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UCMP abstracts 2011 Society of Vertebrate Paleontology (SVP) annual meeting
Phylogenetic mapping of traits of the avian altricial precocial spectrum, and its implications for inferring early avialan life history
Extant birds can be classified according to development of offspring along an altricialprecocial spectrum, with fully-functional, feathered individuals at one end (precocial) and helpless, blind, naked chicks at the other (altricial). However, evolution of the various reproductive strategies along this spectrum has been difficult to understand because few studies have placed these data in phylogenetic context. I separated the common division of the precocial-altricial spectrum into seven character states to map life-history data onto both molecular and morphological avian phylogenies. The two trees imply different results: the former suggests that altriciality was evolved independently at least four times (by Passeriformes, Coraciiformes, Cuculiformes, and Apodiformes), while the latter implies a single origin. Both outcomes underscore the need for an avian phylogeny that integrates morphological and molecular data.
Comparing extant mammalian species diversity to paleospecies richness: Problems and solutions
Recent analyses of current extinction rates in extant animals have suggested that we may be in the midst of a sixth mass extinction. However, assessment of the true size, rate, and timing of this extinction has been made difficult because of the lack of a comparison between the natural paleodiversity baseline and extant species diversity. Here I use the NEOMAP distributed database of mammalian occurrences to create and compare a baseline, as assessed by species-area curves, for the past 30 million years to modern mammalian species diversity. Species-occurrence data was subjected to rarefaction and other sample standardization techniques and, in combination with the Berkeley Mapper software, was used to derive species-area curves by geographic region for distinct time slices from the late Oligocene through the Modern. Preliminary results indicate that mammalian species diversity, while severely depressed during the Holocene, appears to increase during the Modern time interval. Upon closer inspection, it appears that this rise in diversity is a result of a large increase in the diversity of small mammals (Rodentia, Lagomorpha, and Insectivora), primarily members of the rodent families Heteromyidae, Geomyidae, and Sciuridae – groups whose species are often difficult to diagnose in the fossil record. I suggest that this anomalous modern diversity shift is likely an artifact caused by the different taxonomic standards used by paleontologists and neontologists. Therefore, any attempt to assess the magnitude of the current extinction in mammals needs to account for these fundamental differences by employing alternative methodologies such as more detailed taxonomic studies of problematic fossil groups and reassessments of extant species using paleontological techniques.
A third azhdarchid pterosaur from the Two Medicine Formation (Campanian) of Montana
New material of an azhdarchid pterodactyloid pterosaur (MOR 553) was recovered from Jack’s Birthday Site (JBS) in the Two Medicine Formation of northwestern Montana. With few exceptions (e.g. Quetzalcoatlus, Montanazhdarcho), reported members of this group are represented by few or partial elements, or, as in the case of Zhejiangopterus, are two-dimensionally preserved which prevents evaluation of many morphological and osteological details. Taphonomic modification of the Birthday Site material includes disarticulation, some lithostatic compaction, and possibly trampling-induced breakage. Nevertheless, the new material is generally well-preserved and three-dimensional. The broad range of elements allows evaluation of newly recognized post-cranial characters of the humerus, antebrachium, pelvis, and tarsus. The new form shares several elements in common with the two previously described Montana azhdarchids of similar age (including syncarpals and proximal humerus) and character analysis demonstrates their close relationships. Previous functional arguments for land-based feeding strategies have emphasized the anatomy of the skull and cervical vertebrae. The preservation of the several carpal, manus and tarsal bones now allows consideration of these under-represented elements. The robust nature of the carpus and manus and the unique expanded morphology of the proximal phalanges suggests weight-bearing, further supporting the hypothesis that azhdarchids were well adapted to terrestrial locomotion. Jack's Birthday Site represents a small floodplain pond far inland, perhaps 200 km from the Western Interior Cretaceous Seaway. The JBS azhdarchid provides additional evidence for the proposed biogeographic and ecological associations of this group with open environments decidedly far from marine sediments.
