Showing papers in "Philosophical Transactions of the Royal Society B in 1972"

Review Lecture: Adaptive Radiation and Behaviour of the Malagasy Lemurs

Abstract: The systematic distribution of behavioural characters in lemurs can be analysed using the same techniques as for anatomical characters, without considering physiological mechanisms. Behaviour and structure are usually interdependent (functional morphology), so it follows that behavioural features probably evolve hand-in-hand with morphology. Behavioural and morphological characters generally exhibit the same patterns of systematic distribution, though it is not yet clear whether evolution typically operates through selection of inherited behaviour patterns, or through indirect canalization of behaviour which is dependent upon particular structures. The extant Malagasy lemurs and their recent subfossil relatives must be considered together as an integrated lemur fauna, which has undergone great reduction over the last few thousand years. The lemurs appear to form a natural group with the Afro-Asian loris/bush-baby group, certain Miocene lorisoids from East Africa ('Progalago group') and the Eocene Adapinae (Northern Europe) and Notharctinae (North America). This natural group can be referred to as the Strepsirhini. Simpson's classification (1945) implies that these Strepsirhines are closely related to the Tupaiidae (tree-shrews), and to the fossil Anagalidae and Plesiadapidae. Inclusion of these groups in the Order Primates is regarded here as superfluous, and discussion is restricted to the Strepsirhini, as defined above. It is suggested that the Malagasy lemurs and the Afro-Asian bush-babies and lorises had a common origin in Africa (lemur/loris stock), and that this ancestral stock had an earlier common origin with the Adapinae and Notharctinae of the Northern continents. The geographical distribution of the lemurs within Madagascar is examined, and seven basic zones of species distribution are identified. Each of these zones has distinctive climatic and vegetational characteristics which can be expressed on a 'climagramme' incorporating Emberger's pluviothermic quotient. Major physical barriers can be recognized along all of the boundaries between the present distribution zones. A model is suggested, in which climatically and physically demarcated zones of this kind can operate as agents for geographical isolation and speciation. Occasional emigration from zone to zone could produce a dynamic situation in which ecological competition between closely related species would favour a pattern of adaptive radiation with individual species becoming increasingly specialized for distinct ecological niches. In order to discuss the origin of the ancestors of the Malagasy lemurs, the relationship between Madagascar and other land-masses is examined. Although most authors agree that emigration from Africa has provided the main basis for biological invasion of Madagascar, there has been some controversy about the pattern of spatial relationships between Madagascar and Africa over time. Some authors (notably Simpson (1943) and Millot (1952)) have favoured a 'stable continents' hypothesis, and this has led to a concentration of interest on the Northern continents as the seat of Primate evolution. One outcome of this has been the suggestion that lemurs and lorises are separately derived from Northern European Adapinae. New geophysical evidence indicates that the 'stable continents' hypothesis is virtually untenable, and that continental drift theory provides the only coherent explanation of terrestrial evolution. This shifts the emphasis on Primate evolution to the Southern continents (notably Africa), and it seems likely that the lemurs and lorises had a common ancestry in Africa during the early Tertiary (for which no fossil evidence is available). One further consequence of drift theory is the observation that the Mozambique Channel has probably increased in width throughout the Tertiary, and that emigration of mammals to Madagascar from Africa has become increasingly improbable. Having established that Madagascar was probably invaded by a very small number of ancestral lemur species, which subsequently underwent adaptive radiation within the island, the systematic distribution of behavioural characters among living forms is examined. Attention is given to annual and daily patterns of activity, nesting patterns, diet (and some correlated dental features), locomotion (and some skeletal features), reproduction and social behaviour. In each case, it is shown that the Mouse Lemur group (Cheirogaleinae) and the Indri group (Indriidae) are internally cohesive in their characteristic behaviour patterns. The True Lemur group (Lemurinae) exhibits a wide range of behavioural adaptation, which is paralleled by equivalent morphological diversity. Behaviourally, the Aye-aye (Daubentonia) is as distinct as it is in morphological terms. By a process of induction, it is established that the behaviour of the ancestral lemurs was probably quite similar to that now exhibited by some Cheirogaleinae (particularly Microcebus), although living species in this group exhibit a number of probable specializations away from the ancestral condition. This conclusion is not surprising, since the Cheirogaleinae are also the least specialized of the lemurs in morphological terms. However, it is significant that the same ancestral pattern can be deduced for the loris/bush-baby group. Thus, the common ancestor of the Southern Strepsirhini (lemurs + lorises) was probably a small omnivorous form feeding primarily on insects, fruit and sap. The sap would have been gathered with the 'tooth-scraper' in the lower anterior dentition. There was probably a weakly developed spatial system of social organization, with central males of a population nucleus having access to females (a small number to each male), and peripheral males living on the fringe of each population. Competition between males would have provided a basis for selective mating and migration of peripheral males between population nuclei would have ensured exogamy. Extension of Walker's (1967) exemplary study of prosimian locomotion shows that the ancestral lemur/loris probably exhibited hindlimb dominated locomotion based on a grasping function of the extremities (primarily developed in the pes). The ancestral lemur/loris was probably nest-living, giving birth to - and caring for - a small number of well-developed infants after a relatively long period of gestation. There is some evidence that this ancestral form was nocturnal in habits, and it seems likely that the ancestral species which invaded Madagascar would have had a well-developed seasonal pattern of activity. Arboreal adaptation, the attachment to a nest, the small body size, and the ability to survive an adverse period of poor food supply (e.g. on the basis of fat reserves) would have fitted the early lemurs for a period of chance emigration across the Mozambique Channel on natural rafts of vegetation. Such rafts could have been formed from trees and other vegetation torn from forests lining rivers (e.g. the River Zambesi) on the east coast of Africa. Since the common ancestor of the lemurs and lorises was not very far removed from the ancestral Primate stock, many of the characters listed above must have been to some extent developed in the earliest Primates. This provides further evidence for the hypothesis that tree-shrews, anagalids and plesiadapids are quite separately derived from the ancestral Eutherian mammal stock, and that these three groups have no specific relationship to the Order Primates.

