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 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 a “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 shared 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 80 cm 10 - 15 cm larger and long 2* tibia hindlimb 70 cm 10 cm larger next to fibula 3 fibula hindlimb -- -- thinner part of the shin 4* tarsometatarsus hindlimb 53 cm 16 cm thick 5 ungual hindlimb -- -- pointy and nail like 6 metatarsals hindlimb -- -- larger 7 phalange hindlimb -- -- smaller 8 phalange hindlimb -- -- smaller 9 phalange hindlimb -- -- smaller 10 ungual hindlimb -- -- pointy and nail like 11 metatarsals hindlimb -- -- larger 12 phalange hindlimb -- -- smaller 13 phalange hindlimb -- -- smaller 15 metatarsals hindlimb -- -- larger 16 phalange hindlimb -- -- smaller 17 ungual hindlimb -- -- pointy and nail like 18 pubis pelvis -- -- T like 19 ischium pelvis -- -- smaller facing the opposite direction 20 ilium pelvis -- -- largest pelvis bone 21 calcaneum hindlimb -- -- smaller 22 astragalus hindlimb -- -- slightly bigger

f) How many functional digits are there on the foot? (1pt) There are three that are present. 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: the mesotarsal ankle B: upright femur or non-sprawling F: Pelvic girdle and anterior pubis direction H: three claws 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) With the evidence we have so far, my claim would be that this is a theropod as we’ve found all the attributes that would make up a theropod. The mesotarsal ankle and non-sprawling femur are characteristics that both the archosaurs and the ornithodirans share. Then there is the anterior pelvis which is found in the saurischians. All those three traits as well as the three claws found are all shared within a theropod.

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: _ dried streams, swaps, tidalflats, flood plains, lakes and arid deserts b. Ripple Marks: _streams, swaps, deltas, lakes and tidalflats_ 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 had water in it whether that was a lake, river or floodplain in which all of these types of rocks can be found. Silstones, limestones and evaporates can be created by waterways or formed from what once was a water way. Each of these rock types is created by the removal of water, so one day before the stones were made there was water bringing in minerals that compacted together and had water precipitate out of it creating the rock found in the environment today. 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) These fossils can be found within highly wet and pressurized environments. Oftentimes these fossils are preserved in sedimentary rock which can be formed by the disposing of sediment and the cementation over many years. As the fossil sank under ground and as the water that was once there evaporated, the fossils were continuously preserved and imprinted. 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) Lakes would probably be the most accurate depositional environment where all of this evidence can be found. Because of the wet and high pressure environment each of the rocks and the fossil could be formed in this area, as well as fish being a primary animal found within this environment. If I had to guess, there would be a river that flowed into this lake bringing in more and more minerals to form the siltstones and limestone, and not to mention covering the fish fossils sinking them further and further into the group and continuously pressuring them. Over time we could discover this evidence as the lake would need to have evaporated exposing what we have found.