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Loops, circles, spirals and the appearance of guided behaviors from the Ediacaran-Cambrian of Brittany, NW France

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The Ediacaran-Cambrian transition is the place of striking changes in Earth ecosystems, with a diversification of life recorded by a complexification in animal behaviors. In a series of classic papers, Crimes (1974, 1987, 1992a, b) compiled worldwide data on trace fossil distribution from that time period, evaluating their potential as biomarkers and deciphering evolutionary processes. He suspected that many trace fossils typical of Phanerozoic deep-water settings originated in shallower environments. Spiraling is a strategy developed by organisms to survive in environments depleted in nutrient, exemplified by the farming open-burrow system Spirorhaphe (Seilacher, 1977). On the other hand, simple horizontal spirals of deposit-feeders are represented by many ichnogenera, common forms being Spirodesmos and Spirophycus (Buatois et al., 2017). Spiral trace fossils are poorly reported from the Ediacaran-Cambrian transition and remain problematic (e.g. Jensen, 2003; Carbone & Narbonne, 2014). Conversely, simple looping horizontal trails, fully circling (i.e. Circulichnis) or self-overcrossing (i.e. Gordia) are easily and abundantly identified. Crimes (1992a) suspected spiral trace fossils to appear stratigraphically higher than simple looping trails, at the same level of treptichnids (n.b. it is interesting to note that the two spiralling traces at issue, Planispiralichnus and Protospiralichnus, are omitted in another list in Crimes, 1992b; these Russian forms are now suspected to represent circular treptichnids by Marusin, 2011). The Brioverian from central Brittany, NW France, is a thick siliciclastic sedimentary succession that have been intensely deformed due to the successive Cadomian and Variscan orogenetic events. Hence, its stratigraphy, basin architecture and fossil content have been poorly understood, and the position of its uppermost limit within the Ediacaran or the Cambrian is still a pending question. However, recent investigations reported insights of life in the form of simple trace and body fossils in shallow-marine, tidally influenced settings (Gougeon et al., 2018; Néraudeau et al., 2018). Following up this promising start, new investigations were conducted and new ichnofossils were reported from outcrops in Saint-Gonlay, Montfort-sur-Meu (estearn Brittany) and Crozon (western Brittany; Fig. 1). From these, abundant horizontal looping, fully circling and pseudo- to perfect-spiraling trails are found associated with microbially stabilized surfaces. Although the two first forms can be identified as Gordia and Circulichnis respectively, the ichnotaxonomic position of the latest ones is more uncertain. Regardless of their actual name, spiral trails are not uncommon in the section and show that more complex programs (i.e. phobotaxis and thigmotaxis) were already acquired by their tracemakers. An Ediacaran double spiral from Australia closely relates in shape and size to the holotype of Spirorhaphe involute (Jensen, 2003). This trace fossil is transitional with unguided meanders, and the preservation as a trail or burrow is unknown; an affinity with a farming open-burrow system is then difficult to conceive. Beside that report, the oldest true Spirorhaphe is coming from the Ordovician (Pickerill, 1980; Lehane & Ekdale, 2016). Regarding simple deposit-feeder spirals, they are reported from the Ediacaran-Cambrian transition in both shallow- (this study) and deep-marine settings (Carbone & Narbonne, 2014). Microbially stabilized surfaces were pervasive at that time and may have been a wealthy medium for the nutrition of trail producers. Increasing sediment processing by penetrative animals during the Cambrian resulted in the progressive retreat of microbial mats in deep-marine settings (Crimes, 1992a, b; Buatois et al., 2011). After their disappearance by the Ordovician, eventually, organisms adapted their simple spirals of deposit-feeders to these nutrient-poor environments by developing more complex, farming open-burrow systems.
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Loops, circles, spirals and the appearance of guided behaviors from the Ediacaran-
Cambrian of Brittany, NW France
Gougeon, R.1,2,*, Néraudeau, D.2, Poujol, M.2 & Loi, A.3
1Department of Geological Sciences, University of Saskatchewan, Saskatoon, SK, S7N 5E2,
Canada
2Univ Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France
3Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Cittadella
Universitaria, 09042 Monserrato, Italy
*gougeon.romain@gmail.com
The Ediacaran-Cambrian transition is the place of striking changes in Earth ecosystems,
with a diversification of life recorded by a complexification in animal behaviors. In a series of
classic papers, Crimes (1974, 1987, 1992a, b) compiled worldwide data on trace fossil
distribution from that time period, evaluating their potential as biomarkers and deciphering
evolutionary processes. He suspected that many trace fossils typical of Phanerozoic deep-water
settings originated in shallower environments. Spiraling is a strategy developed by organisms
to survive in environments depleted in nutrient, exemplified by the farming open-burrow
system Spirorhaphe (Seilacher, 1977). On the other hand, simple horizontal spirals of deposit-
feeders are represented by many ichnogenera, common forms being Spirodesmos and
Spirophycus (Buatois et al., 2017).
Spiral trace fossils are poorly reported from the Ediacaran-Cambrian transition and
remain problematic (e.g. Jensen, 2003; Carbone & Narbonne, 2014). Conversely, simple
looping horizontal trails, fully circling (i.e. Circulichnis) or self-overcrossing (i.e. Gordia) are
easily and abundantly identified. Crimes (1992a) suspected spiral trace fossils to appear
stratigraphically higher than simple looping trails, at the same level of treptichnids (n.b. it is
interesting to note that the two spiralling traces at issue, Planispiralichnus and
Protospiralichnus, are omitted in another list in Crimes, 1992b; these Russian forms are now
suspected to represent circular treptichnids by Marusin, 2011).
