caa a22 4500 388016779 CHVBK 20180307124913.0 cr unu---uuuuu 161130e199807 xx s 000 0 eng 10.1017/S0022336000040348 doi S0022336000040348 pii (NATIONALLICENCE)cambridge-10.1017/S0022336000040348 Transitional Gryphaeate/exogyrate oysters (Bivalvia: Gryphaeidae) from the Lower Jurassic of Northern Chile [Elektronische Daten] [N. Malchus, M. Aberhan] Sinemurian and Pliensbachian Exogyrinae from northern Chile described herein as Nanogyra? cf. auricularis are considered the oldest members of the subfamily known to date. Comparisons with a large number of Jurassic Nanogyrini and aberrant Gryphaea species suggest that they are most closely related to Nanogyra? auricularis (Münster in Goldfuss) from the Toarcian of France, but probably not identical. Morphotypes of several Chilean specimens are transitional between gryphaeate and exogyrate forms, and their assignment to either Gryphaeinae or Exogyrinae appears arbitrary. In order to solve this taxonomic problem, the microstructures of Nanogyra? cf. auricularis and co-occurring typical Gryphaea species were examined and compared to a large database from previous studies. The results suggest that shell chambering is a feature common to all Exogyrinae but not to Gryphaea sensu stricto. Complex cross foliation and branching cross foliation are characteristic of both groups. However, they are more abundant in Gryphaea and apparently become phylogenetically reduced in the Exogyrinae. The transitory morphotypes and microstructures, especially of the Sinemurian specimens, are further evidence for the evolution of the Exogyrinae from the Gryphaeinae. Obviously, the Chilean specimens are very close in time and space to the origin of the subfamily. Thus, the lowermost Jurassic Andean back-arc basin of western South America is considered a plausible place of origin of the Exogyrinae. Copyright © The Paleontological Society Malchus N. Departament de Geologia, Facultat de Ciencies, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Barcelona), Spain, <nikom@cc.uab.es> aut Aberhan M. Institut für Paläontologie der Universität, Pleicherwall 1, D-97070 Würzburg, Germany, <kmartin.aberhan@mail.uni-wuerzberg.de> aut Journal of Paleontology Cambridge University Press 72/4(1998-07), 619-631 0022-3360 72:4<619 1998 72 JPA https://doi.org/10.1017/S0022336000040348 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S0022336000040348 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Malchus N. Departament de Geologia, Facultat de Ciencies, Universitat Autònoma de Barcelona, E-08193 Bellaterra (Barcelona), Spain, <nikom@cc.uab.es> aut NATIONALLICENCE 700 1- Aberhan M. Institut für Paläontologie der Universität, Pleicherwall 1, D-97070 Würzburg, Germany, <kmartin.aberhan@mail.uni-wuerzberg.de> aut NATIONALLICENCE 773 0- Journal of Paleontology Cambridge University Press 72/4(1998-07), 619-631 0022-3360 72:4<619 1998 72 JPA CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge