Elucidating the morphology and ecology of Eoandromeda octobrachiata from the Ediacaran of South Australia

Eoandromeda octobrachiata is a poorly understood Ediacaran organism, with spiral octoradial arms, found in South Australia and South China. The informal Nilpena member of the Rawnsley Quartzite, Flinders Ranges in South Australia preserves more than 200 specimens of Eoandromeda. Here we use the novel application of rotational geometric morphometrics together with palaeoenvironmental information to provide a better insight into their palaeobiology and ecology, and to address conflicting hypotheses regarding mode of life and taxonomic affinity. We find that Eoandromeda probably had a radially symmetrical shape in life, was cone shaped and had a high relief off the microbial mat. Analysis of the symmetric and asymmetric shape components showed that they deform strongly in the direction of palaeocurrent, therefore they are thought to be made of a flexible material. Almost all specimens are compressed flat. Specimens that appear to have not fully collapsed support the idea that Eoandromeda was probably cone shaped and suggest that they possibly collapsed spirally. Our shape analysis, along with observed morphological features, support a benthic rather than pelagic mode of life. Morphological and ecological inconsistencies do not fully support the hypothesis of a Ctenophora taxonomic affinity.

components showed that they deform strongly in the direction of palaeocurrent, therefore they are thought to be made of a flexible material.Almost all specimens are compressed flat.Specimens that appear to have not fully collapsed support the idea that Eoandromeda was probably cone shaped and suggest that they possibly collapsed spirally.Our shape analysis, along with observed morphological features, support a benthic rather than pelagic mode of life.Morphological and ecological inconsistencies do not fully support the hypothesis of a Ctenophora taxonomic affinity.
T H E Ediacaran period spanned 94 myr (635-539 Ma;Cohen et al. 2013) and included the first record of complex, macroscopic, multicellular life.The Ediacara biota is grouped into three assemblages: the Avalon (c.575-565 Ma), White  and .South Australian fossil sites contain the most morphologically and taxonomically diverse White Sea assemblage (Droser & Gehling 2015;Coutts et al. 2016;Droser et al. 2019).These fossils occur in the Ediacara Member throughout the Flinders Ranges of South Australia, with the upper metres comprising the informal Nilpena Member found only at Nilpena Ediacara National Park (NENP).
Eoandromeda octobrachiata is an enigmatic soft-bodied, octoradial spiral organism found with contrasting preservation in two locations globally: carbonaceous compressions in the Doushantuo Formation (South China) (Tang et al. 2008) and negative impressions (external moulds) in the informal Nilpena member of the Rawnsley Quartzite, South Australia (Zhu et al. 2008).The current hypothesis for the taxonomic affinity is Ctenophora (Tang et al. 2011a;Wang et al. 2020).The ecology of Eoandromeda is uncertain and has been proposed as both pelagic (Wang et al. 2020) and benthic (Zhu et al. 2008).Excavation of extensive fossil surfaces with in situ preservation of Ediacara taxa, including nearly 200 specimens of Eoandromeda at NENP, east of the Flinders Ranges provides an opportunity to examine in situ Eoandromeda in a sedimentological context.
Here we investigate the palaeobiology and ecology of Eoandromeda and address the conflicting life mode hypotheses through the novel application of a shape analysis approach, rotational geometric morphometrics (Savriama 2018).We estimate the shape in life and examine patterns of asymmetry across various fossil beds from NENP to understand how the shape of Eoandromeda is altered by differing burial conditions.Following these analyses, we assess how the shape changed with size to infer how Eoandromeda grew.Based upon all of the results and observations, we discuss the mode of life and taxonomic affinities.

