notoungulates by the substantially greater number of postcranial characters used (41). Colbertia magellanica was used as the outgroup in all analyses. Our initial phylogenetic analysis was limited to only taxa traditionally assigned to the Toxodontia. These included a dozen taxa traditionally considered to be leontiniids, two toxodontids, four notohippids, a homalodotheriid, and two isotemnids. The taxa traditionally classified as leontiniids formed a monophyletic group, in which V-shaped muzzle, caniniform i3, femur with medial suprapatellar ridge, and large wedge-shaped fibular facet of the calcaneum were unequivocal synapomorphies. Colpodon spp. nested within a clade that includes the “tropical” leontiniids, Taubatherium and Huilatherium. Toxodontids and notohippids formed a monophyletic group sister to the leontiniids, with these two clades forming a more inclusive clade that previously had been called the “advanced Toxodontia.” However, when five species of typotheres from three “families” were added to the analysis, the “notohippid” Eurygenium was identified as the nearest outgroup of leontiniids and an “advanced notohippid” plus toxodontid clade (nodes C F). Unequivocal synapomorphies uniting these two nodes were robust calcanonavicular articulation (“reverse alternating tarsus” as evidenced by a distinct navicular facet on the calcaneum) and a distal radius with a styloid process. The presence of an entolophid fossettid in the lower molars and the downturned olecranon process of the ulna were equivocal synapomorphies for this clade. Though lacking the character states that diagnose a more exclusive “notohippid-toxodontid-leontiniid” clade, Eurygenium shared several unequivocal synapomorphies that unite it with these taxa. These include a well-formed fossette of upper molars formed by the posterior cingulum, absence of an entepicondylar foramen of the humerus, lack of a neck on the astragalus, a transversely elongated astragalar head, and absence of the “astragalar buttress” of the navicular.Unconventionally, the interatheriids used in the analysis (Federicoanaya and Protypotherium, both interatheriin

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).

Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands/Savannas in South America

We describe a new taxon of mylodontid sloth from the late Oligocene (Deseadan South American Land Mammal “age”), Salla Beds of Bolivia. This taxon, Paroctodontotherium calleorum, new genus and species, is one of the oldest known sloths, but it is surprisingly derived. It is referable to the Mylodontidae and, with just a little doubt, to the Mylodontinae. It shares a number of derived characteristics with other mylodontids and even mylodontines. These include: a relatively low temporomandibular joint; a relatively short zygomatic process of the squamosal; an elongated, narrow braincase; anteriorly diverging toothrows; broad muzzle; and greatly enlarged external nares. The relative width of the muzzle of Paroctodontotherium is as great as any Pleistocene mylodontid except the giant grazer, Lestodon. We review and critique methods of estimating diets of extinct sloths and propose a hypothesis in regard to the feeding ecology of Paroctodontotherium. Based upon its broad muzzle, the degree of tooth wear, and its presence in a habitat dominated by hypsodont herbivores, we propose that Paroctodontotherium was a bulk feeder that foraged near ground level. Grasses were likely a major component of its diet. The addition of this new taxon, along with other recently discovered taxa, illustrates that late Oligocene sloths had much greater diversity than recognized just a decade ago. This diversity is evident in species richness, variations in body sizes, dental morphologies, and means of locomotion. We regard this relatively sudden sloth radiation as a significant component of the Eocene-Oligocene faunal turnover and was related to the development of more open habitats of post-Eocene South America.

Paleontology and Geochronology of the Deseadan (late Oligocene) of Moquegua, Perú

Subsequent to our initial reports of the discovery of Deseadan fossils in southern Perú, we have obtained new data regarding the paleontology and geology of the upper member of the Moquegua Formation. These data include newly recovered fossil specimens and further analyses of those collected in our earlier field seasons. We have also obtained an ash directly from within the fossil-bearing units near the summit of Cerro Pan de Azúcar. Biotites from this Sugarloaf ash give an age estimate of 26.25 ± 0.10 Ma, thus supporting our previous suggestion that these fossil-bearing horizons are of late Oligocene age (Deseadan South American Land Mammal “Age”) and removing our query regarding a possible early Miocene age. Most of the fossils are of notoungulates and most of these are trachytheriine mesotheriids. Remarkably, three distinct mesotheriid taxa appear to have been present in the Moquegua fauna, none of which are referable to the common Trachytherus alloxus of the nearby and at least partly contemporaneous Salla beds of Bolivia. Other fossils documented here include postcranial elements of the notohippid notoungulate, Moqueguahippus, a macraucheniid litoptern (cf. Coniopternium), an osteoderm of an unnamed species of armadillo (Dasypodidae, cf. Dasypodinae), and a claw of a phorusrhacid bird. We also describe a diminutive new hystricognath rodent, Sallamys quispea, sp. nov. It is similar to, but distinct from, S. pascuali of Salla. Indeed, despite the temporal and geographic proximity of Moquegua to Salla, none of the taxa from Moquegua that can be identified to species are known from Salla. Likewise, we have failed to find any dasypodids from Salla that have osteoderms like that described in this work. Thus, it is appears that distinctive paleogeographic and paleoenvironmental conditions in the late Oligocene led to a regional biotic differentiation for the Moquegua area of coastal Perú.

