Id For A Friend - Texas Echinoid

[LanceH]

Help! I need this echinoid ID'd for a friend who found it. I've looked in the one Texas echinoid source I have and CretaceousFossils.com and can't find a match. It's from the Mainstreet formation in Fort Worth, Texas which is lower Cenomanian age.

Lance

[Mike Murphy]

Lance:

That is a beautiful echinoid specimen. The small size of the test, the presence of single rows of small, perforate and similar sized tubercles above the ambitus on both the amublacra and the interambulacra with numerous surrounding small granules, and the small apical scar indicate that the echinoid is Leptarbacia arguta Clark, 1915, which is found in the Denison Group (Denton to Grayson Formations). The collections that I have read describe it from the Main Street Formation and Grayson Formation (primary). It is listed as Diademopsis (Leptarbacia) arguta (Clark) by Cooke in "Comanche Echinoids" (JP, 1946), but it definitely not Diademopsis. TheTreatise on Invertebrate Paleontology, Volume U and the Texas Cretaceous Echinoids by Akers and Akers list the echinoid as Polydiadema argutum (Clark). I also have problems with this generic description because the genus Polydiadema is a flattened form with a large apical scar. I have left my 2 specimens with the genus as Leptarbacia as a result.

There are fair line drawings in Akers and Akers, which were obviously based on Clark's original illustrations in The Mesozoic and Cenozoic Echinodermata of the United States, by Clark and Twitchell, USGS Monograph 54, 1915. Clark's original illustrations are the best diagnostic illustrations. The ambulacral pore series are not very clear, but appear to be uniserial from the ambitus upwards and then become biserial towards the apical system. The plate arrangement cannot be determined in this photograph but does appear to be compound, however, and likely has 2 to 3 demiplates. Since the photograph provides only a apical to lateral view of the echinoid, further confirmation can be made by looking at the oral surface below the ambitus. There should be an increase from the single primary tubercle on the interambulacral plate to 3 primary tubercles on each interambualcral plate from slightly above to below the ambitus. There does seem to be an increase in the number and size of additional tubercles on the intrambulacra beginning slightly above the ambitus. The peristome should also have prominent buccal notches.

Hope this helps.

Regards,

Mike

[Uncle Siphuncle]

While I cannot come near the level of detail that Mike has offered, I will add that that is an extremely rare find for TX, perhaps the only one many of us will ever see. I for one have never seen this species, not to mention in such impeccable condition. Whoever found it is easy very lucky or very motivated. Show that one to Frank Holterhoff. He might want to take photos for the upcoming Akers sequel.

[Guest N.AL.hunter]

It's finding a fossil like that, in amazing condition, that drives my collecting. To hold in your hand the remains of an organism that lived and died so many millions of years ago, then "survived" who knows what geologic events, and to come out of it in that condition,is so amazing to me. Thanks for showing it to us. And as a side note, there are a lot of echinoids along the road cuts at and near the intersection of I-10 and I-20, but you probably already know this. I did a stop there once for a "stretch break". Or at least that is what I would have told any state trooper.

[Mike Murphy]

It's finding a fossil like that, in amazing condition, that drives my collecting. To hold in your hand the remains of an organism that lived and died so many millions of years ago, then "survived" who knows what geologic events, and to come out of it in that condition,is so amazing to me. Thanks for showing it to us. And as a side note, there are a lot of echinoids along the road cuts at and near the intersection of I-10 and I-20, but you probably already know this. I did a stop there once for a "stretch break". Or at least that is what I would have told any state trooper.

N.AL.hunter:

