Large-bodied Taxa Research Articles

Revision of the Late Jurassic teleosaurid genus Machimosaurus (Crocodylomorpha, Thalattosuchia).

Machimosaurus was a large-bodied genus of teleosaurid crocodylomorph, considered to have been durophagous/chelonivorous, and which frequented coastal marine/estuarine ecosystems during the Late Jurassic. Here, we revise the genus based on previously described specimens and revise the species within this genus. We conclude that there were three European Machimosaurus species and another taxon in Ethiopia. This conclusion is based on numerous lines of evidence: craniomandibular, dental and postcranial morphologies; differences in estimated total body length; geological age; geographical distribution; and hypothetical lifestyle. We re-diagnose the type species Machimosaurus hugii and limit referred specimens to only those from Upper Kimmeridgian–Lower Tithonian of Switzerland, Portugal and Spain. We also re-diagnose Machimosaurus mosae, demonstrate that it is an available name and restrict the species to the uppermost Kimmeridgian–lowermost Tithonian of northeastern France. We re-diagnose and validate the species Machimosaurus nowackianus from Harrar, Ethiopia. Finally, we establish a new species, Machimosaurus buffetauti, for the Lower Kimmeridgian specimens of France and Germany (and possibly England and Poland). We hypothesize that Machimosaurus may have been analogous to the Pliocene–Holocene genus Crocodylus in having one large-bodied taxon suited to traversing marine barriers and additional, geographically limited taxa across its range.

Laryngotracheal and cervical muscular anatomy in the genus Uroplatus (Gekkota: Gekkonidae) in relation to distress call emission

The gekkonid Uroplatus exhibits many autapomorphic features. The laryngotracheal region has long been noted to display unusual characteristics, with a widely expanded and membrane-roofed anterior portion of the trachea being prominent among these. It has been proposed that this tracheal expansion serves as a reservoir for pressurised air that is explosively released and provides the energy for the loud distress calls released by these lizards. To determine whether this hypothesis is supported by associated anatomical features, we examined the laryngotracheal region in more detail, for 6 of 14 of the species within the genus, and compared the results to what is known of the laryngotracheal anatomy of Afro-Malagasy geckos. The muscles of the gular region, and the form and dimensions of the trachea, larynx and their adnexa, are described. Modifications of the gular muscles and their attachments render the larynx of Uroplatus more mobile in the oropharyngeal region, and in large-bodied taxa (U. lineatus, U. sikorae) the trachea exhibits the degree of expansion previously observed for U. fimbriatus. In these taxa the paired gular muscles fail to meet in the ventral midline and are, instead, bridged by fascial sheets. These modifications are consistent with ventral displacement of the anterior terminus of the trachea when charged with pressurised air, prior to the opening of the glottal valve and the release of a loud, harmonically-unstructured and explosive distress call. Such calls are likely directed at avian and mammalian predators to induce a startle response. The range of anatomical form of the laryngotracheal region exhibited within Uroplatus provides insights into the variation of laryngotracheal structure, such as incomplete tracheal rings and a conical trachea, which are exhibited by other Afro-Malagasy geckos.

Patterns in estuarine macrofauna body size distributions: The role of habitat and disturbance impact

Schwinghamer's (1981) habitat architecture hypothesis for body mass spectra in marine sediments predicts a single macrofauna mode in response to the bulk nature of the sediment. This proposition was examined for intertidal macrofauna from a well-studied estuarine system, using kernel density estimation to define modality and the locations of peaks and troughs. Three sedimentary environments and habitats were examined along a disturbance gradient related to eutrophication. Our results indicate that bimodality is likely to occur within the macrofauna size range, which weakens the habitat architecture model and casts doubts on the mechanisms behind other modes in benthic size spectra. The location of the modes and intervening trough were not conservative and not apparently related to sediment grain size or habitat structure, but somewhat dependent on the presence of particular species: the presence or absence of large numbers of individuals of Hydrobia ulvae and larger-bodied taxa such as Scrobicularia plana and Hediste diversicolor. Alternative competing hypotheses are explored for the observed results, including Warwick's (1984) phylogenetic explanation, but taking into consideration both species composition and disturbance impact, it seems most likely Holling's (1992) textural discontinuity hypothesis, as a measure of resilience, could be a plausible explanation.

Ecophysiological forecasting for environmental change adaptation

Ecophysiological forecasting for environmental change adaptation

Can clade age alone explain the relationship between body size and diversity?

