Showing papers in "Biological Journal of The Linnean Society in 1976"

Archaeopteryx and the origin of birds

Abstract: The question of the origin of birds can be equated with the origin of Archaeopteryx, the oldest known bird. Analysis of the five presently known skeletal specimens of Archaeopteryx. and comparison with the skeletal anatomy of the several reptilian groups that have been proposed as possible ancestors of birds (Ornithopoda, Theropoda, Hseudosuchla and Sphenosuchidac), confirm the conclusions (long rejected by most subsequent workers) of Heilmann (1926), Lowe (1935, 1944) and Holmgren (1955), namely, that the skeletal anatomy of Archaeopteryx is extraordinarily similar to that of contemporaneous and succeeding coelurosaurian dinosaurs. Rejection of these similarities as adaptive structures only (parallel or convergent similarities), and therefore of no phylogenetic importance, is here considered invalid. Heilmann was the first to identify the only evidence that has been cited so far for dismissing coelurosaurian-avian ancestral–descendant relationships, the supposed absence of clavicles in all theropods, and on that basis suggested a common Archaeopteryx–dinosaur ancestry among pseudosuchian reptiles. That evidence is negative and thus inconclusive, and is now known to be false. With the exception of fused clavicles and unique ischial morphology, virtually every skeletal feature of Archaeopteryx is known in several contemporaneous or near-contemporary coelurosaurian dinosaurs and many of these conditions are unrelated, specialized features (the detailed morphology of the manus, metacarpus, carpus, humerus, scapulocoracoid, pes, metatarsus, tarsus, femur, pubis, ilium, skull and mandibles). The presence of so many derived characters in common clearly establishes that the closest ancestral affinities ot Archaeopteryx are with coelurosaurian theropods. There is no contrary evidence and any other explanation is illogical. All available evidence indicates unequivocally that Archaeopteryx evolved from a small coelurosaurian dinosaur and that modern birds are surviving dinosaurian descendants. Stated simply, avian phylogeny was: Pseudosuchia Coelurosauria Archaeopteryx higher birds. SUMMARY The question of the origin of birds can be equated with the question of the origin of Archaeopteryx. This last question evokes two possible answers, depending upon how one views the importance of “primitive versus derived characters” in assessing phylogenetic relationships. One possible answer is: Archaeopteryx is a direct descendant of some unknown, but presumably Euparkeria-like pseudosuchian. This answer is predicated on the belief that Archaeopteryx only parallels or converges with various coelurosaurs in certain skeletal similarities. This is the view now held by the majority of biologists– a view that I find unacceptable. The second possible answer is: Archaeopteryx is directly descendant from a small unknown Ornitholestes-like coelurosaurian dinosaur. This answer assumes that skeletal similarities between coelurosaurs and Archaeopteryx are derived from a common ancestor, itself a coelurosaur. This is the view advocated here. There is no evidence to support an ornithischian ancestry of birds. The pubis of Archaeopteryx apparently was not reflected backward as in ornithischians and modern birds, and in any case, the ornithischian pubis is only superficially like that of living birds. Nor is the so-called ornithopod foot like that of birds. Evidence of close theropod–Archaeopteryx relationships, however, is abundant: the presence of the same, multiple, specialized adaptations in both Archaeopteryx and various coelurosaurs (tridactyl manus, metacarpus and carpus morphology, forelimb and pectoral girdle structure, four-toed pes, reversed hallux, metatarsal morphology, mesotarsal joint, hindlimb construction, pelvic form, plus elongated forelimbs, bipedal posture, vertebral structure and formula, and basic cranial morphology). The presence in Archaeopteryx, coelurosaurs and pseudosuchians of several primitive characters in common (thecodont dentition, sclerotic ring, possibly amphicoelous vertebrae, long caudal series, gastralia, pubic symphysis, short coracoids) indicates only a probable common ancestry. It does not establish that the Coelurosauria could not have given rise to Archaeopteryx–and higher birds. There is no evidence (outside of Lagosuchus and Lagerpeton) of shared derived characters to suggest a close evolutionary relationship between classic pseudosuchians and Archaeopteryx. Similarly, there is no clear-cut evidence in the form of shared derived characters to link Archaeopteryx with Sphenosuchus. The absence of clavicles in theropods (now known to be false), once considered as conclusive evidence against a coelurosaurian ancestry of birds, is no more significant than is the absence of a sternum in all known pseudosuchians as evidence against a pseudosuchian ancestry of all other archosaurs. The absence of any known “ideal” coelurosaurian pre-Archaeopteryx is only negative and inconclusive evidence, especially in view of our meagre and exceedingly deficient knowledge about Early and Middle Jurassic terrestrial vertebrates. All available evidence indicates that the immediate ancestor of Archaeopteryx was a small coelurosaurian dinosaur and that the phylogeny of avian ancestry was: Pseudosuchia–Coelurosauria–Archaeopteryx:– higher birds. Ornithopod-Archaeopteryx ancestral-descendant affinities may be dismissed because of the false “avian” organization of the pelvis in the Berlin specimen of Archaeopteryx and the merely superficially bird-like construction of the ornithisehian pelvis. The suite of specialized characters unique to ornithischians (e.g., predentary, tooth morphology), that occur even in Triassic representatives, is further evidence for dismissing close affinity between ornithopods and Archaeopteryx. The supposed close relationship between birds and pseudosuchians is judged to be remote at best, due to the completely primitive nature of the few anatomical features which pseudosuchians have in common with Archaeopteryx. Sphenosuchus, a primitive and early archosaur, is also a potential avian ancestor, but existing evidence consists of primitive archosaurian features plus a few similarities with certain modern birds. These similarities, which are present in two groups that are separated from each other by more than 200 million years, and which cannot be demonstrated in Archaeopteryx, are considered irrelevant to the origins of Archaeopteryx and subsequent birds.

