Finally, early sirenians in Africa

Dear readers, a lot has been going on around here since my last post several months ago. From finishing and successfully defending my dissertation (I now have a PhD), to getting married several days ago. In addition, Caribbean Paleobiology will be moving as I have been offered (and accepted) a postdoctoral position in another institution (more on that later).

What do I mean by the title of this post?

Here's the back story. As some of you may, or may not know, sirenians are closely related to elephants, and more distantly to other African mammals, such as rock hyraxes and aardvarks, among others (Asher et al., 2003); altogether these organisms are classified as Afrotherians (= African beasts). As the name implies, these organisms are either endemic of the African continent, or evolved there originally. The earliest proboscidean (elephants and their kin) appeared in what is now Morocco in the middle Paleocene (~60 million years ago) (Gheerbrant, 2009). This implies that the split between sirenians and proboscideans occurred in the early Paleocene (65.5-61.7 mya) somewhere in the northern half of the African continent. However, as we know, the fossil record is far from perfect, and for many years, that of sirenian implied that they originated outside of the African continent. The oldest-most-primitive sirenians, Prorastomus sirenoides Owen, 1855, and Pezosiren portelli Domning, 2001, (collectively known as prorastomids), were known only from early-middle Eocene (~48-40 million years ago) deposits in the island of Jamaica in the Caribbean region, making the origins of sirenians a paleobiogeographical conundrum. This, however, has changed in the last several months thanks to new discoveries.

Composite skeletal reconstruction of Pezosiren portelli, (modified from Domning, 2001).

Prorastomids in Africa

Last fall, in the August issue of Journal of Vertebrate Paleontology, a paper came out describing the first prorastomid remains from Africa (Hautier et al., 2012). The fossil was found in phosphatic deposits in the country of Senegal in the western part of the continent. Only one fossil was recovered, a single posterior thoracic vertebra. Fortunately, prorastomid vertebrae are quite different from those of other sirenians. The Senegalese fossil shows those telltale features of prorastomid vertebrae, such as the triangular outline of the neural canal, and the T-shaped spinous process (Domning, 2001; Hautier et al., 2012). This fossil, although from slightly younger deposits than the Jamaican prorastomids, confirmed the presence of these ancient sirenians in Africa.

A new fossil confirms the African origin of Sirenia

Just last week a paper by Julien Benoit and colleagues described a sirenian petrosal* found in early Eocene (~50 mya) freshwater deposits in Tunisia (northern Africa). The pretrosals of sirenians, unlike those of cetaceans (whales & dolphins) are not regarded as diagnostic. However the petrosal from Tunisia is distinctively primitive, more so than that of Prorastomus sirenoides (Savage et al., 1994; Benoit et al., 2013). That, combined with the older age of the Tunisian petrosal, confirms the presence of early sirenians in northern Africa. This new find, also adds additional information to the origins of sirenians. Sirenians were though to have gone aquatic earlier and more directly than cetaceans, which went through a freshwater phase (Clementz et al., 2006). The Tunisian sirenian was collected from freshwater deposits, showing that they did went through a freshwater phase first, then became fully marine (and some have eventually gone back to freshwater [i.e. Amazonian manatee]).

*This is the part of the skull that houses the hearing and balance organs; known as the petrous part of the temporal bone in humans. For more information on sirenian petrosals go here.

Comparison of the Tunisian petrosal (A-C) with that of Prorastomus sirenoides (D-F) (from Benoit et al., 2013).

Other questions still remain. Early sirenians, like Pezosiren and most likely Prorastomus and the Tunisian sirenians were amphibious; still having fully developed hindlimbs (see first figure). So, the question is, how did they made it from northern Africa to the Caribbean; did they crossed directly across the Atlantic, or did they followed the nearly continuous coastline present in the northern Atlantic in the early Eocene?
Personally, I favor the first. Cetaceans do seem to have taken the northern Atlantic route, whereas evidence for sirenians doing so, is still lacking (Beatty & Geisler, 2010). In addition, other tetrapods have crossed from Africa to the Caribbean and South America during the Cenozoic. Gavialoids crossed from northwestern Africa to the Caribbean sometime during the late Eocene, giving rise to gryposuchines, an endemic group of Caribbean-South American gavialoids (Vélez-Juarbe et al., 2007). Platyrrhine primates, caviomorph rodents and hoatzins did as well crossed from African to South America during the Eocene and/or Oligocene (Poux et al., 2006; Mayr et al., 2011; Antoine et al., 2012). The distance from Africa to South America and the Caribbean was shorter then than it is now, which likely made these multiple trans-Atlantic crossings more likely.

