Trabajos presentados en el “International Meeting on the Secondary Adaptation of Tetrapods to Life in Water”

Varios integrantes del Grupo de Biología Evolutiva de la UNED han presentado trabajos durante el 9th International Meeting on the Secondary Adaptation of Tetrapods to Life in Water. Este año el SECAD se ha organizado desde Chile y se ha celebrado virtualmente entre los días 19-23 de abril.

A continuación, os dejamos los resúmenes de los trabajos presentados por los integrantes del Grupo de Biología Evolutiva de la UNED:

FIRST STEPS FOR A MORPHOMETRIC APPROACH TO THE SEXUAL DIMORPHISM OF EUROPEAN EXTINCT PLEURODIRAN TURTLES:
The study of sexual dimorphism in the fossil record can provide relevant data about the social structure of several extinct species. Information about this variability is unknown for most vertebrate extinct species, since a considerable sample size and a good preservation are generally necessary to perform such studies, especially when the objective is to analyze sexually variable characters through a quantitative approach. Turtles are a peculiar group of reptiles, characterized by the presence of a shell. Some characters associated with sexual dimorphism can be recognized in this osseous structure. Given that several turtle lineages are part of the current biodiversity, the analysis of their dimorphism can help to understand that of some extinct forms. Thus, a wide variety of sexually dimorphic characters has been demonstrated for extant taxa, opposite trends for some characters occurring between males and females of several lineages. However, relatively few studies focused on sexual dimorphism in extinct forms are available. This study aims to analyze and synthesize the sexual dimorphism present in one of the two clades that is part of the crown Testudines: Pleurodira. This clade is known from the Upper Jurassic to the present and, although it is currently restricted to intertropical regions, its distribution in the past was much greater, being very abundant in both the Upper Cretaceous and the Eocene records of Europe. To achieve the proposed objective, sexual dimorphism was evaluated in the most relevant and best-represented lineages of pleurodiran turtles in the European record, especially considering the taxa recorded in south-western Europe, which belong to Dortokidae, Bothremydidae and Podocnemididae. The morphotypes of the analyzed European species recognized as potentially attributable to sexual dimorphs were compared not only with other extinct forms but also with extant representatives of Podocnemididae, Pelomedusidae and Chelidae. Comparisons were made both by the first-hand study of some specimens and by analyzing the information available in the literature. The sexual variability was analyzed through a quantitative approach, with the landmark-based geometric morphometric method, providing precise results through objective analysis and graphic tools for its quantification and visualization. Thus, several statistical techniques were used to extensively identify and characterize the shell elements affected by sexual variation. The results evidence a significant sexual dimorphism in most pleurodiran lineages, specifically, in the morphology of the anal notch. The comparison of the sexual dimorphism between the main clades provides information to understand different trends acquired throughout the evolutionary history of Pleurodira.

FIRST THREE-DIMENSIONAL NEUROANATOMICAL AND CRANIAL RECONSTRUCTION OF A BOTHREMYDID TURTLE (TESTUDINES, PLEURODIRA)
El uso de la tomografía axial computarizada (TAC) para estudios neuroanatómicos es una técnica no invasiva muy útil para analizar las cavidades craneales y las estructuras internas. Desde finales del siglo veinte, la utilización de estas herramientas ha sido empleada para el estudio de varios taxones extintos de vertebrados. La aplicación de esta técnica para el análisis de tortugas fósiles es más reciente que en otros grupos como en cocodrilos, dinosaurios o mamíferos. De esta manera, la primera reconstrucción neuroanatómica de una tortuga extinta, correspondiente a la de Plesiochelys etalloni del Jurásico Superior europeo, fue publicada hace menos de diez años. Aunque en la actualidad hay disponibles modelos tridimensionales correspondientes a reconstrucciones neuroanatómicas en diferentes clados de tortugas (incluyendo taxones basales y derivados), la información sobre la neuroanatomía de Pleurodira permanece aún muy escasa. De hecho, aunque se han incluido algunas reconstrucciones neuroanatómicas parciales de miembros actuales de Pleurodira en estudios comparativos, tan solo ha sido publicada la neuroanatomía de dos especies fósiles, ambas miembros de Podocnemidoidae. El clado extinto Bothremydidae es uno de los linajes de tortugas pleurodiras mejor representado en el registro fósil durante el Cretácico y Paleógeno de varios continentes, tanto en Laurasia como en Gondwana. A pesar de la gran diversidad y abundante cantidad de restos fósiles disponibles de este exitoso grupo, los únicos estudios disponibles actualmente sobre su neuroanatomía, fueron publicados en los años 1960 y 1970, anterior a la utilización del TAC para sus análisis. La primera de estas publicaciones corresponde al estudio de un molde artificial de látex, y el segundo a un molde fósil natural, ambos pertenecientes a taxones norteamericanos. De esta manera, hasta la fecha de hoy no existe ninguna reconstrucción neuroanatómica completa en este grupo. Como resultado, se presenta aquí la primera reconstrucción tridimensional de la anatomía craneal y la neuroanatomía dentro del clado Bothremydidae. Además, se establece un marco comparativo a partir de la reconstrucción neuroanatómica y el análisis de varias especies de tortugas pleurodiras actuales, correspondientes a varios linajes, observando que los caracteres neuroanatómicos más variables para este grupo corresponden a la forma de la región olfatoria, la expansión lateral de los hemisferios cerebrales, y el desarrollo de la rama vidiana del nervio facial.

A NEW SPECIMEN OF THE TRIASSIC BIZARRE SAUROPTERYGIAN PALUDIDRACO MULTIDENTATUS
El Atance is an Upper Triassic fossil site located on the coast of the El Atance reservoir near Sigüenza (Guadalajara Province. Spain). The site has provided several remains of sauropterygians, including two recently described new taxa, the placodont Parahenodus atancensis and the eosauropterygian Paludidraco multidentatus. The latter is the most abundant sauropterygian there, several individuals being recovered. However, all the information published so far about this form is limited to that corresponding to a relatively complete skeleton (the holotype) and an isolated skull (the paratype), only a brief description being currently available about them. Paludidraco multidentatus is a bizarre simosaurid nothosauroid closely related to Simosaurus gaillardoti, from the Middle Triassic of Europe. Opposite to Simosaurus gaillardoti and other Triassic eosauropterygians, Paludidraco multidentatus has been interpreted as a slow swimmer with filter-feeding habits. Thus, it shows a highly pachyostotic postcranial skeleton and displays a specialized cranial anatomy. Here we present an unpublished specimen of Paludidraco multidentatus, currently under study. This specimen is represented by a partially articulated postcranial skeleton. It presents some posterior cervical vertebrae, the complete dorsal series, and some vertebrae of the sacral region, as well as some appendicular elements and both pectoral and pelvic girdles. This individual is larger than the holotype, and the pachyostosis of the vertebrae and ribs being more developed. Its detailed study, and the comparisons with the holotype, will provide new anatomical information about the species, and will help to broaden the range of intraspecific variability of Paludidraco multidentatus.

THE IBERIAN RECORD OF THE UPPER JURASSIC COASTAL TURTLE PLESIOCHELYS: AN UPDATE
Thalassochelydia (Testudines, Eucryptodira) is currently recognized as the most diverse clade of turtles in the Upper Jurassic fossil record of the Iberian Peninsula. The Upper Jurassic genus Plesiochelys is a member of a successful clade of coastal turtles belonging to Thalassochelydia: the exclusively European clade Plesiochelyidae. This genus shows a relatively abundant record in several European countries (i.e. Switzerland, France, and United Kingdom). Although it has also been recognized in the Iberian Peninsula, only scarce and fragmentary material was identified there, from Tithonian levels. These remains come from two localities, one in Spain and the other in Portugual. The limited availability of characters in these fossils did not allow their specific attribution, so that they were identified as Plesiochelys sp.
New and well-preserved Iberian shells attributable to Plesiochelys, found in two Tithonian outcrops where no remains of this genus had been recognized until now (both located in the Portuguese area of Torres Vedras, in levels corresponding to the Sobral Formation), are presented here. Shell characters not preserved in the previously identified fossils from Spain and Portugal, but considered in the specific diagnoses of the members of the genus, are identified for the Iberian material for the first time. Despite the relatively abundant record of Plesiochelys in Europe, no species that inhabited during the Tithonian was recognized by the shell. Therefore, the new Iberian remains could increase the diversity of the group, or the stratigraphic and geographical distribution of some of the species until now exclusive to other European countries. Furthermore, the potential reattribution to Plesiochelys of one of the oldest thalassochelydian shells identified so far, corresponding to a Spanish Oxfordian specimen with doubtful genetic attribution (i.e., the holotype and only known specimen of ‘Hispaniachelys prebetica’), is discussed. The confirmation of this hypothesis would expand the stratigraphic range of the genus, until now restricted to the Kimmeridgian and Tithonian. Taking all this into account, the specific diversity of Plesiochelys in the Iberian fossil record is discussed.