Estimando la paleodiversidad en Eusuchia en el XVI EJIP

Durante el XVI EJIP, celebrado en Zarautz del 11 al 14 de abril, Ane de Celis presentó un trabajo acerca de estimaciones de paleobiodiversidad en cocodrilos modernos (Eusuchia). Este trabajo, realizado junto a Iván Narváez y Francisco Ortega, resultó ganador de un premio concedido por la Fundación Dinópolis, a los cuales agradecemos el mismo.

En el encuentro se presentó una curva de paleobiodiversidad en bruto y a nivel específico para Eusuchia, obtenida tras una revisión exhaustiva de la bibliografía científica publicada hasta este mismo año 2018. Los resultados muestran que el mayor incremento en el número de especies ocurrió en el Mioceno tardío (11.63-5.333 millones de años). Por otro lado, los resultados sugieren que existe una relación entre los cambios de temperatura y la paleobiodiversidad, de modo que cuando aumenta considerablemente la temperatura media global se observa un crecimiento de la paleobiodiversidad.

A continuación se puede leer el resumen del trabajo en inglés:

INTRODUCTION

Eusuchia conforms a crocodyliform lineage, including crown-group Crocodylia, known since the Lower Cretaceous. Nowadays there are only 23 eusuchian species, but their rich fossil record indicates that they were more abundant and widespread in the past. Previous works assess changes in taxonomic diversity in all Pseudosuchia and Mesozoic Crocodyliformes with appropriate novel techniques to avoid bias. The present work makes a first preliminary approach to understand how the taxonomic diversity of Eusuchia changed since their first appearance in the fossil record.

METHODOLOGY

A new dataset comprising the entire timespan of Eusuchia (129Ma to present) was built. This dataset includes all valid eusuchian species described to date and was built using the latest published literature, in order to assess the validity of the taxa, their phylogenetic position, temporal and spatial range. For this purpose those occurrences named as “aff.” or “cf.” were not included, as well as taxa whose membership to Eusuchia needs further review (i.e. Paralligatoridae, Pachycheilosuchus trinquei or Pietraroiasuchus ormezzanoi among others). The data from 207 species was sorted to stage-level time bins (n=31, Barremian to Holocene), whose absolute dates are from the last published International Chronostratigraphic Chart (v.2017/02). Count of the number of species per stage was done following Tennant et al. (2016), obtaining an uncorrected taxonomic diversity estimate.

RESULTS AND DISCUSSION

The preliminary result, an uncorrected taxonomic diversity estimate of Eusuchia, shows great increases in the number of species at the end of the Cretaceous, early Eocene or middle-late Miocene. Those increases happened when the palaeotemperatures raised in events such as the Cretaceous greenhouse, early Eocene Climatic Optimum (EECO) or the mid-Miocene Climatic Optimum (MMCO) respectively. Conversely, at the early Paleocene, middle-late Eocene, Oligocene, early Miocene and Pliocene-Pleistocene, the number of species substantially decreases. For these periods (excluding the early Paleocene) drops in palaeotemperature such as the Long-Term Eocene Cooling (LTEC), Eocene-Oligocene Transition (EOT), Oligocene-Miocene Boundary (OMB) or the middle Miocene Climate Transition (MMCT) have been respectively reported. These results suggest that there is a relationship between the taxonomic diversity of eusuchians and palaeotemperature; question previously addressed by Markwick (1998) for crocodylians, by Mannion et al. (2015) for pseudosuchians, and by Tennant et al. (2016) for crocodyliforms. These authors concluded that palaeotemperature is a major environmental driver for the group. However, to fit the analysis of the relationships between eusuchian diversity and environmental factors such as palaeotemperature, it would be necessary to previously correct this palaeobiodiversity estimate with methods such as shareholder quorum subsampling (SQS) or true richness estimates using a Poisson sampling model (TRiPS) among other methods. This approach will be the next step to take for this work in the future.

CONCLUSIONS

Preliminary results indicate that several increases and decreases of eusuchian taxonomic diversity may be related to changes in palaeotemperatures. Further analyses are needed to assess properly the strength of these results.