Samuel Zamora

Ordovician edrioasteroids from Morocco: faunal exchanges across the Rheic Ocean

A new edrioasteroid fauna from the Ordovician of Morocco, North Africa includes eight new isorophid species placed in six genera of which three are new. A phylogenetic analysis of Moroccan genera and other taxa places these new edrioasteroids into a phylogenetic framework. Pyrgocystidae is redefined to include plesiomorphic isorophids with hood plates underlying the cover plates. New pyrgocystid taxa include Streptaster nodosus sp. nov., Belochthus? chauveli sp. nov., Argodiscus espilezorum sp. nov. and Moroccopyrgus matacarros gen. et sp. nov. Isorophinid taxa include Isorophus africanus sp. nov., Isorophusella gutii sp. nov., Euryeschatia reboulorum gen. et sp. nov. and the morphological aberrant Anedriophus moroccoensis gen. et sp. nov. These taxa are attached either epibiotically on conulariids or echinosphaeritid rhombiferans, or encrust large bioclasts such as cephalopods and trilobites in a siliciclastic environment that is otherwise devoid of suitable hard substrates. The presence of close relatives of North American taxa in this Perigondwanan section indicates a high degree of communication between North America and North Africa in Ordovician time. Also described are two species of an unusual eocrinoid? Hexedriocystis gen. nov., the type species H. inexpectatus sp. nov. and H. mimus sp. nov., that is a close mimic of isorophid taxa.

Cambrian stalked echinoderms show unexpected plasticity of arm construction

Feeding arms carrying coelomic extensions of the theca are thought to be unique to crinoids among stemmed echinoderms. However, a new two-armed echinoderm from the earliest Middle Cambrian of Spain displays a highly unexpected morphology. X-ray microtomographic analysis of its arms shows they are polyplated in their proximal part with a dorsal series of uniserial elements enclosing a large coelomic lumen. Distally, the arm transforms into the more standard biserial structure of a blastozoan brachiole. Phylogenetic analysis demonstrates that this taxon lies basal to rhombiferans as sister-group to pleurocystitid and glyptocystitid blastozoans, drawing those clades deep into the Cambrian. We demonstrate that Cambrian echinoderms show surprising variability in the way their appendages are constructed, and that the appendages of at least some blastozoans arose as direct outgrowths of the body in much the same way as the arms of crinoids.

Oral region homologies in paleozoic crinoids and other plesiomorphic pentaradial echinoderms.

The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral region of echinoderms is mainly composed of the axial, or ambulacral, skeleton, which apparently evolved more slowly than the extraxial skeleton that forms the majority of the body. Recent phylogenetic hypotheses have focused on characters of the extraxial skeleton, which may have evolved too rapidly to preserve obvious homologies across all these groups. The axial skeleton conserved homologous suites of characters shared between various edrioasteroids and specific blastozoans, and between other blastozoans and crinoids. Although individual plates can be inferred as homologous, no directly overlapping suites of characters are shared between edrioasteroids and crinoids. Six different systems of mouth (peristome) plate organization (Peristomial Border Systems) are defined. These include four different systems based on the arrangement of the interradially-positioned oral plates and their peristomial cover plates, where PBS A1 occurs only in plesiomorphic edrioasteroids, PBS A2 occurs in plesiomorphic edrioasteroids and blastozoans, and PBS A3 and PBS A4 occur in blastozoans and crinoids. The other two systems have radially-positioned uniserial oral frame plates in construction of the mouth frame. PBS B1 has both orals and uniserial oral frame plates and occurs in edrioasterid and possibly edrioblastoid edrioasteroids, whereas PBS B2 has exclusively uniserial oral frame plates and is found in isorophid edrioasteroids and imbricate and gogiid blastozoans. These different types of mouth frame construction offer potential synapomorphies to aid in parsimony-based phylogenetics for exploring branching order among stem groups on the echinoderm tree of life.

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.