Map showing dispersal routes of early sirenians and cetaceans (from Benoit et al., 2013).

In their paper, Benoit et al. (2013) include the map above, which show dispersal routes of early sirenians and cetaceans. I mostly agree with that scheme, except that it implies that protosirenids (another group of early sirenians) originated in North America and dispersed to the Old World. This doesn't hold true in light of the fossil record of protosirenids whose most primitive members are found in early middle Eocene (48.6-40.4 mya) deposits in what is now India and Libya. I hope to cover the subject of sirenian paleobiogeography on a later, longer post, so stay tuned.


For a nice post about the Tunisian sirenian, go read Brian Switek's post over at NatGeo.

References

Antoine, P.-O., L. Marivaux, D. A. Croft, G. Billet, M. Ganerod, C. Jaramillo, T. Martin, M. J. Orliac, J. Tejada, A. J. Altamirano, F. Duranthon, G. Fanjat, S. Rousse, and R. Salas Gismondi. 2012. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B 279:1319-1326.

Asher, R. J., M. J. Novacek, and J. H. Geisler. 2003. Relationships of endemic African mammals and their fossil relatives based on morphological and molecular evidence. Journal of Mammalian Evolution 10:131-194.

Beatty, B. L. J. H. Geisler. 2010. A stratigraphically precise record of Protosiren (Protosirenidae, Sirenia) from North America. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 258:185-194.

Benoit, J., S. Adnet, E. El Mabrouk, H. Khayati, M. Ben Haj Ali, L. Marivaux, G. Merzeraud, S. Merigeaud, M. Vianey-Liaud, and R. Tabuce. Cranial remain from Tunisia provides new clues for the origin and evolution of Sirenia (Mammalia, Afrotheria) in Africa. PLoS ONE 8(1):e54307.

Clementz, M. T., A. Goswami, P. D. Gingerich, and P. L. Koch. 2006. Isotopic records from early whales and sea cows: contrasting patterns of ecological transition. Journal of Vertebrate Paleontology 26:355-370.

Domning, D. P. 2001. The earliest known fully quadrupedal sirenian. Nature 413:625-627.

Gheerbrant, E. 2009. Paleocene emergence of elephant relatives and the rapid radiation of African ungulates. Proceedings of the National Academy of Sciences 106:10717-10721.

Hautier, L., R. Sarr, R. Tabuce, F. Lihoreau, S. Adnet, D. P. Domning, M. Samb, and P. Marwan Hameh. 2012. First prorastomid sirenian from Senegal (Western Africa) and the Old World origin of sea cows. Journal of Vertebrate Paleontology 32:1218-1222.

Mayr, G., H. Alvarenga, and C. Mourer-Chauviré. 2011. Out of Africa: fossils shed light on the origin of the hoatzin, an iconic Neotropic bird. Naturwissenschaften 98:961-966.

Poux, C., P. Chevret, D. Huchon, W. W. de Jong, and E. J. P. Douzery. 2006. Arrival and diversification of Caviomorph rodents and platyrrhine primates in South America. Systematic Biology 55:228-244.

Savage, R. J. G., D. P. Domning, and J. G. M. Thewissen. 1994. Fossil Sirenia of the West Atlantic and Caribbean region. V. The most primitive known sirenian, Prorastomus sirenoides Owen, 1855. Journal of Vertebrate Paleontology 14:427-449.

Tabuce, R., L. Marivaux, M. Adaci, M. Bensalah, J.-L. Hartenberger, M. Mahboubi, F. Mebrouk, P. Tafforeau, and J.-J. Jaeger. 2007. Early Tertiary mammals from North Africa reinforce the molecular Afrotheria clade. Proceedings of the Royal Society B 274:1159-1166.

Vélez-Juarbe, J., C. A. Brochu, and H. Santos. 2007. A gharial in the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile. Proceedings of the Royal Society B 274:1245-1254.

Trip to Chile, pt. 5

After Caldera we spent some days in Santiago. Among the things we did there, was writing manuscripts and visiting the collections at the Museo Nacional de Historia Natural. We spent a lot of time working on abstracts for an upcoming meeting of researchers of aquatic mammals to be held in Puerto Madryn, Argentina. Also, we took some time to relax and do some sightseeing.

Having a nice lunch at El Patio.

One of the many awesome examples of street art we saw in Santiago.

Santiago is at the foot of the Andes and on clear days you can see them.

