Echinorhinus Dermal Denticle

[Northern Sharks]

This is my latest ebay purchase, and one which the seller wasn't sure enough about the ID to say without error that it is an Echinorhinus denticle. I've seen similar pieces labelled as such, but I was wondering if anybody out there can say for sure that it is a Bramble/Prickly shark denticle. It is Pliocene from the Bahia Inglesa Formation in Chile. Brambles are known from the area. If it isn't, then I'm open to suggestions as to what it may be. Thanks in advance

[siteseer]

This is my latest ebay purchase, and one which the seller wasn't sure enough about the ID to say without error that it is an Echinorhinus denticle. I've seen similar pieces labelled as such, but I was wondering if anybody out there can say for sure that it is a Bramble/Prickly shark denticle. It is Pliocene from the Bahia Inglesa Formation in Chile. Brambles are known from the area. If it isn't, then I'm open to suggestions as to what it may be. Thanks in advance

Northern Sharks,

I checked a couple of references for your specimen. It does not appear to be an Echinorhinus denticle - a species similar to a modern form anyway. E. cookei has smaller ones with a multi-pointed star-shaped basal outline (no larger than 4mm in basal diameter). E. brucus denticles can be that big but they are finely ridged and tend to stick out rather straight without protruding from an inflated base (peduncle) as yours appears to do. In E. brucus the denticle rises from a rather thin and flat base with a rounded basal outline. I could not find any remark on Echinorhinus denticles bearing an enameloid coating either.

The Bahia Inglesa is Early Pliocene - not that long ago in terms of time and perhaps not long enough for there to be much of a difference between the bramble sharks of that time and today. I do not believe that there are any confirmed records of E. brucus in the eastern Pacific of the Americas but Bruce Welton (1979) did report a bramble tooth he considered close to E. cookei in the Late Pleistocene San Pedro Sand near Los Angeles.

It's tough to say without more of the base and there aren't a lot of references for dermal denticles. You might try contacting David Ward or Gordon Hubbell.

The references I checked are:

Deynat, P.P. and P.M. Brito. 1994.

Revision des Tubercules cutanes de raies (Chondrichthyes, Batoidea) du Bassin de Parana, Tertiaire d'Amerique du sud. Annales de Paleontologie (Vert.-Invert.) 80 (4): 237-251.

This one is interesting because it compares some ray denticles found in South America to those of other groups, including Echinorhinus.

Garrick, J.A.F. 1960.

The Genus Echinorhinus, with an Account of a Second Speciesfrom, E. cookei Pietschmann, 1928, from New Zealand waters. Studies on New Zealand Elasmobranchii. Part. X. Transactions of the Royal Society of New Zealand. 88 (1): 105-117.

This one clearly shows what E. cookei denticles look like but no good figures for E. brucus.

Welton, B.J. 1979.

Late Cretaceous and Cenozoic Squalomorphii of the Northwest Pacific Region. Unpublished Ph.D. dissertation. University of California, Berkeley.

In this one Welton discusses how to distinguish the teeth of different species of Echinorhinus, fossil and modern.

[Al Dente]

It looks like a malar thorn from a male skate. A good reference for skate and ray material is Gravendeel, Ronald; Van Neer, Wim & Brinkhuizen, Dick (2002): An Identification Key for Dermal Denticles of Rajidae from the North Sea. International Journal of Osteoarchaeology. This reference idenfies modern North Sea rays and skates but can be helpful with fossil material from other locations.

[siteseer]

It looks like a malar thorn from a male skate. A good reference for skate and ray material is Gravendeel, Ronald; Van Neer, Wim & Brinkhuizen, Dick (2002): An Identification Key for Dermal Denticles of Rajidae from the North Sea. International Journal of Osteoarchaeology. This reference idenfies modern North Sea rays and skates but can be helpful with fossil material from other locations.

Al Dente,

Thanks for the reference. I will check that out.

[siteseer]

I found a reference with an illustration of E. brucus dermal denticles. It's in German but it does have pictures and English translations of the captions:

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.

It's an article discussing the possible functions of the head spine and placoid scales of xenacanth sharks with comparisons to the spines and scales of other cartilaginous fishes.

[Northern Sharks]

It's been a while, but I think I have my answer. I received the following info from Dr. John McEachran at Texas A&M, a skate expert:

The specimen is an alar thorn from a skate. Alar thorns occur near the apices of the wings in mature males. The fact that it is barbed suggests that it is from a species in the tribe Rajini that includes the genera Cruriraja, Anacanthobatis, Dipturus, Okamejei, Raja, Rostroraja and two unnamed generic level taxa: the North Pacific assemblage and the amphi-American assemblage. Recently only Dipturus occur off Chile although the amphi-American assemblage occur as far south as Peru.

[Boesse]

Yes, definitely a skate thorn. I've got some weird specimens from the Pliocene of California that look like the bucklers of Raja clavata figured in that paper, but lack a large thorn, and just have a wimpy little enamel nub, making them look more like Dasyatis centroura. It took me a long time to get them confidently identified.

Bobby