1980s Ghost Ranch Coelophysis Quarry Excavations

Palaeoblog has posted photos from the early 1980s Carnegie Museum excavations of the Coelophysis Quarry at Ghost Ranch, New Mexico.  These are courtesy of Greg McDonald who served as the quarry chief.

Further Support for a Causal Relationship Between the CAMP and the End-Triassic Extinction Event

Deenen, M. H. L., Ruhl, M., Bonis, M. R., Krijgsman, W., Kuerschner, W. M., Reitsma, M. and M. J. van Bergen. 2010. A new chronology for the end-Triassic mass extinction. Earth and Planetary Science Letters 291:113–125. doi:10.1016/j.epsl.2010.01.003


Abstract - The transition from the Triassic to Jurassic Period, initiating the ‘Age of the dinosaurs’, approximately 200 Ma, is marked by a profound mass extinction with more than 50% genus loss in both marine and continental realms. This event closely coincides with a period of extensive volcanism in the Central Atlantic Magmatic Province (CAMP) associated with the initial break-up of Pangaea but a causal relationship is still debated. The Triassic–Jurassic (T–J) boundary is recently proposed in the marine record at the first occurrence datum of Jurassic ammonites, post-dating the extinction interval that concurs with two distinct perturbations in the carbon isotope record. The continental record shows a major palynological turnover together with a prominent change in tetrapod taxa, but a direct link to the marine events is still equivocal. Here we develop
an accurate chronostratigraphic framework for the T–J boundary interval and establish detailed trans-Atlantic and marine–continental correlations by integrating astrochronology, paleomagnetism, basalt geochemistry and geobiology. We show that the oldest CAMP basalts are diachronous by 20 kyr across the Atlantic Ocean, and that these two volcanic pulses coincide with the end-Triassic extinction interval in the marine realm. Our results support the hypotheses of Phanerozoic mass extinctions resulting from emplacement of Large Igneous Provinces (LIPs) and provide crucial time constraints for numerical modelling of Triassic–Jurassic climate change and global carbon-cycle perturbations.

More Triassic Repeat Photography - Ned Colbert (AMNH) at the Petrified Forest in 1946

In 1946 the American Museum of Natural History initiated fieldwork in the Chinle Formation of Arizona. Led by Edwin (Ned) Colbert, the goal of the expedition was to add to our knowledge of Triassic vertebrates and expand the museum's collection of Chinle Formation fossils. The previous year Colbert had travelled to the Petrified Forest with Charles L. Camp to check out Camp's old localities from the 1920s. This lead to a full blown, successful field season in 1946 (several amazing stories from this work can be found in one of Colbert's autobiographies - Digging into the Past). Set to return in 1947, Colbert never made it because on the way to the Petrified Forest he stumbled upon the huge deposit of vertebrates at the Coelophysis Quarry at Ghost Ranch, New Mexico. As a side note: he did return to the park briefly in 1947 to take part in the first ever Society of Vertebrate Paleontology field conference (see Camp et al., 1947; Nesbitt and Parker, 2005).

Fantastically, Colbert shot many rolls of Kodachrome (color) slide film of his Triassic work in 1946 and 1947. The 1946 set was purchased by the Petrified Forest shortly afterwards and some of these are still in the collections to this day. Since 2001 I have been actively trying to relocate two of the sites, the first a large bed of fresh water clams that AMNH staff proclaimed the greatest deposit of Triassic freshwater clams (Unionids) ever! Actually dozens of these sites occur throughout the park but when first discovered this was a big deal.

1946 shot of AMNH jeep parked near clam bed.

2009 photo of same site

The second site was where Colbert and crew collected the skull of a pseudopalatine phytosaur. This site was particularly intriguing as in the photo the outcrop being excavated looks very much like strata of the Blue Mesa Member. If this site really is in the Blue Mesa Member, this would represent a very low occurrence of a pseudopalatine phytosaur.

1946 photo of phytosaur skull excavation.

2009 photo of same site.

