title: Shell bone histology of the long-necked chelid Yaminuechelys (Testudines: Pleurodira) from the late Cretaceous-early Palaeocene of Patagonia with comments on the histogenesis of bone ornamentation.
abstract: Yaminuechelys is a long-necked chelid turtle whose remains have been recovered from outcrops of the Santonian-Maastrichtian and Danian of South America. With the purpose of providing data about shell sculpturing origin and palaeoecology, the bone histology of several shell elements (including neural, costal, peripheral and plastral plates) of Yaminuechelys is described herein. Histological analysis reveals that Yaminuechelys shares with Chelidae the presence of interwoven structural fibre bundles in the external cortex, and parallel-fibred bone of the internal cortex. The presence of resorption lines in several samples indicates that the particular ornamentation of the external surfaces originated, at least in part, by focalized resorption and new bone deposition. This mechanism for ornamentation origin and maintenance is here described for the first time in a turtle. Compactness of the shell bones is consistent with an aquatic habitat, which supports previous hypothesis based on palaeoenvironmental and morphological data.
authors.affiliation: Grupo vinculado al IANIGLA-CONICET, San Rafael, Argentina. jjannello@mendoza-conicet.gob.ar.|Museo de Historia Natural de San Rafael, Av. Ballofet s/n, frente al parque Mariano Moreno, CP5600, San Rafael, Mendoza, Argentina. jjannello@mendoza-conicet.gob.ar.
authors.forename: Juan Marcos
authors.identifier: http://orcid.org/0000-0002-3821-0586
authors.initials: JM
authors.lastname: Jannello
authors.affiliation: CONICET, Instituto de Investigaciones en Paleobiología y Geología, Universidad Nacional de Río Negro, Belgrano 1700, Paraje Pichi Ruca (predio Marabunta), CP8300, Cipolletti, Río Negro, Argentina. nachocerda6@yahoo.com.ar.|Museo Carlos Ameghino, Belgrano 1700, Paraje Pichi Ruca (predio Marabunta), CP8300, Cipolletti, Río Negro, Argentina. nachocerda6@yahoo.com.ar.
authors.forename: Ignacio A
authors.initials: IA
authors.lastname: Cerda
authors.affiliation: Grupo vinculado al IANIGLA-CONICET, San Rafael, Argentina. mdelafuente@mendoza-conicet.gob.ar.|Museo de Historia Natural de San Rafael, Av. Ballofet s/n, frente al parque Mariano Moreno, CP5600, San Rafael, Mendoza, Argentina. mdelafuente@mendoza-conicet.gob.ar.
authors.forename: Marcelo S
authors.initials: MS
authors.lastname: de la Fuente
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology* / Q000166:cytology; D000818:Animals; D001118:Argentina; D001842:Bone and Bones / Q000033:anatomy & histology* / Q000166:cytology; D005580:Fossils; D014426:Turtles / Q000033:anatomy & histology* / Q000145:classification*
keywords: Chelidae; Microanatomy; Morphogenesis of bone ornamentation; Palaeoecology