Lake Sediments in Northern Scotland

Abstract: A survey of deep-water sediments in 11 lakes in northern Scotland showed that only under certain conditions does a complete and conformable series of deposits accumulate. In lochs exposed to strong winds there may be no permanent settling of organic sediments in water depths of up to 50 m. Three lake cores (representative of three regions of northern Scotland), which proved to be complete and conformable profiles, were analysed in detail for pollen and certain chemical elements; one was also analysed for diatoms. A series of 14 C dates was obtained for two of these profiles. Changes in pollen content were found to be very consistently related to changes in sediment composition. Pollen zones were defined in terms of characteristic taxa, and variance in sediment composition was expressed as the first component of a Principal Components Analysis; changes in this first component invariably coincided with pollen zone boundaries based on changes in pollen spectra. This close relationship is explained as the consequence of the derivation of these lake sediments from soils on the catchments. Two important features of soil history emerged from this study: first, the general impoverishment of soils, water and biota due to leaching during the early millennia of the 15 000 years covered by these profiles, and secondly the changes in pollen spectra which accompanied chemical evidence for the development of peat on certain of the western catchments since ca . 3000 B.C. Complete analysis of a core from Loch Sionascaig in Wester Ross (pollen, chemical and diatom) has provided a history of the soils and the aquatic and terrestrial vegetation of the Inverpolly National Nature Reserve. Pollen analysis of cores from two small lochs supplemented the evidence from Loch Sionascaig as to late-glacial and early post-glacial vegetation history in the far north-west Highlands. Chemical and biological evidence for the history of blanket peat formation on the Sionascaig catchment which was provided by the lake sediments has been supplemented by examination and pollen analysis of four profiles from blanket peat, in all of which the presence of timber within the peat confirms the evidence of the pollen diagrams that pine-birch forest was present in this region during the period between ca . 2400 and 1500 B.C. Complete late-glacial profiles were found in three lochs in Region 1, the far north-west Highlands, and in Loch Tarff above the Great Glen. Our results confirm and extend those from Loch Droma (Kirk & Godwin 1963), proving that those sites in northern Scotland were free of ice throughout the Late-Weichselian period. The sequence of pollen zones — A ( Rumexzone), B (woody plants zone) and C ( Artemisia zone) — resembles that which has been found at many sites in Highland West Britain, including the closely dated site at Blelham Bog in the Lake District (Pennington & Bonny 1970). In Region 2, the mountainous part of Wester Ross near Beinn Eighe, lake profiles indicate the input of thick and barren laminated sediments, impenetrable to the corers used, during the final cold phase of the Late-Weichselian (Younger Dryas time). During the preceding Late-Weichselian interstadial, which on the evidence from Loch Droma had begun by ca . 10 870 B.C., pollen spectra indicate that the vegetation of northern Scotland must have been Empetrum heath, with juniper present at some sites but not at others, and no trees present. Pre-interstadial pollen spectra ( Rumex zone ) resemble plant assemblages found on immature soils. Chemical analyses indicate continuous and uninterrupted processes of soil maturation through pre-interstadial into interstadial time — accumulation of humus, leaching, and chemical weathering with formation of clay minerals. Pre-interstadial and interstadial diatom assemblages at Loch Sionascaig include many alkaliphilous species and some now characteristic of eutrophic habitats; the present acid poverty of this lake and its catchment must be the result of removal of soil bases by late- and post-glacial leaching. At all sites where it is present, pollen zone C ( Artemisia ) corresponds with sediment of very low organic content, and simultaneous changes in pollen and chemical composition at the boundaries of this zone are interpreted as the results of pronounced and synchronous environmental (climatic) changes at the beginning and end of Younger Dryas time. Above the Artemisia zone, pollen spectra, diatoms and chemical analysis all indicate rejuvenation of soils by the effects of the post-interstadial cold period; the biological evidence points to a repetition, at the opening of the post-glacial period, of pre-interstadial to interstadial plant successions, but in a much shorter time. 14 C dating at two sites shows that the spread of birch forest in northern Scotland was delayed for up to 1000 years after its establishment in northern England. On the evidence of ESR spectra of the humic acid in the Loch Sionascaig sediment, soils in northern Scotland had become acid before the arrival of forest. Post-glacial pollen diagrams are divided into a series of Regional Pollen Zones for northern Scotland; in north-west Scotland the boundaries of these zones have been dated by 14 C at two sites and the pollen zones correlated with chronozones. Early post-glacial Empetrum and juniper zones are followed by a birchhazel zone; from ca . 6000 B.C. onwards the birch-hazel pollen assemblage is replaced progressively by pine—birch. Surviving birch and birch—hazel woods round Loch Sionascaig are interpreted as the relics, on dry flush slopes, of a forest type which was widespread there before 6000 B.C. Chemical evidence suggests that between ca . 6000 and 4400 B.C. pine and pine—birch woods were growing on comparatively dry mineral soils, but from ca . 4400 B.C. the appearance of alder pollen is accompanied by evidence for solutional transport of iron and manganese from increasingly waterlogged soils. By 3000 B.C. formation of blanket peat must have begun on the Sionascaig catchment. For about another 1000 years pines and birches continued to grow on a peaty substratum. In Region 1 the pine forest ended suddenly at about 2000 B.C. ; alternative hypotheses to account for this are examined. In Region 2 the Loch Clair profile shows the continuity of pine—birch forest with the existing Coulin Forest on that catchment. Steeper slopes than in Region 1 must have prevented the general formation of blanket peat, and the poor siliceous soils did not attract prehistoric settlement, so there was no forest clearance, though traces of human influence appear in the pollen spectra from ca . 3400 B.C. In Region 3 the sediments of Loch Tarff show a sequence of post-glacial pollen zones which can be related both to the northern Scotland series outlined here and to the Godwin series of zones which has been widely applied in more southern parts of Britain. This is interpreted as the result of the position of Loch Tarff on the margin of an area of natural mixed-oak forest in the Great Glen; its pollen diagram records the expansion of this forest type in the mid-post-glacial period on which the Godwin zonation is based.

