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Research : PaleoBios
Abstracts (vols. 26 to present)
PaleoBios 26(1), May 15, 2006
Morphology of the skull in Meniscomys from the John Day Formation of central Oregon
SAMANTHA S.B. HOPKINS
Aplodontoid rodents are very diverse through the Oligocene and Miocene in North America. They are represented in the fossil record by a number of morphologically distinct lineages, many of which are represented in the John Day Formation of central Oregon. Although the diversity of dental morphologies in this lineage is well understood, skull morphology is well-described for only the mylagaulid and aplodontine lineages of aplodontoids. Less well-preserved skulls have also been described from the basal paraphyletic group of prosciurines and for the allomyines lineage. This paper describes the morphology of the skull in Meniscomys, a taxon that lies at the transition between Paleogene and Neogene groups of aplodontoids. These groups are quite distinct in dental and cranial morphology and inferred ecology. Examination of the skull of Meniscomys shows that it retains a number of plesiomorphic characters, but shows some evidence of the shortening, broadening, and flattening that characterizes Neogene aplodontoids.
The latest Eocene Badger's Nose flora of the Warner Mountains, northeast California: the "in between" flora
JEFFREY A. MYERS
The 34-35 Ma Badger's Nose flora of the east face of the Warner Mountains, northeastern California, is the only known latest Eocene assemblage from the region between the Willamette Valley of western Oregon and central Colorado. It fills a gap in the paleobotanical succession of the interior Pacific Northwest between the late Eocene Whitecap Knoll flora (~38.8 Ma) and earliest Oligocene (33.6 Ma) assemblages of the Bridge Creek flora. Badger's Nose vegetation consisted of Metasequoia-dominated lake margin woodland that lacked both the abundant and diverse lianas of middle Eocene floras such as the Clarno flora as well as the diverse temperate hardwoods and conifers of the early Oligocene Bridge Creek flora. The composition of the flora was also intermediate, forming a low diversity assemblage that included both thermophilic holdovers from the warm middle Eocene as well as temperate elements that later contributed to the Bridge Creek flora. Many taxa are similar or identical to those in latest Eocene and Oligocene floras of both the coast and the Cordillera. Not surprisingly, the moist, warm temperate Badger's Nose climate was intermediate between that of the middle Eocene and that of the Oligocene, capable of supporting a few hardy warm temperate/subtropical plants, as well as some cooler temperate plants. The Badger's Nose flora is truly an "in between" assemblage as it reflects accrued floristic and vegetational migrations and extirpations caused by climate changes of the late Eocene, and is a precursor to the rise of diverse temperate forests of the Oligocene.
Magnetic stratigraphy of the upper Miocene (Hemphillian) Rattlesnake Formation, central Oregon
DONALD R. PROTHERO1, JONATHAN M. HOFFMAN2, and SCOTT E. FOSS3
The Rattlesnake Formation near Picture Gorge in the John Day region of central Oregon consists of about 120 meters of siltstones and conglomerates punctuated by several tuff beds. This formation is well known for its early Hemphillian mammals, and it was originally part of the Wood Committee's (1941) concept of the Hemphillian. Paleomagnetic samples were collected from the type section of the Rattlesnake Formation between Rattlesnake and Cottonwood Creeks 2 kilometers south of Picture Gorge. Samples were demagnetized with both alternating field and thermal demagnetization, and yielded a stable remanence held mainly in magnetite. After cleaning, the normal and reversed directions passed a reversal test, so the remanence is interpreted to be primary. Almost the entire section is reversed in polarity except for the basal 10 meters and a single site near the top of the section. Based on 40Ar/39Ar dates of either 7.2 Ma or 7.05 ± 0.01 Ma on the Rattlesnake Ash Flow Tuff near the top of the section, we correlate the section with magnetic Chrons C3Bn to C3Br2n (6.97.3 Ma), or late early Hemphillian in age (Hh2 of Tedford et al. 2004).
Magnetic stratigraphy of the lower portion of the middle Miocene Mascall Formation, central Oregon
DONALD R. PROTHERO1, ELIZABETH DRAUS2, and SCOTT E. FOSS3
The Mascall Formation in central Oregon consists of about 350 meters of volcaniclastic floodplain siltstones and sandstones exposed in numerous fault blocks in the John Day region of central Oregon. It yields a famous early Barstovian mammalian fauna (part of the Wood Committee's 1941 original concept of the Barstovian) that includes at least 33 species of mammals, as well as birds, turtles, fish, and freshwater gastropods. The most complete section in the type area was sampled using oriented block sampling. The samples were then subjected to both alternating field demagnetization at 25, 50, and 100 Gauss, followed by thermal demagnetization at 50°C steps from 200 to 630°C. Most samples yielded a stable single component of remanence that passed a reversal test, and was held largely in magnetite with minor goethite overprints. The lower half of the section is of reversed polarity, followed by shorter magnetozones of normal, reversed, and normal polarity to the top of the section. Based on dates of 16.2 ± 1.4 Ma at the base of the section, and 15.77 ± 0.07 Ma in the lower part of the section, we correlate the Mascall Formation with Chron C5Br to Chron C5Bn1n (14.816.0 Ma). This correlation is consistent with the early Barstovian age of the fauna, and it matches the pattern seen in other Barstovian magnetostratigraphic sections, such as those at Barstow, California; Virgin Valley and Massacre Lake, Nevada; and Pawnee Creek, Colorado.
PaleoBios 26(2), October 13, 2006
Revision of the Cretaceous and Paleogene sea turtles Catapleura and Dollochelys (Testudines: Cheloniidae)
The systematics of several Cretaceous and Paleogene cheloniids are reviewed and reconsidered. Catapleura repanda (Cope, 1868) from the Upper Cretaceous and Paleocene of North America and Belgium is diagnosed as a valid taxon of a primitive grade, mainly characterized by a rectangular first costal and a caudally convex pygal without a scale sulcus. Dollochelys casieri, D. atlantica, and D. coatesi are regarded as junior synonyms of C. repanda. Catapleura arkansaw Schmidt, 1944 from the Upper Cretaceous of North America is regarded as a distinct genus from C. repanda by possessing characters of a more advanced grade. Zangerlchelys n. gen. is proposed for this taxon.
