Dominican Republic, part II

Hello there dear readers. Today I bring you the second installment of this series. Like I mentioned in the previous post we moved from the Albian to the Miocene.

The Miocene of the Dominican Republic is probably best known for the amber deposits. These have not only produced beautiful amber, which is used in jewelry, but also a number of fossil taxa have been described based on remains entombed in the amber. These fossils consist mostly of invertebrates, however, several vertebrates have been described as well, including anoles, frogs, and an insectivore. This gives us a glimpse into the smaller fauna that inhabited the island during the Miocene, in contrast to what is known from the same age in Puerto Rico and Cuba where most of the vertebrate fossils of that age consist of larger animals (sloths, rodents, primates, sirenians, crocodylians and turtles). A good summary of the vertebrates known from the Tertiary of the Greater Antilles can be found in table 1 of MacPhee et al. (2003) (free download here).

One of our first excursions into the Miocene was on a Wednesday afternoon. We spent the morning collecting the last samples from one of the outcrops of the Hatillo Limestone and some rudists from near the entrance of a cave in that same limestone unit. We then headed west towards the Monte Plata Province where we knew there was a new road cut exposing units of Miocene age.

The first outcrop of the Miocene that we visited. This is actually one of the best Miocene outcrops I've seen in a while.

By the time we got there it was near the middle of the afternoon, which meant we didn’t had much sunlight left. We stopped in the first large outcrop we saw (Picture above) and it was worth it! We quickly started finding turtle shell fragments, and occasionally we saw cross sections of turtle shells that went into the outcrop. I decided to collect one of these. It was not big, and as I found out after prep work, not too good (see pictures below). However, it was worth going there, as there is more material to be found and collected!

Top left: me overturning the jacket with the turtle shell remains; top right: the jacket back in the lab; bottom left: view of the jacket when it was first opened; bottom right: the fossil turtle remains. (Click on the image to see the larger version.)

Several days latter we had some free time, so we decided to go back to this area. This time we drove in from the north, driving through Los Haitises where we saw beautiful karst topography. Our time was limited in this occasion as well, but we made the most out of it.

The second outcrop we visited, smaller than the first one, but still interesting. Alvin Bonilla for scale.

We hit a couple of outcrops (Picture above) where we found the usual (at least what usual for the Tertiary of Puerto Rico and Cuba); croc teeth, turtle shells and sirenians (which was what I was really after). The sirenian material was in a concretion, half of it which had fallen off the outcrop so it made it easy to collect. The other part is still in the outcrop and I hope to go back sometime in the spring to collect it. Actually, if it wasn't for Alvin, who saw it, I almost stepped on the part that had fallen trying to get a better view of the part still in the outcrop. After some prep work on the sirenian material it turned out to be mostly ribs, and a few vertebrae. However, even if it is a little frustrating, it will nonetheless be an important contribution to the understating of sirenian distribution during the Miocene of the Caribbean and demonstrates that there is probably more, better material waiting to be collected!

Top left: me collecting the concretion with the sirenian remains; top right: view of the jacket in the lab; bottom left: the jacket, recently opened; bottom right: the concretion, as of now, still need some prep work to be done. Oysters (near the center of the concretion and to the right) used some of the ribs as hardground. (Click on the image to see the larger version.)

MacPhee, R. D. E., M. A. Iturralde-Vinent & E. S. Gaffney. 2003. Domo de Zaza, an Early Miocene vertebrate locality in south-central Cuba, with notes on the tectonic evolution of Puerto Rico and the Mona Passage. American Museum Novitates 3394:1-42.

Dominican Republic, part I

It’s been quite a while since I posted something here as I’ve been very busy since the last post, which you should check out, if you haven’t! The absence was mostly because I’ve been distracted with university-related stuff, work (I had a real job over the summer), meetings and a month-long fieldtrip to the Dominican Republic, which will be the subject of this and the following entries.

Top: on our way to Bonao. Bottom: some of the beautiful rice field near Bonao. (Click on the picture to see the larger version.)

