Building Bridges

As the debate on the age of the Isthmus of Panama matures we respond to an eLetter.

Taken from Science Advances

8 November 2016

We thank Erkens and Hoorn for their constructive comments. Like us, they believe that collaboration between biologists, geologists and paleontologists focusing on data and analyses is required to unravel the history of the Isthmus of Panama. We agree with Erkens and Hoorn that the Continue reading

Formation of the Isthmus of Panama

The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.

pdf of the paper

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New opportunities in the O’Dea lab

We are looking for three new interns/fellows to join the O’Dea lab. For more information download the flyers here: opportunities in the O’Dea lab

Project 1 (one position). Interoceanic differences in energy flow. Position open now, send CV and cover letter to odeaa@si.edu.

Project 2 (two positions). The ecological, life history and environmental differences between Holocene and modern Caribbean coral reef fish assemblages using fossil otoliths. To apply follow directions on the flyer.

Isthminia panamensis: the 6 million year old marine ‘river’ dolphin

isthminia panamensis SI

Four years ago Panamanian student Dioselina Vigil discovered a fossil in rocks near the small town of Piña. It turned out to be more than a bunch of bones. After careful preparation under the careful guidance of Smithsonian marine mammal paleobiologist Nicholas Pyenson and his team, the amazing fossil skull, replete with most of its teeth, was revealed to be a new genus of ‘river’ dolphin which we named Isthminia panamensis.

Isthminia, now an extinct lineage, is the closest relative of the Amazon river dolphins but was found in rocks that were deposited in open ocean just 6 million years ago. In this context the evolution of the river dolphins’ ecological shift from the sea to river becomes just a little clearer.

We are extremely proud that all aspects of the study are open-access. 3D models are available from the Smithsonian’s X 3D site for anyone to download, print and study. The paper itself is published in the open-access journal PeerJ. We even made all reviews available to read in this increasingly popular model for publication and divulgation. A 3D print of the specimen is on display at the Panama’s Biomuseo, and I even have a 3D print of the fossil in my lab.

Get the article here, play around with the 3D models and print out your own Isthminia panamensis

Teasing apart the drivers of extinction over 500 million years

From colleague and friend Paul Harnik’s Paleolab Blog: “How does environmental change shape the relationships between ecological traits and extinction risk? The fossil record is an invaluable resource for answering such questions. In a paper now available early online in the journal Global Change Biology, my collaborators and I show that over the last 500 million years global environmental and geochemical changes have had remarkably little effect on the relationship between geographic range size and extinction risk among marine mollusks. In other words, clams and snails with small geographic ranges have been at elevated risk of extinction throughout their evolutionary history regardless of broad-scale environmental conditions. In contrast, we found that mollusks that live in (rather than on) sediments on the seafloor tended to be at lower risk during times of warmer climate.”

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What drives change in the seas?

What drives major ecological and evolutionary changes in the seas? To explore this question we documented changes in the abundance of different clams in the Caribbean over the past 11 Myr.

The structure of clam communities shifted dramatically with an increase in the abundance of attached epifaunal bivalves and a decrease in infaunal bivalves. This was driven by the proliferation of coral reefs, ultimately caused by the closure of the Isthmus of Panama.

These data provide a classic case of proximate and ultimate drivers of evolutionary change. Jill Leonard-Pingel was lead author. Pdf forthcoming….

Extinctions in ancient and modern seas

In the coming century, life in the ocean will be confronted with a suite of environmental conditions that have no analog in human history. Will marine species adapt or go extinct?

The last two years I have been involved in a dynamic working group called “Determinants of extinction in ancient and modern seas” led by Paul Harnik, Rowan Lockwood and Seth Finnegan and funded by NESCent. The aim of the working group is to use the history of life as preserved in the fossil record to help make better predictions about where life is heading in the future, especially in view of the looming sixth mass extinction.

We have just published our first paper in Trends in Ecology and Evolution. The study compares the patterns, drivers, and biological correlates of marine extinctions in the fossil, historical, and modern records and evaluates how this information can be used to better predict the impact of current and projected future environmental changes on extinction risk in the sea.

Download the pdf of the paper by clicking on the image.

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What happened at the end of the Cretaceous?

Even genetically identical animals can look very different if they grow and live in different environments. Think ‘you are what you eat’. I make use of this phenomenon to try to reveal changes in environments in the deep past by first understanding what drives change in morphology in the animals in question and then measuring that morphology in fossils through time.

I applied this paradigm to one of the most studied and certainly most discussed events in the history of life on earth. The K-T (Cretaceous-Tertiary) boundary, 65 million years ago and the demise of the non-avian Dinosaurs and a suite of other animals and plants in the seas and on land. I made detailed measures of morphology in a number of fossil bryozoans in a beautiful K-T section of chalk in Denmark.

Rapid and repeated changes in morphology suggest that there were a suite of environmental changes in the last few thousand years just before the K-T boundary.

Although we dont explore the causes of the extinctions, or the ‘smoking gun’, these results are important for a full understanding of the complex changes associated with major extinctions observed to occur around the world. Click on the image for the pdf.

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Sex in the Caribbean

Evolutionary success was determined by mode of reproduction in cupuladriid bryozoans: Closure of the Panama Isthmus 3 million years ago led to a rapid reduction in primary productivity across the Caribbean. In response, cupuladriid bryozoans underwent a major transition, with evolutionary winners and losers dictated by how much sex they were having. Click on the image to download the pdf.

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Hopping hotspots

Hotspots of high species diversity are a prominent feature of modern global biodiversity patterns. Fossil and molecular evidence is starting to reveal the history of these hotspots. There have been at least three marine biodiversity hotspots during the past 50 million years. They have moved across almost half the globe, with their timing and locations coinciding with major tectonic events. The birth and death of successive hotspots highlights the link between environmental change and biodiversity patterns. The antiquity of the taxa in the modern Indo-Australian Archipelago hotspot emphasizes the role of pre-Pleistocene events in shaping modern diversity patterns. Click on the image for the pdf of the paper.

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Form and life habit in cupuladriids

Since the late Mesozoic, several bryozoan groups have occupied unstable soft-sediment habitats by adopting a free-living and motile mode of life. Today, the free-living bryozoans often dominate epibenthic faunal communities in these expansive habitats, yet their biology and ecology remain poorly understood. This study examines their unique mode of life by exploring the relationship between form and function in the free-living Cupuladriidae of tropical America. Click on the image for the pdf of the paper.

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