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Books > Earth & environment > Earth sciences > Palaeontology > General
Modern videography provides an ever-widening window into subsea
echinoderm life with vast potential for new knowledge. Supported by
video evidence throughout, this Element begins with time-lapse
video made in 1983 on film, using an off-the-shelf camera, flash,
and underwater housings. Although quality has now been
significantly improved by digital imagery, films from over thirty
years ago captured crinoid feeding behavior previously unknown and
demonstrated a great potential to learn about many other aspects of
their biology. This sequence is followed by several examples of
recent digital videography from submersibles of deep-sea crinoids
and remotely operated vehicles (ROVs) (stalked and unstalked), as
well as close-up video of crinoids in aquaria. These recent studies
enabled a new classification of crinoid arm postures, provided
detailed views of food particle capture, and revealed a wide range
of behaviors in taxa never before seen in life.
New material attributable to Deltasuchus motherali, a neosuchian
from the Cenomanian of Texas, provides sampling across much of the
ontogeny of this species. Detailed descriptions provide information
about the paleobiology of this species, particularly with regards
to how growth and development affected diet. Overall snout shape
became progressively wider and more robust with age, suggesting
that dietary shifts from juvenile to adult were not only a matter
of size change, but of functional performance as well. These newly
described elements provide additional characters upon which to base
more robust phylogenetic analyses. The authors provide a revised
diagnosis of this species, describing the new material and
discussing incidents of apparent ontogenetic variation across the
sampled population. The results of the ensuing phylogenetic
analyses both situate Deltasuchus within an endemic clade of
Appalachian crocodyliforms, separate and diagnosable from
goniopholidids and pholidosaurs, herein referred to as
Paluxysuchidae. This title is also available as Open Access on
Cambridge Core.
Recent advances in statistical approaches called phylogenetic
comparative methods (PCMs) have provided paleontologists with a
powerful set of analytical tools for investigating evolutionary
tempo and mode in fossil lineages. However, attempts to integrate
PCMs with fossil data often present workers with practical
challenges or unfamiliar literature. This Element presents guides
to the theory behind and the application of PCMs with fossil taxa.
Based on an empirical dataset of Paleozoic crinoids, example
analyses are presented to illustrate common applications of PCMs to
fossil data, including investigating patterns of correlated trait
evolution and macroevolutionary models of morphological change. The
authors emphasize the importance of accounting for sources of
uncertainty and discuss how to evaluate model fit and adequacy.
Finally, the authors discuss several promising methods for modeling
heterogeneous evolutionary dynamics with fossil phylogenies.
Integrating phylogeny-based approaches with the fossil record
provides a rigorous, quantitative perspective on understanding key
patterns in the history of life.
A classic work from the Yale Peabody Museum of Natural History
describing the mosasaurs, a group of large predatory marine lizards
of the Mesozoic Mosasaurs have captured the imagination of readers
everywhere interested in prehistoric life, and they remain a focus
of paleontological study to this day. This edition of Dale
Russell's Systematics and Morphology of American Mosasaurs presents
the complete, classic text, generously illustrated with more than
one hundred drawings and photographs, and includes a new foreword
by vertebrate paleontologist Jacques A. Gauthier (Yale University
and Yale Peabody Museum of Natural History). Distributed for the
Yale Peabody Museum of Natural History
The stable chromium (Cr) isotope system has emerged over the past
decade as a new tool to track changes in the amount of oxygen in
earth's ocean-atmosphere system. Much of the initial foundation for
using Cr isotopes ( 53Cr) as a paleoredox proxy has required recent
revision. However, the basic idea behind using Cr isotopes as redox
tracers is straightforward-the largest isotope fractionations are
redox-dependent and occur during partial reduction of Cr(VI). As
such, Cr isotopic signatures can provide novel insights into Cr
redox cycling in both marine and terrestrial settings. Critically,
the Cr isotope system-unlike many other trace metal proxies-can
respond to short-term redox perturbations (e.g., on timescales
characteristic of Pleistocene glacial-interglacial cycles). The Cr
isotope system can also be used to probe the earth's long-term
atmospheric oxygenation, pointing towards low but likely dynamic
oxygen levels for the majority of Earth's history.
The history of life on earth is largely reconstructed from
time-averaged accumulations of fossils. A glimpse at ecologic-time
attributes and processes is relatively rare. However, the
time-sensitive and predictability of echinoderm disarticulation
makes them model organisms to determine post-mortem transportation
and allows recognition of ecological-time data within
paleocommunity accumulations. Unlike many other fossil groups, this
has allowed research on many aspects of echinoderms and their
paleocommunities, such as the distribution of soft tissues,
assessment of the amount of fossil transportation prior to burial,
determination of intraspecific variation, paleocommunity
composition, estimation of relative abundance of taxa in
paleocommunities, determination of attributes of niche
differentiation, etc. Crinoids and echinoids have received the most
amount of taphonomic research, and the patterns present in these
two groups can be used to develop a more thorough understanding of
all echinoderm clades.
The quantification of morphology through time is a vital tool in
elucidating macroevolutionary patterns. Studies of disparity
require intense effort but can provide insights beyond those gained
using other methodologies. Over the last several decades, studies
of disparity have proliferated, often using echinoderms as a model
organism. Echinoderms have been used to study the methodology of
disparity analyses and potential biases as well as documenting the
morphological patterns observed in clades through time. Combining
morphological studies with phylogenetic analyses or other disparate
data sets allows for the testing of detailed and far-reaching
evolutionary hypotheses.
Echinoderms elaborate a calcite skeleton composed of numerous
plates with a distinct microstructure (stereom) that can be
modelled into different shapes thanks to the use of a transient
amorphous calcium carbonate (ACC) precursor phase and the
incorporation of an intraorganic matrix during biomineralization. A
variety of different types of stereom microarchitecture have been
distinguished, each of them optimized for a specific function. For
instance, a regular, galleried stereom typically houses collagenous
ligaments, whereas an irregular, fine labyrinthic stereom commonly
bears muscles. Epithelial tissues, in turn, are usually associated
with coarse and dense stereom microfabrics. Stereom can be
preserved in fossil echinoderms and a wide array of investigating
methods are available. As many case studies have shown, a great
deal of important paleobiological and paleoecological information
can be decoded by studying the stereom microstructure of extinct
echinoderms.
The principles of stratigraphic paleobiology can be readily applied
to the nonmarine fossil record. Consistent spatial and temporal
patterns of accommodation and sedimentation in sedimentary basins
are an important control on stratigraphic architecture. Temperature
and precipitation covary with elevation, causing significant
variation in community composition, and changes in base level cause
elevation to undergo predictable changes. These principles lead to
eight sets of hypotheses about the nonmarine fossil record. Three
relate to long-term and cyclical patterns in the preservation of
major fossil groups and their taphonomy, as well as the occurrence
of fossil concentrations. The remaining hypotheses relate to the
widespread occurrence of elevation-correlated gradients in
community composition, long-term and cyclical trends in these
communities, and the stratigraphic position of abrupt changes in
community composition. Testing of these hypotheses makes the
stratigraphic paleobiology of nonmarine systems a promising area of
investigation.
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