Problematica old and new

Jenner, Ronald A.; Littlewood, D. Timothy J.

doi:10.1098/rstb.2007.2240

Cited by 54 publications

(24 citation statements)

References 91 publications

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“…As one can immediately recognize, this list comprises many so-called Problematica, i.e. groups of currently or historically controversial phylogenetic position (see Jenner and Littlewood 2008). 9 These taxa show so many evolutionary changes and lack apparent similarities to other groups that, according to type and Bauplan concepts of all sorts which stress differences (see Scholtz , 2009, they are sometimes classified as 'separate groups'.…”

Section: Darwin -Deconstructing Laws Of Form Types and Bauplä Nementioning

confidence: 99%

Deconstructing morphology

Scholtz¹

2009

Acta Zoologica

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Scholtz, G. 2010. Deconstructing morphology. -Acta Zoologica (Stockholm) 91: 44-63Morphology as the science of form is, in particular, related to the overwhelming diversity of animal forms. Due to its long pre-Darwinian tradition, organismic morphology is partly burdened by ahistorical typological views. On the other hand, the study of organismic form has always implied concepts of transformation, which helped to pave the way for evolutionary theories. This contradictory history and the fact that we need words to describe organismic form lead in many cases to morphological concepts implying a mixture of structural, functional, developmental, ecological, typological, and evolutionary aspects in current morphological approaches. Because these mixed views lead to contradictory and misleading interpretations of animal form, I stress the need to deconstruct morphological concepts at all levels. I propose a morphology that analyses transformation of animal forms strictly at the structural level in combination with genealogical thinking. Function and other biological aspects of form should be considered in an independent second analytical step. A comparative pattern approach, including developmental patterns, of animal structure in an evolutionary framework allows for the analysis of morphological change, in particular, phylogenetic reconstructions, homology assessment, and the recognition of evolutionary independent morphological units.

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Section: Darwin -Deconstructing Laws Of Form Types and Bauplä Nementioning

confidence: 99%

Deconstructing morphology

Scholtz¹

2009

Acta Zoologica

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“…Present debate centres on two competing hypotheses that place Correspondence to: Kate L. Sanders. E-mail: kate.sanders@ adelaide.edu.au pentastomids either with branchiuran crustaceans (ectoparasitic 'fish lice': a grouping termed 'Ichthyostraca'; Zrzavý et al, 1998), or outside (eu)arthropods (Waloszek et al, 2006;Almedia et al, 2008;Jenner & Littlewood, 2008). Sperm ultrastructure (Wingstrand, 1972;Riley et al, 1978;Jamieson & Storch, 2000) and ribosomal and mitochondrial DNA (Abele et al, 1989;Spears & Abele, 1998;Lavrov et al, 2004;Møller et al, 2008) unite pentastomids with branchiuran crustaceans, and thus nest them within crustacean arthropods.…”

Section: Introductionmentioning

confidence: 99%

Arthropod molecular divergence times and the Cambrian origin of pentastomids

Sanders

Lee

2010

Systematics and Biodiversity

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Pentastomida are parasites of tetrapods (especially reptiles) and have had long contentious relationships. Traditionally seen as a separate phylum with arthropod affinities, recent ultrastructural and molecular evidence unites them to branchiuran crustaceans (fish lice). However, the discovery of Cambrian pentastomids has been interpreted to refute the view that pentastomids are closely related to advanced crustaceans (of presumably recent origins). Bayesian phylogenetic and relaxed-clock analyses of molecular data (18S and 28S ribosomal RNA, elongation factor 1α and 2, RNA polymerase II subunit) help reconcile these apparently contradictory views: a pentastomid-branchiuran grouping is recovered, but this clade is the sister group to other Tetraconata, whereas all other crustaceans form a monophyletic group that is sister to hexapods. Crustacean monophyly is widely supported by morphology, but has rarely been retrieved in other molecular studies. Estimated molecular dates for pentastomid origins range from ∼490 to ∼520 million years ago, consistent with Cambrian fossils. The basal position of branchiurans within tetraconatans means pentastomids can be simultaneously related to branchiurans, and also have a deep fossil record. All Cambrian pentastomids are tiny, resembling the larvae of living pentastomids that infect intermediate hosts including fish; as definitive hosts (tetrapods) of modern pentastomids were absent in the Cambrian, it is possible that the small Cambrian forms were adults rather than larvae, and their entire life cycle was confined to small fish-like vertebrates that were then present.

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“…Problematica commonly occur in the fossil record of the Ediacaran and Cambrian (635-484 Mya), during which metazoans underwent a dramatic diversification. Therefore, deciphering fossil problematica from this crucial interval of evolution might provide pivotal insights into the origin and early radiation of metazoan body plans (1). Clarifying the anatomy and phylogenetic placement of some of these problematica has greatly improved our understanding of the evolution of major animal groups such as cnidarians (e.g., refs.…”

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Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity

Han

Zhang

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The early Cambrian problematica Xianguangia sinica, Chengjiangopenna wangii, and Galeaplumosus abilus from the Chengjiang biota (Yunnan, China) have caused much controversy in the past and their phylogenetic placements remain unresolved. Here we show, based on exceptionally preserved material (85 new specimens plus type material), that specimens previously assigned to these three species are in fact parts of the same organism and propose that C. wangii and G. abilus are junior synonyms of X. sinica. Our reconstruction of the complete animal reveals an extinct body plan that combines the characteristics of the three described species and is distinct from all known fossil and living taxa. This animal resembled a cnidarian polyp in overall morphology and having a gastric cavity partitioned by septum-like structures. However, it possessed an additional body cavity within its holdfast, an anchoring pit on the basal disk, and feather-like tentacles with densely ciliated pinnules arranged in an alternating pattern, indicating that it was a suspension feeder rather than a predatory actiniarian. Phylogenetic analyses using Bayesian inference and maximum parsimony suggest that X. sinica is a stemgroup cnidarian. This relationship implies that the last common ancestor of X. sinica and crown cnidarians was probably a benthic, polypoid animal with a partitioned gastric cavity and a single mouth/anus opening. This extinct body plan suggests that feeding strategies of stem cnidarians may have been drastically different from that of their crown relatives, which are almost exclusively predators, and reveals that the morphological disparity of totalgroup Cnidaria is greater than previously assumed.Xianguangia sinica | Chengjiangopenna wangii | Galeaplumosus abilus | ciliary suspension feeder | cnidarian stem group

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Problematica old and new

Cited by 54 publications

References 91 publications

Deconstructing morphology

Deconstructing morphology

Arthropod molecular divergence times and the Cambrian origin of pentastomids

Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity

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