EVOLUTION AND DEVELOPMENT, Issue 1 2005
Monique C. M. Welten
Summary The bird wing is of special interest to students of homology and avian evolution. Fossil and developmental data give conflicting indications of digit homology if a pentadactyl "archetype" is assumed. Morphological signs of a vestigial digit I are seen in bird embryos, but no digit-like structure develops in wild-type embryos. To examine the developmental mechanisms of digit loss, we studied the expression of the high-mobility group box containing Sox9 gene, and bone morphogenetic protein receptor 1b (bmpR-1b),markers for precondensation and prechondrogenic cells, respectively. We find an elongated domain of Sox9 expression, but no bmpR-1b expression, anterior to digit II. We interpret this as a digit I domain that reaches precondensation, but not condensation or precartilage stages. It develops late, when the tissue in which it is lodged is being remodeled. We consider these findings in the light of previous Hoxd-11 misexpression studies. Together, they suggest that there is a digit I vestige in the wing that can be rescued and undergo development if posterior patterning cues are enhanced. We observed Sox9 expression in the elusive "element X" that is sometimes stated to represent a sixth digit. Indeed, incongruity between digit domains and identities in theropods disappears if birds and other archosaurs are considered primitively polydactyl. Our study provides the first gene expression evidence for at least five digital domains in the chick wing. The failure of the first to develop may be plausibly linked to attenuation of posterior signals. [source]

From clergymen to computers,the advent of virtual palaeontology

GEOLOGY TODAY, Issue 3 2010
Russell J. Garwood
Palaeontology was established as a science in the Victorian era, yet has roots that stretch deeper into the recesses of history. More than 2000 years ago, the Greek philosopher Aristotle deduced that fossil sea shells were once living organisms, and around 500 ad Xenophanes used fossils to argue that many areas of land must have previously been submarine. In 1027, the Persian scholar Avicenna suggested that organisms were fossilized by petrifying fluids; this theory was accepted by most natural philosophers up until the eighteenth century Enlightenment, and even beyond. The late 1700s were notable for the work of Georges Cuvier who established the reality of extinction. This, coupled with advances in the recognition of faunal successions made by the canal engineer William Smith, laid the framework for the discipline that would become known as palaeontology. As the nineteenth century progressed, the scientific community became increasingly well organized. Most fossil workers were gentleman scientists and members of the clergy, who self-funded their studies in a new and exciting field. Many of the techniques used to study fossils today were developed during this ,classical' period. Perhaps the most fundamental of these is to expose a fossil by splitting the rock housing it, and then conduct investigations based upon the exposed surface (Fig. 1). This approach has served the science well in the last two centuries, having been pivotal to innumerable advances in our understanding of the history of life. Nevertheless, there are many cases where splitting a rock in this way results in incomplete data recovery; those where the fossils are not flattened, but are preserved in three-dimensions. Even the ephemeral soft-tissues of organisms are occasionally preserved in a three-dimensional state, for example in the Herefordshire, La Voulte Sûr Rhone and Orsten ,Fossil Lagerstätten' (sites of exceptional fossil preservation). These rare and precious deposits provide a wealth of information about the history of life on Earth, and are perhaps our most important resource in the quest to understand the palaeobiology of extinct organisms. With the aid of twenty-first century technology, we can now make the most of these opportunities through the field of ,virtual palaeontology',computer-aided visualization of fossils. Figure 1. A split nodule showing the fossil within, in this case a cockroachoid insect. Fossil 4 cm long (From Garwood & Sutton, in press). [source]

Evolution of M1 crown size and cusp proportions in the genus Homo

JOURNAL OF ANATOMY, Issue 5 2009
Rolf Quam
Abstract Previous research into tooth crown dimensions and cusp proportions has proved to be a useful way to identify taxonomic differences in Pliocene and Pleistocene fossil hominins. The present study has identified changes in both M1 crown size and cusp proportions within the genus Homo, with M1 overall crown size reduction apparently occurring in two main stages. The first stage (a reduction of ca. 17%) is associated with the emergence of Homo ergaster and Homo erectus sensu stricto. The second stage (a reduction of ca. 10%) occurs in Homo sapiens, but the reduced modern human M1 tooth crown size was only attained in Upper Paleolithic times. The absolute sizes of the individual cusps are highly positively correlated with overall crown size and dental reduction produces a reduction in the absolute size of each of the cusps. Most of the individual cusps scale isometrically with crown size, but the paracone shows a negative allometric relationship, indicating that the reduction in paracone size is less than in the other M1 cusps. Thus, the phylogenetically oldest cusp in the upper molars also seems to be the most stable cusp (at least in the M1). The most striking change in M1 cusp proportions is a change in the relative size of the areas of the paracone and metacone. The combination of a small relative paracone and a large relative metacone generally characterizes specimens attributed to early Homo, and the presence of this character state in Australopithecus and Paranthropus suggests it may represent the primitive condition for the later part of the hominin clade. In contrast, nearly all later Homo taxa, with the exception of Homo antecessor, show the opposite condition (i.e. a relatively large paracone and a relatively small metacone). This change in the relationship between the relative sizes of the paracone and metacone is related to an isometric reduction of the absolute size of the metacone. This metacone reduction occurs in the context of relative stability in the paracone as crown size decreases. Among later Homo taxa, both Homo heidelbergensis and Homo neanderthalensis show a further reduction of the metacone and an enlargement of the hypocone. Fossil and contemporary H. sapiens samples show a trend toward increasing the relative size of the protocone and decreasing the relative size of the hypocone. In Europe, modern human M1 cusp proportions are essentially reached during the Upper Paleolithic. Although some variation was documented among the fossil taxa, we suggest that the relative size of the M1 paracone and metacone areas may be useful for differentiating the earliest members of our genus from subsequent Homo species. [source]

