Reconstructing the arrival of Dinosaurs
| Puede leer un artículo del periódico Inglés The Observer sobre la expedición 2001 | ||
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2002 DATES IN THE FIELD: Team Team I: Sep 1-13 Team II: Sep 15-27 Team III: Sep 29-Oct 11
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For more information please check
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Ischigualasto Provincial Park,
Argentina—If you
You'll prospect the sandstone and claystone formations for fossils (which often lie right on the surface), excavate and map the finds, wrap specimens in plaster, screenwash sediments, catalogue plentiful bones, and map geological features. Your leaders are ideally equipped to introduce you to this ancient landscape, training you in the details of orientation with a compass, GPS mapping, geologic features, and reptilian anatomy and taxonomy.
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RESEARCH PLAN
RESEARCH PLAN Our goal is to contribute to the knowledge of the early history of dinosaurs, crocodiles and mammals. The early Mesozoic era, and especially the Upper Triassic, was a critical period in the evolution of life on land. Most of today’s major groups of terrestrial vertebrates (mammals, crocodiles, turtles, lizards, frogs, salamanders, etc.) originated, and dinosaurs and pterosaurs rose to prominence during this period. In recent years this period in the earth’s history has received a great deal of attention, and, in particular, it is now believed that the small vertebrates that lived in the shadows of the first dinosaurs can tell us a great deal about the evolution of what might be termed modern terrestrial ecosystems. The early part of the Triassic was basically a continuation of the Permian, dominated by synapsids, especially cynodonts, in the herbivore and carnivore ecologies. The Middle Triassic was a transition between the synapsids’ dominance to the archosaurs’ dominance. In the late Triassic the synapsids’ dominance declined, and the world was full of archosaurs, including the earliest dinosaurs. Triassic continental sediments that contain vertebrate fossils are rare, thus the importance of the Ischigualasto Basin, which contains a continuous sequence of fossil-bearing continental sediments from the Middle Triassic Chañares Formation and the Los Rastros Formation, through the Upper Triassic Ischigualasto and Los Colorados. In 1958 a joint expedition from Harvard University and the University of La Plata directed by Alfred S. Romer and Rosendo Pascual, discovered the highly fossiliferous nature of the Ischigualasto Basin. Subsequent exploration and research by the University of Tucumán, University of Chicago and the University of San Juan has produced hundreds of specimens. The Ischigualasto Basin documents, especially the changes in evolution and faunal replacement during the Middle Triassic to the end of the Late Triassic, and probably the transition to the Lower Jurassic. A diverse assemblage of fossil vertebrates has been discovered in the Ischigualasto Basin. The fauna includes a very unique “transition fauna” from the Middle Triassic Chañares Formation, a diverse Carnian fauna which includes the most primitive and oldest dinosaurs from the Ischigualasto Formation (228 m.y). At the top is the Los Colorados Formation which documents the latest Triassic faunal assemblage and probably the topmost level in the transition to Lower Jurassic faunas. In addition to scientific interest, there has been a popular and governmental response to the discoveries. Ischigualasto is a harsh but beautiful valley, nicknamed Valley of the Moon, consisting of white and variegated sandstone and claystone, dominated by 500 foot high red cliffs. The total extent is about 5 miles wide and 40 miles long. In 1941, the provincial government of San Juan declared the area a Provincial Park and designated The Museum of Natural History and the University of San Juan as the controlling institutions for research and custody of fossil material. The park is a popular tourist site as well as a principal area of paleontological research. So critical is Ischigualasto to our understanding of archosaur and mammal evolution that this park not only has gained national protection but also has recently been recognized as a World Heritage Site by UNESCO. Six years of Earthwatch supported fieldwork has significantly increased the number of important fossils recovered from the Triassic of Ischigualasto, including a new species of a gracile theropod closely related to the primitive Eoraptor, new specimens of primitive dinosaurs (Herrerasaurus and Eoraptor), the first discovery of infant rhynchosaurs grouped together, two new species of primitive archosauriphorms closely related to the Middle Triassic Chanaresuchus, the first record of postcraneal remains of the proterochampsid Proterochampsa, two new specimens of the rare poposaurid Sillosuchus, a skull of a new carnivorous cynodont and several partial skeletons of aetosaurs. All this findings are contributing to better understand the evolution of these groups and complete our picture of the biodiversity during the Triassic. Graduate students have realized a big part of the descriptions, analysis and interpretation as part of Masters and PhD thesis, so this project has a great impact in education and professional training. Besides the discoveries of new species or new elements of known species, we collected one of the most complete collections in the world of rynchosaurs and cynodonts. Many of these specimens are complete and exquisite preserved skeletons, they are already part of the permanent exhibit of the Museo de Ciencias Naturales in San Juan and also part of traveling exhibits. The Ischigualasto Basin is huge and