The Brioverian from central Brittany, NW France, is a thick siliciclastic sedimentary
succession that have been intensely deformed due to the successive Cadomian and Variscan
orogenetic events. Hence, its stratigraphy, basin architecture and fossil content have been
poorly understood, and the position of its uppermost limit within the Ediacaran or the Cambrian
is still a pending question. However, recent investigations reported insights of life in the form
of simple trace and body fossils in shallow-marine, tidally influenced settings (Gougeon et al.,
2018; Néraudeau et al., 2018). Following up this promising start, new investigations were
conducted and new ichnofossils were reported from outcrops in Saint-Gonlay, Montfort-sur-
Meu (estearn Brittany) and Crozon (western Brittany; Fig. 1). From these, abundant horizontal
looping, fully circling and pseudo- to perfect-spiraling trails are found associated with
microbially stabilized surfaces. Although the two first forms can be identified as Gordia and
Circulichnis respectively, the ichnotaxonomic position of the latest ones is more uncertain.
Regardless of their actual name, spiral trails are not uncommon in the section and show that
more complex programs (i.e. phobotaxis and thigmotaxis) were already acquired by their
tracemakers.
An Ediacaran double spiral from Australia closely relates in shape and size to the
holotype of Spirorhaphe involute (Jensen, 2003). This trace fossil is transitional with unguided
meanders, and the preservation as a trail or burrow is unknown; an affinity with a farming open-
burrow system is then difficult to conceive. Beside that report, the oldest true Spirorhaphe is
coming from the Ordovician (Pickerill, 1980; Lehane & Ekdale, 2016). Regarding simple
deposit-feeder spirals, they are reported from the Ediacaran-Cambrian transition in both
shallow- (this study) and deep-marine settings (Carbone & Narbonne, 2014). Microbially
stabilized surfaces were pervasive at that time and may have been a wealthy medium for the
nutrition of trail producers. Increasing sediment processing by penetrative animals during the
Cambrian resulted in the progressive retreat of microbial mats in deep-marine settings (Crimes,
1992a, b; Buatois et al., 2011). After their disappearance by the Ordovician, eventually,
organisms adapted their simple spirals of deposit-feeders to these nutrient-poor environments
by developing more complex, farming open-burrow systems.
References:
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Néraudeau, D.; Dabard, M.P.; El Albani, A.; Gougeon, R.; Mazurier, A.; Pierson‐Wickmann,
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Seilacher, A. (1977). Evolution of trace fossil communities. In: Developments in Palaeontology
and Stratigraphy (Hallam, A., Ed.), Elsevier, 359-376.
Figure 1 (next page). Looping, circling and spiraling trace fossils from the Brioverian. Scale
bars are 1 cm. 1. Gordia with numerous self-overcrossings. Montfort-sur-Meu (les Grippeaux).
2. Circular Gordia with one self-overcrossing (arrow). Saint-Gonlay (la Lammerais). 3. Tiny
Circulichnis on a microbially stabilized surface. Note that the trail starts (or ends) outside of
the circle (arrow). Saint-Gonlay (la Lammerais). 4. Perfect tiny Circulichnis (top right)
associated with horizontal trails (left) and a pit of indistinct affinity (bottom right). Saint-Gonlay
(la Lammerais). 5. Pseudo-spiraling Gordia with a self-overcrossing (arrow) and an unguided
course. Montfort-sur-Meu (le Bois-du-Buisson). 6. Spiral trail with an uncertain guided course.
Montfort-sur-Meu (le Bois-du-Buisson). 7, 8. Perfect spiral trails with guided courses.
Montfort-sur-Meu (les Grippeaux; 7) and Crozon (8).
... The present materials resemble ring-like trace fossils Circulichnis montanus Vialov, 1971 and "Phycodes" coronatum Crimes and Anderson, 1985. Circulichnis montanus was originally reported from the Upper Triassic and can be convincingly traced back to the Ordovician (Pickerill and Keppie, 1981;Fillion and Pickerill, 1984) and further to the basal Cambrian (Gougeon et al., 2019). Our specimens are similar to the holotype of Circulichnis montanus in tunnel width and diameter for the ring-like portion. ...
... Our specimens are similar to the holotype of Circulichnis montanus in tunnel width and diameter for the ring-like portion. Circulichnis montanus with short branches has also been noted in previous reports (Pickerill and Keppie, 1981;Gougeon et al., 2019). "Phycodes" coronatum shows regularly spaced vertical shafts (a total of 20 ideally) on a ring-like burrow and has only been reported from the lowest Cambrian (Crimes and Anderson, 1985). ...
... Motor control evolution as evidenced by trace fossils may thus provide additional information about evolutionary ecology of benthic faunas. Spiralling/looping and guided movement patterns arose during the Ediacaran-Cambrian transition as shown by the conspicuous appearance of loops, circles, and spirals in the trace fossil record (Marusin, 2011;Gougeon et al., 2019). The lowest Cambrian witnesses the prominent occurrence of several morphologically complex, guided burrows in the shallow-marine environment, such as the systematicprobing Treptichnus pedum that takes curved to strongly looping routes (Jensen, 1997;Wilson et al., 2012), perfect circular galleries with equidistant vertical shafts "Phycodes" coronatum (Crimes and Anderson, 1985), and multi-level helicoidal trace Gyrolithes (Laing et al., 2018). ...
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