Coco

Heterorodontie Of Selachians

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Heterorodontie of selachians

To begin, some words are in french language, because I didn't find them in english (very technical words). I'm sorry.

Selachians (sharks, rays and chimaera) are heterodontes ! What it means ?

In greek language : hetero = different, & donte = tooth

Yes, selachians have different teeth ! We shall take charge here especially to the sharks and to the rays / bates.

SEVERAL SORTS OF HETERODONTIE IN SELACHIANS

- L’hétérodontie ontogénique

the teeth of specimens of the same species are different between youngs and adults.

Here are nice pictures of the marvelous website : http://www.digimorph.org

http://www.digimorph.org/specimens/Heterodontus_francisci/hatchling/

Very young (12 cm long) Heterodontus francisci - horn shark

hetero11.jpg

Adult (58,5 cm long) Heterodontus francisci - horn shark

hetero12.jpg

- L'hétérodontie gynandrique

To the same species, we can observe differences between the teeth of males and females

A female Dasyatis pastinaca - common stingray (jaw : 25 mm / 40 mm)

dasyat10.jpg

A male Dasyatis pastinaca - common stingray (50 mm / 75 mm)

dasyat11.jpg

- L’hétérodontie dignathique

On the same shark or ray, the teeth of the upper jaw are different from those of the lower jaw

A Dalatias licha - kitefin shark (100 mm / 100 mm)

dalati10.jpg

- L'hétérodontie monognathique

on the same shark or ray, the upper teeth (or the lower ones) are different, like for men.

Lamna nasus - portbeagle (150 mm / 165 mm)

lamnan10.jpg

In this last case, he can have various sorts of teeth :

machoi10.jpg

1. symphyseal (alone in the middle of the jaw),

1'. para-symphyseal (one on each side of the symphyseal ones, even if this last one does not exist),

2. anterior (often rather long, they are situated just after para-symphyseal ones),

3. intermediate (often smaller, they are situated after the anterior ones),

4. lateral (the most common teeth, they are situated after the anterior ones, and often more or less tilted towards the corner of the mouth),

5. commissural (teeth which are the closest to the corner of the mouth).

All the sharks and all the rays / skates do not possess all these types of teeth.

SEVERAL SORTS OF DENTAL TYPES IN SELACHIANS

- catchers

generally possess small-sized, sharp and accompanied or not side teeth laterla cusplets, for example Scyliorhinidae, Orectolobidae, Rajidae and Dasyatidae (Essentially males for the last two genus)

Orectolobus ornatus - banded wobbegong (200 mm / 300 mm)

orecto10.jpg

- scrashers out

have teeth with the main cusplet is long and disentangled with a well developed sharp edge and, mostly, accompanies with one or several side lateral cusplets. The sharks possessing this type of teeth can use up to 4 rows of teeth at the same time. We speak here about Odontaspidae or of most of Lamnidae. Not any skates / bates in this type of selachians.

Lamna nasus - portbeagle (150 mm / 165 mm)

lamnan11.jpg

- cutters

whose teeth have the indented sharp edges (for practically all the forms) with a base of the wide tooth. These sharks use generally only a single dental row. Visible on [ i ] Galeocerdo [/i] or [ i ] Carcharodon [/i]. Those whose teeth are not pinked have the very tight teeth in the jaw, and their sharp edge is particularly disentangled as [ i ] Squalidae [/i].

Carcharodon carcharias - great white shark (35 mm on left side - upper tooth / 30mm on right side - lower tooth)

carcha10.jpg

Centrophorus squamosus - leafscale gulper shark (125 mm / 155 mm)

centro10.jpg

In this category, we find the subcategory "catchers-scrashers out". The teeth of the upper jaw and those of the lower jaw are of different type, one of the type catchers and other one of the type cutters. For example Hexanchidae or Carcharhinidae families.

