Penguins are middle- to large-sized sea birds and are widely distributed in the Southern Hemisphere. They have completely lost the capability for the aerial flight, but are highly efficient wing-propelled swimmers and divers. They have a long fossil record over 60 million years, and their origin could possibly extend back to the late Cretaceous. This study aims to elaborate the course of penguin evolution and driving force of changes based on fossil records of penguins. Numerous fossil penguin specimens have been collected and studied from New Zealand, Antarctica, South America, Australia, and Africa. Studies on fossil penguins have spanned about 150 years history since Huxley (1859).
Previous works on fossil penguins have achieved excellent results, but at the same time, left considerable confusion on taxonomy and anatomical interpretation, mainly because of the poor nature of the penguin fossils in early studies. Examination of newly found materials and updated evaluation of previously studied materials are needed, using modern methods.
During about 150 years of fossil penguins study since Huxley1859, more than 40 genera and 70 species have been described. The number of specimens listed in the published literature amounts to more than 1300. Chapter II reviews all those fossil penguins in a summarised and consistent style, aiming to present the taxonomy used in this study as a primary and essential resource for research. The chapter also provides other information on fossil penguins, such as geological data and an assessment of the skeletal association of the specimens referred to a species.
Chapter III introduces the osteology of penguins, by describing and comparing the skeletal characteristics and variation of both extant and fossil species. Though previous works on penguins osteology are extensive, the interpretation of the homology, and resulted terminology, are occasionally inappropriate, or incorrect, because of the highly-specialised structure. Many of the new, yet undescribed, fossils prompt a comprehensive update of those previous studies, to understand the nature of morphological variation in penguins, and to correct or clarify confusion in previous works.
The New Zealand fossil penguin fauna is one of the most significant for fossil penguin studies, but there are many undescribed fossil penguin specimens. Chapter IV provides accounts of such materials. Chapter IV also reviews previously-described New Zealand fossil penguins, usually re-evaluated using new materials. This chapter includes reassessment of the controversial, first-described fossil penguin Palaeeudyptes antarcticus, description of an enigmatic new species (Pakudyptes hakataramea gen. et sp. nov.) which could elucidate the evolutionary pattern of the penguin wing, description of new materials of Platydyptes revealing a unique structure and functional interpretation, and redescriptions with functional interpretation of Pachydyptes and Archaeospheniscus.
Published relationships within penguins have not been adequately discussed but stated within rather rough frameworks, so that the relationships within penguins were unclear. Chapter V provides an explicit framework for the phylogeny of penguins. Osteology-based cladistic analysis was performed to seek out the relationships within penguins, using observations on both extant and fossil penguins. There are several important grades in penguin history, which are structurally distant from each other. Results also agree with the published views in which the extant penguins form a rigid group, but Simpson�s subfamily groupings are only partly supported. A postulated phylogenetic tree includes all known fossil penguin taxa including un-named ones.
Chapter VI, as a synthesis of contents of previous chapters, provides a broad interpretation of penguin evolution through the Cenozoic: origin, body size increase, demise of 'giant penguins', and the emergence of modern penguins. The chapter gives a global picture of the interaction of penguins, pinnipeds, cetaceans, and temperature and sea-level change. Two main sections are: 'Origin of penguins' and 'Evolutionary process of penguins.' The loss of aerial flight and increase of body size were possibly triggered by the K/T mass extinction event which drastically reduced the predatory pressure for early penguins. The 'giant penguins' survived until the Late Oligocene but declined as the oceans modernised, and new forms of whales with advanced feeding function appeared. There is controversy about appearance of modern penguins. The fossil-based hypothesis (relatively recent origin for crown-penguins) contradicts the molecular-based one (ancient origin for crown penguins), though 'hard evidence' at present does not easily refute either hypothesis.
| Identifer | oai:union.ndltd.org:ADTP/266542 |
| Date | January 2007 |
| Creators | Ando, Tatsuro, n/a |
| Publisher | University of Otago. Department of Geology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Tatsuro Ando |
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