Austin J.W. Hendy

Phanerozoic trends in the global diversity of marine invertebrates.

It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.

RESPONSE OF SHALLOW MARINE BIOTAS TO SEA-LEVEL FLUCTUATIONS: A REVIEW OF FAUNAL REPLACEMENT AND THE PROCESS OF HABITAT TRACKING

Abstract Associations of fossil genera and species commonly display repeated and predictable patterns of change in stratigraphic sections. These changes exhibit some analogies with the phenomenon of ecological succession but are longer-term allogenic temporal changes, occurring over time scales of tens to hundreds of thousands of years, that should be referred to as biotic (faunal-floral) replacement. Habitat tracking is one of a suite of possible mechanisms of biotic replacement, but one that may be important in certain marine settings. Evidence of tracking includes (1) recurrence of similar replacement series of differing age; (2) mirroring of vertical replacement of faunas by lateral gradients of species associations along single time planes; (3) the occurrence of similar gradient transects at different time planes; (4) the correlatability of highs and lows of quantitative faunal curves (e.g., variations of detrended correspondence analysis scores) at different localities despite offsets of absolute scores; and (5) the high fidelity recurrence of stenotopic species in particular associations representing narrowly defined environments. The degree of ecological fidelity (e.g., similarity of species richness, guild structure) that is maintained during tracking is variable. Recurrent assemblages in different cycles, separated by as much as several million years, can be very similar in terms of species composition and trophic structure. Common species, however, may show significant differences in rank and relative abundances. This evidence indicates individualistic tracking of preferred habitat by various species. In shallow-shelf and ramp settings, sea-level fluctuations may produce approximately symmetrical patterns of biotic replacement where biofacies are arrayed typically in elongate belts parallel to depositional strike. Asymmetries, however, are common and may result from variations in sediment supply during sea-level fluctuation. Hence, the low siliciclastic input typical of transgressions predictably favors those organisms that require lower sedimentation or turbidity and perhaps firmgrounds to hardgrounds, whereas the regressive half cycle at analogous depths favors more eurytopic organisms that tolerate or prefer higher sedimentation or turbidity. The phenomenon of tracking may be of considerable importance in evolutionary paleoecology. Tracking implies that species commonly respond to long-term physical changes, not by adaptation, but primarily by migration of species to preferred habitats, if the rate or magnitude of environmental change is not too great. Provided that the same basic environment existed through time, despite lateral shifting by up to hundreds of kilometers, most species of benthic invertebrates were capable of surviving with little or no evolutionary change. Tracking may be the primary basis of patterns of morphological stasis, as well as relative stability in biofacies richness, composition, and trophic structure.

The influence of lithification on Cenozoic marine biodiversity trends

Abstract Recent research has corroborated the long-held view that the diversity of genera within benthic marine communities has increased from the Paleozoic to the Cenozoic as much as three-to fourfold, after mitigating for such biasing influences as secular variation in time-averaging and environmental coverage. However, these efforts have not accounted for the considerable increase in the availability of unlithified fossiliferous sediments in strata of late Mesozoic and Cenozoic age. Analyses presented here on the Cenozoic fossil record of New Zealand demonstrate that unlithified sediments not only increase the amount of fossil material and hence the observed diversity therein, but they also preserve a pool of taxa that is compositionally distinct from lithified sediments. The implication is that a large component of the difference in estimates of within-community diversity between Paleozoic and Cenozoic assemblages may relate to the increased availability of unlithified sediments in the Cenozoic.

The effects of taxonomic standardization on sampling-standardized estimates of historical diversity

Occurrence-based databases such as the Palaeobiology database (PBDB) provide means of accommodating the heterogeneities of the fossil record when evaluating historical diversity patterns. Although palaeontologists have given ample attention to the effects of taxonomic practice on diversity patterns derived from synoptic databases (those using first and last appearances of taxa), workers have not examined the effects of taxonomic error on occurrence-based diversity studies. Here, we contrast diversity patterns and diversity dynamics between raw data and taxonomically vetted data in the PBDB to evaluate the effects of taxonomic errors. We examine three groups: Palaeozoic gastropods, Jurassic bivalves and Cenozoic bivalves. We contrast genus-level diversity patterns based on: (i) all occurrences assigned to a genus (i.e. both species records and records identifying only the genus), (ii) only occurrences for which a species is identified, and (iii) only occurrences for which a species is identified, but after vetting the genus to which the species is assigned. Extensive generic reassignments elevate origination and extinction rates within Palaeozoic gastropods and origination rates within Cenozoic bivalves. However, vetting increases generic richness markedly only for Cenozoic bivalves, and even then the increase is less than 10%. Moreover, the patterns of standing generic richness are highly similar under all three data treatments. Unless our results are unusual, taxonomic standardization can elevate diversity dynamics in some cases, but it will not greatly change inferred richness over time.

Phanerozoic trends in the global geographic disparity of marine biotas

Abstract Previous analyses of the history of Phanerozoic marine biodiversity suggested that the post-Paleozoic increase observed at the family level and below was caused, in part, by an increase in global provinciality associated with the breakup of Pangea. Efforts to characterize the Phanerozoic history of provinciality, however, have been compromised by interval-to-interval variations in the methods and standards used by researchers to calibrate the number of provinces. With the development of comprehensive, occurrence-based data repositories such as the Paleobiology Database (PaleoDB), it is now possible to analyze directly the degree of global compositional disparity as a function of geographic distance (geo-disparity) and changes thereof throughout the history of marine animal life. Here, we present a protocol for assessing the Phanerozoic history of geo-disparity, and we apply it to stratigraphic bins arrayed throughout the Phanerozoic for which data were accessed from the PaleoDB. Our analyses provide no indication of a secular Phanerozoic increase in geo-disparity. Furthermore, fundamental characteristics of geo-disparity may have changed from era to era in concert with changes to marine venues, although these patterns will require further scrutiny in future investigations.