Notorhynchus cepedianus - sevengill sharks (175 mm / 275 mm)

notorh10.jpg

- giver up

they are recognizable because teeth are tidied up in staggered rows in the jaw. Teeth are of convex shape, and very often wrinkled. We find this shape especially on the skates like Raja, Dasyatis or Rhynchobatus ; for the sharks on Triakis or Mustelus

Pastinachus sephen - feathertail stingray (110 mm / 18mm)

pastin10.jpg

Mustelus antarticus - gummy shark (100 mm / 110 mm)

mustel10.jpg

- crushers

they have the flat teeth of shape polygonale, imbricated the ones in the othersones, the organization is very useful to crush preys like shells or shellfishes. In this category we shall find Myliobatis , Rhinoptera, Aetobatus, Asteracanthus or Ptychodus

Aetobatus narinari - white-spotted eagle ray (150 mm / 160 mm)

aetoba10.jpg

catchers-crushers group include only one family, Heterodontidae, whose previous (antérieures) teeth are agrippeur type with side denticules, and the side teeth are the crushing type more or less spray-painted

Heterodontus portusjaksoni - Port Jackson shark( 85 mm / 100 mm)

hetero12.jpg

I add a particular adaptation : the sharks saws (sharks) and the sawfishes (skates), which have a rostrum on which are fixed the "rostrales teeth". Their method of hunting is to penetrate into shoals of fish by shaking from right to left this rostrum and to mean some moments later eating fishes so killed. We find them on Pristiophorus and Pristis.

Pristis pectinata - smalltooth sawfish (485 mm)

pristi10.jpg

To finish, here are two pictures to show you a "dental row" and a "dental line".

Dental row, on the same line, from middle road towards the corner of the mouth on an Isurus oxyrhichus (mako shark)

isurus11.jpg

Dental line, from the front towards the back of the mouth on an Isurus oxyrhinchus (mako shark):

isurus10.jpg

I thank you for having read up to the end !

Bibliography

- Types dentaires adaptatifs chez les sélaciens actuels et post-paléozoïques - Cappetta H. 1986

- Les poissons de mer des pêches françaises-Identification, inventaire et répartition de 209 espèces - Quero JC. et Vayne JJ. 1997

- Dents de requins et de raies du tertiaire de la Belgique - Nolf D. 1988

- Condrychthyens - Landemaine o. 1992

All of colour pictures are from me, and specimens from my collection. Text translated with agreement of its author : Anhuta, a french friend.

Coco

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Very nice presentation, Coco. Thanks for sharing this with us here. :D

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WOW, Coco! You put a lot of effort into that and I find

it intriguing. Going to print it so I can save....:D

I love those young horn shark teeth. They look a bit like

dermal denticles.

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Thanks :blush:

The skin dermal denticles of selachians are made of the same material as their teeth. It is the reason for which, sometimes, we can find fossilized dermal denticles.

Coco

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Thanks :blush:

The skin dermal denticles of selachians are made of the same material as their teeth. It is the reason for which, sometimes, we can find fossilized dermal denticles.

Coco

Yes the same material and maybe the same exact teeth but just located

in different positions?

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Thank you Coco; this is valuable information, explained in a very easy to understand way!

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That is wild! Thanks for sharing! :)

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Very interesting! Thanks for posting. cool.gif

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A wonderful reference of comparative material. Thanks, Coco.

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Coco,

Yes, thanks for the review - great photos. The technical terms are very close to the English versions (heterodonty = heterodontie; gynandric = gynandrique; dignathic = dignathique, etc.).

The term "commissural" has fallen out of usage in English though it is an applicable term. "Posterior" is used instead though a few researchers consider posteriors as merely more reduced laterals.

In English "scrashers" would be the "tearing-type" teeth, shaped to rip into thin-skinned, soft-bodied prey - often small enough to be swallowed whole.

"Cutters" is correct, the cutting-type teeth, shaped to bite through tougher tissues (sea turtle shell, thick skin, mammal muscle, large bones) and often serrated to make the task easier. The biting action is a combination of the narrower lower teeth digging into the prey as the uppers saw down, removing a mouthful of flesh from a prey animal too large to be swallowed whole.

"Catchers-scrashers" are the "clutching-tearing type" teeth, shaped to snag bite-sized, thin-skinned, soft-bodied prey.

A "dental line" in English is a "file" as in French (some authors call it a "tooth family").

Cappetta's tooth terms were first published in French but he published them in English as well within his "Chondrichthyes II" from the Handbook of Paleoichthyology series (Cappetta, 1987). Anyone wanting more details can consult that volume.

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Thanks to you all!

Rozzilla, I don't understand exactly your question... Perhaps I could put some pics about shark skins.

