Auroralumina attenboroughii Dunn &amp; Kenchington &amp; Parry &amp; Clark &amp; Kendall &amp; Wilby 2022, gen. et sp. nov.
Creators: name: Dunn, F. S.
name: Kenchington, C. G.
name: Parry, L. A.
name: Clark, J. W.
name: Kendall, R. S.
name: Wilby, P. R.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Auroralumina
Auroralumina attenboroughii

description: <b>Etymology.</b> <i>Aurora</i> (latin) dawn, referencing the great age of the fossil; <i>lumina</i> (latin) light, alluding to the torch-like appearance of the organism; <i>attenboroughii</i>, after Sir David Attenborough for his work raising awareness of the Ediacaran fossils of Charnwood Forest. <b>Holotype.</b> See Figs. 1–3. The holotype specimen remains in situ in the field; the plastotype is housed at the British Geological Survey, Nottingham (GSM 106119). For the Reflectance Transformation Imaging (RTI) image of the holotype specimen (GSM 106352), see Data availability. These casts were taken from primary mould GSM 105874. <b>Diagnosis.</b> Thecate, medusozoan cnidarian with colonial polypoid phase. Equi-sized, bifurcating polyps are encased in goblet-shaped, organic-walled, periderm with deep-corner sulci imparting a polyhedral outline and a form of radial symmetry but without conspicuous external ornament, excepting a thin concentric band near the aperatural rim (Fig. 1). Periderm divided into two regions: the stalk and the cup. Polyp possesses a dense crown of uniform, unbranched tentacles which extend beyond the aperture of the periderm. Genus diagnosis the same by monotypy. <b>Description.</b> The holotype (Fig. 1) is ~20 cm in total length and is surrounded by a subtle microbial mat fabric that shows no indication of wrinkling or folding (Fig. 1). It comprises two, well-defined, subparallel, goblet-shaped impressions that bifurcate from a less distinct area partially obscured beneath a thin cover of sediment: no detail is preserved proximal of this point (Fig. 2). The goblet-shaped structures are equi-sized and are each constructed of a stalk (~12cm in length) which abruptly expands into a distinct cup (~6 cm in length). Each goblet has a well-defined linear ridge, running proximodistally, dividing them into two visible faces which, at their maximum, are ~6 cm wide. The left-hand goblet is divided symetrically by the ridge, which runs its entire length up to the apical margin of the cup, whereas the right-hand goblet is asymmetrically bisected. The apical margin of the cup is defined by a straight rim and by a narrow trench (corresponding to a low ridge in the living organism) that runs parallel to it ~0.8 cm below. No other surface ornament is present. Fringing the apical margin is a dense crown of short (~2.75 cm), apparently uniform and simple projections, each maintaining an approximately constant width and with a blunt termination. These are not contiguous with the apical margins of the cups; instead, they appear to emanate from within them. Aminimum of 30, locally overlapping, projections are distinguishable in the better-preserved (left-hand; Fig. 3a,b) cup. Taphonomy and interpretation The fossil is sharply differentiated from the irregularly textured background substrate and, like all other fossils on the surface, only one side of its lateral exterior is preserved. The left-hand goblet outline is symmetrical across the left and right, suggesting that the other side of the goblet was identical and therefore indicating that the goblet was probably tetraradial (Fig. 3e). Preservation of the goblets and the crowns is markedly different (Fig. 1). The goblets are preserved in negative epirelief with raised rims, in common with most other fossils in the assemblage but the rims are notably sharper and higher and the goblet surfaces are smooth (Fig. 1). The central ridges show the greatest relief of any fossilized remains on the surface (Fig. 1). The absence of evidence for deformation, the sharper definition and the higher relief of the fossil relative to other co-occurring taxa (for example, rangeomorphs) all imply that the goblets were constructed of stiffer material. As these are negative epirelief impressions, the relief of structures is in the opposite sense—so in life, the raised structure would have been a trough, separating distinct faces of the goblet as a sulcus. There is no evidence for the former presence of biominerals (for example, brittle fracture or dissolution features), leading us to conclude that the goblets were originally organic-walled. There is no original carbonaceous material remaining in any Ediacaran Charnwood Forest locality. The preservation of two faces separated by a deep sulcus is common in fossil cnidarians, such as conulariids (Fig. 3e) and is a consequence of the compression of a three-dimensional organism onto a two-dimensional surface during burial (Fig. 3e). 1 Oxford University Museum of Natural History, University of Oxford, Oxford, UK. 2 Department of Earth Sciences, University of Cambridge, Cambridge, UK. 3 Department of Earth Sciences, University of Oxford, Oxford, UK. 4 School of Biological Sciences, University of Bristol, Bristol, UK. 5 British Geological Survey, Cardiff University, Cardiff, UK. 6 British Geological Survey, Nicker Hill, Keyworth, Nottingham, UK. 7 Department of Geology, University of Leicester, Leicester, UK. ✉e-mail: frances.dunn@oum.ox.ac.uk The different bisections of the two goblets imply that they are preserved in different orientations. The occurrence of two symmetrical faces in one goblet (left-hand), and of a similarly sized face and partial face in the other (right-hand), is consistent with each goblet presenting a different view of an originally tetraradially symmetrical structure, much as in fossil conulariids and <i>Carinachites</i> 3, 4 (Fig. 3e). However, it could also represent a biradial structure as with hexangulaconulariids 5 or—if the margins of the left-hand goblet do not represent the margins of the periderm faces—triradial symmetry 6. The preservation cannot be reconciled with pentaradial symmetry, which would require unequal face widths, a condition not currently known in cnidarians with those symmetry states (for example, refs. 7, 8). We view tetraradial symmetry as most plausible because we consider that the margins of the left-hand goblet probably reflect the margins of faces and note that the maximum width of the