Homalocephale calathocercos, Maryanska & Osmolska, 1974

Surmik, Dawid, Słowiak-Morkovina, Justyna, Szczygielski, Tomasz, Wojtyniak, Marcin, Środek, Dorota, Dulski, Mateusz, Balin, Katarzyna, Krzykawski, Tomasz & Pawlicki, Roman, 2023, The first record of fossilized soft parts in ossified tendons and implications for the understanding of tendon mineralization, Zoological Journal of the Linnean Society 198 (3), pp. 747-766 : 751

Homalocephale calathocercos (MPC-D 100/1201)

The cross-section of the tendon shows dispersed primary osteons embedded in mineralized fibrous primary matrix ( Fig. 2A–F ). In some cases, the structural remnant of a primary osteon encapsulates a smaller concentric ring of lamellar bone apparently separated with a cement line, appearing to be a small secondary osteon deposited in the centre of a primary osteon ( Fig. 2D ). These structures probably represent a first generation of secondary osteons (a short cycle of resorption of primary tissue and subsequent deposition of secondary tissue along blood vessels). The osteons are bigger and denser in the innermost part of the tendon, and become less abundant and smaller closer to the periphery ( Fig. 2A, B, E ). Under normal light, in both the longitudinal and cross-section, visible bone cell lacunae are numerous in the centre of the tendon, but rare to absent close to the external margin of the tendon ( Fig. 2A, E ). Under polarized light, the longitudinal section shows bundles of fibres running in a herringbone-like pattern along the tendon ( Fig. 2F ), in the cross-section the fibres form a lattice-like pattern ( Fig. 2B, C ). Thus, the osteons are surrounded by coarse collagenous fibre bundles. The width of the longitudinally sectioned tendon varies from 1.1 to 1.4 mm, its total length is 7 mm.

Figures

Figure 2. Light microscopy and SEM of petrographic thin sections and etched surfaces of fossilized ornithischian tendons of Homalocephale calathocercos: A, B, general view of the cross-sectioned tendon under transmitted normal (A) and polarized (B) light; C, close-up of the middle of the tendon showing a lattice-like pattern of the coarse collagenous fibre bundles under polarized light; D, close-up of secondary osteons with poorly marked cement lines; E, close-up of the periphery of the tendon under normal light; F, longitudinal section of the tendon under polarized light showing the herringbone-like pattern; G, cross-sectioned tendon in the SEM. Green arrows mark primary osteons, yellow arrow points bone cell lacunae, red asterisk indicate secondary osteons.