Lab5_Excavation Stage

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 of 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 Hindlimb 87cm 11cm 2* Tibia Hindlimb 81cm 9cm 3 Fibula Hindlimb 80cm 4cm 4* Tarsometatars us Hindlimb 55cm 10cm 5 Dewclaw Hindlimb 5cm 2cm 6 Phalanges Hindlimb 8cm 3cm 7 Phalanges Hindlimb 7cm 3m 8 Phalanges Hindlimb 6cm 2.5cm 9 Phalanges Hindlimb 4cm 2cm 10 Ungual Hindlimb 5cm 1cm 11 Phalanges Hindlimb 13cm 3cm 12 Phalanges Hindlimb 10cm 3cm 13 Phalanges Hindlimb 7cm 2cm 14 Ungual Hindlimb 10cm 1cm 15 Phalanges Hindlimb 6cm 1cm 16 Phalanges Hindlimb 9cm 2cm 17 Phalanges Hindlimb 12cm 3cm 18 Pubis Pelvic Girdle 60cm 10-32cm 19 Ischium Pelvic Girdle 50cm 8cm 20 Ilium Pelvic Girdle 62cm 25-30cm 21 Calcanuem Hindlimb -- -- 22 Astragalus Hindlimb -- --

f) How many functional digits are there on the foot? (1pt) 3 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) explain your Given the evidence you have so far, what clade of dinosaurs do you have? State your claim (the clade), list your evidence, and reasoning. (6 pts) I believe this skeleton to be a part of the theropod clade as it has three functioning toes and a claw on each end. This also aligns with the hip structure being oriented in the posterior direction. This means it isn’t related to the ornithodirans and the toe/foot structure is not related to the saurischians. Leaving only the theropods.

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. Mud cracks: Floodplain b. Ripple Marks: Shallow Water c. Trackways: Streams or Rivers 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) The environment is most likely a close lake or pond as the evaporites indicate there is little to no inflow. The siltstone shows that the activity in the area is minimal meaning the water is calm, so it rules out the ocean shore. Lastly, the limestone shows the possibility of shallow environments meaning ponds, shorelines, or even some lakes. 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 the depositional environment and provide your reasoning. ( 1 pt) The depositional environment is like as stated before, was most likely a small lake or pond. The size of the fish seems relatively small, which would make sense for the environment it was living in and even give possibilities of perhaps a swamp. However, without proper plant fossils, I am unsure. 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) I believe with all of the evidence that this environment was likely a dried floodplain. The activity would be too high on the ocean shore for siltstone, and the mud cracks would show that the area would be dried up. Limestone is often found in areas that previously had shallow water. The environment was previously covered by shallow water possibly a stream, pond, or floodplain, but dried up, and then the specimen was fossilized.