1,720,982 research outputs found
A diverse assemblage of Permian echinoids (Echinodermata, Echinoidea) and implications for character evolution in early crown group echinoids
No full textAbstractThe Permian is regarded as one of the most crucial intervals during echinoid evolution because crown group echinoids are first widely known from the Permian. New faunas provide important information regarding the diversity of echinoids during this significant interval as well as the morphological characterization of the earliest crown group and latest stem group echinoids. A new fauna from the Capitanian Lamar Member of the Bell Canyon Formation in the Guadalupe Mountains of West Texas comprises at least three new taxa, includingEotiaris guadalupensisThompson n. sp. an indeterminate archaeocidarid, andPronechinus? sp. All specimens represented are silicified and known from disarticulated or semiarticulated interambulacral and ambulacral plates and spines. This assemblage is one of the most diverse echinoid assemblages known from the Permian and, as such, informs the paleoecological setting in which the earliest crown group echinoids lived. This new fauna indicates that crown group echinoids occupied the same environments as stem group echinoids of the Archaeocidaridae and Proterocidaridae. Furthermore, the echinoids described herein begin to elucidate the order of character transitions that likely took place between stem group and crown group echinoids. At least one of the morphological innovations once thought to be characteristic of early crown group echinoids, crenulate tubercles, was in fact widespread in a number of stem group taxa from the Permian as well. Crenulate tubercles are reported from two taxa, and putative cidaroid style U-shaped teeth are present in the fauna. The presence of crenulate tubercles in the archaeocidarid indicates that crenulate tubercles were present in stem group echinoids, and thus the evolution of this character likely preceded the evolution of many of the synapomorphies that define the echinoid crown group.</jats:p
Reorganization of sea urchin gene regulatory networks at least 268 million years ago as revealed by oldest fossil cidaroid echinoid
Full text linkEchinoids, or sea urchins, are rare in the Palaeozoic fossil record, and thus the details regarding the early diversification of crown group echinoids are unclear. Here we report on the earliest probable crown group echinoid from the fossil record, recovered from Permian (Roadian-Capitanian) rocks of west Texas, which has important implications for the timing of the divergence of crown group echinoids. The presence of apophyses and rigidly sutured interambulacral areas with two columns of plates indicates this species is a cidaroid echinoid. The species, Eotiaris guadalupensis, n. sp. is therefore the earliest stem group cidaroid. The occurrence of this species in Roadian strata pushes back the divergence of cidaroids and euechinoids, the clades that comprise all living echinoids, to at least 268.8 Ma, ten million years older than the previously oldest known cidaroid. Furthermore, the genomic regulation of development in echinoids is amongst the best known, and this new species informs the timing of large-scale reorganization in echinoid gene regulatory networks that occurred at the cidaroid-euechinoid divergence, indicating that these changes took place by the Roadian stage of the Permian
Biotic impacts of temperature before, during, and after the end-Permian extinction: A multi-metric and multi-scale approach to modeling extinction and recovery dynamics
No full textExtinction and delayed recovery during the end-Permian extinction and Early Triassic has been linked to environmental instability brought on by volcanic outgassing and greenhouse conditions, but the relative importance of the myriad of environmental stressors at this time on recovery dynamics is not well understood. Previous workers have documented both overall delayed biotic recovery for the entirety of the Early Triassic, but also incipient recoveries that appear to occur relatively early after the initial extinction event. Here, we explore the patterns of extinction and recovery using several metrics of ecological complexity in marine benthic communities using a global dataset, and compare several multiple regression models to determine which set of abiotic factors best predicts extinction and recovery dynamics. We additionally test the importance of temporal scale of analysis in interpretations of recovery dynamics and modeling results, by including analyses at the epoch, stage, and substage scales bracketing the interval of extinction and recovery. We find differences in mode of recovery between the ecological metrics analyzed, with some metrics exhibiting an Early Triassic recovery lag, while others recover continuously or immediately following the initial extinction event. We also find evidence of a global ‘Dienerian minimum’, with overall levels of community complexity significantly lower than earlier Griesbachian communities, suggesting a synchronous disturbance to the progression of recovery at this time. The regression model with δ18Oapatite mean values as the response variable is most often found to be the best-fit model across all time scales analyzed, though proxies of rock record fidelity and paleontological sampling effort become more important in finer timescale analyses, likely due to dwindling sample numbers. Out of the models tested, these results suggest that global ocean temperatures best predict patterns of extinction and recovery across several ecological metrics, and that thermal episodes during the initial extinction event and subsequently in the Early Triassic recovery period significantly suppressed benthic marine community health
Juvenile skeletogenesis in anciently diverged sea urchin clades
Full text linkAbstractMechanistic understanding of evolutionary divergence in animal body plans devolves from analysis of those developmental processes that, in forms descendant from a common ancestor, are responsible for their morphological differences. The last common ancestor of the two extant subclasses of sea urchins, i.e., euechinoids and cidaroids, existed well before the Permian/Triassic extinction (252 mya). Subsequent evolutionary divergence of these clades offers in principle a rare opportunity to solve the developmental regulatory events underlying a defined evolutionary divergence process. Thus (i) there is an excellent and fairly dense (if yet incompletely analyzed) fossil record; (ii) cladistically confined features of the skeletal structures of modern euechinoid and cidaroid sea urchins are preserved in fossils of ancestral forms; (iii) euechinoids and cidaroids are among current laboratory model systems in molecular developmental biology (here Strongylocentrotus purpuratus [Sp] and Eucidaris tribuloides [Et]); (iv) skeletogenic specification in sea urchins is uncommonly well understood at the causal level of interactions of regulatory genes with one another, and with known skeletogenic effector genes, providing a ready arsenal of available molecular tools. Here we focus on differences in test and perignathic girdle skeletal morphology that distinguish all modern euechinoid from all modern cidaroid sea urchins. We demonstrate distinct canonical test and girdle morphologies in juveniles of both species by use of SEM and X-ray microtomography. Among the sharply distinct morphological features of these clades are the internal skeletal structures of the perignathic girdle to which attach homologous muscles utilized for retraction and protraction of Aristotles׳ lantern and its teeth. We demonstrate that these structures develop de novo between one and four weeks after metamorphosis. In order to study the underlying developmental processes, a method of section whole mount in situ hybridization was adapted. This method displays current gene expression in the developing test and perignathic girdle skeletal elements of both Sp and Et juveniles. Active, specific expression of the sm37 biomineralization gene in these muscle attachment structures accompanies morphogenetic development of these clade-specific features in juveniles of both species. Skeletogenesis at these clade-specific muscle attachment structures displays molecular earmarks of the well understood embryonic skeletogenic GRN: thus the upstream regulatory gene alx1 and the gene encoding the vegfR signaling receptor are both expressed at the sites where they are formed. This work opens the way to analysis of the alternative spatial specification processes that were installed at the evolutionary divergence of the two extant subclasses of sea urchins
Exploring the morphospace of cidaroid echinoid spines.
No full textCrown group cidaroids (Echinodermata: Echinoidea: Cidaroida) display a variety of spine morphologies thought to be adapted in response to selective pressures around them. Echinoid spines directly interact with their surroundings and morphologies should reflect environmental conditions changing through time. To quantify trends in morphology through time, 2D geometric morphometrics were applied to cidaroid spines to track changes in morphospace. This was completed through four anatomical landmarks and 250 semi-landmarks to grasp the entirety of the spine shape. Once plotted into multivariate space, trends related to time and morphology were found within one family of cidaroids, Psychocidaridae. These trends coincided with major geologic events, such as the Marine Mesozoic Revolution and Cretaceous-Paleogene extinction. Contractions and shifts in morphospace could then be related to predation and changes in marine community structure. Additionally, modern cidaroids display an expansive morphological diversity, while not being taxonomically diverse
Parasitism and more in the fossil record : constraining and contextualizing the record of crustacean trace-producing symbionts.
No full textBiotic interactions are a critical element of ecology but remain a considerable gap in knowledge of the fossil record and the history of life on earth. Broadening our understanding of biotic interactions in the fossil record will be critical in resolving ecological and evolutionary dynamics across scales, and in modeling long-term ecosystem responses to shifting environments. Although understanding these trends is critical, broad, intensive research effort will be necessary to resolve biotic interactions outside of predation in well-resolved fossil records and lineages.
Here, we present three studies investigating patterns in the preservation and occurrence of fossil traces of biotic interactions of crustaceans. First, we present the first use of finite element analysis (FEA) for the non-destructive preservation modeling of a fossil parasitic swelling, Kanthyloma crusta. We find that the parasitic swellings responded with significantly higher peak stress than healthy regions from the same applied forces, suggesting a shape-related decrease in fossil preservation potential for Kanthyloma crusta. Second, we use experimental taphonomy to investigate the post-mortem preservation of the blue crab, Callinectes sapidus, with and without infestation by the rhizocephalan barnacle parasite Loxothylacus texanus. We find minimal differences in the rate and pattern of degradation between specimens, suggesting no impact on the preservation potential of host Callinectes due to the presence of the parasite. Finally, we survey bivalves and gastropods for the acrothoracican barnacle boring Rogerella in two extensive collections which primarily represent Cenozoic fossil assemblages from the east and west coasts of North America. We find significantly greater size and parasite load among specimens with Rogerella from the east coast of North America as compared to the West Coast. We highlight the necessity of investigating biotic interactions in the fossil record to contribute to our understanding of ongoing ecosystem shifts and suggest avenues for future research. We also advocate for improved sampling, availability, and organization of fossil-associated trace data to facilitate future research
Phanerozoic trends in the ecological tolerance of Lingula and extinction selectivity of marine invertebrates.
