Fossil Forms Research Articles

Sexual dimorphism in a new species of the actinopterygian Peltopleurus from the Triassic of northern Italy

The new species Peltopleurus nuptialis is described on the basis of several well preserved specimens from the uppermost Ladinian Kalkschieferzone of Ca’ del Frate. This new species is characterized by small size and the presence of hook‐like fulcra on all fins except the caudal, and by tubercles on the rostral and nasal bones interpreted as secondary sexual traits. There is also a modified anal fin in supposed males, which probably acted as a gonopodium, pointing to a strong sexual dimorphism. A distinctive morphological variability seems to characterize peltopleurids: a comparison with groups of living fishes also showing morphological plasticity and sexual dimorphism is given in order to hypothesize similar behaviours and adaptations in the fossil forms.

Implications of fossil conifers for the phylogenetic relationships of living families

Fossils have played a central role in our understanding of the evolution of conifers. Interpretation of the seed cone as a compound strobilus and the homologies of the ovuliferous scales of modern conifers with the axillary dwarf shoot of Pennsylvanian forms are based on fossils. Similarly, early evolutionary trends involving the reduction, fusion, and planation of the fertile and sterile elements of the axillary dwarf shoot, leading to structures characteristic of modern families, are documented in Late Permian and Triassic conifers. However, a phylogeny elucidating the derivation of modern families from fossil forms based on shared derived features has been elusive.

İnsanın Evrim Süreci ve En Eski Kültürleri

Philogynetically, man is a member of t/ie zoological order Primates. In spite of the fact that different fossil forms had existed in the past, today he is represented only with n. single species- Homo sapiens- Contrary to aU the other living organisms, man's evolution was not only biological but also cultural. According to the author, man's evolution proper starts with Ardipithecus rant id us about 4.500.000 million yeais B.P. and going through a number of evoiutionaiy phases, reaches its present stage (Homo sapiens sapiens) some 50/40.000 years ago. His earliest cultural ivmains so far discovered. Oldowan tools, go back to some 2.500.000years ago. As of today, the cradle of mankind seems to be Africa but first with Homo erectus to occupy the rost of the Old World (i.e. Asia and Europe), later Homo sapiens sapiens had inhabited the continents of Australia. Americas and the rest of the world. Starting with the Lower Paleolithic (about 400.000 years ago as recently evidenced at the cave of Yarimburgaz). nil the major phases of Pulcoiithics arc icpi-csented in Turkey.

Introduction to the Symposium: What is Evolutionary Physiology?

Organisms in natural populations possess a number of physiological and morphological traits that appear to increase fitness in the natural environment. For example, with regard to cold tolerance these include long fur in Arctic mammals, subcutaneous fat in marine mammals, glycoprotein antifreezes in Antarctic fishes, and the capacity to hibernate in rodents subjected to long winters. Physiological ecologists have long been concerned with elucidating such characters and demonstrating their significance for the survival of organisms in the natural environments (Schmidt-Nielsen, 1990; Bartholomew, 1987). It is assumed that the presence of these traits in extant populations is the result of evolution of the traits in question. It is axiomatic that the adaptive traits evolved under selective pressures favoring organisms that are more fit in the corresponding environment. Considerable insight has been gained over the past two centuries regarding patterns of morphological evolution (Lauder, 1996). Morphological traits are often easily quantified and, if properly chosen, they are accessible in ancestral and extinct species in the form of preserved specimens and fossils. Even with these advantages, the picture emerging from the study of evolution of morphological traits is complex. The importance of genetic pleiotropies and phylogenetic constraints in contorting straightforward evolutionary progress is becoming clear. These present significant challenges to ecologists and evolutionary biologists in their attempts to understand the evolution of life history traits (Rose and Lauder, 1996).

The relationship between climate and rock glacier distribution in the ben ohau range, new zealand

Landforms of ice and debris transport marginal to the glacierized zone of the Southern Alps, New Zealand, have been classified into debris‐covered glaciers, cirque floor lobes, and talus‐derived rock glaciers. Mapping of fossil and active landforms reveals a zonation within the Ben Ohau Range in terms of both landform type and activity status. The dominant distinction of active forms is between relatively ice‐rich forms (glacial origins) in the humid north and relatively debris‐rich forms (periglacial origins) in the more arid south. A secondary altitudinal zonation distinguishes currently or recently active forms at high elevations from fossil forms at lower elevations. Estimates of mean annual precipitation and of the altitude of the –2°C mean annual isotherm indicate that glaciers and active talus rock glaciers are located within the climatic boundaries identified for the European Alps. However, many fossil forms also occur within these boundaries where cirques are broader and shallower. These findings confirm earlier suggestions that permafrost occurs in the Southern Alps, but is restricted to a narrow zone above 2000 m. The study demonstrates the importance of relative ice‐to‐debris fluxes in determining the developmental pathways of landform genesis over both space and time.