A new amynodontid (Mammalia, Perissodactyla) from the Eocene Clarno Formation, Oregon, and its biochronological significance
SPENCER G. LUCAS
Zaisanamynodon protheroi is a new species of large metamynodontinine amynodontid rhinoceros from the Eocene (late Uintan) Hancock quarry local fauna of the Clarno Formation, Oregon, represented by cranial, dental, and postcranial material. Previously, the Hancock amynodont was referred to Procadurcodon, but that genus and its type species are nomina dubia, so specimens from the Hancock quarry, and some of the specimens from Russia previously assigned to Procadurcodon, are reassigned to the valid genus Zaisanamynodon. Z. protheroi is distinguished from Z. borisovi, the type and only other species of Zaisanamynodon, by the following characteristics: relatively long rostrum, anterior margin of orbit above M2, P2 more complex with anterior and posterior crests connected to metaloph, P2-4 have complete lingual cingula, incisors relatively small (especially I3/i3), lower canine relatively massive and straight, less molariform p3 and no labial groove on lower molars. Asian records of Zaisanamynodon borisovi are of Ergilian age, and the record of Z. protheroi in the Hancock quarry suggests it is late Uintan in age, which is older than Ergilian and equivalent to part of the Sharamurunian. This suggests that the specimen of Z. protheroi from Artyom in eastern Russia is of Sharamurunian age.
Biochronologic and lithostratigraphic reappraisal of the upper John Day Formation, north-central Oregon
ROBERT M. HUNT, JR.1,2 AND
The circumstances leading to a revised stratigraphy of the upper John Day Formation (latest Oligocene-early Miocene) are described. Fluvial channel deposits, previously believed to indicate synchronous deposition of coarse gravels, and thus employed in regional correlation of upper John Day rocks, were found to contain mammal faunas of disparate ages, to differ significantly in terms of clast composition and clast size, and to be associated with distinctive suites of tuffaceous sediments. A revised Haystack Valley Member is radioisotopically dated at ~23.8 Ma and bears an early late Arikareean fauna. The Rose Creek Member, angularly unconformable above rocks of the Haystack Valley Member and other John Day units, yields an early Hemingfordian assemblage (~18.218.8 Ma) that is the youngest fauna recognized in the eastern facies of the John Day Formation.
Using paleosols of the Picture Gorge Basalt to reconstruct the middle Miocene climatic optimum
NATHAN D. SHELDON
The Picture Gorge Subgroup of the Columbia River Basalt preserves numerous, minimally altered, interflow paleosols that were formed during the middle Miocene climatic optimum. These paleosols are used to reconstruct a high-resolution paleoclimate record. Between 16.015.4 Ma ago, mean annual precipitation (MAP) was 500900 mm/year and mean annual temperature (MAT) was 8-16°C, which is consistent with independent estimates of paleoprecipitation and paleotemperature from fossil plants and paleosols of the contemporaneous Mascall Formation. The record suggests cooling and aridification similar to marine foraminiferal isotopic records. One possible cause for the middle Miocene climatic optimum is transient elevated atmospheric CO2 levels, though some recently compiled marine isotopic records indicate near-modern CO2 levels. This possibility is explored using an equilibrium model to simulate the formation of the dominant Picture Gorge paleosol type. Model results indicate elevated CO2 levels 23 times present atmospheric levels were necessary to form the observed mineral assemblage and mass-balance characteristics of the paleosols. This result is consistent with stomatal index studies of gingkos and laurels, which indicate CO2 levels 24 times present atmospheric levels.
PaleoBios 26(3), December 22, 2006
Eocene woods of central Oregon
ELISABETH A. WHEELER1,
STEVEN R. MANCHESTER2, and
Eocene terrestrial strata of central Oregon contain abundant and well-preserved fossil woods that are important for understanding past floristic diversity, forest structure, and climate. In addition to the remarkably diverse and well-preserved Middle Eocene wood assemblage of the Clarno Nut Beds in the type area of the Clarno Formation in the John Day basin, there are well-preserved diverse Late Eocene wood assemblages from the vicinity of Post in the Crooked River Basin. The Post assemblages discussed herein share some genera with the Nut Beds flora (Acer, Cercidiphyllum, Quercinium, Ulmus), but also include some new elements that remain to be described in detail, including woods referable to the families Anacardiaceae, Fagaceae, Hamamelidaceae, and Juglandaceae. Comparison of the middle Eocene Nut Beds woods to the younger Post woods documents changes in climate, with the Post assemblages indicating increasing seasonality and an increase in deciduousness.
Forelimb function in the theropod dinosaur Carnotaurus sastrei, and its behavioral implications
PHIL SENTER1 and
J. MICHAEL PARRISH2
Carnotaurus sastrei, a member of the theropod clade Abelisauridae from the Upper Cretaceous of Argentina, has extremely reduced forelimbs. A previous suggestion that the forelimbs were functionless is supported by their extremely low innervation. However, the humeral head of Carnotaurus is enlarged and hemispherical, unlike those of most theropods, suggesting an increased range of motion. Here, we show through manual manipulation of casts that the unusual humeral head of Carnotaurus confers a greater range of humeral elevation (movement away from the ground, in the transverse plane) than in most theropods. In contrast, the elbow is immobile. Close relatives of Carnotaurus such as Masiakasaurus and Elaphrosaurus exhibit Carnotaurus-like humeral heads and unreduced forelimbs. This indicates that the unusual humeral head shape of Carnotaurus is not a mere consequence of forelimb reduction a conclusion that is supported by a lack of similar humeral head shapes among other archosaurs with reduced forelimbs; instead, it is a character-state that evolved earlier in the abelisauroid lineage and is plesiomorphically retained in Carnotaurus. Humeral range of motion in Carnotaurus does not greatly illuminate the behavior of abelisaurids because forelimb function was presumably lost in that clade, as indicated by extreme reduction in forelimb size and innervation and loss of elbow mobility. The enhanced transverse range of motion conferred by the hemispherical humeral head suggests the importance of some arm-elevating behavior in other ceratosauroids with functional, unreduced forelimbs exhibiting such humeral heads. Loss of forelimb function in Carnotaurus also underscores the importance of the mouth, as opposed to the forelimbs, in theropod prey capture.
