Mixosaurid ichthyosaurs (mixosaurs) are a dominant group of Middle
Triassic marine reptiles that was widely distributed in both Tethyan and
Panthalassic terranes. They are represented by many excellently preserved
specimens from all around the world and have been studied for more than one
hundred years. Even so, their morphology is not adequately known. The
systematics of mixosaurs is not well understood and their phylogeny has been
controversial. The nomination of several Chinese mixosaurs makes the situation
even worse. This thesis aims to provide a comprehensive review of Chinese
mixosaurs and discuss their phylogenetic relationships.
The detailed anatomy of only valid Chinese mixosaurid species Mixosaurus
panxianensis is well established in this thesis. Its ontogenetic changes are also
noted and a better diagnosis is given. A new morphotype of mixosaurs from a
recently discovered fossil Lagerst?tte, the Luoping biota, is described in detail.
This morphotype is similar to M. panxianensis but consistent differences are also
present. The ecological comparison to M. panxianensis demonstrates that this
morphotype represents a new taxon that is different from M. panxianensis. A
nearly complete and articulated specimen of Phalarodon atavus from the Middle
Triassic Luoping biota, Yunnan, South China is described. This is the first
specimen of P. atavus discovered outside the Germanic Basin. The discovery of
this specimen demonstrates a cosmopolitan distribution of P. atavus across the
whole Tethyan ocean. The new specimen is also the first one preserving the
postcranial anatomy of this species, providing the potential to evaluate its
swimming ability for the first time. Functional morphology shows that this
species is well adapted for a pursuit attack of prey, consistent with the
distribution pattern of the species. Tooth crown morphology suggests that P.
atavus may prefer externally soft prey such as belemnoids.
Mixosaurs are divided into three ontogenetic stages based on the humeral
morphology. The juvenile stage is characterized by a textured dorsal humeral
shaft surface. The subadult stage is characterized by a smooth humeral shaft in
dorsal view with a rugose humeral head. The adult stage is characterized by a
smooth humeral head. The consistent presence of the surface texture of ventral
humeral shaft is most probably caused by the strong muscle insertion presumably
related to the function of steering of the fore fins in mixosaurs.
Five morphotypes of Chinese mixosaurs are recognized in this study.
Twenty-five more or less new characters are introduced to evaluate the
phylogenetic relationships of mixosaurian-like specimens from China. The
monophyly of mixosaurs including all studied Chinese morphotypes is well
corroborated. Further investigation on the mixosaurs from Monte San Giorgio is
recommended to resolve the phylogenetic relationships of mixosaurs. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/211049 |
| Date | January 2011 |
| Creators | Liu, Jun, 刘俊 |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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