Ordovician geography and faunal provinces deduced from trilobite distribution

Abstract: Lists of families and genera of trilobites from the stratigraphical series of the Ordovician have been compiled, using information considered adequate from various areas in the world. Dissimilarities between these faunas have been assessed at both generic and family level, using Simpson's index. These indices have been analysed by a non-metric multidimensional scaling technique, and the groupings revealed are interpreted as indicating faunal provinces. Four provinces are recognized in the Lower Ordovician, the faunal characteristics and geographical extent of three of them (the Bathyurid, Asaphid and Selenopeltis provinces) being as previously described. A fourth province, here named the Asaphopsis province, is proposed for South American and Australian faunas in the Arenig and Llanvirn; the affinities of faunas from southeast Asia are indeterminate. In the Caradoc, faunas from areas occupied earlier by Bathyurid, Asaphid and Asaphopsis faunas, together with trilobites from south-east Asia, constitute a single province, here named the Remopleuridid. The Selenopeltis province persists in southern Europe and North Africa. These two provinces are recognizable only by a generic analysis in the Ashgill, and the latest faunas of that series are world-wide. It is assumed that a faunal province originally extended over parts of a single continental mass (cf. Wilson 1966), and that migration between provinces is inhibited by width of seas or temperature differences. An assemblage of continental masses consistent with these assumptions, and with palaeomagnetic data, is proposed to give four palaeogeographical maps for the Ordovician period. The position of the proto-Atlantic ocean proposed by Wilson (1966), and Gondwanaland of McElhinney & Luck (1970), are accepted; the remainder of Eurasia is divided into four blocks. The maps suggest relative movements between continental blocks that may have removed barriers to migration and resulted in progressive merging of the faunal provinces. They are models to be tested against distributions of other animal groups, new palaeomagnetic and palaeoclimatic evidence, and theories on lithosphere plates. The geographical reconstructions imply that the faunas of South America, southern Europe and North Africa inhabited cool waters, those of North America, northern Europe, north-east Asia, south-east Asia and Australia, warm waters. Cooler water faunas appear to have been less diverse. Decreasing provinciality of faunas during the Ordovician appears to have been accompanied by a reduction in total diversity; supposed climatic deterioration does not seem to have resulted in increased diversity. The differences between contemporaneous faunas within the Bathyurid and Remopleuridid provinces are investigated, and are shown to reflect differences in environment and evolution and diversification of groups of trilobites which took place in these environments.

