Trace Fossils?

[JavierMS]

Gettings, I was recently visiting the north coast of the Balearic Island of Menorca and what I found there was a moon like landscape formed apparently between the Cambrian and the Devonian period, the area of the island is called Favaritx in case someone feels interested and I saw this strange drawings at some rocks, which I suspect that may be ichnofossils or trace fossils from echinoids or molluscs... What do you think? Thank you very much.

[piranha]

Dictyodora liebeana is reported from Menorca:

 

Orr, P.J., Benton, M.J., & Trewin, N.H. (1996)

Deep marine trace fossil assemblages from the Lower Carboniferous of Menorca, Balearic Islands, western Mediterranean.

Geological Journal, 31(3):235-258  LINK

 

Dictyodora liebeana figures from:

 

Häntzschel, W. (1975)

Treatise on Invertebrate Paleontology: Miscellanea: Trace Fossils and Problematica. Pt. W. Suppl. 1.

Geological Society of America & The University of Kansas, 269 pp.

 

[piranha]

Additional figure from:

 

Knaust, D., & Bromley, R.G. (eds.) 2012

Trace Fossils as Indicators of Sedimentary Environments.

Elsevier Scientific Publishing, 924 pp.

 

[Wrangellian]

Excellent. Were you able to collect any samples?

[piranha]

Seilacher 1967 has some excellent info on Dictyodora.

 

text and figures from:

 

Seilacher, A. (1967)

Fossil Behavior.

Scientific American, 217(2):72-80

 

There is a well-documented instance in which an anatomical change in a trace-fossil animal was accompanied by a change in its behavior.  The fossil Dictyodora is the work of an unknown sediment-feeder that tunneled into the ocean floor and filled its tunnel behind it.  The Dictyodora animal, however, seems to have been equipped with a long, thin siphon that allowed it to maintain contact with the water above it.  As the animal traveled in loose meanders through the sediments, its siphon, dragging behind it, left its own marks in the ooze.

 

From Cambrian to Devonian times, between 600 million and 350 million years ago, Dictyodora animals foraged only a few millimeters down in the sediment.  Their siphons were short.  This particular ecological niche, however, was within reach of many smaller competitors.  By Mississippian times (beginning about 350 million years ago) the Dictyodora animals had become adapted to feeding at a deeper and less crowded level.  Their siphons had become longer and their meandering trails were well below the reach of their sediment-feeding contemporaries.

 

As the Dictyodora animals evolved anatomically they also altered their behavior.  In earlier millenniums they had apparently not begun to feed until they had worked their way down to a specific foraging level.  The Mississippian animals, however, ate their way deep into the sediments, leaving a corkscrew trail behind them, before they began their horizontal meanders.  Moreover, the first several meanders no longer followed the older loose pattern.  Instead they curled concentrically around the initial corkscrew.

 

As time passed the Dictyodora animals' behavior became simpler.  Trace fossils from later Mississippian formations in East Germany show a high percentage of Dictyodora burrows in which loose meanders are altogether absent, concentric meanders taking their place.  Trace fossils from southern Austria, which are possibly even younger, show a further behavioral change.  Most of the burrows have no meanders at all; the central corkscrew trail has simply been drilled deeper.  It is doubtful that the Dictyodora animals remained in the same burrow all their lives.  During their reproductive cycle, for example, the animals probably rose to the surface of the sediment.  Thereafter they would have had to dig new burrows, if they did not begin a new mode of life altogether.

 

[JavierMS]

Thank you very much for the information, seriously. I suspected that those were trace fossils but I am sure now. I would like to collect some samples but they are located at a protected area of the island and it is not possible to collect anything from the ground. I really think that is better this way cause the area receives thousands of tourists during summer season and there would be no stones if people were allowed to collect them. I also find interesting to keep the stones there cause they create a beautiful landscape, I post a picture here.

[piranha]

On 4/18/2017 at 4:21 AM, JavierMS said:

Thank you very much for the information...

 

 

Glad to assist.  Dictyodora is quite an interesting ichnofossil.  Thanks for posting! 

 

[Wrangellian]

Fossils have a way of turning up in parks/protected areas. Unfortunately the fossils are not protected from the weather if left in place. I would agree the landscape should not be marred by uncontrolled collecting, but I hope at least a specimen or two has been collected (by someone who is permitted to) and put into a museum...