An Araucaria (monkey-puzzle tree), evidence that I was indeed in the southern Hemisphere.

David, Nick and Carolina, ponder at the jaws of a sperm whale (Physeter macrocephalus), in exhibit at the Museo Nacional de Historia Natural.

Lovely sunset over the Andes.

This concludes our trip to Chile, we work hard and we had great company and good times! 

Next stop, Peru!!

Previous entries in this series:

Part 1, Part 2, Part 3 and Part 4.

Trip to Chile, pt. 4

After some fieldwork (see previous post) it was time to do some preparation of the material we collected. We did some preliminary prep work at the Cabañas, but most of it was done over at the Museo Paleontológico de Caldera. There was also a lot of additional material collected over past expeditions, and we wanted to take good publication quality photos, specially of the material from Cerro Ballena.

Members of the expedition get some initial prep work done on some of the material we collected over the past few days.

More prep work, this time at Museo Paleontológico de Caldera. Cony and Carolina talk about fossil billfishes, while Ana and David are busy preparing pinniped material.

 Luckily, before we headed back to Santiago, we had time for one more trip to the field. This time we went to some Neogene badlands, that have yielded remains of sharks, cetaceans, pinnipeds and penguins. Our time was limited, but was still fun to be out in the field one last time.

Neogene badlands of the Atacama, even with less plant life than the ones I visited earlier in the year in Baja California Sur. In stark contrast with what I usually deal with in Puerto Rico.

One of several shark teeth we found. This one hints at the age of the deposit.

One last view of the Atacama, as the sun settled and we headed back to Caldera and to Santiago the next morning.

The trip is not over, more to come, so stay tuned!

Go read previous installments of this series: Part 1, Part 2, and Part 3.

Also, go see Nick's here, here, here and here.

Trip to Chile, pt. 3

Like I mentioned in the previous post, we returned to the Cerro Ballena site. There we looked for fossils that might still be exposed in the outcrop. We didn't find much, but we did found some interesting stuff.

David, Nick and Roberto, dig a baleen whale vertebra in Cerro Ballena. Several, nearly complete skeletons were previously collected at this locality and are waiting to be prepared at the Museo Paleontológico de Caldera.

An interesting find was the remains of a billfish. Here David, Cony and Roberto collect the remains, while Nick and Carolina were taking notes on the locality and horizon. Missing from the picture are Ana and Mario, who were in another part collecting remains of the aquatic sloth, Thalassocnus.

We also visited some other localities, including one that yielded remains of Pelagornis chilensis amongst other interesting stuff!

Ana, David and I as we walk to another sites where remains of other marine vertebrates have been collected.

Unfortunately, poachers also know of these sites and go looking for shark teeth and other fossils to sell, which is illegal! So in many places we knew the location of bone beds because of the shattered remains of material thought as uninteresting to poachers.

The example above show some penguin bones that were left behind by poachers. These was actually my first encounter with penguin bones in the field!

More posts to come, so stay tuned!!

Also, go see parts 1 and 2 of this series!

Trip to Chile, pt. 2

Things have been pretty busy over the past several days. Between work at the museum in Caldera, fielwork and spending time working on manuscripts I haven't really been able to post as much as I wanted to. Anyways, like I mentioned on the previous post, we've been spending some time studying fossil material at the museum during the day, while in the afternoon we work on manuscripts, abstracts and the like.

Afternoon in the cabaña after a long day of data collecting. Mario (left) prepares the fire, while Nick, Roberto and Carolina work on manuscripts.

One of the benefits of staying in a coastal town is the fresh seafood, which we buy at the market and then cook it ourselves. Just because we are on the field it doesn't mean we have to eat poorly!

Fresh albacore tuna fillet and shrimp and veggie skewers. It was delicious!!

We've also been out in the field. We revisited the Cerro Ballena site (above), as well as some other localities. More on this on the next post, so stay tuned!

You can see the first part of this series here.

Trip to Chile, pt. 1

So a few days ago,  Nick and I arrived to Chile, where we'll be for the next couple of weeks. The purpose of this trip, is to look at collections and visits Cerro Ballena and some other localities in the Atacama region. Some of our colleagues were waiting for us in Santiago, David, Carolina, Roberto and Anita who live there, and Mario Cozzuol who had arrived earlier in the week from Brazil. That afternoon, we headed out to Caldera, in the northern part of the country.
We are staying in some lovely cabañas, with a nice view to the Bahía de Caldera and the city.

The view at night from the cabañas.

At the cabañas, talking with the owner.

