A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids

Abstract

Fossils from the Jehol Group (Early Cretaceous, Liaoning Province, China) are integral to our understanding of Paraves, the clade of dinosaurs grouping dromaeosaurids, troodontids, and avialians, including living birds. However, many taxa are represented by specimens of unclear ontogenetic age. Without a more thorough understanding of ontogeny, evolutionary relationships and significance of character states within paravian dinosaurs may be obscured and our ability to infer their biology restricted. We describe a complete specimen of a new microraptorine dromaeosaur, Wulong bohaiensis gen. et sp. nov., from the geologically young Jiufotang Formation (Aptian) that helps solve this problem. Phylogenetic analysis recovers the specimen within a monophyletic Microraptorinae. Preserved in articulation on a single slab, the type specimen is small and exhibits osteological markers of immaturity identified in other archosaurs, such as bone texture and lack of fusion. To contextualize this signal, we histologically sampled the tibia, fibula, and humerus and compared them with new samples from the closely related and osteologically mature Sinornithosaurus. Histology shows both specimens to be young and still growing at death, indicating an age for the new dinosaur of about 1 year. The holotype possesses several feather types, including filamentous feathers, pennaceous primaries, and long rectrices, establishing that their growth preceded skeletal maturity and full adult size in some dromaeosaurids. Comparison of histology in the new taxon and Sinornithosaurus indicates that macroscopic signs of maturity developed after the first year, but before cessation of growth, demonstrating that nonhistological indicators of adulthood may be misleading when applied to dromaeosaurids. Anat Rec, 303:963–987, 2020. © 2020 American Association for Anatomy

Assessing ontogenetic maturity in extinct saurian reptiles

“…However, there is a greater amount of disparity in suture closure patterns among reptiles than is commonly recognized, although this posterior‐to‐anterior sequence is often assumed to hold across Archosauria in assessments of maturity (e.g. Irmis, 2007; Griffin, 2018; Poust et al ., 2020).…”

“…For example, separate epiphyseal ossifications that fuse to the diaphysis during ontogeny are present in lepidosaurs (Maisano, 2001, 2002 c ; Frýdlová et al ., 2017) but do not occur at all among archosaurs (Chinsamy‐Turan, 2005) except for disputed cases in some birds (Haines, 1942; Carter, Mikić & Padian, 1998; Holliday et al ., 2010); the pattern of fusion of the neural arches to the centra (i.e. neurocentral suture fusion) can differ between clades (Irmis, 2007), and in only some clades does this feature indicate skeletal maturity has been reached (Griffin, 2018; Poust et al ., 2020); the surface texture of long bones can be either highly informative of maturity (Tumarkin‐Deratzian, Vann & Dodson, 2006) or inconsistent with maturity level (Tumarkin‐Deratzian, Vann & Dodson, 2007), depending on the life history of the group in question; cranial and postcranial bony fusion events are nearly always subclade‐specific and are not widely applicable or comparable across phylogeny (e.g. Griffin, 2018; Poust et al ., 2020); even long bone histology can be inconsistently informative, with some clades destroying annual growth marks via Haversian remodelling or simply seeming not to deposit growth marks at all (e.g.…”

“…neurocentral suture fusion) can differ between clades (Irmis, 2007), and in only some clades does this feature indicate skeletal maturity has been reached (Griffin, 2018; Poust et al ., 2020); the surface texture of long bones can be either highly informative of maturity (Tumarkin‐Deratzian, Vann & Dodson, 2006) or inconsistent with maturity level (Tumarkin‐Deratzian, Vann & Dodson, 2007), depending on the life history of the group in question; cranial and postcranial bony fusion events are nearly always subclade‐specific and are not widely applicable or comparable across phylogeny (e.g. Griffin, 2018; Poust et al ., 2020); even long bone histology can be inconsistently informative, with some clades destroying annual growth marks via Haversian remodelling or simply seeming not to deposit growth marks at all (e.g. Klein & Sander, 2008; Griffin & Nesbitt, 2016 b ; Cerda et al ., 2017).…”

New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous

“…feathers. Several dromaeosaurid taxa have been found to possess feathers, or feather-like structures, such as the Barremian-early Aptian Changyuraptor 44 , the Aptian Sinornithosaurus 45,46 , Zhenyuanlong 47 , and Wulong 48 , and the Albian Microraptor [49][50][51] . Some of these also possess feathers on their hindlimbs and most are confined to smaller body sizes and classified within Microraptorinae, although Zhenyuanlong is larger than the others and has recently been recovered as the sister taxon to Microraptorinae + Eudromaeosauria 29 .…”

Continental diatom biodiversity discovery and description in China: 1848 through 2019

“…Asia has received considerable attention in the context of biodiversity discovery, biogeography and resolving the evolutionary history of a variety of lineages ( Gower et al 2012 ). It is an area harboring many endemic species and broader lineages ( López-Pujol et al 2011 ; Lu et al 2018 ), relicts ( Wu et al 2007 ; López-Pujol and Ren 2009 ; Li et al 2012 a) as well as extinct taxa ( Fu et al 2019 ; Proust et al 2020 ; Zhang 2020). Many diverse lineages have originated, radiated and gone extinct in China.…”