性二态性的表达在软体动物的各种化石群中得到认可,例如Ammonoidea,一组已灭绝的带壳头足类动物。在中生代,在侏罗纪超家族Perisphotoidea中可以看到记录最好的性二态例子。它通常通过不同的成虫大小和反dimorphs之间的孔隙修饰来表达。推定的雄性(也称为微海螺)体积较小,在壳的末端发育,而雌性(大海螺)较大,并带有简单的peristome。可疑的案件是,然而,在那个超家族里,通常与分类学偏差或缺乏诊断特征有关,还有一些人暴露了壳形态和装饰中的“性别逆转”所说明的个体发育异常。
发现了两个CallovianAspidoceratidaePeltocerasathleta(Phillips)标本,同时具有女性和男性的特征,质疑Ammonoidea中“性逆转”的意义和原因。这两个标本始于Peltocerasathleta的大海螺个体发育,并在成虫中表现出明显的雄性变化,如它们的圆形螺纹截面所示,肋骨逆行,微海螺典型的结节和长尾的褪色。很少有其他女性对男性的情况,以及男性对女性的“性逆转”,在化石记录中已知,全部属于侏罗纪的Perisphincetoidea(Perisphinctidae或Aspidoceratidae)。由于所有侏罗纪的Perisphincetoidea都是严格的淋病菌,这些“性逆转”本质上是病理性的,在这里被称为一种新的形式型病理学:即“形式雌雄同体”。
在没有明确的伤害或寄生证据的情况下,我们假设这样的“雌雄同体”个体说明了性欲的病理病例。人们对氨虫类软部分知之甚少,并且不可能确定哪些内部性器官出现在具有男性和女性外壳特征的标本中。异常女性化和/或男性化也发生在现代头足类动物中,后者也只对淋病物种进行分组。这种现象同样可以通过成年人体型的变化以及女性和男性结构的混合来说明。在这种情况下,性欲在人群中要么是有利的,要么是导致不育的。性欲的原因尚不清楚,但现代头足类动物会诱发环境污染物,因为它们充当内分泌干扰物。“性逆转”和/或非功能性生殖异常也是由各种性腺腹足类物种的内分泌干扰物引起的,但是侵扰,遗传异常,温度波动或病毒是多种原因,可以通过直接的性腺影响刺激或抑制神经内分泌活动,最终导致鱼类的女性化或男性化,等足动物,甲壳类动物,腹足类也是.无论“雌雄同体”是由于外生还是内生原因,侏罗纪中双性人Perisphotoidea的记录可以通过对双态对的容易识别来解释,以及易于收集大量且保存充分的化石古种群,在统计上有更多机会发现双性恋标本。
Expression of sexual dimorphism is recognised in various fossil groups of molluscs such as the Ammonoidea, an extinct group of shelled cephalopods. During the Mesozoic, the best-documented sexual dimorphic examples are seen in the Jurassic superfamily Perisphinctoidea. It is usually expressed by distinct adult size and apertural modifications between the antidimorphs. Putative males (otherwise referred to as microconch) are small in size and develop lappets at the end of the shell while the females (macroconch) are larger and bear a simple peristome. Dubious cases are, however, known in that superfamily, which often relate to taxonomic biases or lack of diagnostic characters, and some others expose ontogenetic anomalies illustrated by \'sex reversals\' in the shell morphology and ornamentation.
The discovery of two specimens of the Callovian Aspidoceratidae Peltoceras athleta (Phillips), having both female and male features, questions the significance and causes of \'sex reversals\' in the Ammonoidea. The two specimens have started with the macroconch ontogeny of Peltoceras athleta and show an apparent change toward maleness in the adult, as illustrated by their rounded whorl section, ribs retroversion, fading of the tubercles and lappets typical of the microconchs. Few other cases of female-to-male, as well as male-to-female \'sex reversal\', are known in the fossil record, all belonging to the Jurassic Perisphinctoidea (families Perisphinctidae or Aspidoceratidae). Since all Jurassic Perisphinctoidea are strictly gonochoristic, these \'sex reversals\' are pathological in nature and are herein referred to as a new forma-type pathology: namely \"forma hermaphrodita\".
In the absence of any clear evidence of injury or parasitism, we hypothesize that such \"forma hermaphrodita\" individuals illustrate pathologic cases of intersexuality. Little is known about the ammonoid soft parts, and it is not possible to determine which internal sexual organs occur in specimens having both male and female external shell features. Abnormal feminisation and/or masculinisation also occur in modern cephalopods, the latter also grouping only gonochoric species. This phenomenon is similarly illustrated by a change in the adult body size and a mixing of both female and male structures. In that
case, intersexuality is either advantageous in the population or caused sterility. The causes of intersexuality are not clearly established but environmental pollutants are evoked in modern cephalopods because they act as endocrine disrupters. \'Sex reversals\' and/or non-functional reproductive abnormalities have also been caused by endocrine disrupters in various gonochoric gastropods species, but infestation, genetic abnormalities, temperature fluctuations or viruses are multiple causes, which can stimulate or inhibit neural-endocrinal activity by direct gonadal influence, and ultimately lead to feminisation or masculinisation in fishes, isopods, crustaceans, and gastropods as well. Regardless of whether \"forma hermaphrodita\" is due to an exogenic or endogenic cause, the record of intersex Perisphinctoidea in the Jurassic can be explained by the ready recognition of dimorphic pairs, and the easy collection of large and sufficiently preserved fossil palaeopopulations in which intersex specimens have statistically more chance to be found.