largest face in the right-hand goblet is the same as the maximum width of the equi-sized faces in the left-hand goblet. However, we acknowledge uncertainty that might be resolved by discovery of additional specimens. The basal-most part of the specimen, past our inferred bifurcation point, does not align with the orientation of either of the two goblets individually, which supports our interpretation of the goblets as bifurfcating rather than two separate individuals. The obscured and indistinct nature of the most basal point means that we cannot say how much of the original organism is missing—the specimen we have may have been much larger in life, with additional goblets that are absent from our preserved view of the organism. Unlike the goblets, the crowns are preserved in positive epirelief, recording the upper surface of the organism. They have poorly defined margins and faint wrinkling, recording the combined impressions of multiple overlapping projections (Fig. 3f) as is seen in, for example, multifoliate rangeomorphs 9 wheremultiplebranches overlap. The specimen is preserved in lateral view—as with all other fossils on the surface—so it is not possible to see the arrangement of this crown axially, on the interior of the goblets. The projections in the crown bear greatest similarity to tentacles of living animals, but are preserved as a compound impression rather than as individual tentacles. They lack external ornament and do not appear to taper. The combined taphonomic expression of the fossil suggests stark differences in tissue toughness between the two parts, implying that these were originally constructed of different materials: one more rigid than rangeomorph fronds and able to deform the underlying sediment surface (the goblets) and the other sufficiently less resilient than rangeomorph fronds to have had its volume cast by sediment ingressed from below (the crown) 10, 11. We therefore interpret <i>Auroralumina</i> as a polypoid cnidarian, with a smooth, resistant, organic-walled periderm encasing a soft polyp that bears unbranched tentacles (Fig. 4a). The combination of a polyhedral organic-walled exoskeleton and corner sulci with associated softer tissues emerging from the aperture is compatible with interpretation of this structure as a cnidarian periderm to the exclusion of other potential structures. The body of the polyp would have been inside the cup in life and so only the protruding tentacles are preserved in this lateral view. Phylogenetic position and morphospace occupation Our phylogenetic analysis recovers a topology that agrees with most modern molecular studies (for example, ref. 12) and places <i>Auroralumina</i> in the medusozoan stem group (Fig. 4b and Extended Data Fig. 1). We recover olivooids, <i>Pseudooides</i> and conulariids as stem-group medusozoans, which differs from recent analyses that have resolved them as crown-group scyphozoans (for example, ref. 13). Together, these data reconstruct the medusozoan ancestor as being broadly scyphozoan-like, with a polyp-encasing periderm (Fig. 4b). Our results are stable when ctenophores are constrained as the sister to all other animals (Extended Data Fig. 2a) and when the specific inter-relationships of the Cnidaria are fixed to match recent molecular phylogenies (Extended Data Fig. 2b). We investigated morphospace occupation of tubular fossils (those with an external tubular skeleton within which an animal resided) across the Ediacaran–Cambrian transition as a mechanism to determine whether <i>Auroralumina</i> is significantly different from other Ediacaran tubular fossils and whether it is more similar to those fossils found in the early Cambrian period. As disparity analyses are phylogenetically independent, we incorporated a large suite of Ediacaran tubular taxa including those that are controversial and may or may not represent ancient cnidarians. The disparity matrix used in our analyses was based on characters published previously (refs. 14, 15 and other publications; see Supplementary Data 2 for a full list) which compared various phenotypic features of tubular, exoskeletal fossils across the Ediacaran and early Cambrian periods. Calculating the non-metric multidimensional scaling (NMDS) with four axes produced a fair fit (stress value &lt;0.1), so was used as the basis for further analysis. Inclusion of <i>Auroralumina</i> in the Ediacaran tube morphospace increased all aspects of disparity measured here (Fig. 5). <i>Auroralumina</i> has a major impact on the extent of Ediacaran tube morphospace and brings the Ediacaran tube morphospace closer in position and size to that of the Cambrian. The variance and extent of tubular morphospace occupation is comparatively low in the Ediacaran, indicating that tubular anatomies were not highly distinct, despite an increase in the abundance of tube-forming group(s) at this time 14. <i>Auroralumina</i> ’s location in the morphospace confirms that its anatomy is distinct from all other known Ediacaran tubular fossils and it is nested within Cambrian cnidarians, between presumed anthozoan and medusozoan taxa. Overall, morphospace variance increases into the Cambrian for all metrics we analysed, as tubular body fossils become more distinct and disparate and the distinctive Ediacaran nested tube-in-tube morphology 14 declines. Analysis of variance of disparity by group shows that the morphospace occupied by Ediacaran tubular taxa without <i>Auroralumina</i> is significantly different to the Cambrian morphospace (<i>R</i> 2 Pr(&gt; <i>F</i>) &lt;0.001) but, when <i>Auroralumina</i> is added, the Ediacaran and Cambrian morphospaces are not stastistically distinguishable (<i>R</i> 2 Pr(&gt; <i>F</i>) = 0.586), while the Ediacaran without <i>Auroralumina</i> is significantly different from Ediacaran with <i>Auroralumina</i> (<i>R</i> 2 Pr(&gt; <i>F</i>) = 0.045). This further supports the greater similarity of <i>Auroralumina</i> to Cambrian rather than other Ediacaran taxa.
description: Published as part of <i>Dunn, F. S., Kenchington, C. G., Parry, L. A., Clark, J. W., Kendall, R. S. &amp; Wilby, P. R., 2022, A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK, pp. 1-13 in Nature Ecology &amp; Evolution CLXVI</i> on pages 1-3, DOI: 10.1038/s41559-022-01807-x, http://zenodo.org/record/6908657
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