of scales. Large scutes run along the dorsal side of the tarsometatarsus and toes, whereas smaller scutellae run along the sides. Both structures share histochemical homology with reptilian scales, however work on their evolutionary development has revealed that the scales in bird feet have secondarily evolved via suppression of the feather-building genetic program. Unblocking the feather suppression program results in feathers growing in place of scales along the tarsometatarsus and toes. Dinosaur species very close to the origin of birds have been shown to have had "hind wings" made of feathers growing from these areas, suggesting that the acquisition of feathers in dinosaurs was a whole-body event. The bottoms of bird feet are covered in small, keeled scale-like structures known as reticulae. Evolutionary developmental studies on these scale-like structures have revealed that they are composed entirely of alpha keratin (true epidermal scales are composed of a mix of alpha and beta keratin). These data have led some researchers to suggest that reticulae are in fact highly truncated feathers. Insects and other arthropods The term "scutum" is also used in insect anatomy, as an alternative name for the anterior portion of the mesonotum (and, technically, the metanotum, though rarely applied in that context). In the hard ticks, the Ixodidae, the scutum is a rigid, sclerotised plate on the anterior dorsal surface, just posterior to the head. In species with eyes, the eyes are on the surface of the scutum. The flexible exoskeleton posterior to the rigid scutum of the female tick, is called the alloscutum, the region that stretches to accommodate the blood with which the mature female tick becomes engorged. Males do not engorge nearly as drastically as females, so they do not need a flexible alloscutum; instead the rigid scutum covers practically the entire dorsal surface posterior to the head, and may be referred to specifically as the conscutum. In some species of Opiliones, fused abdominal segments are referred to as a scutum. See also Fish scutes Osteoderms Scale (zoology) Snake scales Keratin Skin Skeleton References Animal anatomy Dinosaur anatomy de:Hornschuppe sv:Fjäll (zoologi)