mikecable Posted January 21, 2013 Share Posted January 21, 2013 Two finds from Saturday. My first trip out since the end of October. I had back surgery on Dec. 7th--a fusion at L5-S1, and a discectomy at L4-L5. Gary and I made a short trip to a small private caliche quarry in Callahan County--Walnut Clay. I've tentatively identified the first, larger echinoid as Tetragramma sp?, and the second, smaller as Physoma sp? Feel free to tell me I'm wrong. I am proud of the larger urchin. Not easy to find them in such nice shape. Link to comment Share on other sites More sharing options...
erose Posted January 21, 2013 Share Posted January 21, 2013 Mike, Glad to know you are back on your feet. I had my back problems when I was young and supposedly fit. I still do prescribed stretches every morning just to keep things straight. No problems for (knock on wood) ten years now. Those are some nice echinoids. Easiest way to tell Phymosoma from Tetragramma is the tubercules. Tetragrammas will be perforate (small hole in tip) while Phymosomas are not. Beyond that you have to start counting the rows between ambulacrals and looking at the pore pairs and such. The large one does look rather tetragrammish... 1 Link to comment Share on other sites More sharing options...
Uncle Siphuncle Posted January 21, 2013 Share Posted January 21, 2013 hi mike, glad to see u back here on the mend. i echo erich's advice, and also add that tet seems to have a higher tubercle density on the bottom compared to top vs phy, just to add an arm's length metric for comparison. this may not be diagnostic however; pls refer back to perf/imperf tubercle analysis for reliable genus determination... Grüße, Daniel A. Wöhr aus Südtexas "To the motivated go the spoils." Link to comment Share on other sites More sharing options...
mikecable Posted January 21, 2013 Author Share Posted January 21, 2013 Erich and Dan Thanks for the input. I checked with a hand lens and the tubercles are perforated on the one I suspect is a Tetragramma, and not on the Physoma. I'll put it under the dissecting scope when I get home and see if I can "count the rows between ambulacrals and look at the pore pairs and such." I may try my hand at sketching what I see. Link to comment Share on other sites More sharing options...
erose Posted January 21, 2013 Share Posted January 21, 2013 Cool. That confirms your original hunch. Dan's advice about number of tubercules and density above and below will help with the species ID. Link to comment Share on other sites More sharing options...
mikecable Posted January 22, 2013 Author Share Posted January 22, 2013 Which species should I be looking at? I know Tetragramma taffi is one possibility. What other species are possible from the Walnut? Link to comment Share on other sites More sharing options...
erose Posted January 22, 2013 Share Posted January 22, 2013 Which species should I be looking at? I know Tetragramma taffi is one possibility. What other species are possible from the Walnut? T. malbosii (Agassiz) [i have one of these from the Walnut at Harker Heights. It looks almost like a [i]Phymosoma texanum[/i] but the tubercules are all perforate.] T. taffi (Cragin) [these tend to be be big so counting rows of tubercules can help.] T. texanum (Roemer) [smith & Rader, 2009 now list this as just T. sp. It is listed in Akers & Akers, 1987, as occurring in the Glen Rose and Fredericksburg] As you go thru the literature take the stratigraphic ranges with a grain of salt. What might be strictly Walnut in one area will be equal to the Comanche Peak in another and the Goodland yet further north. I think stratigraphic ranges are always the most suspect part of a description. 1 Link to comment Share on other sites More sharing options...
Uncle Siphuncle Posted January 22, 2013 Share Posted January 22, 2013 also keep in mind that counties of occurrence as listed in akers and other refs should be considered a subset of today's known occurrences. Grüße, Daniel A. Wöhr aus Südtexas "To the motivated go the spoils." Link to comment Share on other sites More sharing options...
mikecable Posted January 22, 2013 Author Share Posted January 22, 2013 I'm going to operate under the assumption that if a fossil occurs in the Walnut Clay anywhere in Texas it could theoretically appear anywhere else in the Walnut Clay in Texas. If a fossil appears in the Goodland, Comanche, or Glen Rose it might appear in the Walnut Clay even if not described. Am I on the right track? Link to comment Share on other sites More sharing options...
erose Posted January 22, 2013 Share Posted January 22, 2013 I'm going to operate under the assumption that if a fossil occurs in the Walnut Clay anywhere in Texas it could theoretically appear anywhere else in the Walnut Clay in Texas. If a fossil appears in the Goodland, Comanche, or Glen Rose it might appear in the Walnut Clay even if not described. Am I on the right track? I wouldn't go so far as to include the Glen Rose. But there are numerous formations in the Fredericksburg Group that correlate with each other to certain degrees. Plus you have various members or very localized formations such as the Keys Valley here in Central Texas. The best thing is to get your hands on as much stratigraphic data as possible, both old and new, to make sense of the various descriptions. There are definitely regional differences in fossil distribution that the books barely touch on. What is common here near Austin may be sparse up your way. Dan's comment about the listings for counties in some of the the other HGMS books is important. They listed "known"occurrences but that in no way should rule out a fossil from being found in other counties not listed. 1 Link to comment Share on other sites More sharing options...
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