Skeletal Characters Research Articles

Differences in skeletal characters between the disjunct eastern and western populations of ring-billed gulls (Larus delawarensis)

Univariate analyses of variance, multivariate analyses of variance (Manova), and discriminant function analyses were performed on measurements of 51 skeletal characters of adult males and females from the disjunct eastern and western populations of the ring-billed gull (Larus delawarensis) in Canada. The analyses established sufficient differences in skeletal characters to permit correct identification of the origin of 34 of 38 males (90%) and 40 of 42 females (95%). The populations are now expanding in range to the extent where new colonies are established in the Lake of the Woods, Ontario region, the historical hiatus between the two populations. Further expansion and contact may well erase the existing skeletal differences of individuals in these populations.

Evolutionary and Systematic Significance of Temporal Variation in the Fox Sparrow

Morphometric variation was studied among samples of fox sparrows taken in 1926- 1927 and 1978-1980 at seven sites in California. Samples of males were taken at two of the seven sites in both 1978 and 1979, and five samples of males were measured a second time to assess measurement error. Thus, 21 groups of males (14 samples, 2 samples one year apart, and 5 remeasured samples) and 14 groups of females were used in this study. Thirty-one measurements of skeletal characters were taken on 317 males and 142 females, plus on the 101 males that were remeasured. The main objective was to determine if phenotypic change had occurred over a half century, and to quantify the extent of such temporal change relative to levels and patterns of geographic variation. In the temporal samples, an average of 2.2 (7.1%) significant character differences per site was observed. Hence, most characters showed no signif- icant differences over 50 years. Character differences between remeasured, temporal, and geo- graphic samples were quantified by computing average percentage differences between char- acter means. Taxonomic distances were computed between all pairs of samples (sexes separate). Ten characters were excluded from analyses due to relatively high levels of measurement error. Percentage differences for the remaining 21 character means for remeasured samples averaged 0.33 ? SD of 0.31% and resulted in an average taxonomic distance between replicates of 0.25. Average percentage differences in character means over 50 years (0.98 ? 0.79%) were similar to geographic differences (1.14 ? 0.88%) among samples taken during the same time period. Av- erage taxonomic distance between samples taken 50 years apart (0.71 ? 0.21) was somewhat less than that between temporally comparable samples from different sites (0.84 ? 0.16). However, samples taken 50 years apart at a site can be as different as those from sites 100 to 200 km apart and assigned to different subspecies. Multivariate analysis of variance revealed that temporal samples at two (of seven) sites differed significantly, and generalized discriminant analysis obtained significant differences between temporal samples at two additional sites. Temporal phenotypic stability was evident in that the same two groupings of samples were obtained in analyses of both old and new samples. However, patterns of variation in the two time periods, within these two main groupings of samples, are not concordant because of phe- notypic change over time. That is, temporal change altered geographic patterns. Males and females showed different patterns of variation. No clear temporal trends in morphological change were identified, either in individual characters across sites, or in suites of characters within population samples. Characters with the largest relative differences over 50 years did not tend to show large geographic differences. The average taxonomic distance among old samples did not differ from that computed between recent samples; therefore, the populations at these sites are not diverging phenetically. Although the genetic basis of the phenotypic variation measured here is unknown, temporal variation could be adaptive either through phe- notypic response to environmental change or by maintaining a store of morphological vari- ability. (Sparrows; morphometrics; measurement error; temporal variation; geographic variation; microevolution.)

A MULTIVARIATE STATISTICAL ANALYSIS OF DIRECT AND CORRELATED RESPONSE TO SELECTION IN THE RAT.

