bluuebunny/crossref_metadata_2025 huggingface dataset:
Completeness of the mammalian fossil record in the Iberian Neogene
Authors: Alba David M. , Agustí Jordi , Moyà-Solà Salvador
Published: July 2006

We infer the absolute completeness of the mammalian fossil record of the Iberian Neogene, from a compiled database of preserved stratigraphic ranges for both species and genera and by means of the analytical tools developed by Foote and Raup (1996). We conclude that the mammalian fossil record from the Neogene of the Iberian Peninsula is very complete (more than 75% at the specific level, and more than 90% at the generic one), being a good indicator of how complete the record of terrestrial organisms can be at least under certain favorable conditions. Comparison with previously published results for well-known marine invertebrates indicates that the continental Iberian Neogene record is not significantly less complete, thus raising doubts about the importance of more episodic deposition in continental environments. It remains to be seen if continental faunas in general are as complete as the marine invertebrate record.
Differences in growth rate and environment between Tertiary and QuaternaryCrassostreaoysters
Authors: Kirby Michael Xavier
Published: July 2006

Many Tertiary species ofCrassostreaappear to have inhabited shallow-marine environments where they produced extremely large and thick shells. In contrast, livingCrassostreaspecies are restricted primarily by marine predation to brackish, hypersaline, and intertidal environments where they produce comparatively smaller and thinner shells. IfCrassostreapopulations have used estuarine environments as a refuge from predation since the Cretaceous, then their presence in fully marine environments after the Cretaceous is puzzling. In order to interpret differences in environment and shell size, I examined the paleoecology and sclerochronology of two marine and two estuarine populations. Results are consistent with the hypothesis that thicker shells in TertiaryCrassostrea titandeterred increased exposure to fully marine predation. Life spans and growth rates estimated from annually formed growth increments show thatC. titangrew significantly faster in shell thickness, as well as lived two to three times longer, than QuaternaryCrassostrea virginica.Similar or lower valve-height growth rates inC. titan, as well as thinner shell walls in the attachment area, are consistent with exposure to marine predation, but not with alternative factors, such as higher salinity or alkalinity. Thicker valves inC. titanresulted from the successive addition of chalky deposit layers, in contrast toC. virginicavalves, which contain significantly less of this unusual shell structure. A high incidence of incomplete drill holes in juvenileC. titanshells demonstrates that their thick valves were successful in deterring muricid predation. The association ofC. titanwith other large suspension feeders (barnacles and pectenids), as well as with phosphatic-pellet sediments, suggests that elevated planktic productivity may have supported this reefal community and enabledC. titanto grow thicker shells. The occurrence of both shallow-marine and estuarineCrassostreasince the Cretaceous raises the possibility that estuaries have served as refugia from which populations have dispersed into fully marine environments multiple times through the Cenozoic.
Pleistocene adaptive radiation in Globorotalia truncatulinoides: genetic, morphologic, and environmental evidence
Authors: de Vargas Colomban , Renaud Sabrina , Hilbrecht Heinz , Pawlowski Jan
Published: July 2006

Globorotalia truncatulinoides is an extant species of planktic foraminiferans commonly used for stratigraphic and paleoenvironmental analyses. It originated ∼2.8 m.y. ago in subtropical areas of the South Pacific, spread to all subtropical and temperate regions of the world ocean, and expanded its range to southern subantarctic waters between 500 and 200 Ka. The wide geographic distribution of G. truncatulinoides is associated with a latitudinal morphological variability considered as an ecophenotypic variation within a single species. Here, we present the first molecular, morphological, and ecological evidence that G. truncatulinoides corresponds to a complex of four genetic species adapted to particular hydrographic conditions. The different species are separated by significant genetic distances in several ribosomal genes (SSU, ITS-1, 5.8S, ITS-2). Species 1 and species 2 characterize subtropical waters, species 3 is abundant exclusively in the Subantarctic Convergence, while species 4 inhabits subantarctic waters. By using an absolute molecular clock, we deduce the time of divergence between the subtropical and frontal/subantarctic species at ∼300 Ka, which is in agreement with stratigraphic data and suggests an adaptive radiation of the species allowing it to colonize the nutrient-rich and cold subantarctic waters. This genetic dichotomy is associated with a morphological differentiation identified using outline analysis. Species of the same regions are more similar in test shape but can be distinguished by coiling direction. The evolutionary patterns recognized here by combining DNA and morphological analyses from plankton-tow specimens mirror and allow a new interpretation of the data available from Recent sediments. They highlight the importance of adaptation and heterochronic processes, leading to cryptic speciation, in planktic foraminifera.
A multiplicative multifractal model for originations and extinctions
Authors: Plotnick Roy E. , Sepkoski J. John
Published: July 2006

Recent works have suggested that the fossil record exhibits a fractal structure; i.e., that processes, such as extinction, follow a power-law size distribution and their time series show a 1/f power spectrum. This structure has been used as evidence that evolutionary dynamics are an example of a self-organized critical (SOC) process. We have reexamined this claim by analyzing a detailed record of marine genus-level extinctions and originations. Our results indicate that neither extinctions nor origination metrics show the power-law size distribution or a 1/f power spectrum characteristic of SOC and related models. We also believe that the underlying assumptions of SOC are incompatible with our understanding of the processes controlling macroevolutionary patterns.

Statistical analyses of the data sets are compatible, however, with the presence of multifractal self-similarity in both records, consistent with a hierarchical and multiplicative generating process. This model assumes that multiple causal mechanisms, acting over many spatial and temporal scales, interact to promote or inhibit originations and extinctions. In this view, the same event can have quite different impacts depending on the state of the biotic or physical system at the time that it occurs. This may at least partially explain such phenomena as the imperfect correlation between eustatic sea-level changes and macroevolutionary processes and the apparent nonlinear response of biotic systems to bolide impacts.
Digital reconstruction of calcified early metazoans, terminal Proterozoic Nama Group, Namibia
Authors: Watters Wesley A. , Grotzinger John P.
Published: July 2006

A method is presented for the digital reconstruction of weakly calcified fossils within the Nama Group, Namibia. These recently described fossils (Grotzinger et al. 2000) are preserved as calcitic void-fill in a calcite matrix, and individual specimens cannot be freed by conventional techniques. The technique presented here has several integrated steps: (1) the analysis of cross-sections of fossil specimens, (2) the construction of a three-dimensional “tomographic” model that is assembled from the cross-sections, (3) the development of an idealized mathematical model based upon geometric parameters measured from the tomographic model, and (4) the visualization of randomly oriented cross-sections through the mathematical model, which can be compared with fossil cross-sections in outcrop.

In this procedure, rocks containing the fossils are ground and digitally photographed at thickness intervals of 25 μm. A battery of image-processing techniques is used to obtain the contour outlines of the fossils in serial cross-sections. A Delaunay triangulation method is then used to reconstruct the morphology from tetrahedrons which connect the contours in adjacent layers. We found that most of the fossils represent a single morphology with some well-defined characters that vary slightly among individual specimens. This fossil morphology was described by Grotzinger et al. (2000) as Namacalathus hermanastes. A mathematical description of the morphology is used to obtain a database of randomly oriented synthetic cross-sections. This database reproduces the vast majority of cross-sections observed in outcrop.
Modern phylogenetics in paleontology: comments on Vermeij 1999
Authors: Brochu Christopher A. , Bryant Harold N. , Theodor Jessica M. , O'Leary Maureen A. , Adrain Jonathan M. , Sumrall Colin D.
Published: July 2006

In a recent Matters of the Record, Vermeij (1999) identifies what he regards as a fundamental problem with cladistic analysis. “The phylogenetic method,” he states (p. 431), “derives phylogeny in one part of the tree by relying on character-taxon relationships in another part of the tree, in direct violation of the principle that clades, once they have diverged from each other, are independent of one another.” Vermeij fails to appreciate the distinction between pattern-based cladograms, which are hierarchies founded on homology hypotheses, and logically contingent, process-based trees, which are depictions of temporal evolution. As a result, he treats cladograms as literal and direct estimates of evolution and thus confuses the treatment of characters and taxa in parsimony analyses with biological processes and interactions.
Timeless characters: a response to Vermeij (1999)
Authors: Geiger Daniel L. , Fitzhugh Kirk , Thacker Christine E.
Published: July 2006

The use of geologic age or range data in phylogenetic reconstruction is strongly debated (Cracraft and Eldredge 1979; Smith 1994; Fox et al. 1999; Heyning and Thacker 1999). Vermeij (1999) voiced concern regarding ‘rectangular data matrices’ and concluded that stratigraphic data are particularly suitable for improving phylogenetic inference. We find two major problems with his conclusion and question the validity of stratocladistics or any other phylogenetic method incorporating temporal data (e.g., Wagner 1998).
Time and the comparative method
Authors: Vermeij Geerat J.
Published: July 2006

Phylogenetic methodology has always attracted more than its share of controversy, so I expected critical responses to my 1999 piece on the evolutionary implications of character-taxon matrices. In that piece, I argued that the topology of a clade, as inferred from cladistic parsimony analysis of a rectangular matrix of characters and taxa, is influenced by all the taxa considered, including those that fall outside the clade in question. The inferred pattern of branching in the clade is therefore statistically influenced by and dependent on the inferred evolutionary pattern among the other taxa. This dependence is at odds with the principle that, once sister-groups of eukaryotes have diverged, their subsequent pathways of evolution are independent of each other. I also suggested that, along with evidence from ontogeny, times of appearance of taxa as inferred from stratigraphic data be allowed to influence interpretations of which characters are primitive and which are derived.
Beyond Phylogeny Reconstruction—Tree-Based Analyses in Paleontology: Foreword
Authors: Park Lisa , Smith Andrew. B.
Published: July 2006