PALEOECOLOGY OF LATE MIOCENE–EARLY PLIOCENE SIXTH-ORDER GLACIOEUSTATIC SEQUENCES IN THE MANUTAHI-1 CORE, WANGANUI-TARANAKI BASIN, NEW ZEALAND

Abstract The Manutahi-1 core of Wanganui Basin, New Zealand, provides a special opportunity to investigate variations in depositional paleoenvironments by way of high-resolution paleoecologic and sedimentologic studies in a succession that accumulated under the influence of late Neogene rapid glacioeustatic sea-level oscillations. Thirty cyclothems of the Matemateaonga Formation (late Miocene–early Pliocene) have been identified through a 960 m interval of the core. Temporal patterns in both lithofacies distribution and macrofaunal paleoecology indicate a close link with environmental shifts that took place over the duration of these sixth-order sea-level cycles (∼41 kyr duration). Because foraminiferal assemblages have proven to be depauperate in the Manutahi-1 core, macrofossils, especially bivalves and gastropods, are used as the primary source of paleoecologic data. The paleoenvironmental analyses presented here have relied extensively on the transfer of ecologic data from the modern fauna to extant or closely related species observed in the core. Most notably, a relative sea-level curve has been constructed for the Matemateaonga Formation from analysis of bathymetric data for appropriate modern taxa. A range of exploratory statistical approaches, including cluster and ordination techniques, allow rapid, objective, and reproducible classification of macrofaunal associations and the elucidation of large-scale paleoenvironmental patterns. Several implications arise from this study. First, sequence boundaries and other key surfaces are confidently identified on the basis of integrated sedimentologic, taphonomic, and paleoecologic investigation. Second, changes in depositional environment and the responses of benthic communities are revealed at a range of temporal scales. The temporal pattern of paleoecologic change appears to be the result of lateral, facies-related shifting of biofacies (habitat tracking) in response to sea level, sediment flux, and other associated paleoenvironmental variables. Temporal patterns of biofacies occurrence and diversity are, however, strongly overprinted by stratigraphic and taphonomic processes.

Taphonomic Overprints on Phanerozoic Trends in Biodiversity: Lithification and Other Secular Megabiases

Taphonomic biases introduce heterogeneity into the quality of the fossil record and can skew paleontologists’ perception of biodiversity. This paper reviews the temporal extent and consequences of major taphonomic biases, including lithification of sediments, skeletal replacement through silicification and phosphatization, concentration of skeletal hard-parts, and the exceptional preservation of soft-bodied faunas. The frequency of occurrence of particular biases, and their effects of fossil faunas is identified using occurrence-based datasets, such as the Paleobiology Database.

Comparative Taphonomy and Sedimentology of Small-Scale Mixed Carbonate/Siliciclastic Cycles: Synopsis of Phanerozoic Examples

Small scale cycles deposited over 10–100 kyr are a common component of Phanerozoic shelfal deposits. A combination of detailed outcrop analysis and data-mining from published literature of cycles largely deposited in greenhouse regimes reveals a series of recurring sedimentological, paleoecological, and taphonomic motifs. In general, each cycle is composed of three to four components: (a) a basal skeleton-rich bed with evidence of condensation and, in some cases mineralization; (b) a medium-dark gray siliciclastic mudstone/shale interval; (c) a calcareous and/or silty mudstone interval with common concretionary, diagenetic overprint. A series of exemplars are highlighted from proximal and distal shelf settings and described using a depositional sequence approach. The cycles studied include examples deposited under greenhouse (Cambrian, Ordovician, Devonian, Jurassic and Cretaceous) and, for comparison purposes, icehouse (Neogene) conditions. The fact that repetitive patterns can characterize deposits that formed over a 500 million year interval is striking. The primary taphonomic moderator in these cycles is rate of sedimentation, which varies exponentially from sediment-starved concentrations to obrutionary deposits. The occurrence of a persistent motif over this time scale suggests that biological innovations, which might be expected to impact upon fossil preservation, have in fact been overprinted by the extremes of sedimentation preserved in these small-scale cycles. Having a skeleton, which is twice as resistant to abrasion, is of little import when sedimentation is dominated by the extremes: instant obrution or condensation.

Project Paleo: Citizen Curation and Community Science at the Natural History Museum of Los Angeles County

The School and Teacher Programs of the Natural History Museum of Los Angeles County have partnered with the La Brea Tar Pits and Museum (LBTPM) and the Invertebrate Paleontology (LACMIP) collection to create two “citizen curation” exercises dubbed “Project Paleo”. Classroom kits were created with unsorted fossils from either LBPTM or from a local invertebrate paleontological field site, to be sorted and identified by local elementary and middle school students and then returned to the museum for curation, analysis, and research purposes. Each kit contains background information about the project and fossils, and an identification guide to assist the students and teachers. The “Project Paleo: Rancho La Brea” kit contains three tablespoons of unsorted fossil matrix from LBTPM’s Project 23. Groups of students learn about past and present food webs of the Los Angeles Basin, then sort the matrix into several categories (bones, plants, other fossils, and rocks) using a guide with drawn examples of each. An online iNaturalist (inaturalist.org) project also serves as an identification resource as well as a platform by which students can contribute photos for identification by staff researchers. This project is ‡ § ‡ ‡ § | ‡