More Like this

1. Ecological novelty at the start of the Cambrian and Ordovician radiations of echinoderms

   https://doi.org/10.1111/pala.12688  

   Novack‐Gottshall, Philip M.; Purcell, Jack; Sultan, Ali; Ranjha, Isa; Deline, Bradley; Sumrall, Colin D. (January 2024, Palaeontology)

   Abstract The Cambrian and Ordovician radiations marked the origins of all major echinoderm clades and established their Phanerozoic ecological blueprint. Recent claims of modest innovation of early echinoderms and other animals suggest constraints on novelty during the origins of phyla. Here, we document the life‐habit richness, body size, tiering, habitat usage, mobility, diet and foraging habits of 366 Cambrian–Ordovician echinoderm genera across a time‐scaled phylogeny to identify the timing and impact of novelty. Most early echinoderms were sedentary, filter‐feeding microbivores, and their body sizes, diets and modes of locomotion were largely unchanged through time, despite major volatility in taxonomic composition. Cambrian echinoderms lived close to the seafloor, with stylophorans first evolving semi‐infaunality. Many Ordovician echinoderms lived farther from the seafloor, with more complex filter‐feeding organs and tiering structure, often using other organisms as substrates. Mobile carnivores and mass‐feeders emerge then, too, across diverse asterozoans and echinozoans. Most of these novelties coincide with the origins of individual clades during the early and late Cambrian (Terreneuvian/Series 2 and Furongian), and 10–20 million years pass before most become ecologically important. Life‐habit evolution within most taxa involved new variations in these traits, with crinoids and asterozoans better able to shift strategies. The Ordovician radiation records more new variability in pre‐existing Cambrian life habits rather than radical re‐invention, with important novelties (like mobile carnivory and mass‐feeding, increased height off the seafloor, and biotic substrates) becoming ecologically more impactful. Taxa with these strategies were those best able to capitalize on the newly heterogeneous Ordovician world. 

   more » « less
2. Crinoid calyx origin from stem radial echinoderms

   https://doi.org/10.1017/jpa.2023.14  

   Guensburg, Thomas E.; Mooi, Rich; Mongiardino Koch, Nicolás (March 2023, Journal of Paleontology)

   Abstract 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. 

   more » « less
3. A simple skeletal measurement effectively predicts climbing behaviour in a diverse clade of small mammals

   https://doi.org/10.1093/biolinnean/blz085  

   Nations, Jonathan A.; Heaney, Lawrence R.; Demos, Terrence C.; Achmadi, Anang S.; Rowe, Kevin C.; Esselstyn, Jacob A. (July 2019, Biological Journal of the Linnean Society)

   Abstract Arboreal locomotion allows access to above-ground resources and might have fostered the diversification of mammals. Nevertheless, simple morphological measurements that consistently correlate with arboreality remain indefinable. As such, the climbing habits of many species of mammals, living and extinct, remain speculative. We collected quantitative data on the climbing tendencies of 20 species of murine rodents, an ecologically and morphologically diverse clade. We leveraged Bayesian phylogenetic mixed models (BPMMs), incorporating intraspecific variation and phylogenetic uncertainty, to determine which, if any, traits (17 skeletal indices) predict climbing frequency. We used ordinal BPMMs to test the ability of the indices to place 48 murine species that lack quantitative climbing data into three qualitative locomotor categories (terrestrial, general and arboreal). Only two indices (both measures of relative digit length) accurately predict locomotor styles, with manus digit length showing the best fit. Manus digit length has low phylogenetic signal, is largely explained by locomotor ecology and might effectively predict locomotion across a multitude of small mammals, including extinct species. Surprisingly, relative tail length, a common proxy for locomotion, was a poor predictor of climbing. In general, detailed, quantitative natural history data, such as those presented here, are needed to enhance our understanding of the evolutionary and ecological success of clades. 

   more » « less
4. Arm waving in stylophoran echinoderms: three-dimensional mobility analysis illuminates cornute locomotion

   https://doi.org/10.1098/rsos.200191  

   Clark, Elizabeth G.; Hutchinson, John R.; Bishop, Peter J.; Briggs, Derek E. (June 2020, Royal Society Open Science)

   null (Ed.)

   The locomotion strategies of fossil invertebrates are typically interpreted on the basis of morphological descriptions. However, it has been shown that homologous structures with disparate morphologies in extant invertebrates do not necessarily correlate with differences in their locomotory capability. Here, we present a new methodology for analysing locomotion in fossil invertebrates with a rigid skeleton through an investigation of a cornute stylophoran, an extinct fossil echinoderm with enigmatic morphology that has made its mode of locomotion difficult to reconstruct. We determined the range of motion of a stylophoran arm based on digitized three-dimensional morphology of an early Ordovician form, Phyllocystis crassimarginata . Our analysis showed that efficient arm-forward epifaunal locomotion based on dorsoventral movements, as previously hypothesized for cornute stylophorans, was not possible for this taxon; locomotion driven primarily by lateral movement of the proximal aulacophore was more likely. Three-dimensional digital modelling provides an objective and rigorous methodology for illuminating the movement capabilities and locomotion strategies of fossil invertebrates. 

   more » « less
5. Approaches to understanding echinoderm origins. Part 2: Questioning conceptual models

   Mooi, R; Lefebvre, B; Guensburg, T; Nohejlova, M; Dupichaud, C (December 2024, Cahiers de Biologie Marine)

   Davoult, D (Ed.)

   Abstract: The two main approaches in interpreting the significance of non-radial fossil echinoderms (carpoids) have consistently produced the same two distinct clusters of results for over a century of investigation. Studies based on conceptual models imbued with Haeckelian precepts consider bilaterally symmetric or asymmetric morphologies of carpoids plesiomorphic for the phylum. These approaches do not find a place for carpoids within an existing phylogenetic framework for the phylum because it is assumed that they primitively lack pentaradiality. Emphasis on differences between these taxa and pentaradial echinoderms forces them outside of and downward from more crownward clades. It is crucial to examine the data supporting these supposed differences. Is it worth considering non-pentaradial echinoderms as members of a well-known group of echinoderms, the blastozoans, which already includes many secondarily-derived, non-pentaradial members? Followers of an empirical model think so, presenting an integration of paleontology, embryology, body wall homology, and image analysis that derives echinoderms from a bilaterian, archimeric larva, not bilateral adults. Unprecedented modification of a single mesocoel (hydrocoel) initiated the pentaradial adult echinoderm, most parsimoniously with five primary lobes in stem forms of each major clade within the phylum. The unique water vascular system led to rearrangement of adult axes that literally have no parallel with those of any other invertebrate, representing an iconic synapomorphy for the Echinodermata. There are few, if any, developmental or stratigraphic data defending carpoids as 'bilateral precursors'. Their free appendage is now shown to be an ambulacrum, undermining any supposition of a 'head', 'tail', or 'gill slits'. Pentaradiality is plesiomorphic for the phylum, obviating the requirement for a triradial intermediate (helicoplacoids) between carpoids and pentaradial forms. Carpoids, a subset of blastozoans, exploited motility as a feeding mode, leading to extraordinary adaptations that belie their interpretation as ancestral echinoderms. 

   more » « less