No full textEnvironmental affinity analyses of Lingula throughout the Phanerozoic for depth, lithology, grainsize, and latitude using three different affinity metrics reveal that lingulids have high ecological tolerance relative to other brachiopods and marine invertebrates. Lingulids were generalist with regards to depth, grainsize, and latitude, and were siliciclastic specialists throughout much of the Phanerozoic. Generalist behavior was observed for all four metrics following certain mass extinction events such as the end-Permian mass extinction. Logistic regression analyses reveal that generalists and specialists are selected for during many extinction and background times throughout the Phanerozoic. Depth and Lithology ecological tolerance were the most significant determinants of extinction risk. Taxa with a high depth or lithology tolerance were more likely to survive many extinction events, whereas specialist selectivity is more common during background intervals. Overall, ecological tolerance plays a role in determining extinction risk over geologic time and the high ecological tolerance of Lingula could provide a mechanism for its longevity and success following mass extinction events
Data from: Phylogenetic analysis of the Archaeocidaridae and Palaeozoic Miocidaridae (Echinodermata, Echinoidea) and the origin of crown group echinoids
No full textThe archaeocidarids comprise the most derived stem group echinoids and have long been regarded as closely related to the crown group echinoids. The fossil record of echinoids in the Palaeozoic is, however, poor, so details surrounding the initial divergence of crown group echinoids are not well constrained. In order to better understand the phylogenetic relationships of the most derived stem group and most basal crown group echinoids, a phylogenetic analysis was undertaken of the Archaeocidaridae, including the genera Nortonechinus, Devonocidaris, Lepidocidaris, Polytaxicidaris, and Archaeocidaris and the Palaeozoic miocidarid cidaroids from the genus Eotiaris. Our analyses find that Archaeocidaris appears to be paraphyletic with respect to crown group echinoids. Furthermore, we mapped character evolution along our phylogeny and found that the diversification of archaeocidarids and miocidarids may be linked to large-scale macroecological changes taking place in the Late Palaeozoic, including increasing predation pressure and echinoid encrustation by epibionts. We compared the stratigraphic distribution of archaeocidarid and miocidarid occurrences to our resulting phylogenies, and found that the fit of our cladograms to the stratigraphic record of archaeocidarid occurrences is worse than other echinoid groups, supporting the idea that the imbricate plated archaeocidarids have a poor fossil record. In the course of carrying out these analyses, we also felt it necessary to describe a new species of Archaeocidaris, Archaeocidaris ivanovi n. sp. We also provide novel descriptions and interpretations for Devonocidaris primaevus, Archaeocidaris brownwoodensis, Archaeocidaris apheles, and revise the synonymy of Archaeocidaris legrandensis and ?Eotiaris meurevillensis, which may be a crown group echinoid
Biovolume and ecoguild analysis of Late Paleozoic Ice Age benthic communities.
No full textThe Late Paleozoic Ice Age (LPIA), spanning approximately 360-292 Mya, coincided with extinctions observed in the fossil record, and previous work has interpreted the glaciation as a period of sluggish faunal turnover with depressed rates of speciation. Such studies, however, have relied on globally distributed database data, and conventional techniques for assessing community composition often fail to account for taxa that disarticulate readily post-mortem adequately. In this study, biovolume estimation techniques and ecological guild analysis are employed to analyze three benthic paleocommunities from the Pennsylvanian (Late Carboniferous) of Texas. Two in situ bulk samples were extracted from the lower and upper sections of shale strata to assess change in benthic communities over time. The results indicate considerable heterogeneity in benthic community structure through time. These findings emphasize the importance of small-scale paleocommunity analyses for understanding larger scale macroevolutionary trends in the context of the LPIA
Trends in Size Selectivity of Gastropod Prey by Naticid Predators : A Case Study from the Stone City Bluff Member.
No full textPredator-prey interactions often provide data on the health and complexity of an ecosystem. Looking back into the past allows us to understand how the trophic web changes over time. Naticids are a family of extant gastropods that prey upon other mollusks and exhibit size selectivity of prey. They create diagnostically shaped drill holes when attacking their prey to reach the soft-bodied organism inside the shell. We have gathered samples from the Whiskey Bridge and Little Brazos localities of the Stone City Bluff Member (Crockett Formation, Claiborne Group, Middle Eocene, central/southeast Texas) to study trends in size selectivity among naticids using drill holes. In this study, we examine the use of naticid drill holes on other gastropods as a proxy for predator size, calculate frequency of predation between the two locales, and determine what statistically significant differences in prey and predator size there are, if any, between the two locales. We used the Wilcox sum-rank test to determine if there are any statistically significant differences between the distribution of sizes of drilled specimens and undrilled specimens. Then, we used a linear correlation model to examine trends between prey size and predator size. There appears to be size selectivity of slightly larger prey present in the Whiskey Bridge locality and in the combined data from both localities. However, this trend is not present as apparently in the Little Brazos locality. Both localities appear to show a statistically significant correlation between drill hole size and drilled gastropod size indicating that larger naticids tend to target larger gastropod prey and smaller naticids tend to target smaller gastropod prey. To verify these findings, more work should be done by others to repeat this study and contextualize other biotic and abiotic factors influencing these observed trends
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