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Post by arctozilla on Dec 27, 2021 15:21:16 GMT -5
Isn't the Plionarctos the ancestor of all short faced bears?
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Post by Gorilla king on Dec 27, 2021 16:16:38 GMT -5
Isn't the Plionarctos the ancestor of all short faced bears? |
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Post by brobear on Dec 27, 2021 23:59:09 GMT -5
In other words, the question is, what species of Tremarctine bear ventured down from North America into South America?
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Post by Gorilla king on Dec 28, 2021 1:45:41 GMT -5
In other words, the question is, what species of Tremarctine bear ventured down from North America into South America?
Yucatán carnivorans shed light on the Great American Biotic Interchange
Disagreements have occurred over the evolutionary relationship of Arctotherium, Tremarctos and Arctodus, with earlier morphological interpretations placing Arctotherium and Arctodus as sister taxa [26]. Recent genetic analyses indicate Arctotherium is more closely related to Tremarctos, and therefore Arctotherium and Arctodus share morphologies that may relate to their large size and/or dietary behaviour [35]. Based on our understanding of the group, Arctotherium arose from Tremarctos, or a common ancestor that excluded Arctodus.
Arctotherium is the only known bear from the Yucatán Peninsula. In terms of diet, A. wingei has been interpreted as a herbivorous omnivore like Tremarctos ornatus [39,40]. Although T. ornatus occurs in the Andean region of western South America today, it is not known from that continent until the early Holocene [41–43]. While Tremarctos is known from North America until the Pleistocene/Holocene transition [44], there is only one fossil occurrence in Middle America [45]. Identification of this specimen is tenuous because the skeleton is in a Belizean cave. Based on the current record, we propose that competition with Arctotherium in Middle America may have limited the southern distribution of Tremarctos until the former became extinct in the latest Pleistocene or early Holocene.
www.ncbi.nlm.nih.gov/pmc/articles/PMC6548739/#!po=23.3333 |
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Post by Gorilla king on Dec 28, 2021 2:12:00 GMT -5
But, believe it or not, the mystery continues, because "Tremarctos" has only 2 species, Tremarctos Floridanus, which is endemic to North America, and Tremarctos Ornatus, which is endemic to South America and appeared in the late Pleistocene, later than Angustidens of course.
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Post by brobear on Dec 28, 2021 5:02:01 GMT -5
Therefore, either some as yet undiscovered species of Tremarctos or perhaps a group of Tremarctos Floridanus ventured into S. America where they ( in time ) evolved into Arctotherium. Much like when a group of brown bears wondered into the far North where they became stranded and evolved, over time, into polar bears.
There are missing pieces to this puzzle.
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Post by Gorilla king on Dec 28, 2021 7:07:47 GMT -5
Therefore, either some as yet undiscovered species of Tremarctos or perhaps a group of Tremarctos Floridanus ventured into S. America where they ( in time ) evolved into Arctotherium. Much like when a group of brown bears wondered into the far North where they became stranded and evolved, over time, into polar bears. There are missing pieces to this puzzle.
That "common ancestor" is the key. |
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Post by arctozilla on Dec 28, 2021 10:08:06 GMT -5
I think there's actually any possibility that Arctotheriums descend from Tremarctos. Tremarctos is a genus that appeared during Pliocene whereas Arctotherium appeared in Early-Pleistocene. So this is likely but there's just a missing link.
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Post by Gorilla king on Dec 28, 2021 10:08:34 GMT -5
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Post by Gorilla king on Dec 28, 2021 16:26:32 GMT -5
Here is a second email from Soibelzon, he thinks the speciation (the formation of new and distinct species in the course of evolution) could have occurred in Central America:
 Translation:
"Pablo, speciation could have occurred in Central America where the fossil record is terrible. I send you two papers. I apologize for not being able to extend myself further, but I am leaving for Antarctica in 5 days and I don't even have time to breathe.
Greetings
Leopold
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Post by arctozilla on Dec 28, 2021 17:00:39 GMT -5
Therefore, either some as yet undiscovered species of Tremarctos or perhaps a group of Tremarctos Floridanus ventured into S. America where they ( in time ) evolved into Arctotherium. Much like when a group of brown bears wondered into the far North where they became stranded and evolved, over time, into polar bears. There are missing pieces to this puzzle. I still have one question: according to you why did that Tremarctos population evolved into Arctotheriums while the morden Andean bear remained a Tremarctos up our days considering they went to the same location? |
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Post by brobear on Dec 28, 2021 22:42:13 GMT -5
Therefore, either some as yet undiscovered species of Tremarctos or perhaps a group of Tremarctos Floridanus ventured into S. America where they ( in time ) evolved into Arctotherium. Much like when a group of brown bears wondered into the far North where they became stranded and evolved, over time, into polar bears. There are missing pieces to this puzzle. I still have one question: according to you why did that Tremarctos population evolved into Arctotheriums while the morden Andean bear remained a Tremarctos up our days considering they went to the same location? Only idea I can come up with is those that found their way into the high Andean mountains, which, by the way, are larger than the North American rocky mountains, retained their Tremarctos "pedigree" while those of the lower altitudes, with more lush vegetation and large herbivores went through changes. Truth; I'm not sure. |
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Post by Gorilla king on Dec 31, 2021 21:28:37 GMT -5
Anatomical study of the auditory region of Arctotherium tarijense (Ursidae, Tremarctinae), an extinct short‐faced bear from the Pleistocene of South America
Abstract
Here we present the most detailed morphological study of the auditory region of a tremarctinae bear, Arctotherium tarijense Ameghino. In addition, we provide new anatomical information of the Tremarctinae inner ear, such as coplanarity and deviation from orthogonality of the semicircular canals, as an approach to infer the head movements which encountered the extinct forms in locomotion. Based on morphological comparisons, A. tarijense exhibits the following particular features: the cavum tympani presents the highest relative volume compared with other ursids; the processus paraoccipitalis has a foramen that is absent in other tremarctines; there is only one (ventral) recess in the anterior region of the cavum tympani; and the recessus epytimpanicus is the smallest for all ursids studied. In relation to the inner ear, A. tarijense shows the lowest values of orthogonality deviation and highest scores of locomotor agility. Based on this, is possible to make a preliminary proposal that this species had a relative high vestibular sensibility and therefore a better ability to explore different kind of habitats. However, this hypothesis might be contrasted among bears taking into account the orientation of each semicircular canal in a phylogenetic framework.
www.ncbi.nlm.nih.gov/pmc/articles/PMC5108154/#!po=32.1429
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