Carpology, Seed Anatomy and Taxonomic Relationships ofTetracentron(Tetracentraceae) andTrochodendron(Trochodendraceae)

This study of the anatomy and morphology of fruits and seeds ofTrochodendron aralioidesSieb. & Zucc. andTetracentron sinenseOliv. has revealed significant new data in the understanding of their systematic and phylogenetic relationships. The correction of the seed coat type forTrochodendronas (endotestal-) exotegmic (instead of endotestal) and forTetracentronas exotegmic (instead of endotestal) documents a large morphogenetic gap between these putatively advanced types of seed coat and those of other Hamamelididae. Among primitive angiosperms, the combination of a few-layered testa with a markedly differentiated endotesta and a relatively multilayered tegmen with a sclerified tracheidal exotegmen occurs only in the seeds of the family Dilleniaceae (Dilleniales), which occupies a somewhat isolated position within the subclass Dilleniidae. The former features, as well as characteristics of node anatomy, anther dehiscence, pollen, floral and fruit morphology, suggest a close relationship between Trochodendrales and Dilleniales. The intermediate position of Trochodendrales between Magnoliidae and Hamamelididae is rejected, and Trochodendrales are taxonomically transferred from Hamamelididae to Dilleniidae in the rank of a distinct superorder: Trochodendranae. It is considered necessary to reform further the systematics of the artificial complex of the so-called ‘lower’ Hamamelididae and Dilleniidae. The suggested relationship betweenTrochodendronand fossil forms such asTrochodendroides, Nordenskiöldia, TrochodendrocarpusandTrochodendrospermumis also found untenable in light of the carpological survey of modern forms presented here.

Technical note: Modeling primate occlusal topography using geographic information systems technology.

Most functional analyses of primate tooth form have been limited to linear or area measurements. Such studies have offered but a limited glimpse at differences in occlusal relief among taxa. Such differences in dental topography may relate to tooth function and, so, have considerable implications for the inference of diet from fossil teeth. In this article, we describe a technique to model and compare primate molars in three dimensions using Geographic Resources Analysis Support System (GRASS) software. We examine unworn lower second molars of three extant hominoids with known differences in diet (Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus), and two fossil forms, (Afropithecus turkanesis and Dryopithecus laietanus). First, we obtained approximately 400 landmarks on the occlusal surfaces of each tooth using an electromagnetic digitizer. Raster "terrain models" of occlusal surfaces were then created by interpolation of the coordinate data. We used GRASS terrain analysis automated techniques to quantify the volumes and slopes of individual cusps. We also used the GRASS watershed technique to identify the volume of liquid that would accumulate in each tooth's basin (a measure of basin area), and the directions and intensity of drainage over the occlusal surface. In sum, GRASS shows considerable potential for the characterization and comparison of tooth surfaces. Furthermore, techniques described here are not limited to the study of teeth, but may be broadly applicable to studies of skulls, joints, and other biological structures.

Cryptic Species in a “Living Fossil” Lineage: Taxonomic and Phylogenetic Relationships within the GenusLepidurus(Crustacea: Notostraca) in North America

