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Friday 28 Mar, 4.30pm

Neil Chalmers Seminar Room, DC2

 

 

The Evolution of Vertebrate Reproduction

 

by Zerina Johanson, Department of Earth Sciences

 

The early history of the jawed vertebrates, and the evolutionary transition from jawless to jawed vertebrates, is recorded entirely in the fossil record. Phylogenetically, the most basal jawed vertebrates (and some of the most crownward stem gnathostomes) are the placoderms, fossil taxa ranging in age from the early Silurian to the end of the Devonian (435-360mya). As such, placoderms record the origins and evolution of a number of major jawed vertebrate morphologies. A re-examination of the superb three-dimensionally preserved placoderms recovered from the Gogo Formation (Late Devonian, Western Australia) has provided the most detailed knowledge of this group to date.

 

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We review recent information on placoderm embryos as well as previous descriptions of the placoderm pelvic structures and reinterpret the morphology of the pelvic region, in particular the position of the pelvic fin and the relationship of the male clasper to the pelvic girdle. Claspers in placoderms and chondrichthyans develop in very different ways; in sharks, claspers develop from the pelvic fin while the claspers in placoderms develop separately, suggesting that their independent development involved a posterior extension of the ‘zone of fin competence’.

 

 

SciFri is a cross-departmental science seminar series and social event, held on the last Friday of each month. The 45 minute talks are intended to be informal, contemporary, inter-disciplinary and cover a range of fields including the latest research, curation, science policy, library & archives research, publishing, media, fieldwork and science methods.

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Friday 28 Feb, 4.30pm, Neil Chalmers Seminar Room

 

Livestreamed on http://www.youtube.com/user/SciFriSeminars

 

 

Chemosynthesis-based communities through time: a 3.2 billion year history

 

Cris Little, University of Leeds

 

At the beginning of this seminar I will briefly review the ecology of modern chemosynthetic communities at hydrothermal vents, hydrocarbon (‘cold’) seeps and sunken dead whales (whale-falls) touching on biogeography and discussing evolutionary issues, including molecular divergence estimates for several major taxonomic groups.

 

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Then I will turn to the fossil record of these communities, which for vents goes back 3.25 billion years. I will show that vent and seep fossil assemblages have changed in taxonomic structure during the Phanerozoic, from brachiopod dominated communities in the Palaeozoic and early Mesozoic to mollusc (bivalve and gastropod) dominated communities from the later Mesozoic onwards. Some of the ecologically dominant taxa that have chemosymbiotic bacteria (e.g. vesicomyid clams and bathymodiolin mussels) are relative newcomers to vent and seep environments and were preceded by other, now extinct, bivalves that may (or may not) also have had symbionts.

 

Whale-fall communities from the Miocene are similar in structure to modern examples in the so-called sulfophilic stage, but older Oligocene and latest Eocene whale-fall communities lack some of the typical molluscs. This may be related to the small size of whales in their early evolutionary history. Prior to the Eocene whale-fall-like communities may have existed on sunken marine reptiles (e.g. turtles, ichthyosaurs and plesiosaurs), or even large fish carcasses.

 

 

About SciFri

 

SciFri is a cross-departmental science seminar series and social event run by the NHM Science Forum, held the last Friday of each month. The 45 minute talks are intended to be informal, contemporary, inter-disciplinary and cover a range of fields including the latest research, curation, science policy, publishing, media, fieldwork and science methods. If you have ideas for future speakers from any of these areas please contact the seminar organiser Adrian Glover, Life Sciences Department.