How correct is any chronological ordering of the Quaternary Sardinian mammalian assemblages?

摘要

The evolutionary succession of Quaternary Sardinian fauna (from impoverished but balanced, to dis-harmonic, strongly impoverished, and highly unbalanced with respect to faunas inhabiting similar continental ecosystems) has already been outlined. Two main faunal complexes (FCs) and three Quaternary faunal subcomplexes (FsCs) have been depicted. Each FC/FsC gathers local faunal assemblages (LFAs) showing a fairly high taxonomical similarity. FCs and FsCs succeed each other through time, although their temporal extent is uncertain. Although the chronological ordering of Sardinian FCs/FsCs can be regarded as a fairly satisfactory scheme, we are far from to have a reliable biochronological ordering LFAs. The well-known problem of arranging in a correct chronological order LFAs from the terrestrial domain is amplified in the case of the Sardinian insular impoverished and disharmonic Quaternary faunas. The high discontinuity in the fossiliferous sedimentary record, the rarity of long sedimentary sequences, the scantiness of firm geo-chronological constraints and numerical dates limit the possibility of inferring the relative chronological ordering of LFAs and validate the existence of intra-specific evolutionary trends. Fluctuating patterns in morphology and body size of Quaternary Sardinian species might be present, but they are difficult to ascertain because sedimentary successions giving evidence of the superposition of faunal assemblages are rare, and numerical dates are scanty or missing for some key-sites. As a result, the successions of Quaternary Sardinian LFAs thus far proposed are largely approximate, while FC/FsC can be regarded as the "best-fit" allowed by available data. A more robust and detailed chronological ordering needs more stratigraphic analysis and reliable numerical dating.