Its the 10th installment of Fossil Sirenia of the West Atlantic and Caribbean Region!

Today came out the most recent issue of the Journal of Vertebrate Paleontology. Amongst many other interesting papers, there is one by yours truly and former PhD advisor Daryl Domning. In our paper we describe a new sirenian taxon from early Oligocene deposits in Puerto Rico and South Carolina, its our second new species this year, as some months ago we published the description of Metaxytherium albifontanum Velez-Juarbe and Domning, 2014 (read more about it here). The fossil from Puerto Rico, which is fairly complete, comes from the same overall locality as some other fossils I've mentioned in previous posts, like Aktiogavialis puertoricensis Velez-Juarbe et al., 2007, and the oldest West Indian rodent (Velez-Juarbe et al., 2014).  This paper also marks the Tenth (!!!!) installment of the series on Fossil Sirenia of the West Atlantic and Caribbean Region, which Daryl started in 1988 (Domning, 1988)! Such long-lasting series are very uncommon!

The last time a new species of sirenian was described from Puerto Rico was 1959, when Roy H. Reinhart in his monumental work on Sirenia and Desmostylia, described Caribosiren turneri (see picture below) from the San Sebastian Formation in the northwestern part of the island. Caribosiren is a weird dugongid, it has a rostral deflection (downturning of the snout) of nearly 90º, and apparently no tusks!!

Caribosiren turneri Reinhart, 1959, from the San Sebastian Formation of Puerto Rico. Notice the extremely downturned snout  which always reminds me of Gonzo! The tip of the snout, although not preserved very well, hints at a lack of tusks.
(Photo courtesy of N.D. Pyenson) (Click on image to see larger version.)

The new fossil is from the same formation as Caribosiren. We named our new species Priscosiren atlantica, in reference to its ancestral relationship to other fossil dugongids (prisco means ancient, former) and its occurrence in the Western Atlantic region.

Priscosiren atlantica is known from multiple elements of two individuals, one from the Puerto Rico (USNM 542417) the other from South Carolina (SC 89.254). Its one of the most complete early Oligocene sirenians known. (Outline of skeleton modified from Cope, 1890).
(Click on image to see larger version.)

Slides from a talk that Daryl and I gave at the 2013 SVP annual meeting. Here we point out to several of the characters that diagnose Priscosiren atlantica as well as its relationship to other dugongids.
(Click on image to see larger version.)

 Priscosiren is represented by at least two individuals (an adult and a subadult), with associated cranial and postcranial material, making it one of the best known early Oligocene sirenians. This species occupies a special place amongst other dugongids as it seems to be ancestral (hence its name) to a clade that includes Metaxytherium spp. + Hydrodamalinae, and Dugonginae (see above). More interestingly, is that Priscosiren is found in the same formation as Caribosiren in Puerto Rico, and Crenatosiren olseni in South Carolina, and hints at the presence of sirenian multispecies communities (Velez-Juarbe et al., 2012) during the early Oligocene.

The day we found the holotype specimen of Priscosiren (USNM 542417) was the same day we found the holotype of Aktiogavialis puertoricensis, which we were able to collect that same day. In contrast, collecting Priscosiren was an ordeal, it is a long story, of discovery, failed attempts at collecting it, loss of parts, and final recovery. So stay tuned for an upcoming post about that story!

References

Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean Region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:395-426.

Reinhart, R. H. 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1-146.

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

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean Region. IX. Metaxytherium albifontanum. Journal of Vertebrate Paleontology 34:444-464.

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean Region. X. Priscosiren atlantica gen. et sp. nov. Journal of Vertebrate Paleontology 34:951-964.

Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7:e31294.

Velez-Juarbe, J., T. Martin, R. D. E. MacPhee, and D. Ortega-Ariza. 2014. The earliest Caribbean rodents: Oligocene caviomorphs from Puerto Rico. Journal of Vertebrate Paleontology 34:157-163.

