Microvertebrate Assemblages Research Articles

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.

Exceptional Late Pliocene microvertebrate diversity in northwestern Argentina reveals a marked small mammal turnover

Despite a century of paleontological work in Neogene sequences of northwestern Argentina there is still much to learn about the biotic diversity in this area during Pliocene times. We report a rich microvertebrate assemblage recovered from Late Pliocene deposits of Uquía Formation, Jujuy Province, northernmost Argentina. Taxa represented in the studied sample include members of Bufonidae (Amphibia: Anura), Iguanoidea (Reptilia: Squamata), Passeriformes (Aves), Argyrolagidae, Didelphidae, Caviidae, Ctenomyidae, Octodontidae, and Cricetidae (Mammalia). Taphonomic attributes indicate that the bone concentration was produced by owls. The remains were disposed highly concentrated suggesting that the assemblage would have been generated in a short lapse, indicating a low time-averaging, retaining the main ecological signals of the past living community. The studied assemblage is noteworthy because it encompasses at least five new genera of cricetid rodents, illustrating the oldest record in northwestern Argentina for this diverse family of mammals. In spite of clear taxonomic differences at specific and generic levels, the structure of the assemblage is ecologically comparable to modern small mammal communities in terms of body mass distribution, trophic structure and abundance, with a dominance of cricetids over marsupials and caviomorph rodents. Striking differences in taxonomic composition between the Uquian assemblage and the coeval record from central Argentina indicate biogeographical distinctions since the Late Pliocene. The new Uquian cricetids show that the early divergence times for phyllotine genera proposed by several authors cannot be supported. The dominance of phyllotines in the assemblage as well as the record of Microcavia and an octodontid allow inferring arid or semiarid paleoenvironment conditions, in a more or less open habitat. The studied assemblage reflects a noteworthy faunal turnover, which implies the establishment of cricetid rodents as the dominant group in the small mammal communities. This faunal change can be associated to increasing aridity during Late Pliocene worldwide.

The Late Triassic microvertebrate fauna of Tytherington, UK

The Late Triassic fissure fills from the region of Bristol, SW England and S Wales, preserve unique assemblages of small vertebrates derived from an archipelago of palaeo-islands that document aspects of a critical transition in the history of terrestrial ecosystems. Tytherington Quarry, in south Gloucestershire, is the site of several fossiliferous fissures, all dated as Rhaetian (terminal Triassic), and source of abundant remains of the ‘Bristol dinosaur’, Thecodontosaurus antiquus. In addition, the fissure sediments have yielded previously unreported microvertebrate assemblages, including over 400 jaw remains from three genera of sphenodontians and 100 archosaur teeth assigned to 15 morphotypes. The land fauna is dominated by sphenodontians, with Diphydontosaurus by far the most common form, followed by Clevosaurus, then the sauropodomorph dinosaur Thecodontosaurus, and then the sphenodontian Planocephalosaurus. There are, in addition, rare remains of contemporaneous bony fishes, as well as fossils apparently reworked from the Carboniferous limestones, namely conodonts, holocephalian (chimaeroid) teeth, and a shark tooth. Many typical latest Triassic animals, such as temnospondyls, phytosaurs, aetosaurs, rauisuchians, plateosaurids and dicynodonts are not represented at Tytherington, perhaps because these generally larger animals did not live on the palaeo-island, or because their carcasses could not fit into the fissures. The absence of tritylodonts and early mammals is, however, less easy to explain on the basis of size, although it is known that these forms were abundant here by the Early Jurassic.

The long‐term history of dispersal among lizards in the early Eocene: new evidence from a microvertebrate assemblage in the Bighorn Basin of Wyoming, USA

Abstract: Early Eocene mammal faunas of North America were transformed by intercontinental dispersal at the Paleocene–Eocene boundary, but lizard faunas from the earliest Eocene of the same area were dominated by immigrants from within the continent. A new lizard assemblage from the middle early Eocene of Wyoming sheds light on the longer‐term history of dispersal in relation to climate change. The assemblage consists of three iguanid species (including two new species possibly closely related to living Anolis), Scincoideus, ‘Palaeoxantusia’, four anguids, two species of an undescribed new anguimorph clade, Provaranosaurus and a varanoid (cf. Saniwa). Most North American glyptosaurin glyptosaurines are now referred to Glyptosaurus, and Glyptosaurus hillsi is given a new diagnosis. Scincoideus is otherwise known only from the mid‐Paleocene of Belgium, and the specimens described here are the first to document intercontinental dispersal to North America among lizards in the early Eocene. Like in mammals, some immigrant lizard lineages first appearing in the Bighorn Basin in the earliest Eocene persisted in the area long after the Paleocene–Eocene thermal maximum, but other immigrants appear to have been restricted to the Paleocene–Eocene thermal maximum.

