Morphologists have historically had to rely on destructive procedures to visualize the three‐dimensional (3‐D) anatomy of animals. More recently, however, non‐destructive techniques have come to the forefront. These include X‐ray computed tomography (CT), which has been used most commonly to examine the mineralized, hard‐tissue anatomy of living and fossil metazoans. One relatively new and potentially transformative aspect of current CT‐based research is the use of chemical agents to render visible, and differentiate between, soft‐tissue structures in X‐ray images. Specifically, iodine has emerged as one of the most widely used of these contrast agents among animal morphologists due to its ease of handling, cost effectiveness, and differential affinities for major types of soft tissues. The rapid adoption of iodine‐based contrast agents has resulted in a proliferation of distinct specimen preparations and scanning parameter choices, as well as an increasing variety of imaging hardware and software preferences. Here we provide a critical review of the recent contributions to iodine‐based, contrast‐enhanced CT research to enable researchers just beginning to employ contrast enhancement to make sense of this complex new landscape of methodologies. We provide a detailed summary of recent case studies, assess factors that govern success at each step of the specimen storage, preparation, and imaging processes, and make recommendations for standardizing both techniques and reporting practices. Finally, we discuss potential cutting‐edge applications of diffusible iodine‐based contrast‐enhanced computed tomography (diceCT) and the issues that must still be overcome to facilitate the broader adoption of diceCT going forward.
Highlights d Dinosaurs and early birds had similar relative brain sizes d Major shifts in brain-body integration occur in the aftermath of the K-Pg extinction d Rates of brain-body evolution are highest in non-avian dinosaurs, early-diverging birds, parrots, and crows d Corvids, like hominins, evolved larger relative brains and bodies simultaneously
In recent years, there has been increased interest in examining brain evolution in extinct species through the use of virtual endocasts derived from computed tomography (CT) images (Witmer et al., 2008; Walsh and Milner, 2011a; Balanoff et al., 2016). In a similar fashion to mammals (Jerison, 1973), the size of the avian endocranial cavity is a reasonably accurate estimate of actual brain size (Iwaniuk and Nelson, 2002) and shape (Watanabe et al., 2019) (Figure 1), and so avian endocasts can yield major insights into the evolution of the avian brain in both extant and extinct species. The close relationship between endocranial size and brain size, as well as the increasingly widespread use of CT scanning to generate
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.