Trichophycus pedum

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Schematic representation of different forms of Trichophycus pedum , as handed down on layer surfaces.

Trichophycus pedum (or Treptichnus pedum ; earlier also Phycodes pedum and Manykodes pedum ) is a trace fossil in marine sediments of the early Cambrian . It is believed to be the earliest widespread, three-dimensional complex trace fossil. The Ichno species occurs almost worldwide and its first appearance is either in layers that still contain fossils of the Ediacarafauna or in layers immediately above. The producer of Trichophycus pedumis considered to be a more advanced living being compared to the Ediacara organisms, which is why the first appearance of the trace acts as an indicator for the boundary between the Ediacarian and the Cambrian and thus for the boundary between the Precambrian and Phanerozoic . However, after the Precambrian-Cambrian boundary was officially established in the previously selected reference exposure ( GSSP ) in 1992, it was discovered that Trichophycus pedum still occurs below this boundary. The suitability of the trail as a guide fossil is controversial due to its dependency on facies , as it only occurs in shallow marine sediments .

description

3D reconstruction of the feeding track

Trichophycus pedum is a feeding movement track (Fodinichnum) of a sediment eater. The track is mostly raised at the base of thin sandstone banks (convex hyporelief) and differs slightly from the sandstone of the bank in grain size and texture . It runs strictly horizontally (parallel to the layers) and has a moderately complex structure: In its typical form and preservation, the building consists of unbranched corridors that can be straight or curved and sometimes also form loops. A type of segmentation, which gives the track a rope-like appearance, is particularly characteristic. The "segments" are small single passages that lead to the sediment surface of the time.

So far no body fossils of the person responsible for these traces have been found. Aktuo-Paleontological studies and detailed studies of body fossils in frühkambrischen Burgess Shale suggest that treptichnus pedum of Priapswürmern or at least lokomotorisch similar invertebrates may have been generated.

Individual evidence

  1. ↑ a b Shanchi Peng, Loren E. Babcock, Roger A. Cooper: The Cambrian Period. Pp. 437-488 in: Felix M. Gradstein, James G. Ogg, Mark Schmitz, Gabi Ogg (Eds.): The Geologic Time Scale 2012. Elsevier, 2012, ISBN 978-1-234-56789-7 .
  2. ↑ Ed Landing: Precambrian-Cambrian boundary global stratotype ratified and a new perspective of Cambrian time. Geology. Vol. 22, No. 2, 1994, pp. 179-182, doi : 10.1130 / 0091-7613 (1994) 022 <0179: PCBGSR> 2.3.CO; 2 (alternative full text access : ResearchGate ).
  3. ↑ James Gehling, Sören Jensen, Mary Droser, Paul Myrow, Guy Narbonne: Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland. Geological Magazine. Vol. 138, No. 2, 2001, pp. 213-218, doi : 10.1017 / S001675680100509X .
  4. ^ Gerd Geyer: The Fish River Subgroup in Namibia: stratigraphy, depositional environments and the Proterozoic – Cambrian boundary problem revisited. Geological Magazine. Vol. 142, No. 5, 2005, pp. 465-498, doi : 10.1017 / S0016756805000956 .
  5. ↑ a b c d e Adolf Seilacher: Treptichnus pedum. In: Trace Fossils Analysis. Springer-Verlag, 2007, ISBN 978-3-540-47225-4 , p. 182 f.
  6. ↑ Mary L. Droser, Soren Jensen, James G. Gehling, Paul M. Myrow, Guy M. Narbonne: Lower Cambrian Most Ichnofabrics from the Chapel Iceland Formation, Newfoundland: Implications for Cambrian substrate. PALAIOS. Vol. 17, No. 1, 2002, pp. 3-15, doi : 10.1669 / 0883-1351 (2002) 017 <0003: LCIFTC> 2.0.CO; 2 .
  7. ^ Sören Jensen: The Proterozoic and Earliest Cambrian Trace Fossil Record; Patterns, Problems and Perspectives. Integrative and Comparative Biology. Vol. 43, No. 1, 2003, pp. 219-228, doi : 10.1093 / icb / 43.1.219 .
  8. ^ Purnima Srivastava: Treptichnus pedum : An Ichnofossil Representing Ediacaran - Cambrian Boundary in the Nagaur Group, the Marwar Supergroup, Rajasthan, India. Proceedings of the Indian National Science Academy. Vol. 78, No. 2, 2012, pp. 161–169 ( PDF 250 kB).
  9. ^ Mark A. McMenamin, Dianna L. McMenamin: The Emergence of Animals: The Cambrian Breakthrough. Columbia University Press, 1990, ISBN 0-231-06647-3 , p. 41
  10. ^ Jean Vannier, Ivan Calandra, Christian Gaillard, Anna Żylińska: Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary. Geology. Vol. 38, No. 8, 2010, pp. 711-714, doi : 10.1130 / G30829.1 .