Bruce S. Rubidge

Bio: Bruce S. Rubidge is an academic researcher from University of the Witwatersrand. The author has contributed to research in topics: Beaufort Group & Permian. The author has an hindex of 36, co-authored 150 publications receiving 4740 citations. Previous affiliations of Bruce S. Rubidge include DST Systems.

27th Du Toit Memorial LectureRe-uniting lost continents – Fossil reptiles from the ancient Karoo and their wanderlust

Abstract: Fossil discoveries from South Africa have greatly expanded knowledge of the development of life on Earth. In particular, the enormous palaeontological wealth of the Karoo, covering a period of almost 100 million years from the Permian to the Jurassic, has enhanced understanding of the evolution of important tetrapod lineages, including mammals and dinosaurs. These fossils provide the best record of continental Permian to Jurassic faunal biodiversity, and have been crucial to studies of the global Permo-Triassic mass extinction in the continental realm, as well as giving insight into other extinction events. Recent collaborative interdisciplinary studies of stratigraphic and geographic distribution patterns of Karoo fossils have enhanced biostratigraphic resolution and global correlation of vertebrate faunas from the Permian to the Jurassic. This in turn has led to a better understanding of the biodiversity across Pangaea, and the places of origin and initial diversity of early tetrapod evolutionary lineages. Many of these originated in the southern African portion of the Gondwanan super-continent. The combination of palaeontological and sedimentological studies has led to new basin development models and solved problems which each discipline in isolation could not have achieved.

A lamprey from the Devonian period of South Africa

Abstract: Lampreys and hagfish are the only remaining jawless vertebrates and are commonly used as surrogate ancestors for comparative research on living jawed vertebrates. Until recently little was known of the evolutionary history of lampreys as the only known fossils were enigmatic examples from the Carboniferous period, around 300 million years ago. Then earlier this year Nature published a report of a fine specimen from the Cretaceous of China that looked very close to modern forms. This is now joined by a well preserved fossil from the Devonian of South Africa, which at about 360 million years old is the oldest known lamprey. It looks slightly different from modern lampreys, but is the same in essentials and differs from the various now-extinct armoured fishes with which it shared the Devonian world. Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier1,2,3, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period1. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example4 demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa5,6, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples7,8, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.

High-precision temporal calibration of Late Permian vertebrate biostratigraphy: U-Pb zircon constraints from the Karoo Supergroup, South Africa

Abstract: Therapsid and other tetrapod fossils from the South African Karoo Supergroup provide the most detailed and best studied terrestrial vertebrate record of the Middle and Late Permian. The resulting biostratigraphic scheme has global applicability. Establishing a temporal framework for these faunas has proven difficult: magnetostratigraphy has been hampered by a Jurassic overprint, and intercorrelation with Permian marine sequences has been equivocal. Here we report U-Pb zircon isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates for five volcanic ashes interbedded with fossils from the Pristerognathus , Tropidostoma , and Cistecephalus vertebrate biozones of the Beaufort Group. This temporal framework allows correlation to marine zonations and improves understanding of rates of faunal evolution and patterns of basin evolution. Our results identify no correlative vertebrate extinctions in the Karoo Supergroup to the marine end-Guadalupian mass extinction and raise the question of whether there is any record of a terrestrial extinction related to the Emeishan large igneous province.

Evolutionary Patterns Among Permo-Triassic Therapsids *

Abstract: ▪ Abstract A rich fossil record documents nonmammalian evolution. In recent years, the application of cladistic methodology has shed valuable light on the relationships within the therapsid clades Biarmosuchia, Dinocephalia, Anomodontia, and Cynodontia. Recent discoveries from South Africa suggest that Gondwana, rather than Laurasia, was the center of origin and radiation for many early therapsids. Because of their relative abundance and global distribution, therapsids have enjoyed widespread use in biostratigraphy, basin analysis, and paleo-environmental and -continental reconstructions. Synapsids (including therapsids) form the bulk of tetrapod diversity (in terms of both number of species and abundance) from Early Permian to Middle Triassic times and thus can provide critical information on the nature of the Permo-Triassic extinction in the terrestrial realm. Quantitative techniques have produced headway into understanding the relative importance of homoplasy and convergent evolution in the origin of m...