Agriochoerus matthewi crassus (Artiodactyla, Agriochoeridae) of the late middle Eocene Hancock Mammal Quarry Local Fauna, Clarno Formation, John Day Basin, north-central Oregon
The Hancock Mammal Quarry (HMQ) Local Fauna (LF) is from the uppermost part (Unit E) of the Clarno Formation at the HMQ in the John Day Basin of north-central Oregon. The agriochoerid in the HMQ LF, previously assigned to Diplobunops by most workers, now is assigned to the comparatively large agriochoerine Agriochoerus matthewi crassus. The latter taxon is based on the record in the Randlett LF from the lower part of the Duchesnean North American Land Mammal Age (NALMA) stratotype in northeastern Utah. The Randlett LF, considered late Uintan in age by most workers, also includes the brontotheriid Duchesneodus, presumably the Duchesnean index taxon D. uintensis. Agriochoerus m. crassus and D. uintensis also occur in the early Duchesnean Skyline LF of western Texas, but not in the late Uintan Myton LF from the upper part of the Uintan NALMA stratotype, which underlies the Duchesnean stratotype, nor in any other assemblage of undisputed Uintan age. Moreover, A. m. crassus does not occur in any assemblage younger than the Skyline LF or the early Duchesnean NALMA. Based on its P2-M3 length, A. m. crassus is approximately 10 to 15% larger than A. m. matthewi, which occurs in the Myton LF and in the correlative Lower Badwater LF at localities 5 and 6 in west-central Wyoming. For these reasons, the Randlett LF is removed from the Uintan NALMA and reassigned to the early Duchesnean, where it was placed originally. Correspondingly, the Uintan-Duchesnean NALMA boundary in the Uinta Basin is relocated stratigraphically downward, from a level above the Randlett LF and back to its original position between this local fauna and the underlying Myton LF. The other occurrences of A. m. crassus indicate that the HMQ LF also is early Duchesnean, rather than late Uintan, in age. The earliest interval of comparatively large body size in Agriochoerus is characterized by A. m. crassus. Radiometric data from the John Day Basin indicate that the HMQ LF is between 40.0 million and 40.4 million years (Ma) and late middle Eocene in age, and that the Uintan-Duchesnean NALMA boundary is older than 40.0 Ma.
PaleoBios 27(1), April 22, 2007
Phylogenetic definitions in the pre-PhyloCode era; implications for naming clades under the PhyloCode
MICHAEL P. TAYLOR
The last twenty years of work on phylogenetic nomenclature have given rise to many names and definitions that are now considered suboptimal. In formulating permanent definitions under the PhyloCode when it is implemented, it will be necessary to evaluate the corpus of existing names and make judgements about which to establish and which to discard. This is not straightforward, because early definitions are often inexplicit and ambiguous, generally do not meet the requirements of the PhyloCode, and in some cases may not be easily recognizable as phylogenetic definitions at all. Recognition of synonyms is also complicated by the use of different kinds of specifiers (species, specimens, clades, genera, suprageneric rank-based names, and vernacular names) and by definitions whose content changes under different phylogenetic hypotheses. In light of these difficulties, five principles are suggested to guide the interpretation of pre-PhyloCode clade-names and to inform the process of naming clades under the PhyloCode: (1) do not recognize "accidental" definitions; (2) malformed definitions should be interpreted according to the intention of the author when and where this is obvious; (3) apomorphy-based and other definitions must be recognized as well as node-based and stem-based definitions; (4) definitions using any kind of specifier taxon should be recognized; and (5) priority of synonyms and homonyms should guide but not prescribe. Strict priority should not be observed in the pre-PhyloCode era, and should not determine which existing names are permanently established; precedence should begin only with the formal establishment of the PhyloCode.
Late Eocene silicified fruits and seeds from the John Day Formation near Post, Oregon
STEVEN R. MANCHESTER1 and WILLIAM C. MCINTOSH
Silicified fruits and seeds occur in Eocene tuffs in the lower part of the John Day Formation near Post, Oregon. A prominent white tuff immediately overlying the fruit and seed deposit contains sanidine crystals that were used for 40Ar/39Ar radioisotopic dating by the single crystal laser fusion method. The resulting date of 36.21 ± 0.26 Ma (n = 26), provides a good estimate of the actual age of permineralized woods found within the tuff, and a minimum age for the subjacent strata containing fruits, seeds, woods and gastropods. The fruit and seed assemblage includes several genera shared with the middle Eocene Clarno Nut Beds locality (Diploporus, Sabal, Magnolia, Ampelopsis, Vitis, Alangium, Mastixicarpum, Coryloides, Quercus, Pileospermum, Bursericarpum, Cedrela, Aphananthe, Sabia, Meliosma, Platanus) indicating their persistence in this region to at least the late Eocene. Additional genera of the Post flora that have not been recorded in the middle Eocene Clarno Nut Beds include Davidia, Carya, cf. Asterocarpinus, Fagus, and Zanthoxylum. The new radiometric date and new taxonomic identifications improve resolution of the floristic changes that occurred from the middle to late Eocene of this region.
