If you are anything like me, you probably have a neck—a neck you take for granted. Maybe you do not think often about having a neck, given said neck's relatively unobtrusive placement below your head and out of your line of sight. Maybe you are trying to look at your neck right now, pressing your chin against your neck, which remains obscured below your chin, which you also can't see. And yet your ability to even attempt to see your neck is made possible by your neck. Neck-less animals such as valiant Jimothy or every jellyfish have no such rotational privilege.
Perhaps it is unsurprising, then, that science has long neglected the humble neck. "There have been a multitude of studies on the development and evolution of the head and pectoral girdle but little on the region in between," scientists wrote in a 2012 paper about the vertebrate neck in the Journal of Anatomy. Only in the last 30 years has scientific interest in the neck awakened, the researchers write. We here at Defector do not wish to neglect the neck any longer. So please gather round for a long-overdue neck report, because there is breaking neck news.
"Think that fishes and amphibians don’t have necks? Think again"
The above headline stopped me in my tracks when I read it in a press release. I did in fact think that fishes had no necks, though it was more of a passive belief than any conclusion I had actively come to. I had admittedly not developed any opinion on such anatomy in amphibians. This new research, which was recently presented at the Society for Experimental Biology conference in Italy, purported to change the current definition of a neck to be more inclusive of other creatures. I was intrigued. What definition of a neck could encompass a guy like this?
I would argue a fish has even less of a neck than a creature like a jellyfish, given that a jellyfish's anatomy does not have an obvious location where a neck would go. But a fish's does. The neck would go right there, between the head and the body! I was, however, open to thinking again. I read on, and what I learned made me rethink all my preconceived notions of necks and what it means to have them.
What is a neck? In mammals, the neck consists of the part of the vertebral column between the skull and shoulders. The neck allows the head to move and rotate independent of the body. Almost all mammals, from giraffes to mice, have necks made of seven vertebrae. The only exceptions are sloths, which have five to seven vertebrae if they have two toes or eight to nine vertebrae if they have three toes, and manatees, which have six vertebrae.
By the bony definition, invertebrates obviously cannot have necks. And yet there are some seeming exceptions, such as the giraffe weevil, whose long neck is actually an extremely elongated extension of the thorax, jointed to an extremely elongated extension of the head. Such a "neck" might not count in an ossific sense, but if it does the things that necks do, is it not simply a different kind of neck? Or consider the praying mantis, which boasts a specialized joint between the head and the prothorax that allows the insect to rotate its head up to 180 degrees. Does this "neck" not offer even more mobility than our so-called necks do? Such necks seem more than valid to me. I can only conclude that scientists have been needlessly strict in their neck allowances.
According to the sticklers, the world's first official neck appeared in Tiktaalik, the most famous fish with legs. Prior to Tiktaalik, fish had no need for a neck. Animals living in water can easily orient their bodies in the direction of their prey. But land, and Tiktaalik's accompanying invention of legs, presented a new problem. Suddenly a fish found its body fixed to an immovable substrate. Suddenly it became advantageous to be able to move only its head. In 2008, the paleontologist Neil Shubin and colleagues found that Tiktaalik's head bones were not fused to its shoulder bones, allowing the creature to take a look around. In this way, a neck that connects the skull and shoulders was one of the markers of a fish having a Little Mermaid moment, that is, abandoning fins for legs.
This neck—the textbook definition of a neck—applies to all modern birds, mammals, and reptiles. But it has never applied to fish and did not quite fit amphibians. Recently, a group of scientists undertaking a neck investigation realized that many anatomical papers were inconsistent in how they defined the neck in different kind of vertebrates. "This led a broader investigation into historical and contemporary interpretations of the neck and an evaluation of whether a more inclusive definition could be developed that is applicable across all vertebrates," Roxana Taszus, a scientist at the University of Liverpool, said in a statement.
This investigation was not simply in the spirit of neck inclusivity across the animal kingdom. A new, comprehensive definition for necks that actually applied to every vertebrate would allow scientists to better compare the role and evolution of necks in different groups. The scientists first looked to salamanders, which are the closest modern equivalent to Tiktaalik. Like early tetrapods, salamanders spend their lives both in water and on land. The researchers watched oddly cinematic footage of a tiger salamander munching on a maggot to study how its head moved independent of its body.
The new definition the researchers propose is looser than the textbook. "We think 'neck' should mean the bones of the spine that allow the head to move independently of the body," Ariel Camp, a biologist at the University of Liverpool, said in an interview with Earth.com. (Camp is no stranger to the world of novel necks, having previously studied how the vertebral column of a "neck-less fish" could produce "neck-like motions.") The researchers want to differentiate between a morphological neck, meaning vertebrae by the head that have a distinct shape, and a functional neck, meaning the vertebrae that allow the animal to move its head independently.
But what does this mean for fish? Longtime fish neck truthers might point to neck-like oddities in the group to prove their case, such as the flexible necks of seahorses or the fish called the biara that can bend their heads upwards by 45 degrees while lunging at prey. What the researchers are proposing is that all fish have a sort of hidden neck, meaning a small swath of vertebrae that can act like a neck. In 2021, Camp published a paper in Proceedings of the Royal Society B revealing that rainbow trout and giant frogfish can move their heads independently of their bodies. Although these two fish have totally different bodies, the rainbow trout representing the platonic ideal of a fish and the giant frogfish resembling a weathered wad of chewing gum come to life, both were able to rotate their heads by flexing part of their spine. And is this not the purpose of a neck? Can a neck or a neckalike not be defined teleologically?
Where does all this leave us? Perhaps this reminds us that science is an iterative process that changes its definitions over time. Or perhaps this reminds us that you should never underestimate a fish, because they are stranger and more inscrutable than we could even imagine.