The Mediterranean bryozoan Myriapora truncata (Pallas, 1766): a potential indicator of (palaeo-) environmental conditions

LETHAIA, Issue 3 2007
BJÖRN BERNING
Fossil and Recent specimens of the Mediterranean bryozoan Myriapora truncata show considerable intra- and intercolonial differences in branch diameter and zooid size. Statistically significant variability occurs within colonies, between colonies within sites, and between sampled sites, while the presence of intracolonial variability clearly shows that branch diameter is largely controlled by environmental parameters. The three structural traits measured (branch diameter, zooid size and zooid depth) do not correlate, thus indicating a disconnection between the controls on overall zooid size and branch diameter. Possible environmental parameters that may have an influence on morphology are temperature, food supply or current energy. Whereas current energy has an effect on the colony branching pattern (branch spacing), there are indications that temperature may be the main, but not the only, parameter controlling zooid size, and it is suggested that food supply largely determines the branch diameter in M. truncata. However, the identification of the decisive factors and quantification of the relationships between environmental and morphological change is beyond the scope of this study. The results nevertheless show that, if the control factors of morphological variability can be ascertained in Recent M. truncata, this species may prove to be an indicator of environmental conditions and their change at different spatial and temporal scales in Cenozoic to Recent Mediterranean habitats. [source]

Phylogeography of the North American red fox: vicariance in Pleistocene forest refugia

MOLECULAR ECOLOGY, Issue 12 2009
KEITH B. AUBRY
Abstract Fossil, archaeological, and morphometric data suggest that indigenous red foxes in North America were derived from vicariance in two disjunct refugia during the last glaciation: one in Beringia and one in the contiguous USA. To test this hypothesis, we conducted a phylogeographical analysis of the North American red fox within its presettlement range. We sequenced portions of the mitochondrial cytochrome b (354 bp) gene and D-loop (342 bp) from 220 historical red fox specimens. Phylogenetic analysis of the cytochrome b gene produced two clades that diverged c. 400 000 years before present (bp): a Holarctic and a Nearctic clade. D-loop analyses of the Nearctic clade indicated three distinct subclades (, 99% Bayesian posterior probability); two that were more recently derived (rho estimate c. 20 000 bp) and were restricted to the southwestern mountains and the eastern portion of North America, and one that was older (rho estimate c. 45 000 bp) and more widespread in North America. Populations that migrated north from the southern refugium following deglaciation were derived from the colonization of North America during or prior to the Illinoian glaciation (300 000,130 000 bp), whereas populations that migrated south from the northern refugium represent a more recent colonization event during the Wisconsin glaciation (100 000,10 000 bp). Our findings indicate that Nearctic clade red foxes are phylogenetically distinct from their Holarctic counterparts, and reflect long-term isolation in two disjunct forest refugia during the Pleistocene. The montane lineage, which includes endangered populations, may be ecologically and evolutionarily distinct. [source]

Organic-walled dinoflagellate cyst production in relation to upwelling intensity and lithogenic influx in the Cape Blanc region (off north-west Africa)

PHYCOLOGICAL RESEARCH, Issue 2 2005
Ewa Susek
SUMMARY Fossil dinoflagellate cyst assemblages are increasingly used in paleoclimatic research to establish paleoenvi-ronmental reconstructions. To obtain reliable reconstructions, it is essential to know which physical factors influence the cyst production. Most information about the relationship between variations in physical parameters and cyst production is known from middle and higher latitudes. Information from the (sub)tropics is rare. To increase this information, the temporal variation in cyst assemblages from the upwelling area off north-west Africa (off Mauritania) has been compared to environmental conditions of the upper water column. Samples were collected by the sediment trap CB9, off north-west Africa (Cape Blanc, 21°15,2,N, 20°42,2,W) between 11 June 1998 and 7 November 1999 at 27.5-day intervals. Off Cape Blanc, upwelling occurs throughout the year with variable intensity. This region is also characterized by frequently occurring Saharan dust storms. Seasonal variations in dust input, upwelling intensity and sea surface temperature are reflected by the production of organic-walled dinoflagellate cyst assemblages. Several cyst taxa are produced throughout the sampling interval, with the highest fluxes at times of strongest upwelling relaxation and/or dust input (Echinidinium aculeatum Zonneveld, Echini-din ium delicatum Zonneveld, Echinidinium granulaturn Zonneveld, Echinidinium spp., Impagidinium aculeatum (Wall) Lentin et Williams, Impagidinium sphaeri-cum (Wall) Lentin et Williams, Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium stellatum (Wall in Wall et Dale) Rochon etal., Protoperidinium spp., Selenopemphix nephroides (Benedek) Benedek et Sarjeant and Selenopemphix quanta (Bradford) Matsuoka). Species such as, for example, Bitectatodinium spongium (Zonneveld) Zonneveld et Jurkschat and Impagidinium patulum (Wall) Stover et Evitt do not show any production pattern related to a particular season of the year or to specific environmental conditions in the upper water column. The production of cysts of Protoperidinium monospinum (Paulsen) Zonneveld et Dale is restricted to intervals with increased nutrient concentrations in upper waters when sea surface temperatures at the sampling site is below approximately 24°C. [source]

