ABSTRACT
The facial pits of rattlesnakes, copperheads, lanceheads, bushmasters and other American and Asian pitvipers (Crotalinae) are highly innervated and densely vascularized infrared (IR) receptor organs. For over a century, studies have focused on a small sample of model species from North America and Asia. Based on an expanded survey of Central and South American crotalines, we report a conspicuous accessory structure composed of well-defined papillae that project from the anterior orbital adnexa. The papillae are continuous with the inner chamber of the IR receptor organ and our histological and ultrastructural data suggest that they possess a well-developed nervous network and extensive vascularization; however, they lack the characteristic IR-sensitive terminal nerve masses found in the IR-receptive pit membrane. The function of the IR receptor organ papillae is unknown.
Subject(s)
Sensory Receptor Cells/ultrastructure , Viperidae/anatomy & histology , Americas , Animals , Asia , Infrared Rays , Phylogeny , Viperidae/classification , Viperidae/geneticsABSTRACT
Using data for 25,780 species categorized on the International Union for Conservation of Nature Red List, we present an assessment of the status of the world's vertebrates. One-fifth of species are classified as Threatened, and we show that this figure is increasing: On average, 52 species of mammals, birds, and amphibians move one category closer to extinction each year. However, this overall pattern conceals the impact of conservation successes, and we show that the rate of deterioration would have been at least one-fifth again as much in the absence of these. Nonetheless, current conservation efforts remain insufficient to offset the main drivers of biodiversity loss in these groups: agricultural expansion, logging, overexploitation, and invasive alien species.