The reconstruction of phylogenies using cladistic methods is a powerful and well-established tool for evolutionary biologists and paleobiologists. Indeed, the construction of rigorous phylogenetic hypotheses has become widely accepted as an essential first step in the analysis of historical patterns for both extant and extinct organisms. In the past few years, there has arisen a healthy and constructive debate as to the exact methods that will lead to the most accurate tree (for example whether statistical inference or stratigraphic information has any part to play in phylogenetic reconstruction). Although important, this debate has tended to focus on the problems of tree construction and divert attention away from the applications of tree-based research. The construction of a phylogeny is, after all, only a first step, and phylogenetic trees provide the starting point from which to address a wide range of interesting biological and geological topics.
The imbalance of paleontological trees
Authors: Harcourt-Brown Katherine G. , Pearson Paul. N. , Wilkinson Mark
Published: July 2006

One of the most extensively studied aspects of phylogenetic tree shape is balance, which is the extent to which nodes divide a tree into clades of equal size. Several authors have stressed the importance of tree balance for understanding patterns of evolution. It has been remarked that paleontological studies commonly produce very unbalanced trees (also called pectinate cladograms or “Hennigian combs”). This claim is tested here by comparing the balance of 50 paleontological trees and 50 neontological trees, all taken from the recent literature. Each tree was reanalyzed from the published data matrix to ensure its accuracy. The results confirm that paleontological trees tend to be more imbalanced than neontological trees.

That paleontological trees are more imbalanced has been represented as a shortcoming of fossil data sets, but here it is argued that this is the expected result. Even under a simple Markovian model in which all speciations and extinctions occur randomly and with equal probability in all parts of the tree, trees based on taxa from a single time period (e.g., the present day) are generally more balanced than trees based on all taxa that ever existed within the clade. Computer simulation is used to calculate the expected balance and standard deviation of trees for up to 40 terminal taxa over the entire history of a model clade. The balance is measured using Colless's index, Ic, and the expected balance conforms well with published paleontological trees. The study underlines the difficulty of applying neontological tree statistics in paleontology.
How phylogenetic inference can shape our view of heterochrony: examples from thecideide brachiopods
Authors: Jaecks Glenn. S. , Carlson Sandra. J.
Published: July 2006

Heterochrony is considered to be an important and ubiquitous mechanism of evolutionary change. Three components are necessary to describe heterochrony: phylogenetic relationships, size and shape change, and timing of developmental events. Patterns and processes of heterochrony are all too often invoked before all three components have been investigated. Phylogenetic hypotheses affect the interpretation of heterochrony in three ways: rooting of a clade, topology of a clade, and character polarity. To study these effects we examined the distribution of shell microstructure, lophophore support structures, and body size in four different phylogenetic hypotheses of thecideide brachiopods (Triassic to Recent), a group of minute, cryptic, benthic marine invertebrates.

Thecideides are consistently monophyletic in experiments using terebratulide, strophomenate, and spire-bearing outgroups together and separately, varying ingroup membership, and experimentally withholding certain character complexes. Thecideide monophyly is also supported by bootstrap analysis. Hypotheses of heterochrony in thecideide origins and evolution are therefore not merely artifacts of classification and can be pursued further. Using either strophomenate or spire-bearing outgroups, TriassicThecospirais the most primitive thecideide. Trees constructed using terebratulide outgroups are rooted instead atEudesella, a taxon derived in every other phylogenetic reconstruction, and the Triassic thecideides occupy derived rather than primitive positions.

Our phylogenetic results support the traditional interpretation of the reduction or loss of the secondary fibrous shell layer as a paedomorphic pattern, whereas the evolution of lophophore support structures suggests a peramorphic pattern. Reduction in thecideide adult body size is gradual, phylogenetically, and results in an overall paedomorphic pattern. Heterochrony in these three character suites may play a role in the subsequent evolution of the clade, but apparently not in the origin of the clade, as is commonly thought. Heterotopy, rather than—or in addition to—heterochrony, may account for both the origin and evolution of the lophophore support structures and in the reduction and loss of the secondary shell layer. These phylogenetic hypotheses suggest that heterochrony can result from a complex mosaic of processes and provide specific, testable predictions about the processes responsible for producing the patterns, whether heterochronic or not. Categorizing an entire clade (such as thecideides), rather than individual characters, as globally paedomorphic may allow interesting peramorphic patterns in individual characters to be overlooked.
The role of phylogeny in quantitative paleobiological data analysis
Authors: MacLeod Norman
Published: July 2006

