bluuebunny/crossref_metadata_2025 huggingface dataset:
A guide for differentiating mammalian carnivore taxa responsible for gnaw damage to herbivore limb bones
Authors: Haynes Gary
Published: July 2016

Large cats, canids, bears, and hyenas create distinctive types of damage when they gnaw bones. This paper describes the diagnostic characteristics of damage done by each taxon to femora and tibiae of herbivores whose body weights are 300 kg or more. Pleistocene and Recent fossil collections that include gnawed bones might provide data on the presence of carnivores whose own remains are not found in the collections. Information might also be gained about predator and scavenger utilization of prey carcasses, often a reflection of prey vulnerability or availability in past communities.
Extinction is here to stay
Authors: Flessa Karl W. , Jablonski David
Published: July 2016

This summer's meeting season saw five gatherings devoted specifically to the topic of extinction: Chicago's Field Museum symposium in May (see Diamond 1983); a field conference to examine the Cretaceous-Tertiary transition in Montana; a symposium on molluscan extinction at the American Malacological Union meeting in Seattle; a special session at the annual meeting of the Society for the Study of Evolution in St. Louis; and a research conference on the campus of Northern Arizona University in Flagstaff (see also Lewin 1983a,b,c). Several recent books consider the topic (Ehrlich and Ehrlich 1981; Nitecki 1981; Silver and Schultz 1982; Martin and Klein, 1984) and plans are underway to publish the papers presented at the Field Museum, Seattle, and Flagstaff meetings. Our review of the topic is based principally on the themes explored at the St. Louis and Flagstaff meetings.
Speciation in pelagic Protista and its study in the planktonic microfossil record: a review
Authors: Lazarus David
Published: July 2016

The punctuated equilibrium hypothesis, largely derivable from Mayr's peripheral isolate model of speciation, is but one of many possible paleontologic patterns of speciation which may be tested against the deep-sea fossil record of planktonic microfossils. The nature of reproduction and variation within a species has a profound effect on its expected tempo and mode of evolutionary change. Biologic data on pelagic plankton and on protistan genetics and reproduction suggest that speciation in pelagic holoplanktonic protists may also be parapatric, “equal” allopatric, or the result of hybridization. Each of these models is shown to make testable predictions of paleontologic pattern. Published records of speciation in planktonic deep-sea microfossil data are compatible with these alternative models. Existing data sets are not yet sufficiently complete to provide strong tests. Future work needs to integrate taxonomic, paleoecologic, biogeographic, and biometric data in studies of individual speciation events. Micropaleontologic studies of morphologic change through time may thereby contribute to our understanding of speciation mechanisms in the pelagic protistan plankton.
Evolution and hybridization in the radiolarian genera Theocorythium and Lamprocyclas
Authors: Baker Colin
Published: July 2016

Changes in morphological variability within fossil populations of planktonic protists provide insight into the processes responsible for morphological change. Evolution in the radiolarian genera Theocorythium and Lamprocyclas is documented biometrically in Pliocene and Pleistocene core material from the equatorial Pacific and Indian Oceans. The patterns of morphological change in Theocorythium within a single Pacific core could be interpreted as indicating the in situ evolution of T. trachelium trachelium from T. vetulum via intermediate forms during the Pleistocene. However, consideration of biogeographic data shows that this is not the case and supports instead two alternate interpretations: (1) immigration coupled with extensive hybridization and introgression, or (2) multiple polymorphs of a single species changing in frequency along a cline. Analyses of evolutionary change in Theocorythium and the closely related genus Lamprocyclas during the Pliocene suggest that hybridization may be a significant factor in the production of new species. Evolutionary models and phylogenetic analyses should consider that barriers to gene flow may vary significantly with time and permit the exchange of genetic information between populations previously reproductively isolated.
Phenology of morphologic change in radiolarian lineages from deep-sea cores: implications for macroevolution
Authors: Kellogg Davida E.
Published: July 2016

One method of increasing the resolving power of paleontological inquiries is to assess the time distribution, or phenology, of perispeciational change. The rationale for this test is that, while concentration of morphologic change around the time of speciation is consistent with both known microevolutionary mechanisms and punctuated equilibria, punctuated equilibrium theory presupposes that most of the change occurs either before or during initial allopatry to produce morphologically static taxa. Considerable change in the initial phases of speciation could also result from known microevolutionary mechanisms, but if significant change occurs in the neosympatric phase, or at any time after the species have become differentiated, then that change is best explained by known microevolutionary mechanisms.

