New observations on the skeletons of the earliest bryozoans from the Fenhsiang Formation (Tremadocian, Lower Ordovician), Yichang, China

Ma, Jinshuang; Taylor, Paul D.; Fengsheng, Xia

doi:10.1016/j.palwor.2013.08.002

Cited by 15 publications

(13 citation statements)

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“…Esthonioporates typically have granular to indistinctly lamellar wall microstructures. In some species, endozonal walls are granular but exozonal walls are lamellar, perhaps reflecting neomorphism of faster growing endozonal skeleton with a higher Mg content but retention of the original fabric in the slower growing, low‐Mg walls of the exozone (Ma, Taylor & Xia, 2014 b ).…”

Section: Evolutionary History Of Bryozoan Biomineralizationmentioning

confidence: 99%

Biomineralization in bryozoans: present, past and future

2014

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Many animal phyla have the physiological ability to produce biomineralized skeletons with functional roles that have been shaped by natural selection for more than 500 million years. Among these are bryozoans, a moderately diverse phylum of aquatic invertebrates with a rich fossil record and importance today as bioconstructors in some shallow-water marine habitats. Biomineralizational patterns and, especially, processes are poorly understood in bryozoans but are conventionally believed to be similar to those of the related lophotrochozoan phyla Brachiopoda and Mollusca. However, bryozoan skeletons are more intricate than those of these two phyla. Calcareous skeletons have been acquired independently in two bryozoan clades - Stenolaemata in the Ordovician and Cheilostomata in the Jurassic - providing an evolutionary replicate. This review aims to highlight the importance of biomineralization in bryozoans and focuses on their skeletal ultrastructures, mineralogy and chemistry, the roles of organic components, the evolutionary history of bimineralization in bryozoans with respect to changes in seawater chemistry, and the impact of contemporary global changes, especially ocean acidification, on bryozoan skeletons. Bryozoan skeletons are constructed from three different wall types (exterior, interior and compound) differing in the presence/absence and location of organic cuticular layers. Skeletal ultrastructures can be classified into wall-parallel (i.e. laminated) and wall-perpendicular (i.e. prismatic) fabrics, the latter apparently found in only one of the two biomineralizing clades (Cheilostomata), which is also the only clade to biomineralize aragonite. A plethora of ultrastructural fabrics can be recognized and most occur in combination with other fabrics to constitute a fabric suite. The proportion of aragonitic and bimineralic bryozoans, as well as the Mg content of bryozoan skeletons, show a latitudinal increase into the warmer waters of the tropics. Responses of bryozoan mineralogy and skeletal thickness to oscillations between calcite and aragonite seas through geological time are equivocal. Field and laboratory studies of living bryozoans have shown that predicted future changes in pH (ocean acidification) combined with global warming are likely to have detrimental effects on calcification, growth rate and production of polymorphic zooids for defence and reproduction, although some species exhibit reasonable levels of resilience. Some key questions about bryozoan biomineralization that need to be addressed are identified.

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Section: Evolutionary History Of Bryozoan Biomineralizationmentioning

confidence: 99%

Biomineralization in bryozoans: present, past and future

2014

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“…8 m.y. from the younger specimens in the upper Tremadocian of China (Zia et al, 2007; Ma et al, 2013), and restores the confidently established oldest fossils of the penantulaceans to a much younger, Mesozoic interval (Fig. 5).…”

Section: Discussionmentioning

confidence: 52%

“…This zooarium consists of a stem-like 14-hedron composed of at least one or two generations of autozooids with an axial zooid and no extrazooecial structures. Pywackia shows that calcareous biomineralization and the specialized zooid polymorphs of later bryozoans, including the younger late Tremadocian trepostomes and cryptostomes of South China (Xia et al, 2007; Ma et al, 2013), appeared at least eight million years earlier in the history of bryozoan evolution (Fig. 5).…”

Section: Pywackia and Early Bryozoan Evolutionmentioning

confidence: 99%

“…Although repeatedly refered to as the oldest unequivocal bryozoans (Xia et al, 2007, p. 1308; Taylor et al, 2013, Ma et al, 2013), early Ordovician bryozoans from South China are about 8 m.y. younger than Pywackia (Fig.…”

Section: Pywackia and Early Bryozoan Evolutionmentioning

confidence: 99%

“…Two major metazoan groups are peculiar in their seeming absence in the CER and later in the Cambrian; these include the phylum Bryozoa Ehrenberg, 1831, and the coelenterate subclass Octocorallia Haeckel, 1866. The bryozoans have been said to have ‘missed’ the Cambrian radiation and only appeared later in the Early, but not earliest, Ordovician (Taylor and Ernst, 2001, 2004; Xia et al, 2007; Ma et al, 2013). On the other hand, octocorals, particularly the sea pens or sea pencils (order Pennatulacea Verrill, 1865), have a tradition of being regarded as a very archaic metazoan group (e.g., Kölliker, 1880), and pennatulaceans have often been reported in terminal Precambrian (Ediacaran) and Paleozoic fossil assemblages.…”

Section: Introductionmentioning

confidence: 99%

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Distinguishing Earth’s oldest known bryozoan (Pywackia, late Cambrian) from pennatulacean octocorals (Mesozoic–Recent)

Landing¹,

Antcliffe²,

Brasier

et al. 2015

J. Paleontol.

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Bryozoans and all biomineralized metazoan phyla extend back into the Cambrian.PywackiaLanding, 2010 is confirmed as a secondarily phosphatized, late Cambrian stenolaemate bryozoan with colonial habit; mineralized zooarium (originally calcareous); granular/rarely granular-prismatic histology of its trilamellar walls; and polymorphism shown by deep autozooecia with diaphragms and hemiphragms, axial zooecia with diaphragms, and probable nanozooecia. The irregular form ofPywackiareflects growth as a 14-hedron that could not branch and a lack of structures such as thickened walls or styles that maintain regular autozooecial spacing in later stenolaemates.Pywackiais a stem group stenolaemate with a stolon modified into a budding axial zooid and autozooid budding. It is morphologically simpler than the highly evolved late Tremadocian bryozoans of South China with features such as styles, cystiphragms, thickened zooecial walls, and massive or branching colonies. As with some bryozoans,Pywackialacks holdfasts but has lineated living chambers and variably sized autozooecia. The late Cambrian origin of bryozoans, euconodonts, polyplacophorans, and cephalopods set the stage for the Ordovician Radiation’s complex communities.Pywackiais not a pennatulacean octocoral. It lacks both a pennatulacean axial rod histology and a budding zooid that remains confluent with daughter autozooids. Indeed,Pywackiawalled off its axial zooid. Similarity of the 6- and 12-sidedPywackiazooarium with circular to 4-sided pennatulacean axes only includes calcareous composition and the general shapes ofPywackiazooaria and someLituariaaxial rods. The pennatulacean record does not extend from the Mesozoic into the Cambrian, and early cnidarians were not phosphatic. The diagnosis ofPywackiais modified.

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2020

Bryozoan Paleobiology

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New observations on the skeletons of the earliest bryozoans from the Fenhsiang Formation (Tremadocian, Lower Ordovician), Yichang, China

Cited by 15 publications

References 16 publications

Biomineralization in bryozoans: present, past and future

Biomineralization in bryozoans: present, past and future

Distinguishing Earth’s oldest known bryozoan (Pywackia, late Cambrian) from pennatulacean octocorals (Mesozoic–Recent)

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