Are Raw Taxic Counts Really Reflecting Shifts in Diversity Dynamis? A Case Study in Canids
To explore patterns in diversity at macroevolutionary time scales, paleontologists have traditionally counted taxa to estimate paleobiodiversity. Although these methods may be employed in phylogenetic context, they rarely account for the relative amount of evolutionary depth lost for each taxon. Loss of the same number of species may differentially affect the higher-level diversity in a community, depending on the taxa involved and their phylogenetic isolation from other taxa. Other biological methods that account for evolutionary depth may have value in assessing shifts in diversity in the fossil record. We tested these methods for fossil taxa using a species-level phylogeny of borophagine and canine canids and compared shifts in taxonomic versus phylogenetic diversity across the Mid-Miocene Climactic Optimum (MMCO), using methods common in modern conservation biology research. Extant communities are synchronous, and phylogenetic diversity is normally compared among different locations. In our study, phylogenetic diversity (PD) was compared across bins that were defined as time intervals. We examined these trends in canid diversity at two scales: one broader (pre- and post-MMCO), and one finer (5My intervals across the MMCO). Both scales show species richness and PD increasing before the MMCO, but since 15Mya, species richness plateaus or continues to rise (with one fall around 4 mya), while PD has greatly decreased. This shift in diversity pattern correlates with the decline of Borophaginae around the time of the MMCO and the subsequent radiation of Caninae. Borophagines include many long-branched taxa, so their loss greatly affects the PD after the MMCO. For an alternate view of PD on the overall phylogeny, we develop a method called “chainsawing”: for each 5My interval, the tips of the phylogenetic tree extending past that interval in time were cut and branch lengths (equivalent to time) were recalculated. PD was measured with groups identified as either “borophagine” or “canine”. We found that closer to the recent the borophagine diversity explains more of the PD in the tree. In the future, various ways of measuring diversity in a phylogenetic context can be used, for example, by incorporating morphological, developmental, or behavioral information into branches or by defining OTUs as functional guilds. We suggest that PD metrics provide a more complex view of diversity patterns in the fossil record, and can serve as a complementary data set to other diversity measures.
Oxygen isotopic variability and preservation in Tyrannosaurus rex, modern ratites and crocodylians: Revisiting the thermophysiology of T. rex using δ18O
Relying exclusively on the δ18O composition of fossil bone to distinguish between endothermy and ectothermy in Tyrannosaurus remains uncertain due to previous limited sampling, and potential diagenesis. Earlier assessments compared the δ18O of trabecular and cortical bone and evaluated the degree of δ18O covariation between bone phosphate, carbonate, and diagenetic calcite. In this study, millimeter-scale sequential microsampling of a core removed from cortical bone in two femora and a tibia of Tyrannosaurus increased the known value of intrabone δ18Ophosphate from < 1.0‰ to 1.3–3.0‰. These values increase the range in Tyrannosaurus body temperature from < 4.3°C to 5.2–12.9°C, if the δ18O (or offsets) reflect relative body temperature at the time of hydroxyapatite formation as postulated previously. This range in temperature falls within acceptable levels for a mass homeotherm (endothermic or ectothermic).
A comparison of δ18Ophosphate versus δ18Ocarbonate indicates oxygen isotopic equilibrium is preserved in Tyrannosaurus. Oxygen isotope cyclicity and amplitude, and the minimum age of bone deposition estimated from cortical thickness, is suggestive of a seasonal (non-annual) isotopic signal in Tyrannosaurus. Interestingly, the Δ18Ocarbonate-phosphate of ~6.0‰ is 2.0-3.0‰ less than the theoretical 8.0-9.0‰ expected for unaltered modern bone apatite. This offset may reflect taxonomic, behavioral or physiological differences between Tyrannosaurus and the limited modern mammal sample from which this regression is calculated. Alternatively, diagenesis has altered the absolute δ18O values, but the ~6.0‰ offset is useful as an indicator of isotopic equilibrium in Tyrannosaurus.
