Integrative and Comparative Biology, 2008

In his personal copy of Owen's On the Nature of the Limbs, Darwin entered two interesting comments at different times inside the rear cover: I look at Owens Archetypus as more than ideal, as a real representation as far as the most consummate skill & loftiest generalization can represent the parent [present?] form of the Vertebrata.

Human Movement Science, 2000

The dimensional constraints on limb movements were investigated by asking adult participants to move speci®c segments of the upper limb (Experiment 1 ± index ®nger(s); Experiment 2 ± index ®nger, hand, lower arm, whole arm) with random frequency and amplitude over 2 min trials. The results showed that the amplitude±frequency characteristics of the random trials were limited to particular ranges within the respective potential workspace and with distributions that were broader than that of preferred oscillatory trials. The approximate entropy and dimension of the joint motion was higher in the random than the preferred conditions, but the random movements were shown to have a relatively low dimension. The irregularity of the random movements was enhanced in the more distal limb segments. The ®ndings reveal that the structural and functional constraints to planar motion at a single joint coalesce to provide a set of relatively low dimensional boundary conditions. The implication is that the control structure induces a more limited reduction in the dimensionality of the active system degrees of freedom than is typically postulated in theories of movement control. Ó (K.M. Newell). 0167-9457/00/$ -see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 -9 4 5 7 ( 0 0 ) 0 0 0 1 0 -5

Journal of Biosciences, 2006

Life has evolved because organisms are selfishly opportunistic and will take advantage of the slightest gain to broaden their sphere of influence. As diversification continues through time, several forms evolve which have a blend of characters intermediate between their ancestral stock and their descendants -the so-called "missing links". As the rock record in which such organisms are preserved is not temporally continuous, not all missing links are preserved as fossils. However when such rare discoveries are recorded, it is a time for justifiable recognition for the scientists who have made them. Neil H Shubin of the University of Chicago, Edward B Daeschler of the Philadelphia Academy of Natural Sciences and Farish A Jenkins, a Harvard evolutionary biologist have recently reported one such discovery (Daelscher et al 2006) of a 375 million year old transitional form between fish and tetrapods representing four-footed land vertebrates from Ellesmere Island in the Canadian Arctic Circle. This find adds exciting new data to the long chain of events that has eventually shaped our own destiny as humans. Indeed, apart from the fact of the origin of life itself, the conquest of land by animal, plant and microbial life nearly 380 million years ago must rank as one of the greatest landmarks in our evolutionary history. In recent years, the iconic status of fossils such as Archaeopteryx and new icons such as Eocene Indian and Pakistani "walking whales" have again re-emphasized the role of gradual evolutionary change. Startling discoveries in China in the last 15 years have confirmed how small feathered theropod dinosaurs may have taken to flight and these studies have changed our concepts so much that now the basal Aviales are included in the Dinosauria (Padian 2004). Even more remarkable and closer to home in our own subcontinent, a wonderful series of fossils have shown how once land-living mammals arose from artiodactyls (a group which includes hippos, pigs, deer and other even-toed mammals) and transformed themselves with the loss of graviportal limbs into whales, the present denizens of the deep (Thewissen and Bajpai 2001).

Trends in Genetics, 1998

Current Biology, 2002

In the regenerating amphibian limb, positional information has traditionally been considered in terms of short-range cell-cell interactions, not longrange diffusion gradients. A molecule discovered in a differential screen of regenerating limbs turns out to be precisely such a cell surface component, the newt ortholog of mouse CD59.

ANATOMY OF LIMBS , 2023

Anatomy of limbs

Developmental Dynamics, 2011

Science, 1996

The study of many biological processes requires the analysis of three-dimensional (3D) structures that change overtime. Optical sectioning techniques can provide 3D data from living specimens; however, when 3D data are collected over a period of time, the quantity of image information produced leads to difficulties in interpretation. A computer-based system is described that permits the analysis and archiving of 3D image data taken over time. The system allows a user to roam through the full range of time points and focal planes in the data set. The user can animate images as an aid to visualization and can append multicolored labels and text notes to identified structures during data analysis. The system provides a valuable tool for the study of embryogenesis and cytoplasmic movements within cells and has considerable potential as an educational tool. C. Thomas, P. DeVries, and J. White are with the Integrated Microscopy Resource for Biomedical Research

The more than 4,000 living species of mammal have infiltrated almost every habitat in the world. From alpine mountaintops to plains grasslands, from aerial heights to the depths of the ocean, from slender forest branches to narrow subterranean burrows, mammals occupy an extraordinary variety of substrates. Some are capable of running, swimming, or swinging at great speeds, while others creep slowly along limbs or push laboriously through the soil. The limbs of mammals reflect the diversity of their habitats (fig. 15.1). The long, slender legs and two-toed feet of the antelope allow it to survey the plains for predators and bound off at their approach. The short, muscled arms and broad, thick-clawed hands of the mole scrape through soil as the animal searches for worms and grubs. Spidery, elongated hands and fingers with webs of skin between them propel bats on their erratic chases after night-flying insects. Dense, paddlelike fins steer whales through the watery course on which they are propelled by their massive tail flukes. Limbs are crucial for mammalian locomotion, social behavior, and feeding. The functional diversity of mammal limbs is facilitated by sometimes subtle structural differences. A small discrepancy in the proportion of one limb segment and its distal neighbor can translate into significant disparity in running speed. The position of a muscle insertion along a long bone shaft can make the difference between a mammal that can tear its way through thick turf and one that cannot. The fusion of two bones in the forearm or wrist may mean that one animal cannot turn its palm to grasp a limb as it tries to climb, while another species can easily wrap its forelimbs around a tree trunk and scamper to safety. A large part of a mammal's lifestyle can, therefore, be read in the structure of its limbs. This chapter first reviews the anatomical structure of the mammalian limb. Some brief mention of comparative differences is made in relation to structure, but those are reserved for the most striking ones in which the number of elements differs or the structure of homologous elements is particularly diverse. Special emphasis is given to the structures that are most obviously related to function. The chapter then reviews the functional diversity of the mammalian limb from the perspective of gross ecomorphological categories, groups that are primarily locomotory in nature. The chapter then reviews aspects of variation, genetics, and development of the mammalian limb. Finally, the early evolution of the mammalian limb is reviewed.