Paleo Trivia - Did You Know?

[Guest Smilodon]

Over in Fossil ID I mentioned that manatees and kangaroos have something in common. So instead of putting the info in the id section I thought I'd move it over here and maybe get new paleo trivia posts going. Please feel free to share other interesting fossil tidbits. I'll go first.

Kangaroos and manatees couldn't be further apart taxonomically (well I guess they could) but they share something that no other mammals, fossil or living, have ever come up with - a unique tooth replacement system. Most mammals have "baby" teeth replaced by permanent teeth that form underneath in the gum. Kangaroos and manatees system is totally different. Their teeth are on a conveyor belt. Teeth form in the back of the jaw and move forward in the jaw as their front teeth wear down and get spit out.

(time passes)

But wait, some of you say, he doesn't know what he is talking about. Elephants' teeth are on conveyor belts too, they move from the back of the jaw forward too. Well, that part is true, but elephants only have six sets of teeth - once the sixth wears out, there are no more left. Kangaroos and manatees NEVER STOP MAKING NEW TEETH and thus, never run out of them. They are the only mammals in the last 65 million years to come up with that system.

[Cris]

Extremely interesting..I guess that's why manatee teeth are so common in my area. Is there a name for this system?

[Guest Smilodon]

Extremely interesting..I guess that's why manatee teeth are so common in my area. Is there a name for this system?

Not that I'm aware of. Wouldn't it be great never having to go to the dentist?

[danielp]

Isn't that how a shark replaces teeth too?

[MikeD]

That's something I didn't know.

[Gatorman]

That is very interesting. Good fact for the fact files

[siteseer]

Over in Fossil ID I mentioned that manatees and kangaroos have something in common. So instead of putting the info in the id section I thought I'd move it over here and maybe get new paleo trivia posts going. Please feel free to share other interesting fossil tidbits. I'll go first.

Kangaroos and manatees couldn't be further apart taxonomically (well I guess they could) but they share something that no other mammals, fossil or living, have ever come up with - a unique tooth replacement system. Most mammals have "baby" teeth replaced by permanent teeth that form underneath in the gum. Kangaroos and manatees system is totally different. Their teeth are on a conveyor belt. Teeth form in the back of the jaw and move forward in the jaw as their front teeth wear down and get spit out.

(time passes)

But wait, some of you say, he doesn't know what he is talking about. Elephants' teeth are on conveyor belts too, they move from the back of the jaw forward too. Well, that part is true, but elephants only have six sets of teeth - once the sixth wears out, there are no more left. Kangaroos and manatees NEVER STOP MAKING NEW TEETH and thus, never run out of them. They are the only mammals in the last 65 million years to come up with that system.

I don't know much about kangaroos, especially whether their immediate ancestors could replace their teeth across their lifetimes, but the thing about manatees is that they evolved from the dugong group, members of which do replace their teeth the "normal" mammalian way. Manatees developed their tooth replacement system somewhere along their own evolution perhaps only as long ago as the Oligocene.

Smilodon, I should add there is evidence against the claim that a manatee can replace its teeth across its lifetime (Husar, 1977). I don't have the article but can look for it on my next library trip.

Husar, S. 1977.

"Trichechus inunguis." Mamm. Spec. 72: 1-4.

[Harry Pristis]

Over in Fossil ID I mentioned that manatees and kangaroos have something in common. So instead of putting the info in the id section I thought I'd move it over here and maybe get new paleo trivia posts going. Please feel free to share other interesting fossil tidbits. I'll go first.

Kangaroos and manatees couldn't be further apart taxonomically (well I guess they could) but they share something that no other mammals, fossil or living, have ever come up with - a unique tooth replacement system. Most mammals have "baby" teeth replaced by permanent teeth that form underneath in the gum. Kangaroos and manatees system is totally different. Their teeth are on a conveyor belt. Teeth form in the back of the jaw and move forward in the jaw as their front teeth wear down and get spit out.

