The Case Of The Missing Cusp

[PrehistoricFlorida]

Here is a very unique auriculatus tooth that is lacking is the cusp department... Pathologies like this one, and double tipped teeth, are very attractive to me. This is one of only a handful of pathological rics that I've seen. If I remember correctly, I believe Harry has one as well...

[fig rocks]

Very cool and very different!

[Auspex]

Pretty neat; doesn't hurt that it's in such great shape, either! Any theories floating around about why cusps evolved in the first place, and why they were lost?

[Northern Sharks]

Great tooth Nate, here's another one with cusp issues, among other things

[siteseer]

Pretty neat; doesn't hurt that it's in such great shape, either! Any theories floating around about why cusps evolved in the first place, and why they were lost?

Auspex,

I believe the lateral cusplets evolved as a variation that extended the cutting edge of a tooth without enlarging the tooth, while maintaining the dentition count. If an organ can alter its shape within the same space and do more work without costing the body further energy expenditure, that's an evolutionary plus. In shark lineages with cusplets that increased body size over time, the advantage of having cusplets diminished, especially if the shark was evolving a cutting-type dentition (sawing out chunks from larger prey or biting prey in half), as in the case of Carcharocles, away from a tearing-type dentition (ripping chunks without being able to cleanly remove chunks out of large prey. The cutting-type dentition requires a more precise meeting of the teeth (occlusion) while biting. The acquisition of serrated edges increased the efficiency of processing prey, cutting into and through even bone.

In sharks that didn't lose their cusplets, such as the sand tigers, the cusplets act more like accessory hooks to help the main cusp snag smaller prey that can be swallowed whole (fish, squid, etc.). They remain useful so they have not been weeded out of the genetic make-up of that family of sharks. Though, it is interesting that in the extinct sand tiger, Striatolamia, the largest teeth tend to have very small cusplets and the largest teeth of other genera, including the modern ones, can lack them.

I have read that Cretaceous birds lost their teeth as a response to decrease weight in the skull to aid flight. I see that but I have thought that the loss of their teeth was also an energy-saving move, making blood available to other parts of the body (increased brain development, further flight ability tune-ups, etc.). Whether sharks or birds (or pick an organism), it's all about making the most of what you have and building on it.

Edited November 19, 2009 by siteseer

[Auspex]

That makes a lot of sense, and helps to reconcile what we can observe with what we think we know about shark evolution.

As for birds, development of the brain as a "computer" to control the fine nuances of navigating a 3-D environment may have preceded the loss of teeth; a bird's beak is its "hand", with which it manipulates its immediate environment, and quickness of motion (by a reduction of the mass at the end of the "arm") took precedent over the need to take bites out of (and process) large prey. One of the things that makes a bird a bird is the centralization of mass, with the extremities becoming as light as possible.