|Borealopelta markmitchelli |
Brown, Henderson, Vinther, Fletcher, Sistiaga, Herrera & Summons, 2017
• A new armored dinosaur is described based on an exceptionally preserved specimen
• Abundant in situ osteoderms with keratinous sheaths and scales are preserved
• Reddish-brown coloration and crypsis in the form of countershading are indicated
• Crypsis indicates strong predation pressure on this large, heavily armored dinosaur
Predator-prey dynamics are an important evolutionary driver of escalating predation mode and efficiency, and commensurate responses of prey. Among these strategies, camouflage is important for visual concealment, with countershading the most universally observed. 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. Despite thyreophoran dinosaurs’ possessing extensive dermal armor, some of the most extreme examples of anti-predator structures, 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.
Dinosauria Owen, 1842
Ornithischia Seeley, 1888
Ankylosauria Osborn, 1923
Nodosauridae Marsh, 1890
Borealopelta markmitchelli gen. et sp. nov.
Etymology: The generic name Borealopelta is derived from “borealis” (Latin, “northern”) and “pelta” (Greek, “shield”), in reference to the northern locality and the preserved epidermal scales and dermal osteoderms. The specific epithet markmitchelli honors Mark Mitchell for his more than 7,000 hours of patient and skilled preparation of the holotype.
|An illustration of Borealopelta markmitchelli. The study suggests that it displayed a camouflage effect known as counter-shading.|
Illustration: Julius Csotonyi/Courtesy of the Royal Tyrrell Museum of Palaeontology, Canada.
|Figure 1. Photographs of the Holotype of Borealopelta markmitchelli, TMP 2011.033.0001 Top: anterodorsolateral view; bottom: anterodorsal view. Scale bar, 10 cm.|
Holotype: The holotype is Royal Tyrrell Museum of Palaeontology (TMP) 2011.033.0001: an articulated specimen preserving the head, neck, most of the trunk and sacrum, a complete right and a partial left forelimb and manus, partial pes (Figure 1). In situ osteoderms and nearly complete soft tissue integument are preserved across dorsal and lateral surfaces of the axial skeleton, posterodorsal surface of forelimbs, and plantar surfaces of a manus and a pes. Specimen is preserved in multiple large blocks, including slabs and counter-slabs in the sacral region.
Locality and Horizon: Suncor Millennium Mine, Fort McMurray, Alberta, Canada. Wabiskaw Member, Clearwater Formation, Aptian stage. Detailed locality data are available at Royal Tyrrell Museum of Palaeontology.
Diagnosis: A nodosaurid ankylosaur characterized by the following autapomorphies (∗) and suite of characters [character/state]: cranial: dorsal skull ornamentation expressed as a large hexagonal dermal plate in frontoparietal region and multiple (>20) small dermal plates in frontonasal region∗; external nares excluded from view dorsally (shared with Pawpawsaurus) [16:1]; supraorbital ornamentation forming sharp lateral rim dorsal to orbits (shared with Gargoyleosaurus and Kunbarrasaurus) [38:2]; jugal (suborbital) horn triangular with pointed apex (shared with Gastonia, Gargoyleosaurus, and Polocanthus); jugal (suborbital) horn base longer than orbit length∗; osteoderms: cervical and thoracic osteoderms form continuous (abutting) transverse rows completely separated by continuous transverse rows of polygonal basement scales; parascapular spine is the largest osteoderm, recurved, and projects posterolaterally and horizontally (potentially shared with Sauropelta); osteoderm count for transverse rows: cervicals: C1-3, C2-3, C3-3, transition: TR-2, thoracic: T1-6∗; third and sixth transverse thoracic osteoderm rows expressed medially but pinch out laterally∗.
The new taxon can be further differentiated from Pawpawsaurus based on: dermal plate in frontonasal region (central dermal plates) flat; absence of ciliary osteoderm. Can be further differentiated from Sauropelta based on: parietals flat to slightly convex; cervical half ring has 4–6 osteoderms only; medial cervical osteoderms subequal, hexagonal, and bear prominent median ridge with posterior margin projecting beyond the basal footprint.
|The Making of a Most Extraordinary Fossil|
|The Making of a Most Extraordinary Fossil|
Caleb M. Brown, Donald M. Henderson, Jakob Vinther, Ian Fletcher, Ainara Sistiaga, Jorsua Herrera and Roger E. Summons. 2017. An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics. Current Biology. DOI: 10.1016/j.cub.2017.06.071
Despite heavy armor, new dinosaur used camouflage to hide from predators eurekalert.org/e/7ZWJ via @CellPressNews @EurekAlert
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Discover How This Dinosaur Became an Extraordinary Fossil NationalGeographic.com/magazine/2017/06/making-of-a-dinosaur-fossil-nodosaur-illustrations
Heavily armoured dinosaur had ginger camouflage to deter predators – study theguardian.com/science/2017/aug/03/heavily-armoured-nodosaur-ginger-camouflage-predators-borealopelta-markmitchelli
Alberta museum unveils world's best-preserved armoured dinosaur theguardian.com/science/2017/may/15/alberta-canada-museum-unveils-best-preserved-armoured-dinosaur-in-the-world-nodosaur
ติดอยู่ในกาลเวลา ngthai.com/animals/1703 via เนชันแนล จีโอกราฟฟิก (National Geographic) ฉบับภาษาไทย