Don't opt out: click here to learn more about our work.

Link between ancient arthropod groups unearthed

Agnostinids and trilobites found to be long-lost relatives

Link between ancient arthropod groups unearthed

Agnostinids are a group of extinct early arthropods and have long confounded scientists on where they fit in the evolutionary tree.

PhD student Joseph Moysiuk and Associate Professor Jean-Bernard Caron from the Department of Ecology & Evolutionary Biology have discovered that agnostinids may be a sister group to trilobites. The findings were published in Proceedings of the Royal Society B on January 29.

The fossils used for the study come from the Burgess Shale fossil deposit in Kootenay National Park and Yoho National Park in British Columbia and are kept at the Royal Ontario Museum.

The Burgess Shale is significant due to its age and what specimens it preserves.

This fossil deposit dates back to the Cambrian Period, which was over half a billion years ago.

During this period, the Cambrian Explosion occurred, during which “the first representatives of most major living animal groups appear in the fossil record for the first time,” wrote Moysiuk in an email to The Varsity.

Furthermore, the Burgess Shale has preserved specimens exceptionally well, beyond just bones and shells, but also soft tissues such as nervous systems and digestive tracts as well.

Modern examples of arthropods include insects, crabs, and spiders.

Trilobites lived over 250 million years ago and, physically, “can be thought of as resembling a modern horseshoe crab, although they are at most very distant ‘cousins,’” wrote Moysiuk.

Evolutionary relationships can be traced by looking at shared characteristics between species. To determine where agnostinids fit with other arthropods, their fossils were used to note the similarities in “the armor and soft tissues of trilobites and other groups,” wrote Moysiuk.

While they share some similar characteristics with trilobites, agnostinids, which lived almost 100 million years ago, are eyeless and have dumbbell-shaped bodies.

Furthermore, there are six pairs of limbs located in the head of the agnostinid. In comparison, trilobites have four pairs and the mouthparts in a modern insect’s head are actually modified limbs.

The agnostinid specimen used in the study had preserved soft tissues, specifically the limbs. Moysiuk explained that the “first pair of limbs in agnostinids are long sensory antennae. These are followed by oar-like swimming appendages and several sets of walking legs.”

The relationship between the groups was established through a phylogenetic analysis, which “resulted in an evolutionary tree in which agnostinids and trilobites are more closely related to each other than to any other group,” added Moysiuk.

This finding led to a grouping in which agonostinids are part of a sister group to certain trilobites. The study found that the shared characteristics were of soft tissues and the armour — specifically the tergites, or shield-like plate covering, and cephalic shield, which covers the head area.

“The close relationship between trilobites and agnostinids, despite the difference in [the] number of head limbs, supports the notion that the composition of the head in early arthropod groups may have been evolutionarily variable, in contrast to its general stability in many modern groups like insects or spiders,” wrote Moysiuk.

Moysiuk noted that the best preserved specimen was from Marble Canyon, an area first mentioned in 2014 in Kootenay National Park. “This study is just one of a number of exciting discoveries that have come out of this site, with many more to come!”

Further research into the head region of arthropods and the development of early trilobites is needed to determine the relationship between the groups with greater specificity.

The Dawn of Life

The Royal Ontario Museum’s exhibit will travel four billion years back in time

The Dawn of Life

Last week, the Royal Ontario Museum (ROM) finalized plans to build The Willner Madge Gallery, Dawn of Life. As its name suggests, the Dawn of Life will feature fossils from the start of life about four billion years ago until the appearance of dinosaurs over 200 million years ago.

Professor in the Department of Ecology & Evolutionary Biology and Department of Earth Sciences Jean-Bernard Caron and his research team travelled to the Burgess Shale and collected some of the fossils that will become a focus of Dawn of Life.

“Without the close relationship we have with U of T, this would not be possible,” said Caron, who is also the Richard M. Ivey Curator of Invertebrate Paleontology at the ROM. “Without students, my collection would be a pile of rocks.”’

Showcasing Canada’s ancient past

The Cambrian Explosion occured 542 million years ago. This period marked the rapid appearance of diversified animals and mineralized fossils.

The Burgess Shale in British Columbia contains a myriad of fossils from the Cambrian period. In particular, the Burgess Shale is known for its intricate preservation of soft-bodied animals. Many of the fossils from this UNESCO World Heritage site provide a wealth of information that cannot be found anywhere else.

Caron initiated the Burgess Shale projects after joining the ROM in 2006, providing insight into Canada’s ancient past.

In addition to the Burgess Shale, fossils from Mistaken Point in Newfoundland, Parc national de Miguasha and Anticosti island in Québec, and Joggins Fossil Cliffs in Nova Scotia will also be on display.

Featured fossils

The fossils in this exhibit are not only relics of the past, but are also representative of Canada’s rich archaeological history.

In 1886, Canadian geologist Richard G. McConnell collected fossils from the Mount Stephen Trilobite Beds in the Canadian Rockies. McConnell ended up with a collection of trilobites, one of the earliest arthropods. But he also recovered fossils that didn’t belong to trilobites. These fossils had unusual appendages and created confusion among researchers who followed in McConnell’s tracks.

In 1892, Joseph Whiteaves described the specimen as a shrimp. In 1911, Charles Walcott found a complete version of the specimen and described it as a sea cucumber. Other researchers throughout the twentieth century described the specimen as a sponge or jellyfish.

It wasn’t until 1985 that researchers Harry Whittington and Derek Briggs described two of the species in full, one of which is Anomalocaris canadensis, a basal arthropod related to spiders and shrimp.

Anomalocaridids were large predators that dominated the Cambrian seas roughly 535 million years ago.

In the 1990s, researchers from the ROM collected several, complete Anomalocaridids specimens. And in 1996, researcher Desmond Collins described Anomalocaris canadensis in detail.

This specimen is one of many treasures that will be on display in Dawn of Life.


Visitors will also be able to view banded iron formation — from the Nuvvuagittuq Greenstone Belt in northern Québec — which contains the earliest evidence of life on earth.


At the preview last week, visitors had the chance to see Acutiramus macrophthalmus in person. The fossil is the world’s largest specimen of its kind. It’s not evident from its large size, but the 420-million-year-old specimen is a distant relative to horseshoe crabs.


A 370-million-year-old Eusthenopteron fish and a Xenasaphus devexus trilobite are examples of some of the other fossils that will be featured.




Construction of the Dawn of Life is slated to begin in 2019 and the ROM hopes to open the exhibit in 2021. Meanwhile, a preview of the gallery is located on the second-floor rotunda.