An early Cambrian polyp reveals an anemone-like ancestor for medusozoan cnidarians

Extant cnidarians are a disparate phylum of non-bilaterians and their diploblastic body plan represents a key step in animal evolution. Anthozoans (anemones, corals) are benthic polyps, while adult medusozoans (jellyfishes) are dominantly pelagic medusae. A sessile polyp is present in both groups and is widely conceived as the ancestral form of their last common ancestor. However, the nature and anatomy of this ancestral polyp, particularly of medusozoans, are controversial, owing to the divergent body plans of both groups in the extant lineages and the rarity of medusozoan soft tissues in the fossil record. Here we redescribe the enigmatic Conicula striata Luo et Hu from the early Cambrian Chengjiang biota, south China, which has previously been interpreted as a polyp, lophophorate or deuterostome. We show that C. striata possessed features of both anthozoans and medusozoans. Its stalked polyp and fully encasing conical, annulated organic skeleton (periderm) are features of medusozoans. However, the gut is partitioned by ~28 mesenteries, and has a tubular pharynx, resembling anthozoans. Our phylogenetic analysis recovers C. striata as a stem medusozoan, indicating that the enormously diverse medusozoans were derived from an anemone-like ancestor, with the pharynx lost and number of mesenteries reduced prior to the origin of crown group Medusozoa.

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Ancestral morphology of Ecdysozoa constrained by an early Cambrian stem group ecdysozoan

BMC Evolutionary Biology ◽

10.1186/s12862-020-01720-6 ◽

2020 ◽

Vol 20 (1) ◽

Author(s):

Richard J. Howard ◽

Gregory D. Edgecombe ◽

Xiaomei Shi ◽

Xianguang Hou ◽

Xiaoya Ma

Keyword(s):

Feeding Strategy ◽

Phylogenetic Analyses ◽

Morphological Diversity ◽

Early Cambrian ◽

Ancestral State ◽

Crown Group ◽

Stem Group ◽

Chengjiang Biota ◽

Fossil Records ◽

Experimental Decay

Abstract Background Ecdysozoa are the moulting protostomes, including arthropods, tardigrades, and nematodes. Both the molecular and fossil records indicate that Ecdysozoa is an ancient group originating in the terminal Proterozoic, and exceptional fossil biotas show their dominance and diversity at the beginning of the Phanerozoic. However, the nature of the ecdysozoan common ancestor has been difficult to ascertain due to the extreme morphological diversity of extant Ecdysozoa, and the lack of early diverging taxa in ancient fossil biotas. Results Here we re-describe Acosmia maotiania from the early Cambrian Chengjiang Biota of Yunnan Province, China and assign it to stem group Ecdysozoa. Acosmia features a two-part body, with an anterior proboscis bearing a terminal mouth and muscular pharynx, and a posterior annulated trunk with a through gut. Morphological phylogenetic analyses of the protostomes using parsimony, maximum likelihood and Bayesian inference, with coding informed by published experimental decay studies, each placed Acosmia as sister taxon to Cycloneuralia + Panarthropoda—i.e. stem group Ecdysozoa. Ancestral state probabilities were calculated for key ecdysozoan nodes, in order to test characters inferred from fossils to be ancestral for Ecdysozoa. Results support an ancestor of crown group ecdysozoans sharing an annulated vermiform body with a terminal mouth like Acosmia, but also possessing the pharyngeal armature and circumoral structures characteristic of Cambrian cycloneuralians and lobopodians. Conclusions Acosmia is the first taxon placed in the ecdysozoan stem group and provides a constraint to test hypotheses on the early evolution of Ecdysozoa. Our study suggests acquisition of pharyngeal armature, and therefore a change in feeding strategy (e.g. predation), may have characterised the origin and radiation of crown group ecdysozoans from Acosmia-like ancestors.

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Evolution and function of the hominin forefoot

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1800818115 ◽

2018 ◽

Vol 115 (35) ◽

pp. 8746-8751 ◽

Cited By ~ 7

Author(s):

Peter J. Fernández ◽

Carrie S. Mongle ◽

Louise Leakey ◽

Daniel J. Proctor ◽

Caley M. Orr ◽

...

Keyword(s):

Soft Tissues ◽

Common Ancestor ◽

Bipedal Locomotion ◽

Last Common Ancestor ◽

Primary Role ◽

Anthropoid Primates ◽

And Function ◽

Metatarsophalangeal Joints ◽

Selection Of

The primate foot functions as a grasping organ. As such, its bones, soft tissues, and joints evolved to maximize power and stability in a variety of grasping configurations. Humans are the obvious exception to this primate pattern, with feet that evolved to support the unique biomechanical demands of bipedal locomotion. Of key functional importance to bipedalism is the morphology of the joints at the forefoot, known as the metatarsophalangeal joints (MTPJs), but a comprehensive analysis of hominin MTPJ morphology is currently lacking. Here we present the results of a multivariate shape and Bayesian phylogenetic comparative analyses of metatarsals (MTs) from a broad selection of anthropoid primates (including fossil apes and stem catarrhines) and most of the early hominin pedal fossil record, including the oldest hominin for which good pedal remains exist, Ardipithecus ramidus. Results corroborate the importance of specific bony morphologies such as dorsal MT head expansion and “doming” to the evolution of terrestrial bipedalism in hominins. Further, our evolutionary models reveal that the MT1 of Ar. ramidus shifts away from the reconstructed optimum of our last common ancestor with apes, but not necessarily in the direction of modern humans. However, the lateral rays of Ar. ramidus are transformed in a more human-like direction, suggesting that they were the digits first recruited by hominins into the primary role of terrestrial propulsion. This pattern of evolutionary change is seen consistently throughout the evolution of the foot, highlighting the mosaic nature of pedal evolution and the emergence of a derived, modern hallux relatively late in human evolution.

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Platypus immunoglobulin M and the divergence of the two extant monotreme lineages

Australian Mammalogy ◽

10.1071/am03087 ◽

2003 ◽

Vol 25 (1) ◽

pp. 87 ◽

Cited By ~ 8

Author(s):

K Belov ◽

L Hellman

Keyword(s):

Phylogenetic Analysis ◽

Amino Acid ◽

Common Ancestor ◽

Variable Region ◽

Immunoglobulin M ◽

Last Common Ancestor ◽

Constant Region ◽

Sequence Comparisons ◽

Level Sequence ◽

High Level

A full-length cDNA clone encoding the platypus (Ornithorynchus anatinus) immunoglobulin M (IgM) heavy chain was isolated from a spleen cDNA library using a short-beaked echidna (Tachyglossus aculeatus) IgM constant region (Cµ) probe. The isolation of platypus IgM shows that O. anatinus, like all other examined jawed vertebrates, express a classical IgM molecule. Amino acid sequence comparisons of the constant regions of IgM reveals a high level sequence conservation between O. anatinus and T. aculeatus sequences (87%), and only approximately 48% identity between O. anatinus and therian Cµ sequences. The variable region of this clone belongs to clan 3, supporting the view that this family is used preferentially, if not exclusively by O. anatinus, as opposed to the use of all three variable region clans by T. aculeatus. Phylogenetic analysis of Cµ sequences supports the traditional Theria hypothesis and suggests that the O. anatinus and T. aculeatus lineages separated from their last common ancestor approximately 21 million years ago.

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A flagellate-to-amoeboid switch in the closest living relatives of animals

10.1101/2020.06.26.171736 ◽

2020 ◽

Cited By ~ 2

Author(s):

Thibaut Brunet ◽

Marvin Albert ◽

William Roman ◽

Danielle C. Spitzer ◽

Nicole King

Keyword(s):

Epithelial Cells ◽

Common Ancestor ◽

Cell Types ◽

Cell Phenotype ◽

Last Common Ancestor ◽

Animal Evolution ◽

Amoeboid Motility ◽

History Of ◽

Different Cell Types ◽

Amoeboid Cells

The evolution of different cell types was a key process of early animal evolution1–3. Two fundamental cell types, epithelial cells and amoeboid cells, are broadly distributed across the animal tree of life4,5 but their origin and early evolution are unclear. Epithelial cells are polarized, have a fixed shape and often bear an apical cilium and microvilli. These features are shared with choanoflagellates – the closest living relatives of animals – and are thought to have been inherited from their last common ancestor with animals1,6,7. The deformable amoeboid cells of animals, on the other hand, seem strikingly different from choanoflagellates and instead evoke more distantly related eukaryotes, such as diverse amoebae – but it has been unclear whether that similarity reflects common ancestry or convergence8. Here, we show that choanoflagellates subjected to spatial confinement differentiate into an amoeboid phenotype by retracting their flagella and microvilli, generating blebs, and activating myosin-based motility. Choanoflagellate cell crawling is polarized by geometrical features of the substrate and allows escape from confined microenvironments. The confinement-induced amoeboid switch is conserved across diverse choanoflagellate species and greatly expands the known phenotypic repertoire of choanoflagellates. The broad phylogenetic distribution of the amoeboid cell phenotype across animals9–14 and choanoflagellates, as well as the conserved role of myosin, suggests that myosin-mediated amoeboid motility was present in the life history of their last common ancestor. Thus, the duality between animal epithelial and crawling cells might have evolved from a temporal phenotypic switch between flagellate and amoeboid forms in their single-celled ancestors3,15,16.

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Spinopelvic pathways to bipedality: why no hominids ever relied on a bent-hip–bent-knee gait

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2010.0112 ◽

2010 ◽

Vol 365 (1556) ◽

pp. 3289-3299 ◽

Cited By ~ 61

Author(s):

C. Owen Lovejoy ◽

Melanie A. McCollum

Keyword(s):

Fossil Record ◽

Vertebral Column ◽

Common Ancestor ◽

Last Common Ancestor ◽

Early Hominid ◽

African Apes ◽

Locomotor Pattern

Until recently, the last common ancestor of African apes and humans was presumed to resemble living chimpanzees and bonobos. This was frequently extended to their locomotor pattern leading to the presumption that knuckle-walking was a likely ancestral pattern, requiring bipedality to have emerged as a modification of their bent-hip-bent-knee gait used during erect walking. Research on the development and anatomy of the vertebral column, coupled with new revelations from the fossil record (in particular, Ardipithecus ramidus ), now demonstrate that these presumptions have been in error. Reassessment of the potential pathway to early hominid bipedality now reveals an entirely novel sequence of likely morphological events leading to the emergence of upright walking.

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New mid-Cretaceous cryptic slime mold beetles and the early evolution of Sphindidae (Coleoptera: Cucujoidea)

Arthropod Systematics & Phylogeny ◽

10.3897/asp.79.e72724 ◽

2021 ◽

Vol 79 ◽

pp. 587-597

Author(s):

Yan-Da Li ◽

Erik Tihelka ◽

Zhen-Hua Liu ◽

Di-Ying Huang ◽

Chen‑Yang Cai

Keyword(s):

Phylogenetic Analysis ◽

Fossil Record ◽

Slime Mold ◽

Early Evolution ◽

Calibration Point ◽

Crown Group ◽

Slime Molds ◽

The Family ◽

Group Members

Abstract The cryptic slime mold beetles, Sphindidae, are a moderately diverse cucujoid beetle family, whose members are obligately tied to slime molds throughout their life. The fossil record of sphindid beetles is sparse; stem-sphindids and crown-group members of uncertain systematic placement have been reported from Cretaceous ambers. Here we review the Mesozoic fossil record of Sphindidae and report a new sphindid genus and species, Trematosphindus newtonigen. et sp. nov., from Albian/Cenomanian amber from northern Myanmar (ca. 99 Ma). Trematosphindus is set apart from all other sphindids by the presence of distinct lateral cavities on the anterior pronotal angles. Our phylogenetic analysis identifies Trematosphindus as an early-diverging genus within Sphindidae, sister to the remainder of the family except Protosphindus, or Protosphindus and Odontosphindus. The new fossils provide evidence that basal crown slime mold beetles begun to diversify by the mid-Cretaceous, providing a valuable calibration point for understanding timescale of sphindid co-evolution with slime molds.

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The last common ancestor of most bilaterian animals possessed at least 9 opsins

10.1101/052902 ◽

2016 ◽

Cited By ~ 1

Author(s):

MD Ramirez ◽

AN Pairett ◽

MS Pankey ◽

JM Serb ◽

DI Speiser ◽

...

Keyword(s):

Gene Family ◽

Complex Traits ◽

Common Ancestor ◽

Opsin Gene ◽

Last Common Ancestor ◽

Phylogenetic Information ◽

Animal Evolution ◽

Animal Phyla ◽

Evolution Understanding

AbstractThe opsin gene family encodes key proteins animals use to sense light and has expanded dramatically since it originated early in animal evolution. Understanding the origins of opsin diversity can offer clues to how separate lineages of animals have repurposed different opsin paralogs for different light-detecting functions. However, the more we look for opsins outside of eyes and from additional animal phyla, the more opsins we uncover, suggesting we still do not know the true extent of opsin diversity, nor the ancestry of opsin diversity in animals. To estimate the number of opsin paralogs present in both the last common ancestor of the Nephrozoa (bilaterians excluding Xenoacoelomorpha), and the ancestor of Cnidaria + Bilateria, we reconstructed a reconciled opsin phylogeny using sequences from 14 animal phyla, especially the traditionally poorly-sampled echinoderms and molluscs. Our analysis strongly supports a repertoire of at least nine opsin paralogs in the bilaterian ancestor and at least four opsin paralogs in the last common ancestor of Cnidaria + Bilateria. Thus, the kernels of extant opsin diversity arose much earlier in animal history than previously known. Further, opsins likely duplicated and were lost many times, with different lineages of animals maintaining different repertoires of opsin paralogs. This phylogenetic information can inform hypotheses about the functions of different opsin paralogs and be used to understand how and when opsins were incorporated into complex traits like eyes and extraocular sensors.

