Forty years ago an amateur Scottish paleontologist named Stan Wood made a fascinating discovery, uncovering Westlothiana lizziae, nicknamed “Lizzie.” The ancient salamander filled a niche that geologists had been after for years, marking the transition of the first animals from water to land.
The earliest life began with the emergence of more complex creatures, formed around 560 million years ago, in the Earth’s oceans. Lizzie is an ancient tetrapod, and her transition from marine to land was one of the most important evolutions in understanding how life formed on the planet. She resembled a small lizard with four legs and was about 20 cm (~7 inches) in length. She lived in freshwater and likely hunted small creatures within her habitat.
Scotland would have looked very different from what it does today, a veritable rainforest where volcanoes abounded and a treasure trove of ancient tetrapods thrived. Tetrapods are a species that retained some of their fishy features in their evolution from lobe-finned fishes, including fins and gills, but also had four legs and eventually walked on land.
Read More: Animals May Have Evolved from Sea to Land 35 Million Years Earlier Than Once Thought
What is an Amniote and Why is It Important?
Lizzie is one of the oldest known amniotes, the ancestors of reptiles, birds, and mammals, thought to have lived over 300 million years ago. This means that Lizzie is a common ancestor to humans as well. These specimens, known as the “East Kirkland fossils,” play a key role in animal evolution.
Yet this critical fossil had never been properly dated until University of Texas Ph.D. student Hector Garza had the opportunity, publishing the findings in a recent PLOS One article with the help of his professor Elizabeth J. Catlos.
“It came from a museum in Scotland and no one really knew its date,” says study author Elizabeth J. Catlos, a geologist at the University of Texas at Austin.
Once they were provided with part of the specimen, researchers used a technique called radiometric dating, which analyzes the decay of radioactive isotopes to calculate the age of the rock. Catlos was surprised that the technique hadn’t been used before on such an important specimen.
Zircon crystals within the rock provided the information that researchers needed to date the rock 14 million years older than it was previously thought to be, says Catlos. Zircon crystals were originally formed from magma, and because of their durability, they can be used to date extremely old rocks, painting a picture of a world from a very long time ago.
Unlocking the Mysterious Romer’s Gap
The new findings date Lizzie to a period called the Romer’s Gap, where researchers have almost no fossils. It’s a literal black hole in the fossil record. The gap spans from 360 million to 345 million years ago, an early period during the Carboniferous for which researchers have few specimens.
The reasons for the gap aren’t completely clear, but some researchers think that it’s because of a transition in the rocks themselves and the way that they were preserved during this period of time. Alternatively, it might be that the rocks have simply not been discovered yet. But whatever the reason, Lizzie seems to have come from this mysterious period in our Earth’s history.
Catlos says that answering questions like these comes down to museums allowing their specimens to be properly analyzed. She says that often these rocks, which are fragile and priceless, come from museums unwilling to part with them. However, for them to be properly dated, geologists must be able to analyze them using the most modern technology.
In this case, researchers were provided with pieces of the specimen, and they made a big discovery, but so often that’s not the case.
“If we want to answer these big questions, museums need to make the rocks available to us,” says Catlos.
Read More: The Rise of the Tetrapods: How Our Early Ancestors Left Water to Walk on Land
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
National Museums Scotland: Meet 'Lizzie', a 345 million year old fossil
National Museums Scotland: The mysterious 15 million year gap in our evolution
National Park Service: Geology: Radiometric Age Dating
Sara Novak is a science journalist based in South Carolina. In addition to writing for Discover, her work appears in Scientific American, Popular Science, New Scientist, Sierra Magazine, Astronomy Magazine, and many more. She graduated with a bachelor’s degree in Journalism from the Grady School of Journalism at the University of Georgia. She's also a candidate for a master’s degree in science writing from Johns Hopkins University.
