The definition of "carina"

[pachy-pleuro-whatnot-odon]

Hi all,

I recently got into a discussion on the Dutch fossil forum about the definition of the term "carina", which my conversation partner equated to "the cutting edge of a tooth". They then further went on to claim crocodiles don't have carinae but rather apicobasal ridges that span the length of the tooth crown.

 

Now I've used the term lots over the years and know @Jesuslover340 has also used carinae in the context of crocodile teeth. But as I can't find a singular definition of the term as pertains to teeth online, I was wondering how the term is officially defined - whether it might be possible that I may have been using it wrongly and under the wrong assumptions.

 

So, basically:

1. What are carinae? Are they the cutting edges of a tooth, or do they include the apicobasal ridges that are commonly found on the mesial or dorsal end of reptile teeth?
2. Are carinae necessarily serrated?
3. Is use of the term "carina" taxonomically restricted? Does the term apply to crocodiles, for example?

 

I possible, I would like to try and get at an academically recognized definition of the term. Or, failing that, get insight into the academic discussion as to its meaning.

[Troodon]

This is from C Hendrickx paper (2015) on theropod tooth morphology but applies to all teeth:  Croc, Mosasaur etc

 

Carina (ca)—A sharp, narrow, and well-delimited ridge or keel-shaped structure running apicobasally on the crown and, in some cases, on the root base, and typically corresponding to the cutting edge of the tooth (McGraw-Hill, 2003; Reichel, 2012; Brink and Reisz, 2014; Figs. 1D, 2A, B). The carina (used back to the 19th century, e.g., Eastman, 1899) differs from flutes and longitudinal ridges in being a much smaller and better-delimited ridge with acute corners. It can be serrated or not, straight or twisted. The carina can extend either to the crown apex or below it, and can reach the cervix or terminate above or below it. The carina can also be split, which is usually caused by trauma, aberrant tooth replacement or genetic factors (Erickson, 1995). The carina is denoted the ‘keel’ by some authors (e.g., Farlow et al.,1991; Abler, 1992; Holtz et al., 1998).

[pachy-pleuro-whatnot-odon]

Thanks! Seems like I've been using the term correctly then

[Al Dente]

5 hours ago, pachy-pleuro-whatnot-odon said:

I recently got into a discussion on the Dutch fossil forum about the definition of the term "carina", which my conversation partner equated to "the cutting edge of a tooth". They then further went on to claim crocodiles don't have carinae but rather apicobasal ridges that span the length of the tooth crown.

 

Carinae and apicobasal ridges are two different things. A crocodile can have both. Carinae are the cutting edges, apicobasal ridges are the "ornamentation" or "striations" on some teeth. Here is an explanation from a paper with a photo showing the ridges.

 

 

[pachy-pleuro-whatnot-odon]

Thanks, @Al Dente! That's exactly what I thought! 

[Shellseeker]

4 hours ago, Al Dente said:

Carinae and apicobasal ridges are two different things. A crocodile can have both. Carinae are the cutting edges, apicobasal ridges are the "ornamentation" or "striations" on some teeth. Here is an explanation from a paper with a photo showing the ridges.

 

Alligator teeth are common in the Florida fossil records,  Crocodile teeth are rare.  I have thought that gators have carinae, but not apicobasal ridges, which if true becomes a differentiator. This half tooth is 14 mm in length.

[pachy-pleuro-whatnot-odon]

19 minutes ago, Shellseeker said:

Alligator teeth are common in the Florida fossil records,  Crocodile teeth are rare.  I have thought that gators have carinae, but not apicobasal ridges, which if true becomes a differentiator. This half tooth is 14 mm in length.

As I understand it, though crocodiles and alligators can both have carinae, it's only crocodiles that have striae - in some species. Moreover, alligator teeth are typically more rounded and blunt - though beware heterodonty in crocodiles, which may result in very alligator-like teeth being part of otherwise sharp and pointy crocodilian dentition. See for example this post with reference to Brachychampsa and Borealosuchus:

 

The tooth you posted an image of, to me, looks like that of a crocodile, by the way...

[Shellseeker]

13 hours ago, pachy-pleuro-whatnot-odon said:

As I understand it, though crocodiles and alligators can both have carinae, it's only crocodiles that have striae - in some species. Moreover, alligator teeth are typically more rounded and blunt - though beware heterodonty in crocodiles, which may result in very alligator-like teeth being part of otherwise sharp and pointy crocodilian dentition. See for example this post with reference to Brachychampsa and Borealosuchus:

 

The tooth you posted an image of, to me, looks like that of a crocodile, by the way...