Eubrontotherium clarnoensis, a new genus and species of brontothere (Brontotheriidae, Perissodactyla) from the Hancock Quarry, Clarno Formation, Wheeler County, Oregon
MATTHEW C. MIHLBACHLER1, 2
I describe here a new genus and species of brontothere, Eubrontotherium clarnoensis, based on two skulls, a mandible, and several other cranial and mandibular fragments recovered from the Hancock Quarry, Clarno Formation, Wheeler County, Oregon. Eubrontotherium clarnoensis is a member of a group of relatively advanced Asian and North American middle and late Eocene horned brontotheres, informally referred to as "eubrontotheres," that are characterized by small globular upper incisors. Phylogenetic analysis of the Brontotheriidae produces a clade similar to the original eubrontothere concept. This clade is given formal status as the infratribe Brontotheriita. In addition to Eubrontotherium clarnoensis, Brontotheriita includes the North American species Notiotitanops mississippiensis, Protitanops curryi, Duchesneodus uintensis, Megacerops coloradensis, and Megacerops kuwagatarhinus. The Asian species Parabrontops gobiensis and Dianotitan lunanensis also nest within this clade. Based on the possible latest Uintan age of the Hancock Quarry fauna, Eubrontotherium clarnoensis is among the earliest known occurrences of Brontotheriita. The phylogeny of the Brontotheriita is incongruous with age assignments based on land mammal "age" biostratigraphy, thus implying one or more middle to late Eocene ghost lineages.
PaleoBios 27(2), October 11, 2007
First record of Halisaurus (Squamata: Mosasauridae) from the Pacific coast of North America
A partial squamate skeleton collected from the mid-Maastrichtian Tierra Loma Shale of the Moreno Formation, central California, represents the first record of the enigmatic mosasaur Halisaurus from the Mesozoic Pacific coast of North America. Features of the quadrate suggest a close relationship to the coeval Halisaurus platyspondylus, but the incompleteness of the new specimen precludes species determination. The occurrence of both Halisaurus and the globidensine mosasaurine Prognathodon in the Moreno Formation casts doubt upon a previous hypothesis of faunal provinciality and spatial isolation of Pacific mosasaur assemblages from contemporaneous faunas in the Western Interior Seaway.
Tectonic controls on isotope compositions and species diversification, John Day Basin, central Oregon
MATTHEW J. KOHN1 and
THEODORE J. FREMD2
Oxygen isotope compositions of fossil mammal teeth from basins in interior Oregon, including the John Day basin, were measured to investigate the topographic evolution of the central Cascade Range. Compositions of fossil equid, rhinocerotid, and oreodont teeth within the Cascade Range rain shadow indicate a ~1‰ increase in mean d18O from ~27 Ma to ~7 Ma, followed by a dramatic ~4‰ decrease to the present. The isotope composition of fossil teeth is strongly affected by rainout over the Cascades, so these trends likely indicate nearly constant or slightly decreasing elevations between 27 and 7 Ma, followed by an ~800 m increase in range height to 1600 m in the last 7 Myr. These data are most consistent with replacement of cooler metasomatized asthenosphere by hot, mid-ocean ridge type asthenosphere, including possible erosion of subarc lithospheric mantle or conversion to asthenosphere by heating. Consideration of middle to late Cenozoic climate and tectonic evolution in the western United States suggests that the middle Miocene maximum in ungulate diversity resulted from moderate productivity coupled with tectonically driven topographic variability. Both factors fragment ecosystems, thereby increasing habitat diversity. Subsequent late Neogene reductions in ungulate diversity likely resulted from decreased productivity associated with aridity, and the expansion of grasslands, which decreases habitat diversity by coalescing ecosystems. Regional tectonics, reflected in the height of the Cascade Range and development of extensional structures in central and eastern Oregon, appears a likely driver of faunal evolution.
Evidence of archosauriform feeding on dicynodonts in the Late Triassic of southern Brazil
CRISTINA VEGA-DIAS1 and
CESAR LEANDRO SCHULTZ2
An assemblage of isolated dicynodont bones was collected from the Upper Triassic Caturrita Formation in southern Brazil. Whereas the bones are of different sizes and shapes and are in a pelitic matrix, their association does not appear to be the result of fluvial transport and deposition. The bones correspond to at least four specimens of Jachaleria candelariensis, among which is a left scapula displaying perforations and grooves on its medial and lateral sides. The outcrop also yielded isolated archosauriform teeth, and skeletal remains of both an indeterminate phytosaur and Guaibasaurus, a dinosaur known from the same stratigraphic level. The perforations in the Jachaleria scapula match closely in size and shape with the tips of the archosauriform teeth. Although it is not yet possible to assign this predator or scavenger to a specific taxon, Guaibasaurus is a priori excluded because of its small size.
Calocedrus robustior (Cupressaceae) and Taxus schornii (Taxaceae): two new conifers from the middle Miocene Latah Formation of northern Idaho
ZLATKO KVACEK1 and
WILLIAM C. REMBER2
Fossils of two new conifers from the middle Miocene Clarkia flora, Idaho, northwestern USA, are described as Calocedrus robustior Kvacek and Rember n. sp. (Cupressaceae) and Taxus schornii Kvacek and Rember n. sp. (Taxaceae). C. robustior has seed cones partly attached to a twig, dispersed seeds, and sterile foliage shoots with preserved epidermal leaf anatomy. It is similar to the extant east Asian species C. macrolepis Kurz in its thuoid type of dimorphic leaves that cover stalks of seed cones, and in its flattened foliage sprays. It also has seed cone characteristics similar to those of C. decurrens (Torrey) Florin of western North America; however, C. decurrens differs in having weakly dimorphic scale leaves and less-flattened foliage sprays. C. robustior exceeds known fossil species from North America and Eurasia in the size of both seed cones and foliage. Isolated leaves of Taxus schornii Kvacek and Rember n. sp. (Taxaceae) with preserved cuticle structure are similar to those of extant T. brevifolia Nuttal of western North America. Both have narrow stomatal bands and a broad region of nonpapillate cells across abaxial lateral zones. The phytogeographic relationships of Calocedrus reflect the possible effect that the Beringia land bridge had on Neogene floristic exchange between eastern Asia and North America.
