Quantitative methods used for understanding the taxonomy of acritarchs: a case study of the Middle Ordovician genus Frankea Burmann 1970

ABSTRACT

The triangular-shaped acritarch genus Frankea, which displays characteristically branched appendices, has considerable stratigraphical and palaeobiogeographical significance in the Ordovician. High intraspecific variability of terminal processes (appendices) numbers and process lengths within Frankea suggest that the genus could be suitable for use in studying the relationship between morphological characters and environmental conditions. Quantitative multivariate exploratory analyses on Frankea indicate that the length of the appendices varies according to different localities and is most probably ecologically dependent and not age diagnostic as previously suggested. Principal components analyses and discriminant analyses are used to assess the original specific classification of Frankea. The morphometric analyses suggest that usage of quantitative characters, such as the process length, should be taken into consideration during the separation of species. A comprehensive discussion of qualitative and quantitative characters is carried out and suggests there are only three species of Frankea: F. hamata, F. hamulata and F. sartbernardensis.

KEYWORDS:

• Frankea
• acritarchs
• taxonomy
• quantitative methods
• intraspecific variation
• morphometrics
• ecophenotypism

Acknowledgements

This study was initiated while Wang Wenhui was undertaking a post-doctoral fellowship at the University of Lille. Wenhui also thanks Dr Shi Yukun (Nanjing University) and Huang Bing (NIGPAS, Nanjing) for their help with the statistical analysis. Part of Thomas Servais’ contribution for this manuscript was written whilst undertaking a Visiting Fellowship at the Institute of Advanced Study (IAS), Durham University, UK. Thomas Servais also thanks David A.T. Harper (Van Mildert College, Durham) for hosting his visit and for discussion. We acknowledge the Office National des Hydrocarbures et des Mines (ONHYM), Rabat, Morocco, for providing access to the borehole material from Boujad. The palynological treatment of the material from Morocco was performed at the University of Lille 1; Laurence Debeauvais is thanked for technical assistance. We are grateful to Dr Reed Wicander, Dr Cristiana Ribecai and Mr Merrell Miller for their valuable comments that have greatly improved the work. This work is a contribution to IGCP project 653 (The Onset of the Great Ordovician Biodiversification Event).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support from the National Natural Science Foundation of China [grant number 41172001], [grant number 41402010]; MEL Visiting Fellowship [grant number MELRS1709]; and Youth Foundation of Jiangsu Province, China [grant number BK20140602] is greatly acknowledged.

Notes on contributors

Wenhui Wang

WENHUI WANG received her PhD in palaeontology and stratigraphy from Nanjing University in the summer of 2013. She spent another three years at that same institution as an assistant researcher. She has been an associate professor at Central South University, China, since the end of 2016. Her two primary research interests are: (1) Palaeozoic graptolitic palaeontology and stratigraphy – she is now working on several localities yielding graptolitic biostratigraphy from south China near the Cambrian/Ordovician and Ordovician/Silurian boundaries; and (2) studies of Early Palaeozoic palynology. Recently, Wenhui has collaborated with several teams of palynologists and published papers on both acritarch and chitinozoan investigations from South China.

Claude Monnet

CLAUDE MONNET is an invertebrate palaeontologist and ‘research engineer’ at the University of Lille (Sciences and Technologies), France. He received his MSc (1999) in palaeontology from the University of Lyon (France), and his PhD (2005) in palaeontology from the University of Zürich (Switzerland). He got his ‘habilitation’ thesis at the University of Lille in 2016. His major research interests focus mainly on macroevolution/macroecology in deep time, and on quantitative palaeontology. Complementary research topics cover systematics, biostratigraphy, taxonomic biodiversity, morphological disparity and three-dimensional morphometrics. Taxonomic strength and field experience are in Triassic and Cretaceous (Mesozoic) ammonoids (cephalopods) from North America, Europe and North Africa. Current scientific activities concern the use and development of computer tools to quantitatively and statistically investigate various questions/hypotheses on diverse fossil groups (from systematics to biostratigraphy and biodiversity, to phenotypic evolution) in macro-evolution/-ecology.

Thomas Servais

THOMAS SERVAIS is a research director at the French Centre of Scientific Research (CNRS). He trained as a geologist at the universities in Namur and Liège (Belgium), and his PhD (Liège, Belgium) and post-doctoral studies at Liège, Berlin (Germany) and the British Geological Survey (BGS, Keyworth-Nottingham, UK) were focused on the biostratigraphy, palaeobiogeography and palaeoecology of Ordovician acritarchs. His current research is mostly dedicated to a better understanding of the Ordovician Plankton Revolution. He is currently co-leader of IGCP project 653 (The Onset of the Great Ordovician Biodiversification Event) and a Vice-President of the International Paleontological Association.