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(Note: I planned originally make just an image with some text, as I made regulary, but I ended make more images than I expected and all form part of the same context. So, for this time I prefer put all in a journal... the images will be uploaded in my gallery later.)

Between the toxodontids, probably one of the most interesting (at least for me) is Mixotoxodon larensis. Although it lived during the Pleistocene, is far to be known so well as the classic Toxodon platensis or another earlier genera like Nesodon or Adinotherium, and is frequent find only short descriptions, that usually says that is the northern equivalent of Toxodon and that was the only notoungulate that moved outside South America. If you look for images of Mixotoxodon in Google, probably you have this: some good reconstructions, few fossils and a lot of unrelated animals... well, you know that could be worst.

 ClipBoard-8 by Zimices

On another hand, in the scientific literature, frequently there is only fragmentary pieces. Not very informative, if you want to draw it.

 (From Ascanio Rincón, 2003)

 ClipBoard-2 by Zimices

In contrast with the scarce images, it was a very widespread animal, and a series of small but relevant pieces has been discovered in the last years in a variety of places, that make that their geographical range be even larger than previously was imagined:

 File:Mixotoxodon distribution.svg

 

The Mixotoxodon "empire" (every point represents a fossil location). Note that it reach the south of USA and northern Argentina, and is well represented in northern South American and Central America. These locations probably represents a combination of tropical prairies and forests, probably not the best place for the fossilization. Also, its range was different of Toxodon, that lived in the open plains of southern South America, with the Northeastern Brazil as the northern limit. Probably both animals must had different some ecological requirements, although the evergrowing teeth and the isotopes shows that both feed on abrassive plants, like grasses. But, again, how was its physical appearance?

Reading a paper (Lucas et al, 1997), I find a kind of answer. Although is better and worst (at same time) than I expected. Look at this photo:

 ClipBoard-1 by Zimices

Let me introduce you to CMCR-CFM 846 , the only relatively complete skull known for Mixotoxodon, in palatal view. It was recovered during the 1930s in Costa Rica, along a mandible, probably from the same individual, and is in the collections of the Museo Nacional de Costa Rica. But the problem is that this photograph is the only way to imagine how the entire skull was: for unknown reasons, the skull is lost, remaining only a pair of pieces. And sadly, apparently nobody took more photos or made an adequate description of the fossil when it was complete. Therefore, we must conform with this:

 ClipBoard-3 by ZimicesClipBoard-6 by Zimices


CMM as is known today: a left maxillary piece with the three molars and part of the cheek bone, and a isolated fourth premolar, in lateral and ventral view. (From Lucas et al, 1997 and Laurito, 1993)

But we can count with another Mixotoxodon fossils too. We can begin for this premaxilla (the snout) described from northern Argentina in 2012. Look how slender is:

 

 01f04g J by Zimices

And the original remains of Mixotoxodon, from Venezuela. In this case, we have almost all the mandible and teeth (from Van Frank, 1957):

 ClipBoard-4 by Zimices
 

As you can see, a pattern is emerging: the skull is a bit triangular and mandibles are relatively slender, without chin, like in other advanced toxodontids. With this idea, I’ve tempted to draw how could be the entire head of the animal. Have in mind that here I traced the form of the original skull from the photo, but this kind of exercise, with a source image of very low resolution, surely is plagued with anatomical distortions and pareidolia, so must be taken just as a very tentative reconstruction. To help to visualizate what I made, I put in white the areas reconstructed by me and in colors the different real specimens. In A) is the skull of the photo with the Argentinean premaxilla; B) is a diagram of the lower teeth and the lower jaw; C) the skull in lateral view (with only the preserved portion of the maxilla) and the mandible; and D) The skull in frontal view.

Mixotoxodon 1 by Zimices

Compared with Toxodon, the snout is short, and more slender, and the tusk-like incisives are shorter too; the front part of the mandible is cylindrical, different to the wide snout of the former (images taken from here: www.fullblog.com.ar/blogs/arge…, and here:dailyfossil.tumblr.com/post/24…, respectively):



On another hand, these features, and the shape of the mandible remind me a bit to the extraordinary horned toxodontid, Trigodon gaudryi (from Ameghino, 1907):

ClipBoard-5 by ZimicesClipBoard-7 by Zimices

I want to note here that the classification of toxodontids is difficult, and they have been divided in a number of subfamilies across the ayears, but generally are accepted three of them: Nesodontinae (primitive and small forms), Haplodontheriinae (larger forms, with compressed incisors and cranial ornamentation) and Toxodontinae (advanced and large forms with long skulls and flat incisors). I mentioned it due that Trigodon is a Haplodontheriinae, and it shares with Mixotoxodon the cylindrical mandible and a long symphisis (the union of both mandibles) that extends until the first molar in the case of Mixotoxodon. Meanwhile, with Toxodon shares features of the teeth. Is this mixture of features the origin of the very name of Mixotoxodon, and makes harder establish their relationships, although that's another history...

