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

Abstract

Fossils are a key source of data on the evolution of feather structure and function through deep time, but their ability to resolve macroevolutionary questions is compromised by an incomplete understanding of their taphonomy. Critically, the relative preservation potential of two key feather components, melanosomes and keratinous tissue, is not fully resolved. Recent studies suggesting that melanosomes are preferentially preserved conflict with observations that melanosomes preserve in fossil feathers as external moulds in an organic matrix. To date, there is no model to explain the latter mode of melanosome preservation. We addressed these issues by degrading feathers in systematic taphonomic experiments incorporating decay, maturation and oxidation in isolation and combination. Our results reveal that the production of mouldic melanosomes requires interactions with an oxidant and is most likely to occur prior to substantial maturation. This constrains the taphonomic conditions under which melanosomes are likely to be fossilized. Critically, our experiments also confirm that keratinous feather structures have a higher preservation potential than melanosomes under a range of diagenetic conditions, supporting hitherto controversial hypotheses that fossil feathers can retain degraded keratinous structures.

Chemical preservation of tail feathers fromAnchiornis huxleyi, a theropod dinosaur from the Tiaojishan Formation (Upper Jurassic, China)

“…Recent taphonomic experiments in abiotic conditions suggest that the preservation of mouldic melanosomes requires interaction with an oxidant prior to maturation, and that the preservation of melanosomes is probably less frequent than the preservation of keratinous structures in fossil feathers (Slater et al . ). Interestingly, Anchiornis feathers contain both melanosomes and moulds.…”

Novel track morphotypes from new tracksites indicate increased Middle Jurassic dinosaur diversity on the Isle of Skye, Scotland

“…Some qualitative parameters including the length/width ratio, shape and length of the toes, presence or absence of claw impressions, and shape of the 'heel' have been traditionally used to distinguish between theropod and ornithopod trackmakers [38,49]. Over the last thirty years, multivariate analyses of linear track parameters and ratios have also seen use in differentiating between theropod and ornithopod footprints [42,61,64,65] and, more recently, geometric morphometric analyses have been brought to bear to investigate the question [62,66].…”

“…Additionally, the tracks at BP3 often present with asymmetry across the track midline with several tracks showing a disparity of~10˚between the (II^III) and (III^IV). Asymmetry in tridactyl tracks is more strongly associated with theropod footprints (and can be employed to assist in siding isolated pes impressions) [95] while ornithopod footprints are considered more likely to be subsymmetrical [43,66].…”

Chewing, dental morphology and wear in tapirs (Tapirus spp.) and a comparison of free-ranging and captive specimens

“…Note that mesowear is typically scored on the ectoloph, which does not exist in tapirs as such. The original mesowear method was explicitly not intended for dental morphologies lacking an ectoloph [2,36], irrespective of its later applications [reviewed in 37] that also included tapirs [11]. We employed the principles of mesowear scoring to the buccal and lingual side of the cheek teeth.…”

“…For example, Rivals and Lister [10] state that mesowear cannot be applied to tapir teeth. On the other hand, mesowear scoring has recently been applied to fossil tapir species without a proof of concept [11]. One important question in evaluating the applicability of mesowear to a species is whether the signal is stable across several (initial) stages of wear, or whether the mesowear signal varies monotonically with age and wear [12].…”