Back & Forth
|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
Part I : Teeth with serrated cutting-edge
|‘;Taniuchi et al., ‘; Mizue et al., ‘; Nakaya et al.,,‘; Tokai University (The fishes of the Japanese archipelago)D
|(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
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.
Back & Forth
20090601 Fumio Nakagawa
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.
Back & Forth
|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.