δ18Ophosphate vs. δ18Ocarbonate analysis of modern crocodylian and ratite species indicate the Δ18Ocarbonate-phosphate relationship in these extant archosaurs is statistically significant. However, the scatter about the best-fit line is greater than observed in modern mammals. In Tyrannosaurus, the regression of δ18Ophosphate vs. δ18Ocarbonate does not correspond to that of modern mammals, ratites or crocodylians. Thermoregulatory strategies may be one of a variety of factors responsible. As an endothermic heterotherm, Tyrannosaurus could obtain large size and maintain a variable, but limited body temperature range compared to its environment.
Aerodynamic characteristics of feathered dinosaur shapes measured using physical models: a comparative study of maneuvering
Aerial maneuvering was likely a pervasive force shaping the evolution of flying animals. Regardless of how aerial behaviors might have arisen, we can analyze the physical effects of structural changes on aerial maneuvering as they present themselves in fossils and along evolutionary lineages. To accomplish this, we measured the aerodynamic maneuvering characteristics of a series of models based on Mesozoic birds and avian ancestors to determine whether or not measures of aerodynamic performance correlated with morphological changes. Maneuvering characteristics during glides were quantified by measuring static stability (dC/da; the tendency to experience righting moments when deflected from equilibrium) and control effectiveness (dC/dd; the amount of force or moment generated for each degree of movement of a limb or control surface). We found that changes in planform, such as the presence or absence of a feathered tail or of leg feathers or the reconstructed posture of the animal, can drastically alter static stability. In addition, appendage function (e.g. as an elevator, rudder, or aileron, generating control forces and torques in different directions) also depends on posture and glide angle, and the function of appendages can shift dramatically due to reversal or cross-coupling effects. We then mapped the results of our aerodynamic study onto a phylogenetic tree of Avialae, using Microraptor (Dromaeosauridae) and Anchiornis (Troodontidae) as outgroups, in order to test whether or not changes in maneuvering characteristics correlated with changes in morphology during early bird evolution. We specifically examined the performance effects of the shortening of the tail and control effectiveness of leg and tail plumage compared to that of the forelimb wing. We also briefly examined similar trends in the pterosaurs and bats, which also appear to show reduction in tails in derived forms. Our analysis offers a biomechanical perspective to the evolution of avian flight that integrates morphological evidence from fossils with modeled performance in a phylogenetic framework.
PaleoParks: Preservation and conservation of fossil sites worldwide
The paleontological field resources of the world are fast disappearing as development, construction, vandalism, and over-collecting by professionals, amateurs and commercial merchants continues. Small local sites to national or international areas that protect paleontological treasures are essential if we are to preserve and understand the history of life on Earth and provide materials for scientific and educational study now and in the future.
Protection of paleontological field resources varies enormously from country to country and even within single countries. While all are good, some are more effective than others. To date, countries (Ethiopia, Australia, China, United States, Canada, New Zealand, Mexico, France, as well as others) have taken steps to protect the scientific values of such areas, often as tourist attractions. Israel and Mexico have laws against disturbing any fossil site or fossils, while the U.S. protects vertebrate fossil sites, but not others, on any of its federal lands. The Geoparks System of Europe is a wonderful example of parks providing the public with recreation, entertainment and education, and sometimes participation in the scientific discovery of the history of our Earth. Likewise, the National Parks and Monuments, as well as some National Landmarks and State Parks, in the United States provide these same values with the opportunity to participate by camping and hiking through the areas. Even in the countries with national programs, local governments, organizations and individuals also provide protected sites. In Mexico, for example, particularly important sites are being protected by involving the local people as stakeholders who gain both recognition and financial benefits. In general people are interested in these kinds of parks, and are willing to support them on the local level because of the income and attention that they generate. Most of them require professional guidance, but the values of fossils exposed on outcrops or in the ground are clear to most people.
