Two PhD students at Saint Mary’s University spent four months studying hundreds of skulls of horses from Sable Island, and now hope to analyze the data they’ve collected to learn more about the equines’ lives.
Katharyn Chadwick and Richard Orton’s PhD work focuses on different aspects of right whale conservation. They both work with Saint Mary’s Frasier Lab, which has a longstanding relationship with the Sable Island Institute and Zoe Lucas, president of the institute who has spent much of her life studying many aspects of the island, including the horses. Over the years, the Frasier Lab did some genetics work on the Sable Island horses.
“It just came up in conversation that Zoe had this amazing, unique collection of horse skulls she had been collecting since the 80s,” Chadwick said.
The pair got funding from SMUworks, a bursary-based student employment program, to do the project. They’re also working in collaboration with the Museum of Natural History.
Neither Chadwick or Orton have been to Sable Island. Chadwick said she learned about Sable Island and the horses about a year ago when she moved to Halifax. Orton, meanwhile, heard about the island from a friend in the US.
Chadwick and Orton had a collection of 741 skulls to work with.
“The goal is to get everything catalogued in a database,” Orton said. “Maybe the quality of the skull, when it was collected, what sex the skull probably is, maybe group it into an age class. Are teeth missing? Are there any weird growths, that sort of thing. And have it in a database that researchers or anyone in education or academia can access and hopefully do their own research with their data.”
Finding patterns in the measurements
Chadwick and Orton took about 13,000 measurements of the horse skulls and more than 6,000 photographs. For each skull, they took 19 measurements and six photos.
Chadwick said they can determine the sex of the skull by the presence of canine teeth, which are more common in male horses.
Chadwick added that in other populations of horses, 20% to 25% of the females can have canines. That can make it difficult to assign a sex to the skull, still it remains the main metric.
They also studied the teeth of the horses that Lucas had collected over the years. Chadwick said some of the horses had what’s known as “wave mouth,” an uneven wear pattern seen on the horses’ molars caused by misalignment of the upper and lower teeth.
There were also large variations in wear of the teeth. For the Sable Island horses, that wear on the teeth is affected by their diet on the island, but also the sand they sometimes ingest when eating.
Orton said they’ll certainly learn more about the horses as they start to comb through all the data they’ve collected and then go on to filter and analyze that data.
“We’ll be making comparisons with the 19 measurements, for example, between males and females to understand that there might be differences there. Maybe larger eyes or a wider mandible,” Orton said. “We’ll assess differences across different age classes, too, to understand maybe how the skulls developed over time.”
Orton said as they were taking the measurements, they were also tracking where the skull sutures–those are the lines where portions of the skulls–meet.
When the horses are young, the sutures are flexible, like they are in humans when they’re infants. That gives the skull room to move as the brain develops. Over time, the sutures start to fuse.
Orton said out of the more than 700 skulls they measured, there were 100 skulls where the sutures were completely fused. And of those 100 skulls, every one of them was from a male horse.
“This isn’t something, again, that we were looking to test differences, the rate of fusing of sutures between sexes,” Orton said. “But we might have stumbled across something.”
Orton said there could be a few explanations for this. First, they thought maybe the females were dying before they got to an age where the sutures are completed fused, and the males were living longer.
Or Orton said there could be a bone deformation that happens in humans as well that requires surgery where the sutures are fused at birth. In humans, that condition requires surgery. However, they haven’t seen any misshapen skulls in the horse skulls.
Or there could be a biological mechanism for this. Orton pointed to another study in mice where the sutures in their skulls fused more quickly in males than females. Those researchers were able to link that to male mice competing for territory or access to females. If a horse has a stronger skull, it’s more likely to survive.
“It’s possible that there could be some sex selection going on with the horses,” Orton said.
The skulls had other interesting features that could be studied, too. Some of the horse skulls had absesses, including one skull that belonged to a stallion named Machu Picchu. Still others had lichen growth on them from after the horses died.
Chadwick and Orton have so far worked on the project for four months and said it was much different than their other work studying right whales where they’re working on small bits of tissues to understand the genomes of the whales.
Orton said they’re still learning the story of the Sable Island horses through their work, but more will emerge as they go through the data.
“I think we know what we want to ask, but it’s finding the right techniques essentially and the right statistical analyses, and the right equations and math to use to test our hypotheses and to try to get answers to the questions they have,” Orton said.
Orton said part of the reason they chose the measurements they did is because they’re compatible to the stories of other breeds of horses elsewhere.
“One question that could be asked, if not by us, but by someone else, is to take the measurements that we collected and make comparisons to other populations, other museums collections on clydesdales or thoroughbreds and try to understand if there are signals from those breeds that still show in the Sable Island populations.”
Chadwick said while Lucas knows the history of some of the skulls, when the horses were born and when they died, the history of many is unknown.
Analyzing the data
Now that all of the measurements of the horses have been taken, Chadwick and Orton will get back to researching right whale genetics. But they’ll return to the work on the Sable Island horse skulls in the new year. Then they’ll start analyzing the data, refining their questions, and then determining what statistical testing they need to do next.
Chadwick and Orton said they will write and publish a paper on their work, but would like to see someone continue learning from the skulls.
“There are probably people who specialize in equine studies who have 101 ideas,” Chadwick said. “That was the main thing for Zoe and the institute was getting the skulls out there and to starting that process and that ball rolling.”
“Maybe if someone has a particular interest in the horses they can look at more of the dental work, or somebody has the time and connections to look at other populations. I am sure the institute would welcome the opportunity for these guys to be looked at further.”