PhyloPycno · Unravelling early chelicerate evolution and the origin of the sea spiders combining high quality paleontological and genomic data
Horizon 2020 — Marie Skłodowska-Curie Actions
- Duration
- 2021-10-01 → 2023-09-30
- EU contribution
- €212,934
- Participants
- 1
- Scheme
- MSCA-IF
Lines connect the coordinator with its partners.
Results in brief
Unravelling early chelicerate evolution and the origin of the sea spiders combining high quality paleontological and genomic data
Sea spiders, also known as pycnogonids, belong to a group of marine arthropods, like insects, millipedes, centipedes, spiders, and scorpions. Despite their name, they are not spiders. Presently, there are about 1,400 known species of pycnogonids distributed across 11 families. They all share a similar body plan, placing them under the same Order, Pantopoda. They are now widely accepted as chelicerates (such as spiders, scorpions, and horseshoe crabs) thanks to molecular phylogeny, but unambiguous morphological evidence is still missing. Sea spiders are regarded as an early offshoot among arthropods. Therefore, understanding the early evolution of pycnogonids means unravelling the most diversified phylum on Earth. Finding morphological evidence to support the position of Pycnogonida is also paramount to understand the phylogenetic position of many ambiguous arthropod fossils. But extant pycnogonids are morphologically very divergent from other arthropods, making this task difficult. The fossil record can however provide further insight. The fossil record of sea spiders comprises only 11 species from Silurian to Jurassic. These fossils are only poorly understood, due to the limited means of previous studies. The PhyloPycno project aims to reexamine two major sea spider fossil sites, La Voulte sur Rhône (Jurassic, ~160 million years old) and the Hunsrück slate (Devonian, ~400 million years old). By using cutting-edge palaeontology tools such as X-ray microtomography and Reflectance Transformation Imaging (RTI), we aim to deepen our understanding of their morphoanatomy. Additionally, we intend to position these fossils in the pycnogonid Tree of Life and use this information, along with phylogenetics and molecular clock tools, to date critical evolutionary steps in Pycnogonida's history. Conclusions of the action are as follows: - Jurassic pycnogonids of La Voulte sur Rhône all belong to Pantopoda; <i>Colossopantopodus boissinensis</i> belongs to Colossendeidae, <i>Palaeoendeis elmii</i> to Endeidae, while <i>Palaeopycnogonides gracilis</i> belongs to a newly described family, Palaeopycnogonididae. - Devonian pycnogonids of the Hunsrück Slate do not belong to Pantopoda. They can be divided into two clades, one including the swimming pycnogonids (<i>Palaeoisopus problematicus and <i>Pentapantopus vogteli</i>) and the one with a divided femur (<i>Palaeopantopus maucheri</i> and <i>Flagellopantopus blocki</i>). - (<i>Haliestes dasos(</i> belong the swimming pycnogonids clade. - Pantopoda diversified around 485-353 million years ago, i.e., between early Ordovician and early Carboniferous.
Data: CORDIS, © European Union
Project objective
Arthropoda (e.g. insects, crustaceans, spiders and centipedes) comprises the majority of animal biodiversity and includes model organisms like the fruitfly Drosophila melanogaster. A rich fossil record, abundant genomic information, high morphological disparity, and unparallelled diversity, have made arthropods a key model system for macroevolution. Yet, our understanding of arthropod evolution remains incomplete. In part, this is because alternative interpretations of their morphology support different evolutionary hypotheses. For example, the phylogeny of total-group Chelicerata (i.e. the living chelicerates – e.g. sea spiders, horseshoe crabs, spiders and scorpions – and all fossils more closely related to these than to any other arthropod) depends on alternative interpretations for the origin of the chelicerae. These pincer-like first head appendages are found in all living chelicerates, but it is unclear whether they are primitive, derived, or converging characters. Central to this debate are the sea spiders (Pycnogonida), a poorly-understood, marine, chelicerae-bearing lineage, dissimilar in many respects to other chelicerates. It has been suggested that pycnogonids might not be chelicerates and that chelicerae might be convergent or a primitive trait for Arthropoda, which would necessitate a reassessment of early arthropod evolution. Here, I will use a cutting edge computed tomography approach to provide the first detailed study of fossil pycnogonid morphology, and to generate a new morphological dataset spanning all key arthropod taxa. Bayesian and Maximum Likelihood-based total evidence approaches will then be used to combine the new morphological dataset with genomic data and test hypotheses of (1) chelicerate and arthropod relationships, (2) the evolution of the arthropod body plan, (3) the origin and diversification rate of the highly divergent Pycnogonida, and (4) to estimate an evolutionary timescale for Pycnogonida and Chelicerata.
Original text from CORDIS.
Participants
- UNIVERSITY OF BRISTOL · BRISTOLCoordinatorUnited Kingdom
Links
Data: CORDIS, © European Union