Biostratigraphy and biochronology of the Late Miocene of central Argentina: Evidence from rodents and taphonomy

Biostratigraphy and biochronology of the Late Miocene of central Argentina is analyzed through evolutionary patterns of octodontoid rodents. The studied faunas were found in continental sediments assigned to the Cerro Azul and Saldungaray formations (La Pampa and Buenos Aires provinces, respectively). Taphonomic attributes of recovered mammals, linked mostly to the development of paleosols or to predators’ activities, constraint the deposition lapse to short intervals. A biostratigraphic scheme based mainly on the anagenetic pattern of change in the octodontoid rodent lineage Chasichimys-Xenodontomys is proposed. Since there is no stratigraphic superposition among the studied levels, relationships among deposits are established through the polarity evidenced by the stage of evolution of chronomorphs of this lineage. Five new biozones for the Late Miocene of central Argentina are recognized. Evidence of other anagenetic sequences, and general trends of increasing hypsodonty in octodontoids, support this proposal. The results enhance the value of the “stage of evolution” concept as a correlation tool in biostratigraphic and biochronologic studies, mainly when applied through phyletic sequences.     

Leftover prey remains: a new taphonomic mode from the Late Miocene Cerro Azul Formation of Central Argentina

The Cerro Azul Formation (La Pampa Province, Argentina) comprises a rich vertebrate fauna of small mammals dominated by notoungulates and rodents. The fauna pertains to the Late Miocene specifically to the Huayquerian Stage/Age. Taphonomic analysis of micro‐mammals from Estancia Ré locality evidenced that the faunal assemblage was accumulated by the activity of a predator. This assemblage was compared with others from the Cerro Azul Formation in Telén and Caleufú localities (La Pampa Province), previously interpreted as products of predator activities. These microfossil accumulations differ from assemblages attributed to pellets and faeces produced by modern predators (nocturnal and diurnal bird raptors and carnivore mammals). However, due to their anatomical representation, degree of bone breakage and presence of tooth marks, they are interpreted as accumulations of uneaten prey remains discarded by the predator. The predator involved could not be determined with certainty, although the presence of tooth marks in some skeletal remains and the presence of coprolites in Telén and Caleufú suggest that it could be a carnivore mammal. Similarities in the accumulation mechanism, patterns of preservation and sedimentary contexts in the three assemblages support the recognition of a new taphonomic mode, termed ‘leftover prey remains’.     

Dental evolution in Neophanomys (Rodentia, Octodontidae) from the late Miocene of central Argentina

The evolutionary pattern of the molar morphology of the small caviomorph (Octodontidae) Neophanomys from the late Miocene Cerro Azul Formation of central Argentina is analyzed. Two new species (chronomorphs) are recognized, which constitute an anagenetically evolving lineage with a gradual and directional pattern of increasing molar hypsodonty. Dental changes related to increasing hypsodonty are comparable to those of the octodontid lineage Chasichimys also recovered from the Cerro Azul Formation. However, Neophanomys shows comparatively less variation in gross morphology and there are no evidences that this lineage achieved euhypsodonty. In contrast, important changes in enamel microstructure (schmelzmuster) are observed among different populations of Neophanomys, supporting the hypothesis that these changes can occur at least partially independently from modifications in dental gross morphology. The patterns of dental evolution detected in the Neophanomys and Chasichimys-Xenodontomys lineages and the unequivocal polarity of the changes involved, related to increasing hypsodonty, reinforce the hypothesis that chronological differences exist among late Miocene outcroppings of Cerro Azul Formation in central Argentina.     

Taphonomy and paleoecology of mammals preserved in swampy deposits (Formosa Province,Argentina): new light on a key environmental context for the evolution of Quaternary vertebrates in Southern South America

Quaternary continental deposits of South America are characterized by the abundance and diversity of vertebrate remains preserved in different environmental contexts. However, the studies focused on interpreting the origin of the assemblages are scarce. The taphonomic features of the mammal specimens from the Río Bermejo Formation, Formosa Province (Argentina), are analyzed. The bearing levels belong to the Upper Pleistocene-lower Holocene, and were interpreted as swampy deposits that filled channels of the ancient Bermejo River, an environmental context little evaluated from the taphonomic point of view. The assemblage includes Xenarthra, Notoungulata, Carnivora, Artiodactyla and Proboscidea. The evidence suggests that the assemblage is composed by specimens preserved in the place of death or close to it, with short time of subaerial exposure and little or no transport. After burial, the specimens were also affected by diverse processes directly related to the swamp deposits where they were buried. In this case, the taphonomic evidence, along with the sedimentary characteristics of the bearing levels allowed the recognition of the channel-fill mode for this assemblage. Also, this study provides new information for an area that was very important in the evolution of vertebrates in Northeastern Argentina since the Late Pleistocene.     

