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.

Cranial nerves are key features of the nervous system and vertebrate body plan. However, little is known about the anatomical relationships and ontogeny of cranial nerves in crocodylians and other reptiles, hampering understanding of adaptations, evolution, and development of special senses, somatosensation, and motor control of cranial organs. Here we share three dimensional (3D) models an of the cranial nerves and cranial nerve targets of embryonic, juvenile, and adult American Alligators (Alligator mississippiensis) derived from iodine‐contrast CT imaging, for the first time, exploring anatomical patterns of cranial nerves across ontogeny. These data reveal the tradeoffs of using contrast‐enhanced CT data as well as patterns in growth and development of the alligator cranial nervous system. Though contrast‐enhanced CT scanning allows for reconstruction of numerous tissue types in a nondestructive manner, it is still limited by size and resolution. The position of alligator cranial nerves varies little with respect to other cranial structures yet grow at different rates as the skull elongates. These data constrain timing of trigeminal and sympathetic ganglion fusion and reveal morphometric differences in nerve size and path during growth. As demonstrated by these data, alligator cranial nerve morphology is useful in understanding patterns of neurological diversity and distribution, evolution of sensory and muscular innervation, and developmental homology of cranial regions, which in turn, lead to inferences of physiology and behavior.

Highly branched dendritic structures are common in nature and often difficult to quantify and therefore compare. Cranial neurovascular canals, examples of such structures, are osteological correlates for somatosensory systems and have been explored only qualitatively. Adaptations of traditional stream‐ordering methods are applied to representative structures derived from computed tomography‐scan data. Applying these methods to crocodylian taxa, this clade demonstrates a shared branching pattern and exemplifies the comparative utility of these methods. Additionally, this pattern corresponds with current understanding of crocodylian sensory abilities and behaviors. The method is applicable to many taxa and anatomical structures and provides evidence for morphology‐based hypotheses of sensory and physiological evolution.

The examination of endocranial data of archosauriforms has led to advances on the evolution of body size, nerve pathways, and sensory abilities. However, much of that research has focused on bird-line archosaurs, resulting in a skewed view of Archosauria. Phytosauria, a hypothesized sister taxon to or early-branching member of Archosauria, provides a potential outgroup condition. Most previous phytosaur endocranial studies were executed without the use of modern technology and focused on derived members of Phytosauria. We present a comparative CT examination of the internal cranial anatomy of Wannia scurriensis, the most basal known parasuchid phytosaur. Wannia scurriensis shows some overall similarity with extant crocodylians and derived phytosaurs in general endocranial shape, a large hypophyseal fossa, and trigeminal (CN V) innervation, but as a whole, the endocast has noticeable differences to crocodylians and other phytosaurs. The pineal region is expanded dorsally as in other phytosaurs but also laterally (previously unrecognized). CN V exits the pons in a more dorsal position than in Parasuchus hislopi, Machaeroprosopus mccauleyi, or Smilosuchus gregorii. Wannia scurriensis also exhibits a larger hypophyseal fossa relative to brain size than observed in P. hislopi or S. gregorii, which may indicate more rapid growth. The well-preserved semicircular canals have lateral canals that are angled more anteroventrally than in derived phytosaurs. Extensive facial innervation from the large CN V indicates increased rostrum sensitivity and mechanoreceptive abilities as in Alligator mississippiensis. These endocranial similarities among phytosaurs and with Alligator indicate conserved ecological and functional results of an aquatic lifestyle, and highlight a need for further exploration of endocranial anatomy among Archosauriformes.