How can paleontologists and their societies help? The first step is the identification and recognition of the scientific, historic, educational, and tourist values of the resources. Secondly, jurisdictions must be informed that their citizens, and people beyond their boundaries, are interested in past life and that they are willing to visit areas where they can view them, think they are in the midst of a working scientific site, and take pictures, at least. Third, jurisdictions must be encouraged to protect areas identified as interesting and educational, as well as scientifically valuable, so that they are not degraded. Fourth, the criteria for the recognition of such sites should be established as a general guide but site nominations must come from local or professional people familiar with the resource. Fifth, a catalog of protected and conserved sites are being catalogued, both as a resource guide and as examples of previous successful efforts. Sixth, a general plan for the determination of sites that need to be protected worldwide should be drawn and supported. Neither general catalog of preserved sites worldwide nor standardized criteria for the recognition of sites yet exist, but they are goals of the International Paleontological Association. The IPA is an important organization to lead this effort to conserve sites anywhere in the world, in order to provide guidance on their preservation and conservation. An international register of fossil parks may be undertaken perhaps on a web site. IPA seeks the support of its associated societies and all others in this effort. Societies themselves should develop a program to protect sites unique to their interests, and contribute to the IPA database. IPA will support the establishment of PaleoPark sites through letters, connections with appropriate experts, and on-site efforts.
Ontogenetic variation in epiplastral shape among Eocene testudinoid turtles (Echmatemys) of western North America
Testudinoid turtles are common in terrestrial North American Cenozoic and modern faunas, but there has been limited study of their geographic, sexual, and ontogenetic variability. If the morphological features used to distinguish among taxa are ontogenetically or geographically variable, our estimations of species diversity may be too high, especially for fossil taxa. Recent studies have shown age- and sex-related differences in skull morphology in kinosternid and testudinoid turtles, but little work on shell variability has been completed. This is problematic for fossil turtle taxa, which rarely preserve shells and skulls in association, and are usually represented by partial shells or isolated shell elements. In order to address this imbalance, studies of ontogenetic change in shell elements are needed. Epiplastron shape has previously been used to diagnose fossil testudinoids to the species level, but in the absence of statistical analyses of ontogenetic, sexual, or geographic variation, these characters may not be reliable. We performed a 2D geometric morphometric analysis of epiplastron shape (Procrustes principal components analysis) in the extant testudinoid Actinemys (Emys) marmorata (to document age- and sex-related variability) and three Eocene testudinoids: Echmatemys testudinea, E. euthneta, and E. wyomingensis. To counter geographic and temporal variation, only Echmatemys samples from three stratigraphically distinct and geographically limited localities in southwestern Wyoming were used. The mean shape of E. euthneta epiplastra differed statistically from those of the other two taxa, corroborating visual assessments of shape differences, but E. wyomingensis and E. testudinea could not be distinguished with a limited, 5-landmark analysis. A general ontogenetic trend in the angle of the epiplastral horn and the expansion of the lateral side of the element were observed in all taxa, but there were distinct taxonomic differences in the ontogenetic trajectories.
Inclusion of fossil species range data in dispersal-extinction cladogenesis (DEC) analyses corrects low estimates of extinction rate and improves estimates of historical biogeography
A new phylogenetic method of inference in historical biogeography, dispersal-extinction cladogenesis (DEC), currently implemented in Lagrange, is beginning to be employed in studies of extinct taxa. This maximum-likelihood method reconstructs the ancestral range of lineages and estimates rates of dispersal and extinction along time-scaled branches. However, the method was primarily designed for molecular-derived ultrametric trees in which all taxa are extant, and it typically underestimates extinction rate and can overestimate vicariance and ancestral range size. Here we test the utility of DEC in analyses that include fossils. Specifically, we use databases such as MIOMAP to include the geographic range of fossil mammals in the DEC analysis, through a modification of DEC that adds each fossil species extant in each North American Land Mammal Age onto the phylogeny with a short branch. Furthermore, following preliminary studies which showed that DEC does not treat branch endings as extinctions, we modified DEC to recognize branch tips as extinction events. We find that the inclusion of fossils in a DEC analysis improves the biogeographic reconstruction through more realistic estimates of extinction rate, and more precise estimates of biogeographic history. These analyses were conducted on a variety of clades with available high-resolution phylogenies of fossil and extant specIes. These included an extinct clade of equids, extinct and extant clades of canids, and a clade of marmots including extinct and extant species.