Fossils provide better estimates of ancestral body size than do extant taxa in fishes

ACTA ZOOLOGICA, Issue 2009
James S. Albert
Abstract The use of fossils in studies of character evolution is an active area of research. Characters from fossils have been viewed as less informative or more subjective than comparable information from extant taxa. However, fossils are often the only known representatives of many higher taxa, including some of the earliest forms, and have been important in determining character polarity and filling morphological gaps. Here we evaluate the influence of fossils on the interpretation of character evolution by comparing estimates of ancestral body size in fishes (non-tetrapod craniates) from two large and previously unpublished datasets; a palaeontological dataset representing all principal clades from throughout the Phanerozoic, and a macroecological dataset for all 515 families of living (Recent) fishes. Ancestral size was estimated from phylogenetically based (i.e. parsimony) optimization methods. Ancestral size estimates obtained from analysis of extant fish families are five to eight times larger than estimates using fossil members of the same higher taxa. These disparities arise from differential survival of large-bodied members of early branching lineages, and are not statistical or taphonomic artefacts. Estimates of ancestral size obtained from a limited but judicious selection of fossil fish taxa are more accurate than estimates from a complete dataset of extant fishes. [source]

Palaeoenvironmental context of the Late-glacial woolly mammoth (Mammuthus primigenius) discoveries at Condover, Shropshire, UK

GEOLOGICAL JOURNAL, Issue 4 2009
J. R. M. Allen
Abstract In 1986/1987 the remains of several mammoths, Mammuthus primigenius (Blumenbach), were discovered on the spoil heap of an actively working gravel pit at Condover, Shropshire, England. The discovery of the remains posed two questions that could be addressed by analyses of biological proxies. First, as none of the bones was found in situ it was necessary to confirm the stratum in which the remains occurred. Second, what was the environment in which these animals lived and died? A range of biological indicators was used to address these questions, including pollen, spore and algal, plant macrofossil, invertebrate, anuran and biological mineral analyses. Multivariate statistical analyses of palynological and Pediastrum data, along with evidence from the Coleopteran assemblages, support the attribution of the mammoth bones to a unit of dark grey clayey sandy silt, although they may have lived at the time of the overlying green detritus mud. The palaeobiological data supports the correlation of these sediments to the Devensian Late-glacial. The mammoths entered this basin at the start of the Late-glacial Interstadial (Greenland Interstadial 1e) (ca. 14,830,3930 cal. year BP; 12,300,±,110 14C year BP) and became mired in soft cohesive sediments. Palaeotemperature reconstructions, based on the Coleopteran assemblages, from the time when the mammoths actually became mired, show that the climate was temperate with mean July temperatures between 15 and 19°C and mean January temperatures between ,13 and +6°C. Biological indicators from the sediments encasing the mammoths indicate that the landscape surrounding the basin was treeless and dry, contrasting with rich vegetation within the basin itself that had possibly attracted the mammoths to the site. Evidence of sedimentary disturbance suggests that the mammoths caused large-scale bioturbation of the deposits making palaeoenvironmental interpretations difficult. Fossils of terrestrial blowflies, carcass and dung beetles show that some of the decaying corpses must have lain exposed on the land surface for sufficient time for the soft parts to have rotted away and skin and bones to have become desiccated before many of them sank into the dark grey clayey sandy silt. Copyright © 2009 John Wiley & Sons, Ltd. [source]

How good is the fossil record of arthropods?