Thanks for your response. That is a good thread that pretty well highlights differences... I am much less familiar with Crocodiles, either fossil or modern. We get occasional Crocs here is Florida, but they seem to be immigrants from Cuba and stay mostly in the lower everglades. Might find 1 Croc tooth per 1000s of gator teeth. The modern gators do not always stay away from remote hunting locations in the Peace River.

 

 

On the teeth,  I think the following is slightly incorrect.  Gator usually have a single Carina or no carina.  I seems that the statement might be "Alligators at most have 1 Carina,  Crocodiles can have many Apicobasal ridges"

 

Do you know of any Crocodile teeth that display one and only one Carina / Apicobasal ridge?

 

Croc have lots of raised ridges:

[pachy-pleuro-whatnot-odon]

1 hour ago, Shellseeker said:

Thanks for your response. That is a good thread that pretty well highlights differences... I am much less familiar with Crocodiles, either fossil or modern. We get occasional Crocs here is Florida, but they seem to be immigrants from Cuba and stay mostly in the lower everglades. Might find 1 Croc tooth per 1000s of gator teeth. The modern gators do not always stay away from remote hunting locations in the Peace River.

 

Thanks! There's another thread that deals with the differences between crocodile and alligator teeth - may be even better than the one in my previous post - and goes into the identification of a number of different species. It might be more informative in certain aspects, as it adds some additional detail to my summary in the other thread:

 

 

1 hour ago, Shellseeker said:

On the teeth,  I think the following is slightly incorrect.  Gator usually have a single Carina or no carina.  I seems that the statement might be "Alligators at most have 1 Carina,  Crocodiles can have many Apicobasal ridges"

 

You're entirely right. Actually, according to @Jesuslover340's thread above, alligators can even have two carinae. My personal experience with alligator-teeth, however, is rather limited, as I mainly focus on the Mesozoic, when they were not yet around (I believe they first appeared in the Oligocene). Unfortunately, though, I don't quite remember whether I was just trying to be concise (more likely), or whether this is actually an oversight. In any case, it's not reflective of reality, and thus good to have pointed out

 

As to apicobasal ridges and carinae, these are not the same, as I understand it. The ridges are ornamental, whereas carinae are "keels" mesial and/or dorsal to the tooth. I'm not sure whether this is indeed what you meant with "Crocodiles can have many Apicobasal ridges", as I do have a Dyrosaurus phosphaticus tooth in my collection that appears to have three carinae, yet no ornamental apicobasal ridges (which is what the term more commonly applies to, and is also what's illustrated in your last photograph) . This third carina may be pathological, though.

 

1 hour ago, Shellseeker said:

Do you know of any Crocodile teeth that display one and only one Carina / Apicobasal ridge?

 

No, can't say that I do... I believe crocodiles very consistently have two carinae. But I'd be happen to be proven wrong

[pachy-pleuro-whatnot-odon]

An interesting note on the term "carinae" as applies to plesiosaurs:

 

On 2/10/2021 at 11:48 AM, paulgdls said:

A general point Noe makes about carinae [in plesiosauria] and terminology:

 

"The term enamel ridges is adopted here as the ornamentation is raised above the surface of the tooth, elongate and restricted to the enamel of the tooth crown (Owen, 1841: 272). Enamel ridges, extending from the bottom of the enamel to the apex of the tooth, have occasionally been referred to as `carinae' (Sauvage, 1873: 379; Bardet et al., 1993: 12), but this is incorrect usage of the term which suggests opposing enamel ridges with associated flattening of the tooth between them as found in crocodiles (Romer, 1956: 441). As such `carinae' are not found in the Plesiosauria, the term is not applicable and should not be used."

 

This has me wondering a bit, though, especially the part where Noe suggests that use of the term carinae "suggests opposing enamel ridges with associated flattening of the tooth between them as found in crocodiles", as I doubt there is little discussion about whether or not mosasaurs have carinae - yet certain species of mosasaur (most notably Eremiasaurus heterodontus) and certain species of alligator (see above) have only a single carina. As such, carina might need to be redefined as apicobasal structures/ridges along the mesiodistal axis of a tooth, that divide it into labial and lingual sides. Not that it changes whether plesiosaurs have them, but I don't think the number of them or flattening of the tooth should be part of the definition...