Geochemical Stratigraphy and Microvertebrate Assemblage Sequences across the Silurian/Devonian Transition in South China

Abstract:Carbon isotope (δ13Corg) analyses of non‐marine clastic rocks and neritic carbonates and black shales spanning the Silurian/Devonian transition are compared from two richly fossiliferous sequences in Qujing of East Yunnan and Zoige of Sichuan, South China. The two sections, Xishancun and Putonggou sections in South China, reveal positive δ13Corg shifts happening in the Upper Pridoli and Lower Devonian and reaching peak values as heavy as –25.2%‰ (Xishancun) and –19.9%‰ (Putonggou) in the lowermost Lochkovian following the first occurrence of the thelodont Parathelodus and the conodont Icriodus woschmidti woschmidti (only in Putonggou Section and together with Protathyris‐Lanceomyonia brachiopod fauna). These results replicate a globally known positive shift in δ13Corg from the uppermost Silurian to the lowermost Devonian. The δ13Corg variations across the Silurian/Devonian Boundary (SDB) at the two sections in South China exhibit a shift in carbon isotopic composition similar to the detailed SDB curves from the borehole Klonk‐1 drilled at top of the Klonk Global Standard Stratotype‐Section and Point (GSSP) in the Prague Basin, Czech Republic. In addition, four microvertebrate assemblages, including the Liaojiaoshan, Xishancun, Yanglugou and Xiaputonggou assemblages, are recognized from the Silurian/Devonian transition exposed in the Xishancun and Putonggou sections, respectively. The results from both carbon isotope stratigraphy and microvertebrate assemblage sequences suggest that the SDB in South China is located at the base of the Xishancun Formation (between sample QX‐20 and sample QX‐21) in the Xishancun Section and the lower part of the Xiaputonggou Formation (between sample ZP‐09 and sample ZP‐10) in the Putonggou Section. The isotopic trend for organic carbon together with the changes of microvertebrate remains across the SDB can offer an approach to a potential correlation of the SDB from different sedimentary facies, which help to correlate the marine with non‐marine deposits.

Comparative osteohistology of hyperelongate neural spines in the Edaphosauridae (Amniota: Synapsida)

Abstract: The Permo‐Carboniferous Edaphosauridae is an extinct family of omnivorous and herbivorous basal synapsids in which a dorsal sail, comprised of a series of hyperelongate vertebral spinous processes (‘neural spines’), evolved convergently to their sphenacodontid contemporaries. Descriptive and quantitative microstructural analysis of these hypertrophied neural spines allows inferences of sail growth, allometry and structural properties and permits systematic comparisons with other groups (i.e. sphenacodontids). In Edaphosaurus and Ianthasaurus, neural spine microstructure is characterized by a lamellar‐zonal primary bone complex within the cortex, distal cross‐sectional bone density ranging from approximately 0.50 to 0.75, low cortical porosity ranging from 1.0 to 5.0 per cent, relative bone wall thickness ranging from 10 to 25 per cent and presence of a central cavity, fully developed with smooth endosteal margins in both genera. Tubercle growth, however, appears to have been slower and incremental in the specimen of Ianthasaurus examined here. Microstructural similarities further support the position of Lupeosaurus within Edaphosauridae as hypothesized by earlier authors, though most parsimoniously in a basal position (as a central cavity is only incipiently developed and tubercles are lacking). Histological properties of hyperelongate neural spines in Lupeosaurus and other edaphosaurids do not meet previously established requirements of the thermoregulatory hypothesis, either calling into question the sail’s thermoregulatory function in this group or indicating a reconsideration of those putative thermoregulatory adaptations and the purported soft‐tissue correlates of the sail. Conversely, microstructural patterns exhibit variation that is consistent with an intra‐ or interspecific display function. Given the diverse microstructural properties at the family and genus‐level, histological study of hyperelongate neural spines may also aid in recognizing taxonomic compositions of Permo‐Carboniferous microvertebrate assemblages in which only fragmentary materials are known.

