The rise of feathered dinosaurs: Kulindadromeus zabaikalicus, the oldest dinosaur with ‘feather-like’ structures

Diverse epidermal appendages including grouped filaments closely resembling primitive feathers in non-avian theropods, are associated with skeletal elements in the primitive ornithischian dinosaur Kulindadromeus zabaikalicus from the Kulinda locality in south-eastern Siberia. This discovery suggests that “feather-like” structures did not evolve exclusively in theropod dinosaurs, but were instead potentially widespread in the whole dinosaur clade. The dating of the Kulinda locality is therefore particularly important for reconstructing the evolution of “feather-like” structures in dinosaurs within a chronostratigraphic framework. Here we present the first dating of the Kulinda locality, combining U-Pb analyses (LA-ICP-MS) on detrital zircons and monazites from sedimentary rocks of volcaniclastic origin and palynological observations. Concordia ages constrain the maximum age of the volcaniclastic deposits at 172.8 ± 1.6 Ma, corresponding to the Aalenian (Middle Jurassic). The palynological assemblage includes taxa that are correlated to Bathonian palynozones from western Siberia, and therefore constrains the minimum age of the deposits. The new U-Pb ages, together with the palynological data, provide evidence of a Bathonian age—between 168.3 ± 1.3 Ma and 166.1 ± 1.2 Ma—for Kulindadromeus. This is older than the previous Late Jurassic to Early Cretaceous ages tentatively based on local stratigraphic correlations. A Bathonian age is highly consistent with the phylogenetic position of Kulindadromeus at the base of the neornithischian clade and suggests that cerapodan dinosaurs originated in Asia during the Middle Jurassic, from a common ancestor that closely looked like Kulindadromeus. Our results consequently show that Kulindadromeus is the oldest known dinosaur with “feather-like” structures discovered so far.


Supplementary Tables
Supplementary Table S1. X-ray diffraction based compositions of the four igneous rock samples that crop out on top hill. The four samples have a rather similar overall composition (with quartz, feldspars, biotite, and kaolinite), but differ by the relative abundance of their

Supplementary Figures
Supplementary Figure S1. The mineralogy of selected rock samples from Kulinda has been studied by X-ray diffraction (XRD) analysis using a PANanalytical Empyrean diffractometer (at the Royal Belgian Institute of Natural Sciences) with Cu Kα radiation. A tube voltage of 45 kV and a tube current of 40 mA were used. The goniometer scanned from 3° to 69° 2θ for the bulk rock. The semi-quantitative interpretation of data was made using Visual Crystal 6 software.
Intense magmatism occurred during the Permian, Triassic and Early Jurassic in south-eastern Siberia, because of the subduction of the Mongol-Okhotsk oceanic plate beneath Siberia . Granite and granodiorite plutons are therefore widespread in the region, with calc-alkaline rock suites located in the front part of the active continental margin, and sub- Cretaceous and are the consequence of the post-collisional rifting Stupak, Kudryashova & Lebedev, 2016).
Discussion on the composition of the Kulinda dinosaur fauna. All the ornithischian material discovered at Kulinda belongs to the basal neornithischian Kulindadromeus zabaikalicus (Godefroit et al., 2014). An alternative interpretation for the dinosaur fauna at Kulinda was proposed (Alifanov & Saveliev, 2014;2015) and named three new taxa from this locality: the 'hypsilophodontian' ornithopods Kulindapteryx ukureica and Daurosaurus olovus (Alifanov & Saveliev, 2014), and the 'nqwebasaurid' ornithomimosaur Lepidocheirosaurus natalis (Alifanov & Saveliev, 2015). Detailed description of the osteology of the dinosaurs from Kulinda is beyond the scope of this paper, but some brief comments are made below.
It should be noted that these interpretations were not done with the modern taxonomic standards for elaborating the classification schemes: they do not use cladistic methods for inferring the phylogenetic relationships between taxa. Kulindapteryx and Daurosaurus only differ in the structure of their ischia (the only bone that is preserved in both taxa), but those differences can easily be explained by differences in the orientation of the bones: PIN 5434/25a, the holotype of Kulindapteryx ukureica, is clearly exposed in dorsal view, not in lateral view as hypothesized by the authors. We therefore consider Kulindapteryx ukureica and Daurosaurus olovus as nomina dubia, and that the specimens both fall within the Kulidadromeus zabaikalicus hypodigm.
In their paper, the authors claimed that the caudal vertebrae and associated scales referred to However, this interpretation is apparently based on direct comparisons with the ornithopod Hypsilophodon foxii and lacks a broader phylogenetic context (Alifanov & Saveliev, 2015). For example, caudal vertebrae of more basal ornithischians, e.g., the heterodontosaurid Tianyulong confuciusi (see Sereno, 2012, fig.25), closely resemble those discovered at Kulinda: from about the tenth vertebra, the centrum is elongated and spool-shaped in lateral view, the neural spines are reduced to a ridge, and both the pre-and postzygapophyses are long, extending beyond the level of the articular surfaces of the centra. Except for the absence of evidence for ossified tendons, the caudal structure in Tianyulong is remarkably similar to that in dromaeosaurid theropods (Sereno, 2012). Furthermore, the hand of Lepidocheirosaurus natalis from Kulinda closely resembles that of Tianyulong (see Sereno, 2012, fig. 27 (Vakhrameev, 1991). Nevertheless, mosses are widespread in all regions of the world since the Palaeozoic, and some species can occupy harsh environments (Bardunov, 1984).
It should be noted that, at Kulinda, ferns, arthrophytes, and leptostrobaleans are only represented by highly fragmented remains and their identification was possible at the generic level, only.
Gymnosperms are abundant in some layers, and especially Coniferales and Leptostrobales, which formed trees and bushes. Czekanowskia ex gr. rigida is a typical Siberian gymnosperm species characterized by a wide stratigraphic extension: it is known from the Lower Jurassic to the Upper Jurassic (Vakhrameev, 1991;Samylina & Kiritchkova, 1993). The moss Hepaticites arcuatus was originally found in the Middle Jurassic of Yorkshire (Harris, 1961;1964). The absence of epidermal structure in the specimens from Kulinda locality allows the definition of this species in the open nomenclature, only. Elatides ovalis, Schizolepidopsis moelleri, S. elegans, S. levis are also interpreted as Early-Middle Jurassic species (Vakhrameev, 1970;1991;Mogutcheva, 2009).
The modern morphology of the conifers was already established in the early Mesozoic (Andrews, 1961). The evolution of the axillary region led to the formation of seeds with spliced scales, which is a typical feature for the group and particularly for the genus Schizolepidopsis. The first occurrences of Schizolepidopsis are reported from the Triassic of the Fergana Valley in eastern Uzbekistan (Stiksel, 1966). All specimens identified at Kulinda were observed in the Lower Jurassic of Central Asia as well (Turutonova-Ketova, 1950). However, they seem more abundant in the Ukurey Formation, where the presence of unique morphotypes might reflect endemicity.
Abundant bifurcate seed scales of Schizolepidopsis are typical for the Middle and Upper Jurassic deposits of Siberia (Vakhrameev, 1991). The fern Coniopteris appeared in the late Early Jurassic but became common since the Middle Jurassic (Vakhrameev, 1991;Deng & Lu, 2006). Muscites samchakianus is reported in Middle-Upper Jurassic deposits from Transbaikal region (Srebrodolskaya, 1980). The taxonomic composition of the paleofloral assemblages from Kulinda locality cannot therefore give a more detailed age than the Middle Jurassic-Early Cretaceous time range for the deposits.