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Characteristics of Chordata
Animals in the phylum Chordata share four key features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
Chordates and the Evolution of Vertebrates
Chordata contains two subphylums of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets).
The Evolution of Craniata and Vertebrata
Both genomic and fossil evidence suggests that vertebrates evolved from craniates, which evolved from invertebrate chordates.
Characteristics of Vertebrates
Vertebrata is a subphlyum of Chordata that is further defined by their bony backbone.
Agnathans: Jawless Fishes
The superclass Agnatha describes fish that lack jaws and includes the extant species of hagfish and lampreys.
Gnathostomes: Jawed Fishes
Gnathostomes, jawed vertebrates, can be divided into two types of fish: Chondrichthyes (cartilaginous fish) or Osteichthyes (bony fish).
Characteristics and Evolution of Amphibians
Amphibians evolved from fish 400 million years ago and are characterized by four limbs, moist skin, and sensitive inner ear structures.
Amphibians can be divided into three groups: Urodela (salamanders), Anura (frogs), and Apoda (caecilians).
Characteristics of Amniotes
The distinguishing characteristic of amniotes, a shelled egg with an amniotic membrane, allowed them to venture onto land.
Evolution of Amniotes
Modern amniotes, which includes mammals, reptiles, and birds, evolved from an amphibian ancestor approximately 340 million years ago.
Characteristics of Reptiles
Reptiles are ectothermic tetrapods that lay shelled eggs on land and possess scaly skin and lungs.
Evolution of Reptiles
Dinosaurs and pterosaurs diverged from early amniotes and dominated the Mesozoic Era.
Class Reptilia, amniotes that are neither mammals nor birds, has four living clades: Crocodilia, Sphenodontia, Squamata, and Testudine.
Characteristics of Birds
Birds are warm-blooded animals with wings having several adaptations to flight, although not all species can fly.
Evolution of Birds
Modern birds evolved from Saurichia, one of two subgroups of dinosaurs, although it is unclear how flight and/or endothermy arose in birds.
Characteristics of Mammals
Mammalian traits include, among others: specialized glands, modified jaw and inner ear bones, urinary bladder, and hair.
Evolution of Mammals
The modern mammals of today are synapsids: descendants of a group called cynodonts which appeared in the Late Permian period.
Living mammals can be classified in three subclasses: eutherian, metatherians and monotremes.
The Evolution of Primates
Characteristics and Evolution of Primates
All primates exhibit adaptations for climbing trees and have evolved into two main groups: Prosimians and Anthropoids.
Early Human Evolution
Modern humans and chimpanzees evolved from a common hominoid ancestor that diverged approximately 6 million years ago.
evolved 4 million years ago and is believed to be in the ancestral line of the genus
The human genus
, which includes modern humans as well as extinct human relatives, appeared around 2.3 million years ago.
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Plant Form and Physiology
The Plant Body
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