Ancestral Structure Research Articles

Ancestral Nesson Anticline and Associated Geothermal Anomalies: Enhanced Hydrocarbon Generation Controlled by Crustal Structure: ABSTRACT

Hydrocarbon generation in the Williston basin is influenced by crustal motions and geothermal gradient anomalies associated with the ancestral Nesson anticline, a long-lived crustal structure located along 103{degree} longitude. This structure and its effects are particularly important in Canada where most petroleum source rocks were not sufficiently buried to have generated hydrocarbons in a normal geothermal gradient environment. High geothermal gradients associated with this structure raise the oil window and expand the region of source rock thermal maturity. Ancestral Nesson structure subsided differentially throughout the Phanerozoic, controlling paleobathymetry and facies over its crest. During the Upper Ordovician the structure was positive; rich potential petroleum source rocks were deposited on the western flank of the structure, generally excluding them from the zone of elevated heat flows. The total petroleum potential of this oil-source system exceeds 5.5 billion bbl of oil equivalent in Canada alone. Unfortunately, its exclusion from the maturation anomaly results in no more than 200 million bbl of oil being expelled from these sources. During the Middle Devonian, the structure was a negative feature that formed a starved subbasin separating the Winnipegosis and Elm Point carbonate shelves. Rich potential petroleum source rocks that accumulated on the crest of themore » structure at that time now overlie the region of elevated heat that flows and enhanced hydrocarbon maturation. Two billion barrels of oil are estimated to have been expelled from this source rock. Understanding the history and tectonics of the ancestral Nesson anticline is fundamental to a correct appraisal of hydrocarbon resources in the Williston basin.« less

Sequence of the 16S Ribosomal RNA Gene from Methanococcus vannielii: Evolutionary Implications

Summary The complete sequence of a 16S rRNA gene from the methanogenic archaebacterium Methanococcus vannielii was determined. The derived primary structure of 16S rRNA shows a much higher homology to the previously published 16S sequence of a halophilic archaebacterium, Halobacterium volcanii ( Gupta et al., 1983) than to the 16S sequences of eubacterial or eukaryotic organisms; the secondary structure models for the two archaebacterial 16S rRNA's are nearly identical. Although a few specific structural details are “eukaryotic” in nature, the Methanococcus (like the Halobacterium ) sequence shares more primary and secondary structural features with eubacterial than with eukaryotic 16S like rRNA. In comparison with Halobacterium , the Methanococcus 16S rRNA exhibits a higher homology both to eubacterial and eukaryotic 16S like rRNA. This indicates a lower genetic drift of the 16S rRNA from the methanogen as compared to that from the halophile and points to a closer resemblance with an ancestral 16S rRNA structure.

TRNA-rRNA sequence homologies: Evidence for an ancient modular format shared by tRNAs and rRNAs

Homologies between tRNAs and rRNAs are identified in searches using various combinations of Escherichia coli, yeast, Halobacterium volcanii and bovine mitochondrial sequences. As in previously reported comparisons, the homologies are too frequent and long to be attributed to coincidence, and similar frequencies from inter- and intraspecies comparisons preclude evolutionary convergence as an explanation. In contrast to the earlier studies, patterns in the positioning of the homologies are now described. Graphing the positions of the homologies along orthogonal axes that represent numbers of bases in tRNA and rRNA shows recurring patterns in the alignments. Preferred spacings of integral multiples of 9 bases are found, suggesting a periodicity in the ancestral structure from which the tRNAs and rRNAs were derived. The periodicity also suggests persistence of a modular format in both classes of molecules that survived changes in sequence that occured during evolution. A model is proposed for the generation of the ancestral molecule and the early evolution of the coding mechanism. Elongation by self-priming and self-templating gave a hairpin with a 9 base stem. Two additional cycles gave a 70–80 base tRNA-like structure. Additional cycles yielded a tandem repeat of this unit, roughly equivalent in size to the combined rRNAs of prokaryotes. The larger RNA would contain the information and materials for generating the smaller RNAs. It is proposed that multiple recombination among such molecules gave composite structures, presumed progenitors of today's t- and rRNAs. The distribution of the conserved domains among today's species argues for the existence of the ancestral molecule prior to divergence of lines leading to the various kingdoms. Their presence in the different nucleic acids suggests the existence of a nucleic acid with multiple functions prior to partitioning of these functions among the nucleic acids that exist today. The occurrence of overlaps, overlays and consensus alignments among the homologies provides the means for identifying contiguous and neighboring conserved regions and holds promise for the reconstruction of the sequence of an ancestral molecule.

Comparison of the communicative vocalizations and behaviors of group ranging in eastern gorillas, chimpanzees and pygmy chimpanzees

Field observations were carried out on chimpanzees, pygmy chimpanzees and eastern gorillas. Since the communicative behaviors which appear in group ranging are closely related to the grouping of the animals and to the social structure, the communicative behaviors of group ranging were compared in the above three species in order to elucidate the common and different characters of their three much diversified social structures. The following conclusions were drawn: (1) the common ancestor ofGorilla andPan had the territorial call “hoot” and behavior of display, and males were antagonistic between each other in the society; (2) the common ancestral species did not have any special long distance cohesive calling: the society was a small compact one, moving on the ground; and (3) the social structure of the pygmy chimpanzee is very different from the common ancestral social structure when compared with those of the gorilla and chimpanzee, in that the pygmy chimpanzee has lost the behaviors of strong antagonistic character between adult males.

Archaebacteria and eukaryotes possess DNA-dependent RNA polymerases of a common type.

DNA-dependent RNA polymerases of archaebacteria not only resemble the nuclear RNA polymerases of eukaryotes rather than the eubacterial enzymes in their complex component patterns but also show striking immunochemical, i.e., structural, homology with the eukaryotic polymerases at the level of single components. Thus, eukaryotic and archaebacterial RNA polymerases are indeed of the same type, distinct from the eubacterial enzymes, which, however, are also derived from a common ancestral structure.

The Evolution of Allomothering Behavior Among Colobine Monkeys: Function and Opportunism in Evolution

The great majority of Old World monkey females are interested in infants, particularly very young ones. Characteristically, females will approach infants cradled by their mothers and subsequently attempt to touch or hold them. For Cercopithecine monkeys, the subfamily that includes the baboons and macaques, caretaking attempts by females other than the mother are ordinarily unsuccessful, at least during the first two or three weeks of life. Mothers are highly possessive of their offspring and will not surrender them to substitute infant‐caretakers. In striking contrast, among the other major subfamily of Old World monkeys, the Colobines, mothers readily allow extensive and sometimes prolonged infant carrying and handling by other females (allomothering), even on the first day of life. This paper reviews the traditional functional explanations for these different maternal systems. Stressing opportunism in evolution, the paper suggests that the social and/or genetic benefits alone are not adequate to account for the origins of allomothering behavior among Colobines. Instead, emphasis is given to the kind of ancestral social structure and its environmental context that might allow such a behavioral system to begin. It is hypothesized that, relative to the Cercopithecines, who do not exhibit infant‐sharing, the dental morphology and digestive system of the Colobines produced food‐acquiring and food‐processing advantages that, in effect, reduced intragroup feeding competition and, concomitantly, reduced the importance of status differences between females. Such a social structure could permit the emergence of allomothering behavior since, for all the participants in this activity pattern, there are varying benefits that contribute to individual fitness. [Colobine, allomothering, functions, opportunism, dietary adaptations, social structure]

Ancestral inference. III. The ancestral structure of the population of Tristan da Cunha.

A log-linear analysis has been applied to the survival probabilities of the genes of the founders of Tristan da Cunha. This analysis enables a large set of probabilities to be viewed as a single function, and the features of this function to be analysed. Features of the structure of the ancestral genealogy are thereby illuminated, and the dependence and interactions between founders with regard to the descent of their genes to the current population may be quantified.

Studies on soybean trypsin inhibitors. XIII. Preparation and characterization of active fragments from Bowman-Birk proteinase inhibitor.

Soybean Bowman-Birk inhibitor, a double-headed inhibitor of trypsin and alpha-chymotrypsin, was treated with cyanogen bromide and then pepsin to yield two inhibitory active fragments. Structural investigation showed that one of the fragments was derived from the trypsin inhibitory domain and the other from the chymotrypsin inhibitory domain of the inhibitor. In contrast to the unusual stability of the native inhibitor, the separated domains were less stable and could be inactivated with excess proteinases. These results suggest that the legume double-headed inhibitors acquired their unusual stability by duplicating an ancestral single-headed structure.

SEISMIC STRATIGRAPHIC EXPLORATION—PART I

The basic problem to be solved in stratigraphic exploration always has been the same—how to develop and use practical techniques which have the capability of finding large stratigraphic oil reserves at a profit. If the petroleum industry in the United States is going to discover in domestic areas the huge reserves which are obviously required for the future, seismic stratigraphic exploration will have to be accepted by the industry and play a major role in the discovery. Seismic stratigraphic exploration must, therefore, be described in such a way that management can visualize it as practical and potentially profitable with proven past accomplishments, with important new capability not yet in application, and with significant future potential. Past seismic stratigraphic exploration capabilities, which found large amounts of oil with crude tools from 1938 to 1962, are illustrated with three case histories covering the probable direct detection of a hydrocarbon‐saturated sand, the discovery of saturated lenticular sands over the area of a tilted out ancestral structure, and the delineation of a flank type stratigraphic trap. Three additional case histories will be presented in Part II in the next issue of Geophysics.