One of the most striking patterns observed among animals is that smaller-bodied taxa are generally much more diverse than larger-bodied taxa. This observation seems to be explained by the mere fact that smaller-bodied taxa tend to have an older evolutionary origin and have therefore had more time to diversify. A few studies, based on the prevailing null model of diversification (i.e. the stochastic constant-rate birth–death model), have suggested that this is indeed the correct explanation, and body-size dependence of speciation and extinction rates does not play a role. However, there are several potential shortcomings to these studies: a suboptimal statistical procedure and a relatively narrow range of body sizes in the analysed data. Here, we present a more coherent statistical approach, maximizing the likelihood of the constant-rate birth–death model with allometric scaling of speciation and extinction rates, given data on extant diversity, clade age and average body size in each clade. We applied our method to a dataset compiled from the literature that includes a wide range of Metazoan taxa (range from midges to elephants). We find that the higher diversity among small animals is indeed, partly, caused by higher clade age. However, it is also partly caused by the body-size dependence of speciation and extinction rates. We find that both the speciation rate and extinction rate decrease with body size such that the net diversification rate is close to 0. Even more interestingly, the allometric scaling exponent of speciation and extinction rates is approximately −0.25, which implies that the per generation speciation and extinction rates are independent of body size. This suggests that the observed relationship between diversity and body size pattern can be explained by clade age alone, but only if clade age is measured in generations rather than years. Thus, we argue that the most parsimonious explanation for the observation that smaller-bodied taxa are more diverse is that their evolutionary clock ticks faster.

A comparison of analyses of drilling predation on fossil bivalves: Bulk- vs. taxon-specific sampling and the role of collector experience

Taxon-specific (targeted) sampling, although used in many studies of fossil predator–prey interactions, has been considered to yield less robust predation-related data than bulk sampling. In this study, we tested the utility of taxon-specific sampling by comparing drilling predation data from taxon-specific samples collected by novice and veteran collectors with data from bulk samples collected at the same sites. The bivalves Lirophora latilirata, Astarte concentrica, and Cyclocardia granulata were collected by targeted and bulk sampling from the Lower Pleistocene lower Waccamaw Formation at five localities in southeastern North Carolina. Variables studied included shell length and thickness, left-right valve frequency, drillhole site and prey size selectivity, drilling frequency, and prey effectiveness. Of 139 comparisons, 75% yielded no difference between predation metrics from targeted and bulk samples; most significant differences involved size-related variables. When data were size standardized (as is frequently done in predation studies), 97% of 70 tests showed no difference between the two collecting methods. In addition, when samples collected by novice and veteran collectors were compared, 97% of 214 tests showed no significant differences in predation metrics; the only significant differences involved size-related variables. Results were similar for all three species and across localities. Taxon-specific sampling therefore produces reliable quantitative results for studies of drilling predation, especially when data are standardized by specimen size, and may be superior to bulk sampling when rare or large-bodied taxa are studied.

FAUNAL RESOURCES AND HUMAN ENVIRONMENTAL IMPACTS IN THE SAN SIMON VALLEY, SOUTHEASTERN ARIZONA

Material remains (e.g., ceramics, ground stone, and flaked stone) and demographic data show that the San Simon Basin in southeastern Arizona supported numerous small-scale farming communities in the Late Archaic and Pit Structure periods. Residents of the basin during these periods used the resources of their immediate environments more intensively than earlier occupants of the area, and their actions may have contributed to a population crash at the end of the Pit Structure period. The earliest faunal assemblages, with their virtual lack of large-bodied taxa, suggest that residents of the San Simon Basin quickly impacted their fragile desert environment. All San Simon faunal assemblages differ from coeval communities in the nearby Mimbres and Hohokam regions in that they contain fewer taxa and specifically fewer large-bodied taxa (e.g., artiodactyls).

A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora)

Therizinosaurians are among the most poorly understood dinosaurs. Their unusual morphology and fragmentary fossil record has precluded a synthetic understanding of the group since their remains were first discovered over 60 years ago. Although the clade was recently substantiated as a monophyletic group of maniraptoran theropods, little foundational work has been conducted at the species level. A recent plethora of therizinosaurian discoveries – including the most complete primitive and derived members recovered to date – permits an alpha taxonomic and phylogenetic re-evaluation of the clade. The phylogenetic analysis presented is the most comprehensive yet conducted for Therizinosauria, and provides a foundation for scrutinizing previous definitions of Therizinosauria, Therizinosauroidea and Therizinosauridae. Here, support is provided for the maintenance of all three taxa; however, Therizinosauria is redefined and Falcarius is excluded from Therizinosauroidea. In addition, the previously described therizinosauroids, Beipiaosaurus, Enigmosaurus, Suzhousaurus, Segnosaurus and Therizinosaurus, are rediagnosed and photodocumented. In contrast to other analyses, the ingroup topology recovered in this study suggests intermediate (therizinosauroid) status for Neimongosaurus, Erliansaurus and Enigmosaurus (based on relatively primitive pelvic morphology), despite the derived forelimb anatomy evident in the former two taxa. Here, the large-bodied taxa Nothronychus and Nanshiungosaurus brevispinus are recovered as therizinosaurids. This discrepancy indicates a relatively complex pattern of mosaic evolution, which may ultimately be found to correlate with body-size trends in the clade. This work also reviews the chronostratigraphic and biogeographic distribution of therizinosaurian taxa and putatively referred elements and finds no compelling evidence of the clade outside of Asia and North America, nor for the referral of therizinosaurian materials from Kazakhstan to cf. Neimongosaurus. Time calibration of ingroup relationships indicates a pre-Turonian dispersal event is needed to account for the presence of therizinosaurids in the Late Cretaceous of North America and Asia; this conclusion supports previous hypotheses of a Laurasian faunal interchange event during the Albian.