Florida gets a new species of fossil seacow!

Yesterday saw the publication (online) of the second issue of 2014 of Journal of Vertebrate Paleontology. Published in this issue is the description of the first new species of seacow from the Western Atlantic that I get to name. In collaboration with Daryl P. Domning, this is the latest installment in the series titled "Fossil Sirenia of the West Atlantic and Caribbean Region" which Daryl started in 1988 (Domning, 1988). Our new species, named Metaxytherium albifontanum is known from late Oligocene deposits in Florida and South Carolina. The generic name albifontanum translates into white springs (albus = white; fontanus = spring or fountain). But why did we choose that name? and what is Metaxytherium? Keep reading and you'll find out why and more. 

Scientific Names
The scientific name of organisms consist of two parts: the genus and the species. The genus is a more inclusive rank, whereas the species is more unique. In a way, you can think of the genus name as an equivalent to your last name, where there will be more members (e.g. siblings and/or parents) with that same last name, and the species name as your first name; the two, together, will form a unique combination which applies only to you. We use scientific names in order to infer relationships amongst organisms, and these are usually latinized so that they can be understood by anyone, anywhere, as a common language, instead of using the common name which changes by country and language. Now, when describing a new species and giving it a scientific name, you can choose whichever name you think appropriate, as long as its not your own (Linnaeus was the one exception; there are other rules for naming, which you can find here). You can name a species after a musician who was an inspiration, the country where it was found, or in honor of a fellow researcher, just to name a few examples.
Renowned paleontologist George Gaylord Simpson named several fossil sirenians from Florida (Simpson, 1932). Simpson had a thing for using cleverly latinized versions of formation or locality names for his new species. For example, he described some fossils from the Bone Valley district in central Florida and gave them the scientific name Felsinotherium ossivallense*, (ossivallense = Bone Valley), while another one he named Hesperosiren crataegensis*, which takes its name from Crataegus, the genus name of a plant commonly known as hawthorn, which in turn is also the name of the sedimentary unit, the Hawthorn Group, where Simpson's specimen was found. So, as a homage to G. G. Simpson and his work on the fossil sirenians from Florida we decided to use a latinized version of the name of the town of White Springs, FL, which is close to where the holotype (= name-bearing specimen) of our new species was collected; resulting in the combination Metaxytherium albifontanum.
*both Felsinotherium and Hesperosiren were later synonymized with Metaxytherium

Metaxytherium albifontanum is known from multiple elements of several individuals (each color identifies elements represented by one or more specimens; white = unknown). This makes it one of the most complete fossil sirenians known. (Outline of skeleton modified from Cope, 1890). (Click on the image to see larger version.)

What is Metaxytherium
Metaxytherium is a widespread and relatively well-known genus of fossil dugongid. There are now a total of eight species under this genus, it has a wide temporal distribution, ranging from the late Oligocene through early Pliocene, and a broad geographical distribution, with species known from Europe, northern Africa, and the Americas. Most of the species known were described and named between 1822 and the first half of the 1900's, so, unexpectedly, there was a bit of a taxonomic mess (this happens more often than we'd like). Fortunately, since 1987, there have been several papers providing us with detailed descriptions of some of the known species, as well as phylogenetic analyses (e.g. Domning and Thomas, 1987; Domning, 1988; Aranda-Manteca et al., 1994; Domning and Pervesler, 2001; Sorbi, 2008; Sorbi et al., 2012). These works have help clarify some of the taxonomic confusion surrounding some of the old names, and even a new species was described, Metaxyterium arctodites Aranda-Manteca et al., 1994, from Baja California and California. That makes M. albifontanum the first species of Metaxytherium named in 20 years!! Meaning that we are not done learning about the diversity of this group, and more may still be waiting to be described.

