Morphological innovation and the evolution of hadrosaurid dinosaurs

Abstract

The hadrosaurids were a successful group of herbivorous dinosaurs. During the Late Cretaceous, 100 to 66 million years ago, hadrosaurids had high diversity, rapid speciation rates, and wide geographic distribution. Most hadrosaurids were large bodied and had similar postcranial skeletons. However, they show important innovations in the skull, including disparate crests that functioned as socio-sexual display structures, and a complex feeding apparatus, with specialized jaws bearing dental batteries. Little is known about the macroevolutionary processes that produced these evolutionary novelties. Here we provide novel perspectives using evolutionary rate and disparity analyses. Our results show that hadrosaurid cranial evolution was complex and dynamic, but their postcranial skeleton and body size were conservative. High cranial disparity was achieved through multiple bursts of phenotypic innovation. We highlight contrasting evolutionary trends within hadrosaurids between the disparate facial skeleton and crests, which both showed multiple high-rate shifts, and the feeding apparatus, which had low variance and high rates on a single phylogenetic branch leading to the diverse Saurolophidae. We reveal that rapid evolutionary rates were important for producing the high disparity of exaggerated crests and present novel evidence that the hadrosaurid diversification was linked to both a key adaptive innovation in the feeding apparatus and multiple bursts of innovation in socio-sexual displays.

A new basal hadrosaurid (Dinosauria: Ornithischia) from the latest Cretaceous Kita-ama Formation in Japan implies the origin of hadrosaurids

“…The evolutionary rate analyses on pectoral girdle + forelimb phylogenetic characters demonstrate a significantly high evolutionary rate in the branch leading to the clade of Saurolophinae and Lambeosaurinae (Fig. 7 b), as suggested by Stubbs et al 55 in the postcranial characters. Although one concern of this high evolutionary rate is that it could be an artifact of the incompleteness of Yamatosaurus izanagii, as warned by Lloyd 56 , but the same trend is recovered in an analysis without Yamatosaurus izanagii (Supplementary Fig.…”

Body size correlates with discrete-character morphological proxies

“…The availability of large-scale cladistic datasets for a variety of tetrapod clades has seen a recent explosion in the reconstruction of discrete character–based morphospaces and disparity curves in dinosaurs (Brusatte et al 2008a, 2012, 2014; Romano 2017; Cau 2018; Nordén et al 2018; Stubbs et al 2019), pterosaurs (Butler et al 2011; Prentice et al 2011; Foth et al 2012), crocodyliforms (Young et al 2010; Stubbs et al 2013), ichthyosaurs (Thorne et al 2011), procolophonids (Cisneros and Ruta 2010), therapsids (Ruta et al 2013), eutherian mammals (Halliday and Goswami 2016), and early tetrapods (Ruta and Wills 2016). Although these studies are largely palaeobiological in nature, the approach can be extended to any morphology-based character–taxon matrix (e.g., Ericales flowers; Chartier et al 2017).…”

“…Our analyses use dinosaurs as a case study, because they are commonly used to test/formulate macroevolutionary hypotheses from character–taxon matrices (e.g., Brusatte et al 2008a,b, 2012, 2014; Strickson et al 2016; Cau 2018; Nordén et al 2018; Stubbs et al 2019). In our exploration of the effects of body size on ordinated morphological proxies in dinosaurs, we conducted analyses at two conceptual levels.…”

Morphological disparity in theropod jaws: comparing discrete characters and geometric morphometrics

“…Another productive approach could be to use subsets of discrete character data sets that have hypothesized ecomorphological or evolutionary significance (Gerber ; Stubbs et al . ), such as the appendicular skeleton in the fish–tetrapod transition (Ruta & Wills ), the display crests and feeding apparatus in hadrosaurid dinosaurs (Stubbs et al . ) and this contribution.…”

“…), such as the appendicular skeleton in the fish–tetrapod transition (Ruta & Wills ), the display crests and feeding apparatus in hadrosaurid dinosaurs (Stubbs et al . ) and this contribution. Alternatively, researchers could construct or combine new matrices from multiple sources for disparity studies that focus on specific parts of anatomy, such as the teeth (Strickson et al .…”