Amount and rate of morphologic change during each phase of the allopatric speciation process were determined for two cognate species of the radiolarian genus Eucyrtidium. In this case, morphologic change accruing to these species during the neosympatric phase was 2-3 times as great as that which occurred during the initial allopatric phase. Morphologic trends in both these species during the allopatric phase differed significantly from a random walk. The size differential that characterized this speciation event was not the product of a single large step early in the process but of a disproportionate number of small steps in one direction during neosympatry. Therefore, the hypothesis of no statistically significant change following the “first stage” of speciation, which is a major tenet of punctuated equilibrium theory, is falsified for this case.
Biomechanical stability and sudden change in the evolution of the deep-sea ostracode Poseidonamicus
Authors: Benson Richard H.
Published: July 2016

Changes in shape and in the pattern of the reticulate carapace ornament of 63 representative female ostracode specimens of the deep-sea genus Poseidonamicus from 28 Deep Sea Drilling Project Sites, extending over a geographic distance of 40,000 miles and a geologic age of 40 × 106 yr, have been analyzed by Resistant Fit Theta-Rho Analysis, conventional least-squares Theta-Rho Analysis, and by inspection of homologies in the fossae of the reticulum. Through comparison of the relative rates of morphological change on at least three levels of integrated complexity, it is possible to demonstrate that a sudden evolutionary change in the architectural framework of the carapace can be the product of mechanical accommodation under stress to more gradual and general changes in carapace shape. Certain geometric imperatives related to these mechanical needs determine morphologic stability and consequently rates of evolutionary change. In the western deep South Atlantic (near the Vema Channel on the Rio Grande Rise), an important evolutionary “punctuational event” seems to have taken place at about 14 Myr, whereas its concomitant, more gradual transformation is traceable in the shallower eastern South Atlantic (Walvis Ridge). This evolutionary event in Poseidonamicus probably reflects the relatively sudden invasion of deep Antarctic Bottom Water through the Vema Channel resulting from the formation of the East Antarctic Ice Cap, while the more gradual transition in shallower depths of Walvis Ridge represents a temporary transitory refuge. The problems of recognizing allopatric origins of species in the deep sea compared to in situ sudden transitions caused by biomechanical instability are considered.
Phyletic gradualism in the Globorotalia inflata lineage vindicated
Authors: Malmgren Björn A. , Kennett James P.
Published: July 2016

We appreciate Dr. Scott's comments about our paper (Malmgren and Kennett 1981), but wish to clarify some aspects which we hope will help provide a better understanding about the Late Neogene evolution of the Globorotalia (Globoconella) group (Kennett and Srinivasan 1983). We also wish to dispute some of Scott's other criticisms. In effect, Scott's arguments have provided no reason to justify abandonment of our initial contention that this lineage represents one of the best documented cases of phyletic gradualism in any group of fossils.

We support Scott's notion that divergence of the lineage took place near the Miocene-Pliocene boundary, but this divergence is not relevant for our evolutionary study. In fact, the Early Pliocene form resembling Globorotalia conoidea was already recognized by one of us (J.P.K.) 10 yr ago (Kennett 1973). It was distinguished as G. cf. conoidea and not G. conoidea as stated by Scott. In our previous papers (Malmgren and Kennett 1981, 1982) we confined our attention to the evolution that occurred in the primary temperate stock (cool subtropical) water mass—the abundant and dominant forms of Globoconella.
Nautilushard parts: a study of the mineral and organic constitutents
Authors: Lowenstam H. A. , Traub W. , Weiner S.
Published: July 2016

The mineralized hard parts ofNautilus, including the mandibles, statoconia, and uroliths, are more complex with respect to ultrastructure, mineralogy, trace element, and isotopic composition than was previously recognized. X-ray diffraction and amino acid composition analyses of the organic structural hard parts (siphuncle tube, shell wall and septum organic matrix, mandibles, and muscle tendon sheath) show that two different chitin-protein complexes are utilized byNautilus.The mandible mineral hard parts are particularly complex, with five different minerals present in various locations. A comparison of the statoconia ofNautilusspecies with the statoliths of dibranchian cephalopods reveals an evolutionary trend in which carbonate is substituted for phosphate. This study also shows thatNautilususes a number of different crystal-forming processes for constructing its hard parts. The data presented here provide a broad spectrum of information, which, when applied to the fossil counterparts, can be utilized for improving our understanding of ancient nautiloid biology.
Evolution inHomo erectus: the question of stasis
Authors: Wolpoff Milford H.
Published: July 2016

Using a conservative definition of the hominid taxonHomo erectus, the sample of specimens known at this time, 92 individuals in all, is examined to determine whether the species exhibited significant temporal trends or evolutionary stasis. The sample is divided into three low-resolution time spans, and it is shown that significant change characterizes a number of cranial, mandibular, and dental features. Rates of change are comparable to or above rates reported for other fossil vertebrate lineages sampled over a similar duration. The often repeated assertion thatHomo erectusis an example of a species in evolutionary stasis is incorrect.
Effects of stratigraphic completeness on interpretations of extinction rates across the Cretaceous-Tertiary boundary
Authors: Dingus Lowell
Published: July 2016

A rate of extinction must specify both the amount of taxonomic change and the duration of that change. A consistent means of temporal measurement must be used to establish the duration. Terms used to describe the extinction, like catastrophic and gradual, should be quantitatively defined in relation to this framework.