Origin of the human hand.

AbstractA means of determining the phylogenetic implications of similarities between the hands of man and non‐human primates is proposed. The only traits shared by man and non‐human primates accepted as evidence of our ancestral hand structure and functions are those which are incompatible or out of keeping with current behavior of the human hand. They may be assumed to remain only as relics of adaptations to former habits of locomotion and feeding. The relics found through this analysis are all traits that are present in the apes (some of them only in African apes) and probably related to functions of the hand in suspension of the body, fist‐walking, and knuckle‐walking. The presence of these traits in man implies that human ancestors similarly used the hand to suspend the body in the trees and to support it on the back of the flexed fingers.

Comparative anatomical and neurohistological observations on the tongue of slow loris (Nycticebus coucang).

AbstractOn the dorsum of the slow loris tongue there are three vallate papillae, arranged in an inverted V‐shape. They contain abundant plexiform nerves and isolated nerve cells but have many taste buds only in its sides, closely associated with the subgemmal nerve plexus. Some ducts of serous glands locating deeply in this region directly open on the upper surface passing through the papilla. No foliate papillae are observed in the posterolateral region of the tongue, but instead of them is found a papilla of fungiform type, which wholly contains abundant plexiform nerves and has a furrow without serous gland ducts and taste buds. Furthermore, its summit is at the same level as the surface and same as its base in diameter, and has embryonic taste buds. From these neurohistologic characteristics this papilla should be regarded as an interformed papilla between the foliate and the ordinary fungiform papillae. Tongue lyssa consisting of hyalin cartilage and striated muscles innervated with motor end plate and simple sensory nerves seems to play a role as receptive organ of the tongue. Underneath the tongue is found well‐developed sublingua, which consists of hyalin cartilaginous skeleton and mucosa but has no taste buds. From segmental arrangement of neurovascular spaces in the skeleton it may be an ancestral structure of the tongue.

The milk‐molars of Perissodactyla, with remarks on molar occlusion.

SUMMARY. A survey is made of the milk‐molars of Perissodactyla and Condylarthra with a view to determining the evolutionary trends. Molarization of the milk‐molars takes place in a variety of ways, which may be grouped into three main types: (a) the condylarthran type, found also in Plagiolophus, (b) the type found in the Equidae and Brontotheriidae, and (c) that found in the Tapiroidea and Rhinocerotoidea. Each of these types has a characteristic order of development of the cusps. The condylarthran type is considered to be the most primitive. From a study of the wear of the teeth, it is concluded that the occlusal movement in all Perissodactyla is transverse (ectal). The characteristic features of occlusion in the various families are discussed. During molarization the talonid becomes intercalated between two trigonids, the intercalation taking place at a relatively late stage in type (a), earliest in type (b) and at an intermediate stage in type (c). The buccal parts of the trigonid and talonid become functional before the lingual parts. The Palaeotheriidae (excluding Pachynolophus and Propachynolophus) are regarded as a distinct family that retains condylarth features of the milk dentition to a late date, and cannot be derived from Hyracotherium. With the exception of Plagiolophus, they show in their milk‐molars transitional stages leading to the conditions found in other perissodactyls. The hypothesis is put forward that the order of development of the cusps depends upon their different sensitivities to the graded morphogenetic conditions in the developing jaw. Correlated evolution of the upper and lower teeth suggests that occlusion has a morphogenetic basis which affects both jaws. The concepts of homology due to descent from a common ancestral structure, homology due to parallel evolution, and serial homology are considered to be closely related and not sharply separable in practice.