New data on bat fossils from Middle and Upper Pleistocene localities of France

We describe the bat fossils preserved in four sites from the middle and upper Pleistocene, three of them being well-known French localities: the rock shelter of Les Valerots, the caves of l’Escale at Saint Estève Janson and “du Prince” at Grimaldi (Italy), and the filling of Combe-Grenal, all of them containing microvertebrate assemblages with yet undescribed bat fossils. All species represented in these four localities are still presently distributed in France and had been previously recorded in other Pleistocene localities of central and western Europe, including France. The four assemblages differ both in the abundance of bat fossils as in species composition. The characteristics of each assemblage are analysed under modern insights of bat taphonomy and ecology, and compared with those of other bat-bearing French localities of similar age. The relevance of these data concerning the use of the fossil bats to infer past environmental conditions is discussed.

The archaeology and paleoenvironment of an Upper Pleistocene hyena den: An integrated approach

Data of high resolution for reconstructions of archaeological site formation processes can be obtained only by the use of precise excavation methods and comprehensive recovery techniques using fine-mesh water screening, followed by meticulous sorting and quantitative studies of all the small organic components from the screens. These methods are generally used at human occupation sites, but are not often employed at paleontological or mixed human-carnivore sites. At the site of Bois Roche, an Upper Pleistocene hyena den, we have used these meticulous recovery techniques in combination with absolute dating, geoarchaeological observations, taphonomic analyses, studies of microvertebrates and pollen analysis. Correlation of the site environmental data from pollen and microvertebrate assemblages with the vegetation record of a deep-sea core taken in the Bay of Biscay have allowed us to constrain the ages provided by ESR dating of bovid teeth and to reconstruct the physical environment of the site with a degree of confidence rarely achieved by the use of fossil remains from archaeological sites alone. Prior to our excavations, the site was interpreted as containing a mixed assemblage with evidence of hyena activities and human occupation in situ. Quantitative analysis of the small organic components present in large quantities in the sediments (deciduous hyena teeth, coprolite fragments, digested small bone fragments) prove, more than all other lines of evidence, that hyenas were in residence at Bois Roche, thus providing diagnostic criteria for distinguishing between occasional visitors and the main inhabitants of mixed human-carnivore sites. The analytical procedures presented in this paper have a value beyond the significance of the Bois Roche site because they can be applied to other sites.

Diversity and variation of theropod dinosaur teeth from the uppermost Santonian Milk River Formation (Upper Cretaceous), Alberta: a quantitative method supporting identification of the oldest dinosaur tooth assemblage in Canada

The Santonian Deadhorse Coulee Member of the Milk River Formation preserves the oldest dinosaur body fossils found in Alberta. However, vertebrate remains consist almost exclusively of isolated elements and microvertebrate assemblages. Here, 1572 relatively complete shed non-avian theropod teeth from 20 localities in the Deadhorse Coulee Member are measured and analyzed to assess species diversity. Teeth are referred to or similar to Tyrannosaurinae indet., cf. Richardoestesia gilmorei , cf. Richardoestesia isosceles , Dromaeosauridae indet., Dromaeosaurinae indet., Velociraptorinae indet., and cf. Paronychodon lacustris . For the taxa identified, the large sample size allows for the assessment of their range of variation and accurate identification, without the benefit of comparable material of this age. Multivariate statistics, including a principal component analysis and a canonical variate analysis, provide reasonable separation of all taxa, although better results are achieved by separate analyses based on qualitative observations of denticle shape. The best results of the canonical variate analysis identified 96.0% of specimens correctly. This corroborates the qualitative identification of specimens and illustrates a valid way of evaluating diversity in areas and formations from which no described jaw material is known.

Vertebrate taphonomy in loess-palaeosol deposits: A case study from the late Miocene of central Argentina

This paper deals with the taphonomic analysis of the late Miocene bone assemblage from the Cerro Azul Formation at Telén (La Pampa Province, Argentina). The faunal assemblage was assigned to the Huayquerian mammal age (late Miocene). The fossiliferous section shows a homogeneous lithology, and is interpreted as a loess deposit with two similar and slightly developed palaeosols, classified as calcic vertisols. The studied sample comprises 5598 remains anatomically and taxonomically determined. They were collected from an area of about 48,000 m 2, appearing randomly distributed through the section and with low density. Most remains are small- to very small-sized, disarticulated, and very fragmented. Different taphonomical histories are inferred for microvertebrates and macromammals. The microvertebrate assemblage is interpreted as the result of predator activities. After a brief period of pre-burial exposure, remains were dispersed from the original depositional area. On the other hand, a natural and gradual death process is envisaged for macromammals, followed by a long period of exposure to weathering and dispersal by physical agents. Remains of both groups, once buried, suffered the diagenetic processes of the host rock. Consequently, the fossil assemblage from Telén would represent a condensed assemblage corresponding to two distinct time spans, i.e., the accumulation of microvertebrates took place in a short time interval whereas that of macromammals occurred over a longer period, coincident with the development of both soils.