(time passes)

But wait, some of you say, he doesn't know what he is talking about. Elephants' teeth are on conveyor belts too, they move from the back of the jaw forward too. Well, that part is true, but elephants only have six sets of teeth - once the sixth wears out, there are no more left. Kangaroos and manatees NEVER STOP MAKING NEW TEETH and thus, never run out of them. They are the only mammals in the last 65 million years to come up with that system.

Like 'Siteseer', I'm a bit skeptical of this claim, "NEVER STOP MAKING NEW TEETH." Do you have a source? . . . A citation that we can read?

I didn't look very deep into this question, but I found this immediately:

BCB705 Biodiversity: Chapter2 - Evolution of Biodiversity

Kangaroo: The teeth

The second difficulty that grass eaters must overcome is the wear and tear on their teeth. Grass is tough, due to the silicates that occur in them, and breaking it down into a pulp in the mouth is very abrasive on the teeth. Grazers elsewhere have molars with open roots so that wear can be compensated by continuous growth throughout the animal's life. In kangaroos the roots of the teeth are closed, and they have evolved a different system of tooth replacement. There are four pairs of cheek teeth on either side of the jaws. Only the front ones engage. As they are worn down to the roots, they fall out and those from the rear migrate forward to take their place. By the time the animal is fifteen or twenty years old, its last molars are in use. (emphasis added)

[Guest Smilodon]

Harry and siteseer,

My source is a personal conversation about 5 years ago with Dr. Daryl Domning, the world's leading authority on fossil sirenians. emphasis added

[Coco]

Hi,

N'est-ce pas la façon dont un requin remplace la dent aussi? [/ quote]

You are right. All the selachians (sharks, lines and chimaera) replaces their teeth throughout their life, by making them pass of the back in front. They always have them "in manufacturing".

I didn't know that for kangaroos and manatees.

Coco

[Harry Pristis]

Harry and siteseer,

My source is a personal conversation about 5 years ago with Dr. Daryl Domning, the world's leading authority on fossil sirenians. emphasis added

So you posted this bit of trivia based on your five-year-old recollection of a casual remark by Daryl Domning. You didn't do any research to confirm your recollection. I think we can see what went wrong here.

[Guest Smilodon]

So you posted this bit of trivia based on your five-year-old recollection of a casual remark by Daryl Domning. You didn't do any research to confirm your recollection. I think we can see what went wrong here.

Yes I did, if you wish to challenge Daryl, I suggest you contact him. After all, it is not possible for a book to ever be wrong is it? And listening to A LECTURE from the world's leading authority on a subject should never be taken as fact.

By the way, Garcia loved your demeaning little anecdote about him that you've now publicly published twice on this forum. You based that on your recollection of an occurrence what, 25 years ago?

[Bill]

The last sentence here says...

One species of kangaroo, the Nabarlek (Peradorcas concinna), has a seemingly unlimited supply of supernumerary molars, which continue to erupt throughout its life.

[Phoenixflood]

Ok you two

I can understand both sides. One of you is proposing that since the information came from a high authority in the field it is substantial and another wants more sources before they can fully accept or reject the idea.

The desire to know is what drives the growth of human knowledge. If we accepted everything that we read or heard there never would be any new and diverse ideas. It is up to the reader to be discriminant. It is up to the author to post as much as they know about the information they provide.

Those are just some of my thoughts.

[Haddy]

Extremely interesting..I guess that's why manatee teeth are so common in my area. Is there a name for this system?

unlimited molar replacement or "marching molars"

Manatees chew lots of sand and grit mixed in with the plants. When their big grinding molars wear out from all that chewing, they move to the front of the mouth. Eventually, they fall out and are replaced by new ones. The teeth have no roots anchored to the jawbone, which allows for "marching molars". Scientist believe up to 60 new teeth will grow in an average lifetime.

This is from Wikipedia:

Fish, such as sharks, may go through many teeth in their lifetime. The multiple replacement of teeth is known as polyphydontia.

