The location of the area or Urheimat is not known, and various strongly differing proposals have been advocated, but the vicinity of the Ural Mountains is generally accepted as the most likely.
In the early 21st century, these tree-like models have been challenged by the hypothesis of larger number of proto-languages giving an image of a linguistic "comb" rather than a tree.
[2] Thus, the second-order groups of the Uralic phylum would then be: Sami, Finnic, Mordvinic, Mari, Permic, Hungarian, Mansi, Khanty and Samoyedic, all on equal footing.
However, other scholars such as Zhivlov posit the existence of disharmonic *i-a stems in Proto-Uralic, which would imply that vowel harmony was not allophonic.
A general difficulty in reconstructing unstressed vowels for Proto-Uralic lies in their heavy reduction and loss in many of the Uralic languages.
The original bisyllabic root structure has been well preserved in only the more peripheral groups: Samic and Finnic in the northwest, Samoyedic in the east.
[12] A number of roots appear to diverge from the main picture of unstressed syllables in a different way: while Finnic, Samic and Samoyedic languages all have one of the "typical" stem shapes, they may not quite match.
E.g.:[13] The change is, however, masked by the shift of *ë to *a (which later develops to Proto-Samic *uo) in words such as: In a second group, a change *ä-ä > *a-e appears to have taken place in Finnic in words such as:[15] In the consonant system, palatalization, or palatal-laminal instead of apical articulation, was a phonemic feature, as it is in many modern Uralic languages.
The segment has some similarity to the Indo-European laryngeals (to which it can correspond in loanwords): it is reconstructed by certain scholars in syllable-final position in word-stems where a contrastive long vowel later developed (similar to Turkish ğ), best preserved in the Finnic languages, and where Samoyedic features a vowel sequence such as *åə.
[18] *x is also reconstructed word-medially, and in this position it also develops to a Finnic long vowel, but has clear consonantal reflexes elsewhere: *k in Samic, *j in Mordvinic and *ɣ in Ugric.
If a consonant, it probably derives from lenition of *k at a pre-Uralic stage; it is only found in words ending in a non-open vowel, while *k is infrequent or nonexistent in similar positions.
A reconstruction *δäpδä "spleen" exists but is not found in Samoyedic and the most stringent criteria for a Proto-Uralic root thus excludes it.
While voicing was not a phonemic feature, double (i.e. geminate) stops probably existed (*ïppi "father-in-law", *witti "five", *lükkä- "to push").
The singleton–geminate contrast in most descendant languages developed into a voiced–voiceless distinction, although Finnic is a notable exception, e.g. Finnish appi, lykkää.
Further cases are occasionally mentioned, e.g. Robert Austerlitz's reconstruction of Proto-Finno-Ugric[citation needed] includes a seventh, adverbial.
Support for this theory comes from the Finnish agent participle constructions, e.g. miehen ajama auto — car driven by the man, Naisen leipoma kakku — the cake that woman baked.
[26] This is problematic for the ergative theory because the -mV participle, labelled the ergative marker, is a passive marker in most of the languages that use it