Skeletal completeness of the non‐avian theropod dinosaur fossil record

Abstract

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.

Ten more years of discovery: revisiting the quality of the sauropodomorph dinosaur fossil record

“…S2B). We also recovered the statistically significant higher completeness distribution of sauropodomorphs in comparison to theropods found by Cashmore & Butler (2019), but note that the significant difference is lost not only when using Cretaceous data alone, but also with just Jurassic data (Cashmore et al . 2020, table S1).…”

“…This was partially contended by Mannion & Upchurch (2010a) because they noted a coincident drop in sauropodomorph completeness. This J/K decline has also been previously recognized in the theropod fossil record (Cashmore & Butler 2019), and notable drops in completeness can be seen in the crocodylomorph (Mannion et al . 2019a), avialan (Brocklehurst et al .…”

“…There is no significant correlation between sauropodomorph SCM2 and that of either marine reptile group examined (ichthyosaurs and plesiosaurs) through time (Table 2). Unlike Cashmore & Butler (2019), the sauropodomorph and theropod SCM2 time series are now significantly correlated when either including or excluding conservation Lagerstätten (Table 2; Cashmore et al . 2020, fig.…”

“…2015; Verrière et al . 2016; Cashmore & Butler 2019) to more precisely estimate the skeletal proportions of different tetrapod groups. Here we continue to use the proportions defined by Mannion & Upchurch (2010a) to ensure comparability with this earlier work, but we partially modified them to score element completeness on a finer scale (see Cashmore et al .…”

“…To identify shared or diverging completeness signals, the sauropodomorph SCM2 time series was also compared with the records of other Mesozoic tetrapod groups for which skeletal completeness studies have been performed, that is plesiosaurs (Tutin & Butler 2017), ichthyosaurs (Cleary et al . 2015), and theropod dinosaurs (Cashmore & Butler 2019), and groups for which character completeness studies have been performed, that is avialans (Brocklehurst et al . 2012), pterosaurs (Dean et al .…”