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It is essential to survey the dentition of recent sharks systematically for identification of the fossil Carcharhinus.@Carcharhinus is a large genus with some 30 species. I examined dentitions of recent nineteen species mainly from sharks living in the sea off Japan. Comparing fossil sharks from eleven localities of Japan to recent sharks, I found fourteen fossil shark species. Fossil carcharhinids from those assemblages are almost the same as those living in the sea off Japan and there are some fossil shark teeth which seem to be slightly different to those of modern sharks. Among these thirteen species found, only C. amboinensis is not a fish of the Japanese archipelgo.

Fossil shark species; 14species:C. albimarginatus,C. altimus, C. amboinensis, C. brachyurus, C. brevipinna, C. dussumieri, C. galapagensis, C. leucas, C. limabatus, C. longimanus, C. macloti , C. melanopterus, C. obscurus, C. plumbeus, C. sorrah.
Grey fishes of the Japanese archepelago; 16species: C. albimarginatus, C. altimus, C. amblyrhynchoides, C. brachyurus, C. brevipinna, C. dussumieri, C. falciformis, C. galapagensis, C. leucas, C. limbatus, C. longimanus, C. macloti, C. melanopterus, C. obscurus, C. plumbeus,, C. sorrahD
;Taniuchi et al., ; Mizue et al., ; Nakaya et al.,,; Tokai University (The fishes of the Japanese archipelago)D

Part I : Teeth with serrated cutting-edge
(1) Pleistocene, Ichijyuku Chiba Prefecture

(2) Pleistocene, Ami Ibaraki Prefecture

(3) Pliocene, Kakegawa Shizuoka Prefecture

(4) Pliocene, Okinawa Honto

(5) Pliocene, Hirono Hukushima Prefecture

(6) Pliocene, Naarai Chiba Prefecture

(7) Late Miocene, Kyonan Chiba Prefecture

(8) Middle Miocene, Nishikatura Yamanashi Prefecture

(9) Early Miocene, Ichisi Mie Prefecture

(10) Oligocene Ashiya group Hukuoka Prefecture

Part II : Teeth with rough serrations on the distal heel

There are four recent carcharinids with rough serrations on the distal heel of upper tooth as those of the genus Galeocerdo . I collected this type of three fossil carcharhinids (two from Okinawa, one from Kyonan) and compared these fossil species to the four recent species. As a result, fossil sharks from Okinawa were assigned as C. dussumieri.
:*: C. borneensis, C. dussumieri, C. sealei, C. sorrah

Part III : Teeth with smooth cusp

There are four recent sharks with serrations on the heel but without on the cusp. For identification those shark species, I referred to the report described below because I could not obtain those sharks except for C. signatus. C. macloti was the most abundant shark among fossil teeth with smooth cusp I found. C. macloti is a relatively small sized shark and characterized by dental sexual dimorphism.
* : C. hemiodon, C. isodon (C. leiodon), C. macloti, C. signatus
Ref.; NOAA Technical Report NMFS 34 J. A. F. GARRICK, Additions to a Revision of the Shark Genus Carcharhinus: Synonymy of Apriodon and Hypoprion, and Description of a New Species of Carcharhinus (Carcharhinidae)

(6) Middle Miocene, Sekinohana

(6) Early -early Middle Miocene, Ichisi

(7) Oligocene Ashiya

Part IV : unidentified teeth

This sample looks like Glyphis.

I thought it possible to identify upper teeth of the fossil species of Carcharhinus from Japan by analyzing some twenty recent species including sharks living off the sea of Japan. However, it was not exactly that simple. There are many fossils which are not so easy to assign because of their dental variations. The variations, possibly derived from individual difference, male-female difference, maturity level and passage of time, will cause uncertainty of assignment. For accurate dental analysis of the fossil Carcharhinus, we need to research recent shark species, however, in some species, we need to examine many individuals systematically for understanding the species.

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20090601 Fumio Nakagawa

Appendix I
C. obscurus, C. longimanus, and C. galapagensis

Fig. 1. Silhouettes of C. obscurus, C. longimanus, and C. galapagensis. These relatively large sharks show similar dental morphology to each other and distribute worldwide (FAO). They live in the sea near Japan. In the lower teeth, they are easily identifiable while in the upper teeth, assignment is rather difficult.

Appendix II

I assigned unknown extinct species with non-serrated teeth from the Oligocene of Ashiya group as "possibly Carcharhinus sp." (2008 06 02). Here I reassigned them as Isogomphodon. Fossils shown below are assigned Isogomphodon cf. acuarius (top column), probably Isogomphodon (central column), and possibly Isogomphodon (down column).
Assignment of extinct species by teeth only without questions is probably not possible. The genus Carcharhinus and the genus Negaprion bear similar dental morphology to each other, however, the extinct shark was likely to be the genus Carcharhinus because of the variety of the dental morphology. The genus Isogomphodon also shows similar dental morphology to those of the genera. These extinct sharks have been assigned as Isogomphodon by Probst and others. According to them I reassigned those extinct sharks to the Isogomphodon.

Oligocene, Ashiya group

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