Echinoderm Evolution Research Articles

Initial quantitative assessment of the enigmatic clade Paracrinoidea (Echinodermata)

AbstractGreat strides have been made in understanding the phylogeny of the five extant echinoderm classes, however, many Palaeozoic groups have yet to be examined in a rigorous, quantitative framework. The aberrant morphologies of Paracrinoidea, an unusual group of Palaeozoic echinoderms, have hindered their inclusion in large‐scale phylogenetic and morphologic studies. This study uses a combined approach of phylogenetic analysis and morphological disparity to elucidate species relationships within the clade. Findings from this study suggest that Paracrinoidea is a monophyletic group and that respiratory structures, oral plate arrangement, and ambulacral morphologies are important for defining subclades within Paracrinoidea. Examination of paracrinoids in a quantitative framework, facilitates their inclusion in larger projects examining Palaeozoic echinoderm evolution, ecology and biogeography.

Origin and Early Evolution of Echinoderms

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.

Calcite-aragonite seas as a driver of echinoderm evolution? Experimental insight and deep-time decoupling

Abstract Seawater magnesium (Mg) and calcium (Ca) have undergone secular fluctuations throughout the Phanerozoic, controlling whether the dominant calcium carbonate precipitant is calcite or aragonite + high-Mg calcite. Although these oscillations in seawater Mg/Ca ratios have been implicated as an important control on Phanerozoic diversification of calcifying marine organisms, determining the degree to which Mg/Ca ratios affected different clades requires integration of experimental data with historical patterns of biodiversity from the fossil record. We explore short-term and long-term responses of echinoderms to shifting calcite-aragonite seas by combining experimental and deep-time biodiversity investigations. While experimental results support a strong relationship between Mg/Ca ratios and short-term echinoderm regeneration rates, patterns of Phanerozoic echinoderm diversification dynamics show no correspondence with Mg/Ca ratios or calcite-aragonite sea transitions. This decoupling between short- and long-term responses of echinoderms to seawater Mg/Ca ratios suggests echinoderms were relatively unaffected by seawater chemistry throughout their evolutionary history, possibly due to their ability to alter skeletal Mg fractionation and/or adapt to gradual shifts in seawater chemistry. Notably, our results indicate a strict uniformitarian extrapolation of experimental results over geological time scales may not be appropriate for many calcifying marine invertebrates. Instead, the effect of seawater Mg/Ca ratios should be evaluated for individual clades using both experimental and deep-time biodiversity data in a time series.

Formation of pentameria and axial symmetry in the evolution of echinoderms

The formation of pentaradial symmetry in the evolution of echinoderms was based on the possibility of the middle–left coelom to terminally forward growth along the anteroposterior axis and the appearance of a second growth vector along the left–right axis during the replication of the formed ambulacra. Both growth vectors were realized into the pentamerism of modern echinoderms due to the development of coelom asymmetry and subsequent torsion associated with the attachment of the larva to the ground by the anterior end of the body. In this process, the molecular genetic mechanisms of anteroposterior growth and left–right regulation, common to bilateria, and associated with the genes of the Wnt, BMP, Nodal signaling cascades, and Hox system genes, were probably used together. In the process of replication of channels extending from the ambulacral ring, the emerging ambulacral system was the organizer of the symmetry of the skeleton and the nervous and muscular systems. Replication in many fossil echinoderms ended on the three channels extending directly from the ambulacral ring. In crinoids, sea urchins, sea stars, brittle stars, and holothurians, the second stage of the formation of a more perfect five-ray symmetry of the ambulacral ring with five radial canals extending from it appeared, associated with a shift in ontogenesis of the branch point to the early stages of hydrocoel development.

A chromosome-level genome assembly of a deep-sea starfish (Zoroaster cf. ophiactis)

Understanding of adaptation and evolution of organisms in the deep sea requires more genomic resources. Zoroaster cf. ophiactis is a sea star in the family Zoroasteridae occurring exclusively in the deep sea. In this study, a chromosome-level genome assembly for Z. cf. ophiactis was generated by combining Nanopore long-read, Illumina short-read, and Hi-C sequencing data. The final assembly was 1,002.0 Mb in length, with a contig N50 of 376 Kb and a scaffold N50 of 40.4 Mb, and included 22 pseudo-chromosomes, covering 92.3% of the assembly. Completeness analysis evaluated with BUSCO revealed that 95.91% of the metazoan conserved genes were complete. Additionally, 39,426 protein-coding genes were annotated for this assembly. This chromosome-level genome assembly represents the first high-quality genome for the deep-sea Asteroidea, and will provide a valuable resource for future studies on evolution and adaptation of deep-sea echinoderms.

