The Bashkirian Pennsylvanian Carboniferous was the Peak of the Late Paleozoic Ice Age

Ice volume and paleoclimate history of the late Paleozoic ice age from conodont apatite oxygen isotopes from naqing (Guizhou, China)

Authors:

Chen et al

Abstract:

A high-resolution and continuous conodont apatite oxygen isotope record spanning the late Viséan to Middle Permian is reported from South China, which is interpreted with respect to the ice volume and/or tropical sea water temperature history of the Late Paleozoic Ice Age (LPIA). The presented δ18O record shows significant fluctuations in δ18O from the late Viséan to Middle Permian with highest values observed in the Bashkirian (Early Pennsylvanian). The δ18O maximum coincides with a major eustatic sea level fall recorded in low-latitudinal successions, and postdates the significant increases in 87Sr/86Sr and δ13Ccarb measured on well-preserved brachiopod calcite, which can be interpreted as reflecting intensified weathering as consequence of the closure of Rheic Ocean as well as enhanced carbon burial. Both processes may have contributed to lower greenhouse gas levels and cooled down the Earth's surface, triggering the maximum glaciation. The high Bashkirian δ18O values are interpreted to represent the glacial maximum of the LPIA. A coeval change in faunal composition and a decreasing diversity in climate-sensitive marine invertebrates can be ascribed to icehouse cooling and/or loss of habitat. Despite inconsistenceies with earlier interpretations that the Early Permian represented the glacial maximum of the LPIA as inferred from Gondwanan glacial sediments records, the suggested Bashkirian glacial maximum agrees well with ice extent estimates based on the regional tectonic history in Gondwana, which suggests that the Bashkirian glaciation occurred during Gondwana interior uplift promoting maximum ice cover of the entire LPIA. However, maximum glaciation is only poorly represented in the depositional record because large parts of the glacial deposits were possibly removed by erosion as outlined by a major regional unconformity.

Conodont Teeth, Vertebrate Skeleton Are Examples of Parallel Evolution

A comparison between the growth of the ‘teeth’ of the paraconodont

For decades, it was thought that our skeleton and all its characteristic bony tissues originated in the predators, known as 'conodonts'. However new research, led by the University of Bristol and published today in Nature, shows that they were evolutionary copy-cats who evolved tooth-like structures and tissues independently of other vertebrates. The origin of our skeleton is to be found in the armour of our mud-slurping ancestors who evolved bony armour to protect themselves from such predators.

Palaeontologists from Bristol, Peking University and the US Geological Survey collaborated with physicists from Switzerland to study the tooth-like skeleton of conodonts using high energy X-rays at the Swiss Light Source at the Paul Scherrer Institut in Switzerland. They showed that the tooth-like structures found in the mouths of conodonts evolved within their own evolutionary lineage, rather than in an ancestor shared with other vertebrates.

Lead author, Duncan Murdock of the University of Bristol said: "We were able to visualise every tissue, cell and growth line within the bony teeth, allowing us to study their development. We compared the tooth-like skeleton of conodonts to that of their 'paraconodont' ancestors and to teeth in living vertebrates, demonstrating that the tooth-like structure of conodonts was assembled through evolutionary time independently of other vertebrates."

Co-author, Professor Philip Donoghue of the University of Bristol's School of Earth Sciences said: "This removes a key piece of evidence from the hypothesis that teeth evolved before the skeletal armour, and suggests that the common ancestors of conodonts and other vertebrates likely lacked a mineralized skeleton. Rather, it seems that teeth evolved from the armour of our meek filter-feeding ancestors."

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