Vertebrate Evolution Lab: From Gnathostomes to Archosaurs

Name______________________________ TA:___________________ Section Time:___________________ Earth 7: Dinosaurs LAB 3: Vertebrate Evolution: Gnathostomes to Archosaurs In this lab we’ll look at vertebrate evolution from amniotes to ornithodires; in the next lab we start looking at dinosaurs themselves. It’s important to keep in mind the hierarchical nature of a cladogram; a particular group possesses its distinctive evolutionary novelties as well as those of all the more inclusive groups of which it is a member. A crocodile is an archosaur, as well as an amniote, a tetrapod, a gnathostome, etc. When we ask you to determine what group a particular animal belongs to, always make sure that your answer is as specific as the diagnostic features allow.

2 1. Here you see three different gnathostomes. In answering the questions below, be as specific as possible , using the TAXON NAMES on Cladogram 1. a. To which taxon does specimen A belong? (2 pts) b. To which taxon does specimen B belong? (2 pts) c. To which taxon does specimen C belong? (2 pts) d. Draw a cladogram illustrating the relationships among these three animals (and ONLY these three animals). (4 pts) 2. a. Based on the visible skull characters, to which group do these two animals belong? (2 pts) b. Sketch one skull and label the evolutionary novelty on which you base your answer. (4 pts) 3. a. This is a skin impression of Lambeosaurus , a duck-billed dinosaur (hadrosaurid). This kind of skin provides an impermeable (waterproof) barrier. What are the advantages of having this kind of skin? (2 pts) b. What group is characterized by this evolutionary novelty? (2 pts)

3 4. Here are the skulls of two “early tetrapods.” Note the presence or absence of temporal fenestrae—what is the term for the skull condition possessed by these animals? (2 pts) 5. a . This is an alligator skull . Look behind the eye sockets, along the side and top of the skull, and note the presence or absence of temporal fenestrae . What is this skull condition called? (2 pts) b . Are alligators archosaurs? (2 pts) _____________________ c. Is the archosaur clade characterized by antorbital fenestrae? (2 pts) ___________________ d. Does the alligator have antorbital fenestrae? (2 pts) ____________________ e. Your answers in parts b-d are seemingly inconsistent with expectations. What accounts for this inconsistency? (3 pts) 6. a. This specimen is a cast of a juvenile Dimetrodon from West Texas. Based on information visible on the skull could this specimen be a dinosaur? Why or why not? (3 pts) b. If not, to what group does it belong? (2 pts) 7. a. The image below shows a dorsal (top) view of a sauropod dinosaur. Below that, please draw an equivalent dorsal view of the lizard skeleton in from of you, paying close attention to the features that are visible from above (you don’t need to take too much time or include lots of detail; a simple stick figure with the appropriate posture will do). (4 pts)

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4 b. Besides the fact that sauropods have longer necks and relatively smaller heads than lizards, identify the difference in posture between these two animals. (2 pts) 8. This is Tylosaurus , a Mesozoic sea dwelling lizard (mosasaur). Draw this specimen and label 2 things you observe within this fossil. (Hint: Lizards are members of the lepidosaur group.) (4 pts) 9. Compare the overall body shape of Ichthyosaurus , a Mesozoic sea-dwelling reptile, to that of a dolphin. Is the similarity in form between these two animals due homologous or convergent evolution? (2 pts)

5 Clade Evolutionary Novelty + Advantages Vertebrates Skull - protects brain and orbits of the eyes Vertebrae - skeletal rigidity Gnathostomes (Jawed vertebrates) Jaws - wider range of food; predation and defense Pelvic fins - swimming more powerfully through water Osteichthyes (Bony fish) More bone in skeleton → ray fins - faster swimming, better mobility Air sacs - swim bladder for buoyancy (floating in the water) Fleshy-limbed “fishes” Fleshy limbs - muscular paired fleshy fins for swimming control Tetrapods Vertebrae with struts and robust hips attached to spine - supports movement on land Four limbs with fingers - supports aquatic to terrestrial transition Stapes - changes to inner ear for better hearing Amniotes Amniotic egg - fluid-filled membranes; allows the embryos to survive out of the water Internal fertilization - fertilized egg is protected from predators and harsh environments (higher chance of survival) Waterproof skin - prevents desiccation (minimizes water loss) Clade Evolutionary Novelty + Advantages

6 Reptiles Two temporal fenestrae - increase the area and improve the alignment or the attachment of major muscles in skull & jaw Beta-keratin scales - robust scale and/or feather formation Archosaurs Thecodonty - teeth in sockets of bone for eating, predation Antorbital fenestra - associated with the nasal passage and likely housed an air-filled sac, lightening the skull's weight Manidubular fenestra - lengthening the jaw, speed for prey capture Upright posture - narrow track gait, limbs under body instead of sprawled Ornithodires Digitigrade stance - walking on toes, increases stride length (like cats and dogs!) Mesotarsal ankle - hinge joint to improve maneuverability/agility Dinosaurs Bipedality - Expanded ilium - large bone for muscles of the pelvis, hind leg, and tail to attach Lip over open hip socket and femur with inturned head - stabilize hip joint 123 hand - digits 4 and 5 are reduced 234 foot - digits 1 and 5 are reduced

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Lab 3_ Vertebrates (1)

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