Ichnogenus: Rusophycus Hall, 1852

Taxonomic Details

Ichnospecies: (Holland, UGA Strat Lab 2013)

  • Rusophycus carleyi (James, 1885) – McMicken, Southgate, Economy/Fulton
  • Rusophycus cryptolithi (Osgood, 1970) – Economy
  • Rusophycus pudicum (Hall, 1852) – Elkhorn, Whitewater, Liberty, Waynesville, Arnheim, Mount Auburn, Corryville, Bellevue, Fairview, Kope

Stratigraphic Occurrences

Geographic Occurrences

Stratigraphic Description

Sequences (Formations)

  • C6 Sequence (Elkhorn)
  • C5 Sequence (Whitewater, Liberty, Waynesville)
  • C4 Sequence (Arnheim)
  • C3 Sequence (Mount Auburn, Corryville)
  • C2 Sequence (Bellevue, Fairview: Fairmount, Mount Hope)
  • C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)

Identification in Hand Sample

  • General morphology: Small to medium bilobate structures, lobes parallel
  • Branching: None
  • Surface ornamentation: Transverse scratch marks may be preserved
  • Fill: Same as surrounding lithology
  • Lining: None
  • Spreiten: None

Paleoenvironmental Parameters

  • Substrate: Soft- to firmground
  • Oxygen content: Low-high
  • Nutrient content: Low-high
  • Energy: low-high


  • Behavior: Resting, escape, or predation
  • Tracemaker: Bilateral arthropods (trilobites)

Potential Environments

  • Shallow marine
  • Deep-marine flysch deposits
  • Continental (fluvial and shallow lacustrine)

Rusophycus from the Arnheim Formation of Butler, Ohio (MUGM 29451)

Published Description

Hasiotis (KU, 2013):

  • Description: Small to medium bilobate structures, lobes are parallel or sometimes merged near the posterior. Can be formed like elliptical bulges with taperings to one end; can have furrows. Form pits that vary in size and shape, and excavated either deeply or shallowly in the medium. Transverse scratch marks are visible in firmer media.
  • Interpretation: Cubichnia, praedichnia, or fodinichnia; Evidence of a resting animal; can represent concealment or stationary feeding with some position shifts. Can be interpreted as a predatory trace when found superimposed on an endobenthic trace like Helminthopsis; shallow marine settings, but also reported in fluvial and shallow lacustrine soft-ground media. Reported in Cambrian – Ordovician deep-marine flysch deposits; trilobites (Precambrian – recent), starfish, bilateral arthropods, and vertebrates, or other non-sessile benthic dweller (Permian – recent). Larger specimens could be made by vertebrates.

Kushlina & Dronov (2011):

  • Despite much palaeontological and biostratigraphical research on the Ordovician of the Siberian Platform (Kanygin et al., 2007 and reference herein) the ichnology has been relatively overlooked. This report, therefore, represents the first account of large Rusophycus from the Ordovician of this region. According to Silacher (1970) the largest Cruziana and Rusophycus are typical for the Cambro-Ordovician strata and decrease in size from the Silurian onwards. The majority of previous recordings of large Rusophycus confirm this observation. The Ordovician large Rusophycus are known from Canada and Australia. Hoffman (1979) has recorded Rusophycus carleyi from the Middle Ordovician Chazy Group 31 cm in length and 21 cm in width which is exactly the size of one of our specimens. Draper (1980) has recorded forms resembling both Cruziana (=Rusophycus) dilatata and C. (=Rusophycus) carleyi from the Early Ordovician of Mithaka Formation of the Georgina Basin (Australia) up to 31 cm in length. The largest Silurian recordings are by Osgood (1970) who noted Rusophycus up to 25 cm in length from the Clinton Group in Cincinnati and Tansathien and Pickerill (1987) who reported about Rusophycus 35 cm in length and 18 cm in width from the Arisaig Group of Nova Scotia.
  • While there is still controversy as to whether trilobites were responsible for producing all marine Cruziana and Rusophycus (see Whittington, 1980) it is almost universally accepted that in most cases they were responsible for that. The discovery of trilobites preserved in situ within Rusophycus (Osgood, 1970; Draper, 1980) together with closely comparable morphological features preserved in some Rusophycus when compared to the ventral morphology of trilobites leaves little doubt that trilobites were responsible for their production. Since the Rusophycus impressions correspond closely to the dimensions of the trilobite which made them one can deduce that large trilobites at least 30 cm in length and 20 cm in width were inhabitants of the Siberian epicontinental seas in the Middle Ordovician. The problem, however, is that no such a big trilobites have been reported from the Ordovician of Siberian Platform. Judging from the broken fragments the largest exemplars rarely exceeded 20 cm (maximum 24 cm) in length and no more than 10-12 cm in width. These trilobites are from the family Asaphidae (Maksimova, 1962). It is, of course, dangerous to speculate on producers of trace fossils when no positive evidence is preserved. But as aphid trilobites seem to be a reasonable guess.
  • According to morphological analysis of trilobite skeletons the largest trilobites most probably were predators (Fortey and Owens, 1999). The Rusophycus trace fossil attributed to trilobites usually interpreted as a result of the producing organism resting, hunting or seeking protection (Osgood, 1970; Bergstrom, 1973). But the Siberian large Rusophycus (Fig. 2) seems to represent deep resting burrows or “nests”, dug in a slightly head-down position for the reception of eggs. Similar interpretation was suggested by Fenton and Fenton (1937) for the Lower Cambrian burrow “Cruziana” (=Rusophycus) jenningsi. The front (anterior) portions of each of the two traces bear horizontal ridges which seem to represent impressions made by a cephalon pushed forward and from side to side (Fig. 2 A, B). The regularity, symmetry, and depth of the burrows are inconsistent with functions of feeding or hunting. The fact that there are two burrows indicates that they are not accidental. They may be compared with the burrows that modern Limulus digs in sand on a beach as receptacles for its eggs. The horseshoe-like morphological type Rusophycus (Fig. 3) represents a different function. These trace fossils seem to be dug out by trilobites seeking shelter from the strong currents during a tide activity.
  • Rusophycus and Cruziana with 3-clawed scratch marks are known from the Upper Cambrian-Upper Ordovician strata (Seilacher, 2007). This seems to be a maximum precision for global Cruziana stratigraphy nowadays. Regional Cruziana stratigraphy could be more precise but on Siberian Platform we still do not have enough findings on these trace fossils to establish a regional scale. As for trilobite body fossils in the Siberian Ordovician, they are mainly endemics (Maksimova, 1962). Up to now, the Lower Paleozoic trilobite burrows have been reported only from the fragments of ancient Gondwana continent (Seilacher, 2007). This fact has been even used for palinspastic purposes in order to identify terranes of Gondwanan origin that happen to dock at other paleocontinents (Seilacher and Crimes, 1969). The giant specimens of Rusophycus documented herein suggest that either trilobite burrows existed also outside Gondwana in the Ordovician or the trace makers were not trilobites.

