Sauropod Vertebra Picture of the Week

9 Responses to “My hobby:”

1. Paul S. Says:

   
   October 17, 2013 at 10:46 am

   Why don’t giraffes have sauropod tails?
2. Mike Taylor Says:

   
   October 17, 2013 at 10:50 am

   Like so many good questions, this seems an obvious one to ask — once you’ve heard someone ask it. No doubt a more substantial tail would provide a useful counterbalance for the Giraffe’s long neck.

   In this case, I think the problem is phylogeny. Giraffes are descended from artiodactyls which, like most mammals, had evolved their tails away to almost nothing. Re-evolving a meaningful tail is not an overnight project. (And taking full advantage of it by replumbing the muscles of the hindquarter is a huge project.)
3. Paul Stainthorp Says:

   
   October 17, 2013 at 11:02 am

   “Re-evolving a meaningful tail is not an overnight project.”

   …yes, that is my favourite sentence today.
4. tmkeesey Says:

   
   October 17, 2013 at 12:49 pm

   There is a certain group of artiodactyls with VERY meaningful tails. Whale-sized, even.

   That said, I certainly can’t think of any ruminants with powerful tails.
5. Paul Stainthorp Says:

   
   October 17, 2013 at 1:56 pm

   Did primitive cetartiodactyls have powerful tails, I wonder? Or did whales figure out the secret to overnight caudal success?
6. Matt Wedel Says:

   
   October 17, 2013 at 3:45 pm

   Why don’t giraffes have sauropod tails?

   Because unlike non-avian dinosaurs, birds and mammals shifted the main femur-retracting muscles from the tail to the pelvis. After that, whatever advantages big tails conferred do not seem to have outweighed their deficits. The exceptions are mammals that use their big tails for something other than anchoring femur-retracting muscles: swimming (platypus, beaver, otters, manatees and dugongs, cetaceans), or a prop and counterbalance (wallabies, kangaroos, pangolins).

   I’m deliberately leaving out squirrels and monkeys. The fatness of squirrel tails is illusory, they’re basically rat tails with Duck Dynasty beards. And prehensile tails are useful but not very big, in terms of fractions of the animals’ masses.

   For more on dinosaur tail muscles as femur-retractors, see this post by Heinrich Mallison and this open-access paper by Persons and Currie.

   No doubt a more substantial tail would provide a useful counterbalance for the Giraffe’s long neck.

   ORLY? I think there is plenty of room for doubt on that score, and since I’ve always smacked this idea down when someone else proposed it, it’s only fair that I smack it down again.

   I think the tails-balance-necks thing is total hogwash. Evidence: all of the big quadrupedal mammals with heavy heads and/or necks get along fine without them: elephants, rhinos, camels, giraffes, deer (especially with those antlers), large-horned goats and antelope and cattle…. The fact is that the head+neck in all of those animals does not account for more than 10-15% of the body mass–same as the necks and heads of sauropods–and such a small mass is in no danger of toppling the animals over. If a big counterbalancing tail was so useful, you’d think maybe at least one of those clades would have gotten something up and going, despite the paucity of material to start with.

   Further evidence: ceratopsians, the largest-headed of all dinosaurs, are also proportionally the smallest-tailed, outside of birds, exactly the opposite of what we’d expect if the counterbalance hypothesis held any water. Especially since ceratopsians never lost their big tails the way that mammals did, and therefore had a head start on evolving a large, counterbalancing tail. And thyreophorans typically have long tails with heavy weaponry, but titchy necks and heads. If the counterbalance idea has any merit, Euoplocephalus should have needed some kind of big goofy bobble-head to balance its long, beweaponed tail.

   (Aside: you might argue that none of these big-headed but short-necked animals are relevant because the long necks of sauropods put the center of mass of the neck farther out in front of the forefeet. And I would then counter that [1] sauropods didn’t hold their necks horizontally very often, and [2] most of the really long-necked sauropods have considerable taper to their necks [evidence], so the neck COM probably wasn’t that far out.)

   I’m happy with the idea that big tails usefully counterbalance bipeds and saltators like kangaroos, kangaroo rats, and pangolins, but those are all bipeds, at least part-time*, and the tail is clearly counterbalancing everything ahead of the hips, not just the head and neck.

   * Before anyone tells me that pangolins are quadrupeds, just watch this video.

   So I’m issuing a challenge. Subscribers to the tails-counterbalance-necks hypothesis, please come forth with some examples of quadrupedal animals where this counterbalancing might demonstrably be doing on! Sauropods don’t count, unless you lop off the tail of a physical or digital sauropod model and show that the tailless sauropod is now unstable. And while you’re at it, please explain all of the counterexamples–elephants, rhinos, terrestrial artiodactyls, ceratopsians, thyreophorans, and so on–without resorting to special pleading.

   Any takers?
7. Anne Peattie Says:

   
   October 17, 2013 at 4:18 pm

   Saw xkcd last night, wondered what Wedel would say. Woke up this morning, et voilà, Wedel delivers.
8. Heinrich Mallison Says:

   
   October 17, 2013 at 10:05 pm

   Matt says it all!
9. spindoct0rs Says:

   
   October 19, 2013 at 3:14 pm

   Kid’s book teaching evolution, with a VERY on-point illustration of a boy with extra tail vertebrae: http://www.slate.com/articles/double_x/family/2013/10/bone_by_bone_the_picture_book_that_will_show_your_kid_how_evolution_works.html

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