A new basal ornithopod dinosaur from the Lower Cretaceous of China

Abstract

A new basal ornithopod dinosaur, based on two nearly complete articulated skeletons, is reported from the Lujiatun Beds (Yixian Fm, Lower Cretaceous) of western Liaoning Province (China). Some of the diagnostic features of Changmiania liaoningensis nov. gen., nov. sp. are tentatively interpreted as adaptations to a fossorial behavior, including: fused premaxillae; nasal laterally expanded, overhanging the maxilla; shortened neck formed by only six cervical vertebrae; neural spines of the sacral vertebrae completely fused together, forming a craniocaudally-elongated continuous bar; fused scapulocoracoid with prominent scapular spine; and paired ilia symmetrically inclined dorsomedially, partially covering the sacrum in dorsal view. A phylogenetic analysis places Changmiania liaoningensis as the most basal ornithopod dinosaur described so far. It is tentatively hypothesized that both Changmiania liaoningensis specimens were suddenly entrapped in a collapsed underground burrow while they were resting, which would explain their perfect lifelike postures and the complete absence of weathering and scavenging traces. However, further behavioural inference remains problematic, because those specimens lack extensive sedimentological and taphonomic data, as it is also the case for most specimens collected in the Lujiatun Beds so far.

The phylogenetic nomenclature of ornithischian dinosaurs

“…9.13). Recent assessments of the phylogenetic relationships of numerous taxa, particularly those nested near the basal neornithischian-ornithopod transition, but also within some major clades, such as ornithopods, currently provide conflicting results ( e.g ., Norman, 2015 ; Han et al, 2018 ; Madzia, Boyd & Mazuch, 2018 ; Andrzejewski, Winkler & Jacobs, 2019 ; Herne et al, 2019 ; Párraga & Prieto-Márquez, 2019 ; Dieudonné et al, 2020 ; Yang et al, 2020 ; Barta & Norell, 2021 ; Černý, Madzia & Slater, 2021 ). It is extremely difficult, and perhaps impossible at the moment, to list unambiguous diagnostic apomorphies for many clades that have long been associated with widely-used names, and detailed discussion would be far beyond the scope of the paper.…”

“… Ankylosauria and Stegosauria of Yang et al (2020) were placed in quotation marks to highlight that these names have not been necessarily used by the authors as defined in the present study. In turn, Psittacosauridae of Yang et al (2020) was placed in quotation marks because the name has not been formally defined yet. Abbreviation: St .…”

“… Weishampel (2004) preferred a maximum-clade definition and used Triceratops as the internal specifier and Ankylosaurus as the external specifier, while Butler, Upchurch & Norman (2008) applied a minimum-clade definition, using Triceratops horridus and Parasaurolophus walkeri as the internal specifiers. Subsequent authors followed the latter definition ( Boyd, 2015 ; Madzia, Boyd & Mazuch, 2018 ; Herne et al, 2019 ; Yang et al, 2020 ). We apply a minimum-clade definition as well and use Iguanodon bernissartensis , Pachycephalosaurus wyomingensis , and Triceratops horridus as the internal specifiers.…”

“…These definitions were maximum-clade and used Ceratopsidae ( Dodson, 1997 ), Triceratops ( Sereno, 1998 ), or Triceratops horridus ( Sereno, 2005 ) as the internal specifiers and Pachycephalosauridae ( Dodson, 1997 ), Pachycephalosaurus ( Sereno, 1998 ), or Pachycephalosaurus wyomingensis , Heterodontosaurus tucki , Hypsilophodon foxii , and Ankylosaurus magniventris ( Sereno, 2005 ) as the external specifiers. Even though the position of Hypsilophodon foxii and Heterodontosaurus tucki is indeed somewhat unstable across studies (see, e.g ., Han et al, 2018 ; Madzia, Boyd & Mazuch, 2018 ; Herne et al, 2019 ; Dieudonné et al, 2020 ; Yang et al, 2020 ), inclusion of these taxa among the external specifiers is not necessary. We use a definition similar to that of Sereno (1998) but include the mandatory Ceratops montanus as a second internal specifier.…”

A new Heterodontosaurus specimen elucidates the unique ventilatory macroevolution of ornithischian dinosaurs

“…Ornithischian systematics have recently received renewed attention, with multiple new interesting but contentious relationships hypothesized ( Müller and Garcia, 2020 ; Dieudonné et al, 2020 ; Yang et al, 2020 ; Baron et al, 2017a ). Much of this recent inquiry is worthy of attention and further interrogation, but support for these novel interrelationships of major ornithischian clades remains low.…”