To begin with, I had never been to the Dominican Republic before; it was actually my first time in another Caribbean island other than my own, Puerto Rico. I did not know what to expect, but I ended up with a very good impression of the island and its people! There were many things I liked, for example, there seems to be a lot of land dedicated to agriculture (which I think is awesome), the food was delicious and of course, the geology is very interesting!!

The focus of the trip to the DR was to collect rock samples and fossils from Early Cretaceous limestones as part of the thesis project of my friend and colleague Alvin Bonilla-Rodriguez from the Geology Department at the University of Kansas. Our collecting efforts were mainly focused in the central part of the country where Albian-age limestones occur. We stayed most of the time near the towns of Bonao in the Monseñor Nouel Province and in Hato Mayor del Rey in Hato Mayor Province. Other people that joined us during our time there were: Luis Gonzalez from the Department of Geology at the University of Kansas (and Alvin’s advisor) and Wilson Ramírez and Hernán Santos from the Department of Geology at the University of Puerto Rico-Mayagüez. The Servicio Geológico Nacional and its director Santiago Muñoz Tapia were also very helpful in terms of logistics and advise.

At first it was hard finding good outcrops, some were heavily overgrown and in other occasions our compact car was obviously ill-fitted for some of the roads we needed to go through. But, by about the middle of our first week we finally found some outcrops, not the best, but it was a start!

Top: our first official stop, near the southeast corner of Presa Hatillo, the outcrop was completely overgrown. You can see Alvin (left), Luis (right) and Wilson (background), and our (very) compact cars. Bottom: one of the road we manage to get our car trough, there were others which were definitely impassable by our vehicle. (Click on the picture to see the larger version.)

Our luck got better when we moved east towards Hato Mayor. There we found a very nice outcrop (with lots of fossils) of the Hatillo Limestone! The fossils were very important, specially the rudist, for determining the age of the rocks. And yes, we were in the Albian!

Top left: our first outcrop, yes there is an outcrop in there! Top right: the nice outcrop of the Hatillo Ls is in the top of that hill. Bottom left: Coalcomana ramosa, a rudist, finding this particular species meant we were in the Albian. Bottom right: Hernán (left) and Alvin (right) collect rock samples from the Hatillo Ls. (Click on the picture to see the larger version.)

Well, this is it for this first post. Remember there are more to come, so stick around! On the next post we’ll move from the Albian, to the Miocene!

Convergencia: el caso de Odobenocetops ó el delfín que parecía morsa

Convergencia; en biología y paleobiología, se utiliza este término para referirse a instancias donde dos (o más) organismos, de grupos no relacionados, poseen rasgos morfológicos similares los cuales sirven un mismo propósito. Estas similitudes se pueden clasificar como homólogas (aquellas que están compuestas por estructuras similares, como las alas de las aves y las de los murciélagos) o análogas (aquellas que han evolucionado de estructuras distintas, como las alas de las aves y las de una mariposa). Otro ejemplo de convergencia se ve en los mamíferos con dientes hipsodontes. Caballos, algunos roedores y los desmostilios* tienen (o tenían) dientes hipsodontes. Este tipo de diente tiene coronas muy altas, por ende tardan más en desgastarse; esta morfología se correlaciona con dietas abrasivas (como comer grama o comer en lugares donde hay mucho sedimento mezclado con el alimento). Si estos organismos no tuvieran este tipo de dientes sería contraproducente continuar con ese modo de alimentación ya que sus dientes se gastarían muy rápido. Así que la selección natural ha favorecido tener dientes hipsodontes en estos organismos que llevan una dieta que incluye material abrasivo.

*Información adicional sobre desmostilios, incluyendo reconstrucciones, aquí, aquí y aquí.

