MiniAssignment3 - The Biogeography of Cretaceous Sauropods

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Texas A&M University *

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207

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Geography

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Apr 3, 2024

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docx

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Uploaded by Jacobooppo

Mini-Assignment 3: The Biogeography of Cretaceous Sauropods In this assignment, we will delve into the intriguing fields of biogeography – the study of the distribution of species and ecosystems in geographical space – and paleobiogeography, the examination of biogeography over geological time using the fossil record. Understanding where different animals lived or where their remains are found offers critical insights into past ecosystems, climate conditions, and evolutionary processes. It can help us understand how these factors interacted and influenced the diversity and distribution of life on Earth. The location of a species' remains can reveal what kind of environment they lived in, their migratory patterns, and possibly even the reason for their extinction. Paleontologists have a long habit of recording the information about where fossils are found and when in time they were inferred to be deposited. The Paleobiology Database (PBDB) was designed specifically to hold this sort of information. The PBDB is a public database of global fossil data assembled by hundreds of paleontologists from around the world. It allows us to investigate geographic and temporal patterns in the history of life and make scientific inferences based on those data. In this activity, we will use the PBDB to examine the distribution of two Texas dinosaurs, Alamosaurus and Sauroposeidon, and compare their biogeography to what we know about North American geography during the Cretaceous. Completing this assignment will give you the tools you need to complete Lab 2 (Pangea Puzzle) in the upcoming laboratory module. Go to https://paleobiodb.org/navigator/ The Paleobiology Database’s Navigator web-app lets you explore the information in the PBDB in terms of the ‘when’ (age) and ‘where’ (spatial location) of fossil collections for different groups of organisms. Step 1: Map the distribution of fossils on a modern map Type in ‘Alamosaurus’ into the search box, and select the entry for that genus when it drops down (it will say ‘genus’ next to it). After doing that, you’ll see some green dots appear over North America. Click in that region of the map, and you will see that there are a number of finds from the Cretaceous. Investigate further by clicking the time intervals at the bottom (I recommend double-clicking on ‘Cretaceous’ to zoom in on this time interval) or letting your mouse pointer hover over each collection-dot. You will find all of the collections that contain Alamosaurus are assigned either to the Cretaceous (which means the age of those collections is very uncertain and poorly known), the late Cretaceous, or a geologic age within the late Cretaceous. Now type in ‘Sauroposeidon’ into the search box, and select the entry for that genus when it appears in the drop down menu. This will add Sauroposeidon to the small gray menu in the lower left corner of the Navigator map. If you have both Sauroposeidon and Alamosaurus selected (meaning both are listed in the gray menu), you can actually click ‘Early Cretaceous’ and ‘Late Cretaceous’ on the timescale at the bottom of the map to flip between the collections assigned to each dinosaur. This is because both are restricted to a particular time interval – Sauroposeidon only occurs in the early Cretaceous and Alamosaurus only occurs in the late Cretaceous. Step 2: Examine the biogeography on a paleocontinental map

Click on the button in the left toolbox that looks like continents, the collections will be re- mapped onto a paleo-map of how the continents were arranged in the early and late Cretaceous. We call this spatial mapping of locations as they would have been in the geologic past a ‘paleocontinental’ map, however, these will look very similar to modern map because North American has not changed its position much in the last 100 million years. These paleocontinental maps are based on the gplates database ( https://www.gplates.org/ ). • Use a screenshot tool or PrintScreen key to copy the Navigator map showing the distribution of Alamosaurus during the Late Cretaceous and paste it here: •Use a screenshot tool or PrintScreen key to copy the Navigator map showing the distribution Sauroposeidon during the Early Cretaceous and paste it here: Step 3: Interpret the paleobiogeography On the last page of this assignment, you will find paleogeographic maps for the early and late Cretaceous. These maps are different from paleocontinental maps in that they illustrate geographic features such as the location of oceans (shallow sea=light blue, deep ocean=dark blue), mountain belts (highlands, browns), lowland floodplains (greens). Notice that for part of the Cretaceous there was a shallow seaway in North America - this is the Western Interior Seaway. Compare the paleogeographic maps with the distributions of where paleontologists have found Sauroposeidon and Alamosaurus fossils so far and answer the questions below: • What habitats did Alamosaurus (a Late Cretaceous sauropod) seem to live in – lowlands or highlands? Near water or not near water? They seem to live near smaller bodies of water, mainly rivers. It looks like they are positioned in mountainous areas and they are almost perfectly aligned with the Rocky Mountain range. So, they appear to have preferred highlands rather than lowlands. • Did Sauroposeidon (an Early Cretaceous sauropod) live in similar or different habitats? It looks like they are mainly positioned close to water, specifically what is now the Gulf of Mexico. This is far different, and much lower than what the alamosaurus' preferred. • What changes between the Early and Late Cretaceous that might explain the differences between where fossils of these dinosaurs are found? Global warming might have been a factor which may have forced some dinosaurs to seek cooler climates in the mountains, but other factors could include sea level changes and tectonic activity that produced some of these mountains.

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