I know the roadcuts around the I-10 and I-20 junction very well from when I lived in West Texas. I spent many weekends in the 1970's and 1980's on "stretch breaks" in the road cuts east and west of Kent, Texas, collecting primarily echinoids, my specialty. The Cretaceous rocks in these roadcut exposures are the Boracho Formation. There are 2 members in the Boracho Formation, a lower member known as the Levinson member and an upper member known as the San Martine member. The Levinson member (equivalent to Duck Creek and lower Fort Worth) is a mixture of limestone and shale with shale dominant while the San Martine member (equivalent to Upper Fort Worth through Main Street) is a mixture of limestone and shale with limestone strongly dominant. Echinoids are found in both members, but the echinoids are largely different between the members. The Levinson member echinoid fauna is dominated by irregular echinoids such as Heteraster, Washitaster and Macraster and holectypoid echinoids such as large Coenholectypus, Anorthopygus and Globator while the San Martine member echinoid fauna is dominated by regular echinoids such as Salenia, Phymosoma, Loriola, Tetragramma, Dumblea and Orthopsis. The regular echinoids are especially abundant in an 18" to 24" thick zone referred to as the "echinoid zone" in the Sane Martine member. Beautiful Stereocidaris echinoids are present in both members but are rare. The Boracho Formation, especially the San Martine member, is also exposed along I-10 west of Fort Stockton, Texas. What is especially fascinating about the echinoids in the Boracho Formation is the relative abundance of a number of genera that are rarely found in other Texas Cretaceous exposures.

Regards,

Mike

[Uncle Siphuncle]

I've worked that stretch 3 times in the last couple of years but it is quite a long haul for me. The last couple of times I took my 21 foot extension ladder to work the I-10 road cuts as well as the quarries I was able to talk my way into with great success. The only problem with the Boracho is that you have to go through lots of solution etched echies to get to the good ones. It is a numbers game but the numbers are there if you are willing to work for them. One of my favorite finds from out that way is a chunk of matrix with 14 echies of 3 genera. I even found a good hunk of lobster tail out there as well. Sadly though, a softball sized Stereocidaris has eluded me all three trips...

[Guest N.AL.hunter]

Well thank you Mike for the info. I can now label the echinoids I found there as to the formation. I had no idea, just that the stop I made was full of them. Very white limestone mostly. I knew that this spot was no secret, but you sure do have to want to get to it. Talking about the boonies!!

[LanceH]

Mike, I didn't get a picture of the bottom because it was covered with matrix but here's the other pics I took.

[Mike Murphy]

Lance:

I appreciate the additional photograph of the beautiful echinoid specimen. The new oblique view does confirm the increase in the number of primary tubercles from one to two near the ambitus and then appears to increase from two to three near the peristome. The buccal notches are still not evident. The tubercle pattern, the size and design of the apical system, the preforate tubercles and the test shape do indicate that the specimen is Leptarbacia arguta or Polydiadema argutum depending on which description that you accept. The age of the strata also supports this identification.

Regards,

Mike

[MB]

Help! I need this echinoid ID'd for a friend who found it. I've looked in the one Texas echinoid source I have and CretaceousFossils.com and can't find a match. It's from the Mainstreet formation in Fort Worth, Texas which is lower Cenomanian age.

Lance

Congratulations !!! what a find!!!

Whas found in this condition or it was cleaned?

[LanceH]

Well, again, not MY fossil, a friend found it. That's the exact condition it was found in. He said he turned over a rock and there it was.

Congratulations !!! what a find!!!

Whas found in this condition or it was cleaned?

[brian]

I am a geology professor at the University of Louisiana - primarily a carbonate sedimentologist/stratigrapher. I have been working on the Cretaceous outcrops on US 90 west of Del Rio for some time and have a new graduate student whom I plan to have work on the I10-I20 area in West Texas. I had a student working on the Buda there some years ago and am now looking at the Boracho section. I was interested to come across your discussion when I googled "San Martine Limestone" and would appreciate any additional lead-in to the literature anyone can provide. There seem to be a number of UT theses from the 50's but nothing much else.

Brian Lock

[Uncle Siphuncle]

Hey Brian

Have you encountered a small Coenholectypus nanus like form and/or some form of Holaster/Sternotaxis/Plesiocorys in the Boquillas out past Del Rio? I found some along with a few Squalicorax teeth, floating micro crinoids, and other forams in association with Hemiaster jacksoni out that way. I'm curious how much of this stuff outside of H. jacksoni and S. falcatus has already been described.

I've not found much literature on the San Martine or Levinson members of the Boracho past the 50s either, but have collected I-10 road cuts and pits out that direction 3 times in the last 3 years. Lots of echies, a few ammonites and nautiloids, a section of lobster tail, etc came to hand. Unfortunately the acidic conditions out there force you to take lots of echies to get a few good ones. I kept my eyes open for Stereocidaris but to date one hasn't come to hand. These exposures while located far from major cities tend to draw attention from collectors around the state, especially those traveling to Tucson each Feb. For that reason when I go I tend to take a 21 foot extension ladder and hope for light winds.

