DEUTEROSTOMES - BIRDS AND MAMMALS

Occurred 66 million years ago (Ma ago).
Most likely caused by the impact of an asteroid.
Resulted in:
- Significant impact on climate
- Mass extinction including non-avian dinosaurs
Aftermath created opportunities for the survivors!
K-Pg is an abbreviation for Cretaceous-Paleogene, while K-T refers to the Cretaceous-Tertiary.

Amniotes are divided into:
- Synapsida
- Example: Mammals
- Diapsida
- Example: Reptiles such as tuataras, snakes, and birds
Key skull types in Amniotes:
- Synapsid Skull: Single pair of lateral temporal openings.
- Diapsid Skull: Dorsal and lateral temporal openings present.
- Anapsid Skull: Absence of temporal openings.
The structure of the axial skeleton plays a role in locomotion and respiration.
Key characteristics across groups in Amniota:
- Extraembryonic membranes: Amnion, chorion, and allantois.
- Lungs ventilated by negative pressure via ribs.

Birds are considered a specialized lineage of theropod dinosaurs, which include bipedal, generally carnivorous dinosaurs, notably Tyrannosaurus rex and Velociraptor.
Other feathered theropods existed that were capable of gliding, such as Microraptor, which had 4 feathered limbs.

Archaeopteryx is generally regarded as “the first bird.”
Existed approximately 150 million years ago during the late Jurassic.
Discovered in limestone deposits near Solnhofen, Germany, first described in the years 1860/1861.
Characteristics:
- Crow-sized (variable size)
- Reptilian traits:
- Skull with teeth
- Solid bones
- Long tail
- Absence of enlarged breastbone
- Possessing feathers, which likely evolved for insulation.
- Capability of powered flight is debated.

Many fossils more derived than Archaeopteryx are classified as “stem birds.”
Examples include:
- Enantiornithes
- Confuciusornis
These are not classified within Neornithes, which encompasses all living bird species.

Wings represent modified amniote pentadactyl limbs.
Structural changes:
- Five digits are reduced to three in birds.
- Proportions of wing parts are altered, resulting in diverse wing shapes.

Bones are hollow and air-filled to substantially reduce weight, facilitating flight.
The sternum is enlarged and forms a keel, which serves as an attachment point for flight muscles.

Bird lungs facilitate a unidirectional air flow, enhancing gas exchange efficiency, crucial for high metabolic rates.
Birds also possess air sacs that facilitate air storage and exchange; however, gas exchange occurs solely in the lungs.

Over 28 Orders and 166 families comprising 11,000+ species.
Classification breaks down into Palaeognathae and Neognathae.
Palaeognathae: Also called ratites; includes:
- Ostrich, emu, tinamous, kiwi, cassowaries, rheas.
- Most are flightless except tinamous.
- Relatively recently extinct elephant birds belong here.
Neognathae:
- Contains the majority of living bird species; includes orders such as Anseriformes (ducks and relatives) and Galliformes (landfowl; chicken and relatives).
- More than half of living bird species are classified under the order Passeriformes.

Mammals originated from diverse pelycosaurs (in the Permian).
Specialized carnivorous pelycosaurs from the Permian period played a role in mammalian evolution.
Evolution of therapsids occurred in the mid-Permian to Triassic.

The quadrate and articular bones, remnants of the original jaw, become the incus and malleus by evolving into the middle ear bones.
The lower jaw is solely formed from the dentary bone.

Heterodont dentition refers to the presence of specialized teeth with different types in the same mouth.
Examples include:
- Rodents with incisors
- Elephants have tusks derived from incisors.

Cynodonts possessed features such as:
- A complete secondary palate
- Retained turbinate bones for retaining body heat
- Exhibited heterodont teeth

Horizontal body bending (similar to modern lizards) limits movement to short anaerobic sprints.
Vertical bending in mammals enables breathing support during galloping due to spinal anatomy and limb positioning.

Eggs are fertilized internally, and embryos develop within the female uterus.
Embryos are encased in an amniotic sac, sharing a homology with the amniote egg's membranes.
A placenta facilitates nutrient and gas exchange, as well as waste elimination via the mother’s circulatory system.

Tetrapoda consists of:
- Amphibia
- Mammalia
- Comprised of groups such as:
  - Prototheria: Includes monotremes (platypus, echidnas)
  - Metatheria (Marsupials): Approximately 280 species, primarily found in Australia and S. America.
  - Eutheria (Placental mammals): Approximately 5,300 species across 20 groups.
  - Monotremata: Known for egg laying, lack of teeth in adults, and milk secretion onto fur.

Monotremes:
- Including species like platypus and echidnas, known from Australia and New Guinea.
- They are oviparous (egg-laying).
- Lack teeth as adults.
- They secrete milk onto the mother's fur rather than having nipples.
Metatheria (Marsupials):
- Approximately 280 known species, with a majority residing in Australia and S. America.
- Newborn marsupials complete their development attached to the teat of the mother, effectively being embryos at birth.
Eutherians:
- Comprising 5,300 species in 20 groups.
- Characterized by the presence of placentas, leading to more developed offspring at birth than marsupials.
- The major groups diverged rapidly during an explosive adaptive radiation coinciding with the Mesozoic breakup of continents.