Monday, August 10, 2015

Cave Fossil Faunas: Cuba 2015

Once again I am back from exciting fieldwork on the main island of Cuba, the largest of all Caribbean islands. Cuba is an island full of paleobiological treasures and riddles that await to be unraveled. Every year I think of ideas and excuses to return and see things I did not see before.

The Cuban archipelago is comprised of the main island of Cuba, the much smaller Isle of Pines, plus several thousand cays and keys. As you may have noticed from my previous posts, I am biased towards Cuba and the Greater Antilles. This is not only because it is my home country, but because its complex geological history provides a unique opportunity to study the intricacies of the Caribbean's ancient environments and the evolution of its unique biota.

Fig. 1: Pliocene limestone of the Canimar formation on the west banks of the Canimar river, in Matanzas.

This time, I visited with the goal to explore and assess several regions, those rich in caves and fossil remains that were pending from the previous year's roster.

My research involves studying the faunas of the past. In this case, the past faunas of Cuba and the Greater Antilles, which in a way make up an archipelago of their own comprised of the large islands of the Bahamas, Jamaica, Hispaniola, Cuba, Puerto Rico, and their many thousands of keys. With the data, we gather I hope to elucidate the processes of the most recent extinctions there, and the role that humans have played in it, especially the last 5000 years since the arrival of the first Amerindians to the island and later the Europeans. With this, I strive to understand the mechanism and the overall magnitude of their ecological impact. This is, within the scheme of time, mostly after the onset of the last interglaciation, a warm period called the Holocene.

With this in mind, our trip began in the city of Matanzas, on the banks of the Canimar river (fig. 1).

Fig. 2: Cliff cave on the Canimar river gorge, formed on Pliocene limestones of the Canimar fm.

This is a region with deep canyon walls dotted with caves (fig. 2). The caves open up in the limestone of the Canimar formation, rocks that formed between 5 and 2 million years ago in the marine environments that surrounded this region. Then, all this was underwater. Recent tectonic oscillations have risen those lithified marine sediments which the river has carved into a gorgeous, biologically rich gorge; an environment that the Amerindians (native aboriginals) knew how to exploit well.

Fig. 3: The red-legged thrush Tordus plumbeus in the woodlands of the Canimar river. A common member of the local fauna.

The fossil remains of the terrestrial fauna found in the region's cave deposits are very similar to the modern fauna. This fauna is comprised of large rodents called Jutias or Hutias (Capromys spp.), reptiles, amphibians, and a diverse avifauna that includes the red-legged thrush (Tordus plumbeus), like that of figure 3, and the endemic Cuban trogon (Priotelus temnurus) of figure 4.

Fig. 4: The Cuban trogon Priotelus temnurus is a Cuban endemic, and the national bird.

We were targeting caves with large openings or sinkholes (also called dolines) which allow in light, rain, soil, and animals that come to roost within. Other animals wander inside or become trapped, leaving behind the remains of their adventure scattered on the cave floor. As my previous post on Cuban and Hispaniola exploration show (here), these caves are especially important to my research because they have served as a natural reservoir for faunal remains, representative of those that inhabited the region during the last hundred thousand years.

Fig. 5. Large sinkhole complex of Nesofontes' Cave, on Palenque Hill. Here animal
remains accumulated along with other debris that comes in from the outside.

There are few mechanisms that explain the presence of fossil remains within caves. Some fossils are part of the structural rock that makes up the caves. Those fossils are often visible on the cave walls and ceilings. They were part of the marine fauna of the shallow marine environments which gave origin to the limestone that now make up the hills and thus the caves (this process is called karstification if that rock is made out of carbonates like Calcium carbonate). Other fossils are mixed with the soil, plant material, and rock debris that has been dragged into the cave by rain waters or floods over time (fig. 5). Other animals become trapped inside the cave, because they fall in, or are brought in by predators. These are both active and passive mechanisms, both giving way to the accumulation of animal remains within these cavities, and so the treasures of our expeditions.