Biostratigraphical dating of the early history of the South Atlantic Ocean

Abstract: The southern Atlantic has always been a favoured testing ground for the hypothesis of continental drift. Apart from the remarkable agreement in the geographical shape of the coast of western Africa and eastern South America, considerable attention has been paid to the origin of the Mid-Atlantic ridge and these factors have provided a basis for testing the concept of drift. Detailed studies of the geology of NE Brazil and Gabon indicate that both areas had been basins of non-marine sedimentation almost continuously from the Upper Palaeozoic through to the Neocomian. During the Neocomian it would appear that both areas were parts of a large freshwater lake which may have been situated in a zone of subsidence produced by an initial phase in the separation of the two land masses. This structure may have been similar to the Great Rift Valley system of today in East Africa. It would seem that the rift continued to widen during the Neocomian and made connexion with the open ocean during the Aptian, thus developing into a 'protoatlantic' similar in configuration to the present day Red Sea. During the latter part of the Aptian, salt deposits began to accumulate in the narrower parts of the elongated bays. The deposits in Gabon, Angola and Brazil are large and of economic importance. About this time South America seems to have begun a relative clockwise rotational motion, which in its later stages may have resulted in a fracturing and tearing movement of the crystalline basement rocks in the area bounded by the Ivory Coast and Maranhao. The point in time at which northern and southern arms of the protoatlantic became united may be ascertained by means of a biostratigraphical analysis, based mainly on the evidence provided by the ammonites of the critical sequences. The crucial area lies in a zone formed by the states of Rio Grande do Norte, Pernambuco, Alagoas, Sergipe and Bahia in Brazil, and the Ivory Coast down to Angola and Gabon in West Africa. The analysis of the Albian to Turonian invertebrate associations, in particular the dispersion of the genus Elobiceras and the vascoceratid, pseudotissotiid, mammitid and benueitan faunas shows that the final break between South America and Africa may be dated as upper Lower Turonian. Furthermore, the geographical dispersion of Turonian invertebrates shows that the rifting apart was accompanied by a periodic pattern of regressions and transgressions possibly brought about by oscillatory movements of the continental block.

The Secretion and Structure of the Skeleton of Living and Fossil Bryozoa

Abstract: Eighty species of living and extinct bryozoans have been studied to ascertain the mode of secretion of the skeleton and its structural diversity throughout geological time. In the growing tip of the cheilostomes Membranipora and Electra and the ctenostome Bowerbankia , periostracum secreted by a cap of palisade cells expands forwards by intussusception. Older periostracum, left behind by the advancing cell cap in cheilostomes and cyclostomes, becomes the seeding sheet of a calcitic layer (primary layer) of vertically disposed crystallites with minor banding, nodules and lenses, deposited by epithelium generated immediately proximal of the cell cap. The periostracum is composed of mucopolysaccharide and some chitin but its outer surface varies, being a fibrillar triple-unit membrane in cheilostomes and the cyclostomes Berenicea and Lichenopora , and a homogenous granular layer in Bowerbankia and the cyclostome Crisidia . The mineral skeleton of most cheilostomes is secreted on periostracum by succeeding epithelium. But coelocystic structures, deposited within folds of epithelium, also occur and vary from frontal walls and cryptocysts to almost complete skeletons of Cupuladria and Iodictyum . In some living cheilostomes and in most fossil species examined, only a primary shell, more commonly calcitic than aragonitic, is found, but in the majority of living species there occurs an organic-carbonate secondary layer usually composed of discrete laminar or lenticular aggregates of vertically disposed crystallites enclosed in proteinous sheets. In Celleporella , however, the laminae are more strongly defined because they consist of spirally growing calcitic plates separated from one another by simultaneously secreted proteinous sheets. More rarely, a tertiary layer is found in some species. It is almost entirely calcitic or aragonitic and may be banded, granular or composed of acicular crystallites. Puncta and basal kenozooids, as in Schizoporella and Cupuladria, penetrate the shell of some species and accommodate papillae with storage cells. The mineral skeleton of most cyclostomes, including the earliest known genera like the Ordovician Corynotrypa, has always been subperiostracal, and may also be pierced by puncta accommodating storage papillae and distally closed by periostracal plugs (e.g. Crisidia, Berenicea ). The skeleton of Heteropora , Hornera, Lichenopora and related genera which first appeared in early Mesozoic times, is coelocystic. It may also be ornamented by inwardly pointing cones of secondary shell (pseudopuncta) with or without axial rods of granular calcite (e.g. Hornera ) , or include vesicular tissue between radiating rows of zooecia as in Lichenopora . All cyclostomes, however, have always had a double-layered calcitic skeleton consisting of a primary layer of vertically disposed acicular crystallites, granules or tablets altered to a granular texture in the fossil state, and a laminar secondary layer with spirally growing plates and/or overlapping fibres coated by protein sheets. The mineral skeleton of the remaining stenolaemates represented by extinct trepostomes, cystoporates and cyclostomes, is exclusively double-layered and coelocystic. The primary layer is granular, the secondary composed of lenticular fibres. Pseudopuncta were almost invariably developed and interzooecial cavities (mesopores) commonly occurred and were filled with vesicular tissue as in Lichenopora . Phylogenetic considerations suggest that the prototypic bryozoans possessed a pseudopunctate coelocystic skeleton, indented by mesopores and composed of a chitinous or proteinous periostracum, a primary layer of acicular crystallites and a secondary layer of lenticular fibres. This structure was inherited by trepostomes, cystoporates and cryptostomes. It reappeared in Mesozoic cyclostomes subsequent to their divergence from a cystoporate-like ancestor by the development of a variably punctate subperiostracal skeleton which, however, was composed of the same shell types. The subperipheral skeleton of early cheilostomes may have evolved by extension of the ctenostome secretory regime. In any event a new type of secondary shell, composed of acicular crystallites arranged in proteinbound laminae and lentides, became characteristic mainly of Tertiary and Recent species. Nevertheless, a coelocystic skeleton and even a stenolaemate-like secondary shell have already appeared within the Order.