GEOLOGICAL JOURNAL, Issue 3-4 2001
An assessment using the stratigraphic congruence of cladograms
Abstract A total of 179 published cladograms of arthropods was tested for their congruence with the palaeontological record. Congruence for data sets including 510 tetrapod and 157 fish trees was also calculated for comparison. Results provide support for the hypothesis that the fossil record of arthropods is less complete (at levels of stratigraphic and taxonomic resolution pertinent to most macroevolutionary studies) than the records of several other taxa. Differences in tree size, shape, balance and the distribution of first stratigraphic appearances (potential sources of bias) were controlled for by various randomization procedures. Most measures of congruence for arthropods were statistically poorer than those for other groups, even when the sample was divided into broad temporal bins. Many of the most robust and widely reproduced sister groupings of arthropods are attended by ghost ranges of many tens or hundreds of millions of years. Fossils of a number of presently very diverse and abundant arthropod groups are conspicuously absent from the record, despite many spectacular examples of the detailed preservation of others. There is probably no single reason for the apparently poor record of arthropods. Low preservation potential, small size of individuals, small numbers of individuals, and restricted palaeobiogeography almost certainly play a role in particular cases. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Fossils as Neolithic funereal adornments in County Kerry, south-west Ireland

GEOLOGY TODAY, Issue 4 2002
Patrick N. Wyse Jackson
Argument rages in the media on the effects of road-building on sites of archaeological importance. Certainly there have been many cases where sites of value have been lost, but others where sites of importance have been revealed that would probably have gone undetected for a considerable time, if not for ever. One example of a lucky discovery arose from a proposal to widen the road between the towns of Tralee and Killarney in County Kerry, south-west Ireland. A preliminary archaeological survey carried out along the route in 1996 revealed an area of exceptional archaeological richness. What was particularly surprising was that one feature contained a significant collection of fossils used for funereal or ceremonial purposes. [source]

Fossils in mountain belts

GEOLOGY TODAY, Issue 4 2001
David A. T. Harper
No abstract is available for this article. [source]

Fossils explained 31: Sponges 1

GEOLOGY TODAY, Issue 5 2000
Stephen K. Donovan
First page of article [source]

FENESTRATE BRYOZOAN GENERA BASED ON SPECIES FROM IRELAND ORIGINALLY DESCRIBED BY FREDERICK M,COY IN 1844

PALAEONTOLOGY, Issue 4 2006
PATRICK N. WYSE JACKSON
Abstract:, A large number of fenestrate bryozoan species were named in ,A Synopsis of the Characters of the Carboniferous Limestone Fossils of Ireland' by Frederick M,Coy (1844). At the same time, M,Coy named the bryozoan genera Ichthyorachis, Ptylopora and Polypora, each of which by monotypy or by subsequent designation was based on new species within that work. Subsequently, d' Orbigny (1849) named Fenestrellina with the type species Fenestella crassa M,Coy, 1844 as type species; Miller (1961) named Parafenestella with the type species Fenestella formosa M,Coy, 1844 as type species; and Wyse Jackson (1988) named Baculopora with the type species Vincularia megastoma M,Coy, 1844. We re-describe here in more detail than previously the fenestrate type species originally published in M,Coy (1844), provide diagnoses of the genera, and compare the nineteenth century genera with more recently named genera that have been discriminated specifically from them. [source]

A NEW SPECIES OF ISCHYODUS (CHONDRICHTHYES: HOLOCEPHALI: CALLORHYNCHIDAE) FROM UPPER MAASTRICHTIAN SHALLOW MARINE FACIES OF THE FOX HILLS AND HELL CREEK FORMATIONS, WILLISTON BASIN, NORTH DAKOTA, USA

PALAEONTOLOGY, Issue 4 2005
JOHN W. HOGANSON
Abstract:, A new species of chimaeroid, Ischyodus rayhaasi sp. nov., is described based primarily upon the number and configuration of tritors on palatine and mandibular tooth plates. This new species is named in honour of Mr Raymond Haas. Fossils of I. rayhaasi have been recovered from the Upper Maastrichtian Fox Hills Formation and the Breien Member and an unnamed member of the Hell Creek Formation at sites in south-central North Dakota and north-central South Dakota, USA. Ischyodus rayhaasi inhabited shallow marine waters in the central part of the Western Interior Seaway during the latest Cretaceous. Apparently it was also present in similar habitats at that time in the Volga region of Russia. Ischyodus rayhaasi is the youngest Cretaceous species of Ischyodus known to exist before the Cretaceous/Tertiary extinction, and the species apparently did not survive that event. It was replaced by Ischyodus dolloi, which is found in the Paleocene Cannonball Formation of the Williston Basin region of North Dakota and is widely distributed elsewhere. [source]

A New Ichnogenus for Crustacean Trace Fossils from the Upper Miocene Camacho Formation of Uruguay

PALAEONTOLOGY, Issue 1 2004
Mariano Verde
Maiakarichnus currani ichnogen. et isp. nov. is a crustacean trace fossil from the Upper Miocene Camacho Formation of Uruguay. This trace fossil is a subspherical chamber preserved in full relief, with numerous thin shafts radiating in a stratigraphically upward direction mainly from its upper part and from the sides. In the Camacho Formation it can be found intergrading with Ophiomorpha and Thalassinoides. Previous (unnamed) findings of similar material are only from the Pamlico Morphostratigraphic Unit (Pleistocene) of North Carolina; these have been interpreted as callianassid brood structures. In this paper we also interpret Maiakarichnus as a brood structure of callianassid origin based on its association with Thalassinoides and Ophiomorpha. [source]