An important part of many studies in evolutionary biology is the assessment of genetic (i.e., evolutionary) differentiation among a group of related taxa. Over the past 15 or so years, considerable literature has been accumulated on evolutionary divergence at the biochemical level which has been obtained by determining the relative divergence in gene frequencies using allozyme data from electrophoresis. However, a description of the frequencies of allozyme alleles often does not portray the divergence in those complex sets of integrated morphological and physiological traits which are most useful in constructing phylogenies, understanding morphogenesis or clarifying ecological adaptations. Most characters useful in ontogenetic, phylogenetic or taxonomic studies are controlled during development by large numbers of loci where each locus may have a small net effect on the trait in question and pleiotropic effects on many others. Further, it is the integration of these polygenic traits into complex organ systems or developmental processes which are of most interest to evolutionary biologists. The analysis of manifold gene effects in such genetic systems falls in the realm of biometrical or quantitative genetics; however, only in recent years have determined efforts been made to understand biometrical genetic aspects of morphogenesis in an evolutionary framework (Lande, 197 9, 1980; Atchley and Rutledge, 1980; Atchley etal., 1981). In this paper, we explore some quantitative genetic aspects of evolutionary differentiation in closely related taxa by examining the genetic basis of biometrical divergence in the skull and jaw in six selected lines of laboratory rats. This paper provides biometrical data on direct and correlated response to long-term directional selection for weight gain in a suite of highly integrated skeletal characters from the skull and jaw. The experiment mimics a commonly observed phenomenon in evolutionary biology where there has been a subdivision of a genetically homogeneous population followed by strong selection for a single developmental trait, i.e., body weight gain. In this paper we provide information about the following aspects of multivariate variation in the rat skull as a response to long-term selection: 1) relative phenotypic and genetic divergence between selection treatments; 2) phenotypic differentiation between replicates of the same selection treatments; 3) symmetry of response to selection; 4) heritability of the ' Paper number 3 in a series on genetic components of size and shape.

On the affinities of three small sea-star families

Summary The Metrodiridae, Mithrodidae and Valvasteridae are monogeneric sea-star families of obscure affinities traditionally assigned to the generically and morphologically diverse order Spinulosida. Re-valuation of available information, combined with the use of new skeletal characters, has led to reassignment of Metrodira to the spinulosan family Echinasteridae, Mithrodia to the valvatan family Ophidiasteridae, and Valvaster to the family Asteropseidae. The Asteropseidae is in turn assigned to the order Valvatida.

Sensitivity patterns for the induction of homeotic shifts in a favorable strain of mice.

In an effort to develop a prescreening system that is sensitive, is compatible with in-vivo administration of presumptive teratogens, and utilizes morphological endpoints, we are studying the induction of homeotic shifts in the axial skeleton. Our earlier work had demonstrated the existence of critical periods for certain such shifts, even though the (C57BL x NB)F1 hybrid used was not entirely suitable for this purpose. Using 100 R X-rays on successive days during the period of major organogenesis, we have now analyzed the sensitivity pattern of the BALB/c, since this strain normally straddles thresholds for the position of axial borders. Mortality, birthweight, and skeletal anomalies were analyzed, in addition to the homeotic shifts. --Day 9 1/4 postconception was clearly the most sensitive stage for the production of posterior shifts at the thoraco-lumbar border and the lumbo-sacral border, and for increases in the number of sternebrae and costo-sternal junctions. Anterior shift could be induced three days later, on day 12 1/4, but this was confined to only one of the four characters, the thoraco-lumbar border. There are a number of indications that, at given stages during the study period, BALB/c embryos correspond developmentally to chronologically somewhat earlier stages of two strains studied previously. The present results do not support the hypothesis that factors influencing the quantitative skeletal characters act by way of body size. --Since homeotic shifts can be produced by a number of mechanisms and are obvious indications that developmental interference has occurred, and since such shifts are easy to score and convenient to analyze quantitatively, our identification of a highly suitable strain and of stages of maximum sensitivity in this strain should aid in making the system useful in the prescreening for chemical teratogens.

The phylogeny of the Charadriiformes (Aves): a new estimate using the method of character compatibility analysis

Character state trees were devised for 70 mainly skeletal characters of 227 species of charadriiform birds. Character compatibility analysis (described herein) was used to determine the largest sets of mutually compatible characters in the data set. Largest sets of mutually compatible characters were chosen as the best estimators of the phylogenetic history of the order. Smaller and smaller monophyletic groups (as identified by previous analysis of the next larger monophyletic group) were analysed to find locally largest sets of mutually compatible characters until the cladistic information in the data set was exhausted.The results of these analyses indicate that the Charadriiformes consist of three phyletic lines (here treated as suborders): the Scolopaci, the Charadrii and the Alcae. The Scolopaci consist of the birds usually included in the families Jacanidae, Rostratulidae, Scolopacidae, Phalaropodidae and Thinocoridae. The Charadrii consist of two major phyletic branches: one leading to the Lari and the other to the line discussed below. The second branch of the Charadrii gives rise to five lineages: one which leads to Dromas, a second to Pluvianellus and Chionis, a third to Pluvianus and the Burhinidae, a fourth to the Glareolidae, and a fifth to the plovers, lapwings, oystercatchers, Ibisbill, avocets, and stilts.Evidence which supports these findings, that which contradicts them, and relationships in need of further study are discussed.

