Trace-Fossil Systematics - Trace Fossils as Indicators of Sedimentary Environments - page 77

Today, many workers have adopted an ethological classification for trace fos-
sils, and a “ purely morphological classification, without references to any etho-
logical model and without taphonomic interpretation, seems to be one of the dead-
ends of ichnotaxonomy ”( Uchman, 1998 : 107). This trend is only confirmed by
Buatois and M´ngano (2011: 25) who write in their textbook, “ Although there
should be a conscious effort to focus on significant morphological details, there
is no such a thing as a purely morphological classification. The ichnotaxonomic
classification is permeated by our understanding of the ethology ”.
Since H¨ntzschel (1975) , the number of valid ichnogenera has been more than
doubled (increased by 58%) and it becomes increasingly difficult to keep track of
the continual growingnumber of new ichnotaxa. Anoverloadof ichnotaxonomical
data without a proper classification hinders a transformation of this information
into knowledge. This problem not only complicates the introduction and descrip-
tion of new ichnotaxa and the evaluation of their relationships to existing ones but
also hinders the simple application of trace fossils in facies reconstructions.
Despite the preferential application of an ethological classification scheme,
many workers have attempted to group trace fossils morphologically in particular
studies (e.g., Haubold, 1996; Keighley and Pickerill, 2003; Ksi˛ ˙ kiewicz, 1977;
M ¨ gdefrau, 1937; Schlirf, 2000; Seilacher, 2007; Trewin, 1994; Uchman, 1995,
1998 ). Compared with the widely used ethological classification, a key based on
morphological characteristics has the advantage of being descriptive and indepen-
dent from behavioral interpretation and promotes morphological grouping toward
higher ichnotaxonomic levels (e.g., ichnofamilies).
In view of an optimal facies reconstruction and interpretation of sedimentary
environments, trace fossils with assignable producers would be the perfect tool to
perform this task. In the past, sporadic attempts have been made in this direction
(e.g., Dzik, 2005, 2007; Mayoral, 2001; Vialov, 1968 ), but these were subse-
quently rejected because of a too broad approach or ichnotaxonomical issues.
Nevertheless, given the accelerated progress in the assignment of tracemakers
to their trace fossils made in the past few years (e.g., by direct evidence, functional
interpretations, or analogy with modern traces), this approach may be revitalized
in the near future to support a stronger link between ichnology and sedimentology.
This procedure is already a common practice in the analysis of bioerosional trace
fossils (particularly microborings; see Bromley, 2004; Wilson, 2007; Wisshak,
2006 ) and the achievements in terms of environmental reconstructions are obvi-
ous (see Wisshak, 2012 ). However, until then the way out is probably precise
applications of well-defined ichnotaxa at the ichnospecific level, with diagnostic
signatures that result from the activity of distinctive tracemakers.
2. NEED OF A ROBUST ICHNOTAXONOMY AND
TRACE-FOSSIL CLASSIFICATION
Several examples demonstrate the importance of the separationof trace fossils pro-
duced by contrasting groups of organisms, a procedure that favors the approach of
“splitters” rather than “lumpers” ( Bertling et al., 2006 ). For instance, burrows or