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Discovery of the oldest bilaterian from the Ediacaran of South Australia

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2001045117 ◽

2020 ◽

Vol 117 (14) ◽

pp. 7845-7850 ◽

Cited By ~ 7

Author(s):

Scott D. Evans ◽

Ian V. Hughes ◽

James G. Gehling ◽

Mary L. Droser

Keyword(s):

Fossil Record ◽

Common Ancestor ◽

South Australia ◽

Trace Fossils ◽

Last Common Ancestor ◽

Ediacara Biota ◽

Size And Morphology ◽

Animal Communities ◽

Critical Link ◽

Anterior Posterior

Analysis of modern animals and Ediacaran trace fossils predicts that the oldest bilaterians were simple and small. Such organisms would be difficult to recognize in the fossil record, but should have been part of the Ediacara Biota, the earliest preserved macroscopic, complex animal communities. Here, we describeIkaria wariootiagen. et sp. nov. from the Ediacara Member, South Australia, a small, simple organism with anterior/posterior differentiation. We find that the size and morphology ofIkariamatch predictions for the progenitor of the trace fossilHelminthoidichnites—indicative of mobility and sediment displacement. In the Ediacara Member,Helminthoidichnitesoccurs stratigraphically below classic Ediacara body fossils. Together, these suggest thatIkariarepresents one of the oldest total group bilaterians identified from South Australia, with little deviation from the characters predicted for their last common ancestor. Further, these trace fossils persist into the Phanerozoic, providing a critical link between Ediacaran and Cambrian animals.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1701650114 ◽

2017 ◽

Vol 114 (33) ◽

pp. 8835-8840 ◽

Cited By ~ 11

Author(s):

Qiang Ou ◽

Jian Han ◽

Zhifei Zhang ◽

Degan Shu ◽

Ge Sun ◽

...

Keyword(s):

Common Ancestor ◽

Phylogenetic Analyses ◽

Body Cavity ◽

Body Plan ◽

Feeding Strategies ◽

Last Common Ancestor ◽

Gastric Cavity ◽

The Past ◽

Basal Disk ◽

Chengjiang Biota

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 stem-group 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 total-group Cnidaria is greater than previously assumed.

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Vase-shaped microfossils from the Neoproterozoic Chuar Group, Grand Canyon: A classification guided by modern testate amoebae

Journal of Paleontology ◽

10.1017/s0022336000044140 ◽

2003 ◽

Vol 77 (3) ◽

pp. 409-429 ◽

Cited By ~ 76

Author(s):

Susannah M. Porter ◽

Ralf Meisterfeld ◽

Andrew H. Knoll

Keyword(s):

New Species ◽

Common Ancestor ◽

Grand Canyon ◽

Morphological Diversity ◽

Testate Amoebae ◽

Black Shales ◽

Last Common Ancestor ◽

New Genera ◽

Hexagonal Symmetry ◽

Crown Group

Vase-shaped microfossil (VSM) assemblages from early diagenetic carbonate nodules in >742 ± 6 Ma black shales of the Chuar Group, Grand Canyon, provide evidence for affinities with testate amoebae. Not only are VSMs exceptionally preserved in Chuar rocks, they exhibit a much higher degree of morphological diversity than was previously known. Using the taxonomy of modern testate amoebae as a guide, nine new species and eight new genera of VSMs are described, augmenting the eight species and two genera already recognized. Taxa described here areMelanocyrillium hexodiademaBloeser, 1985,Trigonocyrillium horodyskii(Bloeser, 1985) n. comb.,T. fimbriatum(Bloeser, 1985) n. comb.,Cycliocyrillium simplexn. sp.,C. torquatan. sp.,Bonniea dacrucharesn. sp.,B. pytinaian. sp.,Trachycyrillium pudensn. sp.,Palaeoarcella athanatan. sp.,Hemisphaeriella ornatan. sp.,Bombycion micronn. sp., andMelicerion poikilonn. sp. All of the test characters observed in VSM taxa (e.g., collars; indentations; hexagonal symmetry; lobed, triangular or invaginated apertures; curved necks) occur in modern testate amoeban taxa, though not always in the same combinations. Some VSM species have characters found today in diverse extant taxa, making it difficult to assess their relationships. A few species, however, have character combinations that closely approximate those found in specific genera of both lobose and filose testate amoebae, suggesting that at least stem group, and possibly crown group, representatives of these taxa were present ∼742 Ma.These fossils indicate that ecosystems were diverse and complex, that eukaryotic biomineralization had already evolved, and that the last common ancestor of animals+fungi had already appeared by ∼750 Ma.

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