A unified classification of mimetic resemblances

Abstract: The eight possible interactions of a tripartite mimicry system (model, mimic and operator) are defined in terms of positive and negative functions. Five possible states of the system are also recognized in terms of specific composition. From this an eight by five classification matrix is developed, which embraces all normally recognized mimetic situations. Each class is examined for general properties and examples. Special consideration is given to situations (Mullerian mimicry) included here, and to other systems (crypsis, deflective marks) not included, which have been treated differently elsewhere. Mimicry is defined in terms of a tripartite system of living organisms, in which a sensitive signal-receiver ( the operator) misidentifies the mimic as the model. It is emphasized that the system developed here is a classification of mimetic interactions, not a classification of species. Discussion is given on some implications of the system in relation to natural selection, and the classification of ecological interactions, convergence and genetic diversity.

Phenotypic diversity, mimicry and natural selection in the African butterfly Hypolimnas misippus L. (Lepidoptera: Nymphalidae)

Abstract: Hypolimnas misippus, a sexually dimorphic, nymphalid butterfly with a very variable female, was sampled for 41 consecutive months, along with its supposed model, Danaus chrysippus (Danaidae), at Dar es Salaam, Tanzania. Hypolimnas larvae collected in the field were reared to compare their range of variation with that of the wild adult population. Some breeding data are presented. Although I show that the colour variations in Danaus and Hypolimnas are remarkably similar, the frequency rankings of the analogous forms within each species differ markedly in the long term. Moreover, 24% of Hypolimnas are transitional forms which are poor mimics. As the range of variation at Dar es Salaam is similar to that reported from Ghana, where the “model” is of quite different appearance, I conclude that mimetic resemblance is not of over-riding importance to its maintenance and perpetuation. The continuous variation in both fore- and hindwing coloration in the field is reflected in reared broods which fail to segregate into discontinuous phenotypes so that H, misippus is not truly polymorphic at Dar es Salaam. Females with transitional forewings have white on their hindwings more often than do the two extreme phenotypes, misippus and inaria. Transitional or white winged females are abundant only at times of high population density, whereas inaria larvae seem to have an advantage in crowded conditions. The extreme rarity of association between the inaria forewing and white hindwing suggests disruptive selection, the former being associated with the conditions of K selection and the latter with r selection. The calculation of selection coefficients supports this interpretation. Phenotypic diversity is greatest at high population density when the proportion of poor mimics is also maximal. At these times, apostatic selection may be important. At low density, diversity is minimal. Recent evidence concerning the efficiency of D. chrysippus as a model is discussed. The origin of colour variation in H. misippus probably owed much to mimicry but other selective forces such as apostatic selection or perhaps sexual selection are now of greater importance in maintaining it.

Thysanoptera of the genus dichromothrips on old world orchidaceae

Abstract: Species of Dichromothrips are shown to be widespread on Orchidaceae in the Old World Tropics from Africa to New Zealand. The centre of diversity appears to be the Malaysian Region but this may be an artefact resulting from poor collections. The genus is redefined, its relationships discussed and a key provided to the 14 species [australiae sp. nov., borneensis (Pr.); corbetti (Pr.); dendrobii Saki.; indicus sp. nov.; maori sp. nov.;nakahari sp. nov.;nigeriae sp. nov.; orchidis Pr.; phalaenopsidis Saki. (=sakimurai Bhatti syn.nov.); priesneri (Hood); semicognitus Saki.; smithi (Zimm.)j via torus sp. nov.|.Eugeneothrips Hood is synonymised with Dichromothrips.

A geological perspective of the upland biota of Laysan atoll (Hawaiian Islands)

Abstract: Laysan Island, a low atoll in the Leeward Hawaiian Islands, exhibits a biota that contains nine genera of upland and montane lineages of animals and plants usually of restricted range and occurrence and adapted to high island habitats. The geological history of Laysan Island, interpreted in terms of plate tectonic theory and recent ideas on the formation of linear island chains, shows that Laysan existed as an active high volcanic island approximately 15 million years ago. Since that time subaerial erosion and tectonic subsidence have combined to reduce the height of the island. During the past 250,000 years glacioeustatic sea level changes have resulted in Laysan Island fluctuating, geomorphologically, between a high limestone island and an atoll status. Laysan is viewed as a refugium for upland and montane lineages able to keep pace, via great adaptive flexibility, with drastic habitat changes. The thesis that plants of Laysan are recent arrivals is considered unlikely, as regards the upland contingent, in view of the geological history of the island.

A mangrove community in the New Hebrides, south‐west Pacific

Abstract: A general survey of the mangal at Port Stanley, Malekula, New Hebrides, the most extensive mangal in the archipelago, was conducted over an 11-day period in September/October 1971. Seventeen species of true mangrove tree and mangrove associates were recorded. As is characteristic of mangal, this flora was distributed in a zonal pattern, four zones being recognized. Certain anomalies in zonation were attributed to a recent episode of crustal uplift. The aquatic component of the fauna was dominated by molluscs (26 species) and Crustacea (20 species). The terrestrial vertebrate fauna consisted of 4 species of reptiles, 21 birds and 5 mammals. The mangrove community at Port Stanley is an integral part of that of the Indo-West Pacific region. However it is much restricted in number of species, and reasons for this are suggested: distance from Malesia, lack of fresh water, and shallow soils with little silt deposition. Faunal impoverishment is clearly associated with floral impoverishment.

Selective feeding behaviour of the common carp Esomus danricus (Ham.) in its natural habitat

Abstract: Food selectivity by the common freshwater carp, Esomus danricus (Ham.) was studied through Ivlev's equation of electivity. The selective feeding seemed to be influenced by many factors, including the accessibility, abundance and taste, of the food items, the mechanical and physiological adaptations on the part of the fish to capture and digest those food organisms, as also the inherent and instinctive property of the fish to prefer certain types of food over the others. The absence of strong specific selectivity by the fish for a variety of planktonic food organisms was found to be a phenomenon compensatory to stenophagism, in order to make use of whichever food items remained in the habitat at the time when the preferred genera of plankton were not available, due to the process of succession.

T. R. R. Stebbing: A bibliography with biographic notes

Abstract: T. R. R. Stebbing (1835–1926), a specialist on the systematics of amphipod Crustacea, was raised in London in a literary family and studied classics, law and history at Oxford. After his ordination as a priest in 1859 he was a schoolmaster, then, after he married, a private tutor at Torquay. About 1863 he read Darwin's Origin of species and was convinced by it; by 1868 he had become a naturalist and systematist. In 1877 he moved to Tunbridge Wells where he spent the rest of his life studying Crustacea, active in scientific societies, and writing essays and reviews. Stebbing's Darwinism was not particularly original, though he marshalled some good examples from the invertebrates to indicate the importance of variation within and between species. He regarded natural selection as a directing force by which God's plan for organisms was being worked out, and credited it with the origin of language, morality and religion. In taxonomic practice, Stebbing advocated priority of names, simple rules of transliteration and gender, and publication of new names only in a few easily-accessible journals. After the publication of the Regies internationales de la nomenclature zoologique in 1905 his writings on taxonomic practice were confined to minor issues. A bibliography of Stebbing's 242 publications concerned with carcinology, Darwinism, nomenclature and miscellaneous subjects has been compiled.