Data from: Assessing metabolic constraints on the maximum body size of actinopterygians: locomotion energetics of Leedsichthys problematicus (Actinopterygii, Pachycormiformes)

Maximum sizes attained by living actinopterygians are much smaller than
those reached by chondrichthyans. Several factors, including the high
metabolic requirements of bony fishes, have been proposed as possible
body-size constraints but no empirical approaches exist. Remarkably,
fossil evidence has rarely been considered despite some extinct
actinopterygians reaching sizes comparable to those of the largest living
sharks. Here, we have assessed the locomotion energetics of Leedsichthys
problematicus, an extinct gigantic suspension-feeder and the largest
actinopterygian ever known, shedding light on the metabolic limits of body
size in actinopterygians and the possible underlying factors that drove
the gigantism in pachycormiforms. For this, phylogenetic generalized least
squares analyses and power performance curves established in living fishes
were used to infer the metabolic budget and locomotion costs of L.
problematicus in a wide range of scenarios. Our approach predicts that
specimens weighing up to 44.9 tonnes would have been energetically viable
and suggests that similar body sizes could also be possible among living
taxa, discarding metabolic factors as likely body size constraints in
actinopterygians. Other aspects, such as the high degree of endoskeletal
ossification, oviparity, indirect development or the establishment of
other large suspension-feeders, could have hindered the evolution of
gigantism among post-Mesozoic ray-finned fish groups. From this
perspective, the evolution of anatomical innovations that allowed the
transition towards a suspension-feeding lifestyle in medium-sized
pachycormiforms and the emergence of ecological opportunity during the
Mesozoic are proposed as the most likely factors for promoting the
acquisition of gigantism in this successful lineage of actinopterygians.