Lineages which exhibit little morphological change over geologic time are evolutionarily and ecologically interesting, but often taxonomically difficult. For some morphologically conservative groups, not only is it almost impossible to identify significant changes in fossil forms over time, but the relationships among extant populations are often poorly understood due to lack of known characters which clearly delimit species. Notostracan crustaceans are a classic example of such “living fossils.” The paradoxical characteristics of long-term stasis in gross morphology and hypervariability of many individual morphological characters make notostracans an especially taxonomically challenging group. We used molecular and biochemical techniques to investigate the taxonomic and phylogenetic relationships of four nominal species within the genusLepidurusin North America, three of which had been alternately abandoned, resurrected, or synonymized under a single, globally distributed morphospecies since their original descriptions in the 1800s. Data from a 330-bp sequence of the mitochondrial 12S rDNA gene and from nine allozyme loci consistently indicate five highly genetically divergent clades among the populations we used to represent the four nominal species. Diagnostic molecular characters, magnitudes of genetic divergence among clades, and the fact that these genetically distinct clades have broadly overlapping geographical ranges strongly suggest that the five clades are reproductively isolated species. One of the nominal species (L. couesii) is not monophyletic, but rather consists of two species which are not sister taxa. The other three nominal species (L. lemmoni, L. packardi,andL. bilobatus) are supported as valid phylogenetic species. The best current hypothesis for phylogenetic relationships among the five species is provided by a simultaneous analysis of both 12S rDNA and allozyme data, which placesL. bilobatusandL. “couesii”-1 as sister taxa andL.“couesii”-2 as the most basal of all theLepidurusspecies included in this study. These results point to the existence of cryptic species within the current classification scheme forLepidurus,the need for further taxonomic work within the Notostraca in general, and the role that genetic techniques can play in clarifying the systematics of morphologically conservative groups.

THE EVOLUTION OF FAIRNESS NORMS

The evidence is strong that modern hunter-gatherer societies approximate the Marxian ideal in which each contributes according to ability and receives according to need. It has been argued that such a form of social organization can be explained by neither reciprocity nor kinship. Attempts to found evolutionary social contract theories on sociobiological principles therefore seem doomed from the outset, since the same authors believe that modern foraging societies preserve in fossil form the type of social contract from which all later social contracts evolved. This paper outlines the importance of the issue to my own social contract theory. It then uses game-theoretic arguments to argue that reciprocity and kinship are actually the twin pillars that maintain the quasi-utilitarian social contracts of modern hunter-gatherer societies. Finally, the idea that modern foragers have social contracts similar to their prehistoric ancestors is questioned.

Physiological Progenesis in Cephalopod Molluscs.

The coleoid cephalopods (cuttlefish, squid and octopus) arose from their shelled ancestors during the late Devonian; they diversified in the Jurassic but did not radiate substantially until the Tertiary. Since then they have coevolved with the fish (1). Squid are less efficient energetically than fish (2) but have survived alongside them by evolving highly opportunistic reproductive and feeding strategies (3, 4) as well as rapid jetting and inking for escape and defense. Little is known about the life history strategies of the fossil forms, but the only surviving shelled cephalopods, the nautiluses, have relatively long life spans and are iteroparous; that is, in common with most members of other molluscan classes, they breed more than once during their lives. In contrast, all other living cephalopods are generally short lived (usually 1 year) and have monocyclic reproduction and a semelparous life history. The short-lived semelparous coleoids are typified by the mid-latitude ommastrephid squid which provide the basic model considered here. This family is relatively primitive and biologically well known. Its members are essentially monocyclic, but some species may spawn their eggs in batches (5, 6) although there is no evidence of this in laboratory spawnings (7). Most loliginid squid, at least in temperate seas, have a life cycle similar to that of the ommastrephids, despite having different spawning habits. A comparison of the lifetime energetics and growth pattern of benthic, iteroparous molluscs with those of the pelagic, semelparous ommastrephids shows that, although some squid may attain a length of 1 m or more, the allocation of their energy resource among growth components is essentially characteristic of the early life, especially the first year, of iteroparous forms. The life-time energy budget of these squid thus seems to have evolved by physiological progenesis, a process in which maturation is accelerated while other aspects of the physiology are more typical of the juvenile.

Calcareous Nannofossil Genus Scyphosphaera: Structure, Taxonomy, Biostratigraphy, and Phylogeny

Calcareous Nannofossil Genus Scyphosphaera: Structure, Taxonomy, Biostratigraphy, and Phylogeny

The type specimens (Middle Cambrian) of the trace fossil Archaeonossa Fenton and Fenton

The original description of Archaeonossa, from beds considered Early Cambrian but now dated as early Middle Cambrian, included at least two unrelated forms of trace fossils. The ichnogenus and the type ichnospecies are redefined, a lectotype is designated, and the type material is reiilustrated, along with topotype material from Yoho National Park, British Columbia. Although this trace fossil was originally attributed to movement by a gastropod, it is concluded, on the basis of restudy, that the type occurrence should not be used as evidence of activity by Gastropoda.

Endemic African mammals shake the phylogenetic tree.

