Size-frequency distributions derived from trace fossil assemblages [SFD-TF] can be used to reconstruct the size-structure of ancient populations provided that trace fossils are (1) size-correlative with the trace-maker, (2) monospecific, and (3) not biased by taphonomic processes and time-averaging. These three assumptions can be tested and are commonly met. SFD-TFs are most useful when analyzed comparatively because the differences among them are easier to interpret than their absolute characteristics. We suggest here a two-stage research protocol. First, the required assumptions are evaluated with the use of ichnologic, taphonomic, sedimentologic, actualistic and theoretical arguments. Subsequently, SFD-TFs are compared with use of exploratory and confirmatory statistical methods aided by bootstrap randomizations. Two examples illustrate and test the proposed approach. First, an actualistic, two-sample example (Recent lingulide burrows Lingulichnus from tidal flats of northeastern Baja California, Mexico) shows that (1) the size-structure of populations can be inferred from SFD-TFs with high accuracy; and (2) SFD-TFs provide valuable and otherwise unavailable data (even when a trace-maker has a preservable skeleton ton). The second, multisample example (20 samples of Diplocraterion burrows collected from four beds of the Bolsa Quartzite, Cambrian, southeastern Arizona, USA) is analyzed with use of graphic, parametric, non-parametric, and multivariate comparative methods. The results suggest that (1) each bed is dominated by a single cohort (a single settlement event); (2) the beds differ in the duration of settlement; and (3) all four beds can be discriminated; allowing for intrabasinal stratigraphic correlation . The examples show that comparative analyses of SFD-TFs can provide data useful for paleoecology, sedimentary facies analysis and even local stratigraphic correlations.
Trace fossils, population paleoecology, comparative analysis, bootstrapping, Lingulichnus, Diplocraterion, Recent, Cambrian.
C.E.A.M. abstracts of talks