GEOLOGICAL SETTING
The Adelaide Geosyncline is a north-south-oriented rift complex in South Australia dating from the Neoproterozoic to the middle Cambrian (Preiss 2000).Deposits containing the Ediacaran biota occur in the Pound Subgroup (Fig. 1A) (Gehling et al. 2019).In the absence of absolute radiometric dates in the area, the age of the strata bearing Ediacara biota in South Australia is c. 555 Ma, based on dates from the Russian sites, which include Dickinsonia and Kimberella (Martin et al. 2000).The Pound Subgroup (Fig. 1A) consists of the red Bonney Sandstone disconformably overlain by the coarse felspathic Rawnsley Quartzite.The base of this Rawnsley Quartzite is the unfossiliferous Chace Quartzite Sandstone Member (Gehling 2000).The overlying fossiliferous Ediacara Sandstone Member cuts deep channels and canyon incisions into the Chace Quartzite Member, and in some cases into the Bonney Sandstone (Gehling 2000;Gehling & Droser 2012).
Overall, the Ediacara Member is a deltaic succession prograding northwestward, the resulting accommodation space provided by the canyons enabled the development of different facies (Gehling 2000;Gehling & Droser 2012, 2013).Recently, a new member has been informally described that caps the Rawnsley Quartzite: the Nilpena Sandstone member (Fig. 1B There is a well-developed textured organic surface indicative of a mature organic mat (Droser et al. 2022).Oriented fronds indicate a unidirectional current but there is otherwise a lack of current indicators, suggesting that the burial event was not as strong as in the WS-Parv bed.Finally, the LV-Eo bed is dominated by Eoandromeda (c.52 specimens), it has a very well developed textured organic surface and no evidence of current impact on the fossils.

MATERIAL AND METHOD
Specimens from NENP located in the field and in the South Australian Museum collections (SAMA) comprise the 230 Eoandromeda used in this study (Table 1; Fig. 2).However, because not all specimens are complete, the total number of specimens available is 95.Threedimensional (3D) surfaces of these specimens were captured using the HDI Compact C506 and 3Shape TROIS 4 Intraoral 3D laser scanners (accuracies reported to 12 lm and c. 5 lm, respectively).Scans were prepared using the FlexScan3D and TRIOS Design Studio software (correspondingly) and processed (landmarked and measured) in the MeshLab software (Cignoni et al. 2008).
First, arm width was measured at the maximum width to determine whether there was one or more dominant arm/s, to orient the specimens for landmarking.Arm width was chosen given that deformation impeded the view of each arm's full length.Cross-sections of scans were visually assessed, and a wavelength pattern of the arms was determined (Fig. S1).Accordingly, arm width measurements were taken from valley to valley on scans of the complete specimens only.
To account for the rotational symmetry, the landmark data were rotated and relabelled to create eight transformed copies for each specimen using R functions in Savriama (2018) (each specimen has eight possible configurations; Fig. 3A).All transformed copies underwent generalized Procrustes analysis, which superimposes all the landmark configurations and removes translation, scale and rotation (Rohlf & Slice 1990) using the procSym function in Morpho.The resulting Procrustes coordinates are averaged across all configurations to produce a consensus (mean) shape (Fig. 3B) to estimate Eoandromeda's shape in life.
To address how shape and asymmetry varied between the beds, the Procrustes coordinates were subset by bed and ordinated by principal component analysis (PCA) using the gm.prcomp function in geomorph.In rotational geometric morphometrics, PCA decomposes the data into symmetric and asymmetric axes.Shape deformation graphs corresponding to each principal component (PC) axis were plotted to determine differences in asymmetry patterns across the beds, and enable inference of their palaeoenvironmental conditions (Fig. 3C).Additionally, incomplete specimens from the field were categorized on a scale of 0 (perfectly symmetrical) to 3 (completely offset) to ensure analysis of all available specimens (Fig. S2).Furthermore, specimen offset angles were measured against true north for all three beds and compared with palaeocurrent proxies (from Paterson et al. (2017) for WS-Parv) to explore the effect of current strength during burial on their shape.Only 35 of the 52 specimens available on the LV-Eo bed were sufficiently complete to measure.
To evaluate Eoandromeda growth, the allometric relationship between shape and size for each bed was analysed using a multivariate regression (Loy et al. 1998;Monteiro 1999) implemented with the proc.D.lm function in geomorph.Size was taken as log-transformed centroid size (mm), where centroid size is calculated from the 3D landmarks as the square root of the sum of squared distances of a set of landmarks from their centroid (Bookstein 1991).The allometric relationship between the asymmetric shape components and size for all specimens was also analysed to investigate the correlation between deformation and size.To gain another perspective into their growth not captured by landmarks, the mean of linear measurements of the arm widths (per specimen) and of the arm lengths (per specimen) Eoandromeda bed (LV-Eo) and float pieces are combined given that they are from the same event layer (but do not form a contiguous bed).
was calculated.The variables were transformed using the log-shape ratios approach, in which each measurement is divided by size (calculated as the geometric mean of all measurements, or centroid size) and natural logarithm-transformed to obtain the shape variables (Mosimann 1970;Claude 2013).This method corrects for size while retaining the allometric shape variation (Klingenberg 2016).Ordinary least-squares linear regressions were performed on these shape variables and natural logarithm-transformed centroid size to test for allometry.

