The origin and evolution of avian feathers
True powered flight has arisen three independent times in vertebrate evolutionary history encompassing changes in the morphology and function of forelimb structures in the pterosaur, bird, and bat lineages. In all three cases, the leading edge of the wing is stabilized by the forelimb skeletal elements. But, in contrast to the pterosaurs and bats, which use a membranous lifting surface, the majority of the flight surface in birds consists of feathers. Feather-like structures have been found on...
T Eqc
shrimp Artemia, is quite different from Drosophila and other insects. In Artemia, the anterior boundary of Ubx falls at the anterior of the thorax, at the transition from the gnathal head segments which bear feeding appendages to the thoracic segments which bear swimming appendages . Thus the expression of this Hox gene marks a transition in appendage morphology along the Artemia anteroposterior axis, but Ubx is expressed at a more anterior position relative to the insects. Other, more derived...
The Vertebrate Body Plan
The development of the vertebrate body plan has long been a focus of experimental embryology. Many fundamental concepts such as organizers, fields, and morphogens were derived first from observations of vertebrate embryos. The major features of adult vertebrate morphology, including segmented vertebral columns, paired appendages, and skulls, have undergone considerable evolutionary diversification. Therefore, we will focus on the developmental genetics of these major features here, and consider...
Diversification of Insect Segmental Morphology Wings and Legs
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Fins to limbs paired appendages and the tetrapod hand
The adaptive evolution of vertebrates capable of surviving in aquatic, terrestrial, and aerial environments involved the acquisition and modification of paired pectoral and pelvic appendages. These limbs boosted vertebrates' maneuverability and speed in water and later were used as the primary means of locomotion on land. The early history of paired Evolution of vertebrate paired appendages Vertebrate paired appendages evolved in a series of steps. Paired appendages are first encountered in the...
Bre
The c s-regulatory elements of the Ubx gene a Three elements that regulate Ubx expression in the embryo are shown. Each element controls expression in selected subsets of parasegments. b The BRE element contains binding sites for several segmentation proteins Ftz, Hb, En, Tll and a dorsoventral patterning protein Twi within a 500-bp span. c Expression driven by the BRE element in parasegments 6, 8, 10, and 12 is the net output of the various positive and negative regulatory inputs shown in this...
Vertebrate Hox Expression Domains and Axial Patterning
Belting H-G, Shashikant CS, Ruddle FH. Modification of expression and cis-regulation of Hoxc8 in the evolution of diverged axial morphology. Proc Natl Acad Sci USA 1998 95 2355-2360. Burke AC, Nelson CE, Morgan BA, Tabin C. Hox genes and the evolution of vertebrate axial morphology. Development 1995 121 333-346. Cohn MJ, Tickle C. Developmental basis of limblessness and axial patterning in snakes. Nature 1999 399 474-479. Gaunt SJ. Evolutionary shifts of vertebrate structures and Hox expression...