Analysis of longevity in Chordata identifies species with exceptional longevity among taxa and points to the evolution of longer lifespans.

Animals have a considerable variation in their longevity. This fundamental life-history trait is shaped by both intrinsic and extrinsic mortality pressures, influenced by multiple parameters including ecological variables and mode-of-life traits. Here, we examined the distribution of maximum age at multiple taxonomic ranks (class, order and family) in Chordata, and identified species with exceptional longevity within various taxa. We used a curated dataset of maximum longevity of animals from AnAge database, containing a total of 2542 chordates following our filtering criteria. We determined shapes of maximum age distributions at class, order and family taxonomic ranks, and calculated skewness values for each distribution, in R programming environment. We identified species with exceptional longevity compared to other species belonging to the same taxa, based on our definition of outliers. We collected data on ecological variables and mode-of-life traits which might possibly contribute, at least in part, to the exceptional lifespans of certain chordates. We found that 23, 12 and 4 species have exceptional longevity when we grouped chordates by their class, order and family, respectively. Almost all distributions of maximum age among taxa were positively skewed (towards increased longevity), possibly showing the emergence of longer lifespans in contrast to shorter lifespans, through the course of evolution. However, potential biases in the collection of data should be taken into account. Most of the identified species in the current study have not been previously studied in the context of animal longevity. Our analyses point that certain chordates may have evolved to have longer lifespans compared to other species belonging to the same taxa, and that among taxa, outliers in terms of maximum age have always longer lifespans, not shorter. Future research is required to understand how and why increased longevity have arose in certain species.