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A chordate (/ ˈ k ɔːr d eɪ t / KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/ k ɔːr ˈ d eɪ t ə / kor-DAY-tə). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies ) that distinguish them from other taxa .
The calcichordate family tree in its original incarnation, with all chordates originating from a soft bodied ancestor. Later versions of the theory had each chordate group having a mitrate ancestor each, requiring three episodes of loss of stereom. Mitrates are assumed to have evolved from the cornutes. [6]
This article contains a list of all of the classes and orders that are located in the Phylum Chordata. The subphyla Tunicata and Vertebrata are in the unranked Olfactores clade, while the subphylum Cephalochordata is not. Animals in Olfactores are characterized as having a more advanced olfactory system than animals not in it.
A consensus phylogeny of the deuterostomes is: [citation needed] Superphylum Deuterostomia Phylum Chordata. Subphylum Cephalochordata ; Clade Olfactores. Subphylum Tunicata (tunicates) Subphylum Vertebrata. Superclass Agnatha (jawless fish) Infraphylum Gnathostomata (jawed fish) Class Chondrichthyes (cartilaginous fish)
Molecular studies by molecular systematists, based on DNA analysis, in the early 21st century have revealed new relationships among mammal families. Classification systems based on molecular studies reveal three major groups or lineages of placental mammals, Afrotheria, Xenarthra, and Boreoeutheria. which diverged from early common ancestors in the Cretaceous.
Chordate genomics is the study of the evolution of the chordate clade based on a comparison of the genomes of several species within the clade. The field depends on whole genome data (the entire DNA sequence ) of organisms.
Below is a phylogenetic tree of the phylum Chordata. Lines show probable evolutionary relationships, including extinct taxa, which are denoted with a dagger, †. Some groups in this tree (lancelets and tunicates) are invertebrates. The positions (relationships) of the lancelet, tunicate, and craniate clades are as reported.
Extensive molecular phylogenetic analysis has shown convincingly that the Cephalochordata is the most basal subphylum of the chordates, with tunicates being the sister group of the vertebrates.