Resolving rates of extinction in the stratigraphic record is limited by (1) the precision of chronostratigraphic correlations between individual sections and (2) the temporal completeness of litho- and biostratigraphic records in those sections. In this study, temporal completeness is estimated in eight of the best-known fluvial and pelagic sections spanning the K-T boundary. Temporal standardization is provided by correlations to the geomagnetic polarity time scale. A review of the literature documents lithologic criteria that might be used to infer the presence of a hiatus of some length at the biostratigraphically recognized K-T boundary. Rather than rejecting the presence of such gaps, this study argues that a hiatus of some length does exist and tries to estimate both a maximum limit for its duration and the probability that it represents a given duration below that limit.

Pelagic sections are probably more complete than fluvial ones. The section at Caravaca, Spain, can be expected to be the most complete, probably preserving sediment during each 10,000-yr interval of Chron 29R. The section in the San Juan Basin, New Mexico, is expected to be the most complete fluvial section, probably preserving sediment during each 100,000-yr interval of 29R.

Results indicate that our best-known marine and terrestrial sections spanning the K-T boundary should not be expected to document biologically catastrophic rates of extinction. A sufficiently precise means of global correlation that is independent of biostratigraphy and causal hypotheses is still unavailable, and it is very unlikely that the sections examined are complete at the 100-yr or biologically catastrophic level of precision. So, although catastrophic amounts of extinction might have occurred during the K-T transition, it seems unlikely that we can distinguish episodes of extinction lasting 100 yr or less from episodes lasting as long as 100,000 yr. Consequently, acceptance of catastrophic hypotheses based on these stratigraphic records seems improbably optimistic at this time.
The role and status ofNautilusin its natural habitat: evidence from deep-water remote camera photosequences
Authors: Saunders W. Bruce
Published: July 2016

Bottom site remote camera photosequences at depths of 73–538 m on forereef slopes in Palau show thatNautilus belauensisis a highly mobile, chemosensitive, epibenthic scavenger and opportunistic predator. The overall depth range of this species is ca. 70–500 m, but photosequences indicate a preferred range of 150–300 m.Nautilusis active both nocturnally and diurnally, locating bait sites within 1–2 h. Associated macrofauna includes caridean shrimps, crabs, and eels; teleosts are rare below 100 m, but sharks are recorded in most photosequences below 250 m. Summarily,Nautilusexhibits a combination of characters that typify deep-sea strategy, including reproductive tactics, growth rate, and population dynamics. This and other evidence suggest that fossil Nautilidae may have been deep-water forms, in contrast to the typically shallower water ammonoids, and thatNautilusis a normal component of the deep forereef rather than a late Cretaceous refugee from shallow water.
Size-related changes in the primary xylem anatomy of some early tracheophytes
Authors: Niklas Karl J.
Published: July 2016

A survey of the primary xylem anatomy and dimensions of axes (=“stems”) of Upper Devonian plant petrifaction/compression fossils reveals the following: among genera, the primary xylem strand (1) increasingly deviates from a cylindrical geometry (=haplostele) as both the axis diameter and the nonxylem (“ground”) tissue volume increase and (2) increases in geologically younger specimens. (3) The perimeter length to area ratio of the primary xylem strand (or the primary xylem surface area to volume ratio) is dependent upon axis diameter or the area of the ground tissue. This ratio (4) decreases in evolutionary lineages that involve the appearance of larger plants that maintain a haplostelar anatomy (e.g., the evolution of trimerophytes from a rhyniophyte ancestor) or increases in evolutionary lineages involving the appearance of nonhaplostele anatomy (e.g., the evolution of progymnosperms and pteridophytes from trimerophyte ancestors) and (5) the relative amount of primary xylem to ground tissue increases in stratigraphically younger specimens. These trends are interpreted within the context of (1) correlations between the diameter of axes and the complexity of the primary xylem anatomy reported for some extant pteridophytes and (2) changes associated with the evolution of new primary xylem configurations and organographic relationships. Based on the appearance of new ontogenetic patterns and concomitant changes in the anatomy of the primary xylem strand associated with the evolution of derived plant groups, a stria extrapolation of a size to complexity correlation based on ontogenetic studies to the phyletic level is considered suspect.
Branching geometry and function of multiramous graptoloids
Authors: Fortey Richard A. , Bell Adrian
Published: July 2016

We have produced computer simulations of multiramous graptoloids with the intention of defining the rules governing branching strategies and colony form. Close matches between such simulations and real graptolites show that complex rhabdosomes may be produced by the permutation of relatively simple sets of rules. Those designs found in nature produce an efficient and regular distribution of zooids through the area included by an essentially planar rhabdosome. Strikingly geometrical arrays of stipes, such as theGoniograptusand yin/yang patterns, closely approach paradigmatic harvesting arrays. For dichotomously branching anisograptids the evolutionary trend in reduction of “primary stipes” can be explained by the production of larger spreading colonies. Multiramous graptoloids fed during vertical movement through the water column. Changes in a single branching decision may produce considerable changes in rhabdosome morphology, but these are not necessarily of high taxonomic importance; this is proved by a specimen which is a morphological combination of two “genera.” Although primarily under genetic control, certain modifications to colony form were probably the result of inhibitory interaction between adjacent stipes.
Astogeny and phylogeny: evolutionary heterochrony in Paleozoic bryozoans
Authors: Anstey Robert L.
Published: July 2016

