An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics

Abstract

Predator-prey dynamics are an important evolutionary driver of escalating predation mode and efficiency, and commensurate responses of prey [1-3]. Among these strategies, camouflage is important for visual concealment, with countershading the most universally observed [4-6]. Extant terrestrial herbivores free of significant predation pressure, due to large size or isolation, do not exhibit countershading. Modern predator-prey dynamics may not be directly applicable to those of the Mesozoic due to the dominance of very large, visually oriented theropod dinosaurs [7]. Despite thyreophoran dinosaurs' possessing extensive dermal armor, some of the most extreme examples of anti-predator structures [8, 9], little direct evidence of predation on these and other dinosaur megaherbivores has been documented. Here we describe a new, exquisitely three-dimensionally preserved nodosaurid ankylosaur, Borealopelta markmitchelli gen. et sp. nov., from the Early Cretaceous of Alberta, which preserves integumentary structures as organic layers, including continuous fields of epidermal scales and intact horn sheaths capping the body armor. We identify melanin in the organic residues through mass spectroscopic analyses and observe lighter pigmentation of the large parascapular spines, consistent with display, and a pattern of countershading across the body. With an estimated body mass exceeding 1,300 kg, B. markmitchelli was much larger than modern terrestrial mammals that either are countershaded or experience significant predation pressure as adults. Presence of countershading suggests predation pressure strong enough to select for concealment in this megaherbivore despite possession of massive dorsal and lateral armor, illustrating a significant dichotomy between Mesozoic predator-prey dynamics and those of modern terrestrial systems.

Three‐dimensional soft tissue preservation revealed in the skin of a non‐avian dinosaur

“…), in the skin of the Cretaceous nodosaur Borealopelta (Brown et al . ) and in experimental studies (Colleary et al . ).…”

“…Previous investigations of dinosaur skin were performed on the basal ceratopsian Psittacosaurus (Lingham‐Soliar ), a nodosaur (Brown et al . ), and coelurosaurs (Navalón et al . ; Bell et al .…”

Paleoproteomics of Mesozoic Dinosaurs and Other Mesozoic Fossils

“…[], can localize amino acids, as well as di‐and tripeptides and other biological compounds (melanin, e.g., refs. []; heme) directly to tissues with high resolution, but like synchrotron methods, is sensitive to surface composition and care must be taken to eliminate contaminants as a source of signal. It was used to support the presence of molecules consistent with protein in originally keratinous claw sheath material from Rahonavis ostromi , a very basal bird, and as mentioned above, in hollow white filaments recovered from the cervical region of an articulated specimen of the enigmatic alverezsaurid, Shuvuuia deserti , from Mongolia .…”

Taphonomic experiments resolve controls on the preservation of melanosomes and keratinous tissues in feathers

“…) and have provided insights into palaeoecology (Brown et al . ; Smithwick et al . ) and the evolution of communication strategies (McNamara et al .…”