Siteseer, thank you for these complementary precise details. In France, we continue to use "commissural" word because it is more explicit than "posterior".

I knew that this subject would interest you ! It is my Xmas present ! ;)

Coco

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Thanks to you all!

Rozzilla, I don't understand exactly your question... Perhaps I could put some pics about shark skins.

Siteseer, thank you for these complementary precise details. In France, we continue to use "commissural" word because it is more explicit than "posterior".

I knew that this subject would interest you ! It is my Xmas present ! ;)

Coco

Hi Coco,

Thanks for the shark topic! I'm not sure what Rozzila means, but as you know, denticles are not identical to teeth as they have different functions. In open water sharks the denticles, though tiny, add to the animals' hydrodynamic shape. Their arrangement and shape along the body help channel water past the body like tiny fins. They also help discourage parasites. In some rays and skates, their denticles are enlarged as a form of defense from predators and from rubbing or bumping along the sea bottom.

I would like to see your photos of shark skins. I saw a skin of an Echinorhinus once - bramble shark which has little bumps and spines (larger than the average denticle).

A couple of years ago, I found the the book, "Requins, raies, et autres chondrichthyes fossiles," by Patrice Lebrun. It's a nice one.

Joyeux Noel, Coco

Jess

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Siteseer, you are right. Selachian teeth and dermal denticles are just made in the same thing, but their function are very different !

Some recent selachian skins

Here are little parts of shark skins. Each species has its own particular skin. All pictures are from a french friend, D. SENAN.

Centrophorus squamosus - Leafscale gulper shark

centro10.jpg

centro11.jpg

centro12.jpg

centro13.jpg

centro14.jpg

Centroscymnus cœlolepis - Portuguese dogfish

centro15.jpg

centro16.jpg

centro17.jpg

Mustelus asterias - Starry smooth-hound

mustel10.jpg

mustel11.jpg

mustel12.jpg

Scyliorhinus canicula - Small-spotted catshark

scylio10.jpg

scylio11.jpg

scylio12.jpg

Coco

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Thanks for this post. The pictures are very good. The shark skin pictures have a certain beauty. It is an interesting challenge to determine heterodonty for extinct shark species, some with no known natural tooth sets. Comparing with extant species is important. I'll read this post a few times to try an absorb some the details.

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Just love seeing those pics and from a post up there I did get my answer.

Thank you so much....:D

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Coco...... WOW....... thanks for sharing this information with us..... and the images you have used are fabulous.... well done....and thanks for taking the time to put it all together, Im sure the shark collectors are drooling....I notice the Sawfish with the "rostrales teeth"..... Im intrested in your thoughts on the Carb (Xenacanthid) Sharks Headspines that apparently attached to the skull pointing backwards (it is thought).... they to demonstrate spines arranged in a similar manner to the "rostrales teeth". ..... the sawfish adaptation makes sense for hunting purposes, but for what purpose could a shark have backward pointing spine on the head? the only possibility i can think of is to avoid predation itself, from the larger Rhizondonts...a backward pointing barb like a modern 'stickleback' today... maybe....

Heres one I found ..... upper Carb Westphalian in age....

post-1630-12619108189932_thumb.jpg

Edited by Terry Dactyll

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Im intrested in your thoughts on the Carb (Xenacanthid) Sharks Headspines that apparently attached to the skull pointing backwards (it is thought).... they to demonstrate spines arranged in a similar manner to the "rostrales teeth". ..... the sawfish adaptation makes sense for hunting purposes, but for what purpose could a shark have backward pointing spine on the head? the only possibility i can think of is to avoid predation itself, from the larger Rhizondonts...a backward pointing barb like a modern 'stickleback' today... maybe....

Terry,

Yes, it could be partly for defense, especially for juveniles, tough to swallow the fish whole - ouch! An adult xenacanth was a sizable fish so the spine would have been a less useful. As is postulated for stethacanthid sharks which bore a head spine which curved back from its head to point forward, xenacanth males may have bit onto the spine as a way of anchoring itself as it coiled its body around a receptive female as the mating session proceeded (I hope I don't get "bleeped" with all this explicit description). From what I've read, these sharks had eel-like bodies at least as flexible as many of today's more bendable analogues.

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Thanks Terry !