Astogenetic trajectories have constrained evolutionary changes in bryozoans. Rates and timing of astogenetic differentiation have been modified for characters defining the morphology of zooids, subcolonies, and colonies. This paper catalogs 46 examples of bryozoan heterochrony, representing all five skeletonized orders. Heterochrony is inferred to have been a pervasive phenomenon in the evolution of Paleozoic stenolaemates, illustrated by 40 examples, 19 of which produced paedomorphosis and 21 peramorphosis. As a consequence, a restricted range of morphologic states has reappeared repetitively as homeomorphies and evolutionary reversals. Large-scale patterns developed across both geologic time and geographic space reflect variation in heterochronic products irrespective of the developmental processes by which they were achieved. Available evidence indicates that smaller, paedomorphic, and more plastic species inhabited onshore, low-diversity areas. Nonheritable plasticity is inferred to be a correlate of early growth stages and paedomorphosis. Taller, generally peramorphic species with damped plasticity are found in higher diversity, offshore regions. Seven key innovations, which first appeared during the early diversification of bryozoan clades, are peramorphic, and recapitulation was a predominant pattern during their Ordovician radiation. Trends in later phylogeny, on the other hand, have favored paedomorphic derived morphologies, as illustrated by 19 of the 32 examples. Recurrent reverse recapitulation suggests that offshore ancestors frequently gave rise to onshore paedomorphs.
Selective factors in the origin of the mammalian diaphragm
Authors: Ruben John A. , Bennett Albert F. , Hisaw Frederick L.
Published: July 2016

The origin of endothermic homeothermy and of high metabolic rate in mammals is currently believed to be the result of early (Mesozoic) selection in advanced cynodont therapsids and/or early mammals for either (1) enhanced thermoregulatory capacity or (2) increased powers of endurance and stamina. Selective factors underlying the origin of specialized respiration/ventilation-support systems in mammals are possible indices of the validity of these two hypotheses. One such support structure is the diaphragm, a specialized muscle that facilitates lung ventilation. We tested capacity for maintenance of resting metabolic rate, thermoregulation, and for extended, intense exercise in laboratory rats (Rattus rattus) in which diaphragm function had been completely ablated. The results were virtual elimination of aeroboic scope (active metabolic rate — resting metabolic rate) but resting metabolic rate was unaffected. Thermoregulatory capacity was unimpaired to at least 8° below lower critical temperature. These and other data suggest that the origin of the mammalian diaphragm, as well as mammalian metabolic rates, may have been related to selection for greater levels of sustainable activity rather than for functions associated with thermoregulation.
Evolutionary tempo and mode in a sequence of the Upper Cretaceous bivalve Pleuriocardia
Authors: Geary Dana H.
Published: July 2016

This study addresses the question of evolutionary tempo and mode in a sequence of Upper Cretaceous bivalves in the genus Pleuriocardia from the Western Interior Basin of North America. Change between species was probably phyletic (without persistence of ancestors). There is some evidence for weak gradual change within the lineage, but most important change is concentrated in short intervals of time. Detailed examination of the differences among samples reveals pronounced geographic variation, whereas temporal variation within localities is generally minor. The relatively rapid episodes of change fit the model of punctuated equilibrium, but the phyletic nature of species-level change does not.

The value of the debate about the punctuated and gradualistic models has been to force a more criticial examination of fossil sequences, but these sequences should not be forced into narrowly defined categories. A variety of evolutionary patterns may exist in the fossil record, and it is this variation in pattern that will inform us of the underlying processes.
On the value of taxonomic standardization in evolutionary studies
Authors: Culver Stephen J. , Buzas Martin A. , Collins Laurel S.
Published: July 2016

Species duration data for living benthic foraminifera derived from an extensive literature search have been compiled and analyzed to investigate rates and patterns of species origination. The same data subjected to taxonomic standardization through examination of many specimens lodged in museum collections indicate strikingly different, and more realistic, rates and patterns.