Class, order & family unassigned
Genus EOANDROMEDA Tang et al., 2008 Emended diagnosis.Soft-bodied spiral organism with eight arms radiating from a central part.Circular, quadrate to elongated in shape, with the centre sometimes offset to the side.Always spiral anticlockwise when viewed in a fossil bed as a negative hyporelief (external mould), however can spiral in both directions when viewed as a carbonaceous compression.Remarks.Transverse bands appear on the arms of some of the specimens found in South China.After close re-examination of the specimens from South Australia, they were found to be absent despite their proposed presence in Zhu et al. (2008).A specimen was illustrated as having these structures (Zhu et al. 2008, fig.2D), but it cannot be ruled out as an artefact of the sandstone grains.Bends or kinks seen in one arm are also seen in the neighbouring arms.Description.Eoandromeda octobrachiata is subcircular, quadrate or elongated, with a diameter ranging from 5 to 50 mm and arms that consistently spiral anticlockwise when viewed in the bed as a negative hyporelief (thus clockwise in life).When preserved as a carbonaceous compression, spiralling can occur in either direction (original stratigraphic orientation unknown).
The arms tend to be long, tightly coiled, meeting proximally at a centre disc and tapering distally.This suggests that they were joined, forming a circle at the margin of the body (Fig. 2) that collapsed during burial.In some cases, the centre can be offset to the side (with the arms spread out to the side).Specifically for the carbonaceous compressions, in some specimens, transverse bands are visible along the arms (structures running perpendicular along the arms; Tang et al. 2011a, fig.1A, C-F).
The arms appear as lighter stains with the space between appearing darker (Tang et al. 2011a(Tang et al. , 2011b)).In a few specimens a central disc can be clearly seen, analogous to the central structure of the Australian material.
Occurrence.Upper Doushantuo black shales at the village of Wenghui, Jiangkou County, Guizhou Province, China, and Nilpena sandstone member at NENP, Flinders Ranges, South Australia, Australia.

All specimens
Arm width measurements indicate that there was no arm wider than the others (Fig. S1), and thus Eoandromeda was established to have rotational symmetry of order 8.The consensus shape for all of the landmarked Eoandromeda specimens was symmetrical (with respect to rotational symmetry of order 8) with relatively loosely coiled arms (Fig. 3B).PCA of the Procrustes residuals yielded a total of 171 PCs.Only the first 20 PCs were used because they explain 90-95% of the total shape variation; PCs after this are negligible.Of those 20 PCs, c. 71% were asymmetrical and c. 20%, symmetrical (Fig. 3C).In a scatter plot of the PC axes, no significant grouping of shapes was observed (Fig. S3).Two specimens in the SAMA collections appear not to have fully collapsed during or after burial (Fig. 2G-J).Specimens P49301 and P49302 (Fig. 2G-J) have a highrelief, conical centre, with straight arms, which suddenly spiral at the base of the conical centre.P49301 (Fig. 2G, H) has one side that has collapsed where the arms begin spiralling closer to the centre than observed in P49302 (Fig. 2I, J).

Individual beds
Consensus shapes for the WS-Parv, WS-Sub and LV-Eo beds are all symmetrical with arms becoming respectively more loosely coiled (Fig. 3B).On PCA, WS-Parv had 11% symmetric shape variation and 81% asymmetric shape variation (Fig. 4A).WS-Sub had 12% symmetric shape variation and 86% asymmetric shape variation (Fig. 4B).Finally, the LV-Eo bed + float had the highest proportion of symmetric shape variation at 19% and correspondingly the lowest asymmetric shape variation at 72% (Fig. 4C).WS-Parv has evidence of a strong prevailing palaeocurrent measured through felled fronds and tool marks (Paterson et al. 2017), and the measured offset angles of Eoandromeda were found to be strongly oriented with the current (Fig. 4A).Additionally, WS-Sub bed has evidence of a weaker current through felled fronds, and Eoandromeda was also found to be oriented in the general direction of that current (Fig. 4B).The LV-Eo bed does not show evidence of a current (Fig. 4C), which seems consistent with the orientation of Eoandromeda occurring in all directions.Categorizing of incomplete specimens followed similar trends (Fig. S2), with both the WS-Parv and WS-Sub beds having a higher proportion (80% and 93%, respectively) of the categories representing higher asymmetry (2-3) than the LV-Eo bed, which had the lowest proportion (53%).

