Tracefossils - Paleodictyon
Monday, 3. November 2008, 16:28:45
There has been a lot of fuss about dancing dinosaurs lately. Tracks of dinosaur footprints seem to be great news. My post today will be on much smaller traces, but still within the realm of trace fossils.
Tracefossils also known as ichnofossils (ichnos is Greek for "trace" ) are sedimentary structures resulting from biological activity (and do not include “body fossils”). They include burrows and other excavations (“bioturbation”); tracks, trails, footprints (like dinosaur footprints) and resting marks; evidence of feeding activity including patterns of shallow grooves left my mud surface feeders, e.g. snails and slugs.
Paleodictyon is a polygonal (normally hexagonal as on my photo) trail oriented parallel to bedding on bedding plane surfaces, and thus forming a "honeycomb" pattern. Paleodictyon is interpreted as a "farming" trace, where the tracemaking animal made a systematic mucuous-lined trail that it later grazed after some microbial colonies grew on the organics-rich trail. The trace maker may have been a worm-like creature. The critter slimes the burrow with a glue-like mucous (slime) that keeps the burrows hollow. There are hollow "shafts" at each corner into which prey fall. The critter then goes back and eats its prey. You may see it as a sort of farm. It seems that the hexagons, or honeycombs, are the best use of space. The worm-like critter may be using some sort of chemical-sensing system to tell it when to turn when it is making the borrow. (It has of course also been postulated that it cannot be an excavation trace fossil - on mathematical grounds, for whatever they are worth?).
The photo is from the Benkovac Stone Unit. The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. it has been heavily used as ornamental or building stone, as the many (old) quarries in the area can witness. (The Eocene was an epoch from ca. 56 - 34 million years ago).
A paper describing the Benkovac Stone Unit was published in Geologia Croatica (58/2, 163-184, Zagreb, 2005) under the title: The Benkovac Stone Member of the Promina Formation: A Late Eocene Succession of Storm-Dominated Shelf Deposits, by Ervin MRINJEK, Vili PENCINGER, Jasenka SREMAC and Boris LUKŠIĆ. Free (open access) download via the abstract here.
• http://en.wikipedia.org/wiki/Paleodictyon
• http://www.envs.emory.edu/faculty/MARTIN/ichnology/Paleodictyon.htm
• http://museum.gov.ns.ca/mnh/nature/tracefossils/english/sections/whodunnit/traces/paleodictyon.html
• http://palaios.sepmonline.org/cgi/content/abstract/22/4/408
• http://en.wikipedia.org/wiki/Trace_fossil
• http://www.geologia-croatica.hr/abstract/gc-58-2-05.html
PS of 4 November 2008:
Richard Hofmann of Nolögic has just (yesterday 3 Nov. in fact) started a series on trace fossils. In his preface to the series he explains the importance of ichnology in earth system science. I am of course looking forward to his coming posts in the series.
Tracefossils also known as ichnofossils (ichnos is Greek for "trace" ) are sedimentary structures resulting from biological activity (and do not include “body fossils”). They include burrows and other excavations (“bioturbation”); tracks, trails, footprints (like dinosaur footprints) and resting marks; evidence of feeding activity including patterns of shallow grooves left my mud surface feeders, e.g. snails and slugs.
Paleodictyon is a polygonal (normally hexagonal as on my photo) trail oriented parallel to bedding on bedding plane surfaces, and thus forming a "honeycomb" pattern. Paleodictyon is interpreted as a "farming" trace, where the tracemaking animal made a systematic mucuous-lined trail that it later grazed after some microbial colonies grew on the organics-rich trail. The trace maker may have been a worm-like creature. The critter slimes the burrow with a glue-like mucous (slime) that keeps the burrows hollow. There are hollow "shafts" at each corner into which prey fall. The critter then goes back and eats its prey. You may see it as a sort of farm. It seems that the hexagons, or honeycombs, are the best use of space. The worm-like critter may be using some sort of chemical-sensing system to tell it when to turn when it is making the borrow. (It has of course also been postulated that it cannot be an excavation trace fossil - on mathematical grounds, for whatever they are worth?).
The photo is from the Benkovac Stone Unit. The Late Eocene Benkovac Stone Member of the Promina Formation of northern Dalmatia, Croatia, is a thinly bedded succession of alternating carbonate sandstones and calcareous mudstones, ca. 40 m thick, exposed as a narrow, SE-trending outcrop belt near the town of Benkovac. it has been heavily used as ornamental or building stone, as the many (old) quarries in the area can witness. (The Eocene was an epoch from ca. 56 - 34 million years ago).
A paper describing the Benkovac Stone Unit was published in Geologia Croatica (58/2, 163-184, Zagreb, 2005) under the title: The Benkovac Stone Member of the Promina Formation: A Late Eocene Succession of Storm-Dominated Shelf Deposits, by Ervin MRINJEK, Vili PENCINGER, Jasenka SREMAC and Boris LUKŠIĆ. Free (open access) download via the abstract here.
• http://en.wikipedia.org/wiki/Paleodictyon
• http://www.envs.emory.edu/faculty/MARTIN/ichnology/Paleodictyon.htm
• http://museum.gov.ns.ca/mnh/nature/tracefossils/english/sections/whodunnit/traces/paleodictyon.html
• http://palaios.sepmonline.org/cgi/content/abstract/22/4/408
• http://en.wikipedia.org/wiki/Trace_fossil
• http://www.geologia-croatica.hr/abstract/gc-58-2-05.html
PS of 4 November 2008:
Richard Hofmann of Nolögic has just (yesterday 3 Nov. in fact) started a series on trace fossils. In his preface to the series he explains the importance of ichnology in earth system science. I am of course looking forward to his coming posts in the series.
WIDGETIZE