A Comparison of Ecological and Morphological Overlap in a Peromyscus Community

The hypothesis that morphological structure of a community should reflect ecological structure (trophic relationships) was tested in this paper. An assemblage of closely related sympatric species of Peromyscus was studied to see how closely morphological structuring can describe actual food—use relationships in a community. Animals were collected during 4 different seasons and stomach contents were analyzed to reveal the diet of each species. A morphological analysis of the assemblage of Peromyscus was accomplished through the analysis of 4 external and 69 skeletal characters. Morphological and trophic relationships were computed using principal components and distance analysis. A positive relationship between morphological and ecological packing is shown by a correlation coefficient computed between food—use distances and morphological distances. Microhabitat use and foraging behavior are discussed in an attempt to expose actual mechanisms of competitive interactions.

Attached vermiform gastropods in Carboniferous marginal marine stromatolites and biostromes

Tubiform fossils conventionally referred to Serpula cf. advena Salter and species of Spirorbis Lamarck from the British Lower Limestone Shales and Border Group (Lower Carboniferous) are re-examined. They occur in peritidal carbonate environments of schizohaline aspect. These fossils superficially resemble calcareous polychaete tubes but have skeletal characters, including molluscan wall structure, numerous internal septa, and protoconch, which indicate that they represent a new group of substrate-attached, disjunctly coiled gastropods. They resemble archaeogastropods in internal morphology of the skeleton but show parallels in external form and occurrence with the extant Vermetidae. There are two principal modes of occurrence: (1) erect tubes forming intertidal biostromes associated with non-skeletal algal laminites, and (2) prostrate discoidal tubes encrusting subtidal skeletal stromatolites or occasionally forming larger irregular bioherms. These biostromes and bioherms are comparable in structure to Recent vermetid reef developments.

Phenetic affinities of the wood thrush, Hylocichla mustelina (Aves: Turdinae)

A multivariate assessment of phenetic affinities among 11 North American and 2 European thrushes was carried out to characterize further the controversial systematic relationships of the wood thrush, Hylocichla mustelina. Principal components analysis based on 49 skeletal characters revealed that the wood thrush, which formed one of four distinct groups, was intermediate in a linear allometric series ranging from North American Catharus to European Turdus. These results, most similar to the pattern of relationships envisaged by Dorst, are discussed in terms of the findings and methodologies of previous studies. It is noted that the usual practice of interpreting principal components in terms of independent variation in size and shape is often an oversimplification.

Osteology of Bluegill Sunfish, Lepomis macrochirus Rafinesque

The present study was undertaken in order to provide information upon the normal skeletal structure of bluegill sunfish, Lepomis macrochirus RAFINESQUE, to the researchers using it as an experimental animal and to the taxonomists trying to work out the relationship between the members of the Centrarchidae family. This study is based upon the examination of 100 bluegill specimens made by cleaning, staining, and roentgnography. The observations can be summarized as follows: i) Statistical analyses of various skeletal proportions revealed small fluctuations except for the cranium height and width which were observed to be size-dependent. ii) Correlation between external and skeletal characters have been made to predict the position of several skeletal components on the body of fish without subjecting it to the troubles of scissors and forceps. iii) Basic scheme of the arrangement of bones except for their shapes and sizes, has been found out to be more or less the same as that of Sacramento perch studied by DINEEN and STOKELY (1956). However, reduction in the number of certain skeletal components has been observed in bluegill. iv) A second uroneural has been discovered in bluegill which hither-to had not been reported from any other centrarchid including bluegill. v) Comparison of meristic measurements as stated by various authors presented some difference in the number of dorsal soft ray, trunk vertebrae, scales, and gill rakers.

DINOSAUR PHYSIOLOGY AND THE ORIGIN OF MAMMALS.

