Isthmus of Panama Younger than We Thought

Split by the Isthmus of Panama: Species of butterfly fish, sand dollar and cone snail that today live on the Pacific and Caribbean coasts of Central America are very closely related. Genetic sequencing shows that only 4 to 3 million years ago, each pair was a single species, demonstrating that marine connections between the oceans must have existed until that time. (Image by Coppard et al., via The Smithsonian)

It’s probably not something you’ve given much thought to, unless perhaps you’ve visited Central America in the past and experienced first-hand the incredible biodiversity displayed in such a small area. Part of the reason why this little strip of land has so many different species of animals and plants is that it connects two very large continents that used to be separate, but it also has given birth to new aquatic species via evolution, as you can see from the image above. Previous thought on the topic had been that the Isthmus of Panama rose from the ocean roughly between 23 and 15 million years ago, but a very large and very interdisciplinary team of researchers – mostly with some link to the Smithsonian Institution, which has its Tropical Research Institute in Panama City – have reaffirmed that the enormously important geological change occurred around 3 million years ago.

Beth King reports for the Smithsonian Insider website:

Long ago, one great ocean flowed between North and South America. When the narrow Isthmus of Panama joined the continents about 3 million years ago, it also separated the Atlantic from the Pacific Ocean. If this took place millions of years earlier, as recently asserted by some, the implications for both land and sea life would be revolutionary. Aaron O’Dea, staff scientist at the Smithsonian Tropical Research Institute (STRI), and colleagues writing in Science Advances firmly set the date at 2.8 million years ago.

“Recent scientific publications proposing the isolation of the two oceans between 23 to 6 million years ago rocked the generally held model of the continental connection to its foundations,” said Jeremy Jackson, emeritus staff scientist at the Smithsonian. “O’Dea and his team set out to reevaluate in unprecedented, rigorous detail, all of the available lines of evidence—geologic, oceanographic, genetic and ecological data and the analyses that bear on the question of when the Isthmus formed.”

“The timing of the connection between continents and the isolation of the Pacific and Atlantic oceans is important for so many reasons,” O’Dea said. “Estimates of rates of evolutionary change, models of global oceans, the origin of modern-day animals and plants of the Americas and why Caribbean reefs became established all depend upon knowing how and when the isthmus formed.”

The team of researchers from 23 institutions, including nine current or emeritus staff scientists from STRI and the Smithsonian’s National Museum of Natural History and 13 current or previous Smithsonian post-doctoral fellows concluded that records from marine and terrestrial fossils, volcanic and marine rocks and the genes of marine animals split by the formation of the Isthmus all tell the same story.

The study used three key pieces of evidence defined when the land bridge was finally in place:

  • Analysis of the family trees of shallow-water marine animals such as fish and sand dollars from the Pacific and Caribbean (Atlantic) sides of the isthmus show genetic mixing until after 3.2 million years ago.
  • Surface waters from the Pacific and Caribbean mixed until about 2.8 million years ago, as seen in deep-ocean sediments.
  • Massive migrations of land animals between North and South America began sometime before 2.7 million years ago.

Snapping shrimp species on either side of the Isthmus of Panama are morphologically and genetically similar. Shallow water dwelling species are more closely related than deep dwellers, as would be expected by a slowly emerging isthmus. (Image by Arthur Anker)

Read the rest of the article here.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s