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Updated: 21 Oct 2003

Olivooides multisulcatus

Abstract

This page dicusses the Cambrian soft-bodied ?Cnidarian fossil, Olivooides multisulcatus. The primary source reference is Bengtson & Zhao 1997, from which most of this page is derived. Any errors, however, are mine.

Keywords: Cambrian, fossil embryo, Olivooides

Introduction

Soft body preservation is the exception rather than the rule in the fossil record. Nevertheless, there is an abundance of small, superficially non-descript, globular fossils dating back to the Cambrian (and possibly Vendian – read more) times. One example is the genus Olivooides, which is widely reported throughout the basal Cambrian of the Palaeotethyan Belt, a wide belt of Precambrian-Cambrian boundary sequences stretching from Iran to southern China (Brasier 1989 p. 40).

Reports of fossilized eggs and other early developmental stages of marine invertebrates are rare, probably mostly due to the difficulties of recognizing them. However, Zhang and Pratt 1994 reported Middle Cambrian spherical fossils, 0.3 mm in diameter, that under a smooth membrane preserved a polygonal pattern which the authors interpreted as remains of blastomeres belonging to 64- and 128-cell stages of arthropod embryos.

Bengtson & Zhao 1997 found that the globular fossils do indeed contain developing embryos of the co-occurring fossil known as Punctatus. Their material (thousands of eggs and about 10 more or less complete hatched specimens) derives from limestones of an interbedded chert, limestone and phosphorite sequence in the upper part of the Dengying Formation, Shaanxi Province, China.

Associated fossils indicate a Lower Cambrian (Lower Meishucunian) age.

Geological Setting

Stratigraphy

The material derives from limestones of an interbedded chert, limestone and phosphorite sequence in the upper part (beds 23 to 27, fig. 1) of the Dengying Formation in the Shizhonggou section, near Kuanchuanpu village, Ningqiang County, Shaanxi Province, China.

Associated fossils include Anabarites trisulcatus, Siphogonuchites triangularis, and Carinachites spinatus. They indicate a Lower Cambrian (Lower Meishucunian) age.

Preservation

The fossils are preserved as diagenetically phosphatized replacements and encrustations in marine limestones. Early diagenetic phosphatization has tremendous potential for replicating delicate biological tissues but appears to take place under local conditions where pH and activities of P and HCO₃- turn phosphatization on and off, and the conditions conducive to phosphatization are enhanced by bacterial activity. Metazoan eggs are readily phosphatized under experimental conditions, and the occurrences reported by Zhang and Pratt 1994 and by Bengtson & Zhao 1997, from beds where other fossilized nonstructural tissues are absent, suggest that eggs are particularly susceptible to such phosphatization.

Because several instances of this type of preservation have now been found, it may be that metazoan embryos are not uncommon as fossils but have simply been overlooked because of their minute size and nondescript morphology.

Shizhonggou Section Stratigraphic Column (37185 bytes)

Fig. 1: The Shizhonggou section, showing first occurrences of Olivooides multisulcatus (lowest arrow), Anabarites trisulcatus and Siphogonuchites triangularis, (middle arrow), and Turcutheca (top arrow). After Brasier 1989, fig. 3.5.

Systematics

"Punctatus," with its flexible, annulated test, has been compared with the conulariids, a mainly Paleozoic group of biradially symmetrical fossils with a narrow-pyramidal phosphatic test. Although sometimes referred to as an extinct phylum, conulariids share a number of likely synapomorphies with scyphozoan cnidarians.

Olivooides lacks the characteristic biradial symmetry of conulariids. The closely similar coeval hexangulaconulariids, of varying symmetry but frequently biradial, and the also coeval tetraradial carinachitids, appear to provide morphological intermediates, however. More significantly, the periderm of Recent coronate scyphozoan polyps (the basis for the proposed cnidarian affinity of conulariids) forms annulated chitinous tubes with circular cross section and fine longitudinal striations, that is, closely similar to Olivooides tests.

