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Where Are The Scale Trees (And Stigmaria) ? At St. Clair!


hitekmastr

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Rootlets or Grass-Shaped Leaf Appendages? Nancy and I have been debating whether the sharp-tipped, straight or curved appendages coming out from the Stigmaria are all rootlets, or if some of them are above-ground stems or "grass shaped" appendages that look like rootlets. Nan believes they are all rootlets while I believe there are some appendages that come out from the trunk above water and above ground, that look like rootlets and become branches. It makes sense that in a primitive tree, the appendages that come out of the trunk or main roots would be the same, and the appendages coming out underground or underwater would become rootlets while those above ground/water would become branches. Does anyone know if this is really the case, from the paleo literature?

One key to identification is the shape of the scars on the trunk (or root) - if they are round they are roots (stigmaria) and if they are diamond shaped they are part of the trunk.

Nancy recalled that we have this fossil (see pictures below) in our growing little collection and showed this to me to prove her point - we didn't know what this pointed three dimensional structure was in the past and we posted it in Fossil I.D. - HOWEVER - Nancy points out that this is the tip of a rootlet - it is associated with other rootlets on the top of the shale piece. This presents a side view in 3 dimensions of the tip of a rootlet. Because it is preserved in 3 dimensions we can see that it is "cone shaped" and appears to taper to a "point" (see arrows). Most of the time in stigmaria fossils, rootlets show up as flat grass-like structures where actually, as this little tapered rootlet tip shows, they were originally round like any modern stem or root and came to a tapered tip just like the flattened specimens in most of the stigmaria fossils which also have pointed tips. I took some quick closeup photos that show 1) the side view of the rootlet exposed in the shale, 2) the rootlet with arrows pointing to the tapering portion and to the pointed bottom, and 3) a view of the cross-section of the rootlet (top view).

All of these questions continue to intrigue us and it's especially fun using our own fossil finds to answer some of them!

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Ah...starting to get some clarity. Here is a reference I just came across the validates my point about roots and shoots and leaves being similar:

"What appear to be roots at the base of the plant are branched stems, which produced highly modified ribbon-like leaves that functioned as rootlets."

This can be found under "Lycopods" on this website at George Washington University: http://www.gwu.edu/~...ts2/plant2.html

This helps to explain why the rootlets and leaves on the trunk and large stems look identical.

Edited by hitekmastr
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Without travelling back in time to see... Theres some things we can only take a stab at....;)

Cheers Steve... And Welcome if your a New Member... :)

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