Alfred Sherwood Romer

Bio: Alfred Sherwood Romer is an academic researcher from Harvard University. The author has contributed to research in topics: Permian & Carboniferous. The author has an hindex of 38, co-authored 97 publications receiving 6391 citations. Previous affiliations of Alfred Sherwood Romer include New York University & University of Chicago.

The vertebrate body

Abstract: The best ebooks about The Vertebrate Body that you can get for free here by download this The Vertebrate Body and save to your desktop. This ebooks is under topic such as comparative embryology: the vertebrate body vertebrate body organization nicholls organization of the vertebrate body vertebrate body shorter version wmppg vertebrate body shorter version 3ed jbstv vertebrate body 3ed oddnos vertebrate body shorter version chchch vertebrate body 3ed hisnet vertebrate body 4ed nemtc vertebrates mcgraw hill education vertebrate body shorter version preshy vertebrate body 3ed cyclam vertebrate body 3ed decroo patterning the vertebrate body plan ll: the somites and vertebrate body shorter version snozel vertebrate body 4ed cxtech vertebrate body 3ed limtan vertebrate body shorter version cyclam 2008 vertebrate organ systems amherst college vertebrate body 4ed antivi vertebrate body shorter version 3ed bajars vertebrate body shorter version drekly vertebrate body shorter version 3ed nrcgas vertebrate body shorter version whhill vertebrate body 3ed mukasa classification of vertebrates accuteach the vertebrate body biscit vertebrate body shorter version 3ed lagdon vertebrate body shorter version limtan vertebrate body 4ed mukasa maintaining the internal environment mcgraw hill education the vertebrate body axis: evolution and mechanical function vertebrate body shorter version oldvan vertebrate body shorter version 3ed sofaer 2 development of the vertebrate body plan copy the vertebrate body bagabl stem cells, signals and vertebrate body axis extension vertebrate body 3ed sarcom the vertebrate body dateks the circularity of the vertebrate body 9 springer comparative embryology: the vertebrate body on in situ attrition and vertebrate body part profiles

Osteology of the reptiles ..

Abstract: Based on the work of Samuel Wendell Williston and Dr. W.K. Gregory, author and editor of the original title published in 1925, this volume consists of two major parts - a structure-by-structure account of the reptile skeleton, followed by a classification of the various reptile groups based on osteological characters. This update isdesigned to give, in outline form, an account of the nature of the skeletal system of numerous reptile types both living and extinct.

A simple method for estimating evolutionary rates of base substitutions through comparative studies of nucleotide sequences.

Abstract: Some simple formulae were obtained which enable us to estimate evolutionary distances in terms of the number of nucleotide substitutions (and, also, the evolutionary rates when the divergence times are known). In comparing a pair of nucleotide sequences, we distinguish two types of differences; if homologous sites are occupied by different nucleotide bases but both are purines or both pyrimidines, the difference is called type I (or “transition” type), while, if one of the two is a purine and the other is a pyrimidine, the difference is called type II (or “transversion” type). Letting P and Q be respectively the fractions of nucleotide sites showing type I and type II differences between two sequences compared, then the evolutionary distance per site is K = — (1/2) ln {(1 — 2P — Q) }. The evolutionary rate per year is then given by k = K/(2T), where T is the time since the divergence of the two sequences. If only the third codon positions are compared, the synonymous component of the evolutionary base substitutions per site is estimated by K'S = — (1/2) ln (1 — 2P — Q). Also, formulae for standard errors were obtained. Some examples were worked out using reported globin sequences to show that synonymous substitutions occur at much higher rates than amino acid-altering substitutions in evolution.

Exaptation; a missing term in the science of form

Abstract: Adaptation has been defined and recognized by two different criteria: historical genesis (fea- tures built by natural selection for their present role) and current utility (features now enhancing fitness no matter how they arose). Biologists have often failed to recognize the potential confusion between these different definitions because we have tended to view natural selection as so dominant among evolutionary mechanisms that historical process and current product become one. Yet if many features of organisms are non-adapted, but available for useful cooptation in descendants, then an important concept has no name in our lexicon (and unnamed ideas generally remain unconsidered): features that now enhance fitness but were not built by natural selection for their current role. We propose that such features be called exaptations and that adaptation be restricted, as Darwin suggested, to features built by selection for their current role. We present several examples of exaptation, indicating where a failure to concep- tualize such an idea limited the range of hypotheses previously available. We explore several consequences of exaptation and propose a terminological solution to the problem of preadaptation.

Central control of song in the canary, Serinus canarius

Abstract: We have traced central nervous pathways controlling bird son in the canary using a combination of behavioral and anatomical techniques. Unilateral electrolytic brain lesions were made in adult male canaries whose son had been previously recorded and analysed on a sound spectrograph. After severral days of postoperative recording, the birds were sacrificed and their brains processed histologically for degeneration staining with the Fink-Heimer technique. Although large lesions in the neostriatum and rostral hyperstriatum had no effect on song, severe song deficits followed damage to a discrete large-celled area in the caudal hyperstriatum ventrale (HVc). Degenerating fibers were traced from this region to two other discrete nuclei in the forebrain: one in the parolfactory lobe (area X, a teardrop-shaped small-celled nucleus) and a round large-celled nucleus in the archistriatum (RA). Unilateral lesions of X had no effect on song; lesions of RA, however, caused severe song deficits. Degenerating fibers from RA joined the occipitomesencephalic tract and had widespread ipsilateral projections to the thalamus, nucleus intercollicularis of the midbrain, reticular formation, and medulla. It is of particular interest that direct connections were found onto the cells of the motor nucleus innervating the syrinx, the organ of song production. Unilateral lesions of n. intercollicularis (previously implicated in the control of vocal behavior) had little effect on song. One bilateral lesion of HVc resulted in permanent (9 months) and complete elimination of the audible components of song, although the bird assumed the posture and movements typical of song. Preliminary data suggest that lesions of the left hemisphere result in greater deficits than lesions of the right one. This finding is consistent with earlier reports that the left syrinx controls the majority of song components. Results reported here suggest a localization of vocal control in the canary brain with an overlying left hemispheric dominance.

The draft genome of Ciona intestinalis : insights into chordate and vertebrate origins

Abstract: The first chordates appear in the fossil record at the time of the Cambrian explosion, nearly 550 million years ago. The modern ascidian tadpole represents a plausible approximation to these ancestral chordates. To illuminate the origins of chordate and vertebrates, we generated a draft of the protein-coding portion of the genome of the most studied ascidian, Ciona intestinalis. The Ciona genome contains approximately 16,000 protein-coding genes, similar to the number in other invertebrates, but only half that found in vertebrates. Vertebrate gene families are typically found in simplified form in Ciona, suggesting that ascidians contain the basic ancestral complement of genes involved in cell signaling and development. The ascidian genome has also acquired a number of lineage-specific innovations, including a group of genes engaged in cellulose metabolism that are related to those in bacteria and fungi.