The erroneous chondrichthyan egg case assignments from the Devonian: implications for the knowledge on the evolution of the reproductive strategy within chondrichthyans
August 18, 2021
Bernard Mottequin (1), Stijn Goolaerts (2), Adrian P. Hunt (3), Sébastien Olive (1)
The Science of Nature, 108, Issue 36, August 2021. DOI: 10.1007/s00114-021-01751-z
Keywords
Fish egg cases; Bioturbations; Coprolites; Micro-CT imaging; Chondrichthyans; Reproductive strategy
Abstract
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.
How Our Software Was Used
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Author Affiliation
(1) O.D. Earth and History of Life, Royal Belgian Institute of Natural Sciences, rue Vautier 29, 1000 Brussels, Belgium.
(2) O.D. Earth and History of Life & Scientifc Service of Heritage, Royal Belgian Institute of Natural Sciences, rue Vautier 29, 1000 Brussels, Belgium.
(3)Flying Heritage and Combat Armor Museum, 3407 109th St SW, Everett, WA 98204, USA.