Precambrian Animal Life: Probable Developmental and Adult Cnidarian Forms from Southwest China

May combine two claims.

One specimen resembles a modern adult hydrozoan closely, though only a single example is available.

“Though only a single example is available, a microscopic animal remarkably similar to a modern adult hydrozoan is also presented.”

May combine two claims.

The fossil embryos share with the Pachycerianthus gastrula a monopolar invagination, a thin inner layer directly against the outer ectodermal layer, and an amorphous filled interior.

“Their monopolar invagination, with the thin inner layer applied directly to the outer (ectodermal) layer, and the amorphous filled interior, are particular characters that they share with the Pachycerianthus gastrula.”

May combine two claims.

Among the described Doushantuo microfossils are larval stages and a few adult stages, the latter uncommon.

“Included are larval and some adult stages, though the latter are relatively rare, and both anthozoan and hydrozoan clades are probably represented.”

May combine two claims.

The Weng'an fauna lacks other evidence of advanced adult bilaterians and lacks the trace fossils or bioturbation typical of later advanced bilaterian seafloor habitats.

“But no other evidence for adult bilaterian forms of such advanced complexity exists for the Weng'an fauna, nor are there any of the trace fossils or bioturbation that characterizes the later benthic habitats of advanced bilaterians.”

May combine two claims.

The main size class of the 32 fossil embryos has a mean diameter of about 142 μm and a standard deviation of about 14 μm.

“For the main peak, the mean is 142 m and the standard deviation is Ϯ13.7 m.”

• AssumptionRests on an assumption: The 32 fossil embryos with similar topology belong to the same species or developmental stage, so their sizes can be pooled.

May combine two claims.

Under polarized light, the central mass is amorphous phosphate, while the two outer layers have similarly oriented crystalline phosphate aligned symmetrically about the putative embryo axis.

“The central mass is amorphous phosphate while the two outer layers of the embryo display a similarly oriented crystalline phosphate structure, which is symmetrical with respect to the axis of the putative embryo (see legend).”

Probably not a substantial claim: may not pass S3 (load-bearing).

The small complex fossil in Fig. 5A has a diameter of about 60 μm.

“The diameter is only about 60 m”

May combine two claims.

The fossilized embryos are asymmetric, with a double-layered, tightly looped fold at one end on either side of a depression that leads into a solid amorphous interior.

“At one end, always facing the top in Fig. 4, a double-layered, tightly-looped fold can be seen symmetrically on either side of a depression, which leads to a solid, amorphous interior.”

May combine two claims.

The adult cnidarian body parts fall into two groups: tabulates and fossils of animals that might be related to anemones or soft-bodied coral-like organisms.

“These fall into two groups: tabulates, and fossils of animals that might be related to anemones or soft-bodied coral-like organisms.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Evidence for early phosphatization in the Weng'an Phosphorite member includes abundant phosphatized crusts and many phosphatized intraclasts, embryos, algae, and other microfossils.

“Evidence for early phosphatization includes ubiquitous phosphatized crusts and many phosphatized intraclasts, embryos, algae, and other microfossils; 7.4 m.”

May combine two claims.

In the specimen of Figs. 7B and 7C, the peripheral areas are less well preserved and the number of chambers appears to be six rather than eight.

“In the specimen of Figs.7B and 7C (C is shown in polarized light), the peripheral areas are much less well-preserved and the number of chambers appears to be six rather than eight.”

May combine two claims.

The retracted polyp is still tentacular along its distal and lateral margins, with at least six tentacles preserved.

“The retracted polyp is still tentacular along its distal and lateral margins, with at least six tentacles preserved.”

May combine two claims.

Fossils in Fig. 9 lack sufficient morphological detail for a unique interpretation, except that they are radially organized and about 200 μm across or less.

“The fossils in Fig. 9 do not in themselves preserve sufficient morphological detail to afford a unique interpretation, except that they are radially organized, and about 200 m across (Figs.9A and 9B) or less (Fig. 9C).”

May combine two claims.

The tabulate tubes extend to several millimeters in length, but most of their length is inanimate, consisting of formerly occupied chambers.

“The tabulate tubes extend to several millimeters in length, but most of their length is inanimate, consisting of formerly occupied chambers.”

May combine two claims.

These embryos have a partially bilayered structure that may arise from unipolar ingression, lack the distinctive blastopore of the anthozoan-like gastrulae of Fig. 4, and have a center filled with a solid amorphous mass.