Phylogenies provide a rich source of information that should be exploited in designing quantitative hypothesis tests in paleobiological contexts. Viewing such data analysis problems through the prism of phylogenetically structured comparisons can help add realism and depth to paleobiological data-analysis strategies. Two examples of the importance of adopting a phylogenetic perspective are discussed. In the first example, a phylogenetic-comparative approach is used to test correlations between ecological, morphological, and biological characteristics of planktonic foraminifera. Results suggest that the presence of spines and photosynthetic symbionts in Neogene-Recent species are not adaptations to living in shallow-intermediate planktonic depth habitats. In the second, a phylogenetic-comparative approach is used to reveal the presence of morphological correlations with locomotor function in a mammalian carnivore data set. Paleontologists can play an active role in improving comparative data analyses by (1) helping to develop improved phylogenies, especially those that provide better estimates of branch lengths, and (2) helping to resolve a number of outstanding issues surround the question of ancestral character-state specification.
Sea-level change and rock-record bias in the Cretaceous: a problem for extinction and biodiversity studies
Authors: Smith Andrew. B. , Gale Andrew. S. , Monks Neale E. A.
Published: July 2006

The association between mass extinction in the marine realm and eustatic sea-level change in the Mesozoic is well documented, but perplexing, because it seems implausible that sea-level change could actually cause a major extinction. However, large-scale cycles of sea-level change can and do alter the ratio of shallow to deep marine continental-shelf deposits preserved in the rock record both regionally and globally. This taphonomic megabias alone could be driving patterns of first and last occurrence and standing diversity because diversity and preservation potential both change predictably with water depth. We show that the Cenomanian/Turonian faunal event in western Europe has all the predicted signatures expected if taphonomic megabias was the cause. Grade taxa terminating in pseudoextinction and Lazarus taxa are predominantly found in the onshore facies that disappear for extended periods from the rock record. Before other mass extinctions are taken at face value, a much more careful analysis of biases in the rock record needs to be carried out, and faunal disappearances need to be analyzed within a phylogenetic framework.
Global lability, regional resolution, and majority-rule consensus bias
Authors: Sumrall Colin. D. , Brochu Christopher. A. , Merck John W.
Published: July 2006

Evolutionary interpretation of paleontological patterns requires a hypothesis of phylogeny, but our phylogenetic hypotheses may not perfectly mirror organismal phylogeny. Tree summary methods less conservative than strict consensus may increase resolution, but these methods may present a biased summary of the full set of most parsimonious trees. When we fail to acknowledge all equally optimal topologies, we risk disregarding trees that are closer to the correct phylogeny. We discuss a case where two subsets of trees were recovered in the set of most parsimonious trees, each with a profoundly different interpretation of character evolution near the root of Echinodermata. This was caused by the presence of a bimodally labile taxon in the matrix with two different topological subsets, each equally parsimonious but differing in the number of consistent trees. Majority-rule consensus favors the subset with the largest number of trees consistent with the placement of the rogue taxon. This bias favors clusters not because of the biological implications of the tree, but on the basis of great inequality in the sizes of the islands of parsimony. We thus recommend that majority-rule consensus trees not be used to summarize the results of a phylogenetic analysis.
Endosymbiont change as a key innovation in the adaptive radiation of Soritida (Foraminifera)
Authors: Richardson Susan. L.
Published: July 2006

A phylogeny of 54 Recent and fossil species of Soritacea (Foraminifera) was used to test the hypothesis that endosymbiosis has driven the evolution of the clade. Endosymbiosis with photosynthetic eukaryotes is the plesiomorphic condition for the entire clade Soritacea. Living species dwell in tropical-subtropical, shallow-water habitats and are characterized by the possession of rhodophyte, chlorophyte, or dinophyte photosymbionts. Two distinct changes in endosymbiont type are recognized when endosymbiont type is mapped in the cladogram of Soritacea: (1) a change from rhodophyte to chlorophyte endosymbionts occurred in the stem lineage of the least inclusive clade containing New clade B, Orbiculinida, and Soritida; and (2) a change from chlorophyte to dinophyte endosymbionts occurred in the stem lineage of the least inclusive clade containing New clade G, New clade H, New clade I,Sorites, Amphisorus, andOrbitolites.When habitat and ontogeny are optimized on the cladogram of Soritida, the acquisition of dinophyte endosymbionts appears as a key innovation that facilitated a switch in habitat from free-living to attached living on nonphytal and phytal substrata. A subsequent change in the attached habitat from nonphytal to predominantly phytal (seagrasses and macroalgae) substrata is accompanied by a peramorphic trend in the megalospheric tests. The diversification (adaptive radiation) of the crown Soritida subclade resulted from the interplay between the acquisition of a key innovation (dinophyte endosymbionts) and the subsequent change in the ecology of the group (radiation to phytal substrates).
Rate heterogeneity in shell character evolution among lophospiroid gastropods
Authors: Wagner Peter. J.
Published: July 2006

Hypotheses about constraints, selection, and other evolutionary processes often predict different rates of change among different characters. For example, it is thought that gross soft anatomical characters change less frequently than do general shell characters. However, some shell characters on primitive gastropods, such as the sinus and selenizone, are thought to be linked to soft anatomy. If both premises are true, then selenizone/sinus characters should change less frequently than other characters. Workers also have documented active trends among gastropod shell characters. One explanation is a driven trend, where the rate of change in one direction (i.e., gain or loss, increase or decrease) is greater than the rate of change in the opposite direction.