Taphonomic Implications of the Use of Bone as Fuel

This paper explores the effects of the use of bone as fuel on archaeological skeletal part representation. Faunal data from the Paleolithic site of Saint-Césaire show that this activity may present an archaeological signature similar to that of differential preservation. The bones most frequently burned at Saint-Césaire are also those that are the least dense and that contain the most grease. The analysis of faunal remains from Saint-Césaire also suggests that spongy bone fragments from small-bodied and large-bodied taxa are subject to differential identification.

Biological Responses to Contrasting Hydrology in Backwaters of Upper Mississippi River Navigation Pool 25

Water level management in Mississippi River Pool 25 differentially influences off-channel habitats in the mid-pool and lower pool. Hydrologic models indicate lower pool off-channel habitats dry with greater frequency and duration compared to similar habitats at mid-pool. We examined the influence of this contrasting hydrology on substrate characteristics, organic matter, macroinvertebrate, and fish communities in off-channel habitats during 2001--2003. Benthic organic matter standing stocks were stable in mid-pool habitats but lower pool values were variable because of annual differences in moist-soil vegetation production. Generally, small-bodied and multivoltine invertebrate taxa had high community biomass and dominated lower pool habitats, whereas longer-lived and large-bodied taxa were more abundant and had higher community biomass in mid-pool habitats having longer hydroperiods. Fish communities were dominated by cyprinids in both habitats, and mid-pool habitats tended to be higher in overall species richness. Unique fish taxa were collected in each pool, with primarily rheophilic forms in mid-pool habitats and limnophilic forms in lower pool habitats. Results indicate that contrasting hydrology associated with a mid-pool control point directly and indirectly influences biological communities in off-channel habitats. Further, management regimes that promote hydrologic diversity in off-channel habitats may enhance biological diversity at larger spatial and temporal scales.

Population Growth and Body Size in Five Rotifer Species in Response to Variable Food Concentration

ABSTRACT We cultured five species of rotifers (Brachionus angularis, B. calyciflorus, B. patulus, Euchlanis dilatata, and Lepadella patella) under different algal concentrations (Chlorella vulgaris) for a period of 10 to 15 days, and we derived the rate of population growth per day (r) for each rotifer species. Using a regression between food concentration and the r for each rotifer species, we calculated the minimal food level required to maintain a zero growth rate (threshold food concentration). For all the tested species, there was a direct and positive relationship between food concentration and peak population density. The highest peak density (738 ind. mL−l) was achieved by L. patella at 0.4X106 cells mL−1. At this food density, B. calyciflorus was only able to reach about 10 ind. mL−1. The highest r value (0.46 d−1) was observed for L. patella at 0.4X106 cells mL−1; at this food concentration, B. calyciflorus and E. dilatata had much lower r values (0.21 and 0.23 d−1, respectively). On a dry weight basis, L. patella had the lowest threshold food concentration (0.0023 mg C t−1 d−1), while B. calyciflorus needed much higher levels (2.04 mg C L−1 d−1). Larger-bodied taxa had higher threshold food concentrations than the smaller-bodied rotifers.

THE ECOLOGICAL SIGNIFICANCE OF TALLGRASS PRAIRIE ARTHROPODS

Tallgrass prairie (TGP) arthropods are diverse and abundant, yet they remain poorly documented and there is still much to be learned regarding their ecological roles. Fire and grazing interact in complex ways in TGP, resulting in a shifting mosaic of resource quantity and quality for primary consumers. Accordingly, the impacts of arthropod herbivores and detritivores are expected to vary spatially and temporally. Herbivores generally do not control primary production. Rather, groups such as grasshoppers have subtle effects on plant communities, and their most significant impacts are often on forbs, which represent the bulk of plant diversity in TGP. Belowground herbivores and detritivores influence root dynamics and rhizosphere nutrient cycling, and above- and belowground groups interact through plant responses and detrital pathways. Large-bodied taxa, such as cicadas, can also redistribute significant quantities of materials during adult emergences. Predatory arthropods are the least studied in terms of ecological significance, but there is evidence that top-down processes are important in TGP.