“They have a partially bilayered structure such as may arise from a unipolar ingression, but they lack the distinctive blastopore of the anthozoan-like gastrulae of Fig. 4. The center is filled with a solid amorphous mass.”

May combine two claims.

The fossil in Fig. 9A has 12 peripheral discontinuities; the quadrant from about 3 to 6 o'clock in Figs. 9B and 9C is consistent with six centripetally oriented septa separated by chambers filled with dark amorphous material.

“There are 12 peripheral discontinuities in the fossil in Fig. 9A; that in Figs.9B and 9C is not well enough preserved all around to count, but the quadrant from about 3 to 6 o'clock is consistent with the presence of 6 septa, oriented centripetally, and separated by chambers filled with dark, amorphous material.”

May combine two claims.

For 73 specimens, the majority of fossils with this morphology are about 141 ± 8 μm in diameter, and the ratio of inner (endoderm) to outer (ectoderm) diameters is sharply distributed around about 1.4.

“Figures 10Q and 10R summarize the size distribution and the ratio of inner to outer layer diameters for 73 specimens.We see that the morphometric features of this form are highly coherent: the great majority of fossils displaying this morphology are about 141 Ϯ 8 m in diameter, and the ratio of inner (endoderm) to outer (ectoderm) diameters is very sharply distributed around a value of about 1.4.”

May combine two claims.

A set of putative gastrula-stage embryos with morphology different from Fig. 4 is shown in Fig. 10, and these are the most common fossilized embryonic forms encountered.

“A set of putative gastrula-stage embryos of morphology different from that of Fig. 4 is shown in Fig. 10.These are the most common of the fossilized embryonic forms that we encountered.”

Probably not a substantial claim: may not pass S3 (load-bearing).

The Fig. 11 organism was about 1 mm in scale.

“As the bar in Fig. 11 indicates, the organism was on the scale of 1 mm or so.”

May combine two claims.

Sometimes the tubes branch, and in colonial arrays adjacent tubes may share a common wall.

“Sometimes the tubes can be seen to branch, and in colonial arrays, adjacent tubes may share a common wall.”

May combine two claims.

Sinocyclocyclicus guizhouensis is a colonial coral with tabulate-like organization, and its original tubes were nonmineralized, contiguous, and sometimes branching.

“Sections displaying a colonial, tabulate-like coral Sinocyclocyclicus guizhouensis (Xue et al., 1992).This microscopic coral originally had nonmineralized, contiguous and sometimes branching tubes.”

• cites Xue et al., 1992Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The embryos described here, like those of Chen et al. (2000), are not particularly small and fall within the range of modern examples.

“It might be noted that the embryos we describe here, like those of Chen et al. (2000) are not particularly small; they fall within the range of modern examples.”

• cites Chen et al. (2000) sourceNot checked yet

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May combine two claims. The quote only partly states this claim.

The fossil in Fig. 8A has the same topology as the pharyngeal cross-section of Pachycerianthus multiplicatus in Fig. 8B, with three large chambers on each side and possible remains of an elongate pharynx in the middle.

“The tracing shown in Fig. 8C has the same topology as the section in Fig. 8B.There are three large chambers on each side, and what could be the remains of the elongate pharynx in the middle.”

May combine two claims.

The individual tubes are only a few millimeters long and 100-200 μm across, narrower at the bottom.

“The individual tubes are only a few millimeters long and 100 -200 m across, narrower at the bottom.”

May combine two claims.

Twelve specimens of a tabulate coral were recognized in the authors' sections and appear identical to Sinocyclocyclicus.

“Twelve specimens of a tabulate coral were also recognized in our sections, and they appear to be identical to Sinocyclocyclicus.”

May combine two claims.

Only a single specimen of the Fig. 11 fossil has been recovered, so its interpretation must remain tenuous.

“Unfortunately, only a single specimen has yet been recovered, and so its interpretation must remain tenuous as well.”

May combine two claims.

The solitary corallite in Fig. 6E preserves the terminal calice, an elongate vase-shaped structure that may contain an enclosed, withdrawn polyp.

“The solitary corallite shown in Fig. 6E preserves the terminal calice, which is an elongate vase-shaped structure that in this slide has been tangentially sectioned and possibly contains an enclosed, withdrawn polyp.”

Probably not a substantial claim: may not pass S3 (load-bearing).

Bilateria derive from a common ancestor.

“The Bilateria thus derive from a common ancestor, a point repeatedly substantiated in current molecular phylogenies (reviewed in Adoutte et al., 2000;Peterson and Eernisse, 2001).”

