The fossil record of ichthyosaurs, completeness metrics and sampling biases

Cleary, Terri J.; Moon, Benjamin C.; Dunhill, Alexander M.; Benton, Michael J.

doi:10.1111/pala.12158

Cited by 48 publications

(119 citation statements)

References 44 publications

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“…Strong correlations have been found between the two metrics (Mannion & Upchurch ; Cleary et al . ; Tutin & Butler ), but we solely use the latter in this study, as it uses all the information at hand for each species and is more appropriate than arbitrarily nominating a most important specimen (Mannion & Upchurch ; Brocklehurst et al . ; Brocklehurst & Fröbisch ).…”

Section: Methodsmentioning

confidence: 99%

“…For example, Cleary et al . () used different skeletal proportion percentages for ichthyosaur taxa of different geological ages because significant morphological change occurs through time within the group. In contrast to the approximate estimates provided by Mannion & Upchurch (), Brocklehurst & Fröbisch () more precisely estimated the skeletal body proportions of synapsids by modelling each bone as the volume of a cone, cylinder, or a prism, based on skeletal measurements of multiple representatives of morphologically and taxonomically distinct subgroups.…”

Section: Methodsmentioning

confidence: 99%

“…(), and were compared to theropod SCM2 because it has been argued that sea level has a potential influence on the completeness of marine fossil groups (Cleary et al . ; Tutin & Butler ), although whether this relationship holds in the terrestrial realm is subject to debate (Fara ). The number of dinosaur‐bearing formations (DBFs) and dinosaur‐bearing collections (DBCs) for the Carnian to the Maastrichtian were collected from the PBDB.…”

Section: Temporal Correlationsmentioning

confidence: 99%

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Skeletal completeness of the non‐avian theropod dinosaur fossil record

Cashmore

Butler

2019

Palaeontology

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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.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Temporal Correlationsmentioning

confidence: 99%

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Skeletal completeness of the non‐avian theropod dinosaur fossil record

Cashmore

Butler

2019

Palaeontology

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“…This assumption would imply that there is a systematic downward bias in the phylogeny toward recent times, which would be counter to the usual expectation for poor sampling (50,51). Here, to test the effect of such biases, we fitted additional models with appropriate covariates, including stage-level formation counts (because formation count is widely reported to be associated with sampling bias) (9,10,12,35,44,52,53), taxon-specific formation counts (the number of formations in which a taxon is found), taxon-specific collection count (the number of fossil collections in which a taxon is represented), cladewise valid taxa counts (the known underrepresentation in the phylogeny) (54), fossil quality scores (state of preservation) (55), and body size (smaller taxa are less likely to be preserved) (56).…”

Section: Methodsmentioning

confidence: 99%

Dinosaurs in decline tens of millions of years before their final extinction

Sakamoto

Benton

Venditti

2016

Proc. Natl. Acad. Sci. U.S.A.

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Whether dinosaurs were in a long-term decline or whether they were reigning strong right up to their final disappearance at the Cretaceous-Paleogene (K-Pg) mass extinction event 66 Mya has been debated for decades with no clear resolution. The dispute has continued unresolved because of a lack of statistical rigor and appropriate evolutionary framework. Here, for the first time to our knowledge, we apply a Bayesian phylogenetic approach to model the evolutionary dynamics of speciation and extinction through time in Mesozoic dinosaurs, properly taking account of previously ignored statistical violations. We find overwhelming support for a long-term decline across all dinosaurs and within all three dinosaurian subclades (Ornithischia, Sauropodomorpha, and Theropoda), where speciation rate slowed down through time and was ultimately exceeded by extinction rate tens of millions of years before the K-Pg boundary. The only exceptions to this general pattern are the morphologically specialized herbivores, the Hadrosauriformes and Ceratopsidae, which show rapid species proliferations throughout the Late Cretaceous instead. Our results highlight that, despite some heterogeneity in speciation dynamics, dinosaurs showed a marked reduction in their ability to replace extinct species with new ones, making them vulnerable to extinction and unable to respond quickly to and recover from the final catastrophic event.dinosaurs | evolution | speciation | phylogeny | Bayesian methods N onavian dinosaurs met their demise suddenly, coincident with the Chicxulub impact in Mexico around 66 Mya; however, whether there was any long-term trend toward declining diversity leading to the Cretaceous-Paleogene (K-Pg) boundary has been controversial and debated for decades (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). This longstanding dispute has been prolonged partly because of differences in fossil datasets from different parts of the world and difficulties in rock dating but most importantly, methodological weaknesses-previous attempts have been nonphylogenetic, and analyses were conducted on simple time-binned tabulated data, resulting in a lack of statistical rigor (phylogenetic and temporal nonindependence have not been considered), and did not truly investigate evolutionary dynamics, such as speciation and extinction rates. In fact, patterns of speciation and extinction in dinosaurs have gone largely unstudied (8). Here, we study speciation dynamics (relationship between speciation and extinction rates) using an exclusively phylogenetic approach in a Bayesian framework.If speciation and extinction rate were constant (but speciation was higher), we would expect to see a linear increase through time in the logarithm of the number of speciation events along each path of a phylogenetic tree (linear) (Materials and Methods and Fig. 1, model A). If speciation rate decreased through time but remained above extinction rate, then we would expect a curvilinear relationship (Fig. 1, models B and C). Such a relationship would reach an asymptote ...

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“…An additional measure of quality for the fossil record is specimen completeness, or the proportion of the skeleton that is known for a particular taxon as a whole. For example, sauropod dinosaurs (Mannion & Upchurch, 2010b), birds (Brocklehurst et al, 2012), pterosaurs (Dean, Mannion & Butler, 2016) and ichthyosaurs (Cleary et al, 2015) all show reductions in average skeletal completeness over the J/K boundary, coincident with a drop in diversity in the first three groups (see Section III).…”

Section: (2) the Quality Of The Late Jurassic-early Cretaceous Fossilmentioning

confidence: 99%

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

et al. 2016

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The Late Jurassic to Early Cretaceous interval represents a time of environmental upheaval and cataclysmic events, combined with disruptions to terrestrial and marine ecosystems. Historically, the Jurassic/Cretaceous (J/K) boundary was classified as one of eight mass extinctions. However, more recent research has largely overturned this view, revealing a much more complex pattern of biotic and abiotic dynamics than has previously been appreciated. Here, we present a synthesis of our current knowledge of Late Jurassic-Early Cretaceous events, focusing particularly on events closest to the J/K boundary. We find evidence for a combination of short-term catastrophic events, large-scale tectonic processes and environmental perturbations, and major clade interactions that led to a seemingly dramatic faunal and ecological turnover in both the marine and terrestrial realms. This is coupled with a great reduction in global biodiversity which might in part be explained by poor sampling. Very few groups appear to have been entirely resilient to this J/K boundary 'event', which hints at a 'cascade model' of ecosystem changes driving faunal dynamics. Within terrestrial ecosystems, larger, more-specialised organisms, such as saurischian dinosaurs, appear to have suffered the most. Medium-sized tetanuran theropods declined, and were replaced by larger-bodied groups, and basal eusauropods were replaced by neosauropod faunas. The ascent of paravian theropods is emphasised by escalated competition with contemporary pterosaur groups, culminating in the explosive radiation of birds, although the timing of this is obfuscated by biases in sampling. Smaller, more ecologically diverse terrestrial non-archosaurs, such as lissamphibians and mammaliaforms, were comparatively resilient to extinctions, instead documenting the origination of many extant groups around the J/K boundary. In the marine realm, extinctions were focused on low-latitude, shallow marine shelf-dwelling faunas, corresponding to a significant eustatic sea-level fall in the latest Jurassic. More mobile and ecologically plastic marine groups, such as ichthyosaurs, survived the boundary relatively unscathed. High rates of extinction and turnover in other macropredaceous marine groups, including plesiosaurs, are accompanied by the origin of most major lineages of extant sharks. Groups which occupied both marine and terrestrial ecosystems, including crocodylomorphs, document a selective extinction in shallow marine forms, whereas turtles appear to have diversified. These patterns suggest that different extinction selectivity and ecological processes were operating between marine and terrestrial ecosystems, which were ultimately important in determining the fates of many key groups, as well as the origins of many major extant lineages. We identify a series of potential abiotic candidates for driving these patterns, including multiple bolide impacts, several episodes of flood basalt eruptions, dramatic climate change, and major disruptions to oceanic systems. The J/K t...

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The fossil record of ichthyosaurs, completeness metrics and sampling biases

Cited by 48 publications

References 44 publications

Skeletal completeness of the non‐avian theropod dinosaur fossil record

Skeletal completeness of the non‐avian theropod dinosaur fossil record

Dinosaurs in decline tens of millions of years before their final extinction

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

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