Variable preservation potential and richness in the fossil record of vertebrates

Variation in preservation and sampling probability clouds our estimates of past biodiversity. The most extreme examples are Lagerstätten faunas and floras. Although such deposits provide a wealth of information and represent true richness better than other deposits, they can create misleading diversity peaks because of their species richness. Here, we investigate how Lagerstätten formations add to time series of vertebrate richness in the UK, Germany and China. The first two nations are associated with well-studied fossil records and the last is a country where palaeontology has a much shorter history; all three nations include noted Lagerstätten in their fossil records. Lagerstätten provide a larger proportion of China's sampled richness than in Germany or the UK, despite comprising a smaller proportion of its fossiliferous deposits. The proportions of taxa that are unique to Lagerstätten vary through time and between countries. Further, in all regions, we find little overlap between the taxa occurring in Lagerstätten and in ‘ordinary’ formations within the same time bin, indicating that Lagerstätten preserve unusual faunas. As expected, fragile taxa make up a greater proportion of richness in Lagerstätten than the remainder of the fossil record. Surprisingly, we find that Lagerstätten account for a minority of peaks in the palaeodiversity curves of all vertebrates (18% in the UK; 36% in Germany and China), and Lagerstätten count is generally not a good overall predictor of the palaeodiversity signal. Vastly different sampling probabilities through taxa, locations and time require serious consideration when analysing palaeodiversity curves.     

HOW DO GEOLOGICAL SAMPLING BIASES AFFECT STUDIES OF MORPHOLOGICAL EVOLUTION IN DEEP TIME? A CASE STUDY OF PTEROSAUR (REPTILIA: ARCHOSAURIA) DISPARITY

A fundamental contribution of paleobiology to macroevolutionary theory has been the illumination of deep time patterns of diversification. However, recent work has suggested that taxonomic diversity counts taken from the fossil record may be strongly biased by uneven spatiotemporal sampling. Although morphological diversity (disparity) is also frequently used to examine evolutionary radiations, no empirical work has yet addressed how disparity might be affected by uneven fossil record sampling. Here, we use pterosaurs (Mesozoic flying reptiles) as an exemplar group to address this problem. We calculate multiple disparity metrics based upon a comprehensive anatomical dataset including a novel phylogenetic correction for missing data, statistically compare these metrics to four geological sampling proxies, and use multiple regression modeling to assess the importance of uneven sampling and exceptional fossil deposits (Lagerstätten). We find that range‐based disparity metrics are strongly affected by uneven fossil record sampling, and should therefore be interpreted cautiously. The robustness of variance‐based metrics to sample size and geological sampling suggests that they can be more confidently interpreted as reflecting true biological signals. In addition, our results highlight the problem of high levels of missing data for disparity analyses, indicating a pressing need for more theoretical and empirical work.     

Skeletal completeness of the non‐avian theropod dinosaur fossil record

Non‐avian theropods were a highly successful clade of bipedal, predominantly carnivorous, dinosaurs. Their diversity and macroevolutionary patterns have been the subject of many studies. Changes in fossil specimen completeness through time and space can bias our understanding of macroevolution. Here, we quantify the completeness of 455 non‐avian theropod species using the skeletal completeness metric (SCM), which calculates the proportion of a complete skeleton preserved for a specimen. Temporal patterns of theropod skeletal completeness show peaks in the Carnian, Oxfordian–Kimmeridgian and Barremian–Aptian, and lows in the Berriasian and Hauterivian. Lagerstätten primarily drive the peaks in completeness and observed taxonomic diversity in the Oxfordian–Kimmeridgian and the Barremian–Aptian. Theropods have a significantly lower distribution of completeness scores than contemporary sauropodomorph dinosaurs but change in completeness through time for the two groups shows a significant correlation when conservation Lagerstätten are excluded, possibly indicating that both records are primarily driven by geology and sampling availability. Our results reveal relatively weak temporal sampling biases acting on the theropod record but relatively strong spatial and environmental biases. Asia has a significantly more complete record than any other continent, the mid northern latitudes have the highest abundance of finds, and most complete theropod skeletons come from lacustrine and aeolian environments. We suggest that these patterns result from historical research focus, modern climate dynamics, and depositional transportation energy plus association with conservation Lagerstätten, respectively. Furthermore, we find possible ecological biases acting on different theropod subgroups, but body size does not influence theropod completeness on a global scale.     