The genetics of the mimetic butterfly Papilio polytes L

Abstract: Papilio polytes L is a mimetic Swallowtail butterfly widely distributed in South East Asia It has four female forms, three mimetic, and one non-mimetic resembling the monomorphic male in appearance The various female forms are now shown to be controlled by allelomorphs at a single autosomal locus and not by independent genes as previously thought The effects of the allelomorphs controlling the mimetic patterns are sex-limited to the female There is some evidence that the locus is a complex one consisting of two or more tightly linked genes As in previous investigations into mimicry in Swallowtails the dominance tends to be complete between sympatric forms The accuracy of the mimicry depends not only on the presence of the appropriate major genes but also on the rest of the gene complex Thus within a race there is an integrated genetic system and on outcrossing this becomes disturbed, leading to poorer mimicry The system of modifiers controlling the accuracy of the mimetic pattern is closely paralleled by that in P dardanus In particular, in P polytes f theseus appears to differ from f polytes only as a result of the presence of a modifier system, as does f hippocoon from f hippocoonides in P dardanus In P dardanus from Ethiopia it was found that specific modifiers adjusting the tail length of mimetic females have been selected for, thus improving the mimicry An analogous situation has been found in P polytes although here the control is more effective in that the resulting difference in tail length between the mimetic and non-mimetic forms can be as much as 10 mm, whereas in P dardanus it rarely exceeds 3 mm The great similarity in the genetic structure of P polytes and P dardanus (as well as P memnon ) strongly suggests that selection for a mimetic polymorphism results in the evolution of very similar genetic control mechanisms in different species - that is to say it is the nature of the selection rather than the species involved which determines the genetic architecture

The Growth of Children at Different Altitudes in Ethiopia

Abstract: In this study were observed the effects of two widely differing environments on the growth and maturation of children from a presumed genetically homogeneous Ethiopian population. Major environmental differences included altitude above sea level, temperature, probably rainfall and humidity, together with the incidence of infectious disease. The results indicate that highland children, particularly boys, are taller, heavier and bigger in most physical dimensions than are lowland children. In both groups skeletal maturation is retarded (by American White standards) during later childhood; this retardation is more marked in lowlanders. In both groups, however, there is marked acceleration of skeletal maturation during early puberty. Haemoglobin values increase much more rapidly in highland children, but surprisingly, differences in chest dimensions are not particularly marked. It is concluded that hypoxia of the degree found in the high-altitude group (approximately 3000 m) is not sufficient to affect adversely the growth of children. On the other hand, the increased incidence of infectious disease in the 'lowlands' (approximately 1500 m) and possibly the raised ambient temperature, may restrict growth and maturation of children living in this environment. Thus, in contrast to the situation in other high-altitude parts of the world, the highlands in Ethiopia appear to be more favourable to growth than the lowlands.

The skull and skeleton of Eogyrinus attheyi Watson (Amphibia: Labyrinthodontia)

