Palaeophycus Hall, 1847

Domichnia.

Diagnosis. Essentially cylindrical, predominantly horizontal, straight, slightly curved or undulating, ornamented or smooth, branched or un branched, lined burrow. Bifurcations irregular, with out swellings. Filling typically massive, similar to the host rock (compiled after: Pemberton and Frey, 1982; Fillion and Pickerill, 1984, 1990; Keighley and Pickerill, 1995).
 

Palaeophycus is generally interpreted as open burrow, probably produced by polychaetes (PEMBERTON & FREY, 1982).

Diagnosis. Infrequently branched, distinctly lined, essentially cylindrical, predominantly horizontal to inclined burrows in which the sediment infilling is typically of the same lithology and texture as the host bed (Pemberton and Frey, 1982; modified by Frey and Howard, 1985).

Remarks. It is ethologically classified as a dwelling (domichnia) or feeding (fodinichnia) structure of mobile, suspensivorous or predatory worm-like organisms such as annelids (Fillion, 1989). Sediment fill is passive, gravity induced (for further detail on sediment fill see Fillion, 1989). The common type of preservation (epirelief or endichnia) suggests that the activity of the producer took place along sedimentologic interfaces (Pemberton and Frey, 1982).

A similar ichnogenus is Planolites Nicholson, and there has been a longtime debate about the criteria used to separate them (Aceñolaza and Yanev, 2001). Alpert (1975) proposed that the most useful criterion is the presence or absence of branching in Palaeophycus and Planolites, respectively. However, since the work of Pemberton and Frey (1982), this criterion has been disregarded (e.g., Buatois, 1989; Fillion, 1989). According to Pemberton and Frey (1982), Palaeophycus differs from Planolites because of the presence of a wall.
Such features may be of greater taxonomic value, as they reveal ethological aspects (Buatois, 1989).

Trace maker. Palaeophycus are known to be produced by predaceous polychaetes in marine environments (e.g., Gingras et al., 1999), but other makers may have been involved in continental settings, such as semiaquatic insects (orthopteransand hemipterans) or semiaquatic and non-aquatic beetles (Krapovickas et al., 2010).

Branched or unbranched, smooth or ornamented, lined, essentially cylindrical, predominantly horizontal burrows of variable diameter, infilling typically structurless or same lithology as host rock.