Quantifying the completeness of the bat fossil record

Bats (Chiroptera) are one of the most successful extant mammalian orders, uniquely capable of powered flight and laryngeal echolocation. The timing and evidence for evolution of their novel adaptations have been difficult to ascertain from the fossil record due to chronological gaps and the fragmentary nature of most fossil bat material. Here, we quantify the quality of the bat fossil record using skeletal and character completeness metrics, which respectively document for each taxon what proportion of a complete skeleton is preserved, and the proportion of phylogenetic characters that can be scored. Completeness scores were collected for 441 valid fossil bat species in 167 genera from the Eocene to the Pleistocene. All metrics record similar temporal patterns: peak completeness in the Lutetian stage reflects the presence of Lagerstätten, while subsequent stages have very low completeness, except an Aquitanian high and a Pleistocene peak in skeletal completeness. Bat completeness is not correlated with intensity of sampling through geological time but has a weak negative correlation with publication date. There is no correlation between taxonomic richness and completeness, as the bat record predominately consists of diagnostic but isolated teeth. Consequently, bat skeletal completeness is the lowest of any previously assessed tetrapod group, but character completeness is similar to parareptiles and birds. Bats have significantly higher character completeness in the northern hemisphere, probably due to heightened historical interest and presence of Lagerstätten. Taxa derived from caves are more complete than those from fluviolacustrine and marine deposits, but do not preserve highly complete specimens.     

The shape of pterosaur evolution: evidence from the fossil record

Abstract Although pterosaurs are a well‐known lineage of Mesozoic flying reptiles, their fossil record and evolutionary dynamics have never been adequately quantified. On the basis of a comprehensive data set of fossil occurrences correlated with taxon‐specific limb measurements, we show that the geological ages of pterosaur specimens closely approximate hypothesized patterns of phylogenetic divergence. Although the fossil record has expanded greatly in recent years, collectorship still approximates a sigmoid curve over time as many more specimens (and thus taxa) still remain undiscovered, yet our data suggest that the pterosaur fossil record is unbiased by sites of exceptional preservation (lagerstätte). This is because as new species are discovered the number of known formations and sites yielding pterosaur fossils has also increased – this would not be expected if the bulk of the record came from just a few exceptional faunas. Pterosaur morphological diversification is, however, strongly age biased: rarefaction analysis shows that peaks of diversity occur in the Late Jurassic and Early Cretaceous correlated with periods of increased limb disparity. In this respect, pterosaurs appear unique amongst flying vertebrates in that their disparity seems to have peaked relatively late in clade history. Comparative analyses also show that there is little evidence that the evolutionary diversification of pterosaurs was in any way constrained by the appearance and radiation of birds.     

Buoyancy mechanisms limit preservation of coleoid cephalopod soft tissues in Mesozoic Lagerstätten

Coleoid cephalopods are characterized by internalization of their shell, and are divided into the ten‐armed Decabrachia (squids and cuttlefish) and the eight‐armed Vampyropoda (octopuses and vampire squid). They have a rich fossil record predominantly of the limited biomineralized skeletal elements they possess: arm hooks, statoliths, mouthparts (the buccal mass) and internal shell (gladius or pen), although exquisitely preserved soft tissue coleoids are known from several Lagerstätten worldwide. Recent studies have shown that although morphological similarities between extant decabrachian gladii and fossil examples exist, no known examples of fossil decabrachians are currently known. However, molecular clock data and phylogenetic bracketing suggest that they should be present in Lagerstätten that are rich in vampyropod soft tissue fossils (i.e. Hâkel and Hâdjoula Lagerstätten, Cretaceous, Lebanon). We propose that a hitherto unknown taphonomic bias pertaining to the differing methods of buoyancy control within coleoid groups limits preservation potential. Both negatively and neutrally buoyant decabrachians use chemical buoyancy control (ammonia) whereas vampyropods do not. In the event of rapid burial in an environment conducive to exceptional preservation, ammonia dramatically decreases the ability of the decabrachian carcass to generate the required pH for authigenic calcium phosphate replacement, limiting its preservation potential. Moreover, the greater surface area and comparatively fragile dermis further decrease the potential for fossilization. This taphonomic bias may have contributed to the lack of preserved labile soft‐tissues in other cephalopods groups such as the ammonoids.     

Remarkably preserved benthic organisms and their traces from a Middle Triassic (Muschelkalk) mud flat

Knaust, D. 2010: Remarkably preserved benthic organisms and their traces from a Middle Triassic (Muschelkalk) mud flat. Lethaia, Vol. 43, pp. 344–356. A new Fossil‐Lagerstätte is reported from the Middle Triassic of Germany, preserving Foraminifera, Nematoda, Platyhelminthes, Nemertea, Annelida and a range of Arthropoda together with their traces. This is the oldest fossil record of free‐living nematodes and turbellarians, and the first occurrence of nemerteans in the Mesozoic. The rare preservation of the benthic associations together with their traces is unique; especially the abundant occurrence of different phyla as meiofauna (organisms with shortest dimension between 0.06 and 1 mm) provides an insight into the palaeoecological conditions of a 240‐Ma‐old muddy tidal flat. The preservation of benthic animals at the termination of their traces offers the exclusive opportunity to assign producers to the trace fossils. The results show that the discussed phyla were already established in the early Mesozoic in a similar diversity and composition as in modern analogues. The new Fossil‐Lagerstätte has the potential to prove a number of soft‐bodied taxa immediately after the end‐Permian mass extinction, which has wide‐ranging implications for phylogenetic interpretations. □Benthos, soft‐bodied organisms, Fossil‐Lagerstätte, Muschelkalk, trace fossils, Triassic.     

Do different disparity proxies converge on a common signal? Insights from the cranial morphometrics and evolutionary history of Pterosauria (Diapsida: Archosauria)

Disparity, or morphological diversity, is often quantified by evolutionary biologists investigating the macroevolutionary history of clades over geological timescales. Disparity is typically quantified using proxies for morphology, such as measurements, discrete anatomical characters, or geometric morphometrics. If different proxies produce differing results, then the accurate quantification of disparity in deep time may be problematic. However, despite this, few studies have attempted to examine disparity of a single clade using multiple morphological proxies. Here, as a case study for this question, we examine the disparity of the volant Mesozoic fossil reptile clade Pterosauria, an intensively studied group that achieved substantial morphological, ecological and taxonomic diversity during their 145+ million-year evolutionary history. We characterize broadscale patterns of cranial morphological disparity for pterosaurs for the first time using landmark-based geometric morphometrics and make comparisons to calculations of pterosaur disparity based on alternative metrics. Landmark-based disparity calculations suggest that monofenestratan pterosaurs were more diverse cranially than basal non-monofenestratan pterosaurs (at least when the aberrant anurognathids are excluded), and that peak cranial disparity may have occurred in the Early Cretaceous, relatively late in pterosaur evolution. Significantly, our cranial disparity results are broadly congruent with those based on whole skeleton discrete character and limb proportion data sets, indicating that these divergent approaches document a consistent pattern of pterosaur morphological evolution. Therefore, pterosaurs provide an exemplar case demonstrating that different proxies for morphological form can converge on the same disparity signal, which is encouraging because often only one such proxy is available for extinct clades represented by fossils. Furthermore, mapping phylogeny into cranial morphospace demonstrates that pterosaur cranial morphology is significantly correlated with, and potentially constrained by, phylogenetic relationships.     

The completeness of the fossil record of mesozoic birds: implications for early avian evolution

