Spiraxis interstrialis, and its junior synonym Fayolia mourloni, an uppermost Famennian (Upper Devonian) fossil first described as algae and subsequently interpreted as the oldest known chondrichthyan egg case, is reinvestigated based on the discovery of several additional specimens in Belgian collections. New data, in particular from micro-CT imaging, allow to refute S. interstrialis, and by extension also Spiraxis major (the type species of Spiraxis Newberry, non Adams) and Spiraxis randalli from the Famennian of New York and Pennsylvania, as chondrichthyan egg cases. Alternative interpretations of these enigmatic helicoidal fossils are discussed. The first occurrence of oviparity in the fossil record of chondrichthyans is thus not as old as previously thought and is close to the first occurrence of viviparity in this group, both being recognised now in the Mississippian. The question of which of both conditions is plesiomorphic within chondrichthyans, and more widely within vertebrates, is discussed. Also, the presence of the genus Spiraxis in both the USA (east coast) and Belgium reinforces the strong faunal resemblance already observed in both palaeogeographical areas. It suggests important faunal exchanges between these regions of the Euramerica landmass during the Famennian.

Spiraxis interstrialis及其初级同义词Fayolia mourloni，一种最上层法门（上泥盆纪）化石，最初被描述为藻类，随后被解释为已知最古老的软骨鱼类蛋壳，根据在比利时收藏中发现的几个额外标本进行了重新调查。新数据，特别是来自显微 CT 成像的数据，可以反驳S. interstrialis，进而驳斥Spiraxis major（Spiraxis Newberry的类型物种，非 Adams）和Spiraxis randalli来自纽约和宾夕法尼亚的法门，作为软骨鱼类蛋壳。讨论了这些神秘的螺旋化石的替代解释。因此，软骨鱼类化石记录中第一次出现卵生并没有以前认为的那么古老，并且接近该组中第一次出现胎生，两者现在都在密西西比河中得到确认。讨论了这两种情况中的哪一种在软骨鱼类中和更广泛地在脊椎动物中是同形的。此外，Spiraxis属在美国（东海岸）和比利时的存在加强了在这两个古地理区域已经观察到的强烈动物群相似性。它表明在法门年期间欧美洲大陆的这些地区之间存在重要的动物群交流。