The order Insectivora, including living taxa (lipotyphlans) and archaic fossil forms, is central to the question of higher-level relationships among placental mammals. Beginning with Huxley, it has been argued that insectivores retain many primitive features and are closer to the ancestral stock of mammals than are other living groups. Nevertheless, cladistic analysis suggests that living insectivores, at least, are united by derived anatomical features. Here we analyse DNA sequences from three mitochondrial genes and two nuclear genes to examine relationships of insectivores to other mammals. The representative insectivores are not monophyletic in any of our analyses. Rather, golden moles are included in a clade that contains hyraxes, manatees, elephants, elephant shrews and aardvarks. Members of this group are of presumed African origin. This implies that there was an extensive African radiation from a single common ancestor that gave rise to ecologically divergent adaptive types. 12S ribosomal RNA transversions suggest that the base of this radiation occurred during Africa's window of isolation in the Cretaceous period before land connections were developed with Europe in the early Cenozoic era.

Observations on “cryoplanation” benches in Antarctica

A series of benches on nunataks of Alexander Island (Antarctica) are described. An increase in bench size with distance away from the retreating glacier suggests an age spectrum. The benches have thermal contraction cracks (in bedrock) on shallower, upper sections of the risers as well as salt encrusted runnels on the steeper lower section of the tread. The benches also show a distinct orientational preference (orientated to the north through to west) and, from first principles, these seem to be the aspects with optimal freeze-thaw cycles and temperatures conducive to thermal stress fatigue. The extensive dilatation associated with the retreating glaciers is thought to play a significant role in the origin and development of the benches as the combination of extensive jointing and optimal process conditions are thought to constrain where benches begin. The jointing, aided by the thermal contraction cracking, then facilitates extension and continued weathering of the treads. It would appear that these benches are examples of so called “cryoplanation terraces” that have been reported as fossil forms in Europe and North America. The study of such active forms in the Antarctic may provide good analogues for fossil features found in the Northern Hemisphere.

A defence of the calcichordates

Peterson (1994, Short Courses in Paleontology 7, Pal. Soc. & Univ. Tennessee; 1995, Lethaia 28) has claimed that the calcichordate theory of the origin of chordates can be dismissed on purely methodological grounds, without evaluating the anatomy of the calcichordates. He claimed this on the basis of his finding that the interrelationships for extant deuterostomes obtained by a PAUP analysis were not altered by including calcichordate fossils in the analysis, allegedly coded according to the anatomical interpretations of the calcichordate theory. This result, however, was due (1) to acceptance of dubious homologies among extant deuterostomes, (2) to reliance, when asserting that the fossils made no difference, on a majority-rule tree based on 13 equal-shortest trees; and (3) to the use of numerous multi-state characters in coding, which had the effect of denying, a priori, many of the homologies claimed by the calcichordate theory between fossil and extant forms. When these errors are corrected, a new PAUP analysis yields a tree consistent with the calcichordate theory. Peterson's claim therefore fails.

Paleontology and Chronology of Two Evolutionary Transitions by Hybridization in the Bahamian Land Snail Cerion

The late Quaternary fossil record of the Bahamian land snail Cerion on Great Inagua documents two transitions apparently resulting from hybridization. In the first, a localized modern population represents the hybrid descendants of a 13,000-year-old fossil form from the same area, introgressed with the modern form now characteristic of the adjacent regions. In the second case, a chronocline spanning 15,000 to 20,000 years and expressing the transition of an extinct fossil form to the modern form found on the south coast was documented by morphometry of fossils dated by amino acid racemization and radiocarbon. Hybrid intermediates persisted for many thousands of years.

A description ofSiphonophora portoricensisBrandt (Diplopoda: Siphonophorida: Siphonophoridae), with a Catalogue of Ordinal Representatives in the New World

Data on geographical distribution are provided for S. portoricensis Brandt, the type species of Siphonophora Brandt and the oldest species-group name in the genus, family, and Order; it appears to occur throughout Puerto Rico. It is characterized by fusion of the distal three podomeres of the anterior gonopods, which are sublinear in shorter, less mature males and bend caudad for varying lengths in longer individuals. In the New World, the Siphonophorida is represented by both families, the Siphonorhinidae by one genus and one species, Illacme plenipes Cook and Loomis, from San Benito County, California, and the Siphonophoridae by 10 genera, six monotypic, 66 extant nominal species, and one subspecies; two fossil species of Siphonophora have been proposed along with an unnamed fossil form of Siphonocybe Pocock. The following new combinations are officially recorded: Columbianum gracilicornis (Carl), Columbiozonium pearsei (Chamberlin), Cordillerium fuhrmanni (Carl), Yucatanium sabachana (Chamberlin), and ...