Slides from a talk Daryl and I gave at the Society of Vertebrate Paleontology 2013 Annual Meeting. Here we use M. albifontanum to illustrate some of the features that characterize the genus Metaxytherium (top two and bottom left). The phylogenetic tree on the bottom right shows the relationship between Metaxytherium spp. and other sirenians (modified from figure 15 of our paper). (Click on the image to see larger version.) 

Our new species differed from all other known species in the group. Not only that, it is the geologically oldest species of Metaxytherium. Previous assumptions on the origins of Metaxytherium had hypothesized an European origin for the group, our discovery changes that and seems to indicate a Western Atlantic origin for the genus.

Relationships with Other Species

One of the relevant results of our paper is that we got to properly define Metaxytherium. Our phylogenetic analysis (see tree above, bottom right) was consistent with previous work (e.g. Domning, 1994), showing a close relationship between Metaxytherium spp. and hydrodamalines (the group that include Steller's seacow). We also got some interesting results regarding the relationships amongst the different species of Metaxytherium. Our results indicate that the split between Metaxytherium albifontanum and the geologically younger M. krahuletzi (from the early Miocene of Europe), occurred before the late Oligocene, as the latter occupies a more basal position within the tree. The relationships within the group also seem to point to multiple dispersals across the Atlantic and/or a high degree in morphological convergence.

Paleoecology

Metaxytherium albifontanum was part of a sirenian multi-species assemblage in the late Oligocene of Florida, together with Dioplotherium manigaulti and Crenatosiren olseni. As part of that assemblage, we hypothesize M. albifontanum as a consumer of small-sized seagrasses such as eelgrass, while the other species likely fed on larger species. If this sounds familiar is because I wrote about this subject in a previous post. In fact, M. albifontanum was one of the species that inspired the iterative evolution project with Daryl and Nick Pyenson, which resulted in our open access publication in PLoS ONE (Velez-Juarbe et al., 2012). 

Assorted Random Musing: 

• I visited the Florida Museum of Natural History in 2011 to study one of the specimens (UF 49051), little did I know at that time that I would end up as a Postdoc here!
• You can see the name-bearing specimen, UF 49051, in the Florida Fossils: Evolution of Life and Land exhibit at the Florida Museum of Natural History.
• It so happened that I wrote this post from a desk at the Simpson Library of Paleontology, its filled with books and reprints donated by him, and...
• There are a lot of pictures of Simpson in this library, in some, he kind of looks like the long lost brother of Colonel Sanders...

Stay tuned as more new fossils seacows will be showing up here later this year!!

References

Aranda-Manteca, F. J., D. P. Domning, and L. G. Barnes. 1994. A new Middle Miocene sirenian of the genus Metaxytherium from Baja California: relationships and paleobiogeographic implications. Proceedings of the San Diego Society of Natural History 29:191-204.

Cope, E. D. 1890. The extinct Sirenia. American Naturalist 24:697-702.

Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean Region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:395-426.

Domning, D. P. 1994. A phylogenetic analysis of the Sirenia. Proceedings of the San Diego Society of Natural History 29:177-189.

Domning, D. P., and P. Pervesler. 2001. The osteology and relationships of Metaxytherium krahuletzi Depéret, 1895 (Mammalia: Sirenia). Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft 553:1-89.

Domning, D. P., and H. Thomas. 1987. Metaxytherium serressii (Mammalia: Sirenia) from the early Pliocene of Libya and France: a reevaluation of its morphology, phyletic position, and biostratigraphic and paleoecological significance; pp. 205-232 in N. Boaz, A. El-Arnauti, A. W. Gaziry, J. de Heinzelin, and D. D. Boaz (eds.), Neogene Paleontology and Geology of Sahabi. New York (Liss).

Simpson, G. G. 1932. Fossil Sirenia of Florida and the evolution of the Sirenia. Bulletin of the American Museum of Natural History 59:419-503.

Sorbi, S. 2008. New record of Metaxytherium (Mammalia, Sirenia) form the lower Miocene of Manosque (Provence, France). Geodiversitas 30:433-444.

