May 31, 2009
Since we’re spending a few days on neck posture, I thought I’d expand on what Mike said about bunnies in the first post: in most cases, it is awfully hard to tell the angle of the cervical column when looking at a live animal. Because necks lie.
Take this horse (borrowed from here). You can see that the external outline of the neck, which is what you would see in the living animal, is pointed in a different direction than the cervical column.
And here’s why. Many mammals carry their heads and necks so that the cranio-cervical joint is up high and the head is angled down from it. At the base of the neck, tall neural spines on the anterior thoracic vertebrae support the nuchal ligament, which lifts the body profile far above the cervical vertebrae. Basically, the cervicals run from the lower or middle part of the neck at its base to near the top of the neck at the head end.
This mismatch holds no matter how the neck and head are oriented. When the animal lowers its head to graze, the cervical column is still angled up relative to the apparent angle of the neck defined by its dorsal and ventral margins.
But if you think that’s bad, you ain’t seen nothin’ yet.
In most of the smaller birds, like this budgie (from Evans 1969:fig. 5-6) the neck is much longer and more flexible than you would think based on the external profile. And check out the mismatch between the cervical column (in front) and the trachea (behind). That’s not drawn incorrectly; the trachea is outside the bundle of neck muscles that encloses the vertebrae, and it is free to slide around all over the place, and does so in many birds.
Also note that while the neck is extended past vertical, the extension occurs in the middle of the neck, not at the shoulder. The neck actually goes down from the craniocervical joint, not up. My guess is that there is a lot of this in climbing taxa that hold their torsos elevated. Vultures come to mind here, too. A useful reminder that in natural history we are usually dealing with norms, not laws.
In the pigeon, note again the fact that the mid-cervicals are angled up much more sharply than is the external profile of the neck. In fact, the external profile of the neck is angled forward while the mid-cervicals are angled backward. This excellent reconstruction is from this page, which has several others which also show that necks lie.
Lest anyone think that the pigeon was either an outlier or a case of artistic embellishment, here’s yet another rabbit, this time from Vidal et al. (1986: fig. 5a). Again, the mid-cervicals–actually, almost all of the cervicals–are angled backward, but the neck as a whole is pointing slightly forward.
As an aside, I think possibly it has blown some people’s minds that we have used so many rabbits as examples, both in the paper and in our blog coverage. What can we say? Rabbits are awesome.
Of course not all necks lie. With flamingos, what you see is what you get.
Giraffes: 20 feet of reticulated irony
Let’s see here: necks not vertical.
Necks not vertical.
Trying . . . very . . . hard . . . and . . . just . . . getting . . . to . . . vertical!
(I know it looks like the neck is just slightly less than vertical, but remember that necks lie, and the cervical column is steeper. In this animal, you could drop a plumb bob from the ear and it would track the course of the cervical vertebrae just about perfectly.)
Cat, not trying at all: cervical column past vertical (Vidal et al. 1986: fig. 2).
Here’s the irony: for practically as long as sauropod neck posture has been contentious, giraffes have been held up as THE example of the most extreme (dude!) elevated neck postures out there. But in fact giraffes have to really reach to achieve vertical cervical postures that “ordinary” animals like cats, rats, guinea pigs, chickens, and, yes, rabbits, reach or exceed all the time.
Good paleobiology has to start with good biology. It’s high time that the sauropod neck posture debate got a reality infusion. Giraffe necks are extreme in terms of length, but not in terms of posture.
Speaking of sauropods…
All right, you’ve suffered long enough. Here’s your sauropod vert. Care to guess what it is?
- Evans, H.E. 1969. Anatomy of the budgerigar; pp. 45-112 in Petrak, M.L. (ed.), Diseases of Cage and Aviary Birds. Lea and Febiger, Philadelphia.
- Vidal, P.P., Graf, W., and Berthoz, A. 1986. The orientation of the cervical vertebral column in unrestrained awake animals. Experimental Brain Research 61: 549-559.