Parmaichnus stironensis, Pervesler & Uchman, 2009

Pervesler, Peter & Uchman, Alfred, 2009, A new Y-shaped trace fossil attributed to upogebiid crustaceans from Early Pleistocene of Italy, Acta Palaeontologica Polonica 54 (1), pp. 135-142 : 137

Parmaichnus stironensis isp. nov.

Figs. 3 , 4 , 5P–S .

Etymology: After Stirone river, along which the type horizon is located.

Type material: Holotype: INGUJ 200 P11 (a block of impregnated silt containing the burrow) and five photographed and measured specimens in the field.

Type horizon: Distinct discontinuity surface in the Early Pleistocene sediments 17 m above top of the Pliocene.

Type locality: Stirone river valley close to the chapel San Nicomede , 2 km NE from Scipione Ponte, Parma region ( Fig. 1 ) .

Diagnosis.—Y−shaped, vertical to oblique tubular, unlined trace fossil; tubes circular in cross section, composed of the U−shaped upper part and a basal shaft coming out from its lower part. Sub−spherical swellings are present close to the two inflection points in the lower part of the U. Moreover, the swellings occur commonly in the lower part of the shaft and, in some specimens, at the shaft entrance.

Description.—As in the diagnosis, with the following additions: The trace fossil is unlined. The burrow margins are sharp, and commonly ferruginised. The surface is smooth, i.e. with no scratch marks. The burrow is filled with the overlying sandy sediment, commonly containing shell debris. The holotype displays all the described features. It is inclined to the discontinuity surface: the plane of the U−part no more than 40 ° and the basal shaft less than 35 ° in the upper part and only up to 10 ° in the lower part. Other specimens observed in the field are nearly vertical. The tube diameter ranges from 9 to 26 mm and in the holotype from 16 to 20 mm. The chambers are irregularly ovoid to ovoid in shape. In the holotype, two chambers are located in the lower part of the U−shaped burrow, and one chamber is located in the lower part of the shaft. The chambers are 25–36 mm wide. In smaller specimens, the chambers are no less than 15 mm wide. The chambers are irregular subovoid in shape. They are located aside of the axis of the tubes. The distance between the U−part openings is 70 mm in the holotype and ranges from 55 to 70 mm in other specimens. The total vertical extent is at least 120 mm in the holotype, but the trace fossils was originally longer (the basal terminus of the shaft is apparently broken. Given that the shaft is inclined, its length is greater than its vertical extent, and it attains a length of 170 mm (at least 95 mm to at least 145 mm in other specimens). The morphometric parameters of the holotype and other five specimens photographed in the field are listed in Table 1. The basal shaft is curved, commonly in its distal part. It starts from the base of the U, commonly aside from the vertical axis of the U and frequently almost in continuation of one of the U limbs. The juncture with the U is slightly swollen.

Remarks.—This is the only known ichnospecies of Parmaichnus . Potentially, other ichnospecies can be distinguished in the future on the basis of position of the swellings and other morphological features.

Probably, the upper part of Parmaichnus stironensis is truncated by erosion, at least in some cases. This can be judged from significant differences in vertical extent of the U−part of the burrows.

Figures

Fig. 3. Holotype (INGUJ 200P11) of allegedly upogebiid trace fossil Parmaichnus stironensis igen. nov. et isp. nov. Scale bar 100 mm.

Fig. 4. Allegedly upogebiid Y−shaped trace fossil Parmaichnus stironensis igen. nov. et isp. nov. (specimens left in the field) from Early Pleistocene of Italy. A. Specimen P1070182 (numbering from the field photograph collection). B. Specimen P1070193. C. Specimen P1070194. D. Specimen P1070196. Scale bars 50 mm.

Fig. 5. Different Y−shaped trace fossils (B, D, G, U) and Recent burrows compared to Parmaichnus stironensis (P–S). Redrawn from photographs. A. After Seike and Nara (2007: fig. 3c). B. Holotype of Psilonichnus upsilon, Hanna Bay, San Salvador, Bahamas, from AU photograph. C. After Bruce (1987: fig. 6). D. After Fürsich (1981: pl. 3: 2). E. After Curran and Frey (1977: pl. 1e). F. After Frey (1968: text−fig. 1). G. After Seilacher (1990: fig. 5D). H. After Dworschak (2004: fig. 2B); arrows point the turning chambers. I. After Swinbanks and Luternauer (1987: fig. 2.1). J. After Ott et al. (1976: pl. 1: 2). K. After Ott et al. (1976: pl. 1: 3). L. After Dworschak et al. (2006: fig. 1A). M. After Nash et al. (1984: pl. 2a); see also Bromley (1996: fig. 4.32). N. After Curran and Martin (2003: fig. 6). O. After Asgaard et al. (1997: fig. 6). P–S. Parmaichnus stironensis igen. nov. et isp. nov. P. Holotype, ING UJ 200P11, see also Fig. 3. Q. P1070193, see also Fig. 4B. R. P1070182, see also Fig. 4A. S. P1070196, see also Fig. 4D. T. After Atkinson and Taylor (1991: fig. 1f). U. Psilonichnus tubiformis, after Fürsich (1981: pl. 1: 1).

Fig. 1. Location map and the geological section. A. The study region on the map of Italy. B. Location of the study area. C. Location of the studied section. D. The studied section with indication of Parmaichnus stironensis igen. nov. et isp. nov.