PaleoBios 27(3), December 28, 2007
A subadult Stegomastodon (Mammalia, Proboscidea) skull from central Arizona
MICHAEL R. PASENKO
The Gomphotheriidae (Proboscidea, Mammalia) is a diverse family whose fossil record in Arizona is represented by three genera: Rhynchotherium, Stegomastodon, and Cuvieronius. I describe here a partial young adult gomphotheriid cranium from central Arizona. The presence of M1s and M2s and the small diameter of the tusks support this ontogenetic assignment. The position and morphology of the premaxilla, maxilla, zygomatic process, and upper molars allow for assignment to Stegomastodon sp. This is one of only a few Arizona specimens assignable to Stegomastodon and provides rare morphometric data for a young adult. In Arizona, Stegomastodon has been recovered from early Pliocene to early Pleistocene deposits.
Outcrops and mollusks of the "Margaritan" California provincial molluscan stage in the northern Salinas Valley, Monterey and San Benito Counties, central California
CHARLES L. POWELL, II
Comprehensive re-evaluation of the California Tertiary molluscan stages is vital to their utility in future paleontologic, paleogeographic, and stratigraphic studies. This report focuses on the "Margaritan" California provincial molluscan stage (CPMS) by re-examining mollusk collections from the northern Salinas Valley. The data are derived from 179 middle to late Miocene invertebrate fossil localities in Monterey and San Benito counties. Unfortunately, the value of many of the collections is compromised by their lack of sufficient geographic information. In addition, many early workers in the Salinas Valley assumed that large pectinids or oysters were unique to the Santa Margarita Sandstone, and many of those collections were later reassigned to the post-"Margaritan" Pancho Rico Formation. Nearly 40 collections containing "Margaritan" index fossils reveal molluscan faunas of 122 taxa (82 bivalves and 40 gastropods) for Monterey County and 27 taxa (16 bivalves and 11 gastropods) for adjacent San Benito County. Some other collections previously attributed to an unnamed Pliocene formation in the Cosio Knob, Paraiso Springs, and Reliz Canyon 7.5' quadrangles on the western side of the Salinas Valley contain index fossils that suggest or indicate correlation with the "Margaritan" CPMS. More than 480 additional middle and late Miocene invertebrate fossil collections from elsewhere in California and associated literature were also studied to reveal that the entire "Margaritan" molluscan fauna consists of 354 taxa (208 bivalves and 146 gastropods). This is a 6.5% increase from the previously known number of "Margaritan" species. Detailed occurrences of all "Margaritan" taxa are presented.
PaleoBios 28(1), May 12, 2008
Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus
WILLIAM G. PARKER1, 2
A new specimen of Desmatosuchus from northeastern Arizona (MNA V9300) preserves almost the entire vertebral column, the pelvis, and the majority of the armor carapace, allowing for an unprecedented detailed description of the taxon. Articulation and reconstruction of the armor carapace demonstrates that previous reconstructions of Desmatosuchus are erroneous in the orientation and position of the lateral armor. Lateral plates of the anterior dorsal region possess low rounded knobs instead of developed spines. The dorsal flange of the lateral plates of the dorsal region is longer than the lateral or ventral flange making the carapace transversely wider than previously thought. As a result, previous reconstructions articulate the lateral armor not only backwards but also on the wrong sides of the body. Posterior presacral vertebrae are extremely robust and possess fused ribs and the last presacral vertebra has been fused to the sacrum, a character that may be taxonomically useful. A prefrontal bone is also present in Desmatosuchus, contrary to previous descriptions. Reinvestigation of the genus Desmatosuchus suggests that there are only two valid species, D. spurensis and D. smalli. The lectotype of Episcoposaurus haplocerus is referable to Desmatosuchus but indeterminate at the species level, and therefore represents a nomen dubium. Accordingly, D. spurensis is reinstated as the type species of Desmatosuchus and the new Arizona specimen is assigned to this taxon. Acaenasuchus geoffreyi, a purported juvenile form of Desmatosuchus, is not referable to Desmatosuchus.
PaleoBios 28(2), September 26, 2008
Stratigraphy, paleopedology, and geochemistry of the middle Miocene Mascall Formation (type area, central Oregon, USA)
ERICK A. BESTLAND1,
MATTHEW S. FORBES1,
EVELYN S. KRULL2,
GREGORY J. RETALLACK3,
The Mascall Formation in its type area has a minimum stratigraphic thickness of 353 m and consists of middle Miocene alluvial floodplain and channel deposits; its overall lithology is dominated by moderately to well-developed Alfisol-, Vertisol-, and Andisol-like paleosols that developed in a humid temperate climate. The formation is divided here into lower, middle and upper members based on conglomeratic and tuffaceous stratigraphic marker beds interpreted as cut-and-fill units that developed during episodes of climatic transition. Its depositional environment was that of a slowly aggrading alluvial floodplain consisting of fine-grained, pyroclastic-derived detritus with small fluvial channels tens of centimeters to a few meters deep. Much of the formation is organized into fining-upward sequences that are 5 to 10 meters thick each with a sandy, tuffaceous, or conglomeratic unit at its base (channel-levee deposits) and overlain by several moderately to well-developed paleosols. Based on time-of-formation estimates of the paleosols, each sequence spans a few tens of thousands of years. The sequences most likely represent climatically forced episodes of rapid floodplain aggradation (channel-levee deposits) followed by slow floodplain aggradation (paleosols). The Mascall Formation strata are geochemically similar to paleosols and volcaniclastic deposits in the Oligocene Big Basin Member of the John Day Formation. The least weathered pyroclastic strata in the formation are rhyodacitic, consisting of about 67 wt % SiO2, 0.4 wt % TiO2, and 7 to 8 wt. % combined bases (MgO, K2O, Na2O, CaO). Mass balance calculations show the well-developed paleosols have had volume collapse from the primary rhyodacitic parent of about 60%, volume collapse of about 30% when the composition of reworked tuff is used as parent, and less than 10% volume collapse from in situ weathering (calculated from paleosol C horizons as parent).