Abstract: As a preliminary to the redescription of the anatomy ofEogyrinus attheyi Watson, an account is given of the problems of nomenclature of British members of the anthracosaur family Eogyrinidae to which it belongs. There is no evidence to show that the four named genera of British eogyrinids differ from one another in any significant feature not explicable by allometric growth. Reconstruction of a series of allometric curves based on known skull specimens allows estimation of the dimensions of incomplete specimens. The skulls then fall into four size groups which correspond, with some stratigraphical backing, to the four named genera. The lectotype skull of Eogyrinus, from the Low Main Seam, Newsham, Northumberland, has been cleaned using an ' Airbrasive' unit and is used as the basis of a new description of the skull. Additional information is provided by other Newsham specimens and two skulls from the Middle Coal Measures of Lanarkshire. The skull is completely known and is typical of anthracosaurs. The skull roof is closely similar to that of the eogyrinid Palaeoherpeton (' Palaeogyrinus'), but no anterior tectal bone is present above the naris in Eogyrinus. The nature of the dermal ornament is fully described. The palate is Wpically anthracosaur, with toothless vomers, a 'tusk-pair' on each palatine and ectopterygoid, and additional small ectopterygoid teeth. The pterygoids descend below the level of the jaw line posteriorly as in Palaeoherpeton. The braincase is reconstructed from an isolated Newsham specimen, originally attributed by Watson, from the lectotype and from one of the Scottish skulls. The isolated specimen shows the course of the semicircular canals as well as the fenestra ovalis. Most of the cranial nerve foramina are present. A complete reconstruction of the lower jaws is possible both as single rami and in articulation. Description of the jaw articulation allows a reconstruction of the relative movements of the rami in opening and closure. The only associated material of the appendicular skeleton is the lectotype left femur, but an interclavicle from Newsham is certainly eogyrinid and probably pertains to Eogyrinus. Isolated ventral scales are described and their pattern of articulation reconstructed. The material described in this paper is combined with that used in an earlier account of the axial skeleton to give a reconstruction of the whole skeleton of Eogyrinus in articulation, together with a restoration of the appearance of the living animal.

Whaitsiid Therocephalia and the origin of cynodonts

Abstract: The conclusion reached in this paper is that the cynodonts evolved from a therocephalian ancestor, and that among the known therocephalians, the whaitsiids are the forms closest to cynodont ancestry. Certain superficial specializations of the feeding apparatus, however, debar the known whaitsiids from a position of actual cynodont ancestry. The evidence for this thesis lies in new detailed morphology of certain points of the whaitsiid skull, along with reassessment of much of the established cranial anatomy of the relevant groups. It is presented in the form of a series of comparisons of the skulls of whaitsiids, primitive cynodonts, other therocephalians and primitive therapsids respectively, and a summary of this is given in table 1. The morphology of the whaitsiid skull is then discussed from a functional point of view, with particular reference to the design of bones as adaptations to resist the forces involved in the use of the jaws. The changes which must have occurred in the evolution of the cynodonts from a whaitsiid-like therocephalian are considered in this same context and it is argued that the organization of the cynodont skull can be seen as a logical functional development from the more primitive condition. In particular, the streptostylic nature of the jaw articulation, the enlargement of the dentary and reduction of the postdentary bones, and the reduction of the reflected lamina of the angular may all be correlated with the development of a masseter muscle.

The organization of a cephalopod ganglion.

Abstract: The stellate ganglion of cephalopods is sharply divided into a ventral part containing only large cells and a dorsal part where there are also microneurons (amacrine cells). Axons proceed from the larger cells of the ganglion to the stellar nerves in distinct dorsal and ventral roots, which join as they leave the ganglion. The ventral roots contain only large motor fibres, one arising from each of the 30 000 ventral cells. The input to this part is from less than 2000 large fibres of the pallial nerve. These fibres branch abundantly in the ventral neuropil. After severing the pallial nerve massive degeneration occurs there, producing shrinkage of the whole ganglion. There is also degeneration in the dorsal neuropil, which therefore also has input from the pallial nerve. The dorsal roots contain some large fibres, being the axons of the larger dorsal cells. In addition, they contain numerous small fibres. These include efferent chromatophore fibres, which degenerate after severing the pallial nerve and therefore pass through the ganglion presumably without synapse. There are also afferent fibres from the periphery in the dorsal roots and, after severing stellar nerves, degeneration appears in the outer layers of the dorsal neuropil and in the pallial nerve. No degeneration occurs in the central stumps of the ventral roots after this operation. The trunks of the small cells of the dorsal part form characteristic bundles of fine fibres in the outer dorsal neuropil and dorsal roots. These bundles carry varicosities and make plexuses in the bases of the dorsal roots, intertwined with collaterals of the outgoing large fibres and branches of the incoming afferents from the periphery. Probably these microneurons terminate within the ganglion and are concerned with reflex modulation of the output of the dorsal neuropil. The arrangement of the dorsal and ventral divisions of the ganglion and roots of the stellar nerves is similar in Sepia and Loligo to that in Octopus. There are more numerous large terminal knobs in the neuropils of these decapods and these endings are also found within the cell layers, especially in the hind part of the dorsal region. The course of degeneration within the ganglion was followed after section of the pallial and stellar nerves in all three species, more in detail in Octopus. Degeneration of terminations is already advanced 15 h after severing the pallial nerve (at about 24 $^\circ$ C); break-up within the nerve trunks comes later. Degeneration granules have mostly disappeared 3 days after the lesion. Severed stellar nerves of Octopus show very abundant sprouting from the central stump, the fibres turning back to invade the ganglion and form terminal knobs in the neuropil and throughout the cell layers.