En organismos vivos es relativamente fácil determinar si estructuras parecidas son convergentes o no, ya que se pueden hacer observaciones directas sobre el comportamiento o función de la estructuras o morfología que se consideran convergentes. Sin embargo, con los fósiles es distinto ya que generalmente no podemos hacer observaciones directas sobre el comportamiento de un organismo extinto. Es por esto que nos toca entonces interpretar la funcionalidad de esas estructuras comparando con lo que conocemos de organismos vivos. A continuación les traigo un interesante ejemplo de convergencia entre un fósil y un organismo moderno

Odobenocetops

En el 1993, Christian de Muizon describió un fósil de delfínido (el grupo de ballenas que incluye a los delfines) que representa uno de los mejores ejemplos de convergencia que conozco. El fósil consistía en parte de un cráneo (ver la imágen abajo) colectado en el sur de Perú. Los sedimentos donde se encontró el fósil son parte de una secuencia de rocas sedimentarias conocida como la Formación Pisco, de edad Pliocénico Temprano (5.3-3.6 millones de años). El fósil no solo representaba una nueva especie, sino también un nuevo grupo de delfínidos al cual llamó Odobenocetopsidae.

El primer espécimen descrito lo llamaron Odobenocetops peruvianus Muizon, 1993 (ver imagen abajo). Los rasgos morfológicos más distintivos de esta especie consisten en tener el rostro corto (el área frente a los ojos), procesos alveolares de la premaxilla (los espacios para los dientes) agrandados y orientados hacia abajo; los procesos alveolares era donde tenían unos colmillos también agrandados. La premaxilla también tiene varios forámenes y áreas de inserción de músculos bien marcadas que indican la presencia de labios grandes y quizás hasta bigotes. Otras características del cráneo incluye tener las órbitas de los ojos posicionadas dorsalmente y un paladar profundo. Estas características que tanto distinguen a los odobenocetópsidos son reminiscentes a las morsas* más que a otros delfinoideos.

*Vean las imágenes de un cráneo de morsa y comparen.

Odobenocetops peruvianus, arriba, foto del cráneo en vista lateral (anterior hacia la derecha); abajo, ilustración del cráneo mostrando los diferentes huesos que lo componen y el área de la órbita (cículo azul), modificada de Muizon (1993). Abreviaciones: Al = aliesfenoide; Bo = basioccipital; Fr = frontal; Mx = maxila; Na = nasal; Oc = occipital; Or = órbita; Pa = parietal; Pal = palatino; Pmx = premaxila; Ppo = proceso postorbital; Ppr = proceso preorbital; Pt = terigoide; Z = zigomático.

Otra especie adicional fue descrita unos años más tarde (Muizon et al., 1999). Odobenocetops leptodon también fue encontrado en la Formación Pisco, sin embargo, proviene de un horizonte alrededor de un millón de años más joven que donde se encontró O. peruvianus. Algunas de las características que distinguen a esta nueva especie es un rostro más grande y redondeado, mayor tamaño del paladar y la presencia de fosas (depresiones) para los sacos premaxilares. La ocurrencia de esta última estructura que menciono, se correlaciona con la presencia del órgano del melón (Mead, 1975), la cual es una estructura utilizada para ecolocalización. O. peruvianus aparentemente carecía de esta estructura ya que carece de fosas para los sacos premaxilares, sin embargo, la posición de las órbitas y la forma de los procesos supraorbitales le permitía tener visión binocular; en O. leptodon los procesos supraorbitales eran distintos y sus orbitas estaban posicionadas más hacia el lado, careciendo de visión binocular, pero al menos auxiliado por la presencia del órgano del melón y la capacidad de hacer ecolocalización. Así que al parecer, O. peruvianus dependía de la visión para localizar su alimento, mientras que O. leptodon probablemente dependía mayormente de ecolocalización (como es el caso de muchos otros delfinoideos).

Los odobenocetópsidos están relacionados al único otro grupo de cetáceos que tienen colmillos agrandados, los narvales. Estos también tienen un colmillo agrandado (y en ocasiones los dos), pero estos están orientados hacia adelante. En los odobenocetópsidos la función de estos colmillos parece haber sido social ya que presentan dimorfismo sexual; los machos poseen un colmillo (el de la derecha) más agrandado que el otro (algunos hasta midiendo más de un metro), mientras que en las hembras ambos eran más pequeños y similares en tamaño (Muizon et al., 1999; Muizon & Domning, 2002).