The inverse relationship between species diversity and body mass: do primates play by the "rules"?

Evolutionary biologists have long commented on a seemingly universal "rule" of nature-that in large taxonomic assemblages from groups as diverse as bacteria, plants, insects, marine invertebrates, fish, reptiles, amphibians, birds, and mammals, there exists a frequency distribution of body sizes among species that is highly skewed to the right (positive skewness). This distribution reflects the strong inverse, or negative, relationship often noted between mean body size of taxa and the number of species they contain--i.e., the observation that small body size is often associated with high species diversity (speciosity). This is sometimes "explained" by recourse to the idea that smaller-bodied taxa are able to subdivide their environments more finely than larger-bodied taxa. With but few exceptions, the applicability of this "rule" to the Order Primates has not been studied in any detail. In this study I address the following questions of (paleo)anthropological interest: (1) How speciose is the Order Primates? (2) Does this biological "rule" characterize the Order Primates (at any taxonomic level) in any meaningful way? (3) Does the association between speciosity and body mass within the Order Primates provide any useful models for interpreting and/or predicting speciosity in the fossil primate record? Using phylogenetically independent contrasts methods, I conclude that the answers to those three questions are: (1) not very; (2) no; and (3) not particularly (with the possible exception of larger-bodied taxa).

Prehistoric mammals of Australia and New Guinea: One hundred million years of evolution.

IF this book had been written fifty years ago, it would have been rather short. In 1953, the fossil record of Australasian mammals consisted almost entirely of large-bodied taxa from a handful of Plio- Pleistocene localities (up to 5 million years old). Since then, our knowledge of Australasia's fossil mammals has increased exponentially, not only in the number of described taxa, but also in the spatial and temporal spread of known fossil deposits. The fossil record is now estimated to be over 100 million years in extent (hence the subtitle of the book) with over 120 extinct genera so far described and many more known to exist but awaiting formal taxonomic circumscription. These taxa are known from many deposits spread across the Australian continent and also in New Guinea. The authors of this book have all had significant roles in this renaissance in Australasian vertebrate palaeontology.

Empirical estimates of minimum viable population sizes for primates: tens to tens of thousands?

AbstractTheoretical estimates of long‐term minimum viable population (MVP) sizes for mammals indicate MVPs of tens of thousands, even a million. However, data to test the theoretical estimates are effectively non‐existent. I here use information on distributions of primates on islands of southeast Asia to provide empirical estimates of the size of multi‐millennial MVPs following the post‐Pleistocene insularization in the Sunda region. Small Sunda region islands have fewer taxa than do large ones. Assuming extinction on the small islands, the MVP size is somewhere between the population size on the smallest island on which the taxon is extant and that on the largest island on which the taxon no longer exists (population size calculated as density of taxon by area of land available). Results for eight to ten genera (depending on the taxonomy) on 35 islands indicate MVPs of perhaps a few score for Nycticebus (loris) and Macaca (macaque) to several thousands, or scores of thousands, for Pongo (orang‐utan) and Symphalangus (siamang). Large‐bodied taxa have significantly larger MVPs than do small‐bodied taxa. Only four protected areas in southeast Asia are large enough to conserve the smaller MVPs of the siamang and orang‐utan.

Phylogenetic Relationships of the Large-Bodied Members of the African Lizard Genus Pachydactylus (Reptilia: Gekkonidae)

Evolutionary relationships among large-bodied species in the gekkonid genus Pachydactylus were investigated using mtDNA sequences from the cytochrome b and 16S ribosomal RNA genes. We combined these data in parsimony and maximum likelihood analyses to address several systematic issues regarding the eight large-bodied taxa, including their phylogenetic position in Pachydactylus as a whole. The large-bodied Pachydactylus do not form a monophyletic group; rather, large size appears to be plesiomorphic. Neither do the large-bodied species exhibiting regional integumentary loss constitute a natural group, as this unusual predator escape mechanism appears in two disparate clades. Both the namaquensis and bibronii groups are monophyletic, the latter being strongly supported. Pachydactylus tuberculosus and Pachydactylus tetensis are consistently basal across analyses, although their phylogenetic position relative to the sister taxon Rhoptropus is uncertain. Equally weighted parsimony recovered a weakly supported Pachydactylus sensu lato (i.e., Pachydactylus tuberculosus and tetensis), whereas weighted parsimony and maximum likelihood analyses depict tetensis and tuberculosus as taxa sister to Pachydactylus Rhoptropus. Concordance across all analytical methods lends validity to the synonyms Homodactylus Gray and Elasmodactylus Boulenger, which could be resurrected without compromising the monophyly of the remaining Pachydactylus.