Trace-Fossil Systematics - Trace Fossils as Indicators of Sedimentary Environments - page 87

introduced in publications that are either difficult to access, published in a non-
English language, or simply overlooked.
It seems to be natural to separate vertebrate from invertebrate burrows as
practiced by H¨ntzschel (1975) and subsequent workers. However, in some
instances, burrows occur in a transitional field and are not unequivocally assign-
able to one category or another. For instance, Daimonelix was regarded as an
invertebrate trace fossil by H¨ntzschel (1975) but later revealed as the burrow
of vertebrates (see Hembree and Hasiotis, 2008 ). Large burrows (e.g., Katarrhe-
drites , Megaplanolites ) may be produced by invertebrates (e.g., crustaceans) or
vertebrates (e.g., mammals) or both. The fact that only about 3% of all burrows
are attributed to the activity of vertebrates, and no clear boundary can be drawn
between invertebrate and vertebrate burrows, justifies the procedure to include
all burrows within this key. Relevant characteristics for recognizing and
describing vertebrate burrows are discussed by Miller et al. (2001) .
All burrow ichnogenera regarded as valid ichnotaxa and included in the key
( Fig. 2 ) are alphabetically listed (SupplementaryMaterial, List 1: http://booksite.
elsevier.com/9780444538130 ) together with their author, year of publication,
and one or more recent references with more ichnotaxonomic information (such
as diagnoses, descriptions, and interpretations). Furthermore, burrow ichnogen-
era that were introduced since H¨ntzschel (1975) , orwhich statuswas invalidated
after that date, are listed in the same way (Supplementary Material, List 2: http://
booksite.elsevier.com/9780444538130 ) in order to provide a record.
The key for bioerosional trace fossils is kept rather simple and only differen-
tiates branched and unbranched forms, followed by groupings of morphotypes
( Fig. 3 ). Transitional forms, microbioerosion, and superficial etching traces
are highlighted. Similar to burrows, all valid (Supplementary Material, List 3:
http://booksite.elsevier.com/9780444538130 ) and invalid ichnogenera (Supple-
mentary Material, List 4: http://booksite.elsevier.com/9780444538130 ) are
listed with references.
The approach to classify invertebrate trackways ( Fig. 4 ) is based on the
distinguishing of uniserial and biserial trackways and, on a lower hierarchical
level, the maximum number of tracks within a trackway. This latter ichnotaxo-
base includes a relatively high uncertainty which is related to the varying
number of tracks, preservation style, and interpretation biases. For instance, uni-
form tracks may belong to the group of one or even numerous tracks. All valid
(Supplementary Material, List 5: http://booksite.elsevier.com/9780444538130 )
and invalid ichnogenera (Supplementary Material, List 8: http://booksite.
elsevier.com/9780444538130 ) are listed with references.
Imprints are simply classified according to their overall morphology ( Fig. 5 ),
and all valid and invalid ichnogenera are listed with references (Supplementary
Material, Lists 6 and 8: http://booksite.elsevier.com/9780444538130 ) . Trails are
distinguished on the basis of their number of lateral elements (e.g., lobes, grooves,
etc.) and furthermore their overall morphology (e.g., straight, winding, meander-
ing) ( Fig. 6 ). All valid (Supplementary Material, List 7: http://booksite.elsevier.
com/9780444538130 ) and invalid ichnogenera (Supplementary Material, List 8: