Data from: Skeletal and soft tissue completeness of the acanthodian fossil record

Acanthodians are a poorly understood paraphyletic grade of extinct
Palaeozoic fishes. They play an increasingly prominent role in our
understanding of vertebrate evolution as part of the chondrichthyan
stem-group even though their evolutionary history is scarce. The limited
preservation of their mostly cartilaginous skeleton largely results in a
bias towards isolated remains such as fin spines and scales. Here, we
quantify the quality of the acanthodian fossil record by using a variation
of the Skeletal Completeness Metric (SCM), an approach that calculates how
complete the skeletons of individuals are compared to their theoretical
complete skeleton. A novel Soft Tissue Completeness Metric (STCM) is
introduced to estimate the percentage of soft body tissue preserved as an
alternate measurement of completeness. Completeness scores for
>1600 specimens comprising >300 taxa obtained from museum
collection visits and literature surveys were assembled into a database.
Acanthodian completeness peaks in the Lochkovian, Givetian,
Bashkirian-Moscovian, and the Asselian, with lowest scores in the
Llandovery. There is no correlation between acanthodian taxonomic richness
and completeness. Acanthodians show a significantly lower completeness
distribution than many tetrapod groups, but a similarly low distribution
to bats. Skeletons deposited in freshwater are significantly more complete
than in marine environments where sea level significantly negatively
correlates with observed completeness. Our assessment of completeness
reveals only weak spatial biases influencing the acanthodian fossil record
while environmental biases are much higher. Variation in completeness will
have an impact on the utility of characters for assessing the phylogenetic
relationships and inclusion of the various acanthodian groups.