Reconstrucción de Odobenocetops ilustración de Mary Parrish (National Museum of Natural History, Washingon, DC), tomado de Muizon et al. (1999).

¿Que pudo llevar a un delfínido a parecer una morsa?

El parecido de los odobenocetópsidos a las morsas (convergencia) llevó a los paleontólogos que los han estudiado a inferir que su modo de alimentación era muy similar. O sea, que posiblemente, al igual que las morsas, los odobenocetópsidos se alimentaban de bivalvos bentónicos (que viven en el suelo marino), localizándolos con asistencia de los bigotes, aguantando el bivalvo con los labios y utilizando la lengua como un pistón, creando un vacío dentro de la cavidad bucal para lograr succionar el organismo fuera de su concha.

La distribución geográfica de las morsas, tanto vivas como las fósiles, está limitada al hemisferio norte (Deméré et al., 2003). Asumiendo que las especies extintas de morsas tenían las mismas preferencias alimenticias que la especie moderna (y al parecer así era) y al tener una distribución limitada, ese espacio ecológico, ocupado por las morsas en el hemisferio norte, estuvo “vacío” en el sur. Es así que posiblemente surgió este caso de convergencia, donde un delfinoideo termina pareciendo una morsa, ocupando ese espacio ecológico y utilizando los recursos disponibles.

Este es uno de los casos en paleontología donde el presente es la llave del pasado. Si no conocieramos las morsas habría sido muy difícil interpretar la funcionalidad morfológica de estos extraños delfinoideos.

Deméré, T. A., A. Berta & P. J. Adam. 2003. Pinnipedimorph evolutionary biogeography. Bulletin of the American Museum of Natural History 13 (279):32-76.

Mead, J. G. 1975. Anatomy of the external nasal pasajes and facial complex in the Delphinidae (Mammalia, Cetacea). Smithsonian Contributions to Zoology 207:1-72.

Muizon, C. de. 1993. Walrus-like feeding adaptation in a new cetacean from the Pliocene of Peru. Nature 365:745-748.

Muizon, C. de & D. P. Domning. 2002. The anatomy of Odobenocetops (Delphinoidea, Mammalia), the walrus-like dolphin from the Pliocene of Peru and its paleobiological implications. Zoological Journal of the Linnean Society 134:423-452.

Muizon, C. de, D. P. Domning & M. Parrish. 1999. Dimorphic tusas and adaptive strategies in a new species of walrus-like dolphin (Odobenocetopsidae) from the Pliocene of Peru. Comptes-rendus de l’Academie des Sciences, Paris, Sciences de la Terre et des Planetes 329:449-455.

Better late than never: GSA 2009

This has been a particularly long hiatus, and not because I wanted to, but it has been a particularly busy summer.

Anyways, if you missed my poster presentation at the 2009 annual meeting of the Geological Society of America, here is your chance to see it. Below is the abstract (you can also see it here) as well as the poster itself.

Evolution and diversification of Dugonginae (Sirenia: Dugongidae) in the West Atlantic and Caribbean region

Jorge Velez-Juarbe & Daryl P. Domning

Sirenian evolution presumably started in the southern Tethys realm of the Old World. However, the most primitive sirenians have been found in the Caribbean region in rocks that date back to the Early or Middle Eocene, evidence that they took on an aquatic lifestyle early in their history and were able to disperse around the Atlantic. Since then, the West Atlantic and Caribbean (WAC) region has been important for the evolution of this group of mammals, with all four of the known families (Prorastomidae, Protosirenidae, Dugongidae, Trichechidae) occurring in the region. From the Oligocene through Pliocene, the predominant groups in the WAC region were members of the dugongid subfamilies Dugonginae and Halitheriinae, with the former being the more speciose of the two. In some parts of the WAC, dugongines and halitheriines are found in the same deposits, indicating that some form of niche partitioning was occurring among three or even more sympatric species of sirenians, something that is not observed among the living species.