Phylogenomic analyses of echinoid diversification prompt a re-evaluation of their fossil record

Echinoids are key components of modern marine ecosystems. Despite a remarkable fossil record, the emergence of their crown group is documented by few specimens of unclear affinities, rendering their early history uncertain. The origin of sand dollars, one of its most distinctive clades, is also unclear due to an unstable phylogenetic context. We employ 18 novel genomes and transcriptomes to build a phylogenomic dataset with a near-complete sampling of major lineages. With it, we revise the phylogeny and divergence times of echinoids, and place their history within the broader context of echinoderm evolution. We also introduce the concept of a chronospace - a multidimensional representation of node ages - and use it to explore methodological decisions involved in time calibrating phylogenies. We find the choice of clock model to have the strongest impact on divergence times, while the use of site-heterogeneous models and alternative node prior distributions show minimal effects. The choice of loci has an intermediate impact, affecting mostly deep Paleozoic nodes, for which clock-like genes recover dates more congruent with fossil evidence. Our results reveal that crown group echinoids originated in the Permian and diversified rapidly in the Triassic, despite the relative lack of fossil evidence for this early diversification. We also clarify the relationships between sand dollars and their close relatives and confidently date their origins to the Cretaceous, implying ghost ranges spanning approximately 50 million years, a remarkable discrepancy with their rich fossil record.

Micromere formation and its evolutionary implications in the sea urchin.

The micromeres of the sea urchin embryo are distinct from other blastomeres. After they arise through an asymmetric cell division at the 8- to 16-cell stage, micromeres immediately function as organizers. They also commit themselves to specific cell fates such as larval skeletogenic cells and primordial germ cells, while other blastomeres remain plastic and uncommitted at the 16-cell stage. In the phylum Echinodermata, only the sea urchin (class Echinoidea) embryo forms micromeres that serve as apparent organizers during early embryogenesis. Therefore, it is considered that micromeres are the derived features and that modification(s) of the developmental system allowed evolutionary introduction of this unique cell lineage. In this chapter, we summarize the both historic and recent observations that demonstrate unique properties of micromeres and discuss how this lineage of micromeres may have arisen during echinoderm evolution.

Origin and significance of Lovén's Law in echinoderms

AbstractLovén's Law described the position of larger basicoronal ambulacral plates in echinoids. The smaller basicoronal plates form first in ontogeny. We restate Lovén's Law to describe the position of first ambulacral plates using Carpenter's ambulacra and left (L) or right (R) as: AR, BL, CR, DL, ER, with EA the pair of ambulacra both identical and adjacent. First ambulacral plates of the Cambrian edrioasteroid,Walcottidiscus, code identically. The transition from a tri-radiate 1-1-1 pattern to the 2-1-2 ambulacral pattern ofWalcottidiscusand other pentaradiate Paleozoic echinoderms results in Lovén's Law. This provides an hypothesis for the origin of Lovén's Law and predicts its widespread occurrence among echinoderm classes.The ‘BD different’ pattern of primary brachioles in pentaradiate glyptocystitoid Rhombifera results from subterminal branching of the ambulacra. The ontogenetic sequence was triradiate, then lateral ambulacra bifurcated, and finally second brachioles developed. Positions of second brachioles of pentaradiate glyptocystitoids code as AR, BL, CR, DL, ER. Other examples of Lovén's Law occur in Diploporita, Ophiuroidea, Edrioasteroidea, Edrioblastoidea, Holothuroidea, Ophiocistioidea, andBothriocidaris. Our working hypothesis is that Lovén's Law arose with pentaradiality. An objective test requires a reliable independent landmark across all classes, which does not exist currently. Our hypothesis is only parsimonious if Lovén's Law arose just once in echinoderm evolution and is widespread within the phylum. So far, both conditions appear to be met, but edrioasteroid first ambulacral cover plates commonly exhibit an alternative Lovén-like pattern of AL, BL, CR, DL, ER, with AB the identical adjacent ambulacra.UUID:http://zoobank.org/4c40d338-8bfa-4515-9037-934f3bbab153

An edrioasteroid from the Silurian Herefordshire Lagerstätte of England reveals the nature of the water vascular system in an extinct echinoderm.

