The first edrioasteroid echinoderm from the lower Cambrian Chengjiang biota of Yunnan Province, China

Zhao, Jun; Rahman, Imran A.; Zamora, Samuel; Chen, Ailin; Peng, Cong

doi:10.1002/spp2.1465

Cited by 3 publications

(1 citation statement)

References 31 publications

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“…Given the phylogenetic distribution of these morphologies, we interpret the protocrinoid expressions to include deep-seated apomorphies of radial echinoderms, plesiomorphic at the level of blastozoans and crinoids. Even the early Cambrian pentaradial echinoderm, Sprinkleglobus , shows many of these expressions (Zhao et al, 2022). Details further support this conclusion, but not the inference that primary-secondary plating represents a synapomorphy exclusive to blastozoans and crinoids (e.g., Ausich et al, 2015a).…”

Section: Character Evolution Links Early Radial Echinoderms To Protoc...mentioning

confidence: 99%

Crinoid calyx origin from stem radial echinoderms

2023

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Evidence from the earliest-known crinoids (Tremadocian, Early Ordovician), called protocrinoids, is used to hypothesize initial steps by which elements of the calyx evolved. Protocrinoid calyces are composed of extraxial primary and surrounding secondary plates (both of which have epispires along their sutures) that are unlike those of more crownward fossil and extant crinoids in which equivalent calycinal plating is strongly organized. These reductions inspired several schemes by which to name the plates in these calyces. However, the primary-secondary systems seen in protocrinoids first appeared among Cambrian stem radial echinoderms, with primaries representing centers around which secondaries were sequentially added during ontogeny. Therefore, the protocrinoid calyx represents an intermediate condition between earliest echinoderms and crownward crinoids. Position and ontogeny indicate certain primaries remained as loss of secondaries occurred, resulting in abutting of primaries into the conjoined alternating circlets characteristic of crinoids. This transformative event included suppression of secondary plating and modification or, more commonly, elimination of respiratory structures. These data indicate subradial calyx plate terminology does not correspond with most common usage, but rather, supports an alternative redefinition of these traditional expressions. Extension and adoral growth of fixed rays during calyx ontogeny preceded conjoined primaries in earliest crinoids. Restriction with modification or elimination of calyx respiratory structures also accompanied this modification. Phylogenetic analyses strongly support crinoid origination from early pentaradiate echinoderms, separate from blastozoans. Accordingly, all Tremadocian crinoids express a distinctive aggregate of plesiomorphic and apomorphic commonalities; all branch early within the crinoid clade, separate from traditional subclass-level clades. Nevertheless, each taxon within this assemblage expresses at least one diagnostic apomorphy of camerate, cladid, or disparid clades.

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Section: Character Evolution Links Early Radial Echinoderms To Protoc...mentioning

confidence: 99%

Crinoid calyx origin from stem radial echinoderms

2023

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Adaptations to changing substrates in diploblastic dinomischids from the early Cambrian

Zhao,

Chen,

Klug

et al. 2024

Palaeogeography, Palaeoclimatology, Palaeoecology

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Origin and Early Evolution of Echinoderms

Rahman,

Zamora

2024

Annual Review of Earth and Planetary Sciences

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Echinoderms are a major group (phylum) of invertebrate animals with a rich fossil record stretching back to the Cambrian period, approximately 518 million years ago. While all modern species are characterized by pentaradial (i.e., fivefold) symmetry, Cambrian echinoderms also include taxa with different types of symmetry (e.g., bilateral symmetry). These distinct forms were present from very early in the phylum's history, demonstrating that the initial diversification of echinoderm body plans was extremely rapid. The phylogenetic relationships of Cambrian echinoderms have long been debated, hindering efforts to reconstruct the evolution of the phylum, but recent analyses have consistently recovered bilaterally symmetrical forms as the earliest-diverging echinoderms. This reveals the sequence of character acquisition in echinoderm evolution, indicating that radial symmetry is a derived character of the group, which evolved after the acquisition of a mineralized skeleton. Cambrian echinoderms were adapted to diverse modes of life, with ecology an important factor shaping their early evolution. However, the reasons why echinoderms evolved their unique pentaradial body plan remain unclear. ▪ The Cambrian fossil record provides valuable insights into the origin and early evolution of echinoderms over half a billion years ago. ▪ Cambrian echinoderms were morphologically diverse, with several extinct groups exhibiting character combinations that distinguish them from living species. ▪ Phylogenetic analyses of bilateral, asymmetrical, triradial, and pentaradial fossils have allowed us to decipher the assembly of the modern echinoderm body plan. ▪ Echinoderms became ecologically diverse early in their history, with varied modes of feeding, locomotion, and attachment. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 52 is May 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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The first edrioasteroid echinoderm from the lower Cambrian Chengjiang biota of Yunnan Province, China

Cited by 3 publications

References 31 publications

Crinoid calyx origin from stem radial echinoderms

Crinoid calyx origin from stem radial echinoderms

Adaptations to changing substrates in diploblastic dinomischids from the early Cambrian

Origin and Early Evolution of Echinoderms

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