Along the original specimen, Van Frank mentioned some postcranial remains also recovered in the San Miguel site in Venezuela, that could belong to this animal: An broken second cervical (atlas), a single radius, four ulnae (one of these complete), a patella and an astragalus. These elements, in general terms are very similar in proportions to those of Toxodon, although the astragalus and radius are more slender and have specific anatomical differences. In any case, both these bones as the skull show a larger size than Toxodon. The former measures about 1,5 meters until the shoulders, with a skull of 66 cm; if the reconstruction below is right, Mixotoxodon could measure up to 1,70 to the shoulders, with a skull of about 80 cm, cleary bigger than its southern cousin. A recent weight estimation (2012) suggest that Mixotoxodon could reach 3.8 tonnes, which makes sense with this larger body. Oh, and is also the largest notoungulate that ever lived.
Mixotoxodon 2 by Zimices


And finally, I've decided make a quick reconstruction of the head of the animal. I hope you like the result:

Mixotoxodon 3 by Zimices


References:








Add a Comment:
 
:iconanonymousllama428:
AnonymousLlama428 Featured By Owner May 23, 2015  Hobbyist General Artist
I do find the notoungulata a fascinating bunch.
Reply
:iconzimices:
Zimices Featured By Owner May 23, 2015  Hobbyist
Me too! toxodontids, hegetotheriids, homalodotheriids, leontinids, interatheres... there is a lot of things to tell. :)
Reply
:iconnesihonsu:
Nesihonsu Featured By Owner Jun 21, 2014  Hobbyist General Artist
I owe you my deep respect for this work and whole research.
Reply
:iconzimices:
Zimices Featured By Owner Jun 21, 2014  Hobbyist
Thanks very much for the appreciation! is the best reward :hug:
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:iconelectreel:
electreel Featured By Owner Jun 16, 2014
¡Un trabajo majestuoso y de magnitud profesional! :clap:
Las representaciones esqueléticas y la reconstrucción son excelentes :) Es una pena que muchas criaturas como el Mixotoxodon se mantengan tras el velo del misterio a pesar de la relativa abundancia de especímenes. 
Algo que me confunde es la delgadez de la parte frontal de las mandíbulas, que me recuerdan a las de un caballo ¿Realmente eran tan abultados los labios?
Reply
:iconzimices:
Zimices Featured By Owner Jun 16, 2014  Hobbyist
¿Profesional? no hombre, para nada, ese título dejemóselo a Mauricio Antón y compañía :)

Gracias, muchas gracias por el comentario. Ciertamente eso es lo que me inspiró a hacer esto, si algo sueño es con una especie de guía de la megafauna del Pleistoceno de todo el mundo, pero hay muchos animales que son muy pobremente conocidos, así que hay que tratar de hacer algo al respecto, al menos para que se den a conocer un poco más. Y desde luego, esperar a que se vayan descubriendo más fósiles, que ojalá confirmen nuestras especulaciones.

