Animal Origins And The Fossil Record

The fossil record is our primary window into the history of life. It provides many kinds of information that cannot be inferred from living animals. Fossils give us pictures of extinct forms that may be ancestors of modern animals, provide minimal estimates of the time of origin or divergence of particular groups, reveal episodes of extinctions and radiations, and, in favorable circumstances, offer detailed accounts of the evolution of important structures. The search for the origins of modern...

Evolution Of Animal Color Patterns

Mammalian coat and bird plumage colors Some of the most striking and best understood examples of phenotypic divergence are the color patterns of vertebrates. Mammalian coat, bird plumage, and fish scale coloration schemes are wonderfully diverse. Much progress has been made in understanding the genetic control of color formation and of differences within and between species. The most widespread pigment in the animal kingdom is melanin. It occurs in various chemical forms that when polymerized...

General Features Of Animal Design And Diversity

One of the most outstanding features of animal design, particularly of larger bilaterians, is their construction from repeating structures (or modules). The segments of arthropods and annelids and the vertebrae (and associated processes) of vertebrates are the basic units of body plan organization in these phyla (Fig. 1.5a-c). Similarly, many body parts such as the insect wing (Fig. 1.5d) and the tetrapod hand (Fig. 1.5e) are composed of repeated structures. An important trend in the...

Diversification of insect wing morphology

Four Winged Insect Ancestor

Although all modern winged insects bear two pairs of wings, many structural, functional, and morphological differences exist between forewings and hindwings both within and between species (Fig. 5.12). For example, the wings of dragonflies (Odonata) appear rather similar, but the forewings of beetles (Coleoptera) have been modified into hardened coverings that protect the hindwings. Butterfly (Lepidoptera) forewings and hindwings are often of similar size, but have evolved different shapes and...

Evolution of the notochord

The presence of a notochord unites the chordates and is the distinguishing feature that inspired their name. The notochord is a stiff, axial rod of cells that represents the functional precursor of the vertebral column in basal chordates. It acts as an organizer for the early development of the CNS and adjacent axial mesoderm. Efforts to determine the origin of the notochord have often focused on the urochordates because of their relatively simple body plan and their basal position within the...

What Is Morphological Novelty

The history of evolutionary biology is replete with operational definitions of novelty. For our purposes, which are primarily to understand the developmental and genetic basis of the evolution of novel animal forms and patterns, a novelty is defined as a structure or pattern element, or even an entire body plan, that has a new adaptive function. This chapter focuses on the best examples of morphological novelty for which developmental genetic knowledge has been elucidated. We do not address...

The evolution of insect wings and spider spinneretsfrom ancestral gills

Arthropods were among the first metazoans to live on land. The transition from an aquatic to terrestrial environment required a number of changes in their morphology and physiology. Some of these changes represent the evolution of novel structures that led to adaptive radiations of specific arthropod lineages. For example, the evolution of insect wings is recognized as the key innovation behind the evolutionary success of the insects, which account for more than 75 of all known metazoan...

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

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

Evolution of the gene network underlying wing polyphenism in ants. Science 2002 297 249-252. Carroll SB, Weatherbee SD, Langeland JA. Homeotic genes and the regulation and evolution of insect wing number. Nature 1995 375 58-61. Galant R, Carroll SB. Evolution of a transcriptional repression domain in an insect Hox protein. Nature 2002 415 910-913. Palopoli MF, Patel NH. Evolution of the interaction between Hox genes and a downstream target. Curr Biol 1998 8 587-590....

Fins to limbs paired appendages and the tetrapod hand

Tetrapod Limb

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...