Lab5_Excavation Stage I 2

DINOSAUR EXCAVATION STAGE I Part I: Excavation Stage I - Pelvic Girdle and Hindlimb A new fossil site has just been excavated and you are on the team that must identify what has been found. In the next 4 laboratory assignments you will examine different portions of the skeleton and use anatomical clues to narrow down the possible identity the fossil. After completing all 4 assignments, you will be placed in groups to compare your evidence and create a consensus report on your findings. • Find Your Bearings. Below is “site map” image of the excavation site(s). These images, and others you will need to complete this assignment, are available at https://sites.google.com/tamu.edu/geol-207-dinosaur-world-ex1/home . An arrow is labeled in the top right corner of your image indicating the direction of North. On your site map image, each bone has been numerically labeled. • Identify and Catalog the Bones: use the Table 1 below to catalog the bones recovered during the excavation. For each numbered bone, you should identify the type of bone and the region of the body the bone is from (for this lab, “hindlimb” and “pelvis” are appropriate terms for skeletal region). Under notes, provide any features present that are important sharded derived characters that could help you in your identification. You should also provide an approximate measurement for each bone marked with a * using the scale bars on the zoom-in photos available at https://sites.google.com/tamu.edu/geol-207-dinosaur-world-ex1/home . Table I. Bone catalog for Excavation Stage I. (5 pts) Bone Number Bone Identification Skeletal Region Measurements Other Notes Length (cm) Width (cm) 1* Femur Hind Limb 80 20 2* Tibia Hind Limb 80 10 3 Fibula Hind Limb -- -- 4* Tarsometatars us Hind Limb 50 15-20 5 Ungual Hind Limb -- -- 6 phalanges Hind Limb -- -- 7 phalanges Hind Limb -- -- 8 phalanges Hind Limb -- -- 9 phalanges Hind Limb -- -- 10 Ungual Hind Limb -- -- 11 phalanges Hind Limb -- --

12 phalanges Hind Limb -- -- 13 phalanges Hind Limb -- -- 15 phalanges Hind Limb -- -- 16 phalanges Hind Limb -- -- 17 Ungual Hind Limb -- -- 18 Pubis Pelvic -- -- 19 Ischium Pelvic -- -- 20 Ilium Pelvic -- -- 21 Calcaneum Hind Limb -- -- 22 Astragalus Hind Limb -- -- • Interpreting the Skeleton (7 pts) • Having identified the bones present in your specimen, list the order of the hindlimb bones starting with the bones that are most proximal (closest) to the pelvic girdle. (2 pts) Terms to use: tibia and fibula; tarsometatarsus; phalanges; astragalus and calcaneum; femur; ungual • Femur • Tibia & Fibula • Astragalus and Calcaneum • Tarsometatarsus • Phalanges • Ungual • Considering the bones that are present in these regions in the living animal, how complete is this specimen? (1 pt) I would say all the components are completely present. • Bones 21 and 22 of our organism represent the ankle bones. What type of ankle configuration does our organism have? (Appropriate terms could be “ crurotarsal ankle” like in the left figure or “ mesotarsal ankle” like in the right figure. The red line in each is the plane of the ankle hinge). (1 pt) This appears to be a mesotarsal ankle. • What features are present in this portion of the skeleton that make you confident this fossil is a dinosaur? Consider the shared derived characters that are unique to Dinosauria and are not present in other groups. (1 pt) Something that makes me sure is you can see that this specimen has an open acetabulum, which is unique to dinosauria.

• Ripple Marks: ____windy_________ • Trackways: ______close to a body of water or an area with shallow water_________ • Many different types of rocks are found within this field site, including siltstones, limestones, and evaporites. Given this evidence, make a claim about the depositional environment and provide your reasoning. (1 pt) This sounds like it was an area with lots of movement where many stones were carried through. Thus, it was probably a very windy, arid desert. • Some fossils can be used as an indicator of the depositional environment. Within the field site, you find a few fish fossils similar to the fish bones found at the Green River Formation. Given this evidence, make a claim about depositional environment and provide your reasoning. ( 1 pt) This was probably once a river or a body of water before it dried up into a desert. Fish live in water and the mudcracks prove this was once a body of water. • Given all the geological evidence in #1-3, make a claim about the most likely depositional environment and provide a well-reasoned argument. ( 3 pts) The depositional environment was probably a former river that is now a desert. This is clear because ripples are caused by movement from wind, mudcracks are a sign of a dried up body of water, and trackways form near bodies of water, all of which are present at the site. Additionally, the variety of rocks prove that there was lots of movement in this area from wind eroding rocks and depositing them here. Lastly, the fish fossils prove that this area was once a body of water that is no longer wet.