Allometry
Multivariate regression of the symmetric component of shape for all landmarked specimens (Table 2) indicated that only 2.15% of shape change is associated with size (p = 0.001), where the general shape change is from loosely coiled with curved arms in small individuals to tightly coiled, angular arms in larger individuals (Fig. S4).Each bed follows the same trend of shape variation, with only 2.04% of shape variation being unique to each bed (p = 0.001).Asymmetric shape variation was not associated with size (R 2 = 0, p = 1).
Relatively strong linear allometric relationships were found for log arm width and log arm length versus log centroid size, and log arm length versus log width (R 2 = 0.6517, R 2 = 0.5675 and R 2 = 0.4049 respectively) with slope values of -0.4319, 0.2589 and -0.9995 (respectively; p < 0.05 for all) (Fig. 5).

Structure and shape in life
Given that radial organisms tend to be symmetrical (Manuel 2009;Hollo 2015), we hypothesize that Eoandromeda was as well.The consensus shape produced by the generalized Procrustes analysis is what is expected in life, after elimination of taphonomic distortion, which was perfectly radially symmetrical with respect to rotational symmetry of order 8 (Fig. 3B).Distinct patterns of asymmetry in the shape data were observed.Both WS-Parv and WS-Sub had a higher proportion of asymmetric shape components and a lower proportion of symmetric components than the LV-Eo bed (Fig. 4A-C, Fig. S2).A possible explanation for this is the current strength of the burial event.WS-Parv bed has evidence of a strong prevailing current (Paterson et al. 2017) and the WS-Sub bed has evidence of a weaker current through observed felled fronds, which could explain the higher asymmetry on those beds.The LV-Eo bed, however, has no evidence of a current, which is consistent with the lower proportion of asymmetry (Fig. 4C).The level of asymmetry observed on the LV-Eo bed, however, could be explained by the burial event itself.Multivariate regression of the asymmetric shape components against size showed that there is no asymmetric shape change with size (Table S1).Thus, the degree of asymmetry observed between beds was most probably not due to their size, but was more likely to be due to external factors such as current strength during burial.This is further supported by the orientation of deformation with the palaeocurrent on the WS-Parv and WS-Sub beds (Fig. 4D, E) and lack of orientation of deformation on the LV-Eo bed (Fig. 4F).Therefore, any asymmetry observed is interpreted as seemingly due to deformation as a result of palaeocurrent at the time of burial rather than asymmetry present in the body plan.Other taxa on the same beds do not show the same degree of deformation; consequently, it is hypothesized that Eoandromeda was most probably partially fluid-filled or made of a more flexible material with a high relief to be able to deform in the number of ways observed.
It is possible that Eoandromeda had a conical shape in life with a high relief off the microbial mat.The two specimens that appear to not have fully collapsed (Fig. 2G-J) suggest that Eoandromeda may have collapsed in a spiral, accommodating the tension in the arms by coiling, becoming more tightly coiled the more compacted they were.Therefore, the arms could have been more supportive in life, whether protein-or fluidfilled to support a conical shape and explain the compaction pattern.This is observed in the field, such that smaller specimens tend to have loosely coiled arms with very little relief in the centre, while larger specimens tend to have very tightly coiled arms with some relief maintained in the centre (more compaction required for the larger, higher/taller specimens).This shape pattern is also observed in the shape change in the multivariate regression (Fig. S4).However, there are only two specimens with this preservation, which were both found ex situ as an isolated piece, thus no confident claims can be made.