Book review: Tobias in Conversation: Genes, Fossils and Anthropology

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2010
Bernard Wood
No abstract is available for this article. [source]

The evolution of brachiation in ateline primates, ancestral character states and history

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2008
Andrea L. Jones
Abstract This study examines how brachiation locomotion evolved in ateline primates using recently-developed molecular phylogenies and character reconstruction algorithms, and a newly-collected dataset including the fossils Protopithecus, Caipora, and Cebupithecia. Fossils are added to two platyrrhine molecular phylogenies to create several phylogenetic scenarios. A generalized least squares algorithm reconstructs ateline and atelin ancestral character states for 17 characters that differentiate between ateline brachiators and nonbrachiators. Histories of these characters are mapped out on these phylogenies, producing two scenarios of ateline brachiation evolution that have four commonalities: First, many characters change towards the Ateles condition on the ateline stem lineage before Alouatta splits off from the atelins, suggesting that an ateline energy-maximizing strategy began before the atelines diversified. Second, the ateline last common ancestor is always reconstructed as an agile quadruped, usually with suspensory abilities. It is never exactly like Alouatta and many characters reverse and change towards the Alouatta condition after Alouatta separates from the atelins. Third, most characters undergo homoplastic change in all ateline lineages, especially on the Ateles and Brachyteles terminal branches. Fourth, ateline character evolution probably went through a hindlimb suspension with tail-bracing phase. The atelines most likely diversified via a quick adaptive radiation, with bursts of punctuated change occurring in their postcranial skeletons, due to changing climatic conditions, which may have caused competition among the atelines and between atelines and pitheciines. Am J Phys Anthropol, 2008. © 2008 Wiley-Liss, Inc. [source]

Pleistocene Plant Fossils in and near La Selva Biological Station, Costa Rica1

BIOTROPICA, Issue 3 2003
Sally P. Horn
ABSTRACT Radiocarbon dating and 40Ar/39Ar analysis of overlying tephra indicate that plant fossil assemblages exposed by stream erosion and well construction in and near La Selva Biological Station in eastern lowland Costa Rica are Pleistocene in age. We identified plant taxa based on wood, leaves, fruits, seeds, pollen, and spores examined from three sites at ca 30 m elevation. Extrapolating from modern ranges and surface temperature lapse rates suggests paleotemperatures 2.5,3.1°C cooler than at present RESUMEN Dataciones radiocarbónicas y análisis de argon (40Ar/39Ar) de la tefra sobrepuesta indican una edad Pleistocénica para las asociaciones de plantas fósiles expuestas por erosión fluvial y por la construcción de un pozo dentro y cerca de la Estación Biológica La Selva en la bajura oriental de Costa Rica. Se identificaron los táxones vegetales con base en madera, hojas, frutas, semillas, polen, y esporas de tres sitios ubicados a unos 30 m sobre el nivel de mar. Los resultados, basados en la extrapolación de los ámbitos geográficos y del gradiente vertical de la temperatura superficial modernos, sugiere paleotemperaturas 2.5,3.1°C mas frescas que en el presente. [source]

Vestrogothia spinata (Phosphatocopina, Crustacea), Fossils of Orsten-type Preservation from the Upper Cambrian of Western Hunan, South China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009
Zheng LIU
Abstract: Fossils of Orsten-type preservation represented by the crustacean Skaracarida and Phosphatocopida were found in western Hunan, South China in 2005, including the important phosphatocopid species Vestrogothia spinata based on exquisitely preserved soft-bodied specimens that allow the first growth stage to be reestablished. The taxonomy of Vestrogothia spinata is revised employing the character of a two-divided limb stem of the mandible. A new foundation for the phytogeny of the Phosphatocopina using mandible characters related to crustacean appendages is postulated. Vestrogothia spinata has only previously been found from Sweden. [source]

New Fossils of Eoptychopteridae (Diptera) from the Middle Jurassic of Northeastern China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009
Jianying HAO
Abstract: Three new species of the extinct genus of Eoptychopterina from the Eoptychopteridae family, Eoptychopterina antica sp. nov., Eoptychopterina adnexa sp. nov., and Eoptychopterina mediata sp. nov., are described and illustrated. These three new species are established based on fossil specimens with bodies and complete wings. All were collected from the Middle Jurassic Jiulongshan Formation of Daohugou in eastern Inner Mongolia, China. Based on the new materials, the name of two species in Eoptychopterina from China,Eoptychopterina elenae Ren and Krzeminski and Eoptychopterina gigantea Zhang,is sysnonymum Junius. [source]

Discovery of Radiolarian Fossils from the Aiketik Group at the Western End of the South Tianshan Mountains of China and Its Implications

