Fluvial Environments - Trace Fossils as Indicators of Sedimentary Environments - page 339

diverse swim-trace fossils. The overall diversity of trace-fossil types is moder-
ate to high (average 8, range from 4 to 14). Quadrupedal trackways account for
most of this diversity (average 5, range 4-7).
3.9 Additional Vertebrate Ichnofacies
Other proposed vertebrate ichnofacies that are represented by fluvial trace-fossil
assemblages, but include a few case studies, are the Characichnos or Hatcherich-
nus , Chelonipus ,and Brontopodus “ichnofacies”. The Characichnos “ichno-
facies” was proposed to refer to assemblages that contain a majority of
vertebrate swim-trace fossils, mostly groups of parallel scratch traces and sinusoi-
dal trails from lacustrine shorelines ( Hunt and Lucas, 2007 ). From a conceptual
point of view, a considerable overlapwith the Mermia Ichnofacies is envisaged, as
sinusoidal trace fossils are a diagnostic component of it. At least two of the assem-
blages of this ichnofacies have been recorded from fluvial facies. One of them is
composed of a single manus-pes track impression assigned to Hatcherichnus san-
juanensis associated with sauropod tracks on fluvial channel fills of the Jurassic
Morrison Formation ( Foster and Lockley, 1997; Hunt and Lucas, 2007; Lockley
et al., 2010 ). The other case study is from the Permian Carapacha Formation of
Argentina, where swim traces are a minor component of the vertebrate trace-fossil
assemblage ( Melchor and Sarjeant, 2004 ). In consequence, its assignment to the
Characichnos Ichnofacies ( Hunt and Lucas, 2006 ) seems unsupported. At pre-
sent, the definition and status of the Hatcherichnus ichnocoenosis or ichnofacies
are unclear (see the discussion in Lockley et al., 2010 ).
The Chelonipus “Ichnofacies” was proposed to distinguish turtle swim
traces in fluvial channel deposits on the basis of a few cases of Late Triassic
to Cretaceous age ( Lockley and Foster, 2006 ). The only occurrence from inland
fluvial deposits described in detail is from the Jurassic Morrison Formation, and
the remaining cases in similar facies are from the Late Triassic of Europe
(cf. Lockley and Foster, 2006 ).
The Brontopodus Ichnofacies of Hunt and Lucas (2007) was proposed to char-
acterize moderately diverse ichnofaunas with a majority of tracks of terrestrial,
quadrupedal herbivores, with a small proportion of terrestrial carnivore tracks.
Typical environments are coastal plains, siliciclastic and carbonate-marine shore-
lines, and lacustrine shorelines. No objective criterion for the distinction of herbi-
vore trackswas proposed. At least five of the case studies of this ichnofacies belong
to fluvial deposits and the dominant track types are Q 5/5 sl and Q 5/5 st ( Table 1 ).
Three of the case studies are from Permian successions of Italy, Germany, and
SouthAfrica (see Hunt andLucas, 2006 ).The remaining ichnofaunas are fromCre-
taceous units of Mongolia and China ( Currie et al., 2003; Matsukawa et al., 1995 ).
These ichnofaunas display significant variability incompositionandwereassigned
by Hunt and Lucas (2006, 2007) to three different ichnocoenoses.
The Heteropolacopros Ichnofacies is characterized by the presence of
microspiral heteropolar coprolites, assigned to xenacanth sharks or lungfish,