Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...

114 ADVANCES IN PALAEOICHTHYOLOGY
Orientation of bones. The occurrence of preferred orientation of the fossils is also
observed. Convex bones such as placoderm dorso-lateral or ventro-lateral plates of the
trunk shield mainly lie in a hydrodinamically most stable position with the convex
surface facing upwards (more than 86 per cent of all observed convex plates). Azimuthal
orientation data were collected in 1988 and 2001; totally 325 measurements were taken.
Fig. 9. Rose diagrams illustrating azimuthal orientation of fossils from the Pavāri site. A, posterior
ventro-lateral bones (PVL) of Bothriolepis ciecere (n = 138). B, long bones with length/width
ratio larger than 3 (n = 37). C, flat and almost isometric bones (n = 23). D, whole set of analysed
fossils (n = 274). White sectors show orientation of cross bedding, grey sectors demonstrate
orientation of fossils (in percent).
Three groups of fossil bones were selected: convex slightly elongated bones (mainly
placoderm plates; 214 measurements), flat slightly elongated or almost isometric bones
with slightly traced long axes (such bones as median ventral of Bothriolepis, gular
plate, cleithrum or clavicle of Holoptychius etc.; 74 measurements) and long bones
with length/width ratio larger than 3 (such as lower jaws of sarcopterygians and
Ventastega, disarticulated pectoral fins of Bothriolepis, ribs, lepidothichia, and
acanthodian spines; 37 measurements). Isometric and flat round elements such as
Holoptychius scales were excluded from the analysis because they have no long axis
suitable for measurement. Rose diagrams were prepared for each group of bones, and