Stability in meaning and content of taxon names: an evaluation of crown-clade definitions

Most well-known taxon names have traditionally referred to groupings that contain fossil organisms lying outside the diversity of living forms, e. g. Aves has traditionally included Archaeopteryx , and Mammalia, Morganucodon . Many systematists have recently advocated applying well-known taxon names to more restricted groups termed ‘crown-clades’: monophyletic groups bounded by extant forms. These definitions change substantially the contents and diagnostic characters of many of the most familiar taxon names, e. g. under crown-clade definitions, Archaeopteryx is excluded from Aves, and Morganucodon from Mammalia. It has been suggested that crown-clade definitions are more stable than traditional, more-inclusive definitions, in terms of both meaning (the association of a particular taxon name with a clade stemming from a particular ancestor) and content (determination of which organisms belong in a particular named clade). Crown-clades have also been suggested to be more highly corroborated than traditional, more-inclusive clades. These arguments are here found to be poorly supported. All phylogenetic (ancestor-based) definitions of taxon names (e. g. ‘ancestor X, and all its descendants’) are equally stable in meaning, in that the ancestor specified, and thus, the boundaries of the clade, will always remain the same regardless of changes in phylogenetic hypotheses. It does not matter whether the specified ancestor is the most recent common ancestor of living forms (a crown-clade definition), or the common ancestor of a more-inclusive group. Crown-clades are also not more stable in content, or highly corroborated, than more-inclusive clades. This is because the position of certain fossil forms within or outside both types of clades is often uncertain. Many workers have interpreted soft anatomical features as synapomorphic of crown-clades, but not of more-inclusive clades, thus arguing that crown-clades are more highly corroborated. However, interpreting these soft anatomical features as synapomorphies of the crown clades is merely an arbitrary convention: these soft anatomical features might diagnose a more-inclusive clade. Thus, crown-clade definitions of taxon names are not superior to more-inclusive definitions in terms of stability in meaning or content. There is therefore no compelling reason to radically redefine familiar taxon names such as Aves, Mammalia and Tetrapoda to apply to crown-clades. Instead, it is possible (and probably less confusing) to attach such well-known taxon names to more-inclusive groups that closely approximate ‘traditional’ usage.

Viewing Velvet Worms in Amber

The velvet worms, soft-bodied invertebrates that today roam the forest floors of the Southern Hemisphere, have been proposed to be an evolutionary link between the segmented worms, or annelids, and the wildly diverse arthropods. But the velvet worms' family relations have long been a source of debate, in part because their fossil record is so spotty. A Report on page 1370 of this issue presents new specimens, 20 million to 40 million years old and preserved in amber, that may link even more ancient fossil forms and the living creatures.

Glacier debris accumulation and sediment deformation influenced by permafrost: examples from Svalbard

The formation of ice-cored moraines and push moraines is discussed in the light of glacier thermal regime and glacier dynamics. Data from two Svalbard valley glaciers, Erikbreen and Usherbreen are presented. On Erikbreen, fossil forms were investigated, while on Usherbreen a surge ending in 1985 caused the formation of new push-moraine ridges. The push moraines are considered as a soil-mechanical problem. In a theoretical discussion the stress transmitted by the glaciers to the proglacial sediments is estimated. On Usherbreen, the compressive flow results in deformation both in old front ridges and in undisturbed frozen sediment layers in the front sandur. Thus, folding, thrust faulting and overriding all occur. Deformation of proglacial sediments seems to be highly dependent on the mechanical properties of the sediments. The sediments are strongly influenced by permafrost conditions. The unfrozen water content in the sediments governs the deformability, which in turn is partly determined by pore-water salinity. The distribution of push moraines in Svalbard is therefore restricted to areas below the Holocene marine limit, and they occur most frequently in areas of sedimentary bedrock. This study concludes that push moraines and ice-cored moraines require permafrost conditions. Push-moraine ridges are not formed in direct contact with the glacier, so they are geomorphologically not moraines, but deformed permafrost sediments. A model for glacier debris sedimentation and deformation is outlined for Svalbard glaciers ending on land.