Browsing Paleontology Collected Works by Subject "Palaeontology"
Now showing 1 - 2 of 2
Results Per Page
ItemCopulation in antiarch placoderms and the origin of gnathostome internal fertilisation(Nature Publishing Group, 2014-10-19) Long, John A; Mark-Kurik, Elga; Johanson, Zerina; Lee, Michael S Y; Young, Gavin C; Min, Zhu; Ahlberg, Per E; Newman, Michael; Jones, Roger; den Blaauwen, Jan; Choo, Brian; Trinajstic, KateReproduction in jawed vertebrates (gnathostomes) involves either external or internal fertilization. It is commonly argued that internal fertilization can evolve from external, but not the reverse. Male copulatory claspers are present in certain placoderms, fossil jawed vertebrates retrieved as a paraphyletic segment of the gnathostome stem group in recent studies. This suggests that internal fertilization could be primitive for gnathostomes, but such a conclusion depends on demonstrating that copulation was not just a specialized feature of certain placoderm subgroups. The reproductive biology of antiarchs, consistently identified as the least crownward placoderms and thus of great interest in this context, has until now remained unknown. Here we show that certain antiarchs possessed dermal claspers in the males, while females bore paired dermal plates inferred to have facilitated copulation. These structures are not associated with pelvic fins. The clasper morphology resembles that of ptyctodonts, a more crownward placoderm group, suggesting that all placoderm claspers are homologous and that internal fertilization characterized all placoderms. This implies that external fertilization and spawning, which characterize most extant aquatic gnathostomes, must be derived from internal fertilization, even though this transformation has been thought implausible. Alternatively, the substantial morphological evidence for placoderm paraphyly must be rejected. ItemFirst shark from the late Devonian (Frasnian) Gogo Formation, Western Australia sheds new light on the development of tessellated calcified cartilage(PLOS One, 2015-05-28) Long, John A; Burrow, Carole J; Ginter, Michal; Maisey, John G; Trinajstic, Kate; Coates, Michael I; Young, Gavin C; Senden, Tim JHere we present new data from the first well-preserved chondrichthyan fossil from the early Late Devonian (ca. 380–384 Mya) Gogo Formation Lägerstatte of Western Australia. The specimen is the first Devonian shark body fossil to be acid-prepared, revealing the endoskeletal elements as three-dimensional undistorted units: Meckel’s cartilages, nasal, ceratohyal, basibranchial and possible epibranchial cartilages, plus left and right scapulocoracoids, as well as teeth and scales. This unique specimen is assigned to Gogoselachus lynnbeazleyae n. gen. n. sp.