Echinoderms are unique in having a water vascular system with tube feet, which perform a variety of functions in living forms. Here, we report the first example of preserved tube feet in an extinct group of echinoderms. The material, from the Silurian Herefordshire Lagerstätte, UK, is assigned to a new genus and species of rhenopyrgid edrioasteroid, Heropyrgus disterminus The tube feet attach to the inner surface of compound interradial plates and form two sets, an upper and a lower, an arrangement never reported previously in an extant or extinct echinoderm. Cover plates are absent and floor plates are separated creating a large permanent entrance to the interior of the oral area. The tube feet may have captured food particles that entered the oral area and/or enhanced respiration. The pentameral symmetry of the oral surface transitions to eight columns in which the plates are vertically offset resulting in a spiral appearance. This change in symmetry may reflect flexibility in the evolutionary development of the axial and extraxial zones in early echinoderm evolution.

Paleozoic echinoderm hangovers: Waking up in the Triassic

Echinoderms are among the marine invertebrates that underwent the most severe losses at the end-Permian extinction. The prevailing paradigm claims an extreme bottleneck with only very few, if not single, holdovers (“hangovers” herein) sparking the post-Paleozoic radiation. Here we identify previously overlooked Triassic echinoids, ophiuroids, and asteroids as unambiguous members of Paleozoic stem groups. These echinoderm hangovers occurred almost worldwide and had spread into a wide range of paleoenvironments by the Late Triassic. Our discovery challenges fundamentals of echinoderm evolution with respect to end-Permian survival and sheds new light on the early evolution of the modern clades, in particular on Triassic ghost lineages (i.e., inferred but undocumented fossil record) of the crown-group look-alikes of the Paleozoic hangovers.

Paedomorphosis as an Evolutionary Driving Force: Insights from Deep-Sea Brittle Stars.

Heterochronic development has been proposed to have played an important role in the evolution of echinoderms. In the class Ophiuroidea, paedomorphosis (retention of juvenile characters into adulthood) has been documented in the families Ophiuridae and Ophiolepididae but not been investigated on a broader taxonomic scale. Historical errors, confusing juvenile stages with paedomorphic species, show the difficulties in correctly identifying the effects of heterochrony on development and evolution. This study presents a detailed analysis of 40 species with morphologies showing various degrees of juvenile appearance in late ontogeny. They are compared to a range of early ontogenetic stages from paedomorphic and non-paedomorphic species. Both quantitative and qualitative measurements are taken and analysed. The results suggest that strongly paedomorphic species are usually larger than other species at comparable developmental stage. The findings support recent notions of polyphyletic origin of the families Ophiuridae and Ophiolepididae. The importance of paedomorphosis and its correct recognition for the practice of taxonomy and phylogeny are emphasized.

Deep echinoderm phylogeny preserved in organic molecules from Paleozoic fossils

Isolation of organic molecules directly from Paleozoic to Cenozoic fossils has been documented, which raises important, new questions about the conditions of preservation and the range of paleobiological issues that can be addressed with these new data. Herein, molecules are isolated from fossil echinoderms exceeding 445 Ma in age. Previously, morphological data have been insufficient to establish a consensus regarding early echinoderm evolution. Thus, organic molecules extracted from fossil echinoderm specimens (mostly Paleozoic) belonging to the classes Asteroidea, Blastoidea, Crinoidea, Diploporita, Echinoidea, and Edrioasteroidea are used to assess the position of crinoids and blastozoans within competing echinoderm phylogenetic hypotheses. Fluorescence excitation-emission spectroscopy of organic molecules in fossil extracts are used to compare relationships among hypotheses. These new data support the hypothesis that living eleutherozoans diverged early from stemmed echinoderms, crinoids are nested within the clade that includes other blastozoans, and edrioasteroids are a distinct clade.