Fig. 6: Peculiar speleothems within the same cave. This structure testifies to the slow action of carbonatation. 

Caves have interesting water-locked histories. Water that filters through the rocks, laden and heavy with dissolved minerals in their solution, expand cracks within the rocks that eventually, in thousands of years, become caves (like those of fig. 5 and 7). Once these cavities are large enough they start to develop internal microclimates that give way to other secondary formations such as stalactites and stalagmites, collectively called speleothems (fig. 6-8).

Fig. 7: Large lake and sinkhole cave in northeastern Matanzas city: Saturn's Cave. 

Sometimes, parts of the cave's roof or side walls become weak or dissolved by water and collapse, giving origin to the sinkholes mentioned above. These apertures are the key to large deposit formations inside the cavities, and also to the arrival and adaptation of fauna to the different light microenvironments within them. Light does not penetrate into the cave evenly. Instead, light penetrates the cave following square laws that dictate that light is strongest near the opening or source, and weaker or nonexistent deeper into the depths of the cave. This leaves areas of penumbras and umbras in between. Living organisms have evolved to inhabit all these microbiomes.

Fig. 8: Megastalactite speleothems called Columbus Drape at the famous Bellamar Cave
 in Matanzas city. This structure is massive and has taken thousands of years to form. Use hand railing on
the upper left for scale. 

Other caves become inundated creating lakes, pools, and gours. These underwater dark environments are the origination grounds from which specific cave faunas evolve. These organisms range from bacteria to fishes, crabs and shellfish, that in the darkness of the caves have lost their eyes and pigmentation. In this sense, caves can be like islands: laboratories for natural selection and evolution.

The same water that percolates through cracks and crevices can create really marvelous, intricate structures after many thousands of years of drip and drips of water, such as those of figures 6, 9-10.

Fig. 9: Flow-stone grew from dripstone speleothems on Bellamar Cave, Matanzas.

In the same sense that caves are natural laboratories for the evolution of weird organisms, caves are natural laboratories for mineral formations. Out of drips of water, minerals precipitate out forming the aforementioned speleothems. Many of them often forming delicate and aberrant or exuberantly- shaped structures (like the anomolites or anomoliths of figure 10, at Bellamar Cave). These include drip stones, flow-stones (fig. 9), and even structures called "pine trees" or "cave pearls".  In the case of the delicate anemoliths, crystallization of the bicarbonates occurs as the filtered water, higher in CO2 concentrates, encounters the lower CO2 pressure inside the cavity, precipitating these crystals in the direction of the wind (fig. 10). These secondary structures can become natural perches to the volant fauna that inhabit the cave walls.

Fig. 10: Anemoliths of the Bellamar Cave. Peculiar and beautiful secondary formations,
indicative of specific cave microclimates.

Bats are the most famous of cave inhabitants. Many bats are strict cave dwellers, using caves to roost during the day and reproduce. Like the Cuban fruit bat Artibeus jamaicensis of figure 11, bats often select specific rooms inside the cave based on their proximity to the entrances, their internal temperatures, where they can segregate or mix with other species to roost. Other bats are peculiar in being solitary, meeting with their opposite sex only for reproduction during specific seasons, or selecting cave rooms with very high temperatures and humidity. Caves in which temperatures rise higher than 40 degrees Celsius and humidity is greater than 80 percent are called "hot caves", and some bats live exclusively in those. Our research often involves studying such specifically evolved bat fauna.

Fig. 11. Large Cuban fruit bat Artibeus jamaicensis parvipes.

My research also involves studying other faunas, of a more resent epoch. For example, my interests also involve zooarcheology, which is the study of fauna remains associated to human occupied or originated deposits. Such deposits span through aboriginal and colonial deposits, which can help understand the complexity of human-influenced faunal extirpation or domestication.

Fig. 12: El Morrillo, an 18th-century coastal fort on the bay of Matanzas, Cuba. 

