Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany

Abstract

Recent discoveries in Asia have greatly increased our understanding of the evolution of dinosaurs' integumentary structures, revealing a previously unexpected diversity of "protofeathers" and feathers. However, all theropod dinosaurs with preserved feathers reported so far are coelurosaurs. Evidence for filaments or feathers in noncoelurosaurian theropods is circumstantial and debated. Here we report an exceptionally preserved skeleton of a juvenile megalosauroid, Sciurumimus albersdoerferi n. gen., n. sp., from the Late Jurassic of Germany, which preserves a filamentous plumage at the tail base and on parts of the body. These structures are identical to the type 1 feathers that have been reported in some ornithischians, the basal tyrannosaur Dilong, the basal therizinosauroid Beipiaosaurus, and, probably, in the basal coelurosaur Sinosauropteryx. Sciurumimus albersdoerferi represents the phylogenetically most basal theropod that preserves direct evidence for feathers and helps close the gap between feathers reported in coelurosaurian theropods and filaments in ornithischian dinosaurs, further supporting the homology of these structures. The specimen of Sciurumimus is the most complete megalosauroid yet discovered and helps clarify significant anatomical details of this important basal theropod clade, such as the complete absence of the fourth digit of the manus. The dentition of this probably early-posthatchling individual is markedly similar to that of basal coelurosaurian theropods, indicating that coelurosaur occurrences based on isolated teeth should be used with caution.

Fig. 1.

Juvenile megalosaurid Sciurumimus albersdoerferi (BMMS BK 11). (A) Overview of the limestone slab with the specimen as preserved. (B) Skull and hemimandibles under UV light in left lateral view. (C) Forelimbs under UV light. (D) Pelvic girdle under UV light. aof, antorbital fenestra; c, carpal; co, coracoid; f, femur; fu, furcula; h, humerus; hy, hyoid; il, ilium; is, ischium; mc, metacarpal; n, nares; o, orbit; pu, pubis; r, radius; s, sacral vertebra; u, ungual; ul, ulna. (Scale bars: 50 mm in A and 10 mm in B–D.)

Fig. 2.

Anatomical details of Sciurumimus albersdoerferi. (A) Dentition of left premaxilla and anterior end of left maxilla. (B) Disarticulated occiput, atlas, axis, and anterior cervical vertebrae. (C and D) Posterior-most dorsal vertebrae and anterior part of ilium shown in a photograph (C) and in an interpretative drawing (D). All photographs were taken under UV light. ans, axial neural spine; boc, basioccipital; dv, dorsal vertebrae; epi, epipophyses; il, ilium; lfe, left femur; m, maxilla; m1 and m5, first and fifth maxillary tooth, respectively; p1and p4, first and fourth premaxillary tooth, respectively; pm, premaxilla; prel, prezygoepipophyseal lamina; r, rib; rfe, right femur; sv, sacral vertebra; tp, transverse process. (Scale bars: 5 mm in A and 10 mm in B–D.)

Fig. 3.

Soft tissue preservation in Sciurumimus. (A) Overview of skeleton under UV light, with position of magnifications in B–F indicated. (Scale bar: 50 mm.) (B) Fine filaments above the scapular region of the dorsal vertebral column. (C) Anterior midcaudal section with long dorsal filaments (upper white arrow), preserved skin (yellow patch), and fine filaments at the ventral lateral tail flank (lower white arrows). (D) Long filaments, anchored in the skin at the dorsal tail base. (E) Small section of possibly fossilized muscle tissue along the posterior edge of the tibia. (F) Small, fine filaments ventral to the gastralia in the abdominal area (arrows point to individual filaments). (G) Magnification of soft tissues dorsal to the ninth and 10th caudal vertebra. (H) Interpretative drawing showing possible follicles. Greenish white structures are bone, fine greenish lines above the vertebrae are preserved filaments, and yellow parts represent skin structures. Arrow in G points to a filament entering one of the vertical skin structures that might represent follicles. col, collagen fibers in the skin; fil, filaments; fo? possible follicles; tp, transverse process. All photographs were taken under UV light.

Fig. 4.

Phylogenetic position of Sciurumimus in the analysis of Benson et al. (17). Clade names: 1, Ceratosauria; 2, Tetanurae; 3, Carnosauria; 4, Coelurosauria; 5, Allosauroidea; 6, Megalosauroidea; 7, Spinosauridae; 8, Megalosauridae. Numbers on the stem indicate stem-based taxa, numbers on the node indicate node-based taxa.