First Known Feeding Trace of the Eocene Bottom-Dwelling Fish Notogoneus osculus and Its Paleontological Significance

Abstract

BackgroundThe Green River Formation (early Eocene, about 42–53 Ma) at and near Fossil Butte National Monument in Wyoming, USA, is world famous for its exquisitely preserved freshwater teleost fish in the former Fossil Lake. Nonetheless, trace fossils attributed to fish interacting with the lake bottom are apparently rare, and have not been associated directly with any fish species. Here we interpret the first known feeding and swimming trace fossil of the teleost Notogoneus osculus Cope (Teleostei: Gonorynchidae), which is also represented as a body fossil in the same stratum.Methodology/Principal FindingsA standard description of the trace fossil, identified as Undichna cf. U. simplicatas, was augmented by high-resolution digital images and spatial and mathematical analyses, which allowed for detailed interpretations of the anatomy, swimming mode, feeding behavior, and body size of the tracemaker. Our analysis indicates that the tracemaker was about 45 cm long; used its caudal, anal, and pelvic fins (the posterior half of its body) to make the swimming traces; and used a ventrally oriented mouth to make overlapping feeding marks. We hypothesize that the tracemaker was an adult Notogoneus osculus.Conclusions/SignificanceOur results are the first to link a specific teleost tracemaker with a trace fossil from the Green River Formation, while also interpreting the size and relative age of the tracemaker. The normal feeding and swimming behaviors indicated by the trace fossil indicate temporarily oxygenated benthic conditions in the deepest part of Fossil Lake, counter to most paleoecological interpretations of this deposit. Lastly, our spatial and mathematical analyses significantly update and advance previous approaches to the study of teleost trace fossils.

Intermittent and temporally variable bioturbation by some terrestrial invertebrates: implications for ichnology

“…For example, though extremely uncommon in the record, flying animals may leave take-off and landing traces or disturb sediment while flying just above the sediment surface (Walter 1978;Vallon et al 2016) while movements in between leave no trace. Similarly, fish may drag body parts while swimming along the bottoms of water bodies, in addition to feeding there in ways which leave traces which, again, are very rare (Martin et al 2010). An animal may leave an uncompleted burrow in soil to walk on leaf litter on the surface before returning to finish it later.…”

The damselfly palaeofauna from the Eocene of Wyoming and Colorado, USA (Insecta, Odonata, Zygoptera)

“…Martin et al . (2010) identified folding chevrons created by a fish tail drag mark as direct evidence that a binding microbial mat was growing across the bottom of Fossil Lake. This mat, now considered the source of the kerogen, probably played a direct role in preservation of the fossils.…”

The swimming trace Undichna from the latest Devonian Hangenberg Sandstone equivalent of Morocco

“…Both latter ichnotaxa display a combination of continuous and/ or discontinuous sinusoidal trails associated with scattered partial or complete footprints (Braddy et al, 2003 ; Minter & Braddy, 2006 ; Turek, 1989 ; Walter, 1983 ). Such ichnofossils are known from the Carboniferous of Argentina (Buatois & Mangano, 1994 ; Melchor & Cardonatto, 1998 ), Czech Republic (Turek, 1989 , 1996 ), England (Higgs, 1988 ), Spain (Soler-Gijon & Moratalla, 2001 ), and USA (Martin, 2003 ; Martin & Rindsberg, 2004 ; Martin et al, 2010 ), the Permian of the Falkland Island (Trewin, 2000 ), South Africa (Anderson, 1970 , 1976 ) and USA (Minter & Braddy, 2006 ), the Triassic of China (Lu & Chen, 1998 ; Lu et al, 2004 ), Germany (Simon et al, 2003 ), Italy (Todesco & Avanzini, 2008 ), and South Africa (Sciscio et al, 2020 ), the Jurassic of Germany (Schweigert, 2001 ) and USA (Gibert, 2001 ), as well as the Cretaceous of Spain (Gibert et al, 1999 , 2000 , 2001 ). Although this list is likely incomplete, we assume that not many references are missing here; this shows the scarcity of records, which might be partially to blame on the low number of active ichnologists.…”