Historical processes tens to hundreds of millions of years in the past have shaped not only the trajectory of life through time but also the distribution and composition of life today. Studies aimed ...at the origin and evolution of regional biotas promise to forge a stronger link among paleobiology, ecology, and evolutionary biology. Improvements in high-resolution stratigraphic interpretation, numerical modeling of the fossil record, and the application of phylogenetic methods to extinct groups will lead to advances in understanding of (
a
) assembly of regional biotas, (
b
) the ecology of extinct taxa, (
c
) the diversification and environmental expansion of major groups, (
d
) the processes underlying regional ecosystem persistence and pulsed change, and (
e
) whether or not diversity has limits over geologic time.
Mass extinctions can have dramatic effects on the trajectory of life, but in some cases the effects can be relatively small even when extinction rates are high. For example, the Late Ordovician mass ...extinction is the second most severe in terms of the proportion of genera eliminated, yet is noted for the lack of ecological consequences and shifts in clade dominance. By comparison, the end-Cretaceous mass extinction was less severe but eliminated several major clades while some rare surviving clades diversified in the Paleogene. This disconnect may be better understood by incorporating the phylogenetic relatedness of taxa into studies of mass extinctions, as the factors driving extinction and recovery are thought to be phylogenetically conserved and should therefore promote both origination and extinction of closely related taxa. Here, we test whether there was phylogenetic selectivity in extinction and origination using brachiopod genera from the Middle Ordovician through the Devonian. Using an index of taxonomic clustering (RCL) as a proxy for phylogenetic clustering, we find that A) both extinctions and originations shift from taxonomically random or weakly clustered within families in the Ordovician to strongly clustered in the Silurian and Devonian, beginning with the recovery following the Late Ordovician mass extinction, and B) the Late Ordovician mass extinction was itself only weakly clustered. Both results stand in stark contrast to Cretaceous-Cenozoic bivalves, which showed significant levels of taxonomic clustering of extinctions in the Cretaceous, including strong clustering in the mass extinction, but taxonomically random extinctions in the Cenozoic. The contrasting patterns between the Late Ordovician and end-Cretaceous events suggest a complex relationship between the phylogenetic selectivity of mass extinctions and the long-term phylogenetic signal in origination and extinction patterns.
We employ modified tip-dating methods to date divergence times within the Strophomenoidea, one of the most abundant and species-rich brachiopod clades to radiate during the Great Ordovician ...Biodiversification Event (GOBE), to determine if significant environmental changes at this time correlate with the diversification of the clade. Models using origination, extinction and sampling rates to estimate prior probabilities of divergence times strongly support both high rates of anatomical change per million years and rapid divergences shortly before the clade first appears in the fossil record. These divergence times indicate much higher rates of cladogenesis than are typical of brachiopods during this interval. The correspondence of high speciation rates and high anatomical disparity suggests punctuated (speciational) change drove the high frequencies of early anatomical change, which in turn suggests increased ecological opportunities rather than shifting developmental constraints account for high rates of anatomical change. The pulse of rapid evolution began coincident with cooling temperatures, the start of major oscillations in sea level and increased levels of atmospheric oxygen. Our results suggest that these factors permitted major geographical and ecological expansion of strophomenoids with intervals of geographical isolation, resulting in elevated speciation rates and corresponding elevated frequencies of punctuated change.
The stratigraphy of mass extinction Holland, Steven M.; Patzkowsky, Mark E.; Benson, Roger
Palaeontology,
September 2015, 2015-09-00, 20150901, Letnik:
58, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Patterns of last occurrences of fossil species are often used to infer the tempo and timing of mass extinction, even though last occurrences generally precede the time of extinction. Numerical ...simulations with constant extinction demonstrate that last occurrences are not randomly distributed, but tend to cluster at subaerial unconformities, surfaces of forced regression, flooding surfaces and intervals of stratigraphical condensation, all of which occur in predictable stratigraphical positions. This clustering arises not only from hiatuses and non‐deposition, but also from changes in water depth. Simulations with intervals of elevated extinction cause such clusters of last occurrences to be enhanced within and below the interval of extinction, suggesting that the timing and magnitude of extinctions in these instances could be misinterpreted. With the possible exception of the end‐Cretaceous, mass extinctions in the fossil record are characterized by clusters of last occurrences at these sequence stratigraphical horizons. Although these clusters of last occurrences may represent brief pulses of elevated extinction, they are equally likely to form by stratigraphical processes during a protracted period (more than several hundred thousand years) of elevated extinction rate. Geochemical proxies of extinction causes are also affected similarly, suggesting that many local expressions of mass extinction should be re‐evaluated for the timing of extinction and its relation to environmental change. We propose three tests for distinguishing pulses of extinction from clusters of last occurrences produced by stratigraphical processes.
The earliest Paleocene record of calcareous nannoplankton presents a unique opportunity to understand the evolutionary recovery of life from mass extinction. Nannoplankton were devastated at the ...Cretaceous/Paleogene boundary and their subsequent recovery can be studied in great detail because of their abundance in sediments, continuous stratigraphic occurrence, and near global distribution. Here we determine when and where new species of nannoplankton originated and how they dispersed following the Cretaceous/Paleogene mass extinction. Initially, we focus our efforts on North Pacific and South Atlantic deep sea sites with orbital age control to compare the precise timing and dynamics of the recovery between the locations. We then broaden our investigation to six sites from different basins and a variety of environments to study global patterns of the initial recovery. Our results show that many taxa in key Paleogene lineages originated in the North Pacific Ocean and that assemblages comprised primarily of new Paleogene taxa were not observed at other sites for several hundred thousand years. Survivors that were adapted to eutrophic post extinction conditions rapidly expanded in Southern Hemisphere sites where they dominated assemblages for most of the initial recovery. We therefore hypothesize that groups of survivors formed regionally incumbent assemblages in the Southern Hemisphere that limited diversification and dispersal of new Paleogene taxa. The end of survivor dominance correlates to the recovery of the biologic pump and subsequent decrease in surface ocean nutrient concentration 300–400 Kyr after the boundary. Only after survivors were removed did new Paleogene nannoplankton assemblages become abundant globally. Our results indicate that competition from regionally incumbent survivors was as an important control on the K/Pg recovery of nannoplankton.