A brittle star bed from the Miocene of Patagonia, Argentina

Martínez, S., del Río, C.J. & Pérez, D.E. 2010: A brittle star bed from the Miocene of Patagonia, Argentina. Lethaia , Vol. 43, pp. 1–9.
As a consequence of the extremely poor fossil record of brittle stars, every new discovery is important. The Miocene example studied herein involves the recently described species Ophiocrossota kollenbergorum Caviglia, Martínez & del Río recovered from the Chenque Formation of southeastern Argentina. The information used here is derived from unpublished data and a new record from two discrete, thin, monospecific patches. The main taphonomic features of the patches, namely the presence of specimens concordant with bedding planes, (with either aboral or oral side upwards), and the good preservation of the delicate discs (ca. 6 mm wide on average), and the preservation of un-oriented arms complete with fragile tips (not wider than 0.2 mm), point to a suddenly buried census assemblage. Although broken or isolated arms were found, this is attributed to the erosive environmental conditions of the abrasion platform where the studied exposure is located today. Size frequency distributions suggest that both patches were buried at different seasons. Observed densities are 77 and 143 individuals/m², and distances between individuals are random. The arm length/disc diameter ratio indicates that Ophiocrossota kollenbergorum may have been an epifaunal surface dweller. No signs of predation (such as regenerated arms), were identified.     

A new Pitheciin primate from the middle Miocene of Argentina

We report here a new fossil primate from the middle Miocene of Argentina. The material consists of isolated teeth, mandibular fragments, and a talus. The fossils were collected in the Collón Cura formation at Cañadón del Tordillo in Neuquén Province. An age of 15.71 ± 0.07 Ma has been reported for the Pilcaniyeu Ignimbrite, which lies just below the paleosols in which the fossils were found. This material is thus the youngest occurrence of fossil primates in Argentina (hitherto documented in the Santacrucian and older land mammal ages) but still is older than the middle Miocene platyrrhine primates from La Venta, Colombia, in particular the pitheciins Nuciruptor and Cebupithecia. The material is recognized as a new genus and species of Pitheciinae, Propithecia neuquenensis. The mesiodistally compressed, high-crowned incisors are specialized and similar to species in the tribe Pithecini and to the nonpitheciin Soriacebus (early Miocene, Patagonia). We rule out a phylogenetic relationship to the latter because of differences in molar morphology. Propithecia does, however, fit well into the pattern of pitheciin evolution, being more derived than the middle Miocene pitheciin Nuciruptor but not as much as another middle Miocene taxon, Cebupithecia. As such, this makes Propithecia the oldest taxon that can be confidently placed within this modern New World monkey subfamily. By analogy with the molar structures and diets of extant platyrrhines, Propithecia has a molar structure consistent with a variety of low-fiber diets ranging from fruit and gum to seeds. Its incisors suggest seed-eating in much the same way as extant pitheciins, like Pithecia. The talus resembles that of Callicebus, suggesting arboreal quadrupedal locomotion. Am. J. Primatol. 45:317–336, 1998. © 1998 Wiley-Liss, Inc.     

The most ancient caviine rodent (Hystricognathi,Cavioidea) comes from the late Miocene of Northwest Argentina (South America)

The family Caviidae is one of the most diverse groups among South American hystricognath rodents and is represented by three main living lineages: Caviinae (cavies), Dolichotinae (maras) and Hydrochoerinae (capybaras). Caviinae includes the smaller forms of caviids represented by the extant Microcavia, Cavia and Galea. They are distributed in a wide range of environments throughout South America. In addition, three other genera from the late Miocene–Pliocene (Dolicavia, Palaeocavia and Neocavia) are recognised in high latitudes. In northwestern Argentina, the fossil forms of Caviinae have been poorly studied and for most of them there is no precise stratigraphic information. We describe and evaluate the phylogenetic affinities of the most ancient caviine from the Chiquimil Formation, Catamarca province, northwestern Argentina (9.14–7.14 ma). According to the morphological analysis of the mandibular and dental morphology and the results of the phylogenetic analysis, we assigned the new species tentatively to genus Palaeocavia. The phylogenetic position of the new species suggests an earlier origin for the lineage Palaeocavia + Cavia and for the entire clade Caviinae.     

