76 research outputs found
Palaeoecology of Oligo-Miocene macropodoids determined from craniodental and calcaneal data
Analyses of craniodental and calcaneal material of extant macropodoids show that both dietary and locomotor types are statistically distinguishable. Application of the craniodental data to fossil macropodoids from the Oligo-Miocene of South Australia (Lake Eyre Basin) and Queensland (Riversleigh World Heritage Area) shows that these taxa were primarily omnivores or browsers. Specialized folivorous browsers were more prevalent in the Queensland deposits than in those of South Australia, suggesting more mesic conditions in the former. The calcaneal data showed that the Oligo-Miocene taxa clustered with extant generalized hoppers, in contrast to prior speculation that balbarids were quadrupedal rather than bipedal
Home range, habitat selection and diet of foxes (vulpes vulpes) in a semi-urban riparian environment
Between 2000 and 2002 the home range, habitat selection and diet of foxes were examined in the Dandenong Creek Valley, Melbourne, Australia. The mean home range was 44.6 ha (range 19.2–152.6 ha). A significant selection towards blackberry and gorse used as diurnal shelter was found during the day with an active avoidance of less structurally complex vegetation types. Although there was obvious selection of certain habitats, the diet of the foxes was highly general and opportunistic and thus offers little potential as a factor to manipulate in order to reduce fox abundance. Given the strong preference for blackberry and gorse as a shelter resource, a habitat-manipulation strategy is suggested whereby patches of blackberry and gorse are removed and replaced with less structurally complex vegetation. Such a strategy has the potential to influence the density of foxes in semi-urban riparian environments such as those discussed in this study.<br /
Selection on stability across ecological scales
Much of the focus in evolutionary biology has been on the adaptive differentiation among organisms. It is equally important to understand the processes that result in similarities of structure among systems. Here, we discuss examples of similarities occurring at different ecological scales, from predator–prey relations (attack rates and handling times) through communities (food-web structures) to ecosystem properties. Selection among systemic configurations or patterns that differ in their intrinsic stability should lead generally to increased representation of relatively stable structures. Such nonadaptive, but selective processes that shape ecological communities offer an enticing mechanism for generating widely observed similarities, and have sparked new interest in stability properties. This nonadaptive systemic selection operates not in opposition to, but in parallel with, adaptive evolution
Sedimentation rates test models of oceanic detachment faulting
This is the accepted manuscript version.The final version is available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/2014GL061555/full.Long-lived detachment faults play an important role in the construction of new oceanic
crust at slow-spreading mid-oceanic ridges. Although the corrugated surfaces of exposed
low-angle faults demonstrate past slip, it is difficult to determine whether a given fault is
currently active. If inactive, it is unclear when slip ceased. This judgment is crucial for
tectonic reconstructions where detachment faults are present, and for models of plate
spreading. We quantify variation in sediment thickness over two corrugated surfaces
near 16.5°N at the Mid-Atlantic Ridge using near-bottom CHIRP data. We show that the
distribution of sediment and tectonic features at one detachment fault is consistent with
slip occurring today. In contrast, another corrugated surface 20 km to the south shows a
sediment distribution suggesting that slip ceased ~150,000 years ago. Data presented here
provide new evidence for active detachment faulting, and suggest along-axis variations in
fault activity occur over tens of kilometers.This work was supported by the National Science Foundation grant number OCE-1155650
Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA)
Complex body size trends in the evolution of sloths (Xenarthra: Pilosa)
Background
Extant sloths present an evolutionary conundrum in that the two living genera are superficially similar (small-bodied, folivorous, arboreal) but diverged from one another approximately 30 million years ago and are phylogenetically separated by a radiation of medium to massive, mainly ground-dwelling, taxa. Indeed, the species in the two living genera are among the smallest, and perhaps most unusual, of the 50+ known sloth species, and must have independently and convergently evolved small size and arboreality. In order to accurately reconstruct sloth evolution, it is critical to incorporate their extinct diversity in analyses. Here, we used a dataset of 57 species of living and fossil sloths to examine changes in body mass mean and variance through their evolution, employing a general time-variable model that allows for analysis of evolutionary trends in continuous characters within clades lacking fully-resolved phylogenies, such as sloths.
Results
Our analyses supported eight models, all of which partition sloths into multiple subgroups, suggesting distinct modes of body size evolution among the major sloth lineages. Model-averaged parameter values supported trended walks in most clades, with estimated rates of body mass change ranging as high as 126 kg/million years for the giant ground sloth clades Megatheriidae and Nothrotheriidae. Inclusion of living sloth species in the analyses weakened reconstructed rates for their respective groups, with estimated rates for Megalonychidae (large to giant ground sloths and the extant two-toed sloth) were four times higher when the extant genus Choloepus was excluded.
Conclusions
Analyses based on extant taxa alone have the potential to oversimplify or misidentify macroevolutionary patterns. This study demonstrates the impact that integration of data from the fossil record can have on reconstructions of character evolution and establishes that body size evolution in sloths was complex, but dominated by trended walks towards the enormous sizes exhibited in some recently extinct forms
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