Growth
The hypotheses put forth by Wang et al. (2020) suggested that there were three distinct life stages based on an inflection in the regression slope of arm width versus size; juvenile (<10 mm diameter; not present in their dataset), adult (10-30 mm diameter) and senescent (>30 mm diameter) with a declining growth rate through the last two stages and a disproportionate increase of arm thickness and rigidity compared to body size.In our analysis, the negative slope of the regression for arm width versus size lacks an inflection point (Fig. 5B), refuting the hypothesis of distinct life stages and a decline in growth rate from an initial positive incline.Furthermore, the value of the slope (-0.4319) indicates a negative allometric relationship: the width of the arms decreased relative to an increase in body size (Huxley & Teissierr 1936;Gould 1966; Klingenberg 2016).The regression of arm width versus arm length (-0.9995) also shows a negative allometric relationship, signifying that relative arm width also decreased as arm length increased.These results contradict the hypothesis that there is a disproportionate increase of arm thickness compared with body size.
However, the positive hypoallometric regression slope of arm length versus size (0.2589) indicates that arm length increased at a slower rate than body size (Huxley & Teissierr 1936;Gould 1966;Klingenberg 2016).The multivariate regression of all landmarked specimens found that only 2.151% of shape change is expected per unit of increase in size (Fig. S4).The allometric shape change was observed to be the arms becoming more tightly coiled with an increase in size.Therefore, Eoandromeda appears to primarly grow by increasing arm length as this is the only positive allometric relationship measured.The arms appear to grow in a spiral fashion, creating a more tightly coiled pattern in the larger specimens.It cannot be ruled out, however, that the tight coiling may have been a result of deformation rather than morphology and growth during life.
Finally, the linear regressions do not appear to plateau despite the wide size range (c.5-50 mm).This raises the question of whether there was a maximum size of Eoandromeda or whether they had indeterminate growth.Many aquatic soft-bodied invertebrates, such as coelenterates, echinoderms, annelids, molluscs and urochordates, show indeterminate growth and can vary greatly in growth rate, final size and response to environmental conditions (Sebens 1987).The ecological benefit to this growth plan is the facilitation of continuous increased feeding rate and reproductive output without an increased energy investment in growth (Lord & Shanks 2012).Whether Eoandromeda grew continuously is unknown; it was nevertheless capable of substantial growth.

Evidence for benthic life mode
There are three conflicting hypotheses regarding Eoandromeda's life mode: benthic (Zhu et al. 2008), pelagic (Tang et al. 2011a), and pelagic as a 'juvenile' to mostly benthic as an 'adult' (Wang et al. 2020).Expanding upon the most recent hypothesis; Wang et al. (2020) proposed that the lack of preserved 'juvenile' specimens, the disproportionate increase of arm thickness and rigidity to body size in their preserved specimens and the presence of 'featherlike lamellae' and 'skirts' suggested an actively swimming (pelagic) 'juvenile' stage, followed by mostly benthic 'adult' and 'senescent' stages.
The suggestion of an actively swimming 'juvenile' stage is not supported by the results from this dataset.The 'feather-like lamellae' and 'skirts' are absent from all South Australian specimens, and even in some of the figured Chinese specimens (Zhu et al. 2008, fig. 1A-F, I;Tang et al. 2011a, fig. 1L).The absence of these features offers more support to a benthic hypothesis rather than active swimming.However, it is not certain whether the lack of these features is due to preservational differences or whether it is a true absence.Comparisons between smaller specimens from both taphonomic windows are not possible given that there are no specimens <10 mm found in China.All c. 200 specimens consistently rotate in an anticlockwise direction in the beds and no specimens were upside down or completely on the side (only deformation to one side in a current).This is not consistent with a pelagic mode of life because specimens would have been pulled from the water column during the burial events and have multiple orientations and oblique compaction angles and be less likely to be preserved, as is the case of unequivocal pelagic soft-bodied organisms in the Cambrian (Conway Morris & Collins 1996;Cartwright et al. 2007;Han et al. 2016).Additionally, the orientation of specimen deformation in accordance with the burial current on two beds also does not suggest a pelagic lifestyle.Ediacara taxa that are mobile or pelagic (i.e.Dickinsonia, Attenborites and Kimberella) tend to have very distinct and crisp edges while sessile, benthic taxa do not (Darroch et al. 2017;Evans et al. 2019;Droser et al. 2020).Although Eoandromeda has distinct arms, the edge of the specimens is not distinct and tends to fade into the texture of the mat.This is especially apparent on the WS-Sub bed, which has the most mature microbial mat of the three beds, and the specimens have a more 'mangled' appearance (Fig. 2E).Moreover, the abundance of 'juvenile' specimens in our dataset, the lack of significant shape changes with size, and the decrease of arm width with body size do not support the Wang et al. hypothesis but rather the hypothesis from Zhu et al.
(2008) of a fully benthic mode of life.Also, the spiralling of the arms could have manipulated water flow to aid in feeding.There has been a growing list of Ediacaran organisms that are hypothesized to have influenced water flow dynamics for benthic suspension feeding (Penny et al. 2014;Rahman et al. 2015;Wood & Curtis 2015;Gibson et al. 2019;Cracknell et al. 2021) and osmotrophic life habits (Singer et al. 2012).Specifically, in the White Sea assemblage, fluid dynamics studies on radial organisms Tribrachidium heraldicum (Rahman, et al. 2015) and Arkarua adami (Cracknell, et al. 2021), found that their morphology slowed and redirected water flow to specific structures, consistent with passive suspension feeding through gravitational settling.This feeding strategy has been inferred to become more widespread in the White Sea assemblage from the predominantly osmotrophic fronds of the Avalon assemblage (Laflamme et al. 2009;Hoyal Cuthill & Conway Morris 2014;Liu et al. 2015), becoming the feeding strategy for 'reefs' in the Nama assemblage (Penny et al. 2014;Wood & Curtis 2015).Modern invertebrates such as coral (Johnson & Sebens 1993), zoanthids (Koehl 1977), oysters (Bernard 1974) and crinoids (Meyer 1979) have also been reported to utilize passive suspension feeding.Additionally, ridges and grooves in an organism's body plan often relate to their mode of life.Differences in the shell ridges of extant scallops are observed depending on which ecological niche they exploit (i.e.boring, gliding, cementing, nestling, byssal-attaching and free-living) (Stanley 1988;Morton & Thurston 1989;Morton 1996;Serb et al. 2011;Dinesen & Morton 2014;Sherratt et al. 2017).For example, burrowing scallops often have asymmetric sculptural features that aid in gripping sediment during burial (Stanley 1988).Given the apparent widespread utilization of the passive suspension feeding strategy in the White Sea assemblage, the similarity in structure to both Tribrachidium and Arkarua, and the fact that ridges are often related to function, it is reasonable to suggest that the function of Eoandromeda's structure could have been to redirect and slow water flow to facilitate this type of feeding.

