Abstract
AbstractNon‐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.
Highlights
The fossil record has temporal, geographical, environmental and skeletal gaps (Newell 1959; Foote & Raup 1996; Kidwell & Holland 2002), and it is essential that these limitations are considered when making interpretations about the evolutionary patterns of a group
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
Instead we used an alternate but efficient method, whereby we modelled the two-dimensional surface area of each bone for ten morphologically and taxonomically disparate theropod taxa, based on scientifically informed skeletal reconstructions produced by Scott Hartman: Herrerasaurus ischigualastensis, Coelophysis bauri, Majungasaurus crenatissimus, Allosaurus fragilis (Fig. 1), Tyrannosaurus rex, Gallimimus bullatus, Nothronychus graffami, composite alvarezsaur, Khaan mckennai, and Velociraptor mongoliensis
Summary
The fossil record has temporal, geographical, environmental and skeletal gaps (Newell 1959; Foote & Raup 1996; Kidwell & Holland 2002), and it is essential that these limitations are considered when making interpretations about the evolutionary patterns of a group. Over the last two decades, many assessments of the quality of the fossil record have focused on the variation in information content provided by fossil specimens of a group (Benton et al 2004; Fountaine et al 2005; Smith 2007; Dyke et al 2009; Benton 2010; Mannion & Upchurch 2010a; Brocklehurst et al 2012; Walther & Fro€bisch 2013; Brocklehurst & Fro€bisch 2014; Cleary et al 2015; Dean et al 2016; Verriere et al 2016; Davies et al 2017; Driscoll et al 2018; Brown et al 2019). Previous studies have found varying correlations between completeness metrics and changes in diversity and fossil record sampling metrics through time, as well as various geographical and environmental differences between the fossil records of different groups (Mannion & Upchurch 2010a; Brocklehurst et al 2012; Walther & Fro€bisch 2013; Brocklehurst & Fro€bisch 2014; Cleary et al 2015; Dean et al 2016; Verriere et al 2016; Davies et al 2017; Tutin & Butler 2017; Driscoll et al 2018; Brown et al 2019), highlighting major biases that influence different fossil records to various extents
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