• Abstract and Figures
• Public Full-text

NATURE VOL. 233 OCTOBER 15 1971 451 PALAEONTOLOGY A. W. R. Wight (University of Bristol) Bristol) gave an interesting account of described new specimens of Proboscidea the Late Devonian fish fauna of Mammalian Evolution and discussed the Eocene stratigraphy Escuminac Bay, Canada, and Mr D. S. from our Vertebrate Palaeontology of Libya. Dr V. Maglio (Princeton Broad (University of Bristol) described Correspondent University) analysed the rates of appear­ new heterostracans from Arctic Canada THE nineteenth symposium on verte­ ance and replacement of species in the which showed evidence of the growth brate palaeontology and comparative Elephantinae and suggested that the of each plate by accretion around a anatomy was held at Bristol on Sep­ group was in the middle of a phase of small number of original tubercles. The tember 28-29, followed by two days of adaptive radiation when, in the Upper problem of interpreting the patterns of field excursions. The evolution of mam­ Pleistocene, there was a dramatic crash tetrapod tooth replacement was dis­ mals, especially those of Africa, was a from eleven lineages to the present two. cussed by Dr R. DeMar (Liberal Arts principal theme, because there is a large Dr A. W. Gentry (British Museum College, Chicago), who showed that and active group at Bristol concerned (Natural History) ) compared the Edmund's Zahnreihe is only one of a with this subject. New work on the African Pleistocene antelopes with those number of theoretically possible alterna­ earliest known mammals, Eozostrodon/ of the continent today and pointed out tives, and that computer studies can Morganucodon and Kuehneotherium, that, because horn shape is a species show why some of these are not accept­ of the Triassic was described by Profes­ recognition feature, the whole antelope able, because they lead to lengthy gaps sor A. W. Crompton (Harvard Uni­ fauna of anyone time, within which in the tooth row. versity). Some workers have suggested such distinctions were essential, should Dr A. C. Charig (British Museum be considered in any analysis. that each of these two mammals gave (Natural History» pointed out that rise to some of the groups of Jurassic At the other end of the chordate reptiles colonized more new ways of life mammals, but that they are so different evolutionary story, Dr R. P. S. Jefferies in the Triassic than ever before or (British Museum (Natural History» from one another that they must have since, and suggested that this might be arisen from different lines of advanced described a new mitrate echinoderm more than mere coincidence-though mammal-like reptile-so making the which he believed showed evidence of other possible reasons were not obvious. mammals diphyletic. Professor Cromp­ being ancestral to the cephalochordates. A valuable approach to the study of Professor D. Dineley (University of ton strongly dissented from this view, L. pterosaurs was presented by Dr G. R. pointing out a number of similarities between the two Triassic genera. He also noted that the epipterygoid of such cynodonts as Probainognathus is not Visualizing Agglutinin Siles on Cell Surfaces greatly enlarged, indicating that this DURING the past several months the group could be ancestral to all the grids the membranes can then be mammals, including the triconodonts suggestion that transformed cells are stained with the ferritin tagged (whose epipterygoid, unlike that of most more readily agglutinated by plant concanavalin A. other mammals, is small). An interest­ agglutinins than their untransformed The micrographs of stained mem­ ing discovery of early mammals in counterparts because transformation branes from transformed and untrans­ Britain was that of Dr M. Waldman leads to an increase in the number of formed 3T3 cells reveal at a glance the (Stowe School). Though difficult to agglutinin-binding sites exposed on the striking difference in distribution of bind­ detect, and also difficult to remove from cell surface has been abandoned. For ing sites. Single ferritin tagged concana­ the hard matrix, his find of Middle experiments such as those reported by valin A molecules are randomly dis­ Jurassic mammals in the Isle of Skye Cline and Livingston and Ozanne and tributed on the membranes of the un­ is of great potential interest, because the Sambrook in Nature New Biology (232, transformed cells. By contrast the only other mammalian fauna of this 155, 156; 1971) have shown that there tagged concanavalin A molecules are in age comes from the Stonesfield Slate of is apparently no significant difference clusters, which are randomly distri­ Oxford, which is no longer quarried. between the numbers of these binding buted, on the membranes of the cells Professor P. M. Butler (Royal Hollo­ sites on the surfaces of transformed and transformed by SV 40. Although there way College, London) suggested that untransformed cells. These workers are some 3 to 3.5 times more molecules the directions of jaw movement, as have suggested therefore that it is the of bound concanavalin A per unit area indicated by wear striations on the distribution of agglutinin-binding sites of transformed than per unit area of teeth, had passed through three princi­ rather than their numbers which is untransformed cell membrane, Nichol­ pal phases in mammalian evolution. In changed by transformation and in next son points out that the total surface area Jurassic forms, the movement is partly Wednesday's Nature New Biology, of the transformed cells is only about transverse and becomes progressively Nicholson reports observing in the elec­ half that of their untransformed more so, but the teeth shear past one tron microscope just such a change; counterparts. another. Not until the Cretaceous do after transformation by SV40 virus the Nicholson has also shown that after the teeth collide at the end of the jaw concanavalin A binding sites on the exposure to weak trypsin solutions, the movement, so giving a crushing action. surface of mouse 3T3 cells are clustered concanavalin A sites on the surface of This in turn provided the possibility of whereas before transformation they are untransformed cells tend to be clustered, a subsequent movement in another dispersed. but within a few hours of enzyme treat­ direction, so that two different sets of Nicholson was able to make these ment the sites assume their normal dis­ facets can be distinguished in the most elegant observations by preparing tribution. Tertiary herbivores and omnivores. ferritin conjugated concanavalin A and There could therefore scarcely be a The studies of African mammals then devising a new technique for pre­ clearer demonstration of the fact that ranged from the problems of the paring the cell surface membrane for transformation causes a change in the phylogeny of the older forms to those electron microscopy. His technique in­ distribution of these agglutinin-binding of evolutionary rates and the compari­ volves first "strengthening" the cell sites, which presumably accounts for son of later forms with those still extant. membrane by briefly incubating the cells the increased susceptibility of these Mr G. J. Heal (University of Bristol) in 0.1 per cent formaldehyde before transformed cells to agglutination. described sirenians which showed that lysing them on an air-water interface Whether this particular surface change two families of this order were already and then picking up the membrane on also alters the social behaviour of cells distinguishable in the Eocene, and Mr electron microscope grids. Once on the remains to be seen. © 1971 Nature Publishing Group.

Load more

  1

Copy Link