Today and throughout the Cenozoic mammals have been the dominant class of land vertebrates. Mammals are the most conspicuous elements in most terrestrial vertebrate communities, and the vast majority of large land vertebrates (50 kg and larger) are mammals. The success of mammals probably is due in large measure to their high metabolic rates, great scope for increasing metabolism during activity, and their ability to maintain constant body temperatures by complex mechanisms of heat production, insulation, and heat loss. Mammals evolved from their therapsid reptilian ancestors in the Late Triassic, only a few million years after the first dinosaurs appeared (Crompton, 1968). Although they are common and diverse in most Jurassic and Cretaceous terrestrial microvertebrate faunas, mammals showed little or no promise of developing into the grand variety of large animals seen in modern mammalian communities. From their beginnings in the Late Triassic until the very end of the Cretaceous, a total of over 120 million years, twice the length of the entire Cenozoic, mammals were consistently tiny or at most small vertebrates, with the largest herbivores reaching the size of a large squirrel and the largest carnivores, the size of a cat. The greatest Cretaceous mammals were dwarfed by the largest contemporary lizards-the superficially iguana-like herbivore Polyglyphanodon (Gilmore, 1942) reached a length of a full meter, while some of the Cretaceous flesh-eating monitors such as Sanziwa and Parasaniwa (Gilmore, 1928) were even larger. Dinosaurs dominated the JuraCretaceous, but not in all size categories. Although the two orders of dinosaurs (Saurischia and Ornithischia) included virtually all the large fully terrestrial vertebrates, and many dinosaur genera were elephant-size or larger, the fossil evidence strongly suggests that no small (adult weight 10 kg or less) dinosaurs ever existed in either Jurassic or Cretaceous. The smallest, fairly complete dinosaur skeletons usually indicate a length of a meter from nose to tail tip (Compsognathus, Hypsilophodon, Microvenator, Tenontosaurus). But most of these small specimens probably are juveniles. In some cases, other conspecific specimens show that the adult size was much larger-up to 2.5 meters for Hypsilophodon (Galton, in press), and up to seven meters for Tenontosaurus (Ostrom, 1970a). Skeletal characters, such as the open sutures between centra and arches in the Microvenator vertebrae (Ostrom, 1970a) indicate immaturity in other cases. The most convincing proof of the lack of truly small dinosaur species is their absence in the carefully studied microvertebrate concentrates. In the Late Cretaceous localities at Bug Creek, Montana, and Lance Creek, Wyoming, several dozen species of small vertebrates are found including a wealth of lizards (monitors, skinks, teiids, and alligator lizards) and mammals, and yet nearly all the dinosaur specimens are small fragments of large genera (horned dinosaurs, duck-bills, deinonychids-Estes, 1964; Estes and Berberian, 1970). The author has examined the Yale samples from these localities and has found many

Statistical Analysis of Character Correlations in Brewer's Blackbirds

Power, D. M. (Dept. of Ornithology, Royal Ontario Museum and Dept. of Zoology, University of Toronto, Toronto, Ontario, Canada) 1971. Statistical analysis of character correlations in Brewer's Blackbirds. Syst. Zool., 20:186-203.-Character correlations among 37 skin and skeletal characters within a statistically homogeneous sample of Brewer's blackbirds (Euphagus cyanocephalus) were analyzed by component analysis and average linkage cluster analysis in order to isolate structural and/or functional character sets. Associations were assessed using product-moment correlation coefficients, partial correlations that corrected for a general size factor, and a subset of special partial correlations that corrected for a group factor defining high intercorrelations among limb bone length measurements. With ordinary correlations separate associations were identified for limb bone length, flight feather length, bill length, sternum size, bill width, and limb bone thickness. Some characters were predominantly independent. Partial correlations that corrected for covariation due to the group limb bone length factor indicated special associations among wing bones. An overall size factor is defined as that component which accounts for most of the covariation among all characters. Partial correlations correcting for this factor were analyzed and several size-independent associations emerged. The limb bone length assemblage is in part size-dependent. Size-independent associations include wing bone length, flight feather length, bill length, bill width, and limb bone thickness assemblages, and possibly a partial leg bone length set. Association of three sternal characters appears size-dependent, however a special size-independent association between sternum length and keel height was found. In addition, low-level, size-independent associations are found for pelvis width and bill height characters, as well as between the scapula and coracoid in the pectoral girdle. Results suggest the existence of selective factors that affect the development of functional complex as a whole. Comments are given concerning redundant characters in systematic studies and a temporary solution is offered concerning the problem of adequate sample size in studies of character correlations. [Character correlations; Brewer's blackbirds.] Character correlations within populations are the result of individual ontogenetic processes and natural selection. Perhaps the greatest contributions to the quantitative assessment of character relationships, particularly in terms of size and shape, have been in the study of allometry. Gould (1966), in his review of concepts and methods in t-his field, and in his own work, has shown the contributions that can be made here in understanding ontogeny and phylogeny. In the last several years relatively few papers have dealt in depth with covariation in non-growing systems, but the single underlying generality that can be made seems to be that characters related in structure or function tend to be more highly correlated than are others (e.g., Berg, 1960; Olson and Miller, 1958). As Van Valen (1965) has pointed out, it seems necessary to postulate selection for developmental patterns that affect functional complexes as a whole. For populations of adult, non-domesticated birds, very few attempts have been made to investigate correlations or to isolate structural or functional subsets for more *than just a few morphological characters. Nor have there been attempts to investigate covariation independent of sizeoTr general factors at the population level. The present study is an analysis of correlations among a number of morphological characters from four subsamples (two sexes and two localities, treated separately and in combination) of adult Brewer's blackbirds (Euphagus cyanocephalus; Icteridae), a common species widespread in western and central