• cites Adoutte et al., 2000 sourceNot checked yet

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• cites Peterson and Eernisse, 2001 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Bilaterians employ similar fundamental approaches in constructing their varied body forms.

“Over the last decade, an enormous amount of evidence from developmental molecular biology, much of it presented in these same pages, has shown that all Bilateria share a common genetic toolkit for development, and that all Bilateria use the same basic strategies to build their diverse body plans (reviewed in Davidson, 2001;Erwin and Davidson, 2002;Carroll et al., 2001).”

• cites Davidson, 2001Not checked yet

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• cites Erwin and Davidson, 2002 sourceNot checked yet

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• cites Carroll et al., 2001Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Bilaterians possess a shared set of developmental genes.

“Over the last decade, an enormous amount of evidence from developmental molecular biology, much of it presented in these same pages, has shown that all Bilateria share a common genetic toolkit for development, and that all Bilateria use the same basic strategies to build their diverse body plans (reviewed in Davidson, 2001;Erwin and Davidson, 2002;Carroll et al., 2001).”

• cites Davidson, 2001Not checked yet

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• cites Erwin and Davidson, 2002 sourceNot checked yet

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• cites Carroll et al., 2001Not checked yet

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May combine two claims.

The externally visible cleavage forms cannot be confidently identified as sponge embryos, even though their size and shape make that the most probable interpretation.

“While the most likely guess from the morphology and size of these externally visualized cleavage forms is that they are indeed sponge embryos, the same as those seen often in sections, their identity cannot be certainly resolved.”

May combine two claims.

The described microfossils probably represent both anthozoans and hydrozoans.

“Included are larval and some adult stages, though the latter are relatively rare, and both anthozoan and hydrozoan clades are probably represented.”

• AssumptionRests on an assumption: Morphological similarity between fossil structures and modern cnidarian developmental or adult forms is a reliable indicator of cnidarian affinity.

Classified as probably not a substantial claim.

Tabulates are a major extinct cnidarian clade of the Anthozoa.

“Tabulates are a major extinct cnidarian clade of the Anthozoa (Hyman, 1940;Oliver and Coates, 1987).”

• cites Hyman, 1940Not checked yet

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• cites Oliver and Coates, 1987Not checked yet

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May combine two claims.

The age of these Doushantuo embryo microfossils is likely between 570 and 580 mya, 25-35 million years before the Cambrian.

“The age of these microfossils is likely to be between 570 and 580 mya, i.e., 25-35 my prior to the onset of the Cambrian (Fig. 1).”

• cites Chen et al., 2000 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Some protostomial bilaterians, such as certain crustaceans and chaetognaths, have cleavage stages with similar geometry.

“Several protostomial bilaterians produce cleavage stages of similar geometry, e.g., certain crustaceans (Kume and Dan, 1968) and also chaetognaths (Shimotori and Goto, 2001).”

• cites Kume and Dan, 1968Not checked yet

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• cites Shimotori and Goto, 2001Not checked yet

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May combine two claims.

The developmental forms in Figs. 4 and 5 are unlike poriferan embryos, which do not form clear blastoporal invaginations as in Fig. 4 or planula larvae with complex layered endodermal structures as in Fig. 5.

“They are also unlike poriferan embryos, which do not form clear blastoporal invaginations such as seen in Fig. 4, nor planula larvae with complex layered endodermal structures such as seen in Fig. 5.”

May combine two claims. The quote only partly states this claim.

The Weng'an Phosphorite member was deposited in shallow water under high-energy conditions, with tidal currents indicated by tidal channels and herringbone cross-stratification.

“Weng'an Phosphorite member, a phosphate unit deposited in shallow water with high-energy conditions.Erosive surfaces occur commonly.Presence of tidal channels and”

Probably not a substantial claim: may not pass S3 (load-bearing).

Cnidarian fossils occur in Early and Middle Cambrian deposits.

“Cnidarians are also found in the Early and Middle Cambrian (Chen and Zhou, 1997;Briggs et al., 1994), and they may be extensively represented in the late Neoproterozoic Ediacaran fauna as well (Glaessner and Wade, 1966;Brasier et al., 1997;Xiao et al., 1998).”

• cites Chen and Zhou, 1997Not checked yet

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• cites Briggs et al., 1994Not checked yet

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Classified as probably not a substantial claim. May combine two claims.

In Pachycerianthus multiplicatus, gastrulation occurs by unipolar invagination, leaving an open blastopore at one end and forming a two-layered spheroid in which the inner layer becomes the future gastrodermis.