Similarities also exist with certain aschelminths, in particular the loricate priapulid larvae. Priapulids constitute a small living phylum with a fairly diverse Cambrian record. Although bilaterians, they show both tetraradial and pentaradial symmetry in parts of their anatomy, and the processes called scalids are formed by soft cuticle overlying a ciliated epithelium, somewhat similar to what is envisaged for the stellate tissue of Olivooides. Priapulid adults and larvae, however, have a straight gut, and the larval lorica has an apical pore, in contrast to the closed apex of Olivooides, hexangulaconulariids, conulariids, and scyphozoan polyp tubes.

Priapulids – members of the phylum Priapulida – are ecdysozoans (they moult their cuticle, in common with Onychophorans and Arthropods) possessing very many unusual traits despite numbering only about 15 different species. Extreme diversity between a few species suggests that they once were much more numerous and evolutionarily successful, but represent only a remnant of that diversity today. (Read more about pripulids.)

On balance, Bengtson & Zhao 1997 considers that Olivooides is more likely related to cnidarians than to priapulids.

Phylum Cnidaria Hatschek 1888

? Scyphozoa

Genus Olivooides Qian 1977

Occurrence: Representatives of the genus, usually listed as Olivooides sp., have been reported from:

Dengying Formation at Shizhonggou, Ningqiang County, Shaanxi, China (Brasier 1989, p. 47, Zhang and Pratt 1994, Bengtson & Zhao 1997)
Dengying Formation at Meishucun, Jinning, eastern Yunnan, China (Brasier 1989, fig. 3.2 and p. 43)
Lower Tal Formation at the Ganga Valley, Lesser Himalaya, India (Brasier 1989, p. 52)
Soltanieh Formation at Elburz Mountains, Iran (Brasier 1989, fig. 3.9 and p. 55)

Olivooides multisulcatus Qian 1977

	1977	Olivooides Qian
	1980	Punctatus He
	1984	Pyrgites Yue

Description: Globules interpreted as embryos (fig. 2A) range in size from 0.28 to 0.73 mm, suggesting that a number of taxa may be present in the material. The embryos which can be more confidently attributed to Olivooides are apparently represented by embryos, 0.60 to 0.87 mm in diameter, consisting mainly of nonannulated stellate tissue underlying a smooth outer membrane. A narrow region of tightly folded nonstellate tissue is sometimes visible around a constricted aperture.

The globules interpreted as the last prehatching stage of the animal show all the features of the conical form described as Punctatus He 1980, but molded into a spherical structure 0.68 to 0.87 mm in diameter. The area around one pole has an annulated surface beset with stellae, and around the opposite pole there is a tightly folded, finely striated tissue surrounding a rounded aperture. Allowing for the deformation of a flexible cuticle within a spherical egg membrane, the globular fossils are identical with the smallest conical "Punctatus."

The hatched animal is conical, with rounded cross section and distinct transverse annulations (figs. 1A and B).

The test shows evidence of having been flexible: It is commonly distorted without fracturing, and the surface is typically thrown into folds. The stellate cuticle has the appearance of a thin and flexible tissue being draped over a surface with regular sharp protrusions, about 50 痠 apart.

A characteristic surface pattern of star-shaped projections, stellae, in the apical part is replaced in the more apertural parts by fine longitudinal striae (fig. 1B). Growth seems to have taken place by addition of striated tissue: Smaller specimens are dominated by stellate tissue, whereas larger ones may have half or more of the surface covered by striae. The apical part, before the first annulation, has a pentaradial pattern of folds.

The largest specimen is 3.3 mm long.

(A)

(B)

Fig. 2: Reproduction of figs. 1J and K from Bengtson & Zhao 1997, SEM images depicting Olivooides multisulcatus from the basal Cambrian Dengying Formation exposed in the Shizhonggou section. Samples are NGMC (National Geological Museum of China) 9359 and CAGS (Chinese Academy of Geological Sciences) 32372; the scale is the same in both images, scale bar in (A) is 500痠.

Occurrence: Olivooides multisulcatus is known to occur in the Dengying Formation at Shizhonggou, Ningqiang County, Shaanxi, China (Brasier 1989, p. 47, Zhang and Pratt 1994, Bengtson & Zhao 1997).

It is possible that other reports of "Olivooides sp." (see above) may also represent occurrences of this species.

Discussion: Co-occurring globules have a more or less regular polygonal surface pattern reflecting internal compartmentalization. Although this simple pattern may conceivably have arisen by nonbiological processes, the specimens occur with undoubted Olivooides embryos and, furthermore, faithfully duplicate the morphology of modern metazoan embryos undergoing cleavage. Bengtson & Zhao 1997 interprets them as early cleavage stages with preserved blastomere boundaries. Although Olivooides is likely to be represented in this material, the size variation (0.28 to 0.73 mm) of these embryos suggests that other taxa may also be present.

Somewhat irregularly shaped embryos with a distinct polygonal pattern seem to represent stages with a few hundreds to a few thousands of cells. More regular spheres may represent the 64- to 256-cell stages. One specimen is known which has a cellular pattern radiating from a pit. Bengtson & Zhao 1997 interprets this fossil as a gastrula formed by polar ingression.

A broken-open specimen reveals that the surface polygons extend as a prismatic layer toward a central hollow; this is similar to the packing of blastomeres around a blastocoel in, for example, sea urchin coeloblastulas.

Earlier cleavage stages (fewer than about 64 cells) have not been identified with certainty.

(A)

Fig. 3: (A) Reproduction of fig. 1A from Bengtson & Zhao 1997, a SEM image depicting a suggested metazoan embryo – possibly Olivooides multisulcatus – at approximately the 256-cell stage. Sample is NGMC (National Geological Museum of China) 9351 from the basal Cambrian Dengying Formation exposed in the Shizhonggou section, Shaanxi Province, China; scale is 500痠.

Development: The large, spherical eggs with clearly recognizable embryos indicate that Olivooides had direct development, a large yolk content, and no free larval stage. If a planula stage is at all present in Olivooides (given the cnidarian interpretation), it is cuticularized and occurs within an egg membrane; what hatches appears to be a loricate polyp. Although it cannot be ruled out that the hatched specimens represent larvae rather than juveniles, the evidence suggests that size increased regularly after hatching, and there is no sign of metamorphosis.

This mode of development is not typical of marine cnidarians, which normally have a free-swimming planula larva from which a polyp (or in some cases a medusa) develops. However, in several marine cnidarians, the blastopore persists at the site of the future mouth during early planula stages; at the opposite end – the site of future attachment – there are concentrations of gland cells having a single cilium surrounded by villi. Thus, the stellate embryonic stages could correspond to a cuticularized "planula" contained within the egg membrane; metamorphosis is then subdued by the direct transformation of the blastopore into a mouth and the early establishment of a coelenteron. The stellate pattern of the cuticle may then reflect underlying gland cells with cilia surrounded by villi.

relevant section from near the end of Chen et al.

References

Bengtson, Stefan; Yue, Zhao 1997: Fossilized Metazoan Embryos from the Earliest Cambrian. Science 277: 1645-1648.

Brasier, M.D. 1989: China and the Palaeotethyan Belt (India, Pakistan, Iran, Kazakhstan, and Mongolia). In Cowie, J.W. and Brasier, M.D. (eds.) The Precambrian-Cambrian Boundary, pp. 40-74. Clarendon Press.

Qian, Y. 1977: [Hyolitha and some Problematica from the Lower Cambrian Meishucun Stage in Central and Southwest China.] Acta Palaeontol. Sinica 16: 255-278. [In Chinese.]

Zhang, Xi-guang; Pratt, Brian R. 1994: Middle Cambrian Arthropod Embryos with Blastomeres. Science 266: 637-639

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