New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota
Most knowledge concerning Mesozoic Era floras has come from compression fossils. This has been augmented in the last 20 years by rarer permineralized material showing cellular preservation. Here, we describe a new genus of anatomically preserved gymnosperm seed from the Callovian–Oxfordian (Jurassic...
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| Format: | Article |
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PeerJ Inc.
2017-08-01
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| Online Access: | https://peerj.com/articles/3723.pdf |
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| author | Alan R.T. Spencer Russell J. Garwood Andrew R. Rees Robert J. Raine Gar W. Rothwell Neville T.J. Hollingworth Jason Hilton |
| author_facet | Alan R.T. Spencer Russell J. Garwood Andrew R. Rees Robert J. Raine Gar W. Rothwell Neville T.J. Hollingworth Jason Hilton |
| author_sort | Alan R.T. Spencer |
| collection | DOAJ |
| description | Most knowledge concerning Mesozoic Era floras has come from compression fossils. This has been augmented in the last 20 years by rarer permineralized material showing cellular preservation. Here, we describe a new genus of anatomically preserved gymnosperm seed from the Callovian–Oxfordian (Jurassic) Oxford Clay Formation (UK), using a combination of traditional sectioning and synchrotron radiation X-ray micro-tomography (SRXMT). Oxfordiana motturii gen. et sp. nov. is large and bilaterally symmetrical. It has prominent external ribs, and has a three-layered integument comprising: a narrow outer layer of thick walled cells; a thick middle parenchymatous layer; and innermost a thin fleshy layer. The integument has a longitudinal interior groove and micropyle, enveloping a nucellus with a small pollen chamber. The large size, bilateral symmetry and integumentary groove demonstrate an affinity for the new species within the cycads. Moreover, the internal groove in extant taxa is an autapomorphy of the genus Cycas, where it facilitates seed germination. Based upon the unique seed germination mechanism shared with living species of the Cycadaceae, we conclude that O. motturii is a member of the stem-group lineage leading to Cycas after the Jurassic divergence of the Cycadaceae from other extant cycads. SRXMT—for the first time successfully applied to fossils already prepared as slides—reveals the distribution of different mineral phases within the fossil, and allows us to evaluate the taphonomy of Oxfordiana. An early pyrite phase replicates the external surfaces of individual cells, a later carbonate component infilling void spaces. The resulting taphonomic model suggests that the relatively small size of the fossils was key to their exceptional preservation, concentrating sulfate-reducing bacteria in a locally closed microenvironment and thus facilitating soft-tissue permineralization. |
| first_indexed | 2024-03-09T07:57:49Z |
| format | Article |
| id | doaj.art-aa65ffdfd4944e818714ccf6813dec13 |
| institution | Directory Open Access Journal |
| issn | 2167-8359 |
| language | English |
| last_indexed | 2024-03-09T07:57:49Z |
| publishDate | 2017-08-01 |
| publisher | PeerJ Inc. |
| record_format | Article |
| series | PeerJ |
| spelling | doaj.art-aa65ffdfd4944e818714ccf6813dec132023-12-03T00:51:04ZengPeerJ Inc.PeerJ2167-83592017-08-015e372310.7717/peerj.3723New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biotaAlan R.T. Spencer0Russell J. Garwood1Andrew R. Rees2Robert J. Raine3Gar W. Rothwell4Neville T.J. Hollingworth5Jason Hilton6Department of Earth Science and Engineering, Imperial College London, London, UKSchool of Earth and Environmental Sciences, University of Manchester, Manchester, UKSchool of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UKGeological Survey of Northern Ireland, Belfast, UKDepartment of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USASchool of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UKSchool of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UKMost knowledge concerning Mesozoic Era floras has come from compression fossils. This has been augmented in the last 20 years by rarer permineralized material showing cellular preservation. Here, we describe a new genus of anatomically preserved gymnosperm seed from the Callovian–Oxfordian (Jurassic) Oxford Clay Formation (UK), using a combination of traditional sectioning and synchrotron radiation X-ray micro-tomography (SRXMT). Oxfordiana motturii gen. et sp. nov. is large and bilaterally symmetrical. It has prominent external ribs, and has a three-layered integument comprising: a narrow outer layer of thick walled cells; a thick middle parenchymatous layer; and innermost a thin fleshy layer. The integument has a longitudinal interior groove and micropyle, enveloping a nucellus with a small pollen chamber. The large size, bilateral symmetry and integumentary groove demonstrate an affinity for the new species within the cycads. Moreover, the internal groove in extant taxa is an autapomorphy of the genus Cycas, where it facilitates seed germination. Based upon the unique seed germination mechanism shared with living species of the Cycadaceae, we conclude that O. motturii is a member of the stem-group lineage leading to Cycas after the Jurassic divergence of the Cycadaceae from other extant cycads. SRXMT—for the first time successfully applied to fossils already prepared as slides—reveals the distribution of different mineral phases within the fossil, and allows us to evaluate the taphonomy of Oxfordiana. An early pyrite phase replicates the external surfaces of individual cells, a later carbonate component infilling void spaces. The resulting taphonomic model suggests that the relatively small size of the fossils was key to their exceptional preservation, concentrating sulfate-reducing bacteria in a locally closed microenvironment and thus facilitating soft-tissue permineralization.https://peerj.com/articles/3723.pdfPalaeobotanyFossilCycadCycadeospermumCycasOxford Clay Formation |
| spellingShingle | Alan R.T. Spencer Russell J. Garwood Andrew R. Rees Robert J. Raine Gar W. Rothwell Neville T.J. Hollingworth Jason Hilton New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota PeerJ Palaeobotany Fossil Cycad Cycadeospermum Cycas Oxford Clay Formation |
| title | New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota |
| title_full | New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota |
| title_fullStr | New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota |
| title_full_unstemmed | New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota |
| title_short | New insights into Mesozoic cycad evolution: an exploration of anatomically preserved Cycadaceae seeds from the Jurassic Oxford Clay biota |
| title_sort | new insights into mesozoic cycad evolution an exploration of anatomically preserved cycadaceae seeds from the jurassic oxford clay biota |
| topic | Palaeobotany Fossil Cycad Cycadeospermum Cycas Oxford Clay Formation |
| url | https://peerj.com/articles/3723.pdf |
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