Trace-Fossil Systematics - Trace Fossils as Indicators of Sedimentary Environments - page 78

surface trails of the well-known ichnogenus Cruziana d'Orbigny, 1842 were com-
monly produced by trilobites in Paleozoic, shallow-marine shelf deposits, whereas
morphologically similar but overall smaller trace fossils from late Paleozoic and
Mesozoic continental deposits result fromthe activityof notostracan branchiopods
and thus were originally assigned to Isopodichnus Bornemann, 1889 . Moreover,
large and robust burrows with analogous scratches were introduced as Cruziana
seilacheri Zonneveld et al., 2002 , a potential junior synonymof thePaleocene Car-
patichnis zuberi Vialov in Vialov and Fedonkin (1993) , but whichmay be part of a
burrow system that resulted from the activity of lobsters (e.g., Pholeus elongatus ;
Knaust, 2007 ). All three categories of Cruziana differ from each other by their dis-
tinctive size classes, although overlaps can occur.
Another example is the recently introduced ichnogenus Parmaichnus
Pervesler and Uchman, 2009 , which resembles Psilonichnus F¨rsich, 1981 ,
but differs from it by the presence of turning chambers in the upper part of
the burrow ( Fig. 1 ). Parmaichnus is a feeding burrow attributed to upogebiid
decapod crustaceans, while Psilonichnus results from the activity of sheltering
ocypodid crabs. The Psilonichnus Ichnofacies is characteristic of backshore
environments, but a much broader distribution within supra-, inter-, and subtidal
environments was inferred (e.g., Nesbitt and Campbell, 2006 ) before the
strict separation of Parmaichnus and Psilonichnus . The distinction of the two
ichnogenera is thus beneficial to sedimentological studies.
Similarly, only the intensely scratched and passively filled Rhizocorallium
jenense serves for the reconstruction of the Glossifungites Ichnofacies in
connection with firm bedding surfaces and thus may have a greater importance
for sequence-stratigraphic interpretations (see MacEachern et al., 2012 ). In con-
trast, Rhizocorallium commune with its active spreite fill and incorporation of
fecal pellets Coprulus oblongus characterizes predominantly soft substrates of
the Cruziana Ichnofacies ( Knaust et al., 2012 ).
A further example includes the similar ichnogenera Thalassinoides and
Balanoglossites , which are easy to confuse. However, Balanoglossites is a worm
burrow and differs from arthropod-produced Thalassinoides by its U- and
Y-shaped morphology, high irregularity and bluntly terminated side branches
( Knaust, 2008; Knaust and Costamagna, 2012 ).
Finally, the ichnogenus Skolithos Haldeman, 1840 hasdegenerated intoabasket
for simple vertical burrowswith a quiteheterogeneous appearance andproducedby
awide rangeof organisms (different kindsofworms, crustaceans, andplants)which
often hinders the proper ichnospecific assignment of such burrows. However, due
to their poor diagnostic features, a subtle distinctionbasedon the length/width ratio,
departure froma strict vertical orientation, annulations or constrictions, presence or
absence of lining and funnel, ornamentation, burrow termination, etc., would cer-
tainly help to increase the value of Skolithos for paleoenvironmental reconstruc-
tions. For instance, Cylindricum Linck, 1949 (like the similar Capayanichnus
vinchinensis Melchor et al., 2010 ) is known from fluvial deposits and was likely
produced by freshwater crustaceans. This ichnotaxon differs from Skolithos by a
lower length/width ratio ( Hasiotis, 2008 ) and thus justifies its own status.