extremely rich, and the fast erosion provides hundred of new specimens every year, so our work in these outcrops will never end. • Continuous exploration for new species and better-preserved specimens of known forms in the south part of the Ischigualasto Basin near “Agua de la Peña” where the classic locations of the Carnian Ischigualasto Formation are (see map). We will prospect carefully the bottom of levees and crevasse splay channels looking for transported small vertebrates remains and microfossils. We will also prospect the northern outcrops of this Formation near to “La Chilca” (see map). This area has been unprospected for more than 30 years. • Exploration for paleovertebrates in the Los Colorados Formation, especially the middle and upper part of the section. We will prospect with more detail the reduced areas of overbanks deposits, which are in the south of the basin and the north areas known as “Los Jachaleros” and “La Esquina” (see map). The upper part of the formation will be followed laterally in all its extension south-north to determine the existence of Lower Jurassic sediments laying on the top of the Los Colorados Formation. There is no clear information about the exact location of many taxas collected during the last 20 years in the top of the Formation, but the faunal assemblage shows a mixture of Upper Triassic and Lower Jurassic association. • Careful exploration of the transition zone between Ischigualasto and Los Colorados Formation in “La Chilca” area (see map). This is the only part of the basin where paleovertebrates remains were sited in the transition zone. The potential faunal assemblage of this part of the section will give us very important information about the faunal replacement and possible extinctions between the Carnian and Norian. • Gathering sediments for washing and acid treatment as part of the search for microfossils (pieces and fragments of very small individuals of any taxa). We hope to find mammal teeth or small fragments of lizards or amphibians. It is important to note that until recently, no microvertebrates were found in the Ischigualasto Basin. For this reason, we will try exploring different kinds of layers this season and will treat sediments from the Los Colorados Formation for the first time. • Detailed description of fossils in situ and their relationship to the sediments and structures of the layer in which they were found. The description of the skeletons should include, detailed drawings of the specimen, taxa identification, type of preservation, parts of the skeleton found, examination for signs of transportation or action of predators, and description of the surface of the bones to detect weathering before burial. (If the remains where transported we will measure the direction of the current.) The architectural arrangement of the layers where the fossil were found will be described, photographed and mapped. • Detailed mapping of all the paleovertebrate remains found using aerial photographs (scale 1:500) and transparencies. We will use GPS to position all the collected remains. • Exploration for more volcanic ash and basalt layers in the Ischigualasto and Los Colorados Formation. The ashes will be dated using Ar/Ar and the basalts using U/Pb. At present, we have just one trustworthy radimetric date from the bottom of the Ischigualasto Formation, which gives us an age of 228 million years. The exact age for a different part of the section of the Ischigualasto Basin will allow us to determine rates of depositions, global biostratigraphy and correlations with Triassic faunal assemblages from Brazil, USA, China, Europe and Africa. • Detailed documentation and sampling of distribution, nature, architecture, and carbonates of paleosols in the Ischigualasto Formation. Documentation of occurrence and distribution of plant megafossils in the Ischigualasto Formation. Lab analysis of paleosol carbonates to be completed after the field season. All of the data will be used for the paleoclimatic interpretation of the Ischigualasto Formation. Our methods are those standard for geology and paleontology. Geologists will do detailed vertical cross sections using a Jacob Stake, a Brunton compass, a geologic hammer, geologic magnifier glasses and a waterproof field book. We will map on base maps and aerial photos and GPS. Fossils, when discovered by volunteers, will be marked with toilet paper and mapped using a GPS. PIs will check all the findings at the end of the day or the next day. PIs will determine the finding’s importance, and later an extraction list will be made. The fossils to be recovered will be uncovered using brushes and pick or dental tools, then sealed with hardener (lacquer or very thin superglue). Then, they will be protected with aluminum foil and covered with plaster jackets, labeled and catalogued. Most of the time, the extraction will involve the use of heavy hammers, chisels and a power cut saw (saw is not to be operated by volunteers). Vertebrate Paleontology and probably Paleobotany will be the principal beneficiaries of the results of our research. Sedimentary geology and basin analysis will also benefit from our work. Our work has had a positive effect on public policy with regard to preservation of fossil sites. Ischigualasto is the first public park in Argentina to be created on the basis of its paleontological importance. The publicity resulting from discoveries made here has had a significant effect on the public’s awareness of fossils. The Museum has an active School Service division, which will benefit directly from our field work. The increase in specimens makes it possible to loan material to other institutions for display and to make a traveling exhibition to take to schools. 4.1. Scientific Contributions and Thesis 4.1.1 List