Davis (1998):

  • Rusophycus pudicum: Trace fossil. These convex objects are found on the underside of limestone layers. They represent hallows dug into the underlying mud by trilobites and later filled by the calcareous mud which became the limestone. Entire Cincinnatian.

Fossils of Ohio (1996):

  • Rusophycus is a relatively short, bilobed trace. Each lobe commonly has subhorizontal markings. This ichnofossil is commonly found as a convex form on the bottom of beds. Rusophycusis a very distinctive trace, but it may be confused with the longer bilobed trace known as Cruziana. Rusophycus, however, is generally only up to about three times or so as long as wide, while Cruziana is typically longer. There is evidence that some ichnospecies of Rusophycuswere made by trilobites. Commonly in Ordovician rocks, specimens of trilobites or parts of trilobites are found In association with Rusophycus. In the Cincinnati area, thin slabs have been found with Rusophycuson one side with the trilobite that produced Rusophycus on the other side. Groupings of Rusophycus have long been known as trilobite nests implying that they represent egg laying activity, but this origin has not been demonstrated. Rusophycus probably represents a site related to feeding. In addition to Ordovician rocks, Rusophycus and Rusophycus-like ichnofossils are found in younger rocks in Ohio, including the Devonian Ohio Shale.

Treatise on Invertebrate Paleontology, Part W, Miscellanea Supplement 1 (1975):

  • Description: “Short bilobate bucklelike forms, resembling shape of coffee beans; lobes transversely wrinkled by anterolaterally directed coarse of fine striae; with deep median furrow; outline mostly elliptical; generally width equal to one-half to two-thirds length; bilobate pits deeply excavated or shallowly dug; quite variable in size and shape (size of Cincinnatian specimens from 1-25cm); morphology variable and dependent on mechanics of burrow excavation, and therefore difficult to render an unobjectionable “diagnosis.” W. Hantzschel 1975
  • Interpretation: “the most famous of all the ‘fucoids’” (Osgood, 1970 p. 301); originally interpreted as of plant origin; undoubtedly resting excavations made by trilobites digging in sediment to rest there temporarily, interpretation given by Dawson (1864, p. 365, 366; “for shelter or repose” or “places of incubation”); other less probable interpretations: feeding structures or egg depositories; well-preserved specimens may show imprints of segments, pygidia, pleural spines, and other parts of the trilobite; in several cases (U.Ord., USA, Ohio) the producer of the burrow has been found preserved in situ (see Rusophycus pudicum Hall with Felxicalymene meeki (Ossgood, 1970, pl 57, fig 6)). Crimes (1970c, p. 114) has shown that several “forms” of Rusophycus have restricted time range (U. Cam. Or L.Ord.) and thus are useable as guide fossils. Many “species” were established only on small differences in shape; for discussion of nomenclatural status of Rusophycus see Osgood (1970, p.303); with regard to intermediate specimens between Rusophycus and Cruziana, Rusophycus was often regarded as synonym of Cruziana, but Lessertisseur (1955 p. 45), Seilacher (1955, p. 366), and Osgood (1970, p. 303) recommended Rusophycusfor the short bilobate resting trails of trilobite origin, and this is approved by the present author. However, Seilacher (1970, p. 455) recently proposed combining all presumable “resting tracks,” “resting nests,” and “resting burrows” of trilobites in the one ichnogenus Cruziana; for detailed discussions see Seilacher (1955, p. 358-364) and Osgood (1970, p. 301-305).