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GEOL 110 Dinosaurs and Their World NAME: ______________________________ Homework #5 PHYLOGENETICS DUE : Start of class on Monday, 10/30/17 Brief Review of Terms used in Phylogenetic Cladistics: We can infer the evolutionary relationships among a group of dinosaurs using the phylogenetic method of cladistics, which employs parsimony to create a tree of relatedness, called a phylogeny . Remember that parsimony means choosing the simplest explanation as the most likely to be correct. In phylogenetics, parsimony makes use of characters (= traits) to find the phylogeny that most easily explains the data (the data = the distribution of traits among the organisms you are studying). Characters are expressed by organisms in character states , which are either plesiomorphic or apomorphic. The Plesiomorphic character state is the ancestral state; in other words, it is the condition seen in known ancestors. They are generally coded as a state of "0" (zero) in analyses. Apomorphic character states are derived, meaning that they differ from the condition seen in known ancestors because of evolutionary change. They are usually coded as a state of "1" (one) in analyses (Note: if there are multiple possibilities of derived states, they are then coded as states "1", "2", "3" and so on). Characters can vary in their informative value, and they can generally be categorized into the following groups: 1) A utapomorphies are derived characters unique to a single species (or clade) . This type of character is distinctive for a species (Example: the long trunk of elephants is not seen in any other animals). Autapomorphies enable us to identify species, but they tell us nothing about how species are related to one another. 2) Synapomorphies are shared derived characters owing to common descent. Synapomorphies are found in multiple species (or clades) owing to descent from a common ancestor. These are the only characters that really help us to resolve relationships among organisms. For example, if we are trying to create a phylogeny of several goat species and we observe that two of the species have long curved horns while all other goat species have short stubby horns, then it is most parsimonious to infer that possession of long horns is a synapomorphy indicating shared ancestry of the two long-horned species. 3) Homoplasies are shared derived characters resulting from independent evolution . Sometimes a trait can exist in two species (or clades) without it being due to common ancestry. For example, if we were constructing a phylogeny of animals, we would see that both birds and bats have wings, and perhaps we would think that this means that birds and bats are more closely related to each other than they are to any other animals which lack wings. In this case, we’d be incorrect because it turns out that both birds and bats evolved wings independently through convergent evolution at different times and from different ancestors. Therefore, possession of wings in birds and bats is a H omoplasy . Homoplasies can also occur due to evolutionary reversals , in which a species loses a derived character through the process of evolution. For example, both chickens and humans have extremely shortened tails, so much so that neither group has a visible tail. This homoplasy is due to independent loss of long tails in chickens and humans.

When we reconstruct a phylogeny using parsimony, we choose the tree that involves the smallest number of character state changes. In other words, the tree that requires the fewest number of evolutionary steps is the most parsimonious tree. We are basing this on the assumption that most shared derived characters are due to common ancestry, not convergent evolution. For this exercise, we will use a relatively small number of species (6) and a small number of characters, but typical datasets often involve a much larger number of species and can include hundreds or even thousands of characters. Furthermore, the number of possible phylogenies increases exponentially as we increase the number of species we’re looking at. If we were looking at 10 species, there are millions of possible relationships that could exist, and we would not be able to do this exercise by hand. INSTRUCTIONS: ⮚ Carefully review the cranial (head) anatomy of the six dinosaurs below. Look for similarities and differences between the species, including any features unique to single species. Also think about these similarities as potential characters with character states, such as the example below: Character: Horns along outer margin of the frill : 0 = absent 1 = present as small, rounded knobs 2 = present as long pointed horns ⮚ After carefully reviewing these images, proceed to answer the questions on the next page.

Which two of the 6 species above do you think are most closely related to one another, and why ? The torosaurus and the Eoceratops are the most common. Both species have three horns on the front frill. The length of the frill over the neck doesn't have many differences. The two front horns are the same length. 3) If I were to tell you that we know all 6 species above descended from Archaeoceratops , shown to the right, then which one of the 6 species would you think is the most primitive (possesses the most plesiomorphic characters)? The Leptoceratops because it has the keratinous beak Which one of the 6 species above would you think is the most derived (possesses the most apomorphic characters)? The Triceratops because it has the nasal horn and postorbital horn along with the horns on the outer margin of thefrill 4. A) After a careful survey of the 6 dinosaurs above, a paleontologist has devised the following list of characters and character states to discern their phylogenetic relationships: Ch. 1 Keratinous beak : 0 = absent 1 = present Ch. 2 A single horn rising from the nose ("Nasal horn") : 0 = absent 1 = present Ch. 3 Two horns rising from over the eyes ("Postorbital horns") : 0 = absent 1 = present Ch. 4 Horn-like structures present along the outer margin of the frill : 0 = absent 1 = present, with all of them as small rounded knobs 2 = present, with some of them being long pointed horns B) He has then begun coding these character states for the 6 dinosaurs in the Character State Matrix below. Help him fill in the rest of the Character State Matrix table below: Character State Matrix

Ch. 1 Ch. 2 Ch. 3 Ch. 4 Keratinous beak Nasal horn Postorbital horns Horn-like structures present along outer margin of the frill Leptoceratops 1 0 0 0 Eoceratops 1 1 1 0 Centrosaurus 1 1 0 2 Torosaurus 1 1 1 1 Triceratops 1 1 1 1 Styracosaurus 1 1 0 2 Now you will use the information you just gathered to discern the relationship of these 6 dinosaurs… C) Use the scorings in your Character State Matrix to fill in the branches missing in the phylogenetic tree below. The positions of Leptoceratops and Eoceratops have been provided for you, as a starting point: