I have finally handed in my PhD thesis!
I've included the title and thesis abstract below, for anyone so inclined to read it.
So what's the next step? Can I call myself Dr. Syme yet? Not quite. Over the next 3-4 months, two qualified taphonomists will examine the thesis, and note whether any changes to the text or figures need to be made. Once those changes have been incorporated, the thesis can then be formally accepted by UQ!
Now for the waiting game...
I've included the title and thesis abstract below, for anyone so inclined to read it.
So what's the next step? Can I call myself Dr. Syme yet? Not quite. Over the next 3-4 months, two qualified taphonomists will examine the thesis, and note whether any changes to the text or figures need to be made. Once those changes have been incorporated, the thesis can then be formally accepted by UQ!
Now for the waiting game...
Life by the Eromanga Sea: Taphonomy of crocodyliform and osteichthyan fossils from the Lower Cretaceous (upper Albian) portion of the Winton Formation at Isisford central-west Queensland.
ABSTRACT
In 1995, the articulated and semi-articulated fossilised remains of two small crocodyliforms and a large predatory fish were discovered in the Lower Cretaceous (upper Albian) portion of the Winton Formation near the town of Isisford, central-west Queensland (hereafter referred to as ‘Isisford’). Subsequent expeditions yielded further crocodyliform and osteichthyan fossils, as well as those of non-avian dinosaurs. The crocodyliforms were described as a new genus and species, Isisfordia duncani Salisbury et al., 2006. Phylogenetic analysis found that Isisfordia was a basal eusuchian, indicating that modern crocodyliforms may have originated in the Australian part of Gondwana. A partially complete and articulated osteichthyan fossil discovered in 2005 was described as a new species of the ichthyodectiform Cladocyclus, C. geddesi Berrell et al., 2014, expanding the geographic range of this genus outside of Brazil and Morocco. As deposition of the Winton Formation is thought to have occurred in fluvial and lacustrine settings, these taxa are considered to have inhabited freshwater environments.
The preservation and composition of the Isisford vertebrate assemblage is in sharp contrast to that of other vertebrate-bearing localities of the Winton Formation, the best known of which occur near the town of Winton, 240 km north-west of Isisford. The Isisford fossils are found encased in fine-grained sandstone concretions, often ex-situ and laying in Cenozoic and recent alluvium. In contrast, vertebrate fossils found nearer to Winton are typically preserved as disarticulated elements in siltstone hosted ‘bone-beds’. Additionally, taxa found nearer to Winton include sauropod and theropod dinosaurs, freshwater turtles, and lungfish, none of which has been recovered from Isisford. Furthermore, a detrital zircon dating study of the fossil-bearing Winton Formation localities indicates that Isisford is 6–8 million years older than localities nearer Winton. It is not clear if these differences in fossil preservation and faunal composition are temporal, or due to dissimilar environmental or taphonomic processes. It is also not known whether the Isisford fossils are autochthonous or allochthonous, which has bearing on the interpretation of their preferred habitats in life, and in clarifying the nature of the depositional environment in which their remains were interred. With this in mind, the primary aim of this study was to record decay sequences in modern crocodyliforms (C. porosus) to better understand the taphonomy of I. duncani fossils, examine the sedimentology of the Winton Formation at Isisford to identify the depositional setting, and elucidate the taphonomic history of the I. duncani and C. geddesi specimens.
An aquatic actualistic decay experiment using juvenile Indo-Pacific crocodiles (Crocodylus porosus) revealed that on average, carcasses ‘bloat and float’ five days post-mortem then remain at the water’s surface for approximately one month. The majority of disarticulation occurs not during bloat and float, but after the carcass sinks. Excluding rapid burial, it appears that high degrees of articulation and completeness can only occur if the bloat and float phase is either inhibited or eliminated.
Sedimentological analysis indicates that the Isisford concretions consist of feldspathic litharenites cemented with calcite. Given the cement-supported nature of the concretions, along with minimal fossil deformation, this suggests that the concretions formed during early diagenesis prior to sediment compaction. Stable isotopic analysis of calcite 18O/16O and 13C/12C ratios versus Vienna Pee Dee Belemnite (delta 18O VPDB and delta 13C VPDB) indicates that this cement precipitated from brackish pore waters during sulphate reduction and methanogenesis. Given the location of Isisford during the late Albian near the regressing Eromanga Sea, along with the presence of mud rip-up clasts and fossil plant debris, it appears that the concretions formed in a lower deltaic plain or estuarine setting.
The Isisford fossils range in preservation style from fully articulated through to disarticulated skeletal elements, and show minimal signs of abrasion or weathering. The close association of discrete articulated skeletal segments suggests that prolonged bloating and floating did not occur. Additionally, the lack of tetany in these specimens suggests they did not suffer any toxic shock pre- or peri-mortem. I propose that the majority of the fossils are autochthonous or parautochthonous, and that I. duncani and C. geddesi lived and died in a delta or estuary connected to the Eromanga Sea.
The fossil taxa of Isisford should be analysed in the context of more contemporaneous taxa of the late Albian Eromanga Sea – namely those from the Toolebuc Formation, Allaru Mudstone, and Mackunda Formation – rather than taxa from the relatively younger portions of the Winton Formation. Furthermore, studies focussing on the J/K mass extinction event and radiation of crocodyliforms should list the preferred habitat of I. duncani as deltaic or estuarine brackish waters, not freshwater. And no longer do palaeobiogeographical studies involving C. geddesi need to invoke mechanisms for freshwater adaptation, as it appears it was brackish water tolerant, which has already been proposed for other Cladocyclus spp. from South America and Morocco.
ABSTRACT
In 1995, the articulated and semi-articulated fossilised remains of two small crocodyliforms and a large predatory fish were discovered in the Lower Cretaceous (upper Albian) portion of the Winton Formation near the town of Isisford, central-west Queensland (hereafter referred to as ‘Isisford’). Subsequent expeditions yielded further crocodyliform and osteichthyan fossils, as well as those of non-avian dinosaurs. The crocodyliforms were described as a new genus and species, Isisfordia duncani Salisbury et al., 2006. Phylogenetic analysis found that Isisfordia was a basal eusuchian, indicating that modern crocodyliforms may have originated in the Australian part of Gondwana. A partially complete and articulated osteichthyan fossil discovered in 2005 was described as a new species of the ichthyodectiform Cladocyclus, C. geddesi Berrell et al., 2014, expanding the geographic range of this genus outside of Brazil and Morocco. As deposition of the Winton Formation is thought to have occurred in fluvial and lacustrine settings, these taxa are considered to have inhabited freshwater environments.
The preservation and composition of the Isisford vertebrate assemblage is in sharp contrast to that of other vertebrate-bearing localities of the Winton Formation, the best known of which occur near the town of Winton, 240 km north-west of Isisford. The Isisford fossils are found encased in fine-grained sandstone concretions, often ex-situ and laying in Cenozoic and recent alluvium. In contrast, vertebrate fossils found nearer to Winton are typically preserved as disarticulated elements in siltstone hosted ‘bone-beds’. Additionally, taxa found nearer to Winton include sauropod and theropod dinosaurs, freshwater turtles, and lungfish, none of which has been recovered from Isisford. Furthermore, a detrital zircon dating study of the fossil-bearing Winton Formation localities indicates that Isisford is 6–8 million years older than localities nearer Winton. It is not clear if these differences in fossil preservation and faunal composition are temporal, or due to dissimilar environmental or taphonomic processes. It is also not known whether the Isisford fossils are autochthonous or allochthonous, which has bearing on the interpretation of their preferred habitats in life, and in clarifying the nature of the depositional environment in which their remains were interred. With this in mind, the primary aim of this study was to record decay sequences in modern crocodyliforms (C. porosus) to better understand the taphonomy of I. duncani fossils, examine the sedimentology of the Winton Formation at Isisford to identify the depositional setting, and elucidate the taphonomic history of the I. duncani and C. geddesi specimens.
An aquatic actualistic decay experiment using juvenile Indo-Pacific crocodiles (Crocodylus porosus) revealed that on average, carcasses ‘bloat and float’ five days post-mortem then remain at the water’s surface for approximately one month. The majority of disarticulation occurs not during bloat and float, but after the carcass sinks. Excluding rapid burial, it appears that high degrees of articulation and completeness can only occur if the bloat and float phase is either inhibited or eliminated.
Sedimentological analysis indicates that the Isisford concretions consist of feldspathic litharenites cemented with calcite. Given the cement-supported nature of the concretions, along with minimal fossil deformation, this suggests that the concretions formed during early diagenesis prior to sediment compaction. Stable isotopic analysis of calcite 18O/16O and 13C/12C ratios versus Vienna Pee Dee Belemnite (delta 18O VPDB and delta 13C VPDB) indicates that this cement precipitated from brackish pore waters during sulphate reduction and methanogenesis. Given the location of Isisford during the late Albian near the regressing Eromanga Sea, along with the presence of mud rip-up clasts and fossil plant debris, it appears that the concretions formed in a lower deltaic plain or estuarine setting.
The Isisford fossils range in preservation style from fully articulated through to disarticulated skeletal elements, and show minimal signs of abrasion or weathering. The close association of discrete articulated skeletal segments suggests that prolonged bloating and floating did not occur. Additionally, the lack of tetany in these specimens suggests they did not suffer any toxic shock pre- or peri-mortem. I propose that the majority of the fossils are autochthonous or parautochthonous, and that I. duncani and C. geddesi lived and died in a delta or estuary connected to the Eromanga Sea.
The fossil taxa of Isisford should be analysed in the context of more contemporaneous taxa of the late Albian Eromanga Sea – namely those from the Toolebuc Formation, Allaru Mudstone, and Mackunda Formation – rather than taxa from the relatively younger portions of the Winton Formation. Furthermore, studies focussing on the J/K mass extinction event and radiation of crocodyliforms should list the preferred habitat of I. duncani as deltaic or estuarine brackish waters, not freshwater. And no longer do palaeobiogeographical studies involving C. geddesi need to invoke mechanisms for freshwater adaptation, as it appears it was brackish water tolerant, which has already been proposed for other Cladocyclus spp. from South America and Morocco.
