Published on October 15th, 2019 | by David Marshall
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Episode 104: Ediacaran Developmental Biology
The Ediacaran Period is host to the first large and complex multicellular organisms known in the fossil record. This ‘Ediacaran Biota’ has long eluded definitive placement on the tree of life, seemingly falling between even the most fundamental of its branches. At the core of this taxonomic issue are their unique body plans, not seen replicated in any other kingdom.
Amongst the researchers trying to unravel the mystery of these organisms is Dr Frances Dunn of the University of Oxford. Frankie has been researching the developmental biology of the Ediacaran Biota in the hope that we can learn more from how these forms grew, as opposed to what they eventually grew into.
Frankie working on the famous ‘E’ surface of the Mistaken Point UNESCO World Heritage Site. Ediacaran rangeomorph taxa. (A) Beothukis plumosa, Newfoundland, Canada. (B) Fractofusus andersoni, Newfoundland, Canada. (C) Pectinifrons abyssalis, Newfoundland, Canada. (D) Bradgatia sp., Newfoundland, Canada. (E) Charnia masoni, UK. (F) Higher-order branching in an exceptionally preserved Bradgatia sp. specimen from Newfoundland. (G) Stylised interpretation of growth of primary branches in Charnia masoni. (H) The different orders of rangeomorph branches, and their arrangement within Charnia masoni: 1 = primary branch, 2 = secondary branch, 3 = tertiary branch and 4 = quaternary branch. Grey overlay in A–E indicates a primary branch. Scale bars: A, B, D and E = 10 mm, C = 5 cm. Ediacaran dickinsoniomorph taxa. (A) Andiva ivantsovi, White Sea, Russia. [Palaeontological Institute Moscow (PIN) specimen number 3993–5623]. (B, C) Enlargements of the boxed area in A. The areas of unit differentiation are indicated by white arrows, and undivided regions on Andiva and Yorgia are indicated by black arrows. (D) Dickinsonia costata, South Australia [South Australia Museum (SAM) specimen numbers P49354 and P49355]. (E) Yorgia waggoneri, White Sea, Russia (Holotype PIN 3993–5024). (F) Stylised interpretation of growth of Dickinsonia costata, following the growth model proposed in Hoekzema et al. (2017). Scale bars = 10 mm. Ediacaran erniettomorph taxa. (A, B) Pteridinium simplex, Namibia. Numbers identifying the three identified vanes. (C) Swartpuntia germsii, Namibia. (D) Ernietta plateauensis, Namibia. Scale bars = 10 mm. Images courtesy of D. Grazhdankin (A and B from Grazhdankin & Seilacher, 2002), M.D. Brasier (C), and M. Laflamme (D).
Schematic diagram showing the forms of growth observed in extant clades with serial repetition of component units; red indicates the style/feature of growth discussed. (A) Coordinated modular growth, seen in certain metazoan [animal] groups. (B) Parallel modular growth, common in plants and red, green and brown algae, with an aberrant branch highlighted in red. (C, D) Positioning of different central (additional growth zone highlighted with black arrow) and lateral growth zones/tips in extant serially repetitive groups. Single apical axes are seen in green and red algal groups, whereas multiple axes are seen in various metazoan and brown-algal groups. (E) Diffuse growth, as seen in colonial bilaterian groups characterised by colony-wide tip growth.
(A) Interpretive growth models of: 1, Charnia masoni; 2, Dickinsonia costata; 3, Andiva ivantsovi; 4, an extant bilaterian comparator. (B) A simplified eukaryote phylogeny including only groups with serially repetitive body plans to which the Ediacaran morphogroups have been compared. SAR = Stramenopiles, Alveolates and Rhizaria. The potential positions of Charnia, Dickinsonia and Andiva are shown. Green represents metazoan [animal] lineages. Dashed lines indicate the possible position of a group. Frankie and fellow Ediacaran researcher Dr Jack Matthews on sea ice, Newfoundland, Canada.
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