Evolutionary generalizations based on data generated from the literature only are often unreliable and may be directly in opposition to reality. Extensive attempts at taxonomic standardization should be the norm in paleobiological investigations.
Dinosaur tracks symposium signals a renaissance in vertebrate ichnology
Authors: Lockley Martin G. , Gillette David D.
Published: July 2016

The study of tracks is often regarded as a fringe subdiscipline outside the scientific mainstream. Papers dealing with footprints traditionally appear either in popular magazines likeNatural History(Bird 1939, 1944; Brown 1938), or in very obscure publications (Sarjeant 1974). Usually it is only the spectacular discoveries, which are directly applicable to topical debates, that rouse much scientific interest. For example, the discovery of Pliocene hominid tracks (Leakey and Hay 1979) provided unequivocal evidence for the antiquity of bipedalism (cf., Napier 1967). Similarly the tracks of a running theropod allowed for direct estimates of the speed attained by dinosaurs (Farlow 1981), and the tracks of a herd of running theropods fueled debate about gregariousness and stampede behavior (Thulborn and Wade 1984).
Harmonic analysis of periodic extinctions
Authors: Fox William T.
Published: July 2016

Fourier analysis of percent extinction data for genera of fossil marine animals during the past 260 million years indicates the existence of a 26 m.y. extinction cycle. The first three harmonics, which account for 51.7 percent of the sum of squares, show the major extinction trends in the late Paleozoic, Mesozoic and Cenozoic. The first ten harmonics, which account for 89.5 percent of the sum of squares, are aligned with eight extinction peaks. The tenth harmonic, with a period of 26 million years, has an amplitude of 6.5 percent and accounts for 12.7 percent of the sum of squares.

Several different methods are used to test the validity of the apparent 26 m.y. extinction cycle. Analysis of variance indicated that the 26 m.y. extinction cycle is statistically significant at the 95 percent level. When the 260 m.y. sample interval is divided into equal 130 m.y. segments, the phases and amplitudes for the 26 m.y. cycle were almost equal within the two independent segments. When the 260 m.y. interval is divided into 10 shorter time segments of different lengths, the 26 m.y. cycle is represented in each time segment.

A series of experiments is run to test the influence of the Late Permian and Cretaceous peaks on the observed 26 m.y. cycle. When all peaks are smoothed out except for the two major peaks, a pseudo-cycle with a period of 26 m.y. is generated that accounts for 3.0 percent of the sum of squares. When the Permian and Cretaceous peaks are reduced to about half their observed height, the sum of squares accounted for by the 26 m.y. cycle is reduced from 12.7 to 11.0 percent. When the number of extinctions within each stage is used in the harmonic analysis in place of extinction percent, the 26 m.y. cycle accounts for 19.3 percent of the sum of squares.

Therefore, the evidence from harmonic analysis of fossil marine animals points toward a distinct and persistent 26 m.y. cycle in mass extinctions in the late Paleozoic, Mesozoic and Cenozoic.
Tempo of evolution in a Neogene bryozoan: are trends in single morphologic characters misleading?
Authors: Cheetham Alan H.
Published: July 2016

The extent to which perceived patterns of evolution are affected by the use of single characters versus overall morphology or measured versus counted and coded characters is explored empirically, employing multiple-character data from closely spaced sequential populations of the Neogene bryozoan Metrarabdotos. In all nine species examined, the pattern of evolution in overall morphology revealed by discriminant analysis is so highly punctuated that changes within species do not vary significantly from zero. Among the 46 single characters in the nine species, a few statistically significant temporal trends do occur, as apparent departures from the static pattern in overall morphology. However, these exceptions are so poorly related to the morphology that distinguishes inferred ancestor and descendant species from each other, and are so few in number, that they can be interpreted as chance variation from a general condition of no change within species. There is no difference in behavior between measured characters and counted or coded ones, in part because the distinction between the two types of characters can be artificial in bryozoans and other modular organisms. The results suggest that interpretation of single-character changes, in isolation rather than as statistical samples of the change in overall morphology, should be made with caution.
Function and shape in late Paleozoic (mid-Carboniferous) ammonoids
Authors: Swan Andrew R. H. , Saunders W. Bruce
Published: July 2016

Analysis of an exhaustive data base of Namurian ammonoid shell characters indicates that the morphology of the Goniatitida can be explained in terms of functional constraints, resulting particularly from hydrostatic and hydrodynamic properties. Modes of life ranging from benthic to pelagic are inferred on this basis for various goniatitid morphotypes; all morphologic features and facies associations are normally compatible with these inferences. Neutral buoyancy is shown to have been likely for all goniatitids. By contrast, the prolecanitids (Order Agoniatitida) exhibit a number of hydrostatic and morphologic anomalies; these anomalies are not explicable using the same principles and remain problematic. This is noteworthy, in that prolecanitids survived the Permian/Triassic extinctions and gave rise to the diverse ceratitic radiation in the Triassic.