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2002
LI Yuejun
Abstract, The Aiketik Group, distributed at the western end of the South Tianshan Mountains, China, is an important lithostratigraphic unit involved in the South Tianshan orogen. It is separated from the adjacent rocks by faults. Generally, the geologists ascribed it to the Upper Carboniferous according to Pseudostaffella sp., Profusulinella sp. and Fusulinella sp. found from the limestone and sandy limestone of Aiketik. Our radiolarian fossils were obtained from the chert samples collected from the Haladaok section located at the upper Tuoshihan River. The fossils mainly include Albaillella undulata Deflandre, Albaillella paradoxa Deflandre, Albaillella sp. aff. A. paradoxa Deflandre, Albaillella sp. cf. A. deflandrei Gourmelon, Albaillella sp., Albaillella excelsa Ishiga, Kito and Imoto (?), Belowea variabilis (Ormiston et Lane), Callella cf. C. parvispinosa Won, Entactinia cf. E. tortispina Ormiston et Lane, Entactinia aff. E. tortispina Ormiston et Lane, Entactinia variospina Won, Entactinia sp., Eostylodictya rota (Won), Latentifistula impella (Ormistone et Lane) (?), Latentifistula turgida Omiston et Lane, Latentifistulidae gen. et. sp. indet. and Polyentactinia cf. aranea Gourmelon. Among them, Albaillella excelsa Ishiga, Kito and Imoto (?) is a Late Permian species with some elements uncertain as there is only one poorly-preserved fossil of this species found so far. And two radiolarian assemblages can be identified from the other fossils. One is the early Early Carboniferous assemblage represented by Albaillella undulata Deflandre, Albaillella paradoxa and Albaillella sp. cf. A. deflandrei Gourmelon. And the other is the late Early Carboniferous assemblage represented by Eostylodictya rota (Won). This is the first discovery of radiolarian fossils in the Aiketik Group, also the first discovery of Late Permian radiolarian fossils in the South Tianshan Mountains. Meanwhile, this is the current westernmost sampling site of radiolarian fossils in the South Tianshan Mountains. [source]

RAPID ADAPTIVE DIVERGENCE IN NEW WORLD ACHILLEA, AN AUTOPOLYPLOID COMPLEX OF ECOLOGICAL RACES

EVOLUTION, Issue 3 2008
Justin Ramsey
Adaptive evolution is often associated with speciation. In plants, however, ecotypic differentiation is common within widespread species, suggesting that climatic and edaphic specialization can outpace cladogenesis and the evolution of postzygotic reproductive isolation. We used cpDNA sequence (5 noncoding regions, 3.5 kb) and amplified fragment length polymorphisms (AFLPs: 4 primer pairs, 1013 loci) to evaluate the history of ecological differentiation in the North American Achillea millefolium, an autopolyploid complex of "ecological races" exhibiting morphological, physiological, and life-history adaptations to diverse environments. Phylogenetic analyses reveal North American A. millefolium to be a monophyletic group distinct from its European and Asian relatives. Based on patterns of sequence divergence, as well as fossil and paleoecological data, colonization of North America appears to have occurred via the Bering Land Bridge during the Pleistocene (1.8 MYA to 11,500 years ago). Population genetic analyses indicate negligible structure within North American A. millefolium associated with varietal identity, geographic distribution, or ploidy level. North American populations, moreover, exhibit the signature of demographic expansion. These results affirm the "ecotype" concept of the North American Achillea advocated by classical research and demonstrate the rapid rate of ecological differentiation that sometimes occurs in plants. [source]

GENETICS AND RECENT HUMAN EVOLUTION

EVOLUTION, Issue 7 2007
Alan R. Templeton
Starting with "mitochondrial Eve" in 1987, genetics has played an increasingly important role in studies of the last two million years of human evolution. It initially appeared that genetic data resolved the basic models of recent human evolution in favor of the "out-of-Africa replacement" hypothesis in which anatomically modern humans evolved in Africa about 150,000 years ago, started to spread throughout the world about 100,000 years ago, and subsequently drove to complete genetic extinction (replacement) all other human populations in Eurasia. Unfortunately, many of the genetic studies on recent human evolution have suffered from scientific flaws, including misrepresenting the models of recent human evolution, focusing upon hypothesis compatibility rather than hypothesis testing, committing the ecological fallacy, and failing to consider a broader array of alternative hypotheses. Once these flaws are corrected, there is actually little genetic support for the out-of-Africa replacement hypothesis. Indeed, when genetic data are used in a hypothesis-testing framework, the out-of-Africa replacement hypothesis is strongly rejected. The model of recent human evolution that emerges from a statistical hypothesis-testing framework does not correspond to any of the traditional models of human evolution, but it is compatible with fossil and archaeological data. These studies also reveal that any one gene or DNA region captures only a small part of human evolutionary history, so multilocus studies are essential. As more and more loci became available, genetics will undoubtedly offer additional insights and resolutions of human evolution. [source]

THE HISTORY OF A NEARCTIC COLONIZATION: MOLECULAR PHYLOGENETICS AND BIOGEOGRAPHY OF THE NEARCTIC TOADS (BUFO)