Sorbi, S., D. P. Domning, S. C. Vaiani, and G. Bianucci. 2012. Metaxytherium subapenninum (Bruno, 1839) (Mammalia, Dugongidae), the latest sirenian of the Mediterranean Basin. Journal of Vertebrate Paleontology 32:686-707.

Velez-Juarbe, J., and D. P. Domning. 2014. Fossil Sirenia of the West Atlantic and Caribbean Region. IX. Metaxytherium albifontanum sp. nov. Journal of Vertebrate Paleontology 34:444-464.

Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7:e31294.

The Southernmost Atlantic Seacows

Its been a while since I posted news on fossil sirenians. I've been very busy with fieldwork, manuscripts, among other things. The Spring interns have now gone back home. So, while I wait for the arrival of the next round of interns, here's the latest on fossil sirenians.


Where are sirenians found

With the exception of the now extinct Steller's seacow (Hydrodamalis gigas), all extant sirenians have tropical to subtropical distribution, with some species having a notably broad latitudinal and longitudinal distribution (Marsh et al., 2011). But, when we look at the fossil record of sirenians, we see a slightly different pattern of distribution, mostly tied to tectonic and/or climatic events. For example, during parts of the Cenozoic global temperatures were higher than today (Zachos et al., 2001), so you find fossils of sirenians far off their modern range (e.g. Belgium). These climatic variations amongst other physical drivers have played a prominent role in the distribution of seagrasses and seacows (expect more on this in the nearby future).

Nowadays, in the Western Atlantic and Caribbean (WAC) region, the most common and widespread sirenian is the West Indian Manatee (Trichechus manatus) whose range extends from as far north as the Carolina's (with some individuals reaching New England) to northeastern Brazil; another species found in the region is the Amazonian manatee (Trichechus inunguis) which lives in the Amazon basin (see map below). But, it hasn't always been like this. Throughout most of the Cenozoic, dugongids, a group of sirenians are now restricted to the Indo-Pacific region, were the predominant seacow group in the WAC, including multispecies communities in the region (Domning, 2001; Velez-Juarbe et al., 2012a; see previous post on this subject). Fossil of dugongids in the WAC are found in deposits as far north as Maryland, and as far south as Argentina. However, these southernmost dugongids, are poorly known, and have had a somewhat rocky taxonomic history.


From Metaxytherium to Dioplotherium a case of mistaken identity

The most common, and temporally and geographically widespread seacow genus known is the Halitheriine dugongid Metaxytherium. Species of this genus are known from late Oligocene through Pliocene deposits, and are found from the Eastern Pacific, Caribbean, Western and Northern Atlantic, and Western Tethys regions (e.g. Domning, 1988; Sorbi et al., 2012). Therefore it shouldn't have been much of a surprise when Roy H. Reinhart (1976) described a molar from the late Miocene Paraná Formation of Entre Ríos, Argentina as that of Metaxytherium. The importance of this find, lies in that prior to its discovery, the youngest species of Metaxytherium known from the WAC was the middle Miocene M. floridanum, which is not known outside of Florida (Domning, 1988). The Paraná molar was then, the youngest and southernmost record of the genus from the Western Atlantic.

However, species of Metaxytherium display a generally conservative morphology, and because of this, it has had a long, somewhat convoluted, taxonomic history. This is, fortunately, slowly being resolved as most species of Metaxytherium have been re-described (e.g. Domning, 1988; Domning & Pervesler, 2001; Sorbi et al., 2012) and studied in detail within the last 25 years, giving us, paleosirenologist a better idea of the valid species within the genus and variation within each species. Since Reinhart's description, several workers (Cozzuol, 1996; Cione et al., 2000; Domning, 2001) have disagreed with his interpretation regarding the affinities of the Argentinian molar. All of them referring the Paraná molar to Dioplotherium, still a dugongid, but one that belongs to the Dugonginae, a group very different from that to which Metaxytherium belongs. And indeed, the overall morphology of the tooth conforms well with what we know about Dioplotherium, it is in fact, very similar to those of Dioplotherium cf. D. allisoni from the early Miocene of Brazil (Toledo & Domning, 1991). This meant that Metaxytherium may have gone extinct in the WAC at the end of the middle Miocene (Domning, 1988), and that the genus only reached as far south as northeastern Brazil (Toledo & Domning, 1991), or did it?

