Epidermal complexity in the theropod dinosaurJuravenatorfrom the Upper Jurassic of Germany

Abstract

Epidermal scales among modern reptiles are morphologically diverse and serve a variety of functions ranging from moisture balance to chemoreception. Despite being predominantly squamous‐skinned (scaly), the functional implications of this type of integument have never before been explored for a dinosaur. Re‐examination of the holotype of the theropod Juravenator starki (Kimmeridgian, Late Jurassic) reveals previously unseen diversity in its epidermal covering. In addition to the presence of short monofilaments on the dorsal and ventral parts of the tail, we identify distinctive scale patterns corresponding to discrete longitudinal bands of scutate, tuberculate and ornamented scales along the length of the tail. In modern squamous‐skinned amniotes, variation in scale architecture can be linked to functional differences between scale types. In Juravenator, distinctive circular nodes associated with the ornamented scales have recently been interpreted as integumentary sense organs. We also suggest that it is likely that the snake‐like scutate scales on the underside of the tail fulfilled a role related to mechanical protection rather than locomotory function. Whereas the literature on theropod epidermal structures has been dominated by discussions on the evolution and diversity of feathers, this study highlights the complexity of squamous integument in Juravenator, which is revealed as one of the most complex among known theropods. An exploration of the epidermal structures found in Juravenator and other non‐avian theropods reveals great complexity in the type and distribution of these structures across the clade, suggesting potential for the future inquiry into their taxonomic and biological importance.

Morphology and distribution of scales, dermal ossifications, and other non‐feather integumentary structures in non‐avialan theropod dinosaurs

“…9C, D; Appendix S3.4). Rectangular ventral scales, reminiscent of those in extant snakes, also lined the underside of the tail (Bell & Hendrickx, 2021; Fig. 9A, B).…”

“…Theropods, as for other dinosaurs, demonstrated significant interspecific variation in their body coverings. The evolutionary significance and many fundamental questions about scale function (see Bell & Hendrickx, 2020, 2021; Hendrickx & Bell, 2021b), and the roles of ontogeny and sex on scale architecture remain unanswered. Remarkable cases of possible sexual dimorphism have been reported in early‐diverging avialans based on soft tissues [e.g.…”

Evidence of integumentary scale diversity in the late Jurassic Sauropod Diplodocus sp. from the Mother’s Day Quarry, Montana

“…The theropod Juraventator exhibits three distinct scale shapes on its tail, of which the scale shape varies based on whether it is dorsally or ventrally located. Specifically, the scale shapes change ventral to dorsal in the following order: scutate ventral scales, ornamental scales, tuberculate scales, and finally feathers at the most dorsal part of the tail (Bell & Hendrickx, 2020). MDS-2019-028 shows a similar transition, featuring up to six different scale shapes localized on different areas of the integument that change in a "dorsoventral" and "anteroposterior" manner (Fig.…”

“…However, our understanding of scaley dinosaur integument has also changed. Over the past century, the number of studies published on dinosaur scales has dramatically increased (e.g., Brown et al, 2017;Bell, 2014;Bell & Hendrickx, 2020). Despite this, research into sauropod integument remains rather limited compared to research on other dinosaur integument.…”

Laser-stimulated fluorescence reveals unseen details in fossils from the Upper Jurassic Solnhofen Limestones

“…Since the introduction of UV fluorescence in analysing fossils from the Solnhofen limestones in the early twentieth century [31], the technique has been increasingly used in the search for (sensu Croft et al [32]) and analyses of its exceptionally preserved fossils. Studies of Solnhofen fossils using UV include those of decapod crustaceans [33][34][35], ammonites [36,37], fish [38,39], pterosaurs [40,41] and dinosaurs [42][43][44][45][46] among others. In recent years, laser light of 405-532 nm wavelengths has been applied to fossils to induce fluorescence and reveal clearer and/or otherwise unseen details [1,47], especially on soft-tissue bearing fossils pertinent to the study of avian and flight origins and integument evolution [1,[3][4][5][8][9][10][11][12][13]15,16,48,49].…”