Lecture 4 - Tetrapods Flashcards
Name the 4 classes of tetrapods
- Amphibians
- Reptiles
- Aves (birds)
- Mammals
Name the 2 (Major) subclasses of amphibias and describe their significance.
- Labyrinthodontia - Extinct toothy lizard-like amphibians believed to be the ancestor to modern vertebrates
- Lissamphibia - Modern amphibians (Frogs, Toads, Salamanders, caecilians)
Name the 3 subclasses within the Reptile Group
- Anapsids - Most simplistic reptiles (Possibly first subclass to have membrane-bound fetuses…I think), includes turtles, tortoises, etc…
- Diapsids - Develop with two “holes” in the skull (lost later), this subclass includes Lizards, Snakes, Crocodiles, and dinosaurs
- Synapsids - Not as clear - Temporal holes for better bite, believed to be the class of reptiles that would first develop mammal-like features…i dunno, more on this later
Briefly describe the two subclasses of mammals
- Prototheria - Early mammals
2. Theria - Modern mammals. Pretty easy
Describe which subclass/group that were believed to be the first tetrapods
- Devonian Tetrapods (Called that because they emerged around the Devonian Era) were believed to be labyrinthodonts, named for their complex-folded enamel tooth formations.
- Labyrinthodonts are grouped with amphibians, though that’s somewhat disputed.
- The amphibian order, Temnospondyli are believed to have arisen during the later Carboniferous period and are said to be the ancestor for modern amphibians
What order of amphibian, Devonian Tetrapods are the best studied today? Describe their characteristics
- Icththyostega were an order best represented by Lepospondyls, which were smaller than labyrinthodonts
- Vascular gas exchange on their skin (like frogs?), bony scales, and a tail with fin rays. Had basic sensory canals, including a nose. Some had horns.
- Was able to coexist with devonian tetrapods, but no modern variation is currently in existence
What were some other characteristics of early Devonian tetrapods?
- Still probably spent most of their time in the water, but they had well-developed lungs
- Early tetrapods had fish scales, but these would become bony plates, with tougher skin…In the Carboniferous era, these may have become full-on armored skulls
- Had notches on the sides of their head that had a brand new feature: A Tympanic Membrane (eardrum)
One more time now, describe the group of Devonian tetrapods that gave rise to modern amphibians
Temnospondyls - Arose during the Mississippian period, over 6 feet long, Heavily Boned with a 6-feet long skull, and probably quite carnivorous.
Name the 3 modern orders of amphibians and describe their characteristics. Give an example animal for each order
- Caudates (Urodeles) - Had tails (into adulthood?) and include modern salamanders (first appeared in Jurassic Period)
- Anurans - Lacked a tail, includes frogs and first appeared in Jurassic Period. Back then, the vertebra was longer, and the spine was shorter.
- Apodans - Didn’t have any limbs at all, includes the modern-day caecilian. They’re worm-like and burrow like subterranean amphibeans.
What are some characteristics that all modern amphibians have in common?
Pedicellate teeth, cylindrical vertebral centra, and two auditory ossicles, suggesting they belong to a single subclass, but some workers think otherwise.
List and describe the 3 reptilian skull types
(Based on holes and arches on the back sides of the skull)
Anapsids - No holes in their skull apart from orbital and nasal
Synapsid - One additional hole
Diapsid - Two additional holes
Describe anapsids
- Used to include cotylosaurs and chelonia (turtles). But now the turtle part is being second-guessed because they’re more likely modified diapsids.
- Cotylosaurs are the most primitive (stem) reptiles and resembled seymourian tetrapods. They might’ve have been several feet long and probably had some cool dermal armor.
- Their skulls are more laterally flattened than other reptiles.
- They didn’t have much serious jaw strength, started out pretty small and skinny (
List some basic characteristics about diapsids.
- Two openings behind their orbits. Each opening initially has a bony bar. But lizards and snakes have lost one or both bars.
