Registered users receive a variety of benefits including the ability to customize email alerts, create favorite journals list, and save searches.
Please note that a BioOne web account does not automatically grant access to full-text content. An institutional or society member subscription is required to view non-Open Access content.
Contact email@example.com with any questions.
Phosphorites of the uppermost Neoproterozoic Doushantuo Formation (ca. 570 ± 20 Ma) exposed at Weng'an, South China, contain globular microfossils characterized by distinctively sculpted outer coverings and precise patterns of cell division. Forms assigned to the genera Megasphaera and Parapandorina were originally interpreted as problematica and volvocacean green algae, respectively, but newly discovered populations support their reinterpretation as the eggs and embryos of early animals. The fossils' large size (about half a millimeter in diameter), persistent enveloping membrane, precise cleavage pattern, and inferred physiology are fundamentally different from those of volvocaceans or other algae, but are expected features of animal embryos preserved in early stages of cleavage. In this light, Megasphaera is interpreted as an egg enveloped within its egg case, and Parapandorina represents equally and totally cleaving stereoblastulas. Despite their exquisite preservation, the phylogenetic placement of Megasphaera and Parapandorina cannot be resolved with confidence, due largely to the absence of recognizable adult morphologies to which they might be linked. Individual characters of Megasphaera and Parapandorina can be found in eggs and embryos of extant sponges, cnidarians, and bilaterians.
Three other distinctive globular forms, Megaclonophycus onustus, Caveasphaera costata n. gen. and sp., and Spiralicellula? bulbifera? occur in the same deposit. Interpretations of these fossils are more problematic, although they may also be animal embryos.
Moderately well-preserved Late Permian to Middle Triassic radiolarians are identified in chert beds that occur in the Shan-Thai Block of northern Thailand. These radiolarians are identical to the faunas of the Late Permian Neoalbaillella ornithoformis and N. optima Assemblage Zones and the Triassic Parentactinia nakatsugawaensis and Triassocampe coronata Assemblage Zones reported in chert sequences of Japan. We discovered the radiolarian faunas, apparently indicating Late Permian and Early Triassic ages, in almost continuous sequences of chert and shale exposed in the north of Chiang Mai. The occurrence of these radiolarian faunas provides important data to solve the P/T (Permian/Triassic) boundary in pelagic sequences. Our present discovery also furnishes significant data to reconstruct the paleobiogeography of Mainland Thailand during Late Permian to Middle Triassic times. Fifty species belonging to 35 genera, including three unidentified genera, are investigated taxonomically. Four new species Pseudospongoprunum? chiangdaoensis, Cenosphaera igoi, Cenosphaera? rugosa, and Tlecerina? apsornae are described.
A new species of the unusual dinoflagellate cyst genus Geonettiade Verteuil and Norris, 1996a is here described from the Pliocene of the western North Atlantic and eastern England. Geonettia waltonensis new species is only the second species to be formally described for this genus, whose type, G. clineaede Verteuil and Norris, 1996a, has a range of Miocene through Pliocene. Geonettia is a gonyaulacalean, goniodomacean genus of the subfamily Pyrodinioideae and is closely related to EocladopyxisMorgenroth, 1966 and CapisocystaWarny and Wrenn, 1997, also found in the Cenozoic. However, Geonettia is the only known dinoflagellate cyst genus to have plates that dissociate extensively on both epi- and hypocyst during excystment. Geonettia waltonensis has this style of excystment, but its hypocystal tabulation is more akin to Capisocysta lataHead, 1998a than to G. clineae. Comparison of tabulation and other morphological features suggests that during the late Miocene, Capisocysta lata evolved from Geonettia waltonensis or a closely related species through failure of its epicystal plates to dissociate. Geonettia waltonensis probably did not evolve directly from G. clineae but may represent a separate lineage within Geonettia that arose during the Miocene.
Several localities within the heterolithic facies of the St. Lawrence Formation (Upper Cambrian) of Wisconsin and Minnesota yield specimens with phosphatic exoskeletons, quadrate cross sections composed of four equidimensional faces each bearing a midline, and possible holdfast attachment during life. These specimens are here referred to the order Conulariida, class Scyphozoa. Their fine, tuberculate surface ornament and serially invaginated midline structure serve to define a new genus, Baccaconularia, to which two new species, B. robinsoni and B. meyeri, are assigned. Conularia cambriaWalcott 1890, also from the Cambrian of the northern Mississippi Valley and long dismissed as a misidentified trilobite fragment, is illustrated photographically for the first time. This species occurs in rocks stratigraphically beneath the St. Lawrence Formation. Specimens assigned to this species by Walcott are conulariids, but lack features now considered diagnostic of either Conularia or Baccaconularia. Walcott's material is insufficient to permit detailed taxonomic evaluation, and we isolate this name to this material, pending the collection of additional, better preserved specimens. Together, Baccaconularia and Conularia cambria contain the oldest large conulariids, and these narrow a stratigraphic gap between other large conulariids known from the Lower Ordovician onwards, and smaller fossils with conulariid affinities known only from Lower Cambrian rocks.
Phylogenetic relationships within the neogastropod family Nassariidae are poorly understood as are relationships between the Nassariidae and other fossil and extant buccinid taxa. The poor resolution of nassariid and buccinoidean relationships is due to: 1) the complex distribution among these gastropods of characters commonly used in classification; 2) a number of Mesozoic and Paleogene genera whose relationships to extant buccinoidean lineages are poorly constrained; and 3) a lack of previous efforts to address these problems on a rigorous, phylogenetic basis.
The results of a phylogenetic analysis of nassariid genera did not decisively support the monophyly of the family. The buccinid subfamily Photinae was an extant sister group to the Nassariinae in a phylogenetic analysis of extant taxa and on many cladograms from an analysis combining fossil and extant taxa. In addition, Buccitriton (representing the Paleogene Tritiaria group) was a sister taxon to the Nassariinae in all analyses in which it was included, regardless of the identity of the extant nassariine sister group. This suggests that the photines, which likely arose from a Tritiaria ancestor, are the closest living relatives to the Nassariinae. Many Paleogene fossil “buccinoid” taxa appear to be more distantly related to the Nassariinae and possibly to the rest of the nassariids as well. Stratigraphic range data combined with the results of this study suggest that the Nassariinae diversified rapidly in the early Miocene and achieved a cosmopolitan distribution early in their history. A largely Indo-Pacific subclade was consistently deeply-nested within the Nassariinae, suggesting that nassariines invaded the Indo-Pacific region most recently. The timing of this invasion is difficult to estimate but had occurred by the end of the Miocene. Further analyses using molecular sequence data, relative stratigraphic position, or focusing in more detail on the Paleogene taxa are required to resolve the identity of the sister group to the Nassariinae with greater confidence.
The Mississippian ammonoid genus DzhaprakocerasPopov, 1965, well known in the eastern hemisphere, is reported from the Delle Member of the Deseret Limestone at Flux and Lakeside Mountains, Tooele County, Utah. This is the first report of the genus in western North America. The ammonoids, D. gordoni n. sp. and D. djaprakense (Librovitch, 1927) occur with mehli—Lower texanus Zone conodonts indicating a middle Osagean (earliest Viséan) age.
The Hanford Brook Formation, one of the classic Cambrian units of Avalonian North America, contains at least eight species of endemic trilobites, including Berabichia milleri Westrop n. sp., that are assigned to seven genera. The vertical succession of faunas is far more complex than has been recognized previously, with each member containing a lithofacies-specific assemblage. These are, in ascending order: a bradoriid-linguloid Association without trilobites in the nearshore St. Martin's Member, a Protolenus Association in dysaerobic siltstones and sandstones of the Somerset Street Member, and a Kingaspidoides-Berabichia Association in hummocky cross-stratified sandstones of the Long Island Member that overlie a parasequence boundary at Hanford Brook. Due to the breakdown of biogeographic barriers in the late Early Cambrian, two new species-based zones, the Protolenus elegans and Kingaspidoides cf. obliquoculatus zones, share trilobite genera with the Tissafinian Stage of Morocco. This generic similarity has been the basis for correlation of this upper Lower Cambrian interval on the Avalon continent with the West Gondwanan lowest Middle Cambrian. However, the clear facies control on the occurrence of genera in the Hanford Brook Formation and the presence of an abrupt faunal break and unconformity at the base of the Tissafinian in Morocco makes this correlation questionable. The Hanford Brook Formation may represent a late Early Cambrian interval unknown in Gondwana. Sequence-stratigraphic criteria even raise the possibility that the Protolenus Association is the biofacies equivalent of Callavia broeggeri Zone faunas of the Brigus Formation of Newfoundland, Nova Scotia and Massachusetts.