Ctenophore hypothesis
In association with the pelagic hypothesis, Tang et al. (2011a) proposed that Eoandromeda was a stem-group ctenophore based on morphological similarities to extant taxa of this phylum.Tang et al. (2011a) compared transverse bands along the arms to ctenes, the eight arms were related to the eight comb rows, and the apparent tubular structure of the arms interpreted as eight meridional canals.The central structure of Eoandromeda was interpreted to be the aboral ring because it resembles the shape, size and position of those seen in the Cambrian ctenophores (Conway Morris & Collins 1996).However, there are various morphological and ecological aspects that are not consistent with the Ctenophora lineage.
First, Eoandromeda is found on several fossil beds unlike the sparse fossil record of ctenophores, which consists of a handful of specimens in the Cambrian and Devonian (Stanley & St€ urmer 1983;Conway Morris & Collins 1996;Hu et al. 2007;Ou et al. 2015;Klug et al. 2021).This is consistent with a benthic lifestyle for Eoandromeda because pelagic organisms are less commonly preserved.For example, Attenborites is found in large numbers but occurs only on a single bed (Droser et al. 2020), which is consistent with the preservation of known pelagic organisms, such as jellyfish (Cartwright et al. 2007) ris 1978).Although the exact positioning of the individual taxa is debated (Ou et al. 2015;Zhao et al. 2019;Klug et al. 2021;Parry et al. 2021), these are typically placed as stem lineages before the more definitive pelagic Cambrian ctenophores, which have numerous comb rows (24 and greater) and globose body shapes (Conway Morris & Collins 1996;Ou et al. 2015).The addition of Eoandromeda to this complicated evolutionary story would require that ctenophores began somewhat morphologically similar to extant pelagic ctenophores with a spiral arrangement.Rapid evolution produced more complex benthic forms in the early Cambrian, and by the middle Cambrian they had evolved into complex pelagic forms with numerous comb rows.By the Devonian, taxa start to have more crown-group morphology (Stanley & St€ urmer 1983;Klug et al. 2021), leading to the forms extant today (to which Eoandromeda is most morphologically similar), with a small, morphologically simplistic, motile, benthic lineage (Alamaru et al. 2016;Alamaru et al. 2017;Glynn et al. 2017) secondarily evolving from a pelagic ancestor (Moroz et al. 2014;Whelan et al. 2017).This placement is not parsimonious, and requires a complicated and quick evolution involving major anatomical shifts (with and without the presence of the problematic benthic Cambrian ctenophores) (Daley & Antcliffe 2019).Taking this into consideration, it is unlikely that Eoandromeda is a representative of a stem-group ctenophore (Zhao et al. 2019).Rather, Eoandromeda could simply be a representative of early diploblastic organisms (Zhu et al. 2008).