The teeth of reptiles are replaced constantly during their life. Juvenile crocodilians replace teeth with larger ones at a rate as high as 1 new tooth per socket every month. Once adult, tooth replacement rates can slow to two years and even longer. Over all, crocodilians may use 3,000 teeth from birth to death. New teeth are created within old teeth.

Elephants' tusks are specialized incisors for digging food up and fighting. Some of elephant teeth are similar to those in manatees, and it is notable that elephants are believed to have undergone an aquatic phase in their evolution.

Elephants have four molars, one on each side of the upper and lower jaw. Until age 40, these are replaced by larger molars. The new molars shift forward from the back of the jaw as the old wear down. The final set of molars last for about twenty years.

[Guest Smilodon]

Guys just as a point of clarification, I specifically referred to mammals. Yes sharks and reptiles continuously replace their teeth, but not from back to front as these few mammals do.

The shark equivalent would be 6 inch posterior megs. Now that would be something!

[Guest Smilodon]

Those are just some of my thoughts.

I agree phoenix, but I'd like to see a photo of a documented 20 year old kangaroo wearing dentures.

And that's all I plan to say.

[Harry Pristis]

Yes I did, if you wish to challenge Daryl, I suggest you contact him. After all, it is not possible for a book to ever be wrong is it? And listening to A LECTURE from the world's leading authority on a subject should never be taken as fact.

By the way, Garcia loved your demeaning little anecdote about him that you've now publicly published twice on this forum. You based that on your recollection of an occurrence what, 25 years ago?

I'm glad that Frank got a chuckle out of the re-telling of that story. Actually, I wrote down that story hours after the occasion with review by others who were there. I circulated that story as part of a report to collectors across the state on the outcome of the committee hearing. So, I'm sure Frank has read that story before.

So, was it a "personal conversation" with Daryl Domning or was it a "lecture"?

This may be the reference which you understood to include all kangaroos.

(From Walker's Marsupials of the World, Ronald W. Nowak, 2005)

Peradorcas [a small rock wallaby] resembles Petrogale burbidgei but is distinguished by its longer ears and dental characters. Its molar dentition is unigue among marsupials in that there are supplementary replacement molars behind the last regular molar. The actual number of molar teeth is not known, but study suggests that as many as nine molars may erupt successively and that there are seldom more than five molars in place at any one time.

... [Peradorcas eats ferns which] are extremely abrasive, and this factor may be associated with the development of the continual molar replacement found in Peradorcas.

[Phoenixflood]

Ok you two

I can understand both sides. One of you is proposing that since the information came from a high authority in the field it is substantial and another wants more sources before they can fully accept or reject the idea.

The desire to know is what drives the growth of human knowledge. If we accepted everything that we read or heard there never would be any new and diverse ideas. It is up to the reader to be discriminant. It is up to the author to post as much as they know about the information they provide.

Those are just some of my thoughts.

Those are just some of my thoughts.

I agree phoenix, but I'd like to see a photo of a documented 20 year old kangaroo wearing dentures.

And that's all I plan to say.

That would be funny to see wouldn't it

My point in that post above was that you had provided as much information as you knew, which was good, just allow room for people to question. This does not mean that you are wrong about how the teeth move from the back to the front, it just means some people seek out more information to confirm that it is factual because that is just who they are.

[Haddy]

Guys just as a point of clarification, I specifically referred to mammals. Yes sharks and reptiles continuously replace their teeth, but not from back to front as these few mammals do.

The shark equivalent would be 6 inch posterior megs. Now that would be something!

Yup. "Marching Molars" probably wouldn't be an appropriate term for sharks and reptiles.

[Ron E.]

Fascinating post, Smilodon, and very educational. But somehow it just pi$$es me off!!!

