A new North American therizinosaurid and the role of herbivory in ‘predatory’ dinosaur evolution

Abstract

Historically, ecomorphological inferences regarding theropod (i.e. 'predatory') dinosaurs were guided by an assumption that they were singularly hypercarnivorous. A recent plethora of maniraptoran discoveries has produced evidence challenging this notion. Here, we report on a new species of maniraptoran theropod, Nothronychus graffami sp. nov. Relative completeness of this specimen permits a phylogenetic reassessment of Therizinosauria-the theropod clade exhibiting the most substantial anatomical evidence of herbivory. In the most comprehensive phylogenetic study of the clade conducted to date, we recover Therizinosauria as the basalmost maniraptoran lineage. Using concentrated changes tests, we present evidence for correlated character evolution among herbivorous and hypercarnivorous taxa and propose ecomorphological indicators for future interpretations of diet among maniraptoran clades. Maximum parsimony optimizations of character evolution within our study indicate an ancestral origin for dietary plasticity and facultative herbivory (omnivory) within the clade. These findings suggest that hypercarnivory in paravian dinosaurs is a secondarily derived dietary specialization and provide a potential mechanism for the invasion of novel morpho-and ecospace early in coelurosaurian evolution-the loss of obligate carnivory and origin of dietary opportunism.

Rates of dinosaur limb evolution provide evidence for exceptional radiation in Mesozoic birds

“…Maniraptorans possess a highly asymmetrical wrist joint, enabling three segment arm folding [34]. This constrains the forelimb segments to approximately equal lengths [13,34], but allows longer and more functionally versatile forelimbs [13], and is associated with ecological diversification in Maniraptora [18]. It may also have protected their pinnate arm feathers from damage [34] and is an exaptation for flight.…”

“…Numerous recent discoveries of well-preserved Mesozoic birds [6] and a taxon-rich understanding of Mesozoic theropod systematics [17][18][19][20][21][22] allow us to analyse theropod locomotor evolution and taxonomic diversification in an explicit phylogenetic framework. We compiled a dataset of body proportions and phylogenetic relationships among Mesozoic birds and other theropods.…”

Cranial anatomy ofErlikosaurus andrewsi(Dinosauria, Therizinosauria): new insights based on digital reconstruction

“…The discovery of more complete skeletons from China and Mongolia (Perle, 1981;Russell and Dong, 1993) later revealed their derived theropod affinities. Since then, numerous discoveries within the last 20 years have added further to our knowledge of therizinosaurian anatomy and provided more information on their paleobiology (e.g., Xu et al, 2002a;Li et al, 2007;Zanno et al, 2009;Lautenschlager et al, 2012). Challenging the long-held, classical assumption that all theropod dinosaurs were nearly exclusively carnivorous, therizinosaurians appear to have evolved specialized dietary preferences.…”

Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy

“…In contrast most coelurosaurian theropods have shallow or absent extensor pits (e.g. Deinonychus, Nothronychus, Tyrannosaurus, Troodon;Ostrom, 1969;Currie and Russel, 1987;Bochu, 2003;Zanno et al, 2009;Zanno, 2010).…”