NEW! Evolutionary Rate in Xiphosura (Horseshoe Crab), Sam Ocon @coolacanth: GeoProject Series

NAME: Sam Ocon (they/she)

SHORT BIO: Sam Ocon is from the swamps of north-central Florida, where they first fell in love with their organisms of study – horseshoe crabs. Fascinated by the creepy-crawlies of the world, especially those preserved in rock over millions of years, Sam pursued invertebrate paleontology as a career field, getting their bachelor’s degree at the University of Florida and currently working on their master’s at West Virginia University. Alongside their love for fossil arthropods, Sam is also interested in increasing diversity in the geosciences and exploring unique avenues for science communication.

TWITTER: @coolacanth


PROJECT TITLE: Examining Evolutionary Rate in Xiphosura

AREA OF EXPERTISE: Sam has expertise in paleobiology, paleoecology, programming in R, and an overall background in geology. Over the course of their career, they have worked on everything from mammals to plankton to horseshoe crabs.

PROJECT LOCATION: Due to starting my grad degree during the COVID-19 pandemic, my project has relied on digital images of horseshoe crabs from across the world. Technically, I’ve done most of my work from my home office.

PROJECT TIMELINE: Summer 2020 – Spring 2022

What’s the purpose of your project?

Horseshoe crabs have a reputation for being “living fossils”, which is a term commonly used to describe organisms that seem to change very little over large periods of geological time. There are a number of other living things with this label, like ginkgoes, tadpole shrimp, and coelacanths; however, this term has very much fallen out of favor within Paleontology and Biology. Usually, as we take a closer look at the evolutionary history of these organisms, it often reveals a much more complex and dynamic story than the little change implied by the term “living fossil”. The goal of my project is to evaluate this claim in horseshoe crabs.

Horseshoe Crab (Euproops Danae) Fossil ©️2021 Sam Ocon

How are you setting up and testing for your project?

One way we can evaluate evolutionary change in a group of organisms through time is by calculating a metric called “evolutionary rate”, which is basically the number of changes between an ancestor species and descendant species, divided by the amount of time between the occurrences of those two species in the fossil record. This can be calculated for genes, but since I’m working with fossils, I’m looking at overall shape changes. I’ve used three different methods to calculate evolutionary rate in horseshoe crabs, all done in the programming language R. The first was using a discrete character matrix and the package “Claddis”, the second was calculated by hand, also using a discrete character matrix, and the third method was using anatomical landmarks and semi-landmarks placed on 2D photographs of specimens.

Any results yet?

So far, we are seeing higher rates of evolution in the horseshoe crab groups that display more unique morphologies, which are also the groups that tend to explore freshwater habitats. On the other hand, the groups of horseshoe crabs that display more “conservative” body plans and stay in their ancestral marine habitats tend to display lower average evolutionary rates.

What has been the most interesting/challenging?

I thought I was very familiar with R when I started my degree. I was wrong! I’ve hit a lot of coding roadblocks, but working through them has really strengthened my skills as a programmer and as a scientist.

How will this project help society?

Horseshoe crabs are kind of unsung heroes. They’ve been on this planet for at least 480 million years and have survived all 5 major mass extinctions. Right now, modern horseshoe crabs are the reason we can safely be vaccinated – we use a compound in their blood to test for bacterial endotoxins in internal medicines like vaccines or implants. Horseshoe crabs are also a big part of food chains worldwide and are used as bait in multiple fishing industries. Unfortunately, horseshoe crab populations are declining, and we need to protect them to ensure the survival of humans and organisms across the globe. Understanding how horseshoe crabs have responded to past mass extinctions will not only help us better understand the past but will help us predict the future – namely, how horseshoe crabs might respond to the current climate crisis, and how we can make sure they survive another 480 million years.

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