In living organisms, color patterns, behavior, and ecology are closely linked. Thus, detection of fossil pigments may permit inferences about important aspects of ancient animal ecology and evolution. Melanin-bearing melanosomes were suggested to preserve as organic residues in exceptionally preserved fossils, retaining distinct morphology that is associated with aspects of original color patterns. Nevertheless, these oblong and spherical structures have also been identified as fossilized bacteria. To date, chemical studies have not directly considered the effects of diagenesis on melanin preservation, and how this may influence its identification. Here we use time-of-flight secondary ion mass spectrometry to identify and chemically characterize melanin in a diverse sample of previously unstudied extant and fossil taxa, including fossils with notably different diagenetic histories and geologic ages. We document signatures consistent with melanin preservation in fossils ranging from feathers, to mammals, to amphibians. Using principal component analyses, we characterize putative mixtures of eumelanin and phaeomelanin in both fossil and extant samples. Surprisingly, both extant and fossil amphibians generally exhibit melanosomes with a mixed eumelanin/phaeomelanin composition rather than pure eumelanin, as assumed previously. We argue that experimental maturation of modern melanin samples replicates diagenetic chemical alteration of melanin observed in fossils. This refutes the hypothesis that such fossil microbodies could be bacteria, and demonstrates that melanin is widely responsible for the organic soft tissue outlines in vertebrates found at exceptional fossil localities, thus allowing for the reconstruction of certain aspects of original pigment patterns.

Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.

Coleoid cephalopods are characterized by internalization of their shell, and are divided into the ten-armed Decabrachia (squids and cuttlefish) and the eight-armed Vampyropoda (octopuses and vampire squid). They have a rich fossil record predominantly of the limited biomineralized skeletal elements they possess: arm hooks, statoliths, mouthparts (the buccal mass) and internal shell (gladius or pen), although exquisitely preserved soft tissue coleoids are known from several Lagerst€ atten worldwide. Recent studies have shown that although morphological similarities between extant decabrachian gladii and fossil examples exist, no known examples of fossil decabrachians are currently known. However, molecular clock data and phylogenetic bracketing suggest that they should be present in Lagerst€ atten that are rich in vampyropod soft tissue fossils (i.e. Hâkel and Hâdjoula Lagerst€ atten, Cretaceous, Lebanon). We propose that a hitherto unknown taphonomic bias pertaining to the differing methods of buoyancy control within coleoid groups limits preservation potential. Both negatively and neutrally buoyant decabrachians use chemical buoyancy control (ammonia) whereas vampyropods do not. In the event of rapid burial in an environment conducive to exceptional preservation, ammonia dramatically decreases the ability of the decabrachian carcass to generate the required pH for authigenic calcium phosphate replacement, limiting its preservation potential. Moreover, the greater surface area and comparatively fragile dermis further decrease the potential for fossilization. This taphonomic bias may have contributed to the lack of preserved labile soft-tissues in other cephalopods groups such as the ammonoids.