Range expansion of Brewer's blackbird: phenetics of a new population.

The Brewer's blackbird (Euphagus cyanocephalus) is rapidly expanding its range eastward across Ontario and parts of the United States. This study was to determine if phenetic changes have taken place during or immediately after expansion. A sample was collected in 1968 in the vicinity of McKerrow, Ontario, near the periphery of the zone of expansion and where breeding was first recorded in 1962. For comparison, a second collection was made in the stable part of the range near Winnipeg, Manitoba. Statistical comparisons for 37 skin and skeletal characters were made between the two samples for both sexes. Tests for differences in character means suggest that strong directional selection, different from that in the stable part of the range, is not operating in the newly occupied area. Likewise, differences in population variability seem slight and do not show alterations in genetic variability that would be expected during a Carsonian population flush or that would be expected because of a partial founder effect.

Contributions of Chromosomal Analysis to the Systematics of North American Chipmunks

Chromosomes from the bone marrow of 32 chipmunks belonging to the genera Eutamias and Tamias were analyzed using a colcemide, hypotonic citrate, acetic orcein squash technique. The modal diploid chromosome number was 38 in Eutamias minimus caryi, E. m. consobrinus, E. m. neglectus, E. q. quadrivittatus, E. speciosus frater, E. a. amoenus, E. t. townsendii, E. t. cooperi, E. t. senex, E. d. dorsalis and Tamias striatus griseus. Three distinctive chromosomal patterns were observed among these species. The first pattern, found only among specimens of Eutamias minimus was designated Eutamias Karyotype A. Chromosomal patterns of E. quadrivittatus, E. speciosus, E. amoenus, E. townsendii and E. dorsalis were similar and were collectively designated Eutamias Karyotype B. A third chromosomal pattern, found in Tamias striatus, was named the Tamias Karyotype. The sex chromosomes of all species were of the X-Y type. Correlation of chromosomal characters with present concepts of chipmunk systematics suggests that chromosomal data is most meaningful at the generic and infrageneric levels. A close chromosomal relationship was found between Eutamias and Tamias. The observation of two distinct karyotypes within Eutamias suggests there may be two species groups in this genus and zoogeographic data support this new concept. Evolution of chipmunks is discussed and it is postulated that the Nearctic Region was populated by two or possibly three separate eastward invasions of chipmunks from the Palearctic Region. The systematics of the presently recognized chipmunk genera, Eutamias and Tamias, have undergone a number of revisions, each based on a variety of characters. The first extensive revision of the chipmunk genera was presented by Howell (1929) and was based on examination of cranial and external characters from a large series of specimens representing 16 species of Eutamias and one species of Tamias. Howell reviewed the earlier works of Allen (1877, 1890) and others, and relegated all chipmunks to two genera: Tamias for the eastern North American chipmunks; and Eutamias subgenus Eutamias for Asiatic chipmunks, and subgenus Neotamias for the chipmunks of western North America. Ellerman (1940), proposed a different classification of chipmunks in which Eutamias, Neotamias and Tamias were all given subgeneric rank within the single genus Tamias. Cranial morphology, dentition, and external features formed the basis for this decision. In an extensive phylogenetic study of Sciuridae, Bryant (1945) re-evaluated the problem using not only cranial and external characters but other skeletal and dental characters, myology and paleontology as well. He agreed with the classification proposed by Ellerman (1940) and concluded that the differences between eastern and western chipmunks were not of sufficient phylogenetic importance to warrant retention of the two groups as separate genera. More recently, White