Amphibians and small reptiles from the Berriasian Rabekke Formation on Bornholm, Denmark

A diverse microvertebrate assemblage has been extracted from a limnic lowermost Cretaceous (Berriasian) stratum on the island of Bornholm, Denmark. The assemblage includes numerous remains of a wide variety of vertebrate groups including fishes, amphibians, reptiles and mammals. Herein, we describe the amphibian and reptilian (excluding Archosauria and Chelonia) part of the assemblage including indeterminate salamanders, frogs and lizards. The former findings are of particular interest as they represent the first occurrence of Mesozoic amphibians in Denmark.

Synopsis of the Late Miocene mollusc fauna of the classical sections Richardhof and Eichkogel in the Vienna Basin (Austria, Pannonian, MN 9-MN 11)

The Eichkogel and Richardhof sections represent two important reference faunas for the reconstruction of the Late Miocene continental mollusc faunas. New investigations with strong focus on the micro-vertebrate assemblages of the Pannonian in the Vienna Basin by G. D AXNERHOCK (NHMW) allow a rather precise dating of the Vallesian to Early Turolian faunas into the mammal zones MN 9 (samples Richardhof RH A/2, RH A/7), MN 10 (samples Richardhof Rh 1, Rh 3, Rh 5) and MN 11 (Eichkogel). The increase in material and the improved stratigraphic resolution of the formerly intermingled faunas - aside from the fact that the already published taxa are partly hidden in various papers dealing with special taxonomic problems - motivated us to produce a critical synopsis of the knowledge of these faunas. For the first time, the protoconch features are also documented for many of the discussed species. In total, 84 mollusc taxa are known from the sections. Of these, 71 are recorded from the Eichkogel section and 58 from the Richardhof section. Pseudamnicola hoeckae nov. sp., Granaria moedlingensis nov. sp., Janulus

Early Cretaceous frogs from Morocco

The Lower Cretaceous Moroccan locality of Ksar Met-Lili near Anoual has yielded a diverse microvertebrate assemblage including mammals, small reptiles, and amphibians. Here the frogs are described for the first time. Although the material is fragmentary, iliac structure, supplemented by other cranial and postcranial elements, demonstrates the presence of two distinct taxa. One genus is interpreted as a discoglossid, related to members of the Jurassic North American genus Enneabatrachus. The second frog represents a new taxon, and is here named Aygroua anoualensis. It is more difficult to classify, but attributed procoelous vertebrae and a specialized premaxillary-maxillary overlap suggest it is probably a mesobatrachian, possibly a basal pipimorph.

Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas

One of the southernmost North American late Campanian microvertebrate assemblages was collected from the upper Aguja Formation, Big Bend National Park, Texas. The dinosaurs provide additional evidence that distinct southern and northern terrestrial vertebrate provinces occurred contemporaneously during this time due to latitudinal differences in temperature and rainfall. Southern areas, such as west Texas, were warm dry, with non-seasonal climates, and with open-canopy woodlands; they appear to be less fossil-rich and less diverse than northern areas. Nine dinosaurs are present, based on isolated teeth: pachycephalosaurid; hadrosaurid; ceratopsian; tyrannosaurid; Saurornitholestes cf. langstoni (Sues, 1978); Richardoestesia cf. gilmorei (Currie et al., 1990); a new species of Richardoestesia, which is named here; and a undetermined theropod unlike any previously described. Previous reports of Troodon sp. from the Talley Mt. and Terlingua microsites are mistaken; they are a pachycephalosaurid. Many of the dinosaur teeth are small, and are probably from juveniles or younger individuals, evidence that dinosaurs nested in the area. Paleoecologically, the upper Aguja was probably more similar to the lower and more inland faunas of the Scollard Formation (~66 Ma) of Alberta than to contemporaneous northern faunas: both had drier, open environments and lower dinosaur abundance. This connection between climate and dinosaur abundance suggests that climatic factors were important in the Late Cretaceous dinosaur extinctions.