- Divided into two infraclasses:
- Lepidosaurs: Includes snakes, and lizards
- Archosaurs: Includes crocodiles, flying reptiles, dinosaurs, and ancestors to birds.
Dinosaurs were sub-categorized into two different groups. Name them and describe the characteristics of each.
- Ornithishcians: Bird hipped dinosaurs. These had a tetraradiate pelvic girdle and could include both quadripedal and bipedal types. This included the hadrosaur, stegosaur, and triceratops.
- Saurischians: Lizard-hipped dinosaurs. Triradiate pelvic girdle. Included both quadripedal and bipedal forms, this included the Tyranosaurus, Allosaurus, and Apatosaurus.
What are the 3 subgroups of lepidosaurs?
- Sphenodon: Has a “true” diapsid skull and a primitive pectoral girdle. It looks like a lizard, but it’s not. They are/were/not sure/ found in New Zealand.
- Snakes
Lizards
Why do dinosaurs form a paraphyletic group?
First off, since you probably forgot, paraphyletic means a group or selection of species that descended from a common ancestor of another group or species, but doesn’t include them all collectively.
- Case in point, birds are closely related to saurischians, birds are grouped into their own class (Aves)
- Some people refer to birds as feathered dinosaurs. Sounds lame.
What kind of reptillian characteristics remained in early birds
- They first emerged in the Jurassic period. They had a bony tail (not yet feathers), clawlike fingers (not yet talons), and teeth. Mind you, even these weren’t the “first birds.”
- By the Cretaceous period, more modern aquatic birds were being found. They probably “dove” into and out of water.
State some of the theories on the origin of bird flight
- Birds evolved from saurischian (not confirmed).
- May have evolved as a means of thermal insulation.
- May have evolved as an insect-catching net.
- May have allowed for better pursuit of prey or escape from predation.
- May have allowed early archosaurs to roost in trees at night.
Describe synapsids
- Included the class pelycosaurs (earliest) and cynognathids. These appeared in the Permian period about 310 million years ago.
- Synapsids were reptiles believed to have been the bridge between reptiles and mammals. (Somewhere between Permian and Triassic - 230mya)
- Later synapsids were known as therapsids.
Describe pelycosaurs
Generally only a few feet in length.
- NOT contemporary with dinosaurs.
- Some had a large sail-like structure on their back: This structure was highly vascularized. This was thought to have been a thermoregulatory device.
Describe therapsids:
Make up a group of several clades, Cynognathous being the most common one.
- Elbow and knee swung in toward the body.
- Many features of the skull were more mammal-like.
- Transition to mammal-like jaw articulation.
Long one incoming: What are characteristics of mammals that are shared with therapsids?
sigh (1. Secondary Plate Bones), (2. An enlarged dentary bone), (3. Differentiation of Teeth Types), (4. Regional differentiation of ribs and vertebrae), (5. Legs are pulled in and ilium is extended forward), (6. Sacrum is elongated and feet well-developed), (7. Mammal-style Jaw is articulated between mandible and temporal bone), (8. Reptile-style Jaw is articulated between quadrate and articular bone…One therapsid species had both?),
What mammalian characteristics are exclusive from therapsids?
(1. Live Birth), (2. Homeothermy), (3. Respiratory Diaphragm), (4. 4-chambered heart), (5. Neocortex), (6. Double Occipital Condyle), (7. Single Mandible), (8. Bony secondary palate), (9. Loss of inter clavicle {except in egg-laying mammales}), (10. Hair/Fur), (11. Mammary Glands)
What were the earliest mammals documented, and when did they emerge?
What are the two subclasses of mammals?
- Morganucodonts - From the late Triassic Period. They had the denture patterns of a mammal.
1. Prototheria - Egg laying mammals. Extinct except for the platypus and the spiny anteaters.
2. Theria - Marsupials and placentals; Had trituberculate molars. Whatever those are.