Many palaeobiological analyses have concluded that modern birds (Neornithes) radiated no earlier than the Maastrichtian, whereas molecular clock studies have argued for a much earlier origination. Here, we assess the quality of the fossil record of Mesozoic avian species, using a recently proposed character completeness metric which calculates the percentage of phylogenetic characters that can be scored for each taxon. Estimates of fossil record quality are plotted against geological time and compared to estimates of species level diversity, sea level, and depositional environment. Geographical controls on the avian fossil record are investigated by comparing the completeness scores of species in different continental regions and latitudinal bins. Avian fossil record quality varies greatly with peaks during the Tithonian-early Berriasian, Aptian, and Coniacian-Santonian, and troughs during the Albian-Turonian and the Maastrichtian. The completeness metric correlates more strongly with a 'sampling corrected' residual diversity curve of avian species than with the raw taxic diversity curve, suggesting that the abundance and diversity of birds might influence the probability of high quality specimens being preserved. There is no correlation between avian completeness and sea level, the number of fluviolacustrine localities or a recently constructed character completeness metric of sauropodomorph dinosaurs. Comparisons between the completeness of Mesozoic birds and sauropodomorphs suggest that small delicate vertebrate skeletons are more easily destroyed by taphonomic processes, but more easily preserved whole. Lagerst?tten deposits might therefore have a stronger impact on reconstructions of diversity of smaller organisms relative to more robust forms. The relatively poor quality of the avian fossil record in the Late Cretaceous combined with very patchy regional sampling means that it is possible neornithine lineages were present throughout this interval but have not yet been sampled or are difficult to identify because of the fragmentary nature of the specimens.     

Decaying in different clays: implications for soft‐tissue preservation

Lagerstätten, places where soft‐bodied organisms became mineralized, provide a substantial bulk of palaeobiological information, but the detailed mechanisms of how soft‐tissue preservation takes place remain debatable. An experimental taphonomy approach, which allows for direct study of decay and mineralization, offers a means to study the preservational potential of different soft‐bodied organisms under controlled conditions. Here we compare the preservational capacity of two types of clay (kaolinite and montmorillonite) through a long‐term (24 month) experiment involving the burial and decay of small crustaceans. Our experimental design is innovative in that it models catastrophic sedimentation in fine‐grained colloidal suspension, which is believed to form Lagerstätten deposits. We demonstrated better preservation of buried organisms in clays compared to water, and in kaolinite compared to montmorillonite. As aluminium cations were present in high concentrations in kaolinite sediment but not in montmorillonite, the better preservation in kaolinite is attributed to the tanning properties of aluminium, which catalyses cross‐linking in proteins, protecting them from bacterial degradation. Anaerobic environments and acidification also slow down decay, but they are less effective than tanning. Kaolinite and montmorillonite replaced the crustacean integuments differently: in the remains buried in kaolinite, Al and Si were detected in equal proportions, while in those buried in montmorillonite, the Si content appeared to be much higher even in comparison with the initial sample of the clay. These variations probably arose from the different dynamics of acidic hydrolysis in the two clays associated with anaerobic decomposition of organic matter. Our results show that the preservation mechanism includes multi‐component interactions between the solution, mineral, sediment and organic remains; taken separately, any single component explains little. The specific conditions that occur within the colloidal clay sediments can facilitate conservation and start fast mineralization according to chemical properties and elemental content.     

Palaeodiversity and formation counts: redundancy or bias?

A key question in palaeontology is whether the fossil record taken at face value is adequate to represent true patterns of diversity through time. Some methods of assessing data quality have depended on the commonly observed covariation of palaeodiversity and fossiliferous formation counts through time, based on the assumption that the count of formations containing fossils, to a greater or lesser extent, drives diversity; but what if diversity drives formations? Close study of two fossil records, early tetrapods (Devonian–Jurassic) and dinosaurs, shows how the relationship between new taxa and new fossiliferous formations varies through research time. Initially, each new find represents a new fossiliferous formation and discovery follows the ‘bonanza’ model (fossils drive formations). In unexplored parts of the world, new taxa are identified frequently in new regions/formations. Only after time, in well‐explored continents such as Europe and North America, does collecting style switch to a mix of exploration for new formations and re‐sampling of known fossiliferous formations. Data are most striking for dinosaurs, where the Triassic–Jurassic record largely comprises finds from Europe and North America, where new formation discoveries reached their half‐life in 1914. This contrasts with the Cretaceous, which is dominated by rapidly rising discoveries from regions outside Europe and North America and the formation half‐life for these ‘new’ lands is 1986, showing that 50% of new Cretaceous dinosaur‐bearing formations were identified only in the past 30 years. The relationship between dinosaur‐bearing formations and palaeodiversity then combines three signals in variable amounts, reflecting the original diversity (relative abundances of particular taxa in different formations), redundancy (new fossiliferous formations accruing because of new fossil finds) and sampling (intensity of exploration for new fossiliferous formations, and of search within already‐sampled formations). For fossil vertebrates at least, formation counts of various kinds are poor predictors of sampling, missing, for example, the bonanza samples of Lagerstätten such as the Yixian Formation in China: thousands of specimens, dozens of species, but counted as one formation. These observations suggest that formation count cannot be regarded as an unbiased metric of sampling.     