of papers and presentations thanks to Earthwatch support: Sereno P., Martínez
R. and Alcober O. A. 4.1.2. Ph.D.
and Master’s Thesis supported by Earthwatch:
1995 López, Sergio
1996 Alcober, O. A.
4.1.3. Ph.D. and Master’s Thesis in progress supported
by Earthwatch:
____ Heredia, Guillermo The following topics will be covered: · Mapping on air photos and base map · Basic anatomy of tetrapods, especially basic anatomic features to be recognized in the specimens (general archosaurs morphology, dinosaurs, cynodonts, mammals and rynchosaurs). · Different techniques to prospect and find fossils. How to differentiate fossils from concretions. How to mark and catalogue fossils. How to protect and recover vertebrate fossils. · Recognition of geologic features, such as paleosols, paleochannels, faults. Differences between alluvial and lacustrine environments. Sedimentary structures such as cross beddings, concretions, patches, roots, etc. · Basic introduction to archosaurs and synapsids phylogeny and taxonomy. · How to use a GPS and compass. Volunteers will be completely integrated into the project, doing the same tasks as the professional staff members, perhaps at a more basic level. They will always be with a staff member. Work parties will consist of 2, 3 or 4 people. Teams will prospect for fossils, mark locations, map localities, gather and wash sediments, excavate and plaster specimens. Part of the team will backpack into areas of difficult access for preliminary exploration of new areas. In the evening everyone will gather and chop firewood, cook and clean up, after which we will have discussions, write in the field log, classify and catalog specimens. We strongly recommend that volunteers have previous camping experience. Knowledge of Spanish is useful but not essential. Principal
Investigators
Ricardo Martínez,
Mr.D., age 47. Guillermo Heredia,
Mr.D., age 30. Staff
Assistants |
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wanted to put serious money on where you might find
fossils of both the very first dinosaurs and mammals, these colorful desert
badlands would be your best bet. Why here? Because this remote valley's
bizarre eroded formations and soaring cliffs harbor the only unbroken record
yet discovered that spans the entire Triassic period, when dinosaurs first
appeared (and suddenly took over the world for the next 160 million years),
and when mammals, too, made their much more modest debut. It was also the
time when therapsids (rather clumsy, but remarkably physiologically
advanced, mammal-like reptiles) met their end. We're still living in the
wake of that event.
But what caused the change? How and why did
dinosaurs come to rule rhe world? Why did mammals play second fiddle to
dinosuars for millions of years? With the help of Earthwatch volunteers,
palaeontologists Dr. Oscar Alcober, Ricardo Martinez, and
Guillermo Heredia (all of Universidad Nacional de San Juan and Museo
de Ciencias Naturales) have been tracking evolution in the dirt. Finds
exceeded all expectations. They've chiseled out specimens of Eoraptor (the
"dawn" or earliest dinosaur), some Herrerasaurus skeletons (another early
dinosaur), and the first known infant rhynchosaurs. "Maybe this will be the
year we find the oldest mammal," writes Alcober.
"It's only a 2-centimeter
skull in 64,000 hectares of sediment." So critical is Ischigualasto to our
understanding of reptile and mammal evolution that it has gained not only
national protection but also was just recognized as a World Heritage Site. 
Field Conditions: You'll be based in
a wilderness camp without running water and electricity (previous experience
strongly suggested). Help cook dinner with your teammates, and enjoy evening
talks around the campfire, with fine Argentinian wines. There are immensely
important discoveries to be made in Ischigualasto, and your sojourn here
will be an experience you'll savor forever.