New Leontiniids (Class Mammalia, Order Notoungulata, Family Leontiniidae) from the Salla Beds of Bolivia (Deseadan, Late Oligocene)

A revised diagnosis of the Leontiniidae (Class Mammalia, Order Notoungulata) is provided and leontiniids of the Deseadan South American Land Mammal "age" (SALMA; late Oligocene) are summarized. Two new species of leontinids from the Deseadan Salla Beds of Bolivia are described and placed within the new genus, Anayatherium; the smaller A. ekecoa and a much larger A. fortis. A phylogenetic analysis suggests that these species are closely related to the derived Patagonian genera Ancylocoelus and Colpodon, with the loss of the canine serving as a putative synapomorphy uniting these taxa. Although leontiniids are the most frequently encountered taxa at many other Deseadan localities, they are exceedingly rare at Salla. This scarcity, the scarcity of other ungulates with low crowned cheek teeth and the heavy tooth wear of a relatively young individual of A. ekecoa suggest that ungulates with low crowned teeth were at a selective disadvantage at Salla.

Revised age of the Salla beds, Bolivia, and its bearing on the age of the Deseadan South American Land Mammal “Age”

ABSTRACT The Salla beds of Bolivia contain a mammalian faunal assemblage assigned to the Deseadan South American Land Mammal “Age” (SALMA), known elsewhere principally in Patagonia. The earliest platyrrhine monkey Branisella comes from a single stratigraphie level in these beds. The age of the Salla beds is debated; new radiometrie dates constrain the age of the Deseadan SALMA in Bolivia and clarify the timing of the first record of platyrrhines in South America. The oldest vertebrate fossils from the Salla beds are contained within the magnetic polarity interval ClOr, between 28.8 and 29.4 Ma. The youngest fossils occur above the 275 m ash in Chron C7Ar, between 25.65 to 25.82 Ma. The best known faunas, including those of the Branisella level, come from several localities within Chron C8 (25.82 to 27.02 Ma). If the recent suggestion by Flynn and S wisher (1995) that redating indicates that the Deseadan in Patagonia spans only about 27 to 29 Ma, then the bulk of the Salla fauna is younger than that of Patagonia.

New evidence for late mesozoic-early Cenozoic evolution of the Chilean Andes in the upper Tinguiririca valley (35 °S), central Chile

New geologic, paleontologic and isotopic geochronometric results from the Termas del Flaco region in the upper Tinguiririca River valley in central Chile demand considerable revision of the accepted geotectonic history of the Andean Main Range in this region. A diverse, transitional Eocene-Oligocene aged, land-mammal fauna was recovered from several sites in volcaniclastic sediments of the Coya-Machalí (=Abanico) Formation. Major results of our study include: 1) The 1000 + m thick studied deposits, previously attributed to the Cretaceous Colimapu Formation, belong to the Coya-Machalí (=Abanico) Formation. Radioisotopic data from levels immediately above (31.5 Ma) and below (37.S Ma) the fossiliferous horizon indicate a latest Eocene to early Oligocene age for the basal part of the formation and the fauna contained in it. 2) The fossiliferous unit rests with slight angular offset on different Mesozoic units: “Brownish-red Clastic Unit” (BRCU) and Baños del Flaco Formation; in a limited area it also overlies a white tuff dated at 104 Ma. 3) The contacts just discussed (none of which is attributable to faulting), demonstrate the existence of two, or possibly three, unconformities in the region. 4) Sedimentological criteria argue against reference of the BRCU to the Colimapu Formation, and imply correlation of the former unit to basal levels with in the late Cretaceous Neuquén Group of western Argentina. 5) The Coya-Machalí Formation, previously viewed as representing the western volcanic equivalent of Riogrd́ndico Supercycle deposits of western Argentino, is likely coeval to much younger units in that region such as the Agua de la Piedra Formation. 6) Paleomagnetic results from the fossil producing horizon indicate about 20 ° of post-early Oligocene, counterclockwise rotation. 7) Fossil mammals from the Coya-Machalí Formation near Termas del Flaco represent a distinct biochronologic interval not heretofore clearly recognized from elsewhere on the continent. This new fauna helps fill the long recognized post-?middle Eocene, pre-late Oligocene faunal hiatus between the Mustersan and Deseadan South American Land Mammal Ages (SALMA). In addition, it records the earliest known presence of rodents in South America and otherwise differs strongly from the enigmatic Divisaderan SALMA.