Experimental Taphonomy of Keratin: A Structural Analysis of Early Taphonomic Changes

Abstract

The evolution of integumentary structures, particularly in relation to feathers in dinosaurs, has become an area of intense research. Our understanding of the molecular evolution of keratin protein is greatly restricted by the fact that such information is lost during diagenesis and cannot be derived from fossils. In this study, decay and maturation experiments are used to determine if different keratin types or integumentary structures show different patterns of degradation early in their taphonomic histories and if such simulations might advance our understanding of different fossilization pathways. Although different distortion patterns were observed in different filamentous structures during moderate maturation and ultrastructural textures unique to certain types of scales persisted in moderate maturation, neither of these have been observed in fossils. It remains uncertain whether these degradation patterns would ever occur in natural sediment matrix, where microbial and chemical decay happens well before significant diagenesis. It takes some time for remains to be buried, meaning that keratin may not be left for moderate maturation to produce such patterns. Higher, more realistic maturation conditions produce a thick, and water soluble fluid that lacks all morphological and ultrastructural details of the original keratin, suggesting that such textural or distortion patterns are unlikely to be preserved in fossils. Although different degradation patterns among keratinous structures are intriguing, it is unlikely that such information could be recorded in the fossil record. Calcium phosphates and pigments are the surviving components of integumentary structures. Thus, the results here are likely of more relation to the archaeological record than fossil record. Other noteworthy results of these experiments are that melanin may not be the leading factor in determining the rate of microbial decay in feathers but may reduce the rate of degradation from maturation, that the existence of rachis filamentous subunits similar to plumulaceous barbules is supported, and that previously reported dinosaur 'erythrocytes' may be taphonomic artifacts of degraded organic material.

Taphonomic experiments resolve controls on the preservation of melanosomes and keratinous tissues in feathers

“…, ) is controversial (Saitta et al . , ). Chemical evidence of keratin has been reported from various Mesozoic and Cenozoic fossils (Schweitzer et al .…”

“…Conditions using higher temperature and pressure (such as those used in Saitta et al . , ) do not preserve recognizable feather structure.…”

“…, ), however, are disputed (Saitta et al . , ). The other key component of many (but not all) feathers are melanosomes, micron‐sized organelles rich in melanin pigments that occur in two primary forms: eumelanin, a heterogenous polymer derived from oxidation of the amino acid tyrosine (Solano ) and phaeomelanin, derived from tyrosine and sulfur‐rich l ‐cysteine (Ito & Wakamatsu ).…”

“…) , but this hypothesis is not universally accepted (Saitta et al . , ); rather, the matrix surrounding some fossil melanosomes has been interpreted as sediment infill following keratin decay (Saitta et al . ).…”

“…, ); rather, the matrix surrounding some fossil melanosomes has been interpreted as sediment infill following keratin decay (Saitta et al . ). Moulds in fossil feathers have been interpreted as sites formerly occupied by decay bacteria (Moyer et al .…”