Erratum

PalaeontologyVolume 58, Issue 2 p. 391-391 ErratumFree Access Erratum This article corrects the following: Deciphering the early evolution of echinoderms with Cambrian fossils Samuel Zamora, Imran A. Rahman, Andrew Smith, Volume 57Issue 6Palaeontology pages: 1105-1119 First Published online: November 25, 2014 First published: 05 March 2015 https://doi.org/10.1111/pala.12156AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL In Zamora and Rahman (2014), Figure 3 should have been printed in colour and is reproduced below. The publisher wishes to apologize for this error. Figure 3Open in figure viewerPowerPoint Cambrian spiral echinoderms. A, C, the helicoplacoid Helicoplacus gilberti; A, general view of the theca, with a lateral mouth and three ambulacra, UT TMM 2041TX1a (courtesy of Bryan Wilbur); C, view from the interior of the ambulacral flooring plates, NHMUK EE 5343. B, D, the helicocystoid Helicocystis moroccoensis; B, general view of the theca, with a terminal mouth and five ambulacra, NHMUK EE 15375; D, view from the exterior of food groove associated with floor plates, NHMUK EE 15373. Floor plates are indicated in green. All images are photographs of latex casts whitened with NH4Cl sublimate. Scale bars represent 5 mm (A); 1 mm (B, D); 2 mm (C). Reference Zamora, S. and Rahman, I. A. 2014. Deciphering the early evolution of echinoderms with Cambrian fossils. Palaeontology, 57, 1105– 1119. Volume58, Issue2March 2015Pages 391-391 FiguresReferencesRelatedInformation

Deciphering the early evolution of echinoderms with Cambrian fossils

AbstractEchinoderms are a major group of invertebrate deuterostomes that have been an important component of marine ecosystems throughout the Phanerozoic. Their fossil record extends back to the Cambrian, when several disparate groups appear in different palaeocontinents at about the same time. Many of these early forms exhibit character combinations that differ radically from extant taxa, and thus their anatomy and phylogeny have long been controversial. Deciphering the earliest evolution of echinoderms therefore requires a detailed understanding of the morphology of Cambrian fossils, as well as the selection of an appropriate root and the identification of homologies for use in phylogenetic analysis. Based on the sister‐group relationships and ontogeny of modern species and new fossil discoveries, we now know that the first echinoderms were bilaterally symmetrical, represented in the fossil record by Ctenoimbricata and some early ctenocystoids. The next branch in echinoderm phylogeny is represented by the asymmetrical cinctans and solutes, with an echinoderm‐type ambulacral system originating in the more crownward of these groups (solutes). The first radial echinoderms are the helicoplacoids, which possess a triradial body plan with three ambulacra radiating from a lateral mouth. Helicocystoids represent the first pentaradial echinoderms and have the mouth facing upwards with five radiating recumbent ambulacra. Pentaradial echinoderms diversified rapidly from the beginning of their history, and the most significant differences between groups are recorded in the construction of the oral area and ambulacra, as well as the nature of their feeding appendages. Taken together, this provides a clear narrative of the early evolution of the echinoderm body plan.

Hox expression in the direct‐type developing sand dollar Peronella japonica

Echinoderms are a curious group of deuterostomes that forms a clade with hemichordates but has a pentameral body plan. Hox complex plays a pivotal role in axial patterning in bilaterians and often occurs in a cluster on the chromosome. In contrast to hemichordates with an organized Hox cluster, the sea urchin Strongylocentrotus purpuratus has a Hox cluster with an atypical organization. However, the current data on hox expression in sea urchin rudiments are fragmentary. We report a comprehensive examination of hox expression in a sand dollar echinoid. Nine hox genes are expressed in the adult rudiment, which are classified into two groups, but hox11/13b belongs to both: one with linear expression in the coelomic mesoderm and another with radial expression around the adult mouth. The linear genes may endow the coelom/mesentery with axial information to direct postmetamorphic transformation of the digestive tract, whereas the radial genes developmentally correlate with the morphological novelties of echinoderms and/or sea urchins. Recruitment of the radial genes except hox11/13b appears to be accompanied by the loss of ancestral/axial roles. This in toto co-option of the hox genes provides insight into the molecular mechanisms underlying the evolution of echinoderms from a bilateral ancestor.

