Lab5_Excavation Stage I (2)
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Texas A&M University *
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Course
207
Subject
Geology
Date
Apr 3, 2024
Type
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5
Uploaded by AdmiralFogEchidna34
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* 2* 3 -- -- 4* 5 -- -- 6 -- -- 7 -- -- 8 -- -- 9 -- -- 10 -- -- 11 -- -- 12 -- -- 13 -- -- 15 -- -- 16 -- -- 17 -- -- 18 -- -- 19 -- -- 20 -- -- 21 -- -- 22 -- -- Hindlimb
80
20
Femur
70
10
Hindlimb
Tibia
Two separate balls at the end of bone that are classified as two separate bones
Fibula
Hindlimb
Skinnier bone of the hindlimb
Tarsometataursus
Hindlimb
50
10
Biggest bone with the phalanges
The largest bone of the three longer ones
Dewclaw
Hindlimb
Smallest claw separated from other claws
Phalange
Hindlimb
Pelvic
Pelvic
Pelvic
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Hindlimb
Ungual
Ungual
Phalange
Phalange
Phalange
Phalange
Phalange
Phalange
Phalange
Phalange
Astragalus
Calcaneum
Pubis
Ischium
Ilium
Longer and straight edged
Posterior orientation- Saurischian
Has a serrated edge along the bottom
3) Interpreting the Skeleton (7 pts)
a)
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 a.
b.
c.
d.
e.
f.
b)
Considering the bones that are present in these regions in the living animal, how complete is this specimen? (1 pt)
c)
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)
d)
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)
e)
Examine the hip and the orientation of the pubis. What type of hip is present in this specimen? (1pt)
f)
How many functional digits are there on the foot? (1pt)
Femur
Tibia and Fibula
Phalanges
Tarsometatarsus
Ungual
Astragalus and Calacaneum
This is a mesotarsal ankle since the bone reflects the configuration shown in the right figure.
All the bones that make up the hindlimb and pelvis are present, therefore it could be infered that the specimen is complete. The regions presented are in fact complete
The shape of the phalanges, presence of claws, and the proof of the specimen being "lizard hipped" make me confident that the fossil is a dinosaur.
The pelvis is lizard-hipped so that would make the specimen part of the Saurischian orientation.
There are 4 functional digits on the foot presented.
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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) 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)
The pubis being posterior oriented would fall under the letter 'F'. The specimen having a specialized ankle joint falls under the letter 'A'. The phalange formula falls under that of a sauropod so it would be categorized under the letter 'G'. The specimen having 4 digits falls under the letter 'B'.
The clade of dinosaur I believe this specimen falls under is Sauropoda. This is mainly due to the orientation of the pelvis and the phalange formula. The pubis was in the posterior direction which classified it under Saurischians which contains only sauropods and theropods. Also the phalange formula of sauropods is 2-3-4-5-1 and the specimen presented follows that formula almost exactly.
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: _______________ b.
Ripple Marks: _____________ c.
Trackways: _______________ 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)
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)
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)
Hot, desert climates
Environment with a large body of water or water surrounding it
Flat and dry environments
Considering the rocks found in this site and the structures found at the site leads me to believe that this environment was once an ocean or body of water. This is because most of these stones are found within water environments so I imagine it dried out leaving behind the mud and dryness which provided the sediment found.
These fish bones found further proves my claim about this environment once being a body of water but it helps to narrow it down even more. Since these bones are similar to those found in a river formation we can infer that this environment maybe wasn't an ocean but instead was a lake or river.
Due to all the evidence provided, I believe that this depositional environment was once a lake or river. This is because the sedimentary structures show signs of water once being there such as mud, sand, and ripples. The types of rocks found such as siltstones and limestones are more commonly found in bodies of water. Lastly, the fish bones found were similar to those that were found in a river formation, which proves that the body of water was more than likely a smaller one. With all this evidence presented together, it could accurately be assumed that this environment once held a body of water.