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Paleontological Evidence to Date the Tree of Life

Abstract: The role of fossils in dating the tree of life has been misunderstood. Fossils can provide good "minimum" age estimates for branches in the tree, but "maximum" constraints on those ages are poorer. Current debates about which are the "best" fossil dates for calibration move to consideration of the most appropriate constraints on the ages of tree nodes. Because fossil-based dates are constraints, and because molecular evolution is not perfectly clock-like, analysts should use more rather than fewer dates, but there has to be a balance between many genes and few dates versus many dates and few genes. We provide "hard" minimum and "soft" maximum age constraints for 30 divergences among key genome model organisms; these should contribute to better understanding of the dating of the animal tree of life.

The Osteology of the Reptiles

Abstract: IN no domain of zoological science have the con tributions of American naturalists been more splendid than in that of vertebrate palaeontology, and in the list of pioneer workers in this domain an honoured place will always be accorded to Samuel Wendell Williston, who, born and nurtured in obscurity, had by the time of his death in 1918 won his way to recogni tion as the chief authority upon the extinct amphibians and reptiles. Apart from his specialist papers upon fossil vertebrates and upon modern dipterous flies, Williston was well known to the general zoologist for his excellent book on “Water Reptiles of the Past and Present,” published in 1914, and during the last year of his life he was busily engaged in the preparation of a second work of a general character on “The Reptiles of the World, Recent and Fossil.” The volume now under review comprises the main part of this general work, so far as it had been completed at the time of the author's death, put into shape and edited at the competent hands of Prof. W. K. Gregory. The Osteology of the Reptiles. By Prof. Samuel Wendell Williston. Arranged and edited by Prof. William King Gregory. Pp. xiii + 300. (Cambridge, Mass.: Harvard University Press; London: Oxford University Press, 1925.) 18s. 6d. net.

Sequence stratigraphy: methodology and nomenclature

Abstract: The recurrence of the same types of sequence stratigraphic surface through geologic time defines cycles of change in accommodation or sediment supply, which correspond to sequences in the rock record. These cycles may be symmetrical or asymmetrical, and may or may not include all types of systems tracts that may be expected within a fully developed sequence. Depending on the scale of observation, sequences and their bounding surfaces may be ascribed to different hierarchical orders. Stratal stacking patterns combine to define trends in geometric character that include upstepping, forestepping, backstepping and downstepping, expressing three types of shoreline shift: forced regression (forestepping and downstepping at the shoreline), normal regression (forestepping and upstepping at the shoreline) and transgression (backstepping at the shoreline). Stacking patterns that are independent of shoreline trajectories may also be defined on the basis of changes in depositional style that can be correlated regionally. All stratal stacking patterns reflect the interplay of the same two fundamental variables, namely accommodation (the space available for potential sediment accumulation) and sediment supply. Deposits defined by specific stratal stacking patterns form the basic constituents of any sequence stratigraphic unit, from sequence to systems tract and parasequence. Changes in stratal stacking patterns define the position and timing of key sequence stratigraphic surfaces. Precisely which surfaces are selected as sequence boundaries varies as a function of which surfaces are best expressed within the context of the depositional setting and the preservation of facies relationships and stratal stacking patterns in that succession. The high degree of variability in the expression of sequence stratigraphic units and bounding surfaces in the rock record means ideally that the methodology used to analyze their depositional setting should be flexible from one sequence stratigraphic approach to another. Construction of this framework ensures the success of the method in terms of its objectives to provide a process-based understanding of the stratigraphic architecture. The purpose of this paper is to emphasize a standard but flexible methodology that remains objective.