When two ecosystems collided, ichthyosaurs re-evolved the ability to consume large prey

Land contact between North America and South America has long been a source of research. The Isthmus of Panama – the narrow strip of land between the two continents – fully emerged about 3.5 million years ago. It enabled contact between terrestrial mammals of North and South America and led to large-scale invasions of placental mammals in South America and the eventual extinction of most southern marsupials.

At the end of the Jurassic, 150 million years ago, the Earth was emerging from a relatively cold period, the supercontinent Pangea was breaking up and a peak in extinction intensity was affecting ecosystems. During the next period, known as the Lower Cretaceous, the planet warmed, global sea levels and atmospheric oxygen rose, and continents continued to fragment.

As a result, two entirely isolated oceans, the Eastern Pacific and the Western Tethys, which would later become the Atlantic Ocean, came together through the Hispanic Corridor. This union of the oceans at a time of relatively high temperatures created a perfect storm for ecosystem evolution and drivers of new biodiversity in the Neotropics – an event that would transform the course of marine ecosystems for 60 million years. future.

Biodiversity hotspot

Hispanic hallway.
(climate archive), Author provided

Our research team, made up of scientists from Colombia, Canada and Germany, explored the Neotropics using the fossil record of the Paja Formation, an understudied shallow marine deposit in central Colombia that formed deposited just after the formation of the Hispanic Corridor. Our main objective is to understand the origin and evolution of this marine ecosystem, and whether it served as a potential hotspot of ancient biodiversity – an epicenter for the appearance and flourishing of new species.

We have discovered a new species of ichthyosaur, the giant fish-like marine reptile. By examining a beautifully preserved skull specimen of the species we named Kyhytysuka sachicarumwe have recognized that it was the first hypercarnivorous ichthyosaur of the Cretaceous.

photograph of an ichthyosaur skull
The skull of Kyhytysuka sachicarum.
(Cortés, Maxwell, Larsson), Author provided

The new species evolved from Jurassic ichthyosaurs in Tethys, but differed in having unique teeth for an ichthyosaur: there were several different tooth shapes that served different purposes, ranging from drilling to serrated crush cut.

This large ichthyosaur represents a revival of the hypercarnivore (eating large prey). Although some early evolving ichthyosaurs did this, they moved on to smaller fish and invertebrates for the next 70 million years. Kyhytysuka somehow re-evolved the ability to hypercarnivore during this time and place of intense ecological upheaval.

Large sea animals

Kyhytysuka was also one of the last surviving ichthyosaurs. Most ichthyosaurs died out at the end of the Jurassic – only a few reached the Cretaceous, but none survived 100 million years ago. The fossil record of the Paja Formation preserves clues to the evolution of the marine ecosystem.

3D animation of Kyhytysuka sachicarum.

These rocks are home to some of the largest marine animals ever discovered, including several ichthyosaurs, huge whale-sized pliosaurs, the first long-necked elasmosaurs, and a 10-meter-long crocodile that was the last survivor of a long line of Jurassic saltwater crocodiles.

The fossil record also contains the oldest known sea turtles in the lineage of today’s sea turtles as well as the origins of several crustaceans that survive today.

Information in the fossil record helps us reconstruct ancient food web interactions based on what was present in the eastern Pacific and western Tethys prior to their contact and what was present when they contacted the Paja Formation. . Changes to these ancient food webs promise to shed light on the environmental and ecological factors involved in the long-term sustainability of ecosystems.

ALT
An artist’s reconstruction of a Lower Cretaceous ecosystem, created for Hace Tiempothe first illustrated book on the geological history of Colombia.
(Hace Tiempo/C. Jaramillo and Guillermo Torres Carreño), Author provided

Close inspection of fossils from this unique time and place offers a new window into what happens when ecosystems collide. So far, we find that this facilitates the evolution of huge top predators and several evolutionary origins of new lineages that would persist for millions of years.

These results provide relevant data to better understand the consequences of the Jurassic-Cretaceous extinction on marine animals and, ultimately, the advent of current marine ecosystems.