埼玉県立自然史博物館研究報告 第15号 (1997)
秩父盆地中新統産の315個の歯化石にもとずく
カグラザメ属Hexanchus sp.の歯列解析
金子正彦
347-0066埼玉県加須市本町15-29
藤井孝三
350-0065埼玉県川越市仲町3-1
高山義孝
371-0047群馬県前橋市関根町3-15-4
坂本 治
埼玉県立自然史博物館369-1305埼玉県秩父郡長瀞町1417-1
要 旨 秩父盆地中新統産のカグラザメ属Hexanchus sp.の歯化石315本を,現生2種H. griieus, H. nakamuraiとの比較にもとずいて歯列解析を行い,その歯式をD=P L9A2A2L9P_/P L6MIL6P と決定し,顎骨上の位置決定を行った.
上顎前歯は,咬頭に対する歯根の大きさや咬頭の近,遠心の稜線の違いから,第1,第2前歯に分けられる.
上顎側歯は,第1咬頭頂一歯頚前端と第1咬頭頂一歯頚後端とのなす角(θ)が関数的に変異し,側歯数は9個に分けられる.また,下顎側歯は,第1咬頭頂一歯頚前端間距離(α)と歯頚前端−歯根底縁間距離(β)との比(α/β)に関数的変異が見られ,側歯数は6個に分けられる.
下顎正中歯は, 9個の歯化石を採取した事から,変化に富む歯冠と,変化に乏しい歯根を有する事が分かった.歯牙最大高と歯牙最大幅がほぼ等しく, Centralcuspを有するものと無いもの,対称なものと非対称なものがある.
キーワード: Hexanchus,歯列解析,秩父盆地中新統.
図版3.秩父盆地中新統産Hexanchus sp. (埼玉県立自然史博物館所蔵, SMNH-VeF 54)
上顎右第1前歯(1a, 1b),上顎右第2前歯(2a, 2b),上顎右第1側歯(3a, 3b).上顎右第2側歯(4a, 4b),上顎右第3側歯(5a, 5b),上顎右第4側歯(6a, 6b),上顎右第5側歯(7a, 7b),上顎右第6側歯(8a, 8b),上顎右第7側歯(9a, 9b),上顎右第8側歯(10a, lob),上顎右第9側歯(lla, llb),下顎正中歯(12a, 12b),下顎右第1側歯(13a, 13b),下顎右第2側歯(14a, 14b),下顎右第3側歯(15a, 15b),下顎右第4側歯(16a, 16b),下顎右第5側歯(17a, 17b),下顎右第6側歯(18a, 18b), a :唇側面観, b :舌側面観
Analysis of Dental Formula Based on 315 Fossil Teeth of
Hexanchus sp. from the Miocene in the Chichibu Basin, Central Japan
Masahiko KANEKO
15-29 Honcho,Kazo City,Saitama 347-0066
Kouji FUJII
3-1 Nakacho,Kawagoe City,Saitama 350-0065
Yoshitaka TAKAYAMA
3-15-4 Sekine-machi,Maebashi City,Gunma 371-0047
and
Osamu SAKAMOTO
Saitama Museum of Natural History, Nagatoro, Chichibu-gun, 369-1305
Abstract
As the result of analysis of 315 fossil teeth of Hemnchus sp. collected from a bed of the iocene Chichibu basin,by comparing with two Recent species, H. griseus and H. nakamurai. We decided Dental formula and the position of each specimen on the upper and lower jaw bones.We assume that the Dental formula is D=P L9A2A2L9Pm) L6MIL6P.
The upper anterior teeth can be separated into first and second anterior teeth on the basis of the difference in the ridge on the mesial distal face and Size of the root compared with the cusp.
The upper lateral teeth show functional changes in the angle ( θ ) made by two lines of A and B; (A : the line connecting two points of the apex of the primarycusp and the crown-root junction of the mesial base of the primarycusp, B : the line connecting two points of the apex of the primarycusp and the crown-root junction of the distal base of the crown), and we could divide the upper lateral teeth into nine.
The lower lateral teeth show functional changes in the ratio ( α/β ) of the length ( α ) from the apex of primarycusp to the end of the mesial base, and the length ( β ) from the end of the mesial base to the basal line of the root.We could divide the lower lateral teeth into six.
Nine fossil specimens of median teeth were discovered, from that we found that they have much variation in the crown and monotony form of the root. They are about equal in height and width, sometimes have Centralcusp and the sometimes don't, the sometimes have show symmetry and sometimes have asymmetry.