Evolutionary exploitation of design options by the first animals with hard skeletons.
(49/2344)
The set of viable design elements available for animals to use in building skeletons has been fully exploited. Analysis of animal skeletons in relation to the multivariate, theoretical "Skeleton Space" has shown that a large proportion of these options are used in each phylum. Here, we show that structural elements deployed in the skeletons of Burgess Shale animals (Middle Cambrian) incorporate 146 of 182 character pairs defined in this morphospace. Within 15 million years of the appearance of crown groups of phyla with substantial hard parts, at least 80 percent of skeletal design elements recognized among living and extinct marine metazoans were exploited. (+info)
Functional exoenzymes as indicators of metabolically active bacteria in 124,000-year-Old sapropel layers of the eastern Mediterranean Sea.
(50/2344)
Hydrolytic exoenzymes as indicators of metabolically active bacteria were investigated in four consecutive sapropel layers collected from bathyal sediments of the eastern Mediterranean Sea. For comparison, the organic carbon-poor layers between the sapropels, sediment from the anoxic Urania basin, and sediments of intertidal mud flats of the German Wadden Sea were also analyzed. The sapropel layers contained up to 1.5. 10(8) bacterial cells cm(-3), whereas cell numbers in the intermediate layers were lower by a factor of 10. In sapropels, the determination of exoenzyme activity with fluorescently labeled substrate analogues was impaired by the strong adsorption of up to 97% of the enzymatically liberated fluorophores (4-methylumbelliferone [MUF] and 7-amino-4-methylcoumarin [MCA]) to the sediment particles. Because all established methods for the extraction of adsorbed fluorophores proved to be inadequate for sapropel sediments, we introduce a correction method which is based on the measurement of equilibrium adsorption isotherms for both compounds. Using this new approach, high activities of aminopeptidase and alkaline phosphatase were detected even in a 124,000-year-old sapropel layer, whereas the activity of beta-glucosidase was low in all layers. So far, it had been assumed that the organic matter which constitutes the sapropels is highly refractory. The high potential activities of bacterial exoenzymes indicate that bacteria in Mediterranean sapropels are metabolically active and utilize part of the subfossil kerogen. Since a high adsorption capacity was determined not only for the low-molecular-weight compounds MUF and MCA but also for DNA, the extraordinarily strong adsorption of structurally different substrates to the sapropel matrix appears to be the major reason for the long-term preservation of biodegradable carbon in this environment. (+info)
Neanderthal diet at Vindija and Neanderthal predation: the evidence from stable isotopes.
(51/2344)
Archeological analysis of faunal remains and of lithic and bone tools has suggested that hunting of medium to large mammals was a major element of Neanderthal subsistence. Plant foods are almost invisible in the archeological record, and it is impossible to estimate accurately their dietary importance. However, stable isotope (delta(13)C and delta(15)N) analysis of mammal bone collagen provides a direct measure of diet and has been applied to two Neanderthals and various faunal species from Vindija Cave, Croatia. The isotope evidence overwhelmingly points to the Neanderthals behaving as top-level carnivores, obtaining almost all of their dietary protein from animal sources. Earlier Neanderthals in France and Belgium have yielded similar results, and a pattern of European Neanderthal adaptation as carnivores is emerging. These data reinforce current taphonomic assessments of associated faunal elements and make it unlikely that the Neanderthals were acquiring animal protein principally through scavenging. Instead, these findings portray them as effective predators. (+info)
Solution to Darwin's dilemma: discovery of the missing Precambrian record of life.
(52/2344)
In 1859, in On the Origin of Species, Darwin broached what he regarded to be the most vexing problem facing his theory of evolution-the lack of a rich fossil record predating the rise of shelly invertebrates that marks the beginning of the Cambrian Period of geologic time ( approximately 550 million years ago), an "inexplicable" absence that could be "truly urged as a valid argument" against his all embracing synthesis. For more than 100 years, the "missing Precambrian history of life" stood out as one of the greatest unsolved mysteries in natural science. But in recent decades, understanding of life's history has changed markedly as the documented fossil record has been extended seven-fold to some 3,500 million years ago, an age more than three-quarters that of the planet itself. This long-sought solution to Darwin's dilemma was set in motion by a small vanguard of workers who blazed the trail in the 1950s and 1960s, just as their course was charted by a few pioneering pathfinders of the previous century, a history of bold pronouncements, dashed dreams, search, and final discovery. (+info)
Nonavian feathers in a late Triassic archosaur.
(53/2344)
Longisquama insignis was an unusual archosaur from the Late Triassic of central Asia. Along its dorsal axis Longisquama bore a series of paired integumentary appendages that resembled avian feathers in many details, especially in the anatomy of the basal region. The latter is sufficiently similar to the calamus of modern feathers that each probably represents the culmination of virtually identical morphogenetic processes. The exact relationship of Longisquama to birds is uncertain. Nevertheless, we interpret Longisquama's elongate integumentary appendages as nonavian feathers and suggest that they are probably homologous with avian feathers. If so, they antedate the feathers of Archaeopteryx, the first known bird from the Late Jurassic. (+info)
Can fast early rates reconcile molecular dates with the Cambrian explosion?
(54/2344)
Molecular dates consistently place the divergence of major metazoan lineages in the Precambrian, leading to the suggestion that the 'Cambrian explosion' is an artefact of preservation which left earlier forms unrecorded in the fossil record. While criticisms of molecular analyses for failing to deal with variation in the rate of molecular evolution adequately have been countered by analyses which allow both site-to-site and lineage-specific rate variation, no analysis to date has allowed the rates to vary temporally. If the rates of molecular evolution were much higher early in the metazoan radiation, molecular dates could consistently overestimate the divergence times of lineages. Here, we use a new method which uses multiple calibration dates and an empirically determined range of possible substitution rates to place bounds on the basal date of divergence of lineages in order to ask whether faster rates of molecular evolution early in the metazoan radiation could possibly account for the discrepancy between molecular and palaeontological date estimates. We find that allowing basal (interphylum) lineages the fastest observed substitution rate brings the minimum possible divergence date (586 million years ago) to the Vendian period, just before the first multicellular animal fossils, but excludes divergence of the major metazoan lineages in a Cambrian explosion. (+info)
An empirical assessment of taxic paleobiology.
(55/2344)
The analysis of major changes in faunal diversity through time is a central theme of analytical paleobiology. The most important sources of data are literature-based compilations of stratigraphic ranges of fossil taxa. The levels of error in these compilations and the possible effects of such error have often been discussed but never directly assessed. We compared our comprehensive database of trilobites to the equivalent portion of J. J. Sepkoski Jr.'s widely used global genus database. More than 70% of entries in the global database are inaccurate; however, as predicted, the error is randomly distributed and does not introduce bias. (+info)
Timing the radiations of leaf beetles: hispines on gingers from latest cretaceous to recent.
(56/2344)
Stereotyped feeding damage attributable solely to rolled-leaf hispine beetles is documented on latest Cretaceous and early Eocene ginger leaves from North Dakota and Wyoming. Hispine beetles (6000 extant species) therefore evolved at least 20 million years earlier than suggested by insect body fossils, and their specialized associations with gingers and ginger relatives are ancient and phylogenetically conservative. The latest Cretaceous presence of these relatively derived members of the hyperdiverse leaf-beetle clade (Chrysomelidae, more than 38,000 species) implies that many of the adaptive radiations that account for the present diversity of leaf beetles occurred during the Late Cretaceous, contemporaneously with the ongoing rapid evolution of their angiosperm hosts. (+info)