"The new quarry is looking damn good," wrote [paleontologist Grayson] Meade to his colleague Glen Evans in May 1940. "[W]e have found quite a portion of a partially articulated phytosaur skeleton. About four or five feet of the vertebrae are mostly in articulation. There are leg bones, some ribs, and the mandible. ? There is every indication that the skull should be there, and more of the skeleton. I didn't reach the end of it knowingly at any rate."
You can read the rest of this story here. There are dozens of unopened jackets of fossils collected in the late 1930s and early 40s in the basement of the Vertebrate Paleontology Lab at UT Austin. I've previously published on some of the prepared material and it is all just spectacular. These specimens are especially important because the Otis Chalk quarries are possibly older than any Chinle Formation exposures and might be giving us a unique view into latest Carnian or earliest Norian faunal assemblages in the western U.S. I cannot wait to see what the rest of those jackets hold!
Kudos to my friends and colleagues Michelle Stocker and Sterling Nesbitt for their opportunity to work on these fossils and at the original quarries.
Showing posts with label Fossil Preparation. Show all posts
Showing posts with label Fossil Preparation. Show all posts
Enhanced Technique for Separating Microvertebrates from Matrix
The Journal of Paleontological Techniques is an online, open access journal dedicate to publishing papers on fossil preparation. The latest offering is this paper by Mitchell and Heckert describing the use of sodium polytungstate filtration to separate some Upper Triassic microfossils from collected matrix. Although there are some serious caveats to using these chemicals (such as how the chemicals react with metal and glass...ouch), the results are promising and the set-up looks fairly easy. You can download this article free from here.
Mitchell, J. S. and A. B. Heckert. 2010. The setup, use and efficacy of sodium polytungstate separation methodology with respect to microvertebrate remains. Journal of Paleontological Techniques, 7: 1-12.
Abstract - Concentrated deposits of small remains from vertebrates, termed microvertebrate sites or vertebrate microsites, are a unique and detailed source of information about the history of life. Collecting fossils from these sites, however, presents unique challenges. The most time consuming, and thus most deterring, aspect by far is the separation of the fossils from the sediment. This study attempts to quantify to what extent the use of sodium polytungstate (=sodium metatungstate, Na6H2W12O40, abbr. SPT) filtration increases fossil concentration, how quickly fossils sink in SPT solutions, and what is a good working density for SPT. We do this by generally following the methodology set out by previous authors, although with some substantial modifications, on an Upper Triassic deposit dominated by clay minerals and lithic fragments, as well as on a second, smaller quartz sand dominated microsite. We also provide a revised and detailed guide with our modifications to former practices and our recommendations to other workers interested in creating a SPT laboratory, including the strong advisory to work over thin plastic sheets, as SPT can react with metal and adheres strongly to glass when it crystallizes.
Our experiments have shown a significant improvement in fossil concentration (from ~2% of the clasts being fossils to ~19%) at the main site, with a sample from the other site showing the treated concentrate as 25% fossil. We have also found very few fossils in the float (<0.5%), but noticeable rates of fossil loss in SPT solutions above ~2.80 g/mL (up to 16%). Further, we have found that 2.75 g/mL is a good working density for several lithologies, as it is high enough to float most rock, low enough to sink most fossils, and low enough to be manageably maintained. SPT has, in processing one particularly rich site, saved many person-hours that otherwise would have been spent picking through less concentrated sediment.
Mitchell, J. S. and A. B. Heckert. 2010. The setup, use and efficacy of sodium polytungstate separation methodology with respect to microvertebrate remains. Journal of Paleontological Techniques, 7: 1-12.
Abstract - Concentrated deposits of small remains from vertebrates, termed microvertebrate sites or vertebrate microsites, are a unique and detailed source of information about the history of life. Collecting fossils from these sites, however, presents unique challenges. The most time consuming, and thus most deterring, aspect by far is the separation of the fossils from the sediment. This study attempts to quantify to what extent the use of sodium polytungstate (=sodium metatungstate, Na6H2W12O40, abbr. SPT) filtration increases fossil concentration, how quickly fossils sink in SPT solutions, and what is a good working density for SPT. We do this by generally following the methodology set out by previous authors, although with some substantial modifications, on an Upper Triassic deposit dominated by clay minerals and lithic fragments, as well as on a second, smaller quartz sand dominated microsite. We also provide a revised and detailed guide with our modifications to former practices and our recommendations to other workers interested in creating a SPT laboratory, including the strong advisory to work over thin plastic sheets, as SPT can react with metal and adheres strongly to glass when it crystallizes.
Our experiments have shown a significant improvement in fossil concentration (from ~2% of the clasts being fossils to ~19%) at the main site, with a sample from the other site showing the treated concentrate as 25% fossil. We have also found very few fossils in the float (<0.5%), but noticeable rates of fossil loss in SPT solutions above ~2.80 g/mL (up to 16%). Further, we have found that 2.75 g/mL is a good working density for several lithologies, as it is high enough to float most rock, low enough to sink most fossils, and low enough to be manageably maintained. SPT has, in processing one particularly rich site, saved many person-hours that otherwise would have been spent picking through less concentrated sediment.