Colonial occupation in the Caribbean, as in other parts of the New World after European rediscovery, gave way to modification of natural environments, the introduction of exotic-invasive faunas, of which remains can be found in or around colonial structures, such as that on figure 12 and 13.

Fig. 13: Frontal view of the Morrillo fort on the bay of Matanzas.

This fort served, as did fort San Severino of my previous post, in the coastal protection against illicit trade and pirate attacks throughout the colonial period. Generations of human habitation in these structures have left behind a good record of the use of the local and imported fauna. These deposits are often extensive, including faunas from before and after human occupations, which in turn are great for our study of the influence of mankind on natural faunas, and for establishing relative chronologies to these events.

Fig. 14: Sunrise in the Bay of Matanzas, northwestern Cuba.

From Matanzas, we traveled to another important, but much older karstic region: Pinar del Rio, in western Cuba (fig. 15). Pinar del Rio has a long standing history in the study of Cuban paleontology and geology, attracting the attention of prominent Cuban naturalists like Carlos de la Torre, Felipe Poey, and others since the late 18th century. Explorers have found fossils inside its caves and on its rocks. This region has some of Cuba's oldest rocks, and within its rocks is written the life history of the Caribbean region (fig. 15-17).

Fig. 15: Vinales Valley in Pinar del Rio, western Cuba.

In our search for old faunas, we extended our explorations to Vinales, a unique valley within the aforesaid region (fig. 15-16). This region is unique for many reasons. One is its extensive karst development, including uncountable honeycombs of mammoth caves within its limestone (fig. 17). These same limestones date back to the middle Jurassic when the Caribbean basis did not exist. However, these conic "mogote" formations we see are geologically recent, dating approximately to the Pliocene, between 5 to 2 million years ago.

The Guaniguanico mountain range is a unique karts region of the world. It includes 400-500 meter tall conic karts formations that resemble giant elephants such as those of the Sierra de Los Organos (the "Sierra of the Organs"). There are other parts of the world with such conic or cockpit karst.  Formations such as those of figures 15 and 16 are present in Jamaica, Hispaniola, Puerto Rico, and Guangxi in China. With the two extremes being the Vinales and the Chinese Guangxi.

Fig. 16: Giant elephant-like hills over 400 m in height called Mogotes, are formed out of uplifted Jurassic limestones.

Salvador Massip and Sara Isalgue wrote in 1923 "Cuba came from the depths of the ocean..."Vinales limestones contain fossil remains of prehistoric marine reptiles and mollusks, such as Plesiosaurus, ammonites, and belemnites. I went there searching for fossils of the early Cretaceous - a period several dozen million years younger than the Jurassic. I am interested in records which provide signals of oceanic anoxic events (OAE) and their effect, in this case of extinction-origination- of microfaunas such as phytoplankton and zooplankton. Forams, short for foraminifera, are microscopic single celled-organisms (heterotrophic Protists) that are part of the zooplankton. Forams can live in ocean bottom sediments (called benthic) or float along the surface of deep oceans (planktonic). When they die, they accumulate slowly on the ocean bottom, becoming part and originating sediments. Their shells or test then provide a record of the surrounding fauna and an approximation for the climate.

Fig. 17: Hanging caves at different levels within the Mogotes, indicating the effects of water at different uplift levels.

By chemically studying these fossil organisms we can determine if there were reducing or oxidizing conditions in the ancient oceans that may have lead to massive die-offs, such as is the case of the OAEs, which could further an understanding of the environment during the early stages of the embryonic Caribbean basin.

But I apologize. I have allowed my enthusiasm to extend this post larger than expected. I hope it has been interesting. But by no means, does it encompass the natural beauty or scientific attraction that the Caribbean, especially Cuba,  possess for these kinds of research. In the end, the goal is the same across geological time: to elucidate and deepen our knowledge of the awesome history of our "Pale Blue" planet.

Stay tuned for more post!

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