Trace-Fossil Systematics - Trace Fossils as Indicators of Sedimentary Environments - page 81

and surface traces (trackways, imprints, and trails), while other trace-fossil
groups such as coprolites, root traces, plant-insect traces, etc., are excluded. Bio-
claustration, bioimmuration, and embedment structures remain more contro-
versial in respect to their (trace-fossil) origin.
The past comprehensive review of burrows was compiled by H¨ntzschel (1975) ,
whereas bioerosional trace fossils were subsequently reviewed by Taylor and
Wilson (2003) and Bromley (2004) . Information about invertebrate trails, tracks,
and trackways is scattered in many case studies, although Trewin (1994) revised
a morphological system to identify arthropod trackways. Furthermore, Haubold
(2010) provided an update of fossil tetrapod footprints, tracks, and trackways. Edi-
acaran trace fossils require special attention, as they are easily confused with body
fossils and sedimentary structures (see review by Jensen et al., 2006 ). For bryozoan-
produced trace fossils, the reader is referred to Rosso (2008) . The group of coprolites
and fecal pellets (microcoprolites), from both invertebrates and vertebrates, is very
heterogeneous and in need of revision. The interactive database FAVRIS contains
data on structured crustacean coprolites ( Blau, 1993-2000 ), whereas Schmitz and
Binda (1991) and Eriksson et al. (2011) offer classification schemes for vertebrate
coprolites, and Hunt et al. (2007) review Triassic vertebrate coprolites. Plant-insect
trace fossils are assessed by Labandeira (2007) , whereas bioclaustration is reviewed
by Tapanila (2005) . Root traces (rhizoliths, rhizoconcretions, etc.) are important for
paleoenvironmental reconstruction and are usually described in relation to their host
sediment or paleosol. Root-trace classification is approached by Klappa (1980) ,
Bockelie (1994) , Mikul´ˇ (1999) ,and Kraus and Hasiotis (2006) .
The hierarchy of the selected ichnotaxobases may be most controversial, as it
is strongly subject to the investigator and varies considerably fromone ichnotaxon
to another. With respect to burrows, most authors agree on the following ichno-
taxobases with decreasing importance (see Bertling, 2007 ): (1) orientation, (2)
presence or absence of branching, (3) shape, and (4) presence or absence of lining
ormantle. Furthermore, ornamentation is regarded as an accessory ichnotaxobase,
havingminor importance at the ichnogenus level. Based on the highest ichnotaxo-
base, orientation, burrows are classified into (1) subhorizontal, (2) subvertical, and
(3) complex ( Fig. 2 ). Several transition fields hinder a proper discrimination of
different trace-fossil groups. Numerous ichnotaxa can occur as both burrows
and surface traces and thus are highlighted in the key. Transitions between bur-
rows and borings also exist (e.g., Gastrochaenolites , Balanoglossites ). Nests
(e.g., those produced by insects) are commonly regarded as a separate trace-fossil
group (calichnia), although some were created below the surface and partly com-
prise burrow elements. These are included in the key, but for a comprehensive
classification, the reader is referred to Genise (2004) . Other ichnogenera comprise
branched and unbranched ichnospecies such as Palaeophycus , Planolites , Rhizo-
corallium, and Trichichnus . These ichnogenera are indicated accordingly but only
listed once, in the category that is regarded as most significant.
Although the vast majority of invertebrate trace fossils with an ichnotaxo-
nomically valid status is considered in this classification, it cannot be excluded
that a minor number of ichnogenera escaped the critical review, as they were