The applicability of these results to ammonoids outside the Namurian is assessed, and, in particular, morphologic parallels with Mesozoic ammonites are discussed.
Pleistocene extinctions: the pivotal role of megaherbivores
Authors: Owen-Smith Norman
Published: July 2016

Two alternative hypotheses have been advanced to explain the demise of about half of the mammalian genera exceeding 5 kg in body mass in the later Pleistocene. One hypothesis invokes climatic change and resulting habitat transformations. This fails to predict the increased likelihood of extinctions with increasing body size, greater severity in both North and South America than in Eurasia or Australia, lack of simultaneous extinctions in Africa and tropical Asia, and the absence of extinctions at the end of previous glacial periods. The other hypothesis invokes human predation as the primary cause. This fails to explain the simultaneous extinctions of a number of mammalian and avian species not obviously vulnerable to human overkill. I propose a “keystone herbivore” hypothesis, based on the ecology of extant African species of megaherbivore, (i.e., animals exceeding 1,000 kg in body mass). Due to their invulnerability to non-human predation on adults, these species attain saturation densities at which they may radically transform vegetation structure and composition. African elephant can change closed woodland or thicket into open grassy savanna, and create open gaps colonized by rapidly-regenerating trees in forests. Grazing white rhinoceros and hippopotamus transform tall grasslands into lawns of more nutritious short grasses. The elimination of megaherbivores elsewhere in the world by human hunters at the end of the Pleistocene would have promoted reverse changes in vegetation. The conversion of the open parklike woodlands and mosaic grasslands typical of much of North America during the Pleistocene to the more uniform forests and prairie grasslands we find today could be a consequence. Such habitat changes would have been detrimental to the distribution and abundance of smaller herbivores dependent upon the nutrient-rich and spatially diverse vegetation created by megaherbivore impact. At the same time these species would have become more vulnerable to human predation. The elimination of megaherbivore influence is the major factor differentiating habitat changes at the end of the terminal Pleistocene glaciation from those occurring at previous glacial-interglacial transitions.
Clonal growth, algal symbiosis, and reef formation by corals
Authors: Coates Anthony G. , Jackson Jeremy B. C.
Published: July 2016

The occurrence of zooxanthellae in Recent scleractinian corals is strongly correlated with their growth form, corallite size, and degree of morphological integration of corallites. The great majority of zooxanthellate corals are multiserial with small, highly integrated corallites, whereas most corals lacking zooxanthellae are solitary or uniserial colonial forms with large, poorly integrated corallites. Beginning in the Jurassic, fossil scleractinian faunas are morphologically similar to Recent faunas dominated by zooxanthellate species, strongly implying that most scleractinians contained zooxanthellae by that time. Evidence for Siluro–Devonian tabulates and Triassic scleractinians is equivocal but still suggests the presence of zooxanthellae in these corals. In contrast, morphological evidence suggests that rugosan corals lacked zooxanthellae.

Most populations of Recent zooxanthellate corals contribute to reef formation, but many do not. Similarly, fossil corals interpreted to contain zooxanthellae on morphological grounds did not always form reefs. Recent reef formation depends upon a host of environmental factors that have little to do with the possession of zooxanthellae per se. Coral morphology should be a better predictor of the presence of zooxanthellae in fossil corals than their association with reefs.
The origin of crocodilian locomotion
Authors: Parrish J. Michael
Published: July 2016

The morphology of the tarsi, hindlimbs, and pelves of the earliest crocodilians and their nearest relatives,Hallopusand the “sphenosuchians,” indicates that these animals had adaptations for erect posture. The widespread distribution of apparently homologous adaptations for erect gait among the archosaurs with crocodile-normal tarsi suggests that those structures are plesiomorphic for this group, which comprises the Aetosauria, “rauisuchians,” “sphenosuchians,”Hallopus, and the Crocodylia. Adaptations for erect posture are seen most clearly in the structure of the proximal tarsus (astragalus and calcaneum).

An important implication of this argument is that the most primitive crocodylomorphs, comprising the “protosuchian” crocodiles, the “sphenosuchians,” andHallopus, had an erect stance and gait. The sprawling stance and associated gait used by modern crocodilians during swimming and upon entering the water can be viewed as secondary adaptations to an aquatic existence. The environments of deposition and faunal associations of “sphenosuchians” and “protosuchian” crocodiles are consistent with primarily terrestrial habits. Living crocodilians have two types of step cycles, sprawling and erect; the sprawling pattern is overprinted onto the inferred ancestral “high-walk,” and onto the gallop sometimes used by juvenile crocodilians.
Iterative progenesis in Upper Cretaceous ammonites
Authors: Landman Neil H.
Published: July 2016

Pteroscaphites are small, rare species of scaphitid ammonites from the Upper Cretaceous (Turonian-Santonian) of the Western Interior of North America. Their evolution appears to parallel that of the larger species ofScaphitesorClioscaphites, with which they co-occur. To investigate this evolutionary pattern, I constructed a phylogeny of all these species based on their distribution of shared derived characters including ornamentation, ammonitella size, whorl shape, umbilical diameter, sutures, number of whorls, adult size, shape of the adult body chamber, and apertural modifications. This analysis revealed numerous instances of congruence in the preadult morphology of the pteroscaphites and that of the co-occurring scaphites or clioscaphites. However, there is a marked divergence at maturity. Adult pteroscaphites are uniformly small (2.5 postembryonic whorls in their phragmocone) and develop apertural projections. The scaphites and clioscaphites exhibit a number of morphological changes at approximately the same whorl number, but secrete as many as two more whorls in their phragmocone before forming a mature body chamber with a relatively unmodified aperture. Both groups display sexual dimorphism. The process of progenesis may explain this conflicting pattern of congruence prior to maturity and divergence at maturity. Adult pteroscaphites are not mature replicas of the juvenile shells of the larger scaphites or clioscaphites, because maturation produces its own set of morphological modifications. Nevertheless, such features as the apertural projections on adult pteroscaphites may be interpreted as extrapolations of juvenile patterns of growth into maturity. The repeated associations of pteroscaphites with scaphites or clioscaphites in the Upper Cretaceous suggest that progenesis was iterative and may have represented an optional developmental pathway common to all of these species.
Molluscan extinction patterns across the Cenomanian-Turonian Stage boundary in the western interior of the United States
Authors: Elder William P.
Published: July 2016