The next morning we visited the Museo Paleontológico de Caldera, where we met with another of our colleagues, Mario Suarez. At the museo we spent the day looking at the material collected from Cerro Ballena and nearby localities. The fossils from this site includes a wealth of marine mammals, mostly whales and dolphins, but also, aquatic sloths (more on that later)!! 

Here's a view of some of the material collected from Cerro Ballena, nearly each one of those jackets have remains of baleen whales!!

So, stay tune for more upcoming entries from this trip. Also, go over to the Pyenson Lab where there will be posts about this trip as well.

A short trip to Panama

A couple of Friday’s, no, about a year, ago one of my advisors, Nick Pyenson (NMNH), and I were on a flight on our way to Panama. The main purpose of this trip (only a weekend long) was to collect a nearly complete skull of an odontocete, (toothed whales), which we originally thought was a squalodontid (but it isn't, more on that later). We learned of the fossil through Aaron O’Dea of the STRI/CTPA, as one of his students, Dioselina Vigil had spotted the skull while prospecting along the shores of a town called Piña, on the Caribbean coast of the country. The rocks exposed in that area, best seen at low tide (see picture below), are part of the Chagres Formation (Fm.), a sandstone unit that has been dated to between 8-6 million years ago (Ma) (Late Miocene) (Collins et al., 1996).

View of the Caribbean Sea, near the town of Piña, Panama. The rocks seen in the lower half of the picture are part of the Chagres Formation.

By Saturday morning we were in the outcrop, together with Aaron, Dioselina and her brother, as well as other colleagues from STRI and a couple of visitors from Temple U. Our main purpose was to dig out the squalodontid skull as well as do some prospecting. In order to collect the skull we had to make the most of the low tide, which was the only moment that it would be exposed. As we began digging around the fossil, we realized that it was going to take longer than we had expected. Therefore we divided the group, some went prospecting while four of us stayed behind digging out the skull. After a while we realized that the fossil consisted of not only the skull, but that also the mandibles were there. In all, it took us about four hours, with the tide creeping upon us by the last half hour (see pictures below), to collect the fossil. Needless to say we successfully collected the squalodontid skull, and the prospecting team made some interesting finds as well, including additional marine mammal remains (both, whales and seacows!).

Above: Nick, Dioselina and I finish one of the small jackets. This whole area had been exposed earlier that day, this picture was taken within the last hour of low tide. As you can see the sea is creeping around us.

Above: Nick, next to the jackets containing the odontocete remains. Notice in the background that the area where we collected the fossil (between the logs) is now completely covered by water.

The skull is actually not the first marine mammal fossil known from Panama; it is, however the most complete/diagnostic so far. Back in 2010, Mark Uhen and colleagues reported marine mammal remains from three other rock units in Panama: the Tobabe Fm. (7-5 Ma), Gatun Fm. (12-8 Ma), and the Culebra Fm. (23-20 Ma). From the Tobabe they described a thoracic vertebra of a balaenopteroid (the group that includes rorquals and gray whales), from the Gatun odontocete ribs, and from the Culebra a dugongid (seacow: dugong) tail vertebra (Uhen et al., 2010).

Other interesting fossil vertebrates that have been collected from the Chagres Fm., include a fossil marlin, Makaira panamensis which was described by H. L. Fierstine in 1978. This is of particular interest as during out expedition, we also found marlin remains, including one that seems to be complete, head to tail (see picture below)!

Me and the fossil marlin. The tail is the fan or boomerang-like structure seen in the foreground (near the bottom of the picture) I am in the background pointing to the rostrum/beak. This is probably the most exciting fossil fish I’ll ever found!

These finds, as well as the chances finding even more, mean just one thing, we will have to go back to Panama!

You can find out more about this trip by following these links:

Pyenson Lab

And at Smithsonian Ocean Portal where you can find the following:

-Paleobiology Blog: Part 1, Part 2, Part 3

-Slideshow

-Time-lapsed vide of the excavation

Collins, L. S., A. G. Coates, W. A. Berggren, M.-P. Aubry & J. Zhang. 1996. The late Miocene Panama isthmian strait. Geology 24:687-690.

Fierstine, H. L. 1978. A new marlin, Makaira panamensis, from the Late Miocene of Panama. Copeia 1978:1-11.

Uhen, M. D., A. G. Coates, C. A. Jaramillo, C. Montes, C. Pimiento, A. Rincon, N. Strong & J. Velez-Juarbe. 2010. Marine mammals from the Miocene of Panama. Journal of South American Earth Sciences 30:167-175.