Fossil liberation: a model to explain high biodiversity in the Triassic Cassian Formation

With 1429 animal species, the Triassic Cassian Formation in the Dolomites, Southern Alps (Italy), yields the highest species richness reported from any spatially constrained pre-Quaternary formation known to science. The high preserved diversity is partly attributable to a high primary diversity governed by the tropical setting, increasing alpha diversity, and the breadth of habitats spurring beta diversity. More important is the excellent preservation of fossils and the ease with which they can be extracted from the poorly lithified sediments. We propose the term ‘liberation Lagerstätten’ to capture this preservational window. In contrast to conservation Lagerstätten, liberation Lagerstätten like the Cassian Formation originate from normal marine conditions but low-grade diagenesis. Molluscs contribute substantially to species richness, comprising 67% of all invertebrate species in the Cassian Formation. The gastropod dominance (39% of all species) is nearly as great as in Recent tropical settings, contradicting the concept of a substantial Cenozoic rise.     

The mosasaur fossil record through the lens of fossil completeness

The quality of the fossil record affects our understanding of macroevolutionary patterns. Palaeodiversity is filtered through geological and human processes; efforts to correct for these biases are part of a debate concerning the role of sampling proxies and standardization in biodiversity models. We analyse the fossil record of mosasaurs in terms of fossil completeness as a measure of fossil quality, using three novel, correlating metrics of fossil completeness and 4083 specimens. A new qualitative measure of character completeness (QCM) correlates with the phylogenetic character completeness metric. Mean completeness by species decreases with specimen count; average completeness by substage varies significantly. Mean specimen completeness is higher for species‐named fossils than those identified to genus and family. We consider the effect of tooth‐only specimens. Importantly, we find that completeness of species does not correlate with completeness of specimens. Completeness varies by palaeogeography: North American specimens show higher completeness than those from Eurasia and Gondwana. These metrics can be used to identify exceptional preservation; specimen completeness varies significantly by both formation and lithology. The Belgian Ciply Formation displays the highest completeness; clay lithologies show higher completeness values. Neither species diversity nor sea level correlates significantly with fossil completeness. A generalized least squares (GLS) analysis using multiple variables agrees with this result, but reveals two variables with significant predictive value for modelling averaged diversity: sea level, and mosasaur and plesiosaur‐bearing formations (the latter is redundant with diversity). Mosasaur completeness is not driven by sea level, nor does completeness limit the mosasaur diversity signal.     

Fossilized bacteria in a Cretaceous pterosaur headcrest

Pinheiro F.L., Horn B.L.D., Schultz C.L., de Andrade J.A.F.G. and Sucerquia P.A., 2012: Fossilized bacteria in a Cretaceous pterosaur headcrest. Lethaia, Vol. 45, pp. 495–499. We report herein the first evidence of bacterial autolithification in the Crato Formation of Araripe Basin, Brazil. The fossilized bacteria are associated with a tapejarid pterosaur skull, replacing the soft‐tissue extension of the headcrest. EDS analyses indicate that the bacteria were replaced by phosphate minerals, probably apatite. The bacterial biofilm was likely part of the prokaryotic mat that decomposed the pterosaur carcass at the bottom of the Araripe lagoon. This work suggests that bacterial autolithification could have played a key‐role on soft‐tissue preservation of Crato Formation Lagerstätte. □Bacterial autolithification, Crato Formation, phosphatization, pterosaur, soft‐tissue preservation.     

