FINAL 4 MINI ASSIGNMRNT

Mini Assignment 4: Phylogenetic Trees with Sauropodomorphs Phylogenetics is a fascinating area of study that traces the evolutionary history and relationships among individuals or groups of organisms. Imagine it like a detective story, where scientists piece together clues from fossils, genetics, and other evidence to unravel the intricate web of life's history. This history is often depicted in a diagram known as a 'phylogeny', a kind of family tree that shows the relationships between different species or groups. For this mini-assignment, we'll be delving into the world of the largest land animals that ever lived: the sauropodomorphs, a group of long-necked dinosaurs that included famous members like Brachiosaurus and Diplodocus. You'll be given an existing phylogenetic tree, a sort of dinosaur family tree, which was created based on the current understanding of how these giants are related to each other. Using character information, you will place additional taxa on the tree and map how size evolved across the sauropodomorphs. This exercise will not only help you understand the fundamentals of phylogenetics but also expose you to the dynamic and ever-evolving nature of scientific knowledge. Below is the phylogenetic tree we will use in this assignment. This diagram corresponds to the current understanding at large about relationships among sauropodomorphs. Each branch leading to a branching node has been labeled with a letter. See the next page for a table that gives the name of the taxonomic group this branch corresponds to, and the derived characters (synapomorphies) that denote a typical member of that group. Figure 1. Phylogeny showing relationships among 12 sauropodomorphs.

Table 1. Character Changes and Branch Details Node Label (Clade) Corresponding Name of Clade Typical Derived Characters of This Clade A Gravisauria Quadrupedal limb proportions (forelimbs as long or longer than hind limbs) B Eusauropoda Metacarpal bones in forelimb become U-shaped cylindrical pillar, wrist becomes locked in place. Most lose most front toe bones except for a single large ‘ungual’ claw. C Neosauropoda Laterally flared ilia (hip bones) to expand gut space. Teeth shift to front of mouth and now occlude (for browsing rather than chewing). Loss of external mandicular fenestra in jawbone. D Diplodocoidea Loss of suture between pre-maxilla and maxilla in skull. Most descendants have flat snout end. E Flagellicaudata A new depression in the skull in front of the eye sockets (Preantorbital fossa). Most members of this group have long whip-like tails, but not all. F Macronaria Very large naris (openings for nostrils) on the top of their skull, larger than their eye orbitals. G Titanosauriformes The large air cavities in presacral neural arch become more finely divided, about 1-cm in scale. H Somphospondlyii Presacral neural arch pneumatization is very spongy and finely divided, less than 1-cm in scale. I Titanosauria Loss of all front toes, extra-wide flared hips, a gracile (skinny) humerus, and many titanosaurs are found with remains of osteoderms, small bony lumps that formed in their skin. The tail becomes short and connections between caudal (tail) vertebrae become rounded (‘procoelus’). J Lithostrota ? Extra wide cervical vertebrae. Most titanosaurs with osteoderms are in this group, but not all.

 Long neural spines on posterior vertebrae.  A ‘skinny’ humerus  Fragments of a very wide pelvic girdle Which is the sister taxon you chose? The sister taxon I chose for Argentinosaurus is Patagotitan. Was there another sister taxon you considered? Which? A potential sister taxon could be Sauroposeidon. 4) Explain what characters or morphological traits you used to place Argentinosaurus. What character information led you to place it where you did? What uncertainties did you have in your placement? The Argentinosaurus shares many characteristics such as cervical vertebrae with tiny air cavities, long neural spines on posterior vertebrae, a 'skinny' humerus, and fragments of a very wide pelvic girdle. The fragmentary remains of the dinosaur has caused some uncertainty.

Figure 2. Use this tree to show how you think Apatosaurus, Argentinosaurus, and Mamenchisaurus might relate to other species of sauropodomorph dinosaurs.

Table 2. Taxon Information Regarding Size, Dentition, Ecology, Preservation. Genus Estimated Mass Neck Length Teeth Shape Notes Plateosaurus 600 – 4000 kg ~2 m Leaf-Shaped Bipedal Vulcanodon 3000 – 4000 kg 2 – 3 m Unknown Early quadrupedal sauropodomorph from South Africa. No skull known. Cetiosaurus 9000 – 18000 kg 5 – 7 m Spoon-like No skull known, but some teeth found along other bones. Nigersaurus 3000 – 5000 kg 2.5–3 m Pencil-like No side teeth, front teeth are arranged into teeth battery where they were constantly replaced. Regained mandibular fenestra. Amargasaurus 2600 – 5000 kg 2–2.5 m Pencil-like Has long, paired neural spines. Diplodocus 10000 – 15000 kg 6–7.5 m Pencil-like Had a single row of long neural spines. Camarasaurus 15000 – 23000 kg 5 – 6 m Spoon-like Brachiosaurus 28000– 62000 kg 9–12 m Chisel-like Only known from very fragmentary finds – close relative Giraffatitan is more complete and used in its place. Sauroposeidon 40000 – 60000 kg 11–12 m Unknown Thought to look very similar outwardly to brachiosaurs. No skull known. Patagotitan 55000 – 77000 kg 8–11 m Unknown Had long posterior neural spines. No skull known. Alamosaurus 50000 – 73000 kg 7 – 9 m Peg-like Abundantly known from the end of the Cretaceous in North America. However, no skull known. Saltasaurus 6800 – 7800 kg 3 – 4 m Peg-like Apatosaurus 16000 – 22000 kg 7–8.5 m Chisel-like Argentinosaurus 70000 – 100000 kg 7–10 m Unknown Very fragmentary remains – no skull known, only vertebrae, legs, hip. Mamenchisaurus 13000 – 15000 kg 9–11 m Spoon-Like Description of Teeth Shapes Chisel-like: Spatulate teeth with a flat, rounded end, like a chisel. Leaf-shaped: Broad, spatulate teeth with multiple ridges or points, like a pointed leaf. Peg-like: Short and cylindrical teeth. Pencil-like: Long and cylindrical teeth. Spoon-like: Spatulate teeth with a rounded bowl-like depression.

Notice that these definitions aren’t very precise. In particular, the line between peg-like and pencil-like is vague. Keep in mind which shapes are probably easier to ‘evolve’ from other sauropod teeth shapes.

8) You should notice that evolution of sauropod tooth shape seems to follow a particular sequence of change from one tooth morphology to another, with no apparent reversals. This trend can be observed occurring independently in both the Diplocoidea and the Macronaria. What selective pressures might be driving the evolution of tooth shape? (Note: Please remember that all sauropods are strongly believed to be herbivores.) 9) Texas sauropod tracks from the Cretaceous (A, on the left) are known for being wide-gauge, with some distance between the left and right trackways, unlike Jurassic trackways (B, right example, from Portugal). Look over at your phylogeny and the character data, and consider what this implies about the physical traits of different sauropod lineages. Which traits might reflect having a wider body? Which lineages might have those traits, and thus indicate which sauropod lineage is the wide- gauge track maker?

The wide tracks of the Texas Sauropod from the Cretaceous suggests that the dinosaurs had broader bodies compared to the Jurassic Sauropods. This also implies that they likely had sturdier limbs and a bigger structure to support their increased mass. Sauropod lineages are known for their large size, dinosaurs like the Titanosaurus and Diplodocids are candidates for being the wide track makers. What additional evidence in the trackways you might look for to verify your hypothesis of which sauropod makes the wide-gauge trackways? Evidence in the trackways such as the consistency in trackway width, depth of tracks, associated fossils, and comparative analysis with other trackways, could verify the hypothesis of which sauropod makes the wide trackways.