Olfactores is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

within the

Chordata A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (Apomorphy and synapomorphy, synapomorphies) th ...

that comprises the Tunicata ( Urochordata) and the

Vertebrata Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Verte ...

(sometimes referred to as Craniata). Olfactores represent the overwhelming majority of the phylum Chordata, as the Cephalochordata are the only chordates not included in the clade. This clade is defined by a more advanced

olfactory system The olfactory system, is the sensory nervous system, sensory system used for the sense of smell (olfaction). Olfaction is one of the special senses directly associated with specific organs. Most mammals and reptiles have a main olfactory system ...

which, in the immediate vertebrate generation, gave rise to nostrils.

Etymology

The name Olfactores comes from Latin *''olfactores'' ("smellers," from purposive supine ''olfactum'' of ''olfacio'', "to smell," with plural masculine agentive nominalizing suffix ''-tores''), due to the development of pharyngeal respiratory and sensory functions, in contrast with cephalochordates such as the lancelet which lack a respiratory system and specialized sense organs.

Olfactores hypothesis

The long-standing Euchordata hypothesis that Cephalochordata is a sister taxon to Craniata was once widely accepted, likely influenced by significant tunicate morphological

apomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

from other chordates, with cephalochordates even being nicknamed ‘honorary vertebrates.’ The name Olfactores was originally introduced in 1991 as part of the now-disproven calcichordate hypothesis. However, studies since 2006 analyzing large

sequencing In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succ ...

datasets strongly support Olfactores as a clade. Studies suggest that the ancestors of Appendicularia and

were possibly sedentary-pelagic. A rudimentary

neural crest The neural crest is a ridge-like structure that is formed transiently between the epidermal ectoderm and neural plate during vertebrate development. Neural crest cells originate from this structure through the epithelial-mesenchymal transition, ...

is present in tunicates, implying its presence in the Olfactores ancestor also, as vertebrates have a true neural crest.

References

Works cited

* * * * * * * * * * * * {{Taxonbar, from=Q3280581 Chordates Chordate unranked clades