Hypotheses about relative rates and biased change are tested here for lophospiroid gastropods. Likelihood analyses test whether hypotheses positing many different rates predict data significantly better than do hypotheses positing few rates. One tree-based approach assumes that a phylogeny is known and thus treats a tree as a model. A second tree-based approach treats phylogeny as an additional hypothesis. This multiparameter approach allows competing rate hypotheses to “assume” a phylogeny that maximizes their likelihoods.

Likelihood tests reject hypotheses of low rate heterogeneity among lophospiroid characters. The most likely hypothesis (which treats phylogeny as an unknown) posits seven rates, with biased changes among three characters (preferential reduction of both sinus depth and sinus width and preferential addition of ornament). The distribution of rates among different character classes is consistent with the prediction that characters associated with internal anatomy should show generally lower rates of change than those associated with gross shell morphology. Evaluating significance when contrasting hypotheses posit different phylogenies is problematic, but the difference in support (log-likelihood) is overwhelming. Even if a model phylogeny is used, we still reject all hypotheses using fewer than six rates and not invoking trends in sinus characters. Thus, it is difficult to avoid rejecting the hypothesis that shell characters are uniformly plastic.
Role of photosymbiosis and biogeography in the diversification of early Paleogene acarininids (planktonic foraminifera)
Authors: Quillévéré Frédéric , Norris Richard. D. , Moussa Issam , Berggren William. A.
Published: July 2006

Radiations are commonly believed to be linked to the evolutionary appearance of a novel morphology or ecology. Previous studies have demonstrated a close relationship between the evolutionary appearance of algal photosymbiosis in planktonic foraminifera and evolutionary diversification of Paleogene photosymbiotic clades. For example, the evolution of photosymbiosis was synchronous with the abrupt evolution of four major groups of Paleogene planktonic foraminifera including two clades within the genus Morozovella, as well as the genera Acarinina and Igorina. Our new isotopic and biogeographic data suggest that the acarininids evolved from a photosymbiotic ancestor (which we identify as Praemurica inconstans or early representatives of Praemurica uncinata), but also demonstrate that photosymbiosis did not trigger an immediate species-level radiation in this group. Instead, the acarininids remained a low-diversity taxon restricted to high latitudes for nearly 1.8 million years before radiating ecologically and taxonomically. The eventual radiation of the acarininids is tied to an expansion of their geographic range into the mid and low latitudes. Biogeographic analyses of modern plankton suggest that high-latitude environments may be less conducive to establishing radiations simply because there are fewer niches available to be filled than there are in the tropics. Accordingly, the acarininids may have initially failed to diversify because they started off in environments that presented few opportunities to sustain a large radiation. The high-latitude origin of the acarininids continued to retard their overall diversification until they were able to develop strategies that allowed them to expand into tropical environments and fully exploit their photosymbiotic ecology.
Evolutionary trends in coiling of tropical Paleogene planktic foraminifera
Authors: Norris Richard. D. , Nishi Hiroshi
Published: July 2006

Populations of planktic foraminifera display “proportionate” coiling (approximately 50% sinistral and dextral individuals given the data at hand) or may have “biased“ coiling, in which populations are dominated by either sinistral or dextral individuals. The major radiations of planktic foraminifera in the Late Cretaceous, the Paleocene to early Eocene, the middle Eocene, and the Neogene were each initiated by clades with proportionate coiling but subsequently accumulated sinistral and dextral species over time. Upper Maastrichtian foraminifera were predominantly dextral, but only the small number of species with proportionate coiling actually survived the Cretaceous/Paleogene mass extinction. The first Paleocene species with biased coiling appeared about four million years after the extinction and gradually came to represent as much as 50–60% of the tropical species diversity by the latest Paleocene. Tropical taxa with biased coiling suffered a second extinction in the late early Eocene and renewed a trend toward an increased abundance of species with biased coiling in the middle Eocene.