High-resolution stratigraphic analysis of 18 sections spanning the Cenomanian–Turonian Stage boundary in the western interior of the United States has allowed determination of the magnitude and pattern of molluscan extinction and disruption. Composite range data from all sections show that the faunal turnover across the stage boundary occurs in a series of narrow stratigraphic zones, defined by multiple first and last occurrences, separated by intervals displaying little or no taxonomic turnover. Two of the apparent extinction steps (bottom and top of theNeocardioceras juddiiZone) may be intercontinentally developed. The additional steps apparently reflect cyclic changes in water mass and substrate characteristics in the western interior basin produced in response to orbital forcing of climate. An interval (ca. 10-100 k.y. duration) of changing community structure and general biotic deterioration is found below each of the two potentially intercontinentally developed extinction steps. The most affected mollusks were those having intercontinental distributions (ammonites and inoceramid bivalves), suggesting that disruption of planktotrophic larval dispersal may have played a role in increasing extinction and speciation rates near the C–T boundary. The nekto-benthic ammonites were affected earlier and to a greater degree than the pelagic forms, implying progressive upward expansion of the oxygen minimum zone preceding the stage boundary.
Some evolutionary correlates of higher taxa
Authors: Holman Eric W.
Published: July 2016

Nonparametric randomization tests were used to determine whether fossil marine families classified in different higher taxa are significantly different in their durations, their rates of origination and extinction, and their proportion of originations. For each of these properties, significant differences among orders and classes were found that could not be explained by differences at other taxonomic ranks, but no such differences were found among phyla. Thus, orders and classes appear to possess an evolutionary coherence that phyla lack.
Confidence intervals on stratigraphic ranges
Authors: Marshall Charles R.
Published: July 2016

Observed stratigraphic ranges almost always underestimate true longevities. Strauss and Sadler (1987, 1989) provide a method for calculating confidence intervals on the endpoints of local stratigraphic ranges. Their method can also be applied to composite sections; confidence intervals may be placed on times of origin and extinction for entire species or lineages. Confidence interval sizes depend only on the length of the stratigraphic range and the number of fossil horizons. The technique's most important assumptions are that fossil horizons are distributed randomly and that collecting intensity has been uniform over the stratigraphic range. These assumptions are more difficult to test and less likely to be fulfilled for composite sections than for local sections.

Confidence intervals give useful baseline estimates of the incompleteness of the fossil record, even if the underlying assumptions cannot be tested. Confidence intervals, which can be very large, should be calculated when the fossil record is used to assess absolute rates of molecular or morphological evolution, especially for poorly preserved groups. Confidence intervals have other functions: to determine how rich the fossil record has to be before radiometric dating errors become the dominant source of error in estimated times of origin or extinction; to predict future fossil finds; to predict which species with fossil records should be extant; and to assess phylogenetic hypotheses and taxonomic assignments.
Caudofemoral musculature and the evolution of theropod locomotion
Authors: Gatesy Stephen M.
Published: July 2016

Living crocodilians and limbed lepidosaurs have a large caudofemoralis longus muscle passing from tail to femur. Anatomical and electromyographic data support the conclusion that the caudofemoralis is the principal femoral retractor and thus serves as the primary propulsive muscle of the hind limb. Osteological evidence of both origin and insertion indicates that a substantial caudofemoralis longus was present in archosaurs primitively and was retained in the clades Dinosauria and Theropoda. Derived theropods (e.g., ornithomimids, deinonychosaurs,Archaeopteryxand birds) exhibit features that indicate a reduction in caudofemoral musculature, including fewer caudal vertebrae, diminished caudal transverse processes, distal specialization of the tail, and loss of the fourth trochanter. This trend culminates in ornithurine birds, which have greatly reduced tails and either have a minute caudofemoralis longus or lack the muscle entirely.