Phytosaur Skull Preparation IV
Proceedings of the First Annual Symposium on Fossil Preparation and Collections Now Available
Starting in 2008 fossil preparators and collection managers have been meeting once a year in symposia dedicated to sharing methodology and techniques regarding fossil preparation and conservation. The first meeting was held at Petrified Forest National Park and the proceedings volume from this meeting is now available on-line. The PDFs are open access, however; bound copies are also available.
The 2010 meeting is being hosted by the Chicago Field Museum.
The 2010 meeting is being hosted by the Chicago Field Museum.
Phytosaur Skull Preparation III
It's been awhile since any work was done on the phytosaur skull we've been following the preparation on. This is mainly because we have been without a preparator for the last few months. Now we have two new preparators and my interns are getting in on the action as well.
This photo is of my intern Chuck working on the left side of the skull with an air-scribe. These are essentially "mini-jackhammers" that use compressed air to vibrate a sharp stylus on the tip of the tool. This vibration slowly removes the hard rock matrix from the bone. The bone is purple, sandstone matrix is gray, and the white is the field jacket of air conditioning foam soaked in plaster and hardened around the skull and matrix in the field to provide safe transport back to the preparation lab. This field jacket will be slowly cut away and removed as preparation continues and will eventually be replaced by a similarly made cradle for permanent and safe storage.
Here is what has been exposed so far. The entire rear left portion of the skull is very well preserved and the elements are freeing nicely from the sandstone matrix. Anterior (forward) is to the left. Abbreviations are as follows: f, frontal; ltf, lateral temporal fenestra; na, nasal; orb, orbit; po, postorbital; q, quadrate; qj, quadratojugal; and sq, squamosal.
We'll keep following as preparation continues. We are pretty excited about this skull as it appears to be relatively pristine.
Phytosaur Skull Preparation II
I last featured this phytosaur skull undergoing preparation on February 24th and since that time more work has been done. Some of the right side of the skull has now been exposed. Preparation has been slow due to a plethora of other projects combined with a really tough sandstone matrix. Separation is poor in places and in parts the bone is impregnated with hematite, a common condition of bone encased in Chinle sandstones.
The ventral portion of the right side of the skull projects laterally a little too far suggesting that some dorsoventral crushing of the skull has occurred. So far we have exposed the lateral surface of the posterior projection of the squamosal (it is still a pseudopalatine), both frontals, the right jugal and much of the right maxilla. This picture shows the right side of the skull as currently exposed. Anterior (forward) is to the right, posterior (back) is to the left.
Preparation continues and we will follow it here until it is complete.
The ventral portion of the right side of the skull projects laterally a little too far suggesting that some dorsoventral crushing of the skull has occurred. So far we have exposed the lateral surface of the posterior projection of the squamosal (it is still a pseudopalatine), both frontals, the right jugal and much of the right maxilla. This picture shows the right side of the skull as currently exposed. Anterior (forward) is to the right, posterior (back) is to the left.
Preparation continues and we will follow it here until it is complete.
Phytosaur Skull Preparation
Back in November of 2008 I mentioned a new phytosaur skull collected from Petrified Forest National Park during the summer. Encased in a sandstone horizon of the Jim Camp Wash beds of the Sonsela Member (Chinle Formation), the skull is from the type locality of Pseudopalatus jablonskiae and was recovered about 100 meters from the spot where the type skull was collected. As I stated this skull is important because it may represent a second specimen of P. jablonskiae, but more complete than the type skull. Alternatively it could represent another phytosaur taxon which was a contemporary of P. jablonskiae. Because the skull is from the upper Jim Camp Wash beds, above the Jasper Forest bed it should be a pseudopalatine.
The picture on the left shows the initial discovery. The skull is dorsal side up and beneath the rock hammer. Squamosals showing on the left [below the hammer handle] and the external nares showing on the right just below the hammer head. The picture on the right shows the beginning of the excavation. The sandstone was very well indurated and we needed a rock saw and hammers and chisels to block out the skull for removal. The resulting jacket weighed a few hundred pounds.
Late last week we cracked open the jacket and PEFO preparator Matt Brown started removing the rock. As of Tuesday morning this is what was exposed:
The picture on the left shows the initial discovery. The skull is dorsal side up and beneath the rock hammer. Squamosals showing on the left [below the hammer handle] and the external nares showing on the right just below the hammer head. The picture on the right shows the beginning of the excavation. The sandstone was very well indurated and we needed a rock saw and hammers and chisels to block out the skull for removal. The resulting jacket weighed a few hundred pounds.
Late last week we cracked open the jacket and PEFO preparator Matt Brown started removing the rock. As of Tuesday morning this is what was exposed:
As you can see the upper left corner of the skull is now partially exposed. The squamosals are broad in dorsal view, thus the skull does belong to a pseudopalatine. The squamosals are more posteriorly extended than in the type of P. jablonskiae; however, this appears to be a larger specimen. Unfortunately the posterodorsal surfaces of the squamosals were what was exposed at discovery and thus were somewhat eroded. Also, the rock is much harder than we expected and the separation from the bone is not always clean. Some of the bone within the rock is actually fractured as it is softer than the surrounding matrix. Still, during excavation we located the tip of the premaxilla and both quadratojugals, so we are fairly certain that we have a complete and undistorted skull. Only time will tell. Over the next month or two I'm hoping to document the entire preparation process here and we will discover exactly what this skull is and how well it is preserved. Stay tuned.
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