Revision of fossil willows: Salix hesperiaS. inquirenda and Salix subgenus Longifoliae groups
WALTER K. BUECHLER
Salix hesperia (Knowlton) Condit (1944) and S. inquirenda Knowlton (1926) are Miocene plants with an interwoven taxonomic history. Based on an examination of 87 specimens, this study presents a revised synonymy and introduces new distinguishing characteristics, including overall leaf shape, base and apex form, length/width ratios, venation pattern and marginal tooth form. Leaves of S. hesperia have a length/width ratio between 1.9 and 4.3, whereas those of S. inquirenda vary between 3.6 and 7.1. Eighteen percent of specimens are in the overlapping region between 3.6 and 4.3. The fossil species currently assigned to Salix subgenus Longifoliae (viz. S. payettensis Axelrod, 1944c, S. edenensis Axelrod, 1950a, S. taxifolioides MacGinitie, 1953, and S. churchillensis Axelrod, 1991) are problematic because of both poorly preserved holotype specimens and the use of characteristics that are not suitable for species separation. Even in modern Longifoliae species, the state of the leaf margin (toothed vs. entire) is variable and species cannot be distinguished on the basis of characteristics usually preserved on fossil specimens. Ninety-two fossil Longifoliae specimens have been examined for morphological leaf traits. After acknowledging (1) the close general similarity between fossil and modern Longifoliae, (2) that modern taxa cannot be keyed using only fossil characters, and (3) the absence of character state clustering in fossil species, the present study concludes that all fossil Longifoliae species should be included under the name S. payettensis Axelrod sensu nov. Accordingly, it establishes new synonymies and supplementary species descriptions. In both groups of species the range of leaf length and width, as well as the variation in marginal dentition of fossil specimens, were compared to corresponding data of morphologically similar modern species. Such comparisons are helpful in deciding whether fossil specimens should be "split" into several species or "lumped" as one.
PaleoBios 28(3), January 22, 2009
Euclastes coahuilaensis sp. nov., a basal cheloniid turtle from the late Campanian Cerro del Pueblo Formation of Coahuila State, Mexico
MARTHA CAROLINA AQUILLON-MARTINEZ2,
CLAUDIO ARTURO DE LEON DÁVILA2,
DAVID A. EBERTH1 and
We describe Euclastes coahuilaensis sp. nov. on the basis of a series of skulls and shells from the late Campanian Cerro del Pueblo Formation, Coahuila State, Mexico. This species is similar to other species of the genus in having a low skull with an extensive secondary palate but differs in having a short facial region and in the presence of a series of plesiomorphic features, including larger transverse flanges on the pterygoid, a less extensive triturating surface of the upper jaw, a palate with a broad, shallow mid-ventral depression rather than a blunt mid-ventral ridge, and a canalis caroticus lateralis subequal in diameter to the canalis caroticus internus. The carapace is similar to other cheloniids in possessing extensive fenestrae developed between the costals and peripherals, in the shape of the hyo- and hypoplastron, and in lacking of a sutural midline contact between the hyo- and hypoplastron. The plesiomorphic features present in the skull of Euclastes coahuilaensis and its early occurrence relative to other species of the genus indicate that it is the most basal species of the genus yet known. A cladistic analysis of cheloniids including Euclastes coahuilaensis places Euclastes between Toxochelys and Ctenochelys. Nichollsemys is the basal taxon in the clade of cheloniids more derived than Euclastes, Toxochelys and Ctenochelys.
Cenozoic cooling and grassland expansion in Oregon and Washington
GREGORY J. RETALLACK
Many different kinds of paleosols are common in Cenozoic badlands of the high deserts of eastern Oregon and Washington. Pedotypes, taxonomic orders, and climofunctions are three distinct approaches that use paleosol data to reconstruct past climate, ecosystems, topography, parent materials, and landscape stability. Because the back-arc paleotopographic setting, rhyolitic parent material, and rate of subsidence changed little for paleosols of eastern Oregon and Washington over the past 45 million years, these paleosols record primarily changing climate and vegetation. Paleosols of Oregon and Washington are evidence of the transition from a late Eocene (35 Ma) peak of warm, humid forests to cool, desert shrublands in the Oligocene. The reversion to warm-wet forests in the middle Miocene (16 Ma) was followed by general cooling and spread of sod grasslands that culminated in the last ice age (›1.8 Ma). These records are compatible with a greenhouse model for climate change of cooling induced by coevolutionary advances in carbon sequestration and consumption by grassland soils and sediments, punctuated by warming from volcano-tectonic and extraterrestrial perturbations. The abundant Cenozoic paleosols in the Pacific Northwest are multifaceted guides to past global change.
Preliminary body mass estimates for mammalian genera of the Morrison Formation (Upper Jurassic, North America)
JOHN R. FOSTER
Dentitions of Late Jurassic mammals from the Morrison Formation of the Rocky Mountain region of western North America do not closely fit dental patterns of modern small mammals; thus, traditional techniques for estimating body masses of extinct forms based on single molar dimensions may not be appropriate for these Mesozoic taxa. A regression of dentary length to body mass of extant small marsupial mammals is presented here and used for body mass estimates of mammals from the Morrison Formation. Dentary length was more closely correlated to body mass than was molar row length in modern marsupial mammals. The body mass distribution for mammalian genera of the Morrison Formation demonstrates a right-skewed curve and shows a range from 6g to 141 g, a mean weight for individual genera of 48.5 g, and a peak diversity at 5-25 g. The largest and smallest mammals from the Morrison Formation are Docodon at 141 g and Fruitafossor at 6 g.
