A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy

Abstract

A second nearly complete, articulated specimen of the basal troodontid Mei long (DNHM D2154) is reported from the Early Cretaceous (Hauterivian-Valanginian) lower Yixian Formation, Liaoning Province, China. New diagnostic features of Mei long are identified, including: a uniquely shaped maxilla, low with small, low maxillary fenestra; sacrum with an extremely wide caudal portion and elongate 4th and 5th sacral processes; and a large distal articular surface on the tibiotarsus which continues caudally on the tibia. A phylogenetic analysis including new data from the second specimen recovered Mei as a basal troodontid, in keeping with previous analyses. Although the skeleton exhibits several juvenile-like features including free cervical ribs, unfused frontals and nasals, and a short snouted skull, other attributes, full fusion of all neurocentral synostoses and the sacrum, and dense exteriors to cortical bone, suggest a small, mature individual. Microscopic examination of tibia and fibula histology confirms maturity and suggests an individual greater than two years old with slowed growth. Despite being one of the smallest dinosaurs, Mei long exhibits multi-year growth and cortical bone consisting largely of fibro-lamellar tissue marked by lines of arrested growth as in much larger and more basal theropods. This Mei long specimen lies in a similar but mirrored sleeping position to that of the holotype, strengthening the hypothesis that both specimens were preserved in a stereotypical life position. Like many Liaoning specimens, the new specimen also lacks extensive taphonomic and stratigraphic data, making further behavioral inference problematic.

Osteology of a New Late Cretaceous Troodontid Specimen from Ukhaa Tolgod, Ömnögovi Aimag, Mongolia

“…The quadrate foot is robust and mediolaterally expanded, and bicondylar, as is common of paravians (Norell and Hwang, 2004;Mayr et al, 2005;Hu et al, 2009;Pei et al, 2014). The lower portion of the quadrate shaft bearing the condyles is vertically oriented, in agreement with other paravians, such as Mei and Microraptor (Xu and Norell, 2004;Gao et al, 2012;Pei et al, 2014). A deep depression is developed on the posterior surface of the quadrate in Almas ukhaa, as in Sinovenator and Mei Xu and Norell, 2004).…”

“…The jugal is L-shaped in lateral view. It is lightly built and slender as in other troodontids and avialans (Mayr et al, 2005;Gao et al, 2012;Tsuihiji et al, 2014), but different from the broad and platelike jugal of derived dromaeosaurids (e.g., Norell et al, 2006). The suborbital process of the jugal is horizontally positioned.…”

A new species of troodontid theropod (Dinosauria: Maniraptora) from the Horseshoe Canyon Formation (Maastrichtian) of Alberta, Canada

“…The frontal of Mei long from the Yixian Formation of northeastern China has 22 been noted to be unusually broad posteriorly, and appears relatively short, but they are distinct from A. curriei in their convex, inflated morphology (Gao et al 2012). Albertavenator curriei cannot be compared to Byronosaurus (Bever and Norell 2009;Makovicky et al 2003),…”

New material of a troodontid theropod (Dinosauria: Saurischia) from the Lower Cretaceous of Mongolia

“…In order to further infer the phylogenetic position of MPC-D 100/140 within Troodontidae, a cladistic analysis was conducted by adding it to the previously published data-set for coelurosaurian phylogeny by Gao et al (2012) with the addition of Gobivenator (Tsuihiji et al 2014; see Appendix for character coding of MPC-D 100/140). In addition, coding of one character, the hallucal ungual reduced in size relative to those of other pedal unguals (state 0) or not reduced (state 1; character 318), for MPC-D 100/44 was changed from '0' to '?'…”

“…Figure 9. Troodontid portion of the strict consensus of 84 most parsimonious trees resulting from the data-set of Gao et al (2012) with the addition of Gobivenator mongoliensis (Tsuihiji et al 2014) and MPC-D 100/140. A number below each node represents the bootstrap value (%) calculated from 1000 replicates.…”