Systematic position of the Mesotheriidae (Notoungulata) from the Mariño Formation (Miocene) in Divisadero Largo, Mendoza, Argentina

This paper deals with the detailed taxonomic study of the first mammal remains from the Mariño Formation in the Divisadero Largo area, Mendoza, central west Argentina. This area was well-known by the fossils recovered from the Triassic levels and particularly by the faunal assemblage from the Cenozoic levels corresponding to the Divisadero Largo Formation. Until recently, no mammal remains had been accurately reported for the Mariño Formation, Miocene in age. The specimen consists in an almost complete upper jugal series (teeth found separated from the maxillary bone except the M3) of a small Mesotheriidae (Notoungulata), which was preliminary identified as Mesotheriinae indet. The main characteristic of these teeth is their small size, significatively lesser than that of the Miocene genera Eutypotherium, Typotheriopsis and Pseudotypotherium, being closer to Mycrotypotherium from Bolivia and the Chilean species from the Chucal Formation. The direct comparison with these latter forms has allowed a more detailed study and the recognition of the material here described as cf. Altitypotherium chucalensis, with all cautions inherent to the incompleteness of the material.     

Reappraisal of the giant caviomorph rodent Phoberomys burmeisteri (Ameghino, 1886) from the late Miocene of northeastern Argentina,and the phylogeny and diversity of Neoepiblemidae

Phoberomys is a giant caviomorph rodent included in the extinct Neoepiblemidae. It is recorded in the late Miocene-Pliocene of South America (Argentina, Venezuela, Brazil and Peru), and is one of the largest rodents that have ever lived. In this contribution we study specimens of Phoberomys from the ‘Mesopotamiense’, late Miocene of Entre Ríos Province (Argentina), including several unpublished specimens and the holotypes of the five nominal species (Ph. burmeisteri, Ph. praecursor, Ph. insolita, Ph. lozanoi and Ph. minima) previously recognised for this unit. Our study indicates that all Mesopotamian specimens belong to Phoberomys burmeisteri, and that the differences among them reveal individual and ontogenetic variation. Our phylogenetic analysis indicates that Neoepiblemidae is monophyletic and includes Phoberomys, Neoepiblema, and Perimys. Phoberomys species are recovered as a clade, which is more closely related to Neoepiblema than to the Patagonian Perimys. In addition, our study shows that Eusigmomys is not a Neoepiblemidae, but a Dinomyidae.     

Brachypotherium (Perissodactyla,Rhinocerotidae) from the late Miocene of Samburu Hills,Kenya

Several isolated cheek teeth and mandibular specimens of Rhinocerotidae (Mammalia, Perissodactyla) from the upper Miocene Namurungule Formation in Samburu Hills, Kenya, are redescribed. Previously, these specimens had been identified as Chilotheridium pattersoni, Chilotheridium sp., Paradiceros mukirii, and Paradiceros sp. They are reidentified here as documenting the genus Brachypotherium based on their bucco-lingually broad molariform upper premolars with short crochet and flattened buccal walls on both upper and lower molars, the latter having a shallow external groove. Comparisons with other Brachypotherium species suggest that the present specimens belong to Brachypotherium sp. cf. B. minor. The presence of Brachypotherium in the Samburu Hills, at ca. 9.5 Ma, is concordant with the paleoenvironment (presence of lacustrine and river environments) known for this locality during the early late Miocene.     

A new elasmothere (Perissodactyla, Rhinocerotidae) from the late Miocene of the Linxia Basin in Gansu, China

Ningxiatherium euryrhinus sp. nov. is a relatively large elasmothere rhino from the Linxia Basin in northwestern China found in the early Bahean, which corresponds to the early Vallesian (MN 9), ca. 11.1 Ma. It is much larger than the extant Ceratotherium simum and has a single horn. Ningxiatherium is similar to the late Miocene Parelasmotherium from Gansu and Shanxi, but differs in having partially ossified nasal septum, terminal nasal horn boss, shallower nasal notch above the P3/P4 boundary, and much shorter premolars. N. euryrhinus sp. nov. differs from N. longirhinus from the late Miocene of Zhongning, Ningxia in northwestern China by its larger size, relatively wider nasals, shallower nasal notch, and sub-quadrangular occlusal surface of M3. In the Linxia Basin, the other early late Miocene (Bahean or Vallesian) elasmotheres are known from complete skulls or isolated teeth. They include two genera and three species: Parelasmotherium linxiaense, P. simplum, and Iranotherium morgani. They lack a nasal septum, but Ningxiatherium has one. The age of N. euryrhinus is early late Miocene based on direct association with biochronologic indicator taxa, such as Dinocrocuta gigantea, Hipparion dongxiangense, and Chilotherium primigenius. N. euryrhinus is more primitive than N. longirhinus sp. nov. in having a sub-quadrangular M3, a shallower nasal notch, and the presence of DP1 in adults.     

