Will the Amahuacatherium mystery be settled?

'Will the Amahuacatherium mystery be settled?'

The case of a mysterious South American Gomphotherid, 'Amahuacatherium peruvium' has remained controversial ever since its discovery, because the paleontology world has been devided in regards to accepting or not the validity of A. peruvium's specific status and its geological age, the late Miocene.

Prior to the discovery of 'A. peruvium' from Amazonian Peru, it was widely acknowledged that faunal immigration including proboscideans from North & Central Americas to South America only occured after the famous Great American Faunal Interchange(GAFI) during the Pliocene, so it's no wonder why a number of scholars started to disagree over the Miocene presence of a South American gomphotherid. 

Supposedly unique diagnostic features of A. peruvium, i.e., the presence of lower incisors alveoli and its molar and mandibular morphologies have been constantly questioned. Likewise, its geological age has not yet reached a consensus, even though it's been thoroughly investigated by both sides of the argument, based on stratigrahic, lithologic and especially by pro-researchers, magnetostratigraphic data.

Pro and anti Amahuacatherium schools both argue soooo convincingly that it's difficult for us the general public to decide which side to believe!


Most recently, at VII International Mammoths and their relatives conference in 2017, Avilla & Mothe et al., took an 'eclectic' stance, presenting that the fossil of A. peruvium is related to the late Miocene but its exclusive diagnostic features are not valid, i.e., the 'lower incisors alveoli' are the impression of the anterior root of the second molars. They re-identified the specimen as Notiomastodon sp. indet., since its molar and mandibular features are well within the Notiomastodon platensis morphological variation(according to them).

There occured a well documented Miocene mammal immigration pulse between Americas, when two sloths migrated from south to north and a procyonid migrated from north to south. According to Avilla et al., this event coincides with the maximum lowest sea-level recorded for the end of the middle Miocene, which may have facilitated the dispersal of species with swimming skills, so 'Amahuacatherium' (perhaps with its typical proboscidean swimming ability) must be part of this pre-Pliocene GAFI event.

'After the entrance of its ancestor in South America, and its diversification, Notiomastodon remained confined to the northern part of the continent, until the very beginning of the Pleistocene, when the climatic changes probably drivers it to spread all over South America.'
(quotes Avilla et al., 2017)

Personally, I tend to believe that it should not be odd for Notiomastodon in such early evolutional stages as in the late Miocene to have had lower tusks, even though their molars were already within N. platensis molar variation. In relation to that, I'm also interested in the ancestral lineage leading to Notiomastodon, because the new theory seems contradicting the previous idea that Notiomastodon was derived from Cuvieronius during the Pleistocene in South America.

I'd also personally like to know :

1) What was the size of this late Miocene Notiomastodon sp. or whatever Gomphotherid it may turn out to be? Was it smaller or larger compared to the Pleistocene N. platensis or Cuvieronius hyodon?

2) What was 'its ancestor' that entered northern South America during the mid-late Miocene mammal immigration pulse, probably Rhynchotherium sp.? (Cuvieronius is also thought to have derived from Rhynchotherium)*

*However, according to Avilla and Mothé, Notiomastodon varies from Rhynchotherium and Cuvieronius in some important molar characters while the latter two were taxonomically closely related, probably forming a sister group. So, in my opinion, Notiomastodon were perhaps deriving from the still unknown ghost lineage that was somehow related to Sinomastodon, because Sinomastodon were considered by Avilla and Mothé to have been a basal taxon within a monophyletic group that includes Notiomastodon, Sinomastodon, Cuvieronius + Rhynchotherium.

3) If the specimen was really Mocene in age and part of Sebes fauna(my thanks to Zimices for this info), what were its main contemporaneous animals in the region(mammals, reptiles and birds...)?

Also as to pro and anti Amahuacatherium schools, which one do you tend to support, and why?

Opinions?

 

~the Saber Panther