[siteseer]

Harry and siteseer,

My source is a personal conversation about 5 years ago with Dr. Daryl Domning, the world's leading authority on fossil sirenians. emphasis added

I emailed Dr. Domning and he sent me this reply, referring to that paper I cited (Husar, 1977) which provided evidence against manatees continuously producing teeth:

Husar's statement was mistaken. She cited Peter Van Bree as her source, but he subsequently denied ever having made such an observation; and in fact no manatee that had stopped replacing its teeth has ever been observed. They do replace their teeth throughout life; and so does the convergently-evolved Australian rock wallaby Peradorcas concinna. It is definitely a relatively recent adaptation in both animals, not a primitive holdover from Mesozoic mammals.

There are actually three sirenians (all dugongids) described from the Bone Valley Formation: the halitheriine Metaxytherium floridanum (the common one); the large (and rare) dugongine Corystosiren varguezi; and the "pygmy" dugongine Nanosiren garciae.

Sincerely,

Daryl Domning

[Harry Pristis]

I emailed Dr. Domning and he sent me this reply, referring to that paper I cited (Husar, 1977) which provided evidence against manatees continuously producing teeth:

Husar's statement was mistaken. She cited Peter Van Bree as her source, but he subsequently denied ever having made such an observation; and in fact no manatee that had stopped replacing its teeth has ever been observed. They do replace their teeth throughout life; and so does the convergently-evolved Australian rock wallaby Peradorcas concinna. It is definitely a relatively recent adaptation in both animals, not a primitive holdover from Mesozoic mammals.

There are actually three sirenians (all dugongids) described from the Bone Valley Formation: the halitheriine Metaxytherium floridanum (the common one); the large (and rare) dugongine Corystosiren varguezi; and the "pygmy" dugongine Nanosiren garciae.

Sincerely,

Daryl Domning

That's great that you seized the initiative, 'siteseer' -- and it's good that Daryl responded.

My own research turned up the anomalous wallaby, Peradorcas, so the trivia claim was already unsupported.

I don't know a lot about dugongids; but, I do recognize flawed logic when I read it. The claim that "no manatee that had stopped replacing its teeth has ever been observed" is not evidence that manatees endlessly replace molars. That is an attempt to prove a negative.

It is vaporous to argue that manatees replace molars throughout their lives. That's true on it's face. When they stop replacing molars (perhaps at some finite limit), their lives are over. No teeth, no eating . . . end of life. Do you see? The claim that a toothless manatee has never been observed could at least as easily be an artifact of collecting as evidence of endless molars.

[siteseer]

That's great that you seized the initiative, 'siteseer' -- and it's good that Daryl responded.

My own research turned up the anomalous wallaby, Peradorcas, so the trivia claim was already unsupported.

I don't know a lot about dugongids; but, I do recognize flawed logic when I read it. The claim that "no manatee that had stopped replacing its teeth has ever been observed" is not evidence that manatees endlessly replace molars. That is an attempt to prove a negative.

It is vaporous to argue that manatees replace molars throughout their lives. That's true on it's face. When they stop replacing molars (perhaps at some finite limit), their lives are over. No teeth, no eating . . . end of life. Do you see? The claim that a toothless manatee has never been observed could at least as easily be an artifact of collecting as evidence of endless molars.

Harry,

I had emailed him before on another topic so I thought he might indulge me this time (I hope he didn't think it was just the settling of a "bar bet"). It's always best to find out what was actually said. It also flawed logic to simply appeal to an "authority" to support an argument, (hearsay evidence) though Domning is certainly one to consult in this particular matter. If not the leading authority, he's probably a starter on that basketball team.

I see your points. I did ask him if anyone has ever found a manatee that had died of extreme old age but he didn't answer it directly. It is possible that none of the manatees killed or found dead to this point were at their maximum life expectancy especially since they have been listed as endangered (maybe as few as 2000 living individuals). That starts us off with a small sample size so it would be a true rarity to find one that has survived the modern world's hazards to its physiological limit (at least 50 years).

On the other hand it appears that the claim holds up for now according to present research. Maybe you and I could get a grant to look into this or otherwise raise money to end all speculation even if it ends up as another episode of "Monsterquest."