“Gastrulation occurs by a kind of unipolar invagination, leaving the open blastopore at one end, and producing a spheroid with two layers of cells in which the inner layer gives rise to the future gastrodermis.”

• cites Nyholm, 1943Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

The observations of bilaterian-like gastrulae are preliminary and require additional samples to be recovered and examined.

“The observations are preliminary, in that additional samples of these bilaterian-like gastrulae need to be recov- ered and examined.”

Probably not a substantial claim: may not pass S3 (load-bearing).

In some fossil embryos, the amorphous inner mass is dark orange, which may indicate kerogen, an organic carbon-rich residue.

“Sometimes, as in Fig. 4C, the amorphous inner mass has a dark orange color which differentiates it from the outer layers even in polarized light.The dark color may indicate the presence of kerogen, an organic carbon-rich residue.”

The quote only partly states this claim.

The phosphatic fossil in Fig. 5A has a similar topology to a modern actinarian planula.

“The phosphatic fossil in Fig. 5A has a similar topology.”

• cites Chevalier, 1987Not checked yet

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• AssumptionRests on an assumption: Morphological similarity between fossil and modern cnidarian forms is a reliable indicator of taxonomic affinity.

May combine two claims.

Kimberella was probably a protostomial animal, possibly a mollusc.

“Kimberella was probably a protostomial animal, possibly a mollusc (Fedonkin and Waggoner, 1997), and so the latest common bilaterian ancestor predated this.”

• cites Fedonkin and Waggoner, 1997 sourceNot checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The organized crystal structures in the cellular layers of the fossil embryos may reflect original polarization of cytoskeletal architecture preserved during phosphatization.

“The organized crystal structures seen under polarized light in the cellular layers (here similar color indicates similarly oriented crystal axes) may reflect the original polarization of cytoskeletal architecture that was preserved in the initial process of phosphatization.”

• AssumptionRests on an assumption: The Weng'an phosphorite fossils preserve original biological structures sufficiently for morphological comparison.

Probably not a substantial claim: may not pass S3 (load-bearing).

Cnidarians and bilaterians share numerous genes for transcription factors, signaling components, and cell-type proteins.

“The cnidarians share with bilaterians many genes encoding transcription factors, signaling pathway components, and cell type-specific proteins (e.g., Yanze et al., 2001;Schuchert et al., 1993;Gro ¨ger et al., 1999;Mu ¨ller et al., 1999;Smith et al., 1999;Spring et al., 2000).”

• cites Yanze et al., 2001 sourceNot checked yet

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• cites Schuchert et al., 1993 sourceNot checked yet

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• cites Gro ¨ger et al., 1999Not checked yet

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May combine two claims.

These embryos differ from the anthozoan-like forms of Fig. 4, are close to the same size as those in Fig. 4, and could also be another anthozoan-like form or belong to some other cnidarian group.

“They differ from the particular anthozoan-like forms shown in Fig. 4.But they are close to the same size as those in Fig. 4, and they could also be another anthozoan-like form, or belong to some other cnidarian group.”

May combine two claims.

Kimberella appears at least 10-15 million years before the Cambrian Explosion but millions of years after the Doushantuo, was a fairly large bilaterian possibly as long as 14 cm, and likely made its living by scratching sea floor microbial mats with a radula or radula-like structure.

“Kimberella, which as discussed above appears at least some 10 -15 million years before the”

• cites Fedonkin and Waggoner, 1997 sourceNot checked yet

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• cites Seilacher, 1999 sourceNot checked yet

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May combine two claims.

Sinocyclocyclicus was a colonial coral-like animal, probably soft-bodied, consisting of tubes divided into chambers about 10-16 μm apart by cross-walls (tabulae).

“Sinocyclocyclicus was a colonial coral-like animal, probably soft bodied, consisting of tubes that are divided into a series of chambers about 10 -16 m apart by cross-walls (tabulae).”

• cites Xiao et al., 2000 sourceNot checked yet

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• AssumptionRests on an assumption: Morphological similarity between fossil and modern cnidarian forms is a reliable indicator of taxonomic affinity.

May combine two claims.

The variety of forms indicates a variety of food sources and an environment of some complexity.

“The variety of forms indicates a variety of food sources, an environment of some complexity.”

Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing), S4 (based). May combine two claims.

The factor(s) responsible for the high surface-to-volume requirement could be anything generally required by cells of simple marine metazoans to be absorbed, such as oxygen, nutrients, or minerals, or something requiring surface receptors for detoxification.

“The factor(s) responsible could be anything that is generally required by the cells of simple marine metazoans to be absorbed, i.e., oxygen, nutrients, or minerals; or even something that requires surface receptors for detoxification.”