Recent studies have emphasized that faunal change is typically brief and most commonly occurs at sequence boundaries and major flooding surfaces. The Upper Ordovician of the Cincinnati, Ohio, region ...records a major biotic invasion in the Richmondian Stage, which offers an opportunity to test these generalizations and to understand how episodes of faunal change are reflected in the structure of ecological gradients. The early Cincinnatian (C1–early C4 depositional sequences) displays two relatively stable faunal gradients, with the primary gradient reflecting onshore-offshore setting and the secondary gradient reflecting substrate consistency. During the mid-C4 sequence, dominant taxa of the shallow subtidal are extirpated, while deep subtidal taxa expand into those habitats, leading to a loss of cross-shelf faunal differentiation. This faunal breakdown is accompanied into the mid-C5 by a series of ecological epiboles, indicating an ongoing flux in ecological associations. The onshore-offshore gradient is reestablished in the C5, albeit with new associations dominated by or containing immigrant taxa. Recognition of this gradient is hindered by widespread increased abundance of bryozoans and by the delayed appearance of at least seven common genera of brachiopods and corals. The Richmondian Invasion plays out over multiple sequences and is not confined to a brief interval at the beginning of a sequence. These faunal changes do not coincide with sequence boundaries or major flooding surfaces and therefore cannot be sequence stratigraphic artifacts, nor can they represent a geologically instantaneous faunal response to sea-level change.
The geologic history of closed-canopy forests is of great interest to paleoecologists and paleoclimatologists alike. Closed canopies have pronounced effects on local, continental and global rainfall ...and temperature patterns. Although evidence for canopy closure is difficult to reconstruct from the fossil record, the characteristic isotope gradients of the “canopy effect” could be preserved in leaves and proxy biomarkers. To assess this, we employed new carbon isotopic data for leaves collected in diverse light environments within a deciduous, temperate forest (Maryland, USA) and for leaves from a perennially closed canopy, moist tropical forest (Bosque Protector San Lorenzo, Panamá). In the tropical forest, leaf carbon isotope values range 10‰, with higher δ13Cleaf values occurring both in upper reaches of the canopy, and with higher light exposure and lower humidity. Leaf fractionation (Δleaf) varied negatively with height and light and positively with humidity. Vertical 13C enrichment in leaves largely reflects changes in Δleaf, and does not trend with δ13C of CO2 within the canopy. At the site in Maryland, leaves express a more modest δ13C range (∼6‰), with a clear trend that follows both light and leaf height. Using a model we simulate leaf assemblage isotope patterns from canopy data binned by elevation. The re-sampling (bootstrap) model determined both the mean and range of carbon isotope values for simulated leaf assemblages ranging in size from 10 to over 1000 leaves. For the tropical forest data, the canopy’s isotope range is captured with 50 or more randomly sampled leaves. Thus, with a sufficient number of fossil leaves it is possible to distinguish isotopic gradients in an ancient closed canopy forest from those in an open forest. For very large leaf assemblages, mean isotopic values approximate the δ13C of carbon contributed by leaves to soil and are similar to observed δ13Clitter values at forested sites within Panamá, including the site where leaves were sampled. The model predicts a persistent ∼1‰ difference in δ13Clitter for the two sites which is consistent with higher water availability in the tropical forests. This work provides a new framework for linking contemporary ecological observations to the geochemical record using flux-weighted isotope data and lends insights to the effect of forest architecture on organic and isotopic records of ancient terrestrial ecosystems.
The Late Ordovician mass extinction was an interval of high extinction with inferred low ecological selectivity, resulting in little change in community structure after the event. In contrast, the ...mass extinction may have fundamentally changed evolutionary dynamics in the surviving groups. We investigated the phylogenetic relationships among strophomenoid brachiopods, a diverse brachiopod superfamily that was a primary component of Ordovician ecosystems. Four Ordovician families/subfamilies sampled in the analysis (Rafinesquinidae, Strophomeninae, Glyptomenidae and Furcitellinae) were reconstructed as monophyletic groups, and the base of the strophomenoid clade that dominated the Silurian recovery was reconstructed as diversifying alongside these families during the Middle Ordovician. We time‐calibrated the phylogeny and used geographical occurrences to investigate biogeographical changes in the strophomenoids through time with the R package BiogeoBEARS. Our results indicate that extinction was higher in taxa whose ranges were constrained to tropical or subtropical regions. Furthermore, our results suggest important shifts in the diversification patterns of these brachiopods after the mass extinction. While most of the strophomenoid families survived the Late Ordovician event, ecologically abundant taxonomic groups during the Ordovician were either driven to extinction, reduced in diversity, or slowly died off during the Silurian. The new abundant strophomenoid taxa derived from one clade (consisting of Silurian–Devonian groups such as Douvillinidae, Strophodontidae and Amphistrophiidae) that diversified during the post‐extinction radiation. Our results suggest the selective diversification during the Silurian radiation, rather than selective extinction in the Late Ordovician, had a greater impact on the evolutionary history of strophomenoid brachiopods.
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