Left: Map showing the distribution of Miocene seacows throughout the Americas. (ER = Entre Ríos).
Right: Map showing the distribution of extant sirenian in the Americas.
(Click on the map to view larger version.)

New fossils from the Paraná Formation

A couple of years ago I received an email from an Argentinian colleague, Jorge Noriega from CONICET in Diamante, informing me of a new discovery from the Paraná Formation in Entre Ríos. The new fossils consisted of left and right partial maxillae and most of the molars of a single individual (see figure below). At this point I was close to finishing my PhD, which meant that I had look at a lot of specimens and was well acquainted with the morphology of most, if not all Oligocene through Pliocene sirenians. Once I looked at the pictures of the new material, I quickly recognize these as most likely representing a species of Metaxytherium.

Molars of Metaxytherium from the late Miocene Paraná Formation. 1-2) left maxilla and M1-3 in occlusal view. 3-4) right maxilla and M3 (modified from Velez-Juarbe et al., 2012b)

Now, I must admit that dugongid teeth are not the most diagnostic, so figuring out if these actually belonged to Metaxytherium was not an easy and quick task. After a considerable amount of reading, and detailed observations of material from various species of Metaxytherium as well as other dugongids I was confident they belonged to that genus. And so, working together with Jorge and Brenda Ferrero (also from CONICET in Diamante) we took on the task of formally re-designating the fossil described by Reinhart (1976) as well as describing the new material which actually represented a species of Metaxytherium (Velez-Juarbe et al., 2012b). The new Parana molars are quite similar to those of the middle Miocene Metaxytherium floridanum, but, their dimensions are below the range exhibited by M. floridanum and may represents a different species. One of the positive outcomes resulting from this work, was realizing that teeth of dugongids can sometimes be of taxonomic usefulness. We noticed, that the molars of some of the more derived species of Metaxytherium often have additional cusp and/or cuspules, a derived character which is not observed in Dioplotherium or any of its kin (i.e. Dugongines). The contemporaneous presence of both, Dioplotherium and Metaxytherium is not something unheard of. This same duet, occurs in the late Oligocene of Florida, early Miocene of Brazil and possibly in the middle Miocene of California and Baja California (Domning, 2001; Velez-Juarbe et al., 2012a). This again shows that multispecies communities and niche partitioning seems to have been the norm, not the exception, throughout sirenian history.


References

Cione, A. L., M. M. Azpelicueta, M. Bond, A. Carlini, J. Casciotta, M. A. Cozzuol, M. de la Fuente, Z. Gasparini, F. Goin, J. Noriega, G. Scilato-Yané, L. Soibelzon, E. Tonni, D. Verzi, and M. G. Vucetich. 2000. Miocene vertebrates from Entre Ríos Province, Argentina. INSUGEO, Serie Correlación Geológica 14:191-238.

Cozzuol, M. A. 1996. The record of the aquatic mammals in southern South America. Münchner Geowissenschaftliche Abhandlungen A30:321-342.

Domning, D. P. 1988. Fossil Sirenia of the West Atlantic and Caribbean region. I. Metaxytherium floridanum Hay, 1922. Journal of Vertebrate Paleontology 8:295-426.

Domning, D. P. 2001. Sirenians, seagrasses, and Cenozoic ecological change in the Caribbean. Palaeogeography, Palaeoclimatology, Palaeoecology 1:27-50.