EVOLUTION, Issue 11 2004
Gregory B. Pauly
Abstract Previous hypotheses of phylogenetic relationships among Nearctic toads (Bufonidae) and their congeners suggest contradictory biogeographic histories. These hypotheses argue that the Nearctic Bufo are: (1) a polyphyletic assemblage resulting from multiple colonizations from Africa; (2) a paraphyletic assemblage resulting from a single colonization event from South America with subsequent dispersal into Eurasia; or (3) a monophyletic group derived from the Neotropics. We obtained approximately 2.5 kb of mitochondrial DNA sequence data for the 12S, 16S, and intervening valine tRNA gene from 82 individuals representing 56 species and used parametric bootstrapping to test hypotheses of the biogeographic history of the Nearctic Bufo. We find that the Nearctic species of Bufo are monophyletic and nested within a large clade of New World Bufo to the exclusion of Eurasian and African taxa. This suggests that Nearctic Bufo result from a single colonization from the Neotropics. More generally, we demonstrate the utility of parametric bootstrapping for testing alternative biogeographic hypotheses. Through parametric bootstrapping, we refute several previously published biogeographic hypotheses regarding Bufo. These previous studies may have been influenced by homoplasy in osteological characters. Given the Neotropical origin for Nearctic Bufo, we examine current distributional patterns to assess whether the Nearctic-Neotropical boundary is a broad transition zone or a narrow boundary. We also survey fossil and paleogeographic evidence to examine potential Tertiary and Cretaceous dispersal routes, including the Paleocene Isthmian Link, the Antillean and Aves Ridges, and the current Central American Land Bridge, that may have allowed colonization of the Nearctic. [source]

Mitogenomics and phylogenomics reveal priapulid worms as extant models of the ancestral Ecdysozoan

EVOLUTION AND DEVELOPMENT, Issue 6 2006
Bonnie L. Webster
SUMMARY Research into arthropod evolution is hampered by the derived nature and rapid evolution of the best-studied out-group: the nematodes. We consider priapulids as an alternative out-group. Priapulids are a small phylum of bottom-dwelling marine worms; their tubular body with spiny proboscis or introvert has changed little over 520 million years and recognizable priapulids are common among exceptionally preserved Cambrian fossils. Using the complete mitochondrial genome and 42 nuclear genes from Priapulus caudatus, we show that priapulids are slowly evolving ecdysozoans; almost all these priapulid genes have evolved more slowly than nematode orthologs and the priapulid mitochondrial gene order may be unchanged since the Cambrian. Considering their primitive bodyplan and embryology and the great conservation of both nuclear and mitochondrial genomes, priapulids may deserve the popular epithet of "living fossil." Their study is likely to yield significant new insights into the early evolution of the Ecdysozoa and the origins of the arthropods and their kin as well as aiding inference of the morphology of ancestral Ecdysozoa and Bilateria and their genomes. [source]

The evolutionary history of crustacean segmentation: a fossil-based perspective

EVOLUTION AND DEVELOPMENT, Issue 6 2005
Dieter Waloszek
Summary The evolution of segmentation in Crustacea, that is, the formation of sclerotized and jointed body somites and arrangement of somites into tagmata, is viewed in light of historical traits and functional constraints. The set of Early to Late Cambrian ,Orsten' arthropods have informed our current views of crustacean evolution considerably. These three-dimensionally preserved fossils document ancient morphologies, as opposed to purely hypothetical models and, because of the unusual preservation of larval stages, provide us with unparalleled insight into the morphogenesis of body somites and their structural equipment. The variety of evolutionary levels represented in the ,Orsten' including lobopodians, tardigrades, and pentastomids also allows phylogenetic interpretations far beyond the Crustacea. The ,Orsten' evidence and data from representatives of the Lower Cambrian Chengjiang biota in southwestern China, including phylogenetically earlier forms, form the major source of our morphology-based review of structural and functional developments that led toward the Crustacea. The principal strategy of arthropods is the simultaneous development of head somites, as expressed in a basal "head larva," and a successive addition of postcephalic somites from a preterminal budding zone with progressive maturation of metameric structures. This can be recognized in the developmental patterns of extant and fossil representatives of several euarthropod taxa, particularly crustaceans, trilobites, and chelicerates (at least basally). The development of these taxa points to an early somite-poor and free-living hatching stage. Embryonic development to a late stage within an egg, as occurring in recent onychophorans and certain in-group euarthropods, is regarded as achieved several times convergently. [source]

Otx1 gene-controlled morphogenesis of the horizontal semicircular canal and the origin of the gnathostome characteristics

