Environmental Biology of Fishes 63: 309–319, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. Teeth of embryos in lamniform sharks (Chondrichthyes: Elasmobranchii) Kenshu Shimada a,b,c a Environmental Science Program and Department of Biological Sciences, DePaul University, Chicago, IL 60614, U.S.A. b Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL 60607, U.S.A. c Corresponding address: Environmental Science Program, DePaul University, 2320 North Kenmore Avenue, Chicago, IL 60614, U.S.A. (e-mail: kshimada@depaul.edu) Received 25 July 2000 Accepted 17 July 2001 Key words: lamnoid, dentition, dental pattern, tooth replacement Synopsis The dentitions of lamniform sharks possess a unique heterodonty, the lamnoid tooth pattern. However, in embryos, there are ‘embryonic’ and ‘adult’ dentitions. The teeth in the embryonic dentition are peg-like and appear to be attached to the jaw in an acrodont fashion. The adult dentition is characterized by the presence of replacement tooth series with the lamnoid tooth pattern. The embryonic–adult transition in dentitions appears at around 30–60 cm TL. Tooth replacement generally begins before birth in embryos with adult dentitions. The adult dentition becomes functional just before or after parturition. An embryo of one species (Lamna nasus) shows a tooth directly on the symphysis of the upper jaws, marking the first record of a medial tooth for the order Lamniformes. Introduction Intraspecific variation in tooth row count and den- tal morphology occurs in various elasmobranchs. Variation can result from sexual differences (Kajiura & Tricas 1996, Springer 1966) and ontogeny (Reif 1976, 1984). However, data on such dental variations are still limited for most elasmobranchs. The order Lamniformes (mackerel sharks) con- sists of 15 living species in mid to low latitude oceans worldwide, ranging from intertidal zones to deep seas (Compagno 1999; exclude a dubious Carcharias tricuspidatus and an undescribed Alopias sp.; Figure 1). Most lamniforms possess a unique het- erodont dentition called the ‘lamnoid tooth pattern’. The pattern is characterized as ‘teeth usually well dif- ferentiated along jaws, with enlarged anterior teeth, a gap or small intermediate teeth separating the ante- rior teeth from the lateral teeth in the upper jaw, but with posterior teeth not enlarged’ (Compagno 1984, p. 212; see also Shimada 2001). However, in some lamniform species, the dental morphology of embryos differs greatly from that of adults (e.g., Gilmore 1993). Specimens of lamniform embryos are limited due to three reasons. First, reproduction of lamniforms is obli- gate lecithotrophic (Wourms et al. 1988), and catches of pregnant females are uncommon (e.g., Francis 1996, Stevens 1987). Second, in captivity, care is difficult and costs are high (Gruber & Keyes 1981, Murru 1990, Smith 1992, Stevens 1995). Third, embryos of pre- sumably all lamniforms show intra-uterine cannibalism (mostly oophagy), reducing the number of individuals that survive (e.g., Castro et al. 1997, Gilmore 1993, Villavicencio-Garayzar 1996). Scarcity of embryos has hampered studies con- cerning various aspects of early development of lamniforms. The aim of this paper is to investigate early ontogenetic development of lamniform teeth. This study integrates my observation of embryonic specimens with published data.