Siteseer, I think you are right about headspines and self-defense, like stingrays have barb(s) on their tail.

Xenacanthid (freshwater shark) are very old sharks (Devonian), but some of recent sharks have spine on the first dorsal fin, even on both dorsale fins : Squalus acanthias ( Piked dogfish) or Centrophorus squamosus (leafscale gulper shark).

Here is a Squalus acanthias, you can see the 2 spines :

http://upload.wikimedia.org/wikipedia/commons/archive/2/23/20060606000600!Squalus_acanthias.jpg

And a Centrophorus squamosus :

http://fr.academic.ru/pictures/frwiki/67/Centrophorus_squamosus.JPG

Best regards

Coco

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Xenacanthid (freshwater shark) are very old sharks (Devonian), but some of recent sharks have spine on the first dorsal fin, even on both dorsale fins : Squalus acanthias ( Piked dogfish) or Centrophorus squamosus (leafscale gulper shark).

Coco,

Yes, they were one of the early shark groups and they survived a long time - all the way to the Late Triassic. I have read of specimens from Arizona. There was a dealer (Ebay, I think) claiming to have teeth from the Triassic of New Mexico but the ones he photographed were too large to be that species. I believe he was selling the more common Early Permian teeth of Oklahoma (X. texensis) as the less common Late Triassic species (X. moorei).

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siteseer......Thanks for the response, its nice to learn a little more about my finds...

Coco....Thanks for the images to help explain the position of the spine, I can see the 2 spines clearly.....

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Coco, Thanks for posting such an interesting and well illustrated discussion on elasmobranch dental diversity. The amount of evolutionary adaptation and refinement of dentition, spines, and dermal denticles is utterly staggering in both sharks and rays. The dental sexual dimorphism of the dasyatid (stingray) you illustrated is of special interest to me. You may mention that in some rays, such as Dasyatis sabina (Atlantic stingray) males have been well documented to undergo seasonal dental morphological changes. In the non-mating season for Atlantic stingrays, mature males have teeth with rounded cusps just as females of the species do, but during mating season male dentition changes to a sharply pointed curved cuspidate tooth shape to allow males to grasp females securely during copulation.

Looking at your image of the Pristis rostrum, I must point out that it is not from Pristis pectinata as you suggest, but from Pristis zijsron (green sawfish). I base my determination on the inter-tooth space of the anterior versus the posterior-most teeth combined with the high tooth count per side and the overall greenish tint to the rostrum.

Thanks very much for contributing this discussion!

Jason

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Hi Jason,

Thanks. I had difficulties to identify the Pristis rostrum. I will change its name... And search on the web some pics to see the differences.

Coco

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Hi Jason,

Thanks. I had difficulties to identify the Pristis rostrum. I will change its name... And search on the web some pics to see the differences.

Coco

Thanks again for the amazing pictorial review of the elasmobranchs.

Concerning the Pristis zijsron rostrum, let me recommend the following webpage (at end of link below) at the Florida Museum of Natural History for info on the green sawfish and differences in rostral morphology between it and other pristids:

http://www.flmnh.ufl.edu/fish/gallery/descript/greensawfish/greensawfish.htm

Cheers,

Jason

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Thanks a lot Jason for this link which looks like a great website.

Coco

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Thanks Terry !

Siteseer, I think you are right about headspines and self-defense, like stingrays have barb(s) on their tail.

Xenacanthid (freshwater shark) are very old sharks (Devonian), but some of recent sharks have spine on the first dorsal fin, even on both dorsale fins : Squalus acanthias ( Piked dogfish) or Centrophorus squamosus (leafscale gulper shark).

Coco,

Heterodontus, a genus dating back to the Jurassic and one of an order of sharks separate from the squalids you noted, also has two dorsal spines.

In another thread I mentioned an article on xenacanth sharks. It discusses the possible interpretations of the head spine and placoid scales:

Hampe, O. 1997.

Zur funktionellen Deutung des Dorsalstachels und der Placoidschuppen der Xenacanthida (Chondrichthyes: Elasmobranchii; Unterperm). Neues Jahrbuch Geol. Palaont. Abh. 206 (1): 29-51.

The author concludes that the head spine was primarily a defensive weapon and includes an illustration showing the range of movement of the spine as the shark turned its head.

Jess

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