Editing Tetrapod (section)

=== Neck ===
In tetrapodomorph fishes such as ''[[Eusthenopteron]]'', the part of the body that would later become the neck was covered by a number of gill-covering bones known as the [[Operculum (fish)|opercular series]]. These bones functioned as part of pump mechanism for forcing water through the mouth and past the gills. When the mouth opened to take in water, the gill flaps closed (including the gill-covering bones), thus ensuring that water entered only through the mouth. When the mouth closed, the gill flaps opened and water was forced through the gills. 

In ''Acanthostega'', a basal tetrapod, the gill-covering bones have disappeared, although the underlying gill arches are still present. Besides the opercular series, ''Acanthostega'' also lost the throat-covering bones (gular series). The opercular series and gular series combined are sometimes known as the operculo-gular or operculogular series. Other bones in the neck region lost in ''Acanthostega'' (and later tetrapods) include the extrascapular series and the supracleithral series. Both sets of bones connect the shoulder girdle to the skull. With the loss of these bones, tetrapods acquired a neck, allowing the head to rotate somewhat independently of the torso. This, in turn, required stronger soft-tissue connections between head and torso, including muscles and ligaments connecting the skull with the spine and shoulder girdle. Bones and groups of bones were also consolidated and strengthened.<ref>{{harvnb|Clack|2012|pp=29,45–6}}</ref>

In Carboniferous tetrapods, the neck joint (occiput) provided a pivot point for the spine against the back of the skull. In tetrapodomorph fishes such as ''Eusthenopteron'', no such neck joint existed. Instead, the [[notochord]] (a rod made of proto-cartilage) entered a hole in the back of the braincase and continued to the middle of the braincase. ''Acanthostega'' had the same arrangement as ''Eusthenopteron'', and thus no neck joint. The neck joint evolved independently in different lineages of early tetrapods.<ref>{{harvnb|Clack|2012|pp=207,416}}</ref>

All tetrapods appear to hold their necks at the maximum possible vertical extension when in a normal, alert posture.<ref name="taylor14">{{Cite journal | doi = 10.7717/peerj.712| title = Quantifying the effect of intervertebral cartilage on neutral posture in the necks of sauropod dinosaurs| journal = PeerJ| volume = 2| pages = e712| year = 2014| last1 = Taylor | first1 = M. P.| pmid=25551027| pmc=4277489| doi-access = free}}</ref>