Rodents and insectivores from the late Miocene of Romerales (Fortuna Basin,Southern Spain)

Abstract

The Neogene Fortuna Basin (Murcia Region, SE Spain) is rich in microvertebrate sites. Its continental sections include localities extended from the middle Turolian (MN12) to the early Ruscinian (MN14). However, there are few works dealing with the taxonomy of these fossil assemblages. In this paper we provide a complete taxonomic study of the rodents and insectivores from three levels (ROM-2B, ROM-2C and ROM-3A) within the Romerales section. We infer a late Turolian age (late Messinian) for these levels, among which the richest and most diverse level is ROM-C, including at least 11 different taxa. In addition, the paleoecological analysis of these fossil assemblages suggests the dominance of open herbaceous meadows under temperate climate during the formation of these sites, with a slight decrease in temperature and humidity from ROM-2B to ROM-2C.     

The deciduous lower dentition of Ouranopithecus macedoniensis (Primates, Hominoidea) from the late Miocene deposits of Macedonia, Greece

Two mandibular fragments with associated milk teeth assigned to the late Miocene hominoid primate Ouranopithecus macedoniensis are analyzed. The fossils, which belong to a single individual, were found in the Vallesian locality of "Ravin de la Pluie" of the Axios Valley (Macedonia, Greece). The material is described here and compared with extant and extinct hominoids, allowing assessment of the evolutionary trends in the deciduous lower dentition within the Hominoidea. Hylobatids represent the more primitive pattern. Gorilla is slightly more derived than hylobatids, but less derived than Pongo and Pan, the latter being the most derived. With relatively smaller deciduous canines and more molarized deciduous premolars, Ouranopithecus is more derived than both Pan and Gorilla. Among the fossil hominoids, Proconsul, representing the primitive condition, has a very simple dp(3)and a dp(4)that has a trigonid that is taller than the talonid and which lacks a hypoconulid. Griphopithecus is more derived than Proconsul in having a dp(4) with a lower trigonid, a hypoconulid, and a less oblique cristid obliqua. Australopithecus and Paranthropus possess a similar morphology to that of Homo, while Ardipithecus appears to be more primitive than the latter genera. Ouranopithecus has a more derived lower milk dentition than Proconsul and Griphopithecus, but less derived than Australopithecus and Paranthropus. The comparison of the lower milk dentition of Ouranopithecus confirms our previous conclusions suggesting that this fossil hominoid shares derived characters with Australopithecus and Homo.     

陕西蓝田灞河组晚中新世Gazella羚羊的形态特征与分类（英文）

Gazella羚羊是"三趾马动物群"中常见成员,在晚中新世至更新世地层中广泛分布,演化速率相对较快,具有重要的生物地层学及生态指示意义,但在我国尚未有保德期之前的化石报道。本文研究的化石发现于陕西蓝田灞河组中部,磁性地层学资料显示其年代为晚中新世灞河期。化石标本包括了5个近乎完整的头骨、下颌以及颅后骨骼。根据发现的标本装架起第一个完整的Gazella羚羊骨架。形态对比与测量数据表明,蓝田标本与巴基斯坦西瓦里克发现的Gazella lydekkeri非常相近,而不同于欧洲晚中新世常见的Gazella各种以及我国发现的种类。从肢骨的形态分析与测量比例数据来看,Gazella cf.G.lydekkeri适合快速奔跑运动,可能生活在相对开阔的环境中,与灞河期动物群的生态类型以及与灞河组沉积学、同位素地球化学等研究所指示的相对干旱、半干旱的开阔草原环境相一致。     

Musteloids and feloids (Mammalia, Carnivora) from the late Miocene locality of Pikermi (Attica, Greece)

Some relatively rare carnivore remains from Pikermi are studied. The present specimens include Simocyon primigenius(ROTH and WAGNER, 1854), Promeles palaeatticus(WEITHOFER, 1888), Martes woodwardiPILGRIM, 1931, Felis atticaWAGNER, 1857 and Machairodus giganteus(WAGNER, 1848), as well as some postcranial remains that resemble Enhydriodon? latipesPILGRIM, 1931 and are assigned to Mustelidae gen. et spec. indet. Some of these species were not known until now but from their holotypes as M. woodwardi and E.? latipes. Other species such as F. attica and M. giganteus are better known but from relatively scant material. Since the material of the earlier mentioned species comes from Pikermi, their type locality, it is of especial importance and improves our knowledge for the Pikermi carnivores and their relationships to other species. In some cases where the material comes from ossiferous blocks, the accompanying faunal context is discussed.     