Insect Faunas of Late Devensian and Flandrian Age from Church Stretton, Shropshire

Abstract: Invertebrate faunas consisting mainly of insects, from deposits in the Church Stretton valley, are described and discussed. These deposits fall into two periods: (a) Late Devensian, which follows an episode of glaciation and precedes a period of accumulation of frost-shattered gravel fans; and (b) Flandrian, which post-dates the gravels and has been placed in the post-Glacial pollen zones VI and VII. The faunas of these two episodes are dealt with separately in Parts I and II respectively. Part I. From two sites in which sequences containing clays, peats and silts were examined five radiocarbon dates are available, the oldest being 13 555 $\pm$ 620 years B.P. and the most recent 11 000 $\pm$ 200 years B.P. The faunas include a substantial number of species not now found in Shropshire, many not in Britain. Inferences on the changing ecology and thermal environment of the area are drawn from these faunas and are compared with the pollen analytical zones. This comparison shows that, according to the insects, the warmest part of the episode was late zone I, and that zone II (the Alleroslashd), often considered to be the climatic optimum of the period, appears to have been a time of gradually deteriorating summer temperatures. Part II. Deposits from three late Flandrian sites are discussed. Although only one radiocarbon date was obtained, of 8101 $\pm$ 138 years B.P., pollen analysis was carried out by Rowlands throughout each sequence and this showed that the earliest deposit, at Little Stretton, dated from zone VIa and at all three localities deposition continued into zone VIIb. An examination of the insect assemblages shows that completely different biotopes, from open pasture to dense woodland, were existing side by side in the Church Stretton valley in late Flandrian time. Summer temperatures at least as high as those of today are inferred. The possibility exists that during the period represented here the climate was even warmer than that of the present but until more information is available it is not possible to be more definite on this point.

Studies on the Onychophora VIII. The relationship between the embryos and the oviduct in the viviparous placental onychophorans Epiperipatus trinidadensis Bouvier and Macroperipatus torquatus (Kennel) from Trinidad

Abstract: Viviparity in the neotropical Onychophora is based on a placental relationship between the embryo and the maternal oviduct, analogous in certain ways to that of mammals. The embryo develops a stalked placenta which becomes intimately associated with the oviduct wall. The tissues of the oviduct wall become highly modified in the placentation zone. The present study provides the first detailed account of the formation and structure of the placentation zone in the neotropical Onychophora and of the events involved in the movement of the embryos along the oviduct. Macroperipatus torquatus is more specialized in certain ways than Epiperipatus trinidadensis , but the general course of gestation is similar in both. The oviduct has a proximal growing region. Each fertilized egg released from the ovary becomes implanted at the midpoint of a newly formed length of proximal oviduct. As the embryo develops, it remains within its associated length of oviduct, while additional lengths containing younger embryos are added more proximally. The embryo is enclosed in an epithelial sac, formed by cells of the lining epithelium of the oviduct. A placental stalk attaches the embryo to the equatorial inner surface of the sac. As the embryo grows, the epithelial sac extends in both directions along the associated oviducal part. The wall of the sac becomes specialized equatorially as an inner placental ring. The wall of the oviducal part develops an outer placental ring external to the inner placental ring, but is partially resorbed and simplified elsewhere along its length. Segment formation and the preliminary differentiation of organ systems are completed while the embryo is enclosed in the epithelial sac. The embryo eventually fills the sac, which then occupies the full length of the associated oviducal part. The embryo now escapes from the epithelial sac and moves into the lower region of the oviduct, where embryonic growth continues. Each escape of an embryo in this way follows the birth of the largest embryo previously contained in the lower region of the oviduct. The placentation zone and associated oviducal part vacated by the escaping embryo are added to the proximal end of the lower region of the oviduct, where resorption of both the placentation zone and the general oviduct wall continue. The lower region of the oviduct is encircled by a sequence of vestigial placentation zones, each indicative of a prior birth. Thus, the neotropical Onychophora combine placentation with the progression of a sequence of embryos towards the genital opening by a simple device. Each embryo occupies a fixed position in the oviduct until its organ systems are fully formed, but the oviduct grows at the proximal end and is resorbed towards the distal end. This procedure is unique among the Onychophora. The embryos of non-placental species are moved along the lumen of the oviduct by muscular action in the normal way. The onychophoran placenta is functionally analogous to the mammalian yolk-sac placenta, but no functional equivalent of a chorio-allantoic placenta is developed in the Onychophora. Most of the growth of the onychophoran embryo takes place after the placenta has been resorbed.