Mesozoic marine tetrapod diversity: mass extinctions and temporal heterogeneity in geological megabiases affecting vertebrates

The fossil record is our only direct means for evaluating shifts in biodiversity through Earth''s history. However, analyses of fossil marine invertebrates have demonstrated that geological megabiases profoundly influence fossil preservation and discovery, obscuring true diversity signals. Comparable studies of vertebrate palaeodiversity patterns remain in their infancy. A new species-level dataset of Mesozoic marine tetrapod occurrences was compared with a proxy for temporal variation in the volume and facies diversity of fossiliferous rock (number of marine fossiliferous formations: FMF). A strong correlation between taxic diversity and FMF is present during the Cretaceous. Weak or no correlation of Jurassic data suggests a qualitatively different sampling regime resulting from five apparent peaks in Triassic–Jurassic diversity. These correspond to a small number of European formations that have been the subject of intensive collecting, and represent ‘Lagerstätten effects’. Consideration of sampling biases allows re-evaluation of proposed mass extinction events. Marine tetrapod diversity declined during the Carnian or Norian. However, the proposed end-Triassic extinction event cannot be recognized with confidence. Some evidence supports an extinction event near the Jurassic/Cretaceous boundary, but the proposed end-Cenomanian extinction is probably an artefact of poor sampling. Marine tetrapod diversity underwent a long-term decline prior to the Cretaceous–Palaeogene extinction.     

Exceptionally well‐preserved vegetal remains from the Upper Cretaceous of ‘Lo Hueco’, Cuenca,Spain

Vegetal remains are considered labile structures that quickly become decayed in ecosystems. However, certain lignified tissues (woody plants) can largely resist decomposition, becoming sometimes exceptionally well preserved. At the Upper Cretaceous site of ‘Lo Hueco’ (Cuenca, Spain), those woody remains (trunks and branches) with resinous material in the inner tracheids and parenchyma cells that were buried rapidly under anoxic conditions experienced a low degree of maturation, becoming exceptionally well preserved. Those woody remains deposited under oxic conditions (sub‐aerial or sub‐aquatic exposure) were more intensely biodegraded and subsequently carbonified, partially or completely mineralized in gypsum and covered by a ferruginous crust. These two modes of preservation are scarce, with silicification or carbonification processes much more common, and both can be considered as ‘exceptional preservation’. Other vegetal remains, such as carbonified leaves, stems and roots, were collected in the site. The different modes of preservation depend directly on: depositional micro‐environment (sandy distributary channel, muddy flood plain); and type (trunk, branch, stem, leave, root) and state (presence or absence of resinous material) of the material. The great abundance and diversity of fossils in ‘Lo Hueco’ identify it as Konzentrat‐Lagerstätten, sequentially formed by alternated events of flooding and drying depositional events, but the exceptional quality and rarity of determinate vegetal macroremains preservation suggest that certain deposits of this site can be considered as conservation deposits.     

The fossil record of ichthyosaurs,completeness metrics and sampling biases

Ichthyosaurs were highly successful marine reptiles with an abundant and well‐studied fossil record. However, their occurrences through geological time and space are sporadic, and it is important to understand whether times of apparent species richness and rarity are real or the result of sampling bias. Here, we explore the skeletal completeness of 351 dated and identified ichthyosaur specimens, belonging to all 102 species, the first time that such a study has been carried out on vertebrates from the marine realm. No correlations were found between time series of different skeletal metrics and ichthyosaur diversity. There is a significant geographical variation in completeness, with the well‐studied northern hemisphere producing fossils of much higher quality than the southern hemisphere. Medium‐sized ichthyosaurs are significantly more complete than small or large taxa: the incompleteness of small specimens was expected, but it was a surprise that larger specimens were also relatively incomplete. Completeness varies greatly between facies, with fine‐grained, siliciclastic sediments preserving the most complete specimens. These findings may explain why the ichthyosaur diversity record is low at times, corresponding to facies of poor preservation potential, such as in the Early Cretaceous. Unexpectedly, we find a strong negative correlation between skeletal completeness and sea level, meaning the most complete specimens occurred at times of global low sea level, and vice versa. Completeness metrics, however, do not replicate the sampling signal and have limited use as a global‐scale sampling proxy.     

The bivalved arthropods Isoxys and Tuzoia with soft‐part preservation from the Lower Cambrian Emu Bay Shale Lagerstätte (Kangaroo Island,Australia)

Abstract: Abundant material from a new quarry excavated in the lower Cambrian Emu Bay Shale (Kangaroo Island, South Australia) and, particularly, the preservation of soft‐bodied features previously unknown from this Burgess Shale‐type locality, permit the revision of two bivalved arthropod taxa described in the late 1970s, Isoxys communis and Tuzoia australis. The collections have also produced fossils belonging to two new species: Isoxys glaessneri and Tuzoia sp. Among the soft parts preserved in these taxa are stalked eyes, digestive structures and cephalic and trunk appendages, rivalling in quality and quantity those described from better‐known Lagerstätten, notably the lower Cambrian Chengjiang fauna of China and the middle Cambrian Burgess Shale of Canada.     

