Trace Fossils, Cretaceous

[Dammonite]

Here's an interesting trace fossil from the lower Cretaceous Duck Creek formation at Lake Texoma, Texas. Typical finds from this location include ammonites, inoceramus, and exogyra. Trace fossils are common, usually worm tubes that wind through chunks or flakes of rock. But here's one I haven't seen before. There are four pairs of symetrical markings on this small slab that looks to me like they resulted from the passing of a sea creature on the ocean floor. There is no fossilized organic material here. These are not shark teeth. What do you think? Thanks!

[Auspex]

My first impression is swim marks from a fish. Pretty neat whatever it proves to be!

[Fossildude19]

I agree with Auspex, ... this looks like Undichna, or a fish swimming trace fossil.

First thing that came to mind.

Very cool ichnofossil! Rather unusual, I think. You may consider contacting a local museum or university as it could be of interest to them.

Thanks for posting this.

Regards,

[Wrangellian]

Cool, Haven't seen one like that before!

[Carl]

Wow... Very cool! (Thanks for the heads-up, Auspex!) I don't see Undichnia here, which is usually one or more narrow, sinuous grooves. But you have something there. One thing to consider is something being carried in the current and bouncing along leaving sequential impressions. This "thing" could be organismal remains (and thus the mark would be a fossil) or non-organismal. If it was made from current-carried organismal remains it would NOT be called a trace fossil, Trace fossils (=icnofossils) only record the activites of living organisms, not what their remains do after death. As odd as it may sound, it would still be considered a body fossil.

[Dammonite]

Thanks to all for your responses. Three things here. (1) I will take your suggestion, Fossildude19, and show this to someone more knowledgeable than I. I am a member of the Dallas Paleontological Society, and professionals in that group willingly share their experience. I'll report their observations here. (2) On close inspection of the rock itself, I see that there are actually five pairs of in-line impressions, not four, as I initially reported. Also, there is another set of similar marks elsewhere on the rock. (3) Finally, the photo in my post shows only one half of a split chunk of mudstone. That's the "positive" side, and it's still in the field because it was too heavy for me to lug. The matching "negative" side is with me because it was easy to carry. I will try to retrieve the "positive" side.

[Tom Dill]

A mark in the sediment formed by the movement or impression of a dead organism would not be a body fossil. A body fossil is the organism itself, or parts of it. Also, it is impossible to know whether the clam bouncing along the bottom in an undertow, or an ammonite rolling along the bottom in a turbidity current, is actually dead or is still alive and is helplessly being transported. It may be dying, it may already be dead, or it may have survived it's unwanted trip. In all cases, I think the best choice between "body fossil" and "trace fossil" is the latter. A sedimentologist would call all the resulting marks on the sediment surface "tool marks", but that fails to communicate that these particular tools are indications of past life - and therefore, are fossils.

[Carl]

I would mostly agree. But I would still not call any impression of a dead animal a trace fossil since traces are evidence of the activities of living organisms. And even a foot print is a trace AND a body fossil because it is a record of activity AND a replica of a body part. Agreed, we can not tell if a bouncing animal is alive or dead, which is why I choose the more neutral non-trace interpretation.