Sea Lily Muscle Lacks a Troponin-Regulatory System, While it Contains Paramyosin

Troponin, a Ca(2+)-dependent regulator of striated muscle contraction, has been characterized in vertebrates, protochordates (amphioxus and ascidian), and many invertebrate animals that are categorized in protostomes, but it has not been detected in echinoderms, such as sea urchin and sea cucumber, members of subphylum Eleutherozoa. In this study, we examined the muscle of a species of isocrinid sea lilies, a member of subphylum Pelmatozoa, that constitute the most basal group of extant echinoderms to clarify whether troponin is lacking from the early evolution of echinoderms. Native thin filaments were released from the muscle homogenates in a relaxing buffer containing ATP and EGTA, a Ca(2+)-chelator, and were collected by ultra-centrifugation. Actin and tropomyosin, but not a troponin-like protein, were detected in the filament preparation. The filaments increased Mg(2+)-ATPase activity of rabbit skeletal muscle myosin irrespective of the presence or absence of Ca(2+). The results indicate that Ca(2+)-sensitive factor, troponin, is lacking in the thin filaments of sea lily muscle as in those of the other echinoderms, sea urchin and sea cucumber. On the other hand, a paramyosin-like protein that is absent from chordates was detected in sea lily muscle as in the muscles of the other echinoderms and invertebrate animals of protostomes.

The oldest record of predation on echinoids: evidence from the Middle Jurassic of Poland

Competition and predation are regarded as important ecologicaland evolutionary factors. The importance of competition (Barnes& Kuklinski 2003, 2004) and especially predation (see Kowalew-ski & Kelley 2002; Kelley et al. 2003 for comprehensive reviews)is clearly reflected in the ability of predators to regulate popula-tion densities and abundance of individuals. It controls faunaldistribution and structure, and functions as a causative mecha-nism of evolution due to adaptive (induced) responses in prey(e.g. spines, thicker shells, ornamentation, motile life style, infau-nalization). Bambach (2003) summarized that predators affectvirtually every major ecological and evolutionary aspect (Kelleyet al. 2003). This led Vermeij (1977, 1987) to recognize the esca-lation of predation as a driving force of the so-called ‘MesozoicMarine Revolution’ (MMR).Other authors have concluded that predation is also importantin the Cambrian Revolution (Walker & Brett 2002), the Mid-Pal-aeozoic Revolution (the Palaeozoic precursor to MMR; Signor B Aronson 1991; McKinney 1995;Tomasovych 2008). Due to some doubts (Aberhan et al. 2006;Madin et al. 2006), alternate hypotheses that do not invokepredation as an evolutionary age nt have also been proposed (Cohen2005). Gould (2002) amongst ot hers found macro-evolutionaryprocesses as caused by biotic or abiotic factors separately oreven exclusively.Until recently, studies of predator–prey interactions havefocused mostly on groups such as molluscs, crinoids or brachio-pods, whereas the role of echinoids as prey has received littleinterest despite their potential importance (see Kowalewski N see also McNamara 1994). As aresult, the role of biotic interactions in the evolutionary historyof echinoids remains poorly known. Today, echinoids are preyfor many organisms, including fish, sea otters, crabs, asteroids,gastropods, birds and humans. The earliest record of predationon echinoids comes from the Upper Kimmeridgian (UpperJurassic), regurgitates found in lithographic limestones at Nusp-lingen, Germany (Baumeister et al. 2000). Other reports fromyounger strata are mostly based on drilling and bite/regenerationtraces on tests of irregular echinoids (Zinsmeister 1980; Thies1985; Nebelsick & Kowalewski 1999; Zlotnik & Ceranka 2005).Rare direct evidence for predation on fossil echinoids come alsofrom the echinoid remains preserved as gut content in the stom-achs of Jurassic vertebrates (reviewed in Kriwet 2001). Othersources of data for predation on echinoids such as bite marks orregeneration of spines remain unexplored. The only other evi-dence for the presence of echinoids in regurgitates originatesfrom the Middle Miocene of Austria. Kroh (2005, plate 82, fig. 3)identified spines of spatangoid echinoids as regurgitated materialamongst other fossil remains. These studies suggest more or lesscontinuous predation record on echinoids for the last 100 Ma;that is, since the Late Cretaceous to the present (cf. Kowalewski& Nebelsick 2003). However, according to pre-existing reports,echinoids were a target of predators for more than 150 Ma.In this study we report cidaroid echinoid remains in Bajocian–Bathonian (Middle Jurassic) vertebrate (most probably fish)regurgitates from southern Poland. Our finds predate any previ-ous record by more than 20 myr. The aim of this paper is toelaborate this new find, to date only mentioned by Zaton et al.(2007), and to discuss its broader significance for the ecologyand evolution of echinoids. This provides a source of data for thereconstruction of food webs in the fossil record and is importantas evidence for the role of predation in echinoderm evolution,being currently increasingly reported (Baumiller & Gahn 2004;Baumiller et al. 2010; Sallan et al. 2011; Gorzelak et al. 2012).