May combine two claims.

Since the divergence of cnidarians from the bilaterian lineage must predate the appearance of fully evolved cnidarians, the two branches were already separate by Doushantuo times, and bilaterian ancestors also existed.

“That is perhaps the most important implication of the discovery of what looks to be a highly evolved cnidarian fauna in Doushantuo times: since the divergence of the cnidarians from the bilaterian lineage must predate the appearance of fully evolved cnidarians, the two branches were by then clearly separate, and so bilaterian ancestors also existed.”

• AssumptionRests on an assumption: The divergence of cnidarians from the bilaterian lineage predates the appearance of fully evolved cnidarians.

May combine two claims.

Figures 7-9 could all be sections across a stalk or a polyp, though the plane of section in Fig. 8 is probably oblique.

“Figures 789all could be sections across a stalk or a polyp (though the plane of section in Fig. 8 is probably oblique).”

May combine two claims.

The walls and septa in these fossils are interpreted as cellular structural elements, epithelia similar to those in Fig. 4H or Fig. 5, while the amorphous material is interpreted as fill within former chamber lacunae.

“We interpret the walls and septa as cellular structural elements, epithelia similar to those that can be seen, e.g., in Fig. 4H or Fig. 5, and the amorphous material as fill within what were the lacunae of the chambers in the living organism.”

May combine two claims.

The individual tabulae were probably about 2-3 μm thick in life but appear thicker in sections due to mineral cement growth on either side.

“The individual tabulae were probably about 2-3 m thick in life, but appear thicker in the sections due to growth of a mineral cement on either side”

May combine two claims.

The polyp lived in the terminal chamber or calice and secreted new chamber floors as it grew.

“The polyp evidently lived in the terminal chamber or calice and it secreted new chamber floors as it grew.”

May combine two claims.

Sinocyclocyclicus is most likely a stem-group tabulate, differing from Paleozoic tabulates by its small size and absence of external mineralization.

“Most likely it is a stem-group tabulate which differs from Paleozoic tabulates in its small size and lack of external mineralization.”

• cites Xiao et al. (2000) sourceNot checked yet

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May combine two claims.

The small total number of these forms found among thousands of slides reduces concern about the lack of longitudinal sections, because cross-sections would be more common than longitudinal sections if the animals had stalks long relative to their width.

“This would be a cause for concern, except for the small total number of examples of these forms that we have found in all the thousands of slides examined.There would of course be many more opportunities for cross-sections than for longitudinal sections if these animals had stalks that are long with respect to their width.”

May combine two claims.

The microscopic size of these cnidarian carnivores is not satisfactorily explained as an adaptation to very sparse food supply, and that idea would not explain why Doushantuo spongiforms are also small despite subsisting on algae and bacteria.

“So it is not satisfying to imagine that the microscopic size of these cnidarian carnivores could be explained as an adaptation to very sparse food supply.Furthermore, that idea would not explain why the spongiforms of the Doushantuo deposits are also small, as these must have subsisted instead on algae and bacteria.”

• AssumptionRests on an assumption: The Weng'an cnidarians were carnivores.
• AssumptionRests on an assumption: The Doushantuo spongiforms subsisted on algae and bacteria.

May combine two claims.

At least various kinds of cnidarians with affinities to modern anthozoans were likely present in the Weng'an fauna, and possibly hydrozoan-like cnidarians as well.

“At least various kinds of cnidarians with affinities to modern anthozoans were likely present, and possibly hydrozoan-like cnidarians as well.”

May combine two claims.

The phosphatic fossil in Fig. 7A closely resembles a modern octocoral polyp cross-section, allowing for opaque mineral in most peripheral chambers and dark amorphous material in one chamber and the pharyngeal cavity.

“The phosphatic fossil in Fig. 7A bears a great resemblance to this, if allowance is made for the presence of opaque mineral in the chambers of all but one of the peripheral compartments, replaced by a dark amorphous substance in the other chamber and also in what was the pharyngeal (Nyholm, 1943).”

• cites Nyholm, 1943Not checked yet

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May combine two claims.

The similarity of Fig. 8A to Pachycerianthus suggests the specimen could be an adult from the same group as the embryos of Fig. 4, a miniature cnidarian resembling modern ceriantharians at both embryonic and adult stages.

“The similarity suggests that this specimen could come from an adult from the same group as produced the embryos of Fig. 4, i.e., a cnidarian which though miniature in size bears morphological resemblance to modern ceriantharians at both embryonic and adult stages.”