A dimorphism of sexual origin is recognized and has been convincingly demonstrated in ammonites for a long time (e.g. Makowski, 1962; Callomon, 1963). Sexual maturity is usually associated with several morphological traits characteristic of adulthood. These changes distinguish the antidimorphes (macroconchs and microconchs) by differences in size, coiling (opening of the umbilicus or uncoiling of the shell), changes in the peristome, changes in ornamentation, or all four combined, depending of the groups you consider...

thanks a lot..

more info could be found here:

Callomon J.H. (1963) Sexual dimorphism in Jurassic ammonites // Trans. Leicester Liter., Philos. Soc. Vol. LVII. P. 21-56.

http://ashipunov.info/jurassic/j/Callomon,%201963-%20Sex.%20Dimorph.%20Jura.%20Am..pdf

Makowski H. (1962) Problem of sexual dimorphism in ammonites // Paleont. Polonica. no.12. 92 p.

http://ashipunov.info/jurassic/j/Makowski,1962_dimorphism-ammonites.pdf

Makowski H. (1971) Some remarks on the ontogenetic development and sexual dimorphism in the Ammonoides // Acta geol. Pol. V.21. no.3. Р.321-340. 

http://ashipunov.info/jurassic/j/Makowski,%201971_ontogeny%20&%20dimorphism%20in%20ammonites.pdf

Palframan D.F.B. (1969) Taxonomy of sexual dimorphism in ammonites: morphogenetic evidence in Hecticoceras brightii (Pratt) // Int. Union of Geol. Sci. Ser.A. no.1. P.126-154.

http://ashipunov.info/jurassic/j/Palframan,%201969-sexual%20dimorphism.pdf

Rollier L. (1913) Sur quelques Ammonoïdes Jurassiques et leur dimorphisme sexuel // Arch. Sci. Phys. et Natur. Geneve. Sér.4. T.XXXV. P.263-288.

http://ashipunov.info/jurassic/j/Rollier,1913_dimorphism_amm_Jurassique.pdf

Westermann G.E.G. (1969) Proposal: Classification and nomenclature of dimorphs at the genus-group level // Int. Union Geol. Sci. Ser. A. № 1. Sexual dimorphism in fossil Metazoa and taxonomic implications. Stuttgart: Schweizerbart. P. 234-238. 

http://ashipunov.info/jurassic/j/Westermann,%201969Proposal.pdf

Westermann G.E.G. (1969) Supplement: Sexual Dimorphism, Migration, and Segregation in living Cephalopoda // Int. Union Geol. Sci. Ser. A. № 1. Sexual dimorphism in fossil Metazoa and taxonomic implications. Stuttgart: Schweizerbart. P. 18-20. 

http://ashipunov.info/jurassic/j/Westermann,%201969Supplement.pdf

see also Ammonoid Paleobiology, 1996

p.s. For alternative view on ammonite dimorphism see:

Matyja B.A. (1986) Developmental polymorphism in Oxfordian ammonites // Acta geol. polon. V.36. no.1-3. P.37-68. http://ashipunov.info/jurassic/j/Matyia,%201986_developmental_polymorphism.pdf

Matyja B.A. (1994) Developmental polymorphism in the Oxfordian ammonite subfamily Peltoceratinae // Proc. 3rd Pergola Int. Symp., Pergola, 25-30 october 1990. Paleopelagos Spec. Publ.1. P.277-286

http://ashipunov.info/jurassic/j/Matyja,1994_peltoceraspolymorphism.pdf

very good... thanks a lot professor Mikhail Rogov

A very intesting possibility is described by Parent, Scherzinger and Schweigert in this paper:

Parent, H., Schwerzinger, A., Schweigert, G. 2008, Sexual phenomena in Late Jurassic Aspidoceratidae (Ammonoidea). Dimorphic correspondence between Physodoceras hermanni (Berckhemer) and Sutneria subeumela Schneid, and first record of possible hermaphroditism. Palaeodiversity 1: 181–187

There is also a short introduction to the topic in the German magazine Fossilien:

http://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.fceia.unr.edu.ar%2Ffisiografia%2Flpb%2Fparent%2FSchweigert_etal_Fossilien_28.pdf&ei=2eE_VMPjPKT4yQPY14L4Dw&usg=AFQjCNG6WoeIz4wsRwSkZC74VrBd3bIziA&bvm=bv.77648437,d.bGQ

Dr. Jens Carl  very very thanks