The oldest echinoderm faunas from Gondwana show that echinoderm body plan diversification was rapid

The earliest fossil echinoderms have, until now, come almost exclusively from North America and are represented by few taxa, all of which have a radiate body plan. Here we report the discovery of two new echinoderm faunas from the early part of the Cambrian of Morocco (West Gondwana). The former represents the oldest echinoderm fauna from Gondwana, approximately equivalent in age to those from North America, and the latter the oldest diversified fauna from Gondwana. In both cases, the appearance of well-preserved echinoderms coincides with a change in palaeogeographic regime. The presence of four markedly different echinoderm body plans in these earliest faunas indicates that considerable diversification had already taken place by 510 Ma. Yet all share the same distinctive biomineralized skeleton that, based on the fossil record and ocean geochemistry, probably evolved just 10-15 my earlier. This suggests that a rapid rate of morphological divergence took place during the initial stages of echinoderm evolution.

Traumatic brain injury, paraquat exposure, and their relationship to Parkinson disease

Traumatic brain injury (TBI) increased risk of Parkinson disease (PD) in many but not all epidemiologic studies, giving rise to speculations about modifying factors. A recent animal study suggested that the combination of TBI with subthreshold paraquat exposure increases dopaminergic neurodegeneration. The objective of our study was to investigate PD risk due to both TBI and paraquat exposure in humans. From 2001 to 2011, we enrolled 357 incident idiopathic PD cases and 754 population controls in central California. Study participants were asked to report all head injuries with loss of consciousness for >5 minutes. Paraquat exposure was assessed via a validated geographic information system (GIS) based on records of pesticide applications to agricultural crops in California since 1974. This GIS tool assesses ambient pesticide exposure within 500 m of residences and workplaces. In logistic regression analyses, we observed a 2-fold increase in risk of PD for subjects who reported a TBI (adjusted odds ratio [AOR] 2.00, 95% confidence interval [CI] 1.28-3.14) and a weaker association for paraquat exposures (AOR 1.36, 95% CI 1.02-1.81). However, the risk of developing PD was 3-fold higher (AOR 3.01, 95% CI 1.51-6.01) in study participants with a TBI and exposure to paraquat than those exposed to neither risk factor. While TBI and paraquat exposure each increase the risk of PD moderately, exposure to both factors almost tripled PD risk. These environmental factors seem to act together to increase PD risk in a more than additive manner.

Plated Cambrian Bilaterians Reveal the Earliest Stages of Echinoderm Evolution

Echinoderms are unique in being pentaradiate, having diverged from the ancestral bilaterian body plan more radically than any other animal phylum. This transformation arises during ontogeny, as echinoderm larvae are initially bilateral, then pass through an asymmetric phase, before giving rise to the pentaradiate adult. Many fossil echinoderms are radial and a few are asymmetric, but until now none have been described that show the original bilaterian stage in echinoderm evolution. Here we report new fossils from the early middle Cambrian of southern Europe that are the first echinoderms with a fully bilaterian body plan as adults. Morphologically they are intermediate between two of the most basal classes, the Ctenocystoidea and Cincta. This provides a root for all echinoderms and confirms that the earliest members were deposit feeders not suspension feeders.