Middle Cambrian echinoderms from north Spain show echinoderms diversified earlier in Gondwana

New fossil discoveries in the middle Cambrian of Spain have considerably expanded our knowledge of the temporal and spatial distribution of some major clades of echinoderms including sucocystid cinctans, isorophid edrioasteroids, cothurnocystid stylophorans, ctenocystoids, and a new group of blastozoans (“eocystitids”). Because many of these taxa appear close to the beginning of the middle Cambrian, it seems likely that their origins must be placed in the early Cambrian. These results, based on articulated specimens provided from Echinoderm Lagerstatten, agree with the hidden diversity provided from isolated ossicles from other Gondwanan areas.

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.

A new Middle Cambrian stem−group echinoderm from Spain: Palaeobiological implications of a highly asymmetric cinctan

A new exquisitely preserved stem group echinoderm (cinctan), Lignanicystis barriosensis gen. et sp. nov., is described from the Middle Cambrian of Los Barrios de Luna, North Spain. This displays a unique asymmetrical body plan with ventral projecting nodes that raised the lower surface above the substratum. There are four openings through the body wall: mouth, anus, atrium, and an aligned row of suturai pores of uncertain function. Unlike other cinctans, Lignanicystis has a strongly asymmetrical shape convergent with that of some cornute carpoids. Like cornutes, the test is also elevated above the substratum to allow water flow beneath the theca. In both cases this is probably an adaptation to life in higher water flow regimes.

PELMATOZOAN ECHINODERMS AS COLONIZERS OF CARBONATE FIRMGROUNDS IN MID-CAMBRIAN HIGH ENERGY ENVIRONMENTS

Abstract New echinoderm holdfast discoveries from Gondwana demonstrate that pelmatozoans have been cementers able to attach to carbonate firmgrounds since the basal middle Cambrian. Echinoderms were thus colonizing shallow, high-energy environments well before the appearance of the first true carbonate hardgrounds in the Furongian. Morphological innovations and adaptations to firmground media ( = substrates) were first developed in softground, clayey, offshore environments where echinoderms cemented to shell fragments. This preadaption allowed echinoderms to quickly and effectively exploit the newly emerging hardground habitats in the Furongian to Early Ordovician.

The oldest isorophid edrioasteroid (Echinodermata) and the evolution of attachment strategies in Cambrian edrioasteroids

Two new middle Cambrian edrioasteroid (Echinodermata), Protorophus hispanicus gen. et sp. nov., and Isorophida gen. et sp. indet., are described from the early middle Cambrian (Cambrian Series 3, Stage 5) of Spain. These are the oldest and probably the most primitive isorophids, a clade previously known from the upper Cambrian onwards. Specimens are attached to trilobite fragments indicating that edrioasteroids had by this time separated into two lineages each with different strategies for attachment, sediment attachers and hard substrate attachers. The single U-shaped ambulacral flooring plates of Protorophus are unique while Isorophida gen. et sp. indet. shares the presence of spines in common with some pyrgocystitid isorophids. The shift from facultative soft-bottom attachment to obligate hard-ground attachment in edrioasteroids involved the retention of a juvenile trait into adulthood and was already underway by the middle Cambrian.

Cambrian spiral-plated echinoderms from Gondwana reveal the earliest pentaradial body plan

Echinoderms are unique among animal phyla in having a pentaradial body plan, and their fossil record provides critical data on how this novel organization came about by revealing intermediate stages. Here, we report a spiral-plated animal from the early Cambrian of Morocco that is the most primitive pentaradial echinoderm yet discovered. It is intermediate between helicoplacoids (a bizarre group of spiral-bodied echinoderms) and crown-group pentaradiate echinoderms. By filling an important gap, this fossil reveals the common pattern that underpins the body plans of the two major echinoderm clades (pelmatozoans and eleutherozoans), showing that differential growth played an important role in their divergence. It also adds to the striking disparity of novel body plans appearing in the Cambrian explosion.