comment on this calibration
Metazoa
| node name Metazoa Look for this name in NCBI Wikipedia Animal Diversity Web | ||
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recommended citations http://palaeo-electronica.org/content/fc-1 Benton et al. 2015 |
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node minimum age 550.25 Ma The White Sea Biota, in which Kimberella is most common, has been dated using U-Pb zircon dates to either 558 Ma ± 1 Myr (Martin et al., 2000) or 552.85 ± 2.6 Ma (Narbonne et al., 2012; Gradstein et al., 2012). Specimens are also known from the Ediacara of Australia (Glaessner and Wade, 1966; Wade, 1972), but the age of this unit is less well constrained. We select the date published in 2012 as our minimum hard constraint. | ||
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node maximum age 833 Ma A soft maximum constraint can be established on the approximately coeval (Halverson et al., 2005; Halverson et al., 2007) middle Neoproterozoic Lagerstätten in the Bitter Springs Formation of central Australia (Schopf, 1968) and the Svanbergfjellet Formation of Spitsbergen (Butterfield et al., 1994) which preserve in three dimensions at a cellular level of fidelity prokaryotes, sphaeromorph acritarchs, multicellular algae and multifarious problematica, but nothing that could be interpreted as a total group metazoan. The absolute age of the Bitter Springs Formation is the better constrained, through correlation to a volcanic sequence in the upper Loves Creek Formation, allied to the Gairdner Dyke Swarm (Hill et al., 2000; Hill and Walter, 2000), dated at 827 Ma ± 6 Myr, thus 833 Ma. | ||
| primary fossil used to date this node | ||
PIN 3993/4003 | ||
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phylogenetic justification
Kimberella preserves several features that demonstrate it is a bilateral metazoan with an anterior-posterior axis (Fedonkin and Waggoner, 1997; Fedonkin et al., 2007; Ivantsov, 2009, 2010). Specimens are often found associated with a distinct bipartite feeding trace emerging from one end of the body, indicative of a feeding apparatus with two major denticles and a grazing behavior. There appears to be a ventral creeping sole surrounded by concentric units of tissue and a dorsal soft-bodied carapace. The morphology and feeding behavior has been accredited to a molluscan affinity. No coherent argument has been presented that calls into question the lophotrochozoan affinity of Kimberella (see Discussion). |
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phylogenetic reference(s)
Fedonkin, M.A., and Waggoner, B.M. 1997. The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism. Nature, 388:868-871.
Fedonkin, M.A., Gehling, J.G., Grey, K., Narbonne, G.M., and Vickers-Rich, P. 2007. The Rise of Animals: Evolution and Diversification of the Kingdom Animalia. Johns Hopkins, Baltimore.
Ivantsov, A.Y. 2010. Paleontological evidence for the supposed Precambrian occurrence of mollusks. Paleontological Journal, 44:1552-1559.
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| tree image (click image for full size) | ||
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Figure 1 from Benton et al. (2014).
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