Domning, D. P., and P. Pervesler. 2001. The osteology and relationships of Metaxytherium krahuletzi Depéret, 1895 (Mammalia: Sirenia). Abhandlungen der Senckenbergischen Naturforschenden Gessellschaft 553:1-89.

Marsh, H. D., T. J. O'Shea, and J. E. REynolds, III. 2011. Ecology and conservation of the Sirenia: dugongs and manatees. Cambridge University Press, 521p.

Reinhart, R. H. 1976. Fossil sirenians and desmostylids from Florida and elsewhere. Bulletin of the Florida State Museum, Biological Sciences 20:187-300.

Sorbi, S., D. P. Domning, S. C. Vaiani, and G. Bianucci. 2012. Metaxytherium subapenninun (Bruno, 1839) (Mammalia, Dugongidae), the latest sirenian of the Mediterranean Basin. Journal of Vertebrate Paleontology 32:686-707.

Toledo, P. M., and D. P. Domning. 1991. Fossil Sirenia (Mammalia: Dugongidae) from the Pirabas Formation (Early Miocene), northern Brazil. Boletim do Museu Paraense Emílio Goeldi, Série Ciencias da Terra 1:119-146.

Velez-Juarbe, J., D. P. Domning, and N. D. Pyenson. 2012a. Iterative evolution of sympatric seacow (Dugongidae, Sirenia) assemblages during the past ~26 million years. PLoS ONE 7(2):e31294.

Velez-Juarbe, J., J. I. Noriega, and B. S. Ferrero. 2012b. Fossil Dugongidae (Mammalia, Sirenia) from the Paraná Formation (late Miocene) of Entre Ríos Province, Argentina. Ameghiniana 49:585-593.

Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686-693.

Chevron weirdness in a sirenian

Following up on a comment I made over at Updates from the Vertebrate Paleontology Lab, I here bring you pictures of an unusual sirenian chevron from the Late Oligocene of Puerto Rico.

These fossils were collected as part of a partial articulated postcranium which I mentioned here. Chevrons, also known as hemal arches, are (normally) V-shaped* bones, consisting of two rami that meet ventrally, hence the shape. They protect blood vessels.

*More like Y-shaped due to the length of the symphysis in some specimens.

In the picture above you can see left lateral views of two of the chevrons I collected with that specimen. The chevron on the left seems to represent fused chevron 2 + 3 (missing part of its ventral edge), and the other one is chevron 4, which is normal.

Here is a posterior view, again, the one on the left likely represents fused chevron 2 + 3, and on the right is chevron 4, which is missing the right ramus.

To me this seems to have been a developmental anomaly rather than occurring due to an injury. Apparently, this is a first, at least for Sirenia! As I mentioned above these are part of an articulated partial postcranium, belonging to a new dugongine taxon from the Late Oligocene of northern Puerto Rico (you can see the skull here).

So, leave a comment, let me know what you think about this unusual bone!

Domningia and other Indian sirenians

Over the last 12 years a number of fossil sirenians have been described from Eocene through Miocene deposits from India. This has not stopped as, new taxa are been discovered and described; much of the effort is spearheaded by Sunil Bajpai of the Dept. of Earth Sciences, Indian Institute of Technology and J. G. M. Thewissen of the Dept. of Anatomy and Neurobiology, NEOUCOM (Thewissen Lab). So far all the fossil sirenians from India have been collected from outcrops in the Kachchh District near the western coast of the country; this area is better known for primitive cetaceans such as remingtonocetids (Kumar & Sahni, 1986).

Eocene

The oldest Indian sirenians come from the Middle Eocene Harudi Formation; a total of three species representing two families: Protosiren sp. (Protosirenidae), Eotheroides babiae, Eosiren sp. (Dugongidae, Halitheriinae) (Bajpai et al. 2006). Other species belonging to those genera are found in Eocene deposits in northern Africa (Domning, 1996) indicating a southern Tethyan influence, better referred to as the Indo-African Region of the Tethys Realm (Harzhauser et al. 2002). There should be more on Eocene sirenians from India, sometime this year.