A new species of Gaimanophis (Serpentes,Boidae) from the Miocene of northwestern Argentina with remarks on the Neogene boids of South America

Gaimanophis is an extinct boid genus represented so far by a single species (Gaimanophis tenuis) known by isolated vertebrae from the early Miocene of Patagonia. In this paper, a new species of Gaimanophis is described from the India Muerta Formation (late Miocene) of Tucumán province (Argentina). Gaimanophis powelli sp. nov. distinguishes itself from G. tenuis mainly in its larger size, prezygapophyses less slanting, neural spine shorter dorsally than ventrally, and zygosphene straight bearing an anteriorly protruding tongue. This record indicates a wider temporal and geographical distribution of the genus from the early Miocene of Patagonia to the late Miocene of northwestern Argentina. The recognition of a new species of boid in South America increases the known diversity of this group. Although boids have inhabited in this territory since the Paleocene, fossils belonging to the group only show a glimpse of the real past diversity in the continent.     

Hypsosteiromys (Rodentia, Hystricognathi) from the Early Miocene of Patagonia (Argentina), the only Erethizontidae with a tendency to hypsodonty

Hypsosteiromys is the only New World porcupine that shows a tendency to hypsodonty. It is recorded exclusively from the Colhuehuapian Age (Early Miocene) of central Patagonia (Argentina). In addition to the type species, a second one, Hypsosteiromys nectus(AMEGHINO, 1902), is recognized, from the southern cliff of Colhuehuapi Lake (Chubut province). It differs from the type species in the lesser development of the anterolabial and posteroflexid notches of the m1-3, shorter p4 and dp4, and more slender incisors. Dental morphology suggests that the species of Hypsosteiromys lived in more open areas than most fossil and living Erethizontidae.     

A contribution to the herpetofauna from the late Miocene of Gritsev (Ukraine)

Excavations in the locality Gritsev (karstic fillings of the upper Miocene age in a limestone quarry in Shepetovsky District, Khmelnitsky Region, Ukraine) revealed, since 1983 when excavations started, a rich vertebrate fauna that includes also amphibians and lizards. The material is rich enough to assess individual and developmental variation within some taxa (e.g., Pseudopus pannonicus). Although the fragmentary nature of the disarticulated bones does not sometimes allow precise taxonomic assignment, morphological differences in, e.g., dental characteristics suggest the presence of some other ones, not formally named forms. Thus, the list of the amphibian and reptilian taxa from Gritsev is by far not complete, but their osteological characteristics are representative to such a degree that they can provide information for comparisons with other European Miocene herpetofaunas.     

A fossil record of the Eastern clade of Blanus (Amphisbaenia: Blanidae) from the late Miocene of Ukraine

The fossil history of worm lizards in Eastern Europe is very patchy because of the small number of localities and the fragmentary vertebral material available. A new record of the genus Blanus from the late Miocene of the Egorovka 1 and 2 localities in Ukraine is reported here. Based on its dental morphology, Blanus from Egorovka differs from all extinct species of the genus and from the extant B. cinereus complex. It is most closely related to the Eastern clade of Blanus (B. strauchi complex) in having enlarged second and small third dentary teeth. Blanus from Egorovka is the second fossil record of the B. strauchi complex and the first record of the Eastern clade outside of its current geographical range. It indicates a wider past range of the Eastern European Blanus, including the northern Black Sea coastal area.     

Additional specimens of Diceros (Perissodactyla,Rhinocerotidae) from the Upper Miocene Nakali Formation in Nakali,central Kenya

An upper incisor and upper and lower cheek teeth of Rhinocerotidae from the Upper Miocene of Nakali in central Kenya are described. Those specimens are identified as Diceros sp. The present study confirms the presence of Diceros in sub-Saharan East Africa during Vallesian as noted by several studies. The present result and the fossil records of Diceros in Africa and Eurasia suggest that Diceros might have migrated to Eurasia from Africa by Vallesian, although more fossil records and detailed phylogenetic analysis of Diceros are needed to discuss this hypothesis.