Lab5_Excavation Stage I

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. 1) 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.

2) 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 Lower Leg 80 12 2* Tibia Lower Leg 80 10 3 Fibula Lower Leg -- -- 4* Tarsals Foot 55 15 5 Distal Foot -- -- 6 Medial Cuneiform Foot -- -- 7 Metatarsal Foot -- -- 8 Phalanges Foot -- -- 9 Distal Phalanx Foot -- -- 10 Distal Phalanx Foot -- -- 11 Intermediate Cuneiform Foot -- -- 12 Metatarsal Foot -- -- 13 Phalanges Foot -- -- 14 Distal Phalanx Foot -- -- 15 Lateral Cuneiform Foot – – 16 Proximal Phalanges Foot -- -- 17 Terminal Phalanx Foot -- -- 18 Pubis Appendicular Skeleton -- -- 19 Ischium Appendicular Skeleton -- -- 20 Wing of ilium Appendicular Skeleton -- -- 21 -- -- 22 -- --

e) Examine the hip and the orientation of the pubis. What type of hip is present in this specimen? (1pt) It looks like it has a saurischian hip. f) How many functional digits are there on the foot? (1pt) There are four functional digits on the foot. 4) Evaluate your evidence to reach a preliminary identification (10pts) Below is a phylogeny depicting the major groups of dinosaurs. The letters depict possible positions of shared derived characters on the phylogeny. Describe where the shared derived characters you came across when examining the pelvis and hindlimbs would fall on the phylogeny using the letters. [You should have at least 4 characters to place from #3.] (4 pts) A: Three toed hind foot B: forward pointing pubis C: longer femur than tibia D: Metatasals that are fused together

Given the evidence you have so far, what clade of dinosaur do you have? State your claim (the clade), list your evidence, and explain your reasoning. (6 pts) Given the evidence I think I have a dinosaur of the saurischian clade. My evidence is that the dinosaur has a three-toed hind foot, the dinosaur has a forward-pointing pubis, and the dinosaur has a femur that is longer than the tibia. My reasoning is that all of these characteristics are shared only with the saurischian clade. 5) Interpreting the Depositional Environment (8 pts) Sedimentary structures are geologic features of the substrate that were preserved and provide evidence for the environment of deposition ( e.g., streams, deserts, etc). Use supplementary table 1 to answer the following questions: 1. A few sedimentary structures discovered at the dig site are mud-cracks , ripple marks , and trackways. In what type of environment would we expect to see each of these sedimentary structures? (3 pts) a. Mudcracks: Wet and dry conditions. b. Ripple Marks: Environments with a lot of water flow. c. Trackways: Environments near bodies of water. 2. 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) Siltstones are fine-grained sedimentary rocks that may form in a variety of aquatic environments, such as lakes, rivers, and shallow seas. They describe a sediment-rich environment with slow water movement. Limestones are usually associated with seaside locations. 3. 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) The discovery of this fish suggests a freshwater or lake environment. 4. 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 information suggests that the environment around freshwater lakes fluctuates between wet and dry conditions. Trackways, ripple marks, and mudcracks are all proof of changing water levels and sediment interaction. the fossils of the fish indicate a freshwater environment. Rather than being entirely marine, limestone formations most likely reflect the impact of shallow waters or estuaries. Any dry environment is ruled out by the lack of large evaporites. Overall, the data point to a freshwater lake.