Parazhijinites cf. guizhouensis Qian and Yin, 1984

Clausen, Sébastien & Álvaro, J. Javier, 2006, Skeletonized microfossils from the Lower-Middle Cambrian transition of the Cantabrian Mountains, northern Spain, Acta Palaeontologica Polonica 51 (2), pp. 223-238 : 229-230

Parazhijinites cf. guizhouensis Qian and Yin, 1984

Fig. 4F .

Material.—Two phosphatic sclerites from the Middle Cambrian “Beleño” facies, section Cr 4.

Description.—Elongate sclerites, subhexagonal in outline and posteriorly expanded (650 µm long and 400 µm wide), bilaterally symmetrical; anterior spine perpendicular to slightly bent at its extremity (400 µm long), with oval cross−section

(160 µm in diameter), except at its tip where it is round; surface smooth.

Remarks.— Bengtson et al. (1990) indicated that cambroclavids exhibit a wide morphological variability within the same scleritome, so that additional material seems necessary to complete the description and systematic assignment of the Cantabrian taxon. Parazhijinites guizhouensis shows a widespread morphological variability, and the most noticeable feature of this species is the elongate spine arising from a small base (Conway−Morris et al. 1997: 179). Although Conway Morris and Chen (1991) placed questionably Z. guizhouensis Qian and Yin, 1984 in synonymy with Z. longistriatus Qian, 1978, the former only differentiable by the presence of a slipper−like base and a very elongate spine, Conway Morris et al. (1997) reported them as separate species. The Cantabrian sclerites have all the characters visible in some Chinese sclerites of Meishucunian ( Zhou et al. 2001: 212, fig. 4.2) to Atdabanian ( Conway Morris et al. 1997) age. This paper reports the youngest occurrence of Parazhijinites within the lowest trilobite biozone of the Iberian Middle Cambrian.

Figures

Fig. 4. Scanning electron micrographs of skeletonized microfossils from the Lower–Middle Cambrian transition of the Esla Nappe, Cantabrian Mountains, Spain. A, B. Chancelloria sp. A; chancelloriid sclerites; section Cr4, “Beleño” facies, upper member of the Láncara Formation, early Leonian. A. DGO 21129, longitudinal section. B. DGO 21130, lateral view. C–E. Chancelloria sp. B; chancelloriid sclerites; section Cr4, “Beleño” facies, upper member of the Láncara Formation, early Leonian. C. (1+6) sclerite, DGO 21131, lateral views. D. (1+5) sclerite, DGO 21132, upper view. E. Incomplete (1+7) sclerite, DGO 21133, upper view. F. Parazhijnites cf. guizhouensis Qian and Yin, 1984; cambroclavid sclerite; section Cr4, “Beleño” facies, upper member of the Láncara Formation, early Leonian; DGO 21134, oblique (F1) and lateral (F2) views. G–J. Torellella sp.; hyolithelminth tubes; section Cr4, ooid/bioclastic limestone, lower member of the Láncara Formation, latest Early Cambrian. G. DGO 21135, lateral view. H. 21136, lateral view. I. DGO 21137, lateral view showing elliptic perforation (I1) and detail of the faint growth lines (squared area on I1; tilt adjust). J. DGO 21138, lateral (J1) and distal (J2) views. K. Phosphatic undefined tube; section Cr4, ooid/bioclastic limestone, lower member of the Láncara Formation, latest Early Cambrian; DGO 21139, lateral view (K1) and detail of broken termination (K2). Scale bars 250 µm, except I2 and K2 for which are 50 µm.