EXCEPTIONAL PRESERVATION AND THE FOSSIL RECORD OF TETRAPOD INTEGUMENT

The fossil record of exceptionally preserved soft tissues in Konservat-Lagerstätten provides rare yet significant glimpses into past behaviors and ecologies. It has been recognized that these deposits are not evenly distributed through time and occur in a variety of environmental settings. Previous assessments of the distribution of these records though time focused on those in marine environments preserving chemically heterogeneous tissues from across animals. Here, we focus on one type of preserved soft tissue, records of tetrapod integument. We investigate the distribution of alpha- and beta-keratin integumentary structures through time and in distinct depositional environments. We also evaluate previously proposed potential biotic and abiotic controls on the distribution of these records through time in a multivariate statistical framework. Of 144 Konservat-Lagerstätten, known from the Permian to the Pleistocene, most are predominantly lacustrine. Occurrences in fluvial environments are more common than lagoonal, near-shore marine settings, or preservation in amber units. Lagerstätten preserving skin and scales were significantly more common in fluvial environments, while those preserving feathers, the most abundant integument type, are more common in lacustrine environments. Interestingly, hair is five times less common than most other integument types, and only filaments share a similar depositional history. The sparse fossil record of hairs suggests that hair may evolved earlier than previously recognized in early synapsids. This work suggests that among-integument variation in preservation could lead to biases in the reconstructed first origin of novel integumentary structures and has implications for predicting where, and in what depositional environments, to expect further discoveries of exquisitely-preserved tetrapod integuments.