Oligocene

So far only one Oligocene sirenian is known from this region, Bharatisiren indica (Dugongidae, Dugonginae) from the Maniyara Fort Formation of Late Oligocene age (Bajpai et al. 2006). This is the oldest dugongine found in this region, and it is as old as the dugongines, Crenatosiren olseni and Dioplotherium manigualti from the Western Atlantic (Domning, 1989; Domning, 1997) and a new taxon from Puerto Rico. Dugongines are a group that is thought to have evolved in the Western Atlantic and Caribbean Region (Domning, 2001), the occurrence of B. indica seems to point to a latest Eocene or Early Oligocene origin for the group with subsequent trans-Atlantic dispersal to the Indo-African Region. An alternative scenario, is the origin of dugongines in the Mediterranean region of the Tethys Realm with subsequent east and west dispersal, unfortunately no Early or Late Oligocene dugongines are known from this region (the names of the paleobiogeographic areas based on Harzhauser et al. 2002).

Lateral view of the skull of B. indica from Bajpai et al. (2006).

Miocene

During the Early Miocene there seems to have been a radiation of dugongines in this region. With at least two taxa known Bharatisiren kachchhense, Domningia sodhae* from Khari Nadi Formation (Bajpai & Domning, 1997; Thewissen & Bajpai, 2009), and another currently under study, it is an good example of multispecies communities like the ones present in the Western Atlantic and Caribbean Region (Domning, 2001). As you can see in the composite picture below, a notable difference between B. kachchhense and Domningia sodhae is the rostral deflection, which probably reflects different degrees of specializations for bottom feeding (Domning, 2001). They seem to have had similar shape of their tusks, large and more-or-less oval in cross-section, this morphology most likely aided in obtaining large seagrass rhizomes (Domning, 2001; Domning & Beatty, 2007), although probably at different levels due to the differences in rostral deflection. Interestingly, it seems that there were no post-Eocene halitheriines.

*Domningia sodhae was aptly named after Dr. Daryl P. Domning of Howard University, world renowned paleosirenologist, a well deserved recognition.

Lateral view of B. kachchhense (top; from Bajpai & Domning, 1997) and Domningia sodhae (bottom; image reversed, from Thewissen & Bajpai, 2009).

Where are the halitheriines?

So far no post-Eocene halitheriines are known from the Oligocene and Miocene of India, at least two possible explanations come to mind: (1) they were present but no fossils have been found yet, or; (2) they were totally absent. An explanation for the second alternative could be provided by the invertebrate fauna. Based on gastropod fauna it seems that, during the Oligocene, changes in the geological settings in the Tethys Realm led to changes in the ocean currents and what was previously known as the Indo-African Region was subsequently divided into the Mediterranean-Iranian and Western Indian-Eastern African provinces of the Western Tethyan Region (Harzhauser et al. 2002). Subsequently, during the Early Miocene, further fragmentation of the Western Indian-Eastern African Province led to an increase of South-East Asian influence and the formation of the Proto-Western Indian Ocean Province; this separation was further augmented by the closure of the Eastern Mediterranean seaway during the latest Early Miocene (Harzhauser et al. 2002). The progressive isolation of what would become the Proto-Western Indian Ocean Province from a Tethyan influence might have prevented halitheriines from entering the region, especially after the Late Oligocene, leading to specialization and radiation of dugongines in this part of the world.

 References

Bajpai, S. & D. P. Domning. 1997. A new dugongine sirenian from the Early Miocene of India. Journal of Vertebrate Paleontology 17(1):219-228.

Bajpai, S., J. G. M. Thewissen, V. V. Kapur, B. N. Tiwari & A. Sahni. 2006. Eocene and Oligocene sirenians (Mammalia) from Kachchh, India. Journal of Vertebrate Paleontology 26(2):400-410.

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