Organically preserved musculature in a fossil salamander. (a) Chelotriton sp. (MNCN 12555) with an outline of soft tissues defined by a carbonaceous layer. Scale bar, 10 mm. (b) Musculature in situ adjacent to vertebrae and (c) a freshly fractured surface through a sample. Scale bar, 1 mm. (d, arrow) SEM images of muscle illustrating chevron pattern of cracks, hollow blood vessel in transverse section and (e, arrow) separation of sarcolemma from sarcoplasm. Scale bars: (d) 100 µm and (e) 30 µm. (f) Semithin transverse section through the muscle with (g) explanatory drawing, showing the arrangement of fibres (dark grey) in parallel sheets separated by endomysium (light grey); arrow in (f), blood vessel in the transverse section. (f) Scale bar, 20 µm.
(a,c,e,g) TEM images of transverse sections of skeletal muscle tissue from MNCN 12555 and (b,d,f,h) corresponding features in the extant salamander A. mexicanum. Images except (c), (e) and (g) are from stained sections. (a,b) Sarcoplasm showing myofilaments in the transverse section at A-band. (c,d) Margin of fibre showing sarcolemma (sl) attached to sarcoplasm (sp); inset in (d) shows local thickening of sarcolemma. (e,f) Margin of fibres showing sarcolemma (sl) detached from sarcoplasm (sp). (g,h) Endomysial circulatory vessels surrounded by endomysium. Inset in (g) shows electron-dense, friable, solidified blood residue within the circulatory vessel. l, lumen of capillary; r, resin. Scale bars (a,b) 50 nm and 2 µm for all other images.