Search the Community

On November 27 of this year my mother and I went hunting in a new housing development exposing the Austin Chalk in North Texas. The first and only site that we got to was covered in this rock that has been brought in from somewhere else. It was odd in that it looked like someone had just poured a bunch of it in an empty lot in no particular pattern. It was all next to a man made hole in the ground in the middle of the lot, but I don't see how that could be related. We have seen bags of this matrix in drainage ditches before and had also seen it variously thrown about at different Austin Chalk sites. I had found a few things in it that were intriguing, but for some reason I had largely (and very incorrectly) assumed that there was probably not much that one could find in it, so I never seriously hunted it. But my mother proved me very wrong! When we got to the site and I saw that much of it was covered in this stuff, I was somewhat annoyed since it was covering up some of the Austin Chalk. But we both got out anyways and began hunting. I went off towards the ditch where more of the Austin Chalk was exposed while she was looking around in the foreign matrix. I wasn't having much luck and she was commenting on how she was seeing some layered patterns in the matrix, pictured in F31. I didn't think much of it and kept hunting away from the pile of unknown matrix. Then less than a minute later my mother let out something along the lines of, "Hey! Hey! Hey! What is this?!" When she does that, I know she is not kidding around! So I went over there and saw her pick this up off of the ground. We both immediately knew that it was an echinoid. What made this specimen really special are the facts that this is the largest or at least second largest echinoid that we have ever found, the first echinoid from a formation other than the Austin Chalk, and our first regular echinoid all in one. Its a sad thing that it is so beat up, but then again its not surprising since it was probably hauled in a bag in the back of some guy's pickup for possibly hundreds of miles. Only two tubercles that have not been knocked off are visible, though perhaps there are one or two more buried under the chunk of matrix stuck to the side of the specimen. It is also missing most of its adoral side and most of its apical disc, with bits of the disc still in the depression that is left. Its test is pretty scuffed up in general, but at least most of it is still left and I don't think that it is too beat up to be identifiable. I took pictures of the site while I was there (pictures in F1-F4) and brought home a lot of matrix to experiment with and to photograph later to aide in identifying the formation from which it came. When I got home I consulted @Bill Thompson's book on Texas echinoids and I have been able to narrow this specimen down to the genus Temnocidaris for sure. I am hoping that you guys can help me find out what formation the matrix came from, which would greatly help to narrow down the species possibilities. Out of the four species of Temnocidaris listed in Thompson's book as being reported from Texas only two of them have there tests pictured, T. borachoensis and T. hudspethensis, with the other two species only described from their spines. Now I am not an echinoid expert by an stretch of the imagination, but I am personally leaning towards this being T. borachoensis from the Boracho Formation of Upton county or a nearby county in West Texas. My reasoning is twofold: First, to me its test much more resembles T. borachoensis than T. hudspethensis in two ways. They are that the interabulacrum tubercles are closer together than T. hudspethensis and that its test is a bit more squat than T. hudspethensis, even if it still had its base. Coincidently, just a little over a month ago @KimTexan posted for identification a Temnocidaris specimen from the Edwards Formation of Johnson county that very much resembles mine, though I can't say for sure it is the same species as mine since her specimen is missing much of its aboral side while mine is missing much of its adoral side, making a comparison between them a bit difficult. Second, from what I have seen the matrix most closely resembles the San Martine member of the Boracho Formation. If I want to learn a bit about Texas paleontology that I didn't know before I will usually look up one of @Uncle Siphuncle's Fossil hunting reports. Here is one which contains pictures of a lot of matrix and a few fossils from the Boracho formation, starting with Figure 91. The most striking resemblance I see is that the matrix has a lot of red/orange matrix streaks running through it like mine does. But because I have never hunted in the Boracho Formation other than possibly this brought in matrix, I don't know for sure. I also noticed what appears to be the same layered fossil shown in F31 in Figures 136-138. After seeing this post, I tend to think that it is oyster related material. This matrix is a lot more dense than the Austin Chalk that I am used to, making it noticeably heavier. It bubbles when I put vinegar on it indicating that it is limestone, though perhaps not as vigorously as vinegar on the Austin Chalk. I scraped some matrix with a dentist's pick in the places weakened by vinegar and places I didn't treat with vinegar, and while it did scratch the limestone matrix, the untreated matrix was harder than untreated Austin Chalk. I have tried to see if the sandy red/orange matrix bubbles, but my experiments were inconclusive because the limestone is always nearby, skewing the results. I would assume that it does not bubble on its own. After cleaning the echinoid, a few other fossils, and chunks of matrix, the toothbrush fibers had turned orange indicating that the sandstone it is not that hard, at least when wet. Also the limestone matrix is just packed full of calcite crystals, which is very noticeable in direct sunlight! The specimen its self, excluding any matrix, is 53mm in diameter by 36mm in height, though it would be taller if it still had its base. It appears to me that it is only infilled with the sandstone while there is an actual limestone chunk stuck to the side of it, shown specifically in F12. Notice the red patch on the matrix, a characteristic not unique to this chunk but seen on another chunk of matrix shown in F32. All of the pictures were taken in sunlight, so the color that you see is how it really looks. Thanks for any help in advance. F1-F4. On site photos. F2 F3