The fulcrate thorax of Stygina has the articulating furrow and a long articulating halfring, no pleural furrow, and the facetted outer portion of the pleura has the doublure terminating outside the fulcrum. In the type species the glabella is inflated and the axial furrows partially effaced; in other species inflation is not accompanied by such effacement. Distinctions between genera of Stygininae are based on cephalic characters, including the length (sag. and exs.) of the preglabellar area; the variability of these characters makes such distinctions difficult to define. Eobronteus has the forwardly-expanding glabella, three pairs of glabellar furrows, rostral plate and hypostome typical of Siluro-Devonian Scutelluinae. The relationship between the two subfamilies is shown by morphology and by ontogeny. It is doubted that Styginidae had an origin in common with Illaenidae; the characters suggesting a relationship between Nileus and illaenids are explored. To improve the classification of Trilobita, the search for Cambrian ancestors of Ordovician families needs to be intensified, and characters of the entire axial region should be taken into account. The impendent condition of the hypostome is homeomorphic and is of less significance in classification than the natant and conterminant conditions. Effacement of axial furrows of the cephalon is a trend displayed in Stygininae, and is another homeomorphic character that is not a reliable guide to relationship.
Plate homologies are identified and discussed in primitive representatives of cornute and mitrate stylophorans. Comparative morphological analysis suggests that: 1) Lagynocystida are digital-bearing mitrates; 2) Peltocystida are glossal-bearing mitrates; 3) in Mitrocystitida, glossal and digital are incorporated into a closed marginal thecal frame or modified into articulated posterior spines (Anomalocystitidae); 4) Ovocarpus? circularis is synonymized with O. moncereti; 5) Chauvelia discoidalis and Mitrocystites riadanensis are both assigned to the genus Aspidocarpus; 6) Mitrocystella barrandei is assigned to the new genus Promitrocystites. The original reconstruction of Vizcainocarpus dentiger proposed by Ruta, (1997a) is modified, as a result of the identification of two additional plates in the posterior portion of the theca. The new species Vizcainocarpus rutai from the Tremadoc (Lower Ordovician) of Shropshire (England) is described and represents the oldest record of mitrocystitidan mitrates. V. rutai differs from V. dentiger in the relatively broader size of its zygal and marginals and in the presence, on the lower thecal surface, of a peripheral fringe of fibrillar stereom. A cladistic analysis of selected stylophoran taxa based on the proposed plate homologies indicates that: 1) cornutes and mitrates are sister-groups, both deriving from a Ceratocystis-like ancestor; 2) Peltocystida and Mitrocystitida are sister-groups; 3) Lagynocystida is sister-group of (Peltocystida Mitrocystitida); 4) Lobocarpus is not a cornute but a primitive Cambrian mitrate belonging either to the stem-group of Mitrocystitida or to the stem-group of (Peltocystida Mitrocystitida); 5) Anomalocystitidae represents a family of the suborder Mitrocystitida.
A partial skeleton of a short-necked plesiosaur excavated from the Upper Cenomanian of the Middle Yezo Group of Hokkaido, Japan, includes disarticulated vertebrae, the right half of the pectoral girdle, fragments of the pelvic girdle, ribs, gastralia, and gastroliths. Gastroliths are unusual in short-necked plesiosaurs. Skeletal characters indicate that the specimen belongs to the Family Polycotylidae, well known from North America, the former Soviet Republics, and possibly from New Zealand. They are rare in East Asia and hitherto unknown from Japan. Extensive ossification indicates that this specimen is an adult individual, yet it is smaller than the adult specimens of other known polycotylids. The elongated epipodial bones are a unique character of the specimen but are probably plesiomorphic. The fossil is evidence of biogeographical diversification of the family at the beginning of the Late Cretaceous.