EVOLUTION AND DEVELOPMENT, Issue 4 2000
Sylvie Mazan
SUMMARY The horizontal semicircular canal of the inner ear is a unique feature of gnathostomes and is predated by the two vertical semicircular canals, which are already present in lampreys and some fossil, armored jawless vertebrates regarded as close relatives of gnathostomes. Inactivation in mice of the orthodenticle -related gene Otx1 results in the absence of this structure. In bony fishes and tetrapods (osteichthyans), this gene belongs to a small multigene family comprising at least two orthology classes, Otx1 and Otx2. We report that, as in the mouse, xenopus and zebrafish, Otx1- and Otx2 -related genes are present in a chondrichthyan, the dogfish Scyliorhinus canicula, with an Otx1 expression domain in the otocyst very similar to those observed in osteichthyans. A strong correlation is thus observed in extant vertebrates between the distribution of the horizontal semicircular canal and the presence of an Otx1 ortholog expressed in the inner ear, which supports the hypothesis that the absence of this characteristic in Otx1 -/- mice may correspond to an atavism. The same conclusion applies to two other gnathostome-specific characteristics also deleted in Otx1 -/- mice, the utriculosaccular duct and the ciliary process. Together with functional analyses of Otx1 and Otx2 genes in mice and comparative analyses of the Otx gene families characterized in chordates, these discoveries lead to the hypothesis that some of the anatomic characteristics of gnathostomes have appeared quite suddenly and almost simultaneously in vertebrate evolution, possibly as a consequence of gene functional diversifications following duplications of an ancestral chordate gene. [source]

Timing primate evolution: Lessons from the discordance between molecular and paleontological estimates

EVOLUTIONARY ANTHROPOLOGY, Issue 4 2008
M. E. Steiper
Abstract The molecular clock has become an increasingly important tool in evolutionary biology and biological anthropology. Nevertheless, a source of contention with respect to this method is the frequent discordance with fossil-based estimates of divergence times. The primate radiation is a case in point: Numerous studies have dated the major primate nodes (reviewed in Steiper and Young,1, 2) and there are many instances where molecular and fossil-based estimates of divergence times differ (Fig. 1). Some investigators have recently focused on phenomena such as stratigraphic dating, the stochastic nature of molecular time estimates, and other sources as potential biases in molecular clock estimates.3, 4 In this paper we do not focus on accuracy or statistical error; rather, we argue that discordance is a predictable phenomenon that provides valuable information about the tempo and mode of primate molecular and morphological evolution. Using this perspective, we reexamine the principal theoretical and methodological factors that lead to discordance between molecular and fossil estimates of the origins of taxa and discuss how a better understanding of these factors can help to improve our understanding of primate evolution. [source]

Lesbosoxylon gen. nov., eine neue Morphogattung mit dem Typus Lesbosoxylon ventricosuradiatum sp. nova aus dem Tertiär der Insel Lesbos, Griechenland

FEDDES REPERTORIUM, Issue 1-2 2010
Herbert Süss Professor Dr.
Für Protopinaceae-Hölzer aus dem Tertiär von Lesbos mit der Merkmalskombination "nur vertikale Harzgänge und große Holzstrahlen mit Idioblast-artigen Zellen" wird die Morphogattung Lesbosoxylon gen. nov. aufgestellt und der Typus L. ventricosuradiatum sp. nova beschrieben. Die mit dieser Merkmalskombination von Süss & Velitzelos (1994, 2009) als Pinoxylon -Arten der Insel Lesbos beschriebenen Fossilien werden zu Lesbosoxylon gestellt. Der Erhaltungszustand des Fundstücks und die Besonderheiten der Morphogattung Lesbosoxylon gen. nov. werden in eigenen Kapiteln besprochen (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Lesbosoxylon gen. nov., a new morphogenus with the typus Lesbosoxylon ventricosuradiatum sp. nova from the Tertiary of the Isle of Lesbos, Greece For Protopinaceae-woods from the Tertiary of Lesbos with the combination of features "only vertical resin channels and big rays with idioblast-like cells" the morphogenus Lesbosoxylon gen. nov. are put up and the typus L. ventricosuradiatum sp. nova described. The fossils described by Süss & Velitzelos (1994, 2009) as Pinoxylon -species with this combination of features are now placed to Lesbosoxylon. The maintenance of the fossil and the details of the morphogenus Lebosoxylon are described in separate chapters. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Major discoveries on the dermal skeleton of fossil and Recent polypteriforms: a review

FISH AND FISHERIES, Issue 2 2001
Jacques Daget
Abstract Following the discovery of the first living polypterid, Polypterus bichir, in 1802, almost two centuries later we now know of 15 living species (including four subspecies), 14 belonging to the genus Polypterus and one to the genus Erpetoichthys (Calamoichthys) all inhabiting intertropical Africa. The polypterid fossil record was for a long time reduced to some scarce, disarticulated bones, mainly scales, found in various African deposits covering a wider area than the actual geographical distribution. With the discovery, on one hand, of polypterid scales, vertebrae, dermal bones of the cranium and dorsal spiny rays in South America and, on the other hand, of scales and numerous dorsal spiny rays in Niger and Sudan, and two articulated fossils in Morocco, the story of the polypteriforms has revealed some of its mysteries. The discovery of isopedine between dentine and bony basal plate in the scales of living and fossil polypterid species is considered a synapomorphy of the group, and has been an important aid in discriminating polypterid scales from other ganoid scales. A review of the main findings during the last 20 years is presented. [source]