The park also has a very old map where Charles Camp's localities as well as those of National Park staff had been plotted. Colbert's 1946 sites were added to this map. Unfortunately, numerous visits to where these two sites were plotted failed to match up the photographs. By 2009 I had eliminated all possibilities except for one area of badlands south of a place called Billing's Gap. This past summer the interns and I were finally able to precisely relocate these sites. Interestingly both were situated very close to each other geographically and over 1.5 miles away from where they had been mapped! Also of interest was that the sites were in the upper portion of the Sonsela Member, thus no low occurrence of a pseudopalatine.

How fortunate we are that past researchers such as Colbert photographed their work (and he did it in color in 1946!). Even with dots on a map (and GPS coordinates) photos are indispensable for relocating sites and determining stratigraphic position of historic specimens. Nowadays with digital photography, there is no excuse for researchers not to photodocument every single site where fossils are collected.

For those interested in historic documentation of paleontology I encourage you to please check out the 2005 article I did with Sterling Nesbitt for a SVP field trip that year. It includes many previously unpublished photos from the 1947 field conference which was attended by notable VP'ers such as Romer, Gregory, Simpson, Colbert, etc... You can order the entire volume (with papers on the vertebrate faunas and plants of the Moenkopi and Chinle Formations from the Arizona Museum of Natural History.

REFERENCES

Camp, C.L., Colbert, E.H., McKee, E.D., and S.P. Welles. 1947. A guide to the continental Triassic of Northern Arizona. Plateau 20:1-8.

Nesbitt, S.J., and W.G. Parker. 2005. The 1947 Society of Vertebrate Paleontology Triassic fieldtrip, then and now, and its significance to Triassic vertebrate paleontology. Mesa Southwest Museum Bulletin 9:1-12.

When the Large Block in the Quarry Becomes a Piece of Furniture

I've always found this transformation amusing. When you first uncover your specimen you do so delicately and worry about every little chip and fragment. You carefully outline the specimen, determining the edges of your blocks (and hope that they stay small), plastering edges as you trench to protect the delicate bones from knees, flying rocks, etc.. Finally you apply your thick plaster cap and start widening and deepening your trench. It is at this stage of the excavation that this transformation occurs. The transformation from a plastered block of fossils to a piece of furniture.

Here is a picture of a large (six feet by three feet) block from a current excavation. We have now focused our attention on the trench around the specimen and isolated elements we are finding in the trench. Notice how nonchalant we have become regarding the previous center of our attention. It has now become a seat, a foot rest, a table for the iPod and speakers, and a place to put drinks, tools, etc...

Amazing!

Phytosaurs Everywhere

Easily the most common type of fossil in the Chinle Formation are the skulls of phytosaurs. Historically researchers from the University of California Museum of Paleontology, the United States National Museum, and the American Museum of Natural History came to the Petrified Forest to collect Triassic fossils for their collections and inevitably came away with several phytosaur skulls as the result of their labor.

Since I started at the park in 2001 my students and I have discovered and collected eleven complete and partial skulls, seven of them in the last two summers. Our most recent was discovered this last Tuesday and we were able to get it back to the lab by Wednesday afternoon.

The photo below shows the upper portion of the skull after being exposed. Half of the lower jaw is also present and slightly visible under the boulder to the left.

Below is a photo of the rear portion of the left side of the skull. The squamosal bone (the dark gray mass in the center of the photo) is narrow in dorsal (top) view and deep in lateral (side) view. Thus the skull is almost certainly that of a "Leptosuchus". Interestingly in 1921 Annie Alexander and Charles Camp of the University of California Museum of Paleontology collected the holotype skull of "Machaeroprosopus" ("Leptosuchus") lithodendrorum from a spot close by and at the same stratigraphic horizon.

The forward portion of the lower jaw was in a very hard sandstone matrix underneath a very large boulder at the site. In this third photo you can see the upper part of the skull already plastered and one of my interns is taking a turn under the boulder freeing the lower jaw. We were able to get it out and back to the preparation lab.

This hopefully will prove to be another nice skull for our collections.