CONCLUSION
Our study provides strong evidence that places Eoandromeda down on the sea floor as a benthic, sessile, radially symmetrical organism that was possibly cone shaped.The present results suggest that Eoandromeda was highly susceptible to deformation in accordance with burial conditions and therefore most probably consisted of a more flexible material and/or was fluid filled.We observed varying allometric relationships for the different morphological features, which suggest that the arms grew in a spiral, creating larger specimens that appear more tightly coiled than smaller ones.Together our results do not support the stem-group ctenophore hypothesis (despite some superficial morphological similarities), therefore it remains unknown as to where Eoandromeda fits into the tree of life.However, aforementioned proposed ecological and morphological traits bear a striking likeness to processes still widely utilized by marine organisms demonstrating the early evolution of common modern traits and the complexity of the Ediacara biota.
) (Gehling et al. 2019).This member is characterized by the presence of Phyllozoon hanseni, Eoandromeda octobrachiata, Arkarua adami and Tribrachidium.It is geographically restricted to the central Flinders Ranges, at both the NENP and some sections of the Heysen Range.The Eoandromeda specimens used in this study occur at the NENP site in the Planar-Laminated & Rip-Up Sandstone Facies (J.Gehling, M. Droser & D. Garc ıa-Bellido, pers.obs.2020), which is interpreted to represent deposition below wave base with gravity and/or unidirectional flow, and deposition (Gehling & Droser 2013; Tarhan et al. 2017).Specimens occur on three beds at the NENP: WS-Parv (West Side Parvancorina bed), WS-Sub (West Side Sub bed) and LV-Eo (Lake View Eoandromeda bed) as well as on float pieces around the LV-Eo bed.These beds are not stratigraphically constrained with respect to each other but are in the same facies succession.The WS-Parv bed is fine grained, with evidence of a strong unidirectional current as indicated by tool marks and oriented frond stalks, and is dominated by Parvancorina with only 15 Eoandromeda specimens (Droser et al. 2019).The WS-Sub bed is dominated by Coronacollina (Droser et al. 2019) with 14 Eoandromeda specimens.

F I G . 3 .
Workflow for the shape analysis of Eoandromeda octobrachiata.A, original landmarked specimen (LV-Eo Bed 277S 129E) and its seven standardized rotated copies.B, consensus (mean) shape for all specimens and each bed.C, bar plot of the first 20 principal components (PCs); symmetrical components are identified as single PCs, asymmetrical components are paired PCs (arranged by the proportion of variance they explain); shape configuration graphs are given for key PCs, the shape of the minimum and maximum scores for the axis.Material.Approximately 200 specimens located on three separate beds (WS-Parv, WS-Sub and LV-Eo) with additional specimens on float pieces around the LV-Eo bed.

F
I G . 4 .Comparison of principal components (PCs) for each bed with current orientations.A-C, bar plots of the first 20 PCs for: A, WS-Parv bed; B, WS-Sub bed; C, LV-Eo bed; symmetrical components are identified as single PCs, asymmetrical components are paired PCs (arranged by the proportion of variance they explain); shape configuration graphs are given for key PCs, the shape of the minimum and maximum scores for the axis.D-F, offset angles of Eoandromeda octobrachiata (examples of offsetting illustrated) compared with palaeocurrent proxies: D, WS-Parv bed (proxies from Paterson et al. 2017); E, WS-Sub bed; F, LV-Eo bed (no evidence of a current).TA B L E 2 .Multivariate regression results for shape change with size (first row), shape change by bed (second row) and shape change with size by bed (third row).
(2020)    F I G . 5 .Linear regressions of Eoandromeda octobrachiata.A, log centroid size vs diameter (mm) (for comparison/context).B, log centroid size vs log mean arm width (mm).C, log centroid size vs log mean arm length (mm).D, log mean arm length vs log mean arm width (mm).Complementary to multivariate regression (looking at different aspects of growth that landmarks do not capture, directly testing the analyses of Wang et al. 2020).
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