[Auspex]

...I tend to take a 21 foot extension ladder and hope for light winds.

You should post this under "advice for beginners".

[brian]

Hi, Dan,

I have seen abundant echinoids in the top part of the Boquillas near Langtry - mostly H. jacksoni but also large numbers of a tiny (juvenile) regular echinoid, 1 or 2 mm in diameter with hair-like spines. I illustrated both in a paper in 2006 Transactions of the Gulf Coast Association of Geological Societies. The best specimen of the juveniles I sent to an acquaintance in Mississippi but I haven't had an identification. My main interest in the Boquillas was with the sedimentology and sequence stratigraphy. I am leading a day of a Geological Society of America field trip through that area in October. I am regretting that I left the best slab with H. jacksoni (also illustrated in the paper) in the outcrop to show off for the field trip, but someone has since collected it. The microcrinoids (saccocomids, I believe) are very abundant in the lower Boquillas and best seen in thin section.

Like you, I find a compact extending ladder a critical piece of field equipment. On one occasion I bought a regular aluminum ladder and had it on the top of my SUV, but the wind whistling past the hollow rungs drove me crazy. Not recommended.

[Uncle Siphuncle]

Brian

Was your MS buddy George Phillips?

[Mike Murphy]

Brian:

Outside of the several theses that were done in the late 1940's and early 1950's, there were only a few published papers on the Boracho Formation. Two of the publications were published in the AAPG Bulletin. The best stratigraphic reference that I had found was "Comanchean Stratigraphy of Kent Quadrangle, Trans-Pecos Texas" by John P. Brand and Ronald K. DeFord, AAPG Bulletin v. 42 No. 2, February 1958, pp. 371-386 and also reprinted as Bureau of Economic Geology (University of Texas) Report of Investigations 34, 1958. This paper also lists several of the theses and other papers related to the early Cretaceous of Trans-Pecos, Texas. The other primary publication that covered the Boracho Formation (and the only relatively recent publication) was "Paleoenvironments of late Albian Stage (early Cretaceous) of eastern Trans-Pecos, Texas", T.L. Cheatham, AAPG Bulletin, April 1984, 461 pp. In addition, there was a paper "Cretaceous Echinoids from Trans-Pecos Texas" by Jerome S. Smiser from the Journal of Paleontology (Journal of Paelontology, September 1936, Vol. 10 No. 6, pp. 449-480) that included some of the echinoids from the Boracho Formation.

These were the primary references that I used when I lived in West Texas and collected from the Levinson and San Martine members of the Boracho Formation in the 1980's. The Boracho Formation is also mentioned to some extent in various publications from the 1950's and 1960's of the Bureau of Economic Geology in Austin, Texas, most of which are now out of print but are accessible through various libraries.

Can you provide more information on your paper that was published in the Gulf Coast Association in 2006? I would be interested in obtaining a copy of the paper as I used to collect the same echinoid species as Dan Woehr from the upper Boquillas Formation. Other than Hemiaster jacksoni (originally described by Maury from Brazil), none of the Boquillas echinoids have been reported in the literature. According to my collection notes, the echinoids that Dan and I have been previously discussing from the Boquillas were from the Rock Pens member. I have been going back through my piles of papers and books, but I have not yet found the notes on the Rock Pens member, although I have determined through GEOLEX that "Rock Pens member of the Boquillas Formation" is still a valid Texas stratigraphic name. Did you identify the stratigraphy of the Boquillas where you studied the formation?

Regards,

Mike

[brian]

Brian

Was your MS buddy George Phillips?

Yes indeed. He was interested in specimens for the Mississippi Museum of Natural Science, of H. jacksoni. I also sent him the juvenile specimens that I illustrated - figured it was best for figured specimens to be accessible in a museum collection.

[Uncle Siphuncle]

Brian

I'm on board with you. I've arranged to send my friend George some supplementary specimens next week. In fact I guided him on a 2-3 day echie trip across South TX last fall and if he can make it again before long I'll take him to this Boquillas site and allow him to take what he wants for the museum and take his own field notes as well.