Contributions to the geology and palaeontology of Chiloe Island, southern Chile

Abstract: During the Royal Society Expedition to southern Chile in 1958 geological observations were made at Chepu and on the San Pedro tableland in the island of Chiloe. The island is composed of schist, Tertiary sediments, fluvioglacial deposits and volcanics. The schist, of uncertain age, forming the basement at Chiloe, is an extension of the schist of the coastal range of southern Chile, and falls in the chlorite zone (greenschist facies). It includes greenschists and altered gabbroic rock as well as normal quartzofeldspathic schist, flat lying at San Pedro but strongly crumpled and folded on the west coast. Tertiary or Quaternary volcanic rocks, of limited distribution, include banded rhyolite, partly spherulitic, and altered vesicular hypersthene andesite. Upper Tertiary sandstone unconformably overlying the schist on the coast south of Chepu contains abundant fossil invertebrates (mainly Mollusca) attributed to the Lower Pliocene. The Chepu assemblage is intermediate in character and apparently in age between the Miocene (Navidad and Ranquil) faunas and the Middle Pliocene (Coquimbo) fauna of Northern and Central Chile, containing persistent Miocene elements together with Pliocene immigrant elements that do not occur together in the better known faunas of more northerly districts. Two new species of Ocenebra and a new subspecies of Acanthina crassilabrum Lamarck are described.

The Genetics of Mimetic Colour Polymorphism in the Large Narcissus Bulb Fly, Merodon equestris Fab. (Diptera: Syrphidae)

Abstract: Genetical studies have revealed six gene loci concerned with body hair colour in Merodon equestris. These are: (i) Bulborum. Darkens all the thorax including the scutellum except the anterior. The dark allele is dominant. (ii) The modifier U. In conjunction with bulborum this produces the morph subvalidus. This is characterized by some sexual dimorphism. These are certain sex differences in the degree of darkening of the second abdominal segment and the female shows a degree of darkening of the anterior thorax. The dominant dark allele only expresses itself when the dominant allele of bulborum is present. (iii) The modifier V. In conjunction with the dominant alleles of bulborum and the modifier U only the dominant allele of the modifier V gives the sexually dimorphic colour type validus. The second abdominal segment is more or less completely blackened and in the female only the anterior of the thorax is completely blackened. (iv) Equestris. The dominant allele produces a black thoracic band like bulborum except that the scutellum is coloured. (v) Transversalis. Expression is limited to the female, although the locus is inherited autosomally. There is a black band on the third abdominal segment. (vi) Ground colour. There are three alleles determining the distribution of orange and yellow over the thorax and abdomen. They are YOYO, OOYY and OOOO, the letters referring to yellow or orange coloration from the anterior of the thorax to the abdomen tip. The dominance is simple: YOYO is dominant to OOYY and OOOO and OOYY is dominant to OOOO. Within the colour types YOYO and OOYY there are colour variants YYYO, YOYY, YYYY and OOOY, OOYO respectively. Orange is dominant to yellow in the YOYO category and yellow dominant to orange in the OOYY category. The OOOO can be regarded as a universal recessive and can be treated as a separate category or as a variant of the OOYY category. Linkage has been detected between three of the loci. These are equestris, bulborum and ground colour and the order of mention is the order of linkage on the chromosome. Linkage, however, is not very strong so that some recombination occurs. Some aspects of the population genetics of the colour polymorphism have been studied using such little data as are available. Linkage disequilibrium has been found in the field for the linked genes bulborum and ground colour appears to be strongly maintained. A listing of potential models for the 34 colour types of M. equestris reveals that the colour types most commonly occurring, and maintained at high frequency and in linkage disequilibrium, are the best mimics of bumble bees in the United Kingdom. Some aspects of the evolution of the colour polymorphism in Europe, particularly in relation to the related species M. flavus are discussed. The chromosome number found confirms that found by other workers (2n = 12) and polytene chromosomes have been demonstrated in a variety of tissues.

Endemic Goitre in the Gilgit Agency, West Pakistan

Abstract: A study has been made of an iodine-deficient population living in an extended village in the Karakoram Himalayas. There is evidence that the incidence of goitre increases towards the lowest part of the village, in accordance with the findings of McCarrison, who worked in the same region in the early years of the twentieth century. McCarrison ascribed the variation of goitre incidence to increasing pollution of drinking water as it travelled downstream, and postulated a bacteriological goitrogenic factor. However, the observations reported here show no correlation between goitre incidence and the bacterial concentration of drinking water, nor are there iodine-metabolizing micro-organisms present in the water. It may be that a differential iodine deficiency throughout the village can account for the variation in goitre incidence, since the soil can adsorb appreciable amounts of radio-iodine. The indices of thyroid function show that all the inhabitants are exceptionally iodine-deficient, although most of them are clinically euthyroid. As well as having a greatly enhanced mean thyroid iodide clearance the population has a mean renal iodide clearance which is lower than normal. Intra-muscular injections of iodized oil were acceptable to the villagers, and 477 injections were administered. Fingerprints and palm prints were collected from a sample of the population, yielding a pattern distribution comparable with other populations in the Indian subcontinent. The ratio of PTC tasters to non-tasters among the inhabitants is not significantly different from the ratio found in Europe.