Early Paleozoic starfish

The fossil starfish described here are mainly from the Lower Ordovician (including the Tremadocian). Only brief descriptions of these starfish have been given previously. They are the earliest starfish known, and arrived in a series of transgressions which began in the Tremadocian and persisted throughout the immediately succeeding beds. Each of the transgressions brought in new faunas. Cephalopods arrived in the Tremadocian and locally graptolites in the basal Arenig. The grouping of the starfish adopted here is based upon the activities of the arms, especially during feeding. Three groups of starfish are recognized. Two of these groups are recognizable as Asteroidea and Ophiuroidea. In both these groups the arms are functional, but the arm activities have different mechanisms. The asteroid arm from the beginning is adapted for a carnivorous diet of large food, whilst the arm of the primitive ophiuroid is adapted for feeding on the small food present in or near the sea bottom. It is suggested that the primitive Ophiuroidea, like the recentAmphiura, had a ‘burrowing habit’. The third group had no functional arms. The forms belonging to this group appear slightly earlier (Tremadocian) than do either the Asteroidea (Lower Arenig) or the Ophiuroidea (basal Arenig). The tube feet are placed in position by changes in body shape. They seem to have lived on small food either from the planktonic shower (Villebrunastern.g.) or from that in the upper layers of the bottom (Archegonaster). Their skeleton shows many primitive characters. The name Somasteroidea n.subclass is suggested for this third group. Its members show the first stages in the differentiation of a starfish. It is noticeable that these first stages show no sign of an ambulacral groove, a character which previously has been regarded as primitive and used to link starfish with certain non-crinoid Pelmatozoa (Edrioasteroidea Bather; Thecoidea Jaekel). The view held (Spencer 1905) that the asteroid groove was present in early Echinoidea must also be abandoned. Early representatives of all these groups have characters which link them with a common ancestral structure. Each tube foot is housed on two ambulacralia in all Asteroidea (living and fossil), in the Somasteroidea and in the extinct primitive Ophiuroidea. Some groups of Ophiuroidea retain this character throughout the early Palaeozoic, whilst other groups acquired ‘vertebrae’. Each vertebra, a modified ambulacral, acquires its own tube foot. All early representatives have a mouth frame with radial V’s. It is suggested that the presence of the V’s is associated with a primitive oral opening, the stomodaeum, which had radial slits, the buccal slits.* The Somasteroidea have an aboral skeleton composed of ossicles which are little more than spicules radiating from a number of centres. The arrangement can be compared to that in the early stages of the skeletal components of recent forms. No other fossil echinoderm is known with ossicle components in a condition as primitive as this. It would seem that starfish arose at a very early stage in the development of echinoderm stocks.

ECHINODERM EMBRYOLOGY AND THE ORIGIN OF CHORDATES

Summary1. Development in echinoderms may be indirect, involving pelagic, bilaterally symmetrical, larval forms, or more or less direct, with the larval stage either reduced or omitted. Of the five living classes, only the Echinoidea are characterized by being predominantly of the type with indirect development.2. It is possible to regard the dipleurula stage of the classes Asteroidea, Ophiuroidea, Echinoidea and Holothuroidea as recapitulating a common ancestral Dipleurula. It is no longer possible to regard any of the other types of echinoderm larvae as anything but specialized forms without broad phylogenetic significance.3. Embryos and larvae of echinoderms are extremely plastic, often exhibiting convergence, divergence and adaptation, susceptible to evolutionary modifications of structure which may act quite independently of the adult stage. Ancestral structure cannot be deduced from such forms.4. In the Echinoidea larval evolution seems to have occurred subsequently to the separation of the main orders and families. Within relatively small groups larval evolution has followed similar trends, so that characteristic larvae occur in various sub‐groups, where the young stages may follow similar ontogenies; but such independent evolution tends to obscure the phylogenetic relationships between the class as a whole and the other classes.5. In the Asteroidea larval evolution has occurred along channels not so markedly correlated with the taxonomy of the adults. Phylogenetic speculations based on such larval stages prove incompatible with other evidence.6. In the Holothuroidea and Ophiuroidea larval evolution cannot at present be related with adult taxonomy, save in one or two cases too unimportant to have general significance.7. The egg of echinoderms is liable to undergo changes in volume. Increase of volume is directly related to increase in cytoplasm and its product, the yolk material. Such increases have led to direct development.8. Increase in cytoplasm and yolk has not greatly affected the cleavage process, which is almost always total. A distinction between micromeres and macromeres frequently results.9. With increasing cytoplasm, the wall of the blastula becomes thicker, and the blastocoel is in extreme cases reduced to a vestige in the animal hemisphere. The mesenchyme fails to separate as such, but projects as a solid mass into the blastocoel. Invagination is reduced to a solid inpushing of cells, and epiboly may ensue. The archenteron may become vestigial, in which case the definitive enteron is excavated in the solid endoderm by splitting. The enterocoele become reduced or lost, and the coelom and its adjuncts may arise by schizocoelous splitting in mesenchyme.10. In Ophiuroidea a succession of stages in reduction of the ophiopluteus may be seen, suggesting a recession backwards in time of the moment at which metamorphosis is initiated. In extreme cases the gastrula itself becomes radially symmetrical and the larva is completely lost.11. By convergent evolution among echinoderms with yolky eggs, a special vitel‐laria larva has arisen independently in Holothuroidea, Ophiuroidea and Crinoidea. The vitellaria is characterized by its barrel shape, and the transmutation of the ciliated band into annuli. In the Crinoidea this is the only larva as yet known.12. Viviparity does not seem to have been an important factor in causing direct development, though it may influence the physiology and morphology of the young stages.13. If larval stages of echinoderms are interpreted as recapitulating ancestral stages, the conclusions reached are seriously discordant with other evidence. Therefore it is not possible to base phylogenetic interpretations on larval stages alone.14. Echinoderm embryology cannot provide any valid support for the hypothesis that chordates arose from echinoderms.