Showing papers in "Palaeontology in 2021"

Comparing surface digitization techniques in palaeontology using visual perceptual metrics and distance computations between 3D meshes

Abstract: Berliner Hochschulprogramm fur Wissenschaftlerinnen und Kunstlerinnen ‚DiGiTal – Digitalisierung: Gestaltung und Transformation‘

Evolution of ecospace occupancy by Mesozoic marine tetrapods

Abstract: Ecology and morphology are different, and yet in comparative studies of fossil vertebrates the two are often conflated. The macroevolution of Mesozoic marine tetrapods has been explored in terms of morphological disparity, but less commonly using ecological-functional categories. Here we use ecospace modelling to quantify ecological disparity across all Mesozoic marine tetrapods. We document the explosive radiation of marine tetrapod groups in the Triassic and their rapid attainment of high ecological disparity. Late Triassic extinctions led to a marked decline in ecological disparity, and the recovery of ecospace and ecological disparity was sluggish in the Early Jurassic. High levels of ecological disparity were again achieved by the Late Jurassic and maintained during the Cretaceous, when the ecospace became saturated by the Late Cretaceous. Sauropterygians, turtles and ichthyosauromorphs were the largest contributors to ecological disparity. Throughout the Mesozoic, we find that established groups remained ecologically conservative and did not explore occupied or vacant niches. Several parts of the ecospace remained vacant for long spans of time. Newly evolved, radiating taxa almost exclusively explored unoccupied ecospace, suggesting that abiotic releases are needed to empty niches and initiate diversification. In the balance of evolutionary drivers in Mesozoic marine tetrapods, abiotic factors were key to initiating diversification events, but biotic factors dominated the subsequent generation of ecological

Sporopollenin chemistry and its durability in the geological record: an integration of extant and fossil chemical data across the seed plants

Abstract: © 2021 The Authors Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association Sporopollenin is a highly resistant biopolymer that forms the outer wall of pollen and spores (sporomorphs) Recent research into sporopollenin chemistry has opened up a range of new avenues for palynological research, including chemotaxonomic classification of morphologically cryptic taxa However, there have been limited attempts to directly integrate extant and fossil sporopollenin chemical data Of particular importance is the impact of sample processing to isolate sporopollenin from fresh sporomorphs, and the extent of chemical changes that occur once sporomorphs enter the geological record Here, we explore these issues using Fourier transform infrared (FTIR) microspectroscopy data from extant and fossil grass, Nitraria (a steppe plant), and conifer pollen We show a 98% classification success rate at subfamily level with extant grass pollen, demonstrating a strong taxonomic signature in isolated sporopollenin However, we also reveal substantial chemical differences between extant and fossil sporopollenin, which can be tied to both early diagenetic changes acting on the sporomorphs and chemical derivates of sample processing Our results demonstrate that directly integrating extant and late Quaternary chemical data should be tractable as long as comparable sample processing routines are maintained Consistent differences between extant and deeper time sporomorphs, however, suggests that classifying fossil specimens using extant training sets will be challenging Further work is therefore required to understand and simulate the effects of diagenetic processes on sporopollenin chemistry

Ups and downs of belemnite diversity in the Early Jurassic of Western Tethys

Abstract: Although belemnites form a major clade of extinct cephalopods, the early stage of their diversification remains poorly known in time and space. Here we investigate the first diversification episodes of belemnites (order Belemnitida) using a new species-level database encompassing the Hettangian–Aalenian interval (Early Jurassic – earliest Middle Jurassic) and covering the Western Tethys. Rarefied richness shows a four-fold increase from the Planorbis chronozone to the Ibex chronozone, a strong decrease between the Margaritatus and Spinatum chronozones, followed by a drop in the Spinatum–Serpentinum interval that is coeval with the second-order Toarcian biological crisis. The Bifrons chronozone records a high richness that departs significantly from those of the surrounding chronozones. A last richness peak in the Dispansum chronozone precedes a decrease towards the Aalenian. Biogeographical analyses do not reveal any clear large-scale provincialism for belemnites, in sharp contrast with ammonoids. Such a long-term homogeneous spatial distribution of belemnites is probably due to: (1) the relatively poorly-documented fossil record of belemnites, especially in Mediterranean localities; and (2) contrasted dispersal abilities of belemnites compared to ammonoids over the studied time interval.

A method for mapping morphological convergence on three-dimensional digital models: the case of the Mammalian Sabre-Tooth

Abstract: We are grateful to Stephan Lautenschlager and an anonymous reviewer for providing important advice. 79 specimens included in the present study are from the PhD database of DT, whose PhD project received support from the ‘Avvio alla Ricerca 2019’ funding which is financed by the University of Rome ‘La Sapienza’. DT also received support from the SYNTHESYS Access programme that is financed by the European Community Research Infrastructure Action under the FP7 (ES-TAF-2750 awarded to DT). LMW acknowledges support from the United States National Science Foundation (IOB-0517257, IOS-1050154, IOS-1456503).

Crypsis in the pelagic realm: evidence from exceptionally preserved fossil fish larvae from the Eocene Stolleklint Clay of Denmark

Abstract: Marine deposits of earliest Eocene age in northern Jutland, Denmark, are renowned for yielding diverse teleost assemblages that have proved central for enhancing our understanding of the early evolution of many extant actinopterygian clades. In this study, we investigate diminutive larval fish fossils from the Stolleklint Clay, Olst Formation, that retain multiple soft-tissue features preserved as distinct dark-coloured stains. To examine the elemental and molecular composition of these soft parts, we employed a combination of time-of-flight secondary ion mass spectrometry (ToF-SIMS), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Our analyses revealed that the preserved structures contain chemically identifiable eumelanin intimately associated with densely aggregated microbodies that are morphologically consistent with melanosome organelles. Thus, we conclude that the carbonaceous structures represent traces of originally melanized body parts, including the eyes and peritoneum. Comparable pigmentation patterns are seen in many extant teleost larvae that use semi-transparency as a means of camouflage in pelagic environments, to suggest a similar visual appearance of the Stolleklint Clay fish fossils. This in turn suggests that adaptations for concealment and UV-protection had already evolved by the beginning of the Eocene, notably during a time interval characterized by an extreme greenhouse climate, when the global fish fauna become increasingly modern in composition. (Less)

Patterns of bilateral asymmetry and allometry in Late Devonian Polygnathus conodonts

Abstract: Conodont animals were early jawless vertebrates equipped with a feeding apparatus composed of several tooth-like elements. The P1 elements, at the rear of the apparatus, were characterized by a robust shape and rapid morphological evolution. Occlusion occurred between paired right and left P1 elements, occasioning some bilateral asymmetry, which, together with allometric growth, may partially obliterate the temporal differences. The present study aims to disentangle these different components of morphological variation in Late Devonian Polygnathus P1 conodont elements. An extensive 2D geometric morphometric analysis of the platform shape was performed through the Famennian record of two outcrops. This analysis was completed by a 3D study on a subset of conodont elements. The 2D and 3D morphometric quantifications provided highly congruent results, showing that the 2D shape constitutes a good approximation of the element geometry. The 3D analysis delivered further insights into the relationship between the geometry of the elements and the constraints related to occlusion. The 2D analysis allowed a quantitative assessment of the variation among species and through time. Allometry and bilateral asymmetry were differently expressed depending on the species considered, suggesting that constraints imposed on pairing by the morphology of the elements varied even among related species. The within-species variation was so important that it largely obliterated temporal trends; a relationship of Polygnathus shape and conodont biofacies variations through the Famennian nevertheless suggested an evolution driven by ecological interactions between conodont genera.