PaleoBios 29(1), June 22, 2009
Pleistocene lagomorphs from Cathedral Cave, Nevada
CHRISTOPHER N. JASS
Faunal data from Cathedral Cave, Nevada, provide insight into biotic changes that occurred within the Great Basin prior to the latest Pleistocene. Taxonomic identifications of lagomorphs from Cathedral Cave were made using a morphological approach intended to minimize geographic and temporal assumptions. Although this approach to identification is conservative, the resultant data set is appropriate for inclusion in future analyses of regional biotic change. Lagomorphs recovered from the site include new regional records of two extinct taxa, Aztlanolagus agilis and Brachylagus coloradoensis. Other lagomorphs from Cathedral Cave include Brachylagus idahoensis, Ochotona sp., and Sylvilagus or Lepus sp. The presence of a posterorinternal reentrant fold on the p3 of some specimens of Ochotona sp. suggests that the range of variation present in the individual teeth of pikas needs to be described in further detail. In contrast to a previously established hypothesis of increasing enamel complexity in the p4 of Aztlanolagus agilis, evaluation of crenulation patterns of Aztlanolagus agilis from Cathedral Cave showed no distinct trends.
A new immigrant mustelid (Carnivora, Mammalia) from the middle Miocene Temblor Formation of central California
ZHIJIE JACK TSENG1,2, XIAOMING WANG2, J.D. STEWART2
A new mustelid genus from the Barstovian (middle Miocene) marine Temblor Formation in California is described. The material of Legionarictis fortidens includes an incomplete cranium with partial upper dentition. The straight lingual border and slightly expanded posterointernal cingulum of M1 are plesiomorphic traits, as in the European Dehmictis. However, the M1 is not as posteriorly expanded, and the P4 does not have a lingual hypoconal crest, differentiating L. fortidens from younger North American forms. Furthermore, the P4 protocone is posteriorly placed from the parastyle crest, as in the extant South American Eira. An autapomorphic feature of L. fortidens is its highly hypertrophied P4 paracone with a bulbous crown. The robust upper carnassial, very strong development of the sagittal crest, and derived enamel microstructure all suggest a hard food component in its diet. The coastal depositional environment indicated by the presence of marine taxa in the Temblor Formation suggests that hard shelled invertebrates might have been a food source of L. fortidens. A combination of plesiomorphic and derived dental characteristics puts the new form at an evolutionary stage basal to otters and closer to the living Eira. Cladistic analysis of craniodental characters suggests that L. fortidens is more derived than generalized basal mustelines of the Old World, and may have diverged from the lutrine lineage in a separate immigration event to the New World.
New record of an extinct fish, Fisherichthys folmeri Weems (Osteichthyes), from the lower Eocene of Berkeley County, South Carolina, USA
Fisherichthys folmeri Weems 1999 (Sciaenidae?) is an extinct teleostean fish occurring in marine strata of the Gulf and Atlantic coastal plains, USA. We report isolated teeth collected from a lower Eocene (Ypresian) deposit in Berkeley County, South Carolina. Crowns of unworn teeth bear apical papillae surrounding a central depression, but these features are lost as teeth are worn through in vivo usage. The pulp cavity appears to become reduced in size as the tooth matures in the alveolus. Fisherichthys folmeri is thus far only known from Mississippi, South Carolina, and Virginia in strata ranging in age from 50.8 to 55 Ma.
The earliest North American record of the Antilocapridae (Artiodactyla, Mammalia)
BRIAN L. BEATTY1,
LARRY D. MARTIN2
The Family Antilocapridae is considered to have first appeared in the Early Hemingfordian of western North America. Here we report a mandible of a merycodontine antilocaprid from the Late Arikareean Harrison Formation of eastern Wyoming. The mandible has three lower molars preserved and mandibular ramus features that allow it to be differentiated from other contemporaneous selenodont artiodactyl families, yet the lack of detailed understanding of intraspecific variation in Paracosoryx and Merycodus warrant caution in assigning this to a genus. This new material predates the previous first appearance of antilocaprids by approximately 3–4 million years and suggests that antilocaprid immigration from Eurasian ruminant stock occurred earlier than previously assumed and that caution should be exercised when using first appearances in broader analyses.
PaleoBios 29(2), November 5, 2009
New soft-shelled turtles (Plastomeninae, Trionychidae, Testudines) from the Late Cretaceous and Paleocene of North America
J. HOWARD HUTCHISON
Two new genera (Derrisemys and Plastomenoides) and three new species (D. sterea, P. lamberti, P. tetanetron) of plastomenine trionychids from Montana and Wyoming are described. They are unique within the Trionychidae in having the entoplastron locked into notches in the hyoplastra and restricting midline kinesis. D. sterea occurs in the Lancian NALMA (North American Land Mammal Age) of Montana and Wyoming and Puercan NALMA of Montana. P. tetanetron occurs in the Puercan NALMA of Montana. P. lamberti occurs in the Torrejonian NALMA of Montana and Tiffanian NALMA of Wyoming and Utah. Plastomenus acupictus Hay 1907 from New Mexico is referred to Derrisemys. The age of D. acupictus is uncertain but is likely from early Paleocene (Torrejonian NALMA).
Revised large mammal biostratigraphy and biochronology of the Barstow Formation (Middle Miocene), California
A new biostratigraphic zonation for the middle Miocene Barstow Formation based on the mammalian megafauna is presented. Four biostratigraphic zones are outlined, two containing fossil assemblages of early Barstovian (Ba1) age, and two with late Barstovian (Ba2) assemblages. Recommendations are made for defining and characterizing the Barstovian North American Land Mammal Age (NALMA). The Ba1 biochron is defined based on the first occurrence of Plithocyon, and the base of the Ba2 biochron is revised based on the first appearance of the antilocaprid Ramoceros.
