[1] The genus receives its name from the occlusal (chewing surface) pattern of the molars[2] and is derived from the Ancient Greek eliktos (ἑλικτός, "winding") and odontas (ὀδόντας, "toothed").

And while splitting E. bolsonensis from E. typus would leave the latter non-monophyletic as regards because of incomplete lineage sorting, the two differ weakly but consistently in several molecular and morphological characters.

[5] Altogether, this seems to represent a case of ongoing parapatric speciation, with a population of E. typus becoming separated at the northern and upper limit of its range not more than a few 100,000 years ago.

Increasing aridity as a consequence of the beginning Quaternary glaciation combined with the uplift of the Patagonian Andes during the latter Pliocene (late Piacenzian to Gelasian, about 3–1.7 mya) split the population into a lowland and a montane lineage.

The same happened somewhat later, at the beginning of the Early Pleistocene (about 2–1.5 mya[10]) at the northern end of the genus' range, with the separating Altiplano population becoming the ancestors of E. hirtipes.

Finally, in the Middle Pleistocene local uplifts in the Pampean region separated the ancestors of E. moreni and E. puerulus, and the lowlands population, isolated form its relatives since more than one million years, began also expanding into the uplands, yielding E. (t.) bolsonensis which currently well on its way to become another highly distinct species.