Vertebrate Lineages Flashcards
Reptiles
the dominant terrestrial vertebrates ~250-66 MYA, and clade of Sauropsides called DIAPSIDS, which are the ancestors of lizards, snakes, turtles, crocodilians, dinosaurs, and birds
Diapsids
defined by the presence of 2 temporal openings (holes) in each side of the skull; this structure allows for attachment of larger + stronger jaw muscles and wider jaw openings, compared to Amniotes lacking these skull holes
Reptiles: Respiration
- use lungs to breathe and have scaly skin containing keratin + waxy lipids, which reduces water loss from the skin
- this thick, impermeable skin means reptiles cannot use their skin for respiration like Amphibians, thus all breath with LUNGS
Reptiles: Heat
- ECTOTHERMIC (main source of body heat comes from the environment)
- categorized as poikilotherms (animals whose body temp. vary rather than remain stable)
- they have behavioral adaptions to regulate body heat like basking in sunny or shady spots
- advantages of ectotherms is the low metabolic energy needed to survive
Reptiles: Evolution
- earliest reptiles appear in the FR ~320 MYA, and the earliest known true reptile was an ANAPSID (unlike modern reptiles), meaning it had a solid skull with no holes
- no holes = smaller jaw muscles = weaker jaw strength
Birds
only group of dinosaurs still living; evolved ~100-150 MYA from a group of dinosaurs called THEROPODS
Birds: Evolution
- the Archaeoptery is a fossil of an animal intermediate between theropods and birds
- the fossil appears to have characteristics of both animals; the fossilized skeleton + teeth is that of a dinosaur and it had flight feathers like modern birds
Birds: Feathers
- characteristic that sets birds apart from other modern vertebrates
- modified scales
- allow for flight
- effective insultation to decrease heat loss
- play roles in camouflage or social signaling
Birds: Heat
- birds are ENDOTHERMIC (produce their own body heat via their metabolism)
- endothermy requires more energy + food
- since birds fly, they require high energy and have a high metabolic rate
Mammals
evolved ~200-230 MYA from a group of reptile-like amniotes called SYNAPSIDS
Synapsids
defined by the presence of a single hole in each side of the skull that allows for attachment of larger, stronger jaw muscles and wider jaw openings
Mammals: Evolution
- evolved from a group of synapsids called Therapsids, and the cynodonts are the group of therapsids that include the MRCA of all mammals
- amniotes that retain the feature of the amniotic egg, though only one group (monotremes) still lay eggs
- all mammals produce milk from mammary glands for their offspring
Mammals: Skeletal System
- lower jaw consists of just one bone
- additional jaw bones found in other vertebrates have been modified to function in hearing and form the 3 small bones in the mammalian ear (one way to distinguish mammals from other synapsids)
- the musculature of the jaw allows side to side movement and makes chewing possible
- Chewing is unique to mammals, and most have different types and shapes of teeth
Mammals: Hair
heavily modified scales; hair, feathers, and scales are homologous structures of amniotes
- effective insulation to decrease the rate of heat loss
- hair coloration play roles in social signaling + camouflage
Mammals: Heat
are ENDOTHERMIC; evolved independently in mammals and birds and is NOT a homologous trait
Mammals: Clades
living mammals belong to 3 clades; many other clades are now extinct:
1. Eutherians (placental mammals like humans)
2. Marsupials (metatherians which have like birth but no placenta, and the young develop in a pouch (kangaroos)
3. Monotremes (lay eggs like platypus)
Vertebrate Adaptations to Dry Environments OVER GEOLOGIC TIME
- First vertebrates were fish-like aquatic animals that lived early-Paleozoic
- The capable of leaving the water were amphibians (evolved mid-Paleozoic). This era featured swampy, wet conditions amphibs flourished in, where they could survive and reproduce. The Carboniferous Period saw amphibian tetrapods become dominant predators on land
- First Amniotes evolved mid-Paleozoic, but were largely outcompeted by amphibians occupying many available land niches. As conditions became drier, amniotes flourished due to adaptations
Amniotes Water to Land Adaptations
- Amniotic Egg (allowed them to reproduce away from water)
- Lungs (allowed for evolution of desiccation resistant skin covering like scales, feathers, and hair since gas exchange did not have to take place in the skin if lungs were present)
- Scales/Feathers/Hair (provided protection against dehydration while moist amphibians required sufficient water to prevent dehydration)