EPIGENETIC POLYMORPHISM OF THE RODENT SKELETON

One type of discontinuous variation, genetic polymorphism, has been studied frequently, in animal populations. This paper deals with another type, here called epigenetic polymorphism, which is developmental in origin and due to the action of a threshold on underlying continuous variation. Both genetic and environmental factors are important in causation. This type of polymorphism is known to be common in wild mouse populations with respect to many skeletal characters. The present survey is concerned with the situation in the rodents as a whole, samples of the following species being classified for forty‐nine variants: Sciurus carolinensis, Cavia porcellus, Peromyscus maniculatus, Lemmus lemmus, Microtus agrestis, Micromys minutus, Mus musculus, Rattus norvegicus, Rattus rattus and Rattus exulans. All show extensive polymorphism, some variants being ubiquitous while others are confined to one or a few species. A rare variant in one species is sometimes present in all representatives of another species. There is some association between the frequency of a few variants and overall size, but none was found with respect to domestication. The genetic and evolutionary aspects of this kind of polymorphism are discussed, as well as its possible use in systematic studies. Various types of epigenetic polymorphism (transient etc.) seem to occur, some probably being important in micro‐evolution. Changes in the frequencies of variants may often be due entirely to chance, but selective forces may also operate and are probably best envisaged on the lines of Waddington's (1953 a, 1961) concept of genetic assimilation. However, their relative importance cannot be assessed in the present investigation.

The Pneumatic Fossa of the Humerus in the Passeres

ONE of the greatest hinderances to the successful unravelling of the interrelationships between passerine families is the shortage of morphological features varying sufficiently between these groups to be useful as taxonomic indicators. The search for potential taxonomic characters has concentrated largely on the skeleton, which is, in spite of other shortcomings, the easiest and most convenient anatomical material to collect and study. Except for some features used to divide the perching birds into suborders, almost all of the past anatomical-systematic work was based on skeletal characters, and indeed this work has rested almost entirely on cranial features. But, although the skull can and does provide many good clues to relationships between passerine birds, a shadow of doubt always hangs over the conclusions because of the convergence hazard resulting from similar feeding habits in unrelated groups. No matter how many different cranial features are employed, all may be functionally associated and thereby are under the influence of the same selection force; hence they should be considered as members of a single character complex (= functional complex or functional unit). Evaluation and comparison of the individual components of a character complex in taxonomic work is exceedingly difficult, and even when the greatest care has been used, the results may still be subject to question. In systematic work it is safest to consider a character complex (e.g., the skull and associated structures) as a single unit or taxonomic character. It would, therefore, be most desirable to be able to check taxonomic conclusions based on cranial features by the use of postcranial skeletal characters; these latter structures are, in most instances, not directly influenced by feeding habits and hence do not belong to the same character complex as do the cranial features. Unfortunately, the postcranial skeleton is highly uniform throughout the Passeres except for differences in proportions and other minor features, such as variations in the number of the ribs and vertebrae. These proportional and numerical differences have little, if any, value in showing affinities between groups of perching birds. Any feature of the postcranial skeleton varying between passerine families is consequently of great importance to the student of avian classification as a potentially valuable taxonomic character. The pneumatic fossa of the humerus is one of the few postcranial features exhibiting marked variation within the passerine birds. Although this variation was already known in the last century (Shufeldt, 1888), it has received little attention from avian anatomists. For example, it is not mentioned in the standard texts of Fiirbringer, Gadow, and Beddard, nor

Post-Cranial Skeletal Characters of Bison and Bos. Stanley J. Olsen. Papers of the Peabody Museum, Harvard University, Vol. 35, No. 4, Cambridge, 1960. vii + 61 pp., 24 figs. $1.75.