Our results for the Paleogene reflect a recurring theme in foraminifer evolution. In each radiation, once the founding species of a clade developed a biased-coiling mode, the descendants tended to maintain biased coiling until the extinction of the clade. The iterative evolution of biased coiling appears to represent an example in which a fundamental feature of development becomes fixed in a clade and inhibits reversion to an ancestral state. Apparently, coiling patterns are heritable in contrast with previous interpretations that coiling is environmentally controlled. On evolutionary timescales, species with proportionate coiling are less susceptible to extinction than species dominated by sinistral or dextral forms. Differential survivorship ensures that each radiation is initiated from founders with proportionate coiling following mass extinction. Hence, coiling preferences represent a case where the establishment of an evolutionary trend is caused by drift away from a “limiting boundary,” much like the evolution of large body size from ubiquitous small ancestors.
Spatial variations inAlbinaria terebraland snail morphology in Crete (Pulmonata: Clausiliidae): constraints for older and younger colonizations?
Authors: Welter-Schultes F. W.
Published: July 2006

A spatial approach was employed to test whether the conchological differentiation of the Recent land snailAlbinaria terebrafrom southern central Crete (Greece) is decreased in areas that have been more recently colonized by the species. The eastern Mediterranean genusAlbinariahas produced more than 120 species, probably in pre-Tortonian events of radiation.A. terebraoccupies a compact range of 550 km2consisting partly of late Cenozoic deposits of different ages, partly of pre-Cenozoic formations. The morphological study was based on 300 samples distributed over the entire range of the species. Shell size, shape, whorls, and teleoconch rib densities exhibited no evident correlation with environment but were subjected to considerable spatial variations. The differentiation, determined as the difference of the mentioned shell parameters between one population and another population 2–4 km distant, was found to increase continuously with the time (1–12 Myr) the land has been exposed to air. The populations with the highest degrees of spatial variation came from two areas that have never been submerged in the late Cenozoic, possibly the oldest populations of the species. It is plausible that the other areas were colonized by range expansion after late Neogene periods of tectonic uplift. The results are consistent with previous conclusions derived from molecular studies setting the radiation ofAlbinariaprior to the Tortonian and imply that we might be in possession of a new tool to detect information on the phylogeographic history of land snail species.
Growth patterns and biological information in fossil fish otoliths
Authors: Woydack Andrea , Morales-Nin Beatriz
Published: July 2006

Teleost otoliths are located in the membranous labyrinth and are mainly composed of aragonite and a small amount of organic matrix. Their rhythmic growth may provide important data about age, growth, maturity, and life-history events.

This article presents insights into paleoecological and evolutionary details from a study of the otolith microstructure of Trisopterus kasselensis, Trisopterus sculptus, and Pterothrissus umbonatus (Oligo-Miocene, North Sea Basin). Otoliths of Recent Trisopterus minutus were analyzed using the same methods (light and electron microscopy, thin slides) as a basis for comparison with the fossil sample.

Growth structures similar in size and aspect to the seasonal and daily growth increments in living fish indicate both individual age and early life transitions in habitat and life strategy suggesting planktonic larvae and benthic juveniles. The aspect of rhythmic growth patterns is due to lunar periodicity, a common feature in fish otoliths. Moreover, fossil Trisopterus show an phylogenetic increase in otolith—and consequently—somatic growth, indicating a change of life strategy during evolution (Oligocene to Recent).

Thus the internal structure of fossil otoliths allows the determination of growth, age composition, and early life history of fossil fish, as well as their direct comparison with living relatives.
Size evolution of the lower incisor ofMicrotia, a genus of endemic murine rodents from the late Neogene of Gargano, southern Italy
Authors: Millien Virginie , Jaeger Jean-Jacques
Published: July 2006

The Neogene paleoisland from the area of Gargano, Italy, has yielded numerous fossil vertebrates, some of them showing extraordinary morphological peculiarities due to island evolution. Among them,Microtia(Freudenthal 1976) is the dominant rodent genus in the Gargano palaeofauna and is represented by at least three evolutionary lineages. The incisors are used to describe the size evolution in these lineages, and we come to the conclusion that these lineages did not follow the same evolutionary trend: two of them evolve toward larger size, while the third one shows a slight decrease in size. In addition, we describe the evolution of the curvature of the lower incisor, compared with that of body-size. The evolution ofMicrotiais characterized by a specialization for burrowing, which may be accompanied by either an increase or a decrease in size. Finally, we propose that the evolutionary change among these three sympatric lineages allowedMicrotiato minimize competition between species, by avoiding size overlaps.
Probing the cassiduloid origins of clypeasteroid echinoids using stratigraphically restricted parsimony analysis
Authors: Smith Andrew. B.
Published: July 2006

Clypeasteroid echinoids are a familiar and easily defined clade with a cryptic origin. They first appear in the late Paleocene and are believed to have arisen from cassiduloid ancestry, but identifying sister-group relationships more precisely has proved difficult. Two factors are responsible for this problem, the extreme morphological conservatism of cassiduloids, which has given rise to high levels of character exhaustion, and the origin of crown-group clypeasteroids through paedomorphosis. Previous analyses, based on extant representatives alone or including all Mesozoic to Recent genera, have proved unsatisfactory.

