Horse Tooth Growth

[Shellseeker]

I have been OUT this week... twice to the Peace River. It is hard to communicate how happy that makes me. Neither adventure found a large volume, but there were a couple of high quality fossils, even 2 very similar.

1st on Monday.

Horse teeth form below the gum line, 1st the enamel "cap",  then from looking at this one the dentine, and finally the roots. I have an enamel cap, no dentine, without the roots. This horse dies at a very young age while the tooth was forming.  I'm thinking this may be mighty small for Equus, but that may be because I am fixated on pre_Equus small horses.

 

Interesting, but then maybe the fossil gods are sending me a message. On Wednesday, I went back out to a different location and found ANOTHER very similar tooth...

 

Once again, Enamel cap & dentine, but no roots... In this case, the tooth is used !! chewed on.. How does that happen??  I am missing something here.  This is a bigger tooth, Equus but the width is still very small at 8mm. I might have to send an email to Richard Hulbert, but I am hoping that someone else has traveled this path of understanding horse teeth growth. I am going to submit and add the occlusal and root view as a reply...  Jack

[Shellseeker]

Here are the 2 missing views of the last tooth.. The quality of this tooth is excellent. Note that the chewing wear has not yet reached the entire occlusal surface. 

[ynot]

Sweet teeth!

[Tidgy's Dad]

It's just so great to get out hunting again, isn't it? 

The finds are good, but it's the hunt that's the thing. 

[Harry Pristis]

Hmmm.  I think the first horse tooth is actually a fragment of mammoth tooth plate.  I've never seen a horse tooth with the crenulated surface that one has.  The second tooth is, I think, a deciduous tooth on which wear has exposed the entire occlusal surface.  Assuming this is equus, these deciduous teeth are retained for three years.  The roots have broken away.

 

Comments on mammal tooth development. Dentin and cementum are deposited within the crypt in a complicated progression: a kernel or "shard" of dentin is the first step. enamel, then orthodentine, more dentin, then cementum. The softest of these different materials, cementum, is often lost in fossil teeth, and sometimes death intervenes to interrupt late-stage tooth development.
 
The timing of cementum deposition could cause confusion. It is the enamel epithelial sheath, which encloses the enamel crown, that must be breached before cementum can be deposited. That breach takes place at the cellular level. That is a different thing from the tooth erupting from the alveolar crypt.

Beginning with a sieve-like penetration by mesodermal cells, part of the enamel epithelial sheath breaks down. Cementum-producing osteoblasts ("cementoblasts" of some authors) from surrounding tissue then deposit cementum on the now-available crown enamel. Dentin continues to be deposited on the interior (pulp cavity).
 
Then, osteoclasts open the bone which protects the crypt. In the case of a premolar, the osteoclasts also attack the roots of a deciduous antecessor. The tooth emerges under hydrostatic pressures. Once the tooth crown emerges from the crypt, the "cementoblasts" are no longer supported and are finished with their work on the crown.

The fact that there are to be found rootless, hollow enamel shells of teeth is an accident of when the animal died in this sequence of tooth development.

I have relied for this information on Bernhard Peyer's COMPARATIVE ODONTOLOGY as translated and edited by Rainer Zangerl with a forward by A. S. Romer. Maybe there is newer, better information published now.

 

 

[Shellseeker]

57 minutes ago, Harry Pristis said:

Hmmm.  I think the first horse tooth is actually a fragment of mammoth tooth plate.  I've never seen a horse tooth with the crenulated surface that one has.  The second tooth is, I think, a deciduous tooth on which wear has exposed the entire occlusal surface.  Assuming this is equus, these deciduous teeth are retained for three years.  The roots have broken away.

 

Comments on mammal tooth development.........

 

Harry,

All I can say is that your responses are excellent and this one is Outstanding. crammed with knowledge and top_shelf pictures..

I am going to have to take the time and go slowly thru your discussion of tooth development just so I better understand this complicated process.  That will generate some additional questions on my part. I am out to dinner in a couple of hours and then hunting  2 of the next 3 days.

I will also craft an email to Richard on the 1st tooth,   Thanks Jack

 

This Wikipedia article seems to have some collaborating info.

Quote

Horses are diphyodontous, erupting a set of first deciduous teeth (also known as milk, temporary, or baby teeth) soon after birth, with these being replaced by permanent teeth by the age of approximately five years old. The horse will normally have 24 deciduous teeth, emerging in pairs, and eventually pushed out by the permanent teeth, which normally number between 36 and 40. As the deciduous teeth are pushed up, they are termed "caps". Caps will eventually shed on their own, but may cause discomfort when still loose, requiring extraction.

and....

Quote

Continuous eruption and loss

A horse's incisors, premolars, and molars, once fully developed, continue to erupt as the grinding surface is worn down through chewing. A young adult horse's teeth are typically 4.5–5 inches long, but the majority of the crown remaining below the gumline in the dental socket. The rest of the tooth slowly emerges from the jaw, erupting about 1/8" each year, as the horse ages. When the animal reaches old age, the crowns of the teeth are very short and the teeth are often lost altogether. Very old horses, if lacking molars to chew, may need soft feeds to maintain adequate levels of nutrition.

Older horses may appear to have a lean, shallow lower jaw, as the roots of the teeth have begun to disappear.^[6] Younger horses may seem to have a lumpy jaw, due to the presence of permanent teeth within the jaw.

 

[Harry Pristis]

 

When I suggested that the deciduous teeth are retained for 3 years, this is the schedule I relied upon.  As you can see, if the adult teeth (p2, p3, and p4) emerge between 2.5 and 3.5 years, the deciduous predecessors must be lost (barring a pathology) in the same time span.

 

[Sacha]

Harry, how do you know all this stuff???

[digit]

On 3/22/2019 at 5:23 PM, Sacha said:

Harry, how do you know all this stuff???

I'd say it is a subject that is near and dear to him and so he's done a deep dive to learn more about horse teeth than the average big animal vet may remember. I'm just glad it gets passed on here so we can all up our game a bit.

 

I agree with Harry (nice to be able to say that) that the texture on the first specimen instantly made me think mammoth. The occlusal surface supports that idea as it also resembles the chewing end on the mammoth teeth I have in my collection.

 

Glad that you were able to get out. The recent rains have spiked up the river but it does seem to be dropping back again. Looks too high for my deeper sites but I'm wondering what it would be like at the more shallow sites. I'm supposed to be guiding 16 kids and a dozen parents on a fossil hunt (planned and reserved months ago) on the Peace River. I may have to drive out early and do a bit of groundtruthing.

 

 

Cheers.

 

-Ken

[Shellseeker]

1 hour ago, digit said:

Glad that you were able to get out. The recent rains have spiked up the river but it does seem to be dropping back again. Looks too high for my deeper sites but I'm wondering what it would be like at the more shallow sites. I'm supposed to be guiding 16 kids and a dozen parents on a fossil hunt (planned and reserved months ago) on the Peace River. I may have to drive out early and do a bit of groundtruthing.

 

I went out last Monday and again last Wednesday when the Zolfo gauge was slightly lower than it is right now.

I could only hunt the river edges,  as the center of the river was too deep to hold traction while digging. Even then I was digging in chest deep water, trying to reach the deepest gravel.

Hopefully the water depth drops before you go out...  Jack

[Plantguy]

Enjoyed seeing the latest Jack. congrats--glad you are getting out! 

I was thinking the other day I should put my limited horse tooth finds together and look at the differences more closely. Ill put it on the todo list.

Great thread!

Regards, Chris