Assessing bite force estimates in extinct mammals and archosaurs using phylogenetic predictions

Abstract: Bite force is an ecologically important biomechanical performance measure that is informative in inferring the ecology of extinct taxa. However, biomechanical modelling to estimate bite force is associated with some level of uncertainty. Here, I assess the accuracy of bite force estimates in extinct taxa using a Bayesian phylogenetic prediction model. I first fitted a phylogenetic regression model on a training set comprising extant data. The model predicts bite force from body mass and skull width while accounting for differences owing to biting position. The posterior predictive model has a 93% prediction accuracy as evaluated using leave-one-out cross-validation. I then predicted bite force in 37 species of extinct mammals and archosaurs from the posterior distribution of predictive models, generating posterior predictive distributions of null expectations given body mass, skull width and phylogenetic position. Biomechanically estimated bite forces from the literature fall within the posterior predictive distributions for all except four species of extinct taxa and are thus as accurate as predicted from body size and skull width, given the variation inherent in extant taxa and the amount of time available for variance to accrue. Biomechanical modelling remains a valuable means to estimate bite force in extinct taxa and should be reliably informative of functional performances and serve to provide insights into past ecologies.

Go large or go conical: allometric trajectory of an early Cambrian acrotretide brachiopod

Abstract: Acrotretides are extinct micromorphic brachiopods that exhibited considerable morphological variation during their rapid evolution in the early Palaeozoic. The plano-conical shells of acrotretides are distinct in comparison to other brachiopod groups and despite their diversity and abundance in early Palaeozoic communities, their origins, early evolution, life history and phylogeny are poorly understood. Here, we employ advanced geometric morphometrics to quantitatively investigate ontogenetic variation and allometry in the ventral valve of the oldest known acrotretide species from the early Cambrian of South China. Our results identify substantial shape variation for Eohadrotreta zhenbaensis, along with a parabolic morphological trajectory through ontogeny, demonstrating a remarkable reversal to PC1 values equivalent to those obtained for juveniles, during later ontogenetic stages. The evolutionary novel body plan (diminutive and plano-conical) of Acrotretida was established gradually during two phases of allometry, formed initially during the final stage of the Cambrian evolutionary radiation from an ancestral low, equivalved lingulide body plan. The development of a conical shaped valve seems to have resulted in an overall smaller body size, when compared with non-conical forms. The heterochronic processes responsible for generating these ontogenetic modifications at different allometric phases may have facilitated the evolutionary diversification of acrotretide brachiopods during the early Palaeozoic.

Dryopithecine palaeobiodiversity in the Iberian Miocene revisited on the basis of molar endostructural morphology

Abstract: Extensive fieldwork at Abocador de Can Mata (north-east Iberian Peninsula) has uncovered a previously unsuspected diversity of catarrhine primates in the middle Miocene (12.5-11.6 Ma) of Europe. However, the distinction of the great ape genera Pierolapithecus and Anoiapithecus from Dryopithecus (supported by craniodental differences) has been disputed by some authors. Here we revisit the diversity of great apes (dryopithecines) from the Iberian Miocene based on molar 3D endostructural morphology (relative enamel thickness, enamel distribution, and enamel-dentine junction (EDJ)). Using microtomography, we inspected an extensive sample of 49 hominoid molars representing at least five species from 12 localities. 2D and 3D relative enamel thickness values indicate that Dryopithecus and 'Sivapithecus' occidentalis (species inquirenda) display the thinnest and thickest enamel, respectively, while the remaining taxa (Hispanopithecus, Anoiapithecus, Pierolapithecus) show intermediate values. Upper molar enamel distribution maps exhibit a similar pattern in P. catalaunicus, A. brevirostris, D. fontani, H. laietanus and H. crusafonti whereas for the lower molars they reveal differences between H. laietanus and H. crusafonti. Lower molar enamel distribution and EDJ morphology of 'S.' occidentalis support the distinction of this species but do not resolve whether it is a junior synonym of Anoiapithecus brevirostris or Pierolapithecus catalaunicus. Overall our results support the distinction of middle Miocene dryopithecins from late Miocene hispanopithecins, the distinction of Pierolapithecus and Anoiapithecus from Dryopithecus among the former, and the distinct species status of H. crusafonti compared to H. laietanus among the latter. Our results highlight the potential of inner tooth morphology for hominoid alpha-taxonomy.