Here a parsimony analysis is undertaken using a restricted set of all stem-group clypeasteroids and cassiduloid taxa that existed immediately prior to the appearance of crown-group clypeasteroids. Inclusion ofTogocyamus, the fossil taxon lying closest to the origin of crown-group clypeasteroids, is phylogenetically uninformative because that taxon is highly paedomorphic and has only generalized juvenile characteristics. However, earlier stem-group plesions provide critical data that identify Apatopygidae as extant sister group to the Clypeasteroida. Stratigraphically restricted analyses cannot eradicate the problems that arise from character exhaustion, but can minimize these with respect to specific phylogenetic questions.
The hierarchical structure of organisms: a scale and documentation of a trend in the maximum
Authors: McShea Daniel. W.
Published: July 2006

The degree of hierarchical structure of organisms—the number of levels of nesting of lower-level entities within higher-level individuals—has apparently increased a number of times in the history of life, notably in the origin of the eukaryotic cell from an association of prokaryotic cells, of multicellular organisms from clones of eukaryotic cells, and of integrated colonies from aggregates of multicellular individuals. Arranged in order of first occurrence, these three transitions suggest a trend, in particular a trend in the maximum, or an increase in the degree of hierarchical structure present in the hierarchically deepest organism on Earth. However, no rigorous documentation of such a trend—based on operational and consistent criteria for hierarchical levels—has been attempted. Also, the trajectory of increase has not been examined in any detail. One limitation is that no hierarchy scale has been developed with sufficient resolution to document more than these three major increases. Here, a higher-resolution scale is proposed in which hierarchical structure is decomposed into levels and sublevels, with levels reflecting number of layers of nestedness, and sublevels reflecting degree of individuation at the highest level. The scale is then used, together with the body-fossil record, to plot the trajectory of the maximum. Two alternative interpretations of the record are considered, and both reveal a long-term trend extending from the Archean through the early Phanerozoic. In one, the pattern of increase was incremental, with almost all sublevels arising precisely in order. The data also raise the possibility that waiting times for transitions between sublevels may have decreased with increasing hierarchical level (and with time). These last two findings—incremental increase in level and decreasing waiting times—are tentative, pending a study of possible biases in the fossil record.
How were vendobiont bodies patterned?
Authors: Valentine James W.
Published: July 2006

It is difficult to assign the animal-like body fossils of the late Neoproterozoic to crown metazoan phyla. Many Neoproterozoic fossils appear to share an architectural theme, which was characterized by Seilacher (1984, 1989) as modular; he noted that the modules, named pneus, could be arranged in a series of distinctive geometries to produce many of the Neoproterozoic fossil morphologies. The assemblages of pneus formed “quilted” constructions. Seilacher further suggested that these fossils might represent a multicellular clade that evolved independently of Metazoa–in effect, that they represented a kingdom of their own, which he named the Vendozoa. In later contributions, Seilacher (1992) renamed putatively quilted forms as the Vendobionta, and Buss and Seilacher (1994) considered Vendobionta to be a possible sister to Eumetazoa. The affinities suggested for vendobionts by various workers form a long list, ranging from protistans through fungi to several animal groups. Many vendobionts appear to be at the tissue grade of construction, and in this respect resemble cnidarians, to which they are most often compared. Neoproterozoic fossil assemblages also contain numbers of forms that are unlikely to be vendobionts, including a variety of “medusoids,” tentaculate fossils such asHiemoloraandEdiacaria(see Fedonkin 1992) that somewhat resemble sea anemones and may well be stem anthozoans. Additionally, numbers of Neoproterozoic forms have been suggested to be bilaterians, most notably the sluglikeKimberella(Fedonkin and Waggoner 1997). The contents and morphological limits of Vendobionta, and of some other higher taxa proposed for Neoproterozoic forms, are uncertain.
Uncorrelated change produces the apparent dependence of evolutionary rate on interval
Authors: Sheets H. David , Mitchell Charles E.
Published: July 2006

An intriguing phenomenon in the study of evolutionary rates of morphological change measured from fossil lineages has been the dependence of these rates on the inverse of the measurement interval. This effect has been reported across wide ranges of species as well as within single lineages, and has been interpreted as representing a smooth extension of evolutionary rate from generational timescales to paleontological timescales, suggesting that macroevolution may be simply microevolution extended over longer intervals. There has been some debate about whether this inverse dependence is a real feature of evolutionary change, or a mathematical or psychological artifact associated with the interpretation of data.

Our analysis indicates that the strong inverse dependence of rate on interval is an artifact produced by the phenomenon of spurious self-correlation. Spurious self-correlation can appear in any calculation when a ratio is plotted against its denominator, as is done in plotting rate versus interval, and when these two quantities are not well correlated with one another. We demonstrate that the effect of spurious self-correlation appears in seven published data sets of evolutionary rate that range from taxonomically broad compendia to studies of single families. The effect obscures the underlying information about the dependence of evolutionary change on interval that is present in the data sets. In five of the seven data sets examined there is no significant correlation between the extent of evolutionary change and elapsed time. Where such a correlation does exist, the inverse dependence of rate on interval length is weakened. We describe the role played by taxonomic, dynamic, and character inhomogeneity in producing the lack of correlation of change with interval in each of these data sets. This lack of correlation of change with interval, and the accompanying inverse correlation of rate with interval, most likely arises from discontinuous modes of evolutionary change in which a distinct long-term dynamic dominates net change over geological time spans. It is poorly explained by the extrapolationary microevolutionary models that have been said to account for this phenomenon.
The description and classification of evolutionary mode: a computational approach
Authors: Roopnarine Peter D.
Published: July 2006

