Convergent avialan brain morphology in Sinovenator (Troodontidae, Theropoda)

Abstract

Multiple modifications to the skull and brain anatomy occurred along the lineage encompassing bird-line theropod dinosaurs and modern birds. Anatomical changes to the endocranium include an enlarged endocranial cavity, relatively larger optic lobe that implies elevated visual acuity, and proportionately smaller olfactory bulbs that suggests reduced olfaction. Here, we use micro-computed tomographic (CT) imaging to reconstruct the endocranium and its brain structures from an exceptionally well-preserved skull of Sinovenator changii (Troodontidae, Theropoda). While its overall morphology resembles the typical endocranium of other troodontids, Sinovenator also exhibits unique endocranial features that are similar to other paravian taxa and non-maniraptoran theropods. Landmark-based geometric morphometric analysis on endocranial shape of non-avialan and avian dinosaurs points to the overall brain morphology of Sinovenator most closely resembling that of Archaeopteryx, thus indicating convergent evolution of avialan brain morphology in troodontids and wide existence of such architecture in Maniraptora. Institutional abbreviations: IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China. PMOL, Paleontological Museum of Liaoning, Shenyang 110034, China.

Paleoneurology of stem palaeognaths clarifies the plesiomorphic condition of the crown bird central nervous system

“…In many extant birds, the brain is flexed along its rostral‐caudal axis with a ventralized connection to the spinal column. This condition contrasts with the stem avian and nonavian theropod condition in which the rostral and caudal extremities of the brain are roughly aligned, and the brain connects caudally with the spinal column (Bever et al, 2011; Chiappe, Navalón et al, 2022; Hofer, 1952; Witmer & Ridgely, 2009; Witmer et al, 2008; Yu et al, 2024). Both Lithornis endocasts exhibit a caudally positioned occiput and show little flexion in the brains, which is typical of all extant palaeognaths (Chiappe, Navalón et al, 2022; Corfield et al, 2008).…”

“…Little Mesozoic avialan endocranial material exists for comparison with Lithornis . The brains of dromaeosaurid theropods and early avialans such as Archaeopteryx are clearly unflexed, with the foramen magnum and thus the occiput positioned caudally (Balanoff et al, 2013; Chiappe, Navalón et al, 2022; Yu et al, 2024) (Figure 7). The endocasts of the crownward ornithurine Ichthyornis (Torres et al, 2021) and the putative ornithurine Cerebavis are also unflexed, with the foramen magnum opening caudally, although the precise phylogenetic affinities of the latter are uncertain due to the holotype specimen's incompleteness (Kurochkin et al, 2006; Walsh et al, 2016).…”