1978, 1984 Fraser & Grigg, 1984 Franklin & Seebacher, 2003 Seebacher & Franklin, 2004, 2007) and it is well understood how crocodilians control body temperature during warming and cooling. The number of publications focusing on behavioral thermoregulation in crocodilians is high (Smith, 1976, 1979 Drane et al. For example, Johnson ( 1974) reported that a temperature differential between the head and body occurs in crocodilians such that, similar to other reptiles (Crawford, 1972), the head warms slower than the body under certain conditions, especially during gaping.
Indeed, physiological thermoregulation in the head has been investigated to some degree in crocodilians. 1997, 2002), and thus is expected on phylogenetic grounds in crocodilians. Selective brain temperature regulation has been demonstrated in squamates (Heath, 1964, 1966 Crawford, 1972 Crawford et al. Determining the role of blood vessels in cephalic physiological thermoregulation is crucial for understanding how crocodilians regulate brain temperature. The available published research is over 100 years old (Rathke, 1866 Hochstetter, 1906 Reese, 1914, 1915), with the exception of Sedlmayr's ( 2002) extensive investigation into the vascular anatomy of extant crocodilians and Almeida & Campos's ( 2011) work on encephalic arteries. Research into the cephalic vasculature of crocodilians has, unfortunately, not received the same level of scrutiny as have that of birds, squamates, or mammals. A clear understanding of the physiological abilities and the role of blood vessels in the thermoregulation of crocodilians neurosensory tissues is not available but vascular anatomical patterns of crocodilian sites of thermal exchange indicate possible physiological abilities that may be more sophisticated than in other extant diapsids. The evolutionary history of crocodilians is complex, with large‐bodied, terrestrial, and possibly endothermic taxa that may have had to deal with thermal loads that likely provided the anatomical building‐blocks for such an extensive vascularization of sites of thermal exchange. The venous drainage routes from the nasal region offer routes directly to the dural venous sinuses and the orbit, offering evidence of the potential to directly affect neurosensory tissue temperatures. The nasal region in crocodilians is probably the most prominent site of thermal exchange, as it offers a substantial surface area and is completely surrounded by blood vessels. Anastomotic connections with the nasal region, however, may provide an alternative route for palatal venous blood to reach neurosensory tissues. The most direct route of venous drainage of the palatal plexus was through the palatomaxillary veins, essentially bypassing neurosensory tissues. The palatal region demonstrated a vast plexus that comprised both arteries and veins. The venous drainage of the orbital region showed connections to the dural sinuses via the orbital veins and cavernous sinus. Within the orbital region, both the arteries and veins demonstrated consistent branching patterns, with the supraorbital, infraorbital, and ophthalmotemporal vessels supplying and draining the orbit. Blood vessels to and from sites of thermal exchange were studied to detect conserved vascular patterns and to assess their ability to deliver cooled blood to neurosensory tissues.
Sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in evaporative cooling and cephalic thermoregulation in other diapsids. The specimens were then dissected to confirm CT results. Blood vessels were digitally isolated to create representations of vascular pathways. The cephalic vascular anatomy of extant crocodilians, particularly American alligator ( Alligator mississippiensis) was investigated using a differential‐contrast, dual‐vascular injection technique and high resolution X‐ray micro‐computed tomography (μ CT). Therefore, the anatomical and physiological roles that blood vessels play in crocodilian thermoregulation need further investigation to better understand how crocodilians establish and maintain cephalic temperatures and regulate neurosensory tissue temperatures during basking and normal activities. Sizes that can be subject to higher heat loads. Extant crocodilians are a highly apomorphic archosaur clade that is ectothermic, yet often achieve large body