Research

Major Innovations in Plant Evolution

Over the course of their evolutionary history, plants have developed a series of major innovations that have allowed them to dominate the terrestrial ecosphere. These include vascular structures, ovules and seeds, and flowers and fruits. We are using 3D imaging to illuminate critical aspects of origin, evolution and functionality of these three groups of major innovations.

1. Shi, G... Clark, E. G. et al. 2021. Mesozoic cupules and the origin of the angiosperm second integument. Nature 594: 223-226.
2. Herrera, F... Clark, E. G. et al. 2022. A permineralized Early Cretaceous lycopsid from China and the evolution of crown clubmosses. New Phytologist. https://doi.org/10.1111/nph.17874
3. Shi, G... Clark, E. G. et al. 2022. Silicified cupulate seed-bearing structures from the Early Cretaceous of eastern Inner Mongolia, China: rethinking the corystosperm concept. Journal of Systematic Palaeontology 20: 1-33.

New Approaches to Skeletal Mechanics with 3D Digital Modeling

Brittle stars use hundreds of muscles and skeletal elements in their arms to generate a unique form of rapid locomotion. We used micro-CT imaging of live brittle stars to build 3D digital models of the arm skeleton. Through this method we were able to visualize, for the first time, the inner workings of the arm as it moves.

4. Clark, E. G. et al. 2018. Integrating morphology, skeletal mobility, and in vivo behavioral observations with digital models to infer function in brittle star arms. Journal of Anatomy 233: 696-714.
5. Clark, E. G. 2019. Ophiuroid locomotion from fundamental structures to integrated systems. Zoosymposia 15: 13-22.
6. Stohr, S., Clark, E. G. et al. 2019. Exploring 3D imaging techniques for phylogenetic inference in brittle stars (Echinodermata: Ophiuroidea). Zoosymposia 15: 146-158.

The First Platform for 3D Biomechanics of Fossil Invertebrates

We created the first objective, data-driven methodology for analyzing fossil invertebrate biomechanics in 3D through a case-study on organisms known as "the strangest-looking animals of all time." We also developed a technique for generating high-quality 3D models of fossil specimens from 3D imaging data. This methodology was designed to be broadly applicable across invertebrate organisms with hard skeletons and represents a major step forward in the field of fossil invertebrate biomechanics.

7. Clark, E. G. et al. 2020. Arm waving in stylophoran echinoderms: three-dimensional mobility analysis illuminates cornute locomotion. Royal Society Open Science 7: 200191.
8. Clark, E. G. et al. 2020. Three-dimensional morphology and locomotion of ophiuroids from the Devonian Hunsrück Slate. Royal Society Open Science 7: 201380.
9. Clark, E. G. et al. In review. Back to life: Techniques for developing high-quality 3D reconstructions of plants and animals from digitized specimens. PLOS ONE.

Advancing Robotics with Brittle Star Research

Brittle stars, relatives of sea stars and sea urchins, coordinate +2500 moving parts for locomotion without using a brain, and rapidly adjust their movement strategy when injured for a near-minimal decrease in ability. We identified key aspects of the decentralized control setup underlying this resilient locomotion strategy. These insights are currently being applied to build the next generation of resilient robots.

10. Clark, E. G. et al. 2019. The function of the ophiuroid nerve ring: How a decentralized nervous system controls coordinated locomotion. Journal of Experimental Biology 222: 1-10.
11. Kanauchi, D., Clark, E. G., et al. 2019. "How Brittle Star Determines the Direction of Movement" Proceedings of the 31st Distributed Autonomous System Symposium. (in Japanese)
12. Kano, T., Clark, E. G., et al. 2019. Decentralized Control Mechanism for Determination of Moving Direction in Brittle Stars with Penta-radially Symmetric Body. Frontiers in Neurorobotics 13: 1-7.

The Inner Workings of an Ancient System for Hydrostatic Locomotion

Brittle stars and their relatives use a musculoskeletal system coupled with a hydraulic system for movement and locomotion. As these systems have unique structures and functions in all living groups, it is difficult to determine the steps underlying their evolution. We found the first fossil brittle star ever to be discovered with 3D preservation of the internal hydraulic system using micro-CT scanning. This provides key insights into the evolution of the workings of their unique strategy for movement.

13. Clark, E. G. et al. 2017. Water vascular system architecture in an Ordovician ophiuroid. Biology Letters 13: 20170635.

Analyzing Unique Biomaterials with Synchrotron Imaging

Brittle star tendons and ligaments are made of a material unique to echinoderms that can stiffen and stretch under nervous control to exert forces independent of the actions of the muscles. These interesting material properties are important in autotomy (self-mediated arm loss). We developed a new technique using synchrotron imaging and 3D printed models to visualize the changes in stiffness of the tendons and ligaments in brittle stars. This illuminated how the tendons and ligaments work to effect motion in the arm, and how they function during autotomy.

14. Clark, E. G., et al. 2019. A farewell to arms: using x-ray synchrotron imaging to investigate autotomy in brittle stars. Zoomorphology 138: 419-424.

Examples of Additional Scientific Collaborations

Vertebrates:
15. McCoy, V. E... Clark, E. G. et al. 2016. The Tully Monster is a vertebrate. Nature 532: 496-499.

Protists:
16. Darroch, S. A. F... Clark, E. G. et al. 2016. Taphonomic disparity in foraminifera as a paleo-indicator for seagrass. Palaios 31: 242-258.
17. Burke, J. E... Clark, E. G. et al. In review. Low allometric scaling of respiration rates may explain gigantism in pelagic protists. Limnology and Oceanography.

Plants:
18. Shaw, A. J... Clark, E. G. et al. 2014. Intercontinental genetic structure in the amphi-Pacific peatmoss Sphagnum miyabeanum (Bryophyta: Spagnaceae). Biological Journal of the Linnean Society 111: 17-37.

Arthropods:
19. Luque, J... Clark, E. G. et al. 2021. Crabs in amber reveal an early colonization of freshwater during the Cretaceous. Sciences Advances 7: 1-12.

EBooks:
Kano, T., Clark. E. G., et al. 2021. Decentralized control mechanism for determination of moving direction in brittle stars with penta-radially symmetric body. In: Biology-Inspired Engineering and Engineering-Insipired Biology. (eds. Braun, J.-M. et al.). Frontiers in Neurorobotics.

Doctoral Dissertation:
Clark, E. G. 2018. How to build a brittle star: An investigation of the evolutionary history, morphological features, and integrated systems underlying ophiuroid locomotion. Doctoral dissertation. Yale University.