Phylogenetic distribution of ecological traits in the origin of bats
Living bats differ from other flying vertebrates (birds and pterosaurs) in having poor sight, echolocating, stressing slow, maneuverable flight, and seldom gliding. It has generally been assumed that gliding is a necessary precursor to flight, but phylogenetic analyses show that no gliding forms are found among the closest relatives of flying forms, and many gliding lineages have evolved with no apparent tendencies to powered flight. The most basal known bats could fly, but the most basal Onychonycteris lacked bony specializations for echolocation, which has suggested that flight evolved first. However, other mammals such as the tenrec do not fly but can echolocate in a more rudimentary way, and they lack chiropteran bony specializations for this. Nocturnal animals generally evolve enhanced vision, but animals that live in almost total darkness (e.g., caves) tend to reduce sight. Cave insects also tend to lose flight capacity. The visual capabilities of the earliest bats are ambiguous, but nearly all living bats are crepuscular, roosting in dark places.
We mapped traits related to echolocation, locomotion, vision, diet, and habitat in crown and stem bats. Results suggest that echolocation may be an "evolvable," modular trait that has been hard-wired to various degrees in mammals. Basal bats are inferred to have been insectivorous, but they may have hunted differently than living bats do. Phylogenetic mapping shows that neither the ability to fly well nor to echolocate well may have been basal to bats; living in caves and feeding on poorly mobile insects may have been basal habits at least for crown-group bats. No outgroups to bats are or apparently were bipedal; thus the forelimbs of bats could only be freed to evolve powered flight if they were no longer necessary to standard quadrupedal locomotion. All bats can climb quadrupedally and this seems basal for crown-group bats. Caves have fewer predators than trees, and the ability to suspend the body from the roofs of caves appears to have been possible for all known Chiroptera, living and extinct. The features of cave habitats, although poorly fossilized, may explain much about the origin of bats.
Using paleontological databases to assess spatial and temporal conservation of mammalian community structure as an aid to conservation planning
Environmental and ecological changes are proceeding rapidly today, thus it is critical to conservation efforts that we understand natural ranges of variability experience by ecosystems in the past. Toward that end we used the NEOMAP database to examine how mammalian size and dietary guilds varied through time and space in the Great Plains and Great Basin. Temporal variation was assessed using species occurrence data for the Northern Great Plains biogeographic province in the Holocene, Rancholabrean, Hemphillian, Clarendonian, and Barstovian, encompassing marked climate changes. Spatial variation was examined for the Rancholabrean across four regions (Northern and Southern Great Plains, Northern and Southern Great Basin) that represent pairs of neighboring biogeographic provinces that have been ecologically, topographically, and climatologically distinct since the Oligocene.
Species were grouped by dietary guild and body size (15 distinct groups) to investigate whether the distribution of species in diet/body size classes: (1) has changed over the past 16 million years, and; (2) differs among biogeographic provinces during a single time interval. We used pairwise Fisher's exact tests to compare the distribution of species in diet/body size classes among provinces and time periods. The numbers of species in each dietary guild and body-size class showed no significant differences between the four Rancholabrean biogeographic provinces, nor did they show significant differences through time in the Great Plains. However, the Holocene fauna has a significantly different trophic and body size structure than that observed over the previous 16 million years: extra-large (> 44 kg) and small (< 500 g) herbivores and small insectivores dramatically decline in diversity relative to the four previous time intervals. The long-term stability of diversity within these size and diet groupings suggests that tracking this metric into the future may be useful for monitoring whether current human activities are significantly changing existing faunal patterns.
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