Niche partitioning among sympatric sirenian species is most obviously explained by differences in: (1) tusk morphology; (2) rostral deflection; and (3) body size. The most primitive members of the Dugonginae are found in the WAC region. Their distinctive cranial morphology seems to have evolved as a specialization for harvesting larger seagrass rhizomes that were out of reach of the less specialized halitheriines. New fossils from Puerto Rico, Florida, and Yucatán help to reinforce our ideas about niche partitioning among sympatric sirenian species as well as establish the WAC region as the center of known dugongine diversity.

This was my first poster presentation about one of the topics that I’m working on as part of my thesis. The poster was a success! I was awarded runner-up of the 2009 Paleontological Society Poster Award. Congratulations to the first place and to the other runner-up too! It was a great meeting with very interesting talks as well as getting to spend some time with good friends!!

Enjoy the poster and feel free to ask question or make comments!

Answer to the last post

Ok, so while I slowly prepare a more lengthy post. Here’s the answer from last post. The skull I showed last time is that of a species of Metaxytherium, exactly which one, well, I’ll talk about that in the future. That skull is from Early Oligocene deposits, therefore it is several million years older than other reported species of Metaxytherium.

Here’s the skull in lateral and dorsal views. (Notice that part of the rostrum is missing.)

It is somewhat similar to M. crataegense (=M. calvertense [Aranda-Manteca et al., 1994]) from the Early Miocene of the Western Atlantic and Caribbean, as well as to other species of Metaxytherium, but, it also displays plesiomorphic conditions not seen in those other species.

Another possibility would be Caribosiren turneri (drawing above modified from Reinhart, 1959), from the Early Oligocene of Puerto Rico. But, unlike Caribosiren the rostrum of this critter doesn’t seem to have been as extremely downturned; also it belonged to an animal at least 15% larger than Caribosiren. Other Oligocene halitheriines such as Halitherium schinzii from the European Early Oligocene, have different morphology of the parietal as well as much larger nasals; Eosiren imenti, known from the Early Oligocene of Egypt (Domning et al., 1994), is even more primitive than Halitherium schinzii, as it still has permanents premolars and canines, among other characteristics.

So, as far as I can tell, it seems to be a primitive Metaxytherium. There are other skulls from Early or Late Oligocene of the western Atlantic, which are very similar to this one, possibly the same species, that’s one thing I have to figure out as part of my thesis. If you’re going to the SVP meeting this year, you might learn more about this critter.

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.

Domning, D. P., P. D. Gingerich, E. L. Simons and F. A. Ankel-Simons. 1994. A new Early Oligocene dugongid (Mammalia, Sirenia) from Fayum Province, Egypt. Contributions from the Museum of Paleontology, the University of Michigan 29(4):89-108.

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

A river runs through an Oligocene sea: parte III

So, keeping up with stuff I’ve collected at the Río G locality (for previous entries about this locality go here and here), I bring you some of the sirenian material that I collected last January. It is not much, but it adds to stuff I’ve collected previously (as you’ll see).

In tropical regions, a lot of times, good outcrops are along riverbanks. Puerto Rico is no exception and that is why the Rio G locality is so good, the exposure is kept “fresh” because of the nearly constant river erosion. Of course the drawback is that fossils are also lost if nobody visits these type of localities at least once a month or after big rainstorms (at least that’s what I used to do).

The picture above shows one such example. I spotted this bone fragment on the wall, very close to water level (a little more than half a meter). And, as you can see in the inset, the surface facing away from the rock looks freshly broken. I did collect the fossil, and unsuccessfully looked for additional fragments nearby.