The incorporation of the random walk model into stratophenetic analysis marked a turning point by presenting a potential null model for microevolutionary patterns. Random walks are derived from a family of statistical fractals, and their statistics can be reconstructed using appropriate techniques. This paper lays the foundation for the explicit and uniform description of evolutionary mode in stratophenetic series using random walk null models and the information contained within incompletely preserved time series.

The method relies upon the iterative analysis of subseries of an original stratophenetic series by measuring the presence of deviations from statistical randomness as the lineage evolves. This measure, and its probability of significance (evaluated using a randomization test), forms the dimensions of a descriptive space for microevolutionary modes. Each stratophenetic series can then be viewed as a journey through this space. Computer simulation of various evolutionary modes demonstrates that different modes, for example stasis and gradualism, have differing trajectories and occupy different regions of the microevolutionary space. The method is applied to two published foraminiferal stratophenetic series, the Mio-PlioceneGloborotalia plesiotumida-tumidapunctuated transition and an anagenetic trend in the Late CretaceousContusotruncana fornicata-contusalineage. An anagenetic trend is strongly supported in the latter example, whereas transformation of theGloborotaliaspecies seems to result from the fluctuating effectiveness of constraining processes.
Evaluating hypotheses of instar-grouping in arthropods: a maximum likelihood approach
Authors: Hunt Gene , Chapman Ralph E.
Published: July 2006

The ontogeny of arthropod exoskeletons is punctuated by short periods of growth following each molt, separated by longer stages of unchanging morphology called instars. The recognition of instar clusters in size distributions has been important in understanding the growth and evolution of fossil arthropods. Generally, these clusters have been identified by inspection, but this approach has been criticized for its subjectivity. In this paper, we describe a statistical framework for evaluating hypotheses of clustering based on maximum likelihood analysis of mixture models. The approach assumes that individuals are normally distributed within instars; thus an arthropod size distribution can be considered a mixture of normal distributions. This methodology provides an objective framework to compare various plausible hypotheses of grouping, including the possibility that there is no significant grouping at all.

We apply this method to evaluate clustering in two trilobite species,Ampyxina bellatulaandPiochaspis sellata.Both of these data sets show statistically significant evidence of clustering, a phenomenon rarely documented for holaspid-stage trilobites. After consideration of alternative causes of clustering, we argue that the observed groupings are best explained as instar groups. In these two species, growth increments between molts were similar throughout the observed portion of ontogeny, although subtle yet significant variation can be seen within the ontogeny ofAmpyxina bellatula.
Anomalies of embryonic shell growth in post-Triassic Nautilida
Authors: Chirat Régis
Published: July 2006

No egg of any fossil nautiloid has yet been discovered. However, anomalies of embryonic shell growth, described for the first time in several Mesozoic Nautilida, provide important clues on morphology, structure, and size of their egg capsules; on the physical characteristics where egg laying occurred; and on the hatching processes. Roughness inside the inner egg capsule–caused by hard and uneven egg-laying substrate, locally and temporarily slowing down or stopping the apertural shell growth–could cause temporary deformations of growth lines. Such roughness, caused by stone, is described inside an egg capsule of Nautilus, which was fixed obliquely relative to the egg-laying substrate. This reduced the space between the inner and outer capsules, which locally fused together. The lateral-umbilical grooves, furrows, and deformations of growth lines were probably caused by the inner egg capsule during the prehatching stage. In fossil Nautilida, as in Nautilus, the size of this capsule was relatively small compared with the shell diameter at hatching. During the last stages of embryonic development, the shell extended backwards outside the egg capsule before hatching. This prehatching stage, during which the egg capsule continued to press against the shell, can be marked by a prehatching constriction. In fossil species, as in Nautilus, the inner capsule constituted a kind of “straitjacket” during the last stages of embryonic development. The expansion in whorl width at hatching, in normal as well as in abnormal shells, marks release of this straitjacket. Important deformations of the whorl section probably result from an abnormal form and size of the egg capsules mainly caused by the manipulations by the female during the egg laying on a hard and hollow substrate, increasing the straitjacket effect. An alternative explanation could be that the chorion did not expand adequately. From relatively early embryonic stages (approximately 180° adapical of the nepionic constriction) to hatching, both flaps of the hyponome could be turned backward under the shell, jammed between the inner wall of the egg capsule and the mantle margin, resulting in the formation of paired ventral parallel grooves. Many normal features of the embryonic development of nautiloids can be clarified through the study of the anomalies of embryonic shell growth.