PaleoBios 29(3), June 1, 2010
Estimating polyploidy levels in fossil Salix: A critical review of cell size proxy methods
WALTER K. BUECHLER
Studies have used cell size as a proxy to estimate polyploidy levels, the number of chromosome sets in somatic cells, in modern and fossil plant species. This paper critically evaluates these methods by reviewing cell size- and polyploidy-related literature, and provides new cell size data from herbarium material and fossil remains of willow genus Salix. The 40 extant taxa used in the study include most of the polyploidy levels encountered in Salix (2n = 38, 76, 114, 152, 190). Diploid and tetraploid species were morphologically similar to the fossil specimens. Specimens from alpine and arctic regions, forms rarely found in the fossil record, were included to extend the range of polyploidy levels. Measurements taken for this study were on the petiole epidermal cells of fossil and herbarium specimens and the stomatal guard cell complexes of herbarium material. A literature review reveals cell size may not relate only to DNA content, but to a plant’s age, nutritional state and the seasonal timing of organ development. Cell size measurements show that cultivated plants grown at elevations more than 800 m below their original place of growth have a significant increase in cell size. Leaf length-to-width ratio, infrageneric classification, and adaptation to dry or humid environments also correlate with cell size. Cell size proxies for estimating polyploidy levels in fossil willows provide only accurate results if morphologically similar modern plant material from natural habitats is used as a reference for comparison. Leaves should be similar in overall shape, base and apex shape, blade length and width, length-to-width ratio, petiole length, petiole-to-blade length ratio, venation pattern, and margin dentition.
A Machairodont felid (Mammalia; Carnivora; Felidae) from the latest Hemphillian (Late Miocene/Early Pliocene) Bidahochi Formation, northeastern Arizona
A lower jaw from the White Cone local fauna of the latest Hemphillian Bidahochi Formation in northern Arizona is the first description of a felid from this fauna and the first positively identified occurrence of the smilodontine machairodont Paramachairodus in North America. This lower jaw has characters identical to those seen in a similar sized machairodont felid from the Bone Valley Formation of Florida, suggesting that the same taxon is present in Florida. The diversity of the Hemphillian machairodonts and the taxonomic status of Megantereon hesperus is reviewed. The characteristics of the ramus corpus and dentition places Paramachairodus firmly within the Smilodontini and adds further support that the more derived smilodontine machairodonts, Megantereon and Smilodon, had their origins in North America.
PaleoBios 30(1), February 18, 2011
Herpetocetine (Cetacea: Mysticeti) dentaries from the Upper Miocene Santa Margarita Sandstone of Central California
ROBERT W. BOESSENECKER
Two fossil baleen whale (Mysticeti) dentaries from the Upper Miocene (10-12 Ma) Santa Margarita Sandstone of Central California preserve several distinct features similar to the enigmatic herpetocetine whale Herpetocetus. These features include an elongate coronoid process, a mandibular condyle with a planar articular surface, and a posteriorly extended angular process. The dentary is unknown for several Herpetocetinae (and the more inclusive clade Cetotheriidae), including the coeval Nannocetus eremus. This occurrence would extend the known record of Herpetocetus by 6 Ma. Given the currently poor knowledge of Pacific Cetotheriidae during the Miocene, these specimens are identified to the subfamily Herpetocetinae, despite the similarity of these specimens to Herpetocetus. As the morphology of the supposedly distinctive lectotype dentary of Herpetocetus scaldiensis (the type species of Herpetocetus) may not be unique to Herpetocetus, this study suggests that the mandibular morphology of fossil mysticetes may be more homoplastic (or conservative) than previously assumed. Mysticete taxonomy should employ autapomorphic characters beyond the morphology of the dentary alone.
The carpometacarpus of the Pliocene turkey Meleagris leopoldi (Galliformes: Phasianidae) and the problem of morphological variability in turkeys
THOMAS A. STIDHAM
I describe the first known carpometacarpus attributable to the extinct late Pliocene (Blancan) turkey Meleagris leopoldi that was apparently collected with the type material at the type locality in Cita Canyon, Texas. Although known to previous workers, this specimen has never been discussed or described. The size and morphology of the carpometacarpus indicates that M. leopoldi may be distinct from the extant M. gallopavo and is similar to Meleagris progenes and Inglis 1A (Florida) material. However, this fossil does not clarify the relationship to and possible synonymy of M. leopoldi and M. anza, but it adds support to the idea that M. progenes is a junior synonym of M. leopoldi. The extreme morphological variation among fossil turkey specimens and recognized species obscures the phylogenetic relationships among Meleagris taxa. The presence of certain variable characters in geologically older Meleagris taxa may provide a clue to assess character polarity. Given these data, it appears that Meleagris leopoldi was a widely distributed late Pliocene species that was replaced in its geographic range by M. gallopavo during the Pleistocene.
The skull of Postosuchus kirkpatricki (Archosauria: Paracrocodyliformes) from the Upper Triassic of the United States
JONATHAN C. WEINBAUM*
The skull of Postosuchus kirkpatricki Chatterjee 1985 is known from the holotype and paratype specimens along with disassociated skull elements from several Triassic localities in the southwestern and eastern United States. Recent preparation of the holotype skull allows for more careful examination of the cranial elements and comparison with related taxa. This description indicates that Postosuchus shares several previously unrecognized synapomorphies with crocodylomorphs, including fossae and foramina in the dermatocranium that are not present in other basal pseudosuchians. The sutural arrangements of the skull of Postosuchus presented in this paper differ considerably from previous descriptions, due in part to the reassignment of what was previously considered the prefrontal to the palpebral bone. Also, further preparation of skull elements revealed morphologies that differ from previous descriptions. This new description also indicates a close relationship with Polonosuchus silesiacus Sulej 2005. The only autapomorphic characters of the skull are a distinct, rounded lateral ridge on the maxilla and a foramen present in a large fossa on the anteromedial surface of the maxilla.
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