Post-Cranial Skeletal Characters of Bison and Bos. Stanley J. Olsen. Papers of the Peabody Museum, Harvard University, Vol. 35, No. 4, Cambridge, 1960. vii + 61 pp., 24 figs. $1.75. - Volume 26 Issue 4

Comparative Osteology of Serranid Fishes of the Genus Roccus (Mitchill)

HE serranid genus Roccus occurs between the parallels 50'N and 25?N and is represented by six species; saxatilis, chrysops, americanus and interruptus in North America, labrax and punctatus in Europe. The six species formerly were assigned to as many as five genera by authors. Jordan and Gilbert (1883:528-531), first to revise the genus, relegated the four American species to the genus Roccus (with Morone as a subgenus) and tentatively included the two European species. External characteristics were used as criteria. Later Berg (1949: 1012-1013) assigned them to a single genus, Morone, with three subgenera, and gave as diagnostic generic characters: (1) separate dorsal fins, (2) teeth present on the base of the tongue, and (3) absence of a supramaxillary bone. His classification of subgenera was also based primarily on external characters. The present osteological study was undertaken to check the validity of a monogeneric classification. Five species, saxatilis, chrysops, americanus, interruptus and labrax, were compared. The findings indicate that biologically the species are of a single genus. Subgenera may be defined using combinations of skeletal characters. Starks (1901: fig. 45, pls. 63-65) used the skeleton of saxatilis in illustrating the synonymy of the fish skeleton and with the exception of the trunk skeleton the same illustrations appeared in Jordan (1905: figs. 22-26 and 28). Excellent figures of the head skeleton are given by Gregory (1918: figs. 1, 2, 6, 7). He (1933: figs. 1 and 119) also discusses and illustrates the head skeleton in his monograph on fish skulls. Merriman's (1940: 55-64) fine paper describes the trunk skeleton of saxatilis and includes detailed drawings of the parts. Giinther (1859: 66) described the skeleton of americanus, and a dorsal view of the skull of labrax appeared in Boulenger (1895: 125). Terminology for the skull components follows Gregory (1933); that of the trunk skeleton is after Merriman (1940). In the present study the skeletons of five species of Roccus are compared. Lack of readily available study material of punctatus precluded its use here. Mitchill (1815: 415) refers to an aberrant form of saxatilis which has broken or inter-

IV.—The Morphology and Relationships of a Complete Therocephalian Skeleton from the Cistecephalus Zone of South Africa

SynopsisA description is given of a new genus of mammal-like reptile,Mirotenthes, of which a remarkably complete and well-preserved skeleton was collected in 1936 by Professor Camp of the University of California, from the late Permian deposits of the South African Karroo.Unlike the majority of Permian mammal-like reptiles,Mirotentheswas an agile form of small dimensions. Many of the skeletal characters exhibit a significant approach towards the mammalian threshold. The limb structure is very advanced and the digital formula is mammalian. The differentiation of ribs to form a definite rib-cage of mammalian type is particularly noteworthy and may indicate the presence in this genus of a mammalian respiratory mechanism.The systematic study of this complete skeleton does much to bridge the gap between the primitive basal groups of mammal-like reptiles and the advanced Triassic groups from which the mammals derive. It has been known for many years that small, fast-moving carnivorous forms were present in the late Permian fauna, but the evidence has been fragmentary. The complete skeleton described in this paper throws new light on these hitherto poorly known genera.

Genetical studies on the skeleton on the mouse

1. An account is given of the causes of variation in twenty skeletal characters found in the pure lines A and C 57 BL, percentages of the total variance due to each causative factor being summarized in Tables 62 and 63. 2. Genetic differences within a subline, possibly due to a dominant gene reducing the frequency of foramina transversaria imperfecta, were found only once. 3. In C 57 BL there is about as much genetic differentiation between closely related sublines as between those separated by over forty generations. 4. Residual intangible non-genetic factors, acting independently on individuals or sides, account for over 80% of the variance in three-quarters of the characters studied. 5. In 60% of lateral variants, one side (usually the right) is significantly more frequently affected. 6. Where maternal age and/or parity have significant effects, a tendency is invariably found for early litters from young mothers to have the highest percentage of abnormals. 7. Anomalies involving structural shifts are generally susceptible to maternal age effects; otherwise, there is no marked tendency for similar variants to be influenced by the same tangible factors. 8. In both strains there is a high correlation between pregnancy prolongation and the number of young being suckled. 9. Nearly all the variants are visible in foetal cartilage preparations.