The theropod dinosaur Sinosauropteryx. (a) A new specimen of Sinosauropteryx IVPP V12415 (chevrons and tip of tail are displaced). Numerals 1–4 represent main areas of study (material courtesy of Dr Zhonghe Zhou, Beijing Museum, Chinese Academy of Sciences). (b) The holotype Sinosauropteryx, a small specimen, possibly a juvenile (photo courtesy of Dr Pei-Ji Chen, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences). Scale bars, (a,b) 5 cm.

Sinosauropteryx IVPP V12415. Integumental structures. (a) Overview of the area with significant soft-tissue preservation within the body rather than coronal. Integumental structures occur in the tail recess and overlying the vertebrae; the chevrons have been displaced. (b) Detail in (a). Red arrows show some isolated integumental structures; white arrows show integumental structures closely associated to give the impression of branching; white circle shows two closely associated integumental structures (detail in figure 3b₅); large black arrows shows the vertical part of the excavation in which the best preservations occur. (c) Integumental structures at the juncture between the neck and body, detail in circle shows the angles of the beaded fibres (site 2 in figure 1a); numerals 1, 2, indicate integumental structures of the frill and skin/muscle, respectively, and 3, the cervical vertebrae, curved arrow shows the sharp backward recurvature of the neck; arrowheads show straight fibres. (d) Integumental structures in the distal part of the tail showing gaps between preserved tissues (cf. holotype, figure1b). (e) Detail, showing beaded integumental structures. (f) Schematic of (d). Scale bars, (a,d) 2 cm and (b,c) 1 cm.

Integumental structures in Sinosauropteryx IVPP V12415. (a) Integumental structures in the proximal tail area (area 1 in figure 1a); at the top, they are in regular parallel association (red bracket); below the integumental structures are more random. (b) Isolated integumental structures from various parts of the preservation, reoriented for ease of viewing; b_1–6,8, from the integument within body outline; b₅ circled in (figure 2b), b₇ represents integumental structure overlying well-preserved vertebrae (see text). (c) Integumental structures in the last but three terminal caudal vertebrae preserved. (d) Detail of (c) showing integumental structures as part of a matrix of connective tissue at their lower half, while in the distal half, the individual structures are more evident (circled), becoming progressively more degraded towards the tips; circle shows mid-stage of regular, tight, parallel fibre associations. Scale bars, (a,b) 1 mm, (c) 1 cm and (d) 2 mm.

Integumentary structures in Sinosauropteryx NIGP 127587. (a) Integumental structures (fibres) in at least three stages of preservation as (1) architecture of numerous parallel strands in tight formation (our inserted arrows show four broad bands of parallel fibres along the ventral area of the preservation), (2) parallel slightly thicker strands (onset of diagenesis) and (3) short, disorganized, occasionally sinuous structures (degraded). Between the chevrons the fibres parallel the long axis of the tail (Reprinted with permission from Chen et al. (1998). Copyright © Macmillan Publishers Ltd). (b) Our detail shows the above three stages (numbered 1–3) including initialization of the breakdown of the geometric architecture (1) both within and along the edges, analogous to threads pulled from clothing (red arrows). Fibre structures in (a,b) are at higher magnifications than in Chen et al. (1998), where these structures are not mentioned. Scale bar, 1 cm.