The origin of annelids

Annelids are a phylum of segmented bilaterian animals that have become important components of ecosystems spanning terrestrial realms to the deep sea. Annelids are remarkably diverse, possessing high taxonomic diversity and exceptional morphological disparity, and have evolved numerous feeding strategies and ecologies. Their interrelationships and evolution have been the source of much controversy over the past century with the composition of the annelid crown group, the relationship of major groups and the body plan of the ancestral annelid having undergone major recent revisions. There is a convincing body of molecular evidence that polychaetes form a paraphyletic grade and that clitellates are derived polychaetes. The earliest stem group annelids from Cambrian Lagerstätten are errant, epibenthic polychaetes, confirming that biramous parapodia, head appendages and diverse, simple chaetae are primitive for annelids. Current evidence from molecular clocks and the fossil record suggest that crown group annelids are a Late Cambrian – Ordovician radiation, with clitellates radiating in the Late Palaeozoic. Their body fossil record is largely confined to deposits showing exceptional preservation and is punctuated by the acquisition of hard parts in major groups. The discovery of an Ordovician fossil with soft tissues has shown that machaeridians are in fact a clade of crown polychaetes. They were in existence for more than 200 million years and possess unique calcitic dorsal armour, allowing their mode of life and phylogeny to be interpreted in the context of the annelid body plan. We identify a novel clade of machaeridians, the Cuniculepadida, which exhibit a series of adaptations for burrowing.     

Pterosaur dietary hypotheses: a review of ideas and approaches

Pterosaurs are an extinct group of Mesozoic flying reptiles, whose fossil record extends from approximately 210 to 66 million years ago. They were integral components of continental and marginal marine ecosystems, yet their diets remain poorly constrained. Numerous dietary hypotheses have been proposed for different pterosaur groups, including insectivory, piscivory, carnivory, durophagy, herbivory/frugivory, filter‐feeding and generalism. These hypotheses, and subsequent interpretations of pterosaur diet, are supported by qualitative (content fossils, associations, ichnology, comparative anatomy) and/or quantitative (functional morphology, stable isotope analysis) evidence. Pterosaur dietary interpretations are scattered throughout the literature with little attention paid to the supporting evidence. Reaching a robustly supported consensus on pterosaur diets is important for understanding their dietary evolution, and their roles in Mesozoic ecosystems. A comprehensive examination of the pterosaur literature identified 314 dietary interpretations (dietary statement plus supporting evidence) from 126 published studies. Multiple alternative diets have been hypothesised for most principal taxonomic pterosaur groups. Some groups exhibit a high degree of consensus, supported by multiple lines of evidence, while others exhibit less consensus. Qualitative evidence supports 87.3% of dietary interpretations, with comparative anatomy most common (62.1% of total). More speciose groups of pterosaur tend to have a greater range of hypothesised diets. Consideration of dietary interpretations within alternative phylogenetic contexts reveals high levels of consensus between equivalent monofenestratan groups, and lower levels of consensus between equivalent non‐monofenestratan groups. Evaluating the possible non‐biological controls on apparent patterns of dietary diversity reveals that numbers of dietary interpretations through time exhibit no correlation with patterns of publication (number of peer‐reviewed publications through time). 73.8% of dietary interpretations were published in the 21st century. Overall, consensus interpretations of pterosaur diets are better accounted for by non‐biological signals, such as the impact of the respective quality of the fossil record of different pterosaur groups on research levels. That many interpretations are based on qualitative, often untestable lines of evidence adds significant noise to the data. More experiment‐led pterosaur dietary research, with greater consideration of pterosaurs as organisms with independent evolutionary histories, will lead to more robust conclusions drawn from repeatable results. This will allow greater understanding of pterosaur dietary diversity, disparity and evolution and facilitate reconstructions of Mesozoic ecosystems.