Je, tienes razón en lo de la delgadez de las mandíbulas, es algo que leía en el artículo de donde saqué la foto del cráneo perdido, que la cabeza del animal desde abajo tiene una peculiar forma triangular, con mandíbulas más estrechas que en Toxodon, ciertamente se parece más a un caballo que a ese hocico de hipopótamo del Toxodon, supongo que es porque su hábitat no era de planicies abiertas y no necesitaba tener un hocico de pala para recoger pasto, tal vez era más generalista y por ello necesitaba un hocico para ramonear también.
En cuanto al labio, pues por lo que pude apreciar en los cráneos de toxodóntidos los labios debieron tener una musculatura importante, aunque tal vez exageré con su longitud. 
Reply
:iconelectreel:
electreel Featured By Owner Jun 27, 2014
Eso no quita que el trabajo que has hecho sea admirable. 
Si alguna día te animas a trabajar en semejante locura como una guía del Pleistoceno no dudes en contactar conmigo para colaborar :D 
Reply
:iconzimices:
Zimices Featured By Owner Jun 27, 2014  Hobbyist
Bueno, en ese caso, ten cuidado: te puedo tomar la palabra el día menos pensado :D
Reply
:iconbran-artworks:
Bran-Artworks Featured By Owner Jun 13, 2014  Student General Artist
Buen trabajo, todo un trabajo detectivesco, en efecto es uno de los toxodontes mas interesantes, el que migro, acá esta presente en un par de locaciones y como no es sorpresa son restos muy fragmentarios también.
Reply
:iconzimices:
Zimices Featured By Owner Jun 13, 2014  Hobbyist
Gracias, en efecto es toda una paradoja, parece que fue común ya que se lo conoce de varias partes pero solo sabemos a ciencia cierta algunas cosas de él, y justamente es interesante por haber sido exitoso migrando, curiosamente algunos de los restos centroamericanos están entre los más interesantes y fueron los primeros en ser conocidos por la ciencia, ya al final del siglo XIX.
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:iconbran-artworks:
Bran-Artworks Featured By Owner Jun 13, 2014  Student General Artist
Sabes que otra cosa es curiosa, como los animales suramericanos tienden a hacerse mas grandes conforme se mueven hacia el norte, como este y Eremotherium por ejemplo, me parece curioso...
Reply
:iconzimices:
Zimices Featured By Owner Jun 13, 2014  Hobbyist
Hmm... nunca he tenido claro si de verdad Eremotherium es más grande que su primo sureño Megatherium, creo que en ambos casos hay ejemplares muy grandes que rondan las 5-6 toneladas. También he oído que Xenorhinotherium de Venezuela y Brasil era mayor su primo Macrauchenia, aunque tampoco eso es claro. Lo cierto es que parece que los herbívoros suramericanos parece que formaron faunas diferenciadas pero con equivalencias en el sur y el norte, sería interesante saber si esas diferencias eran "de peso" :)
Reply
:iconbran-artworks:
Bran-Artworks Featured By Owner Jun 14, 2014  Student General Artist
Me parece tambien haber leido algo sobre un gran Macraucheniopsis pero nunca supe mas.
Reply
:iconzimices:
Zimices Featured By Owner Jun 15, 2014  Hobbyist
Lo malo de Macraucheniopsis es que casi no hay nada en Internet, solo puede dar con este artículo en francés: fumdham.org.br/pesquisas/paleo… Ahí solo lo describen brevemente, pero al menos confirman que su talla es mayor que la de Macrauchenia (pero no dicen qué tanto) :(
Reply
:iconbran-artworks:
Bran-Artworks Featured By Owner Jun 15, 2014  Student General Artist
Es lo que nunca averigüe, me parece que en el libro ´´Bestiario Fósil´´ igualmente mencionaban que era de una gran talla pero sin especificar :(...
Reply
:iconzimices:
Zimices Featured By Owner Jun 16, 2014  Hobbyist
Yo también leí ese libro y no recuerdo que lo mencionaran, eso es lo malo de la parquedad de los datos. Incluso quien realizó su primera descripción científica, Carlos de Paula-Couto hizo un libro sobre mamíferos extintos y solo lo menciona de pasada, otra vez diciendo que es un poco más antiguo y más grande que Macrauchenia... Por lo visto habrá que teletransportarse a Buenos Aires para leerlo y salir de la duda, o más bien ver si se puede consultar a algún experto. Y no me faltan ganas de intentar lo último...
Reply
:iconwillemsvdmerwe:
WillemSvdMerwe Featured By Owner Jun 12, 2014
Great work you did here, and very informative!  I do hope more fossils of Mixotoxodon turn up.
Reply
:iconzimices:
Zimices Featured By Owner Jun 12, 2014  Hobbyist
Thanks, I hope that in the future some nice skeleton come to light! and if I'm wrong or right, in any case I'll be happy :)
Reply
:iconevenape:
Evenape Featured By Owner Jun 12, 2014  Student Traditional Artist
Nice scientific exploration and great art! :D
Reply
:iconzimices:
Zimices Featured By Owner Jun 12, 2014  Hobbyist
Thanks a lot! I glad you like it :)
Reply
:iconevenape:
Evenape Featured By Owner Jun 12, 2014  Student Traditional Artist
You're welcome :D
Reply
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