Above is the picture of the fossil, in dorsal view (anterior towards the top), and the interpretative drawing. As it turns out the fossil was part of a sirenian skull. What was left of the fossil, is the anterior part of the frontals (Fr) and the nasals (N), the supraorbital processes of the frontals are missing. The convex frontal roof and shallow nasal incisure (the concave area between the frontals) are some characters that identify this fossil as belonging to a halitheriine dugongid. In fact, it is very similar to the same part of a much more complete skull that I collected from that locality several years ago (see below).

The figure above shows the more complete skull. A and B show a close-up dorsal view (anterior towards the top) of the area that was preserved in the fragmentary fossil. C is a dorsal view of the skull (anterior to the right) with the outline of the enlarged area in A. As you can see the frontal and its relationship with the nasals look much the same as the fragmentary fossil. It also displays a shallow nasal incisure at the posterior end of the mesorostral fossa (MRF) and convex frontal roof. In the more complete skull the premaxilla (Pmx) partially cover the nasals and the supraorbital processes (SOP) are preserved. (In A and C it is missing the left nasal process of the premaxilla which is loose and needs to be re-attached, but I was able to put it in the drawing).

I’m pretty certain that the fragmentary fossil belongs to the same species as the more complete specimen; it was a pity that part of it was lost previous to it being found. If you’re well acquainted with extinct sirenians, you can probably guess what genus this skull belongs to. So, go ahead and make a guess!

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!

A river runs through an Oligocene sea: part II

This is the first post of the year and, hopefully, more will follow. Anyways, today I bring you a brief overview of fieldwork that I did back in January while I was in Puerto Rico. I had written in a previous occasion about this locality (you can read part I here) and unlike back then, I did find some vertebrate fossils.

The picture above shows one of the most productive outcrops along this locality. As you can see there are about four distinct units. I and III are paleosols (ancient soil horizons) whereas II seems to be shallow marine/brackish and IV shallow marine deposits. Unit II has yielded good fossils in the past, including a sirenian skull and associated axial skeleton, croc teeth, rodent teeth and some nurse shark teeth (gynglymostomatids) (update: you can read about newer discoveries at this site and other nearby ones here, here, here, here, and here). These beds are part of the San Sebastian Formation of early Oligocene age, which in the past have yielded other interesting fossils such as the sirenian Caribosiren turneri (Reinhart, 1959) and the gharial Aktiogavialis puertoricencis (Vélez-Juarbe et al. 2007), among others.

Like I mentioned in the intro, this time around I did find some cool stuff!

In the photo above you can see a closeup of unit II showing some of the fossils as I found them and before I started digging. The red circles are for turtle shell fragments while the green is a sirenian rib. Yes, I know, they are somewhat difficult to see but click on the picture and look carefully, you’ll see them.

The sirenian rib was isolated and easy to collect; it is fairly normal to find isolated sirenian ribs in the San Sebastian Fm and other Oligocene and Miocene localities in Puerto Rico. In contrast, while digging around the turtle shell fragments shown in the picture above, I kept stumbling upon more fragments, until it was apparent that this represented a partially disarticulated turtle shell. Not only that, but there was also an associated left pelvis (shown in the picture below), not bad!!

One of the first posts on this blog was an overview of what's known of the fossil side-neck turtles from Puerto Rico. In it I mentioned that some pelomedusid (a more technical name for side-necks) material from the San Sebastian Fm. had been described by Wood (1972) as an unknown taxon. In fact, Wood (1972) not only described an incomplete shell and plastron but also an associated pelvis. Maybe this material I collected represents additional specimens of that unknown taxon. However, comparison with the description as well as with other turtle fossils from the overlying Lares Limestone will have to wait until after the specimens are prepared (you can get a glimpse of the preparation process here). Below you can see the jackets with the specimens inside.

Preliminarily, I am quite certain that this San Sebastian turtle is a pelomedusoid just by the morphology of the pelvis. Also, there was one other fossil collected that day (is in the jacket in the far left), which was both interesting and frustrating, but I'll leave that for next time!

Recommended Literature

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

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

Wood, R. C. 1972. A fossil pelomedusid turtle from Puerto Rico. Breviora 392:1-13.

This post was updated April 28, 2020