The poorly-known, long bodied, limb-reduced marine lizard Adriosaurus suessiSeeley, 1881, is reassessed. Adriosaurus and a number of other marine lizards are known from Upper Cretaceous (Upper Cenomanian-Lower Turonian) marine carbonate rocks exposed along the Dalmatian coast of the Adriatic Sea, from Komen, Slovenia, to Hvar Island, Croatia. A revised vertebral count reveals 10 cervical, 29 dorsal, and at least 65 caudal vertebrae. The projections previously interpreted as hypapophyses are instead transverse processes. Openings on the anterior part of the skull, previously described as external nares, are probably internal nares. Important features not noted previously include accessory articulations on all presacral vertebrae, pachyostosis of dorsal vertebrae and ribs, and the presence of two pygal vertebrae. Phylogenetic analysis of 258 osteological characters and all the major squamate lineages suggests that Adriosaurus and dolichosaurs are successive sister-taxa to snakes. This is consistent with their long-bodied, limb-reduced morphology being intermediate between typical marine squamates (e.g., mosasaurs) and primitive marine snakes (pachyophiids). The analysis further reveals that up to five successive outgroups to living snakes (pachyophiids, Adriosaurus, dolichosaurs, Aphanizocnemus, and mosasauroids) are all marine, suggesting a marine (or at least, semi-aquatic) phase in snake origins. These phylogenetic results are robust whether multistate characters are ordered or unordered, thus refuting recent suggestions that snakes cluster with amphisbaenians and dibamids (rather than aquatic lizards) if multistate characters are left unordered. Also, the recent suggestion that Pachyrhachis shares synapomorphies with advanced snakes (macrostomatans) is shown to be poorly supported, because the reinterpretations of the relevant skull elements are unlikely and, even if accepted, the character states proposed to unite Pachyrhachis and advanced snakes are also present in more basal snakes and/or the nearest lizard outgroups, and are consequently primitive for snakes.
Reinterpretation of cranial materials of the diadectomorphs Limnoscelis and Diadectes has prompted a reconsideration of the origin and early evolution of the amniote occiput. The basic approach is a phylogenetic study of major groups of Paleozoic tetrapods based on the occiput and closely associated elements of the skull roof. A lack of adequate anatomical data has forced the elimination of only a few relevant higher-level taxa from consideration, and, using Acanthostega as the reference outgroup, a cladistic analysis of the interrelationships of the Lepospondyli, Temnospondyli, Seymouriamorpha, Baphetidae (=Loxommatidae), Anthracosauria, Diadectomorpha, Synapsida, and Reptilia has produced the following results: 1) the ingroup taxa exhibit a basal dichotomy in which one division consists of the unresolved relationships of Lepospondyli, Temnospondyli, and Seymouriamorpha; 2) the pattern of relationships of the second division of the ingroup taxa is a series of nested clades, terminating with the Diadectomorpha and Synapsida as sister taxa sharing a more recent common ancestor than either does with Reptilia. This relationship requires assignment of Diadectomorpha to Amniota; and 3) the Anthracosauria and Baphetidae are progressively more distant clades or sister taxa. On the basis of the cladistic analysis, the attainment of the amniote occiput is described as passing through four morphological grades of organization. Each grade of the series is characterized by a set of derived character states that defines the progressively more-derived nodes and from which branch a clade containing the unresolved trichotomy of Lepospondyli, Temnospondyli, and Seymouriamorpha; the Baphetidae clade; the Anthracosauria clade; and the Diadectomorpha Synapsida and Reptilia clades, respectively.
A diverse near-shore marine fauna existed during the early Miocene in what is today an arid inland region about 90 km south of the Caribbean coast of northern Venezuela, a poorly known area geologically and paleontologically. The fossil locality consists of more than 100 m of section exposed in an area of about 1 km2. We report the discovery of 20 molluscan species, one crab (Portunus oblongus), at least three sharks (Hemipristis serra and Carcharhinus spp.), one turtle (“Podocnemis” venezuelensis), one crocodile (Crocodylidae), two whales (Odontoceti) and a three dimensional cast of the mesocarp or endocarp of a palm fruit. Several taxa are reported for the first time in Venezuela or in northern South America. The fauna indicates, or at least is consistent with, an early Miocene age for the locality, and a near-shore and shallow water marine depositional environment. We suggest that the earliest mammal previously reported from Venezuela, the pyrothere Proticia venezuelensis, was collected in Miocene rocks of the Castillo Formation instead of Eocene rocks of the Trujillo Formation.