Jorge Velez Virtual Poster

Abstract

17 new additions to the list of fossils vertebrates of Quarry Nine include one chelonian, two fishes, two squamate, three anuran, one pterosaur, one sauropod, two ornithopods and five theropods. The theropods were identified by measuring the fore-aft base length of the teeth and the amount of serrations per millimeter. The occurrence of fossilized remains of frogs and salamanders provide evidence that freshwater lacustrine conditions were prevalent at the site. This is also supported by the abundance of turtle and crocodile remains and by the occurrence of freshwater plant fossils. The results of this research indicate that Quarry Nine was a lacustrine environment formed during seasonal wet and dry extremes.

Introduction

The Late Jurassic Morrison Formation is one of the richest dinosaur-bearing strata in the world (Dodson et al. 1980), and has provided a wealth of data on life during this time interval. It represents a semi-arid river floodplain environment where dinosaurs, mammals and other vertebrates flourished. Unfortunately, the paleoecology of this environment remains poorly understood. This is partly because most Morrison sites preserve only large animals. Small vertebrates, such as amphibians and lizards, are uncommon but can be important indicators of temperature, salinity, and other environmental factors. In 1879 William Reed discovered a microvertebrate site in the Late Jurassic Morrison formation at Como Bluff, Wyoming, while working for O.C. Marsh (Ostrom and McIntosh 1999). The locality, called Quarry Nine, yielded the single most important collection of Late Jurassic mammals and other small vertebrates (Simpson 1926a). The mammals represent the most abundant fossils and include 244 of the 250 mammal specimens known from the Jurassic of North America (Prothero 1981). The other vertebrates found in this locality have also been studied, but mostly for taxonomic purposes. Quarry Nine is a remarkable window into Late Jurassic ecosystems, but despite this, its paleoecological implications have not been studied since Simpson (1926a).

Previous works

The microvertebrates from Quarry Nine were originally described by O.C. Marsh (Simpson 1926a). The mammals were later studied by Simpson (1927, 1928) and Prothero (1981). The rhynchocephalians were studied by Gilmore (1909) and Simpson (1926b), while the amphibians were studied by Evans and Milner (1993). Nearly all of these works are taxonomic, however. The only comprehensive paleoecological relationship of the fauna was done by Simpson (1926a) who proposed a food chain relationship between the organisms. Dodson et al. (1980) reported that Quarry Nine occurs in their lithofacies C (drab mudstone), representing channels and channel tops occurring in poorly drained floodplain, but this information has not been integrated into the site’s paleoecology. Fossils collected from Quarry Nine of the Late Jurassic Morrison Formation were identified and analyzed for data concerning their taphonomy, environment of deposition and paleoecology. With this information it was possible to develop a paleoecological reconstruction of the Quarry Nine material and the importance of microvertebrates in paleoecological interpretations and re-examine Simpson’s (1926a) original paleoecological hypothesis.

Materials and Methods

The fossils analyzed are part of the vertebrate paleontology collection at the National Museum of Natural History in Washington D. C. and at the Peabody Museum of Natural History in New Haven Connecticut. Identification and analysis of fossils was done using a Zeiss Stemi SV 6 microscope, and photo documentation of fossils using a Kodak digital camera. Theropod teeth were divided in three groups; theropod teeth type 1: teeth with serrations on all the mesial and distal edges; theropod teeth type 2: teeth with serrations on the upper region of the mesial edge and complete on the distal edge, and; theropod teeth type 3: teeth with no serrations on the mesial edge, but with serrations on the distal edge. Once divided in these groups, their fore-aft base length and the number of serration per millimeter on the distal edge were measured. These measurements were later plotted on graphs to determine the relationship between the fore-aft base length and number of serrations per millimeter.

Results and Discussion

A revision of existing faunal list of Quarry Nine (Ostrom and McIntosh 1999) include the addition of 17 fossil vertebrates, including one chelonian, two fishes, two squamate, three anuran, one pterosaur, one sauropod, two ornithopods and five theropods. The theropod teeth were tentatively identified and divided in five groups named theropod A, B, C, D, E (Chart 1-3). The faunal component (Chart 4) shows that the majority of the fauna was composed of mammals followed by theropods and anurans respectively. A size distribution chart (Chart 5) shows that most of the organism living in the area were small (85%). The occurrence of fossilized remains of frogs and salamanders provide evidence that freshwater lacustrine conditions were prevalent at the site, sedimentological evidence supports this interpretation. This is also supported by the abundance of turtle and crocodile remains and by the occurrence of charophyte oogonia and valvatid gastropods. No articulated elements were found and most are only fragments of isolated skeletal elements, which might have been caused by sub-aerial exposure of the skeletal remains after death of the organisms but before burial. This combination of situations indicates that Quarry Nine was a lacustrine environment formed during seasonal wet and dry extremes.

Acknowledgements

I would like to acknowledge the National Science Foundation Research Experiences for Undergraduates program for funding this project through a grant awarded to the NMNH Research Training Program, Award Number DBI-0243512. I am most thankful to Jennifer Young, Karen Moreno and Jason Head for their help in the identification of some specimens and helpful comments. Dr. Walter Joyce (Peabody Museum of Natural History) was of great help for allowing examination of the Quarry Nine material at the Peabody Museum. Last but not least I am most grateful to Mary Sangrey for keeping the RTP program running and making possible this unique experience for undergraduate students.

References cited

Dodson, P., A. K. Behrensmeyer, R. T. Bakker and J. S. McIntosh. 1980. Taphonomy and paleoecology of the dinosaur beds of the Jurassic Morrison Formation. Paleobiology 6:208-232.

Evans, S. E. and A. R. Milner. 1993. Frogs and salamanders from the Upper Jurassic Morrison Formation (Quarry Nine, Como Bluff) of North America. Journal of Vertebrate Paleontology 13:24-30.

Gilmore, C. W. 1909. A new rhynchocephalians reptile from the Jurassic of Wyoming, etc. Proceedings of the U. S. National Museum 37: 35-42.

Ostrom, J. H. and J. S. McIntosh. 1999. Marsh’s Dinosaurs, the collection from Como Bluff. Yale University Press, New Haven, Connecticut, 388 pp.

Prothero, D. R. 1981. New Jurassic Mammals from Como Bluff, Wyoming, and the interrelationship of non-tribosphenic theria. Bulletin of the American Museum of Natural History 167:281-325.

Simpson, G. G. 1926a. The fauna of Quarry Nine. American Journal of Science 12:1-11.

Simpson, G. G. 1926b. American terrestrial rhynchocephalia. American Journal of Science 12:12-16.

Simpson, G. G. 1927. Mesozoic mammalia. VI. Genera of the Morrison pantotheres. American Journal of Science 13:409-416.

Simpson, G. G. 1928. Mesozoic mammalia. VII. Taxonomy of Morrison multituberculates. American Journal of Science 14:36-38.

Want to ask a question? Visit the Message Board

Virtual Poster Session Message Board
Here you can to read other messages and comments, post your own message or comment, and then receive feedback from the RTP participants.

Research Training Program
Schedule of Events | Poster | Student Abstracts | Photo Gallery
Virtual Poster Session

The information presented here represents preliminary research as the result of ten-weeks of investigation in-residence at the National Museum of Natural History. This is not an official publication of the information.

As preliminary information, results and/or findings should not be cited as part of conclusive work. Please contact the authors first if you wish to utilize the information presented here.


	Highlights

Research Training Program VIRTUAL POSTER SESSION 2004

Research Training Program
VIRTUAL POSTER SESSION
2004