The impact of the Pull of the Recent on extant elasmobranchs

Modern elasmobranchs have a long evolutionary history and an abundant
fossil record. Many fossil taxa have living representatives. However, the
representation of extant taxa in the fossil record is unknown. To begin to
understand the geological history of extant elasmobranchs, here we assess
the quality of their fossil record. We do so by assessing the Pull of the
Recent (herein, POR). The POR can bias the fossil record because the
rather complete record of living taxa allows
palaeontologists tobridge time bins where fossils are absent. We
assessed the impact of the POR by quantifying the proportion of extant
elasmobranchs that have a fossil record, but do not occur in the last 5
million years. We found that the POR does not affect orders and families,
but it does affect 24% of elasmobranch genera. Although modest, the impact
of the POR in extant elasmobranch genera is higher than that found in
other taxa. Overall, the geological history of elasmobranchs contradicts
the usual assumption that the fossil record becomes worse backwards in
time. This is the case across geographical regions and tooth size, further
suggesting that sampling intensity and outcrop availability can help
explain the POR effect on sharks and rays.