Theropod diversity and the refinement of avian characteristics

“This four-winged body plan may represent a transitional step in the evolution of powered flight (Longrich, 2006; Hu et al., 2009), though its optimization on the evolutionary tree is complicated by the extreme similarity between basal members of the three principle paravian lineages and hence some phylogenetic labilit…”

“…regarding the brain size of nonavian dinosaurs, theropods show a progressive increase in EQ throughout their evolutionary history and reconstructedEQvalues frombrain endocasts of various extinct maniraptorans approach those of the basal lineages of living birds (Dominguez Alonso et al., 2004).”

“Given that a number of primitive avian taxa including Archeopteryx (Erickson et al., 2009), Confuciusornis Theropod Diversity and the Refinement of Avian Characteristics 19”

“The bipedal posture, hinge-like ankle, hollowed bones, and long S-shaped neck of birds were inherited from deep dinosaurian ancestors [43,44], the wishbone (furcula) and threefingered hands of birds first appeared in primitive theropods, the reversion of the pubis and associated forward movement of the center of mass…”

“that ultimately gave rise to extant birds [9].”

“…studies demonstrating that key flight preadaptations up to and including vaned feathers and well-developed wings evolved in terrestrial contexts millions of years prior to the origin of crown avian flight (Makovicky & Zanno, 2011; Brusatte et al., 2014; Dececchi, Larsson & Habib, 2016; Cau, 2018).”

“Finally, tradeoffs between wings and legs may have influenced the evolutionary acquisition of flight among theropod dinosaurs, the ancestors (e.g., Gauthier 1986; Makovicky and Zanno 2011) of birds.”

“Though superficially individualized, these plates are integrally part of the jaw bone, and are histologically continuous with the adjacent bone (be it the dentary, maxilla, or premaxilla; [99]; contra [13]; contra [36, 37]).”

“…a renaissance, including a greater understanding of the nonlinear nature of trait acquisition and the lack of a clear demarcation between “birds” and “nonavialan dinosaurs” (Makovicky and Zanno, 2011; Godefroit et al., 2013; Brusatte et al., 2014; Cau, 2018; Hu et al., 2018; Pei et al., in press).”

“Therefore, we refrained from inferring medial translation of the femoral head beyond the inner acetabular rim as suggested by Chatterjee and Templin (2007) and Makovicky and Zanno (2011).”

“Although most of the skeletal features differentiating birds from other extant vertebrates can be tracked back to the Mesozoic dinosaurs (Makovicky & Zanno, 2011; Xu et al., 2014a), the integration of the fossil record of stem-avians (all taxa closer to birds than crocodiles) with the developmental…”

“…size and feather morphology; flapping velocity also presumably differs because adult birds, but not non-avian theropods and basal avialans, have large ossified keels for the attachment of powerful flight muscles (Prum and Brush 2002; Norell and Xu 2005; Makovicky and Zanno 2011; Wang et al. 2011).”

“of features traditionally attributed to birds [2,18,28].”

“Overwritten upon this basic Bauplan are several overarching trends within theropods (Dececchi and Larsson, 2009; Makovicky and Zanno, 2011; Turner et al., 2012; Brusatte et al., 2014) such as body size reduction (Turner et al., 2007; Dececchi and Larsson, 2013; Lee et al., 2014; Benson et al.,…”

“…a herbivorous diet, requiring more space in the abdominal cavity than carnivorous, piscivorous or omnivorous ones (Weishampel & Norman 1989; see also Zanno & Makovicky 2011) given that an entirely plant-based diet generally needs a longer intestinal tract compared to others (Chivers & Hladik 1980).”

“Birds, as living dinosaurs (Makovicky & Zanno, 2011; Smith et al., 2015), might provide an alternative model for predicting hydrodynamic sorting patterns for the bones of non-avian dinosaurs, and data already exist for extant pigeons (Trapani, 1998).”

“Moreover, these two modules may be linked 198 through avian eggs, the shape of which is suggested to be correlated with both the pelvic shape (Dyke & 199 Kaiser 2010; Mayr 2017) and flight ability (Stoddard et al. 2017).”

“” With two exceptions—digital homology (for reviews see: James and Pourtless 2009; Xu et al. 2009; Larsson et al. 2010; Makovicky and Zanno 2011; Young et al. 2011; Feduccia 2012, 2016, 2020; Xu and Mackem 2013; Salinas-Saavedra et al. 2014; Guinard 2016) and the mode in which avian flight originated—Havstad and Smith…”

“Modern birds are now generally recognized to be one derivative line of the otherwise extinct theropod dinosaurs (Figure 1) [25], and the behavioral complexity of those extinct theropods has been a source of considerable speculation.”

“In this context, the compelling poss ture of the oviraptor Citipati suggests that it was reducc ing the energetic cost of brooding by sheltering its eggs beneath elongated wing feathers (Makovicky and Zanno, 2011; O'Connor et al., 2011).”

“Currently, the prevailing view point on the origin of avian feathers is that they originated from filamentous integumentary structures found in some dinosaur fossils, which might constitute an adaptation for thermal isolation in endothermic cursorial theropods (Prum 1999; Makovicky and Zanno 2011; Chatterjee 2015).”