LATE CAMPANIAN SOUTHERN DINOSAURS, AGUJA FORMATION, BIG BEND, TEXAS

One of the southernmost North American late Campanian microvertebrate assemblages was collected from the upper Aguja Formation, Big Bend National Park, Texas. The dinosaurs provide additional evidence that distinct southern and northern terrestrial vertebrate provinces occurred contemporaneously during this time due to latitudinal differences in temperature and rainfall. Southern areas, such as west Texas, were warm dry, with non-seasonal climates, and with open-canopy woodlands; they appear to be less fossil-rich and less diverse than northern areas. Nine dinosaurs are present, based on isolated teeth: pachycephalosaurid; hadrosaurid; ceratopsian; tyrannosaurid; Saurornitholestes cf. langstoni (Sues, 1978); Richardoestesia cf. gilmorei (Currie et al., 1990); a new species of Richardoestesia, which is named here; and a undetermined theropod unlike any previously described. Previous reports of Troodon sp. from the Talley Mt. and Terlingua microsites are mistaken; they are a pachycephalosaurid. Many of the dinosaur teeth are small, and are probably from juveniles or younger individuals, evidence that dinosaurs nested in the area. Paleoecologically, the upper Aguja was probably more similar to the lower and more inland faunas of the Scollard Formation (~66 Ma) of Alberta than to contemporaneous northern faunas: both had drier, open environments and lower dinosaur abundance. This connection between climate and dinosaur abundance suggests that climatic factors were important in the Late Cretaceous dinosaur extinctions.

Pterosaurs from the Lower Cretaceous (?Berriasian) of Anoual, Morocco

A report on the pterosaurian remains from the Lower Cretaceous of Anoual, Morocco, is presented. The material consists of teeth possibly documenting two groups. One of them cannot be clearly established but might be ornithocheirid, while the most numerous teeth are reminiscent of those of gnathosaurine. This possible attribution might be consistent with a Berriasian age for the calcareous lens containing the microvertebrate assemblages of Anoual.

A review of placoderm scales, and their significance in placoderm phylogeny

ABSTRACT An historical review of the literature relating to placoderm scales preserved in association with articulated dermal plates, or as isolated units in microvertebrate assemblages, is followed by a discussion of their relevance in phylogenetic analyses of the Placodermi. The dentinous tissue forming the tubercles of Early Devonian acanthothoracid scales and dermal bone is similar to that of the dermal bone ornament of some osteostracans, and denticles of the vertebrate Skiichthys from the Ordovician Harding Sandstone. This similarity supports the proposition that the gnathostomes are the sister-group of the Osteostraci, with the Placodermi branching earliest within the gnathostomes, and the Acanthothoraci branching earliest within the Placodermi. The meso-semidentine in acanthothoracid tubercles, rather than semidentine (sensu stricto), is most likely to be synapomorphic for the Placodermi.

Microborings in mid-Cretaceous fish teeth

SUMMARY Fish teeth and other remains from the British Cretaceous contain abundant evidence for post-mortem colonization by endolithic organisms. The borings are here recognized as occurring in three morphotypes, including a flask-shaped form not previously recorded. There is strong evidence to suggest that each of these boring types shows a strong preference for a particular substrate histology. The damage and destruction of vertebrate remains by microborings is here considered to exert a major taphonomic conrol on microvertebrate assemblages. The relationships between the intensity of colonization of vertebrate material by endolithic organisms and palaeoenvironment have implications for using these bone microborings as palaeoenvironmental indicators.

Microvertebrate assemblages from the Upper Silurian of Cornwallis Island, Arctic Canada

Microvertebrate assemblages from four Upper Silurian (?Ludlow-Pridoli) localities on Cornwallis Island, Arctic Canada, comprise mainly scales, plus dentition cones and jaw fragments from ischnacanthid acanthodians, with rare scales assigned to heterostracan Lepidaspis? sp., ?chondrichthyan Arauzia? sp., and Placodermi? gen. et sp. indet. Most of the scales in sample C-11460 are assigned to the poracanthodid acanthodian Poracanthodes canadensis sp.nov., which shows closest affinity to Poracanthodes punctatus Brotzen variants from the Baltic Pridoli. The flank scales of the new species resemble those of P. punctatus s.s. (Silurian variant; the zone fossil for the late Pridoli in the Standard Silurian microvertebrate scheme), with their superposed crown growth zones, rows of small pores aligned with the underlying zones, number of radial canals, and "arcade" canals connecting these radial canals. They differ in having numerous anterior crown riblets, "zig-zag" rather than straight crown pore rows, and V-shaped arcade canals.

Microvertebrate assemblages from the Upper Silurian of Cornwallis Island, Arctic Canada

Microvertebrate assemblages from the Upper Silurian of Cornwallis Island, Arctic Canada