Scientists have forever studied fossils in an attempt to uncover the various mysteries surrounding evolution. However, the lack of fish fossils prior to 360 million years ago has kept one such mystery in the dark – where exactly did vertebrates first originate? Vertebrates are defined by the presence of backbone or spinal columns and have thought to diversify around 480 million years ago, splitting into groups that would become jawless fish, cartilaginous fish, and bony fish. It’s this last group that evolved into amphibians, reptiles, birds, and mammals. However, the reason why backbones first appeared and the place of its origin has remained a hotly debated topic in paleontology.
That debate can now be put to bed, as recent research has come up with a robust answer to the aforementioned question. Lauren Sallan, a paleobiologist at the University of Pennsylvania have teamed up with researchers from the University of Birmingham to delve directly into the mystery. The researchers created a database that consisted of 2,728 early records for jawed and jawless fishes. Carbon dating the fossils confirmed the era from which they emerged – in between 480 to 360 million years ago – the period when the first vertebrates on earth came about. The team used mathematical modeling to reconstruct missing information in the fossil record, which allowed them to make informed predictions regarding the habitat type in which these ancestors of various vertebrate groups emerged.
By comparing the fossil features to the environment in which they were preserved, the researchers now had their definitive answer. The first vertebrates’ lives near seashores, in areas often described as the intertidal zone, or shallow lagoons. “We found that all vertebrates, from the first jawless forms to sharks and bony fishes, originated in very restricted shallow waters hugging the coastline,” says Sallan. She also suggests that these shallow water environments may have encouraged the evolution of vertebrates because their bones helped them withstand swirling or crashing waves found in such locations.
The finding has surprised the paleo-community, as big evolutionary steps are usually associated with biodiversity hotspots, such as coral reefs. However, the data suggest that fishes first occurred in shallow, salt-like environments like tidal areas and lagoons – after which they either moved on to fill the sea or developed amphibian-like characteristics to inhabit the land.
The findings of the study also help in answering one important question – why was it so hard to find fossils of early vertebrates? If these fishes first lived on the edges of the ocean, there is a possibility that the forceful waves may have blasted the fossils into tiny fragments. Hence, the presence of relatively few fossils of early vertebrates indicate that they must have originated in a location where their remains were decimated by the force of nature.
As anthropogenic climate change results in ocean acidification, the coral reefs of the planet are depleting in large numbers, reducing biodiversity. “One of the things we want to know is whether these shallow waters are still the biological pump that is feeding the reef,” Sallan says. “Where is the current site of innovation?” If these shallow waters are still feeding the reef to this day, maybe scientists shouldn’t be too worried about coral reefs getting depleted. Instead, they can create a biological hotspot in shallow waters.