As derived theropod dinosaurs, birds represent the best living model for reconstructing extinct nonavian theropods. Bipedal, digitigrade locomotion on fully erect limbs is an avian feature inherited from theropod ancestors. However, the primitive saurian mechanisms of balancing the body (with a large tail) and retracting the limb (with the caudofemoralis longus) were abandoned in the course of avian evolution. This strongly suggests that details of the orientation (subhorizontal femur) and movement (primarily knee flexion) of the hind limb in extant birds are more properly viewed as derived, uniquely avian conditions, rather than as retentions of an ancestral dinosaurian pattern. Although many characters often associated with extant birds appeared much earlier in theropod evolution, reconstructing the locomotion of all theropods as completely birdlike ignores a wealth of differences that characterize birds.
Biochemical analyses of fossil enamel and dentin
Authors: Glimcher Melvin J. , Cohen-Solal Lola , Kossiva Dora , de Ricqles Armand
Published: July 2016

Amino acid analyses of undecalcified samples of fossil crocodile and rhinoceros enamel and dentin from mature teeth revealed that the total protein content of these mineralized fossil tissues varied from ~0.01–0.007% by weight. Except in one instance, amino acid analyses of the enamel proteins revealed them to be free of collagen and to have an amino acid composition similar to the proteins obtained from the enamel of mature modern vertebrates. Molecular sieving of the acid soluble enamel proteins demonstrated that the components consisted principally of small peptides and free amino acids, as in the enamel of modern vertebrates.

Based on the presence of hydroxyproline (hyp) and hydroxylysine (hyl), collagen was detected in undecalcified mature dentin of fossil rhinoceros, but not in undecalcified crocodile dentin. It was only by sequential extraction procedures that the presence of collagen in the dentin of fossil crocodile was established, emphasizing the utility and importance of analyzing the soluble components in specific extracts of the fossil. Based on these data and the concentrations of hyp and hyl in the material solubilized by the various solvents, the dentin of fossil rhinoceros contained considerably more collagen per weight and as a percentage of the total protein in the dentin than did the dentin of fossil crocodile.

As with modern dentin, EDTA and dilute acid solubilize the noncollagenous proteins and peptides found in fossil enamel and dentin, some of which contain O-phosphoserine [Ser(P)], an amino acid unique to mineralized connective tissues. Similar to recent reported findings from fossil bone, less of the original content of the noncollagenous proteins, including those phosphorylated, is degraded and removed from the enamel and dentin during fossilization than the percentage of dentinal collagen and the nonphosphorylated domains of the enamel proteins which are removed. This selective resistance to degradation and removal of the noncollagenous proteins, including phosphoproteins, may reflect the strong interaction of these proteins with the mineral phase of fossilized tissues. The amount and close packing of the inorganic crystals may also inhibit the interaction of the proteins in the interior of the enamel and dentin with the geochemical environment.
Experimental disintegration of regular echinoids: roles of temperature, oxygen, and decay thresholds
Authors: Kidwell Susan M. , Baumiller Tomasz
Published: July 2016

Laboratory experiments on regular echinoids indicate that low water temperatures retard organic decomposition far more effectively than anoxia, and that the primary role of anoxia in the preservation of articulated multi-element calcareous skeletons may be in excluding scavenging organisms. When tumbled at 20 rpm, specimens that were first allowed to decay for two days in warm seawater (30°C) disintegrated more than six times faster than specimens treated at room temperature (23°C) and more than an order of magnitude faster than specimens treated in cool water (11°C). In contrast, the effects of aerobic versus anerobic decay on disintegration rates were insignificant. The longer the period that specimens were allowed to decay before tumbling, the greater the rate at which specimens disintegrated, until a threshold time that appears to mark the decomposition of collagenous ligaments. This required a few days at 30°C, about two weeks at 23°C, and more than 4 weeks at 11°C forStrongylocentrotus. Up until this threshold, coronas disintegrate by a combination of cross-plate fractures and separation along plate sutures; cross-plate fractures thus can be taphonomic in origin and are not necessarily related to predation. Specimens decayed for longer-than-threshold periods of time disintegrate virtually instantaneously upon tumbling by sutural separation only. Undisturbed coronas can remain intact for months, sufficient time for epibiont occupation. Rates of disintegration were documented semi-quantitatively by recognizing seven stages of test disarticulation, and quantitatively by tensometer measures of test strength and toughness. The effects of temperature and oxygen on decay and the existence of a decay threshold in disintegration should apply at least in a qualitative sense to many other animals whose skeletons consist of multiple, collagen-bound elements.

Regular echinoids should still be perceived as taphonomically fragile organisms, but our results suggest the potential for latitudinal as well as bathymetric gradients in the preservation of fossil echinoid faunas. Echinoid preservation under any given set of conditions should also be a function of taxonomic differences in test construction (particularly stereom interlocking along plate sutures) as suggested by previous workers, although our experiments indicate that these effects should only be significant among post-threshold specimens. A survey of regular echinoids from Upper Cretaceous white chalk facies of Britain substantiates the basic experimental patterns, yielding examples of all disarticulation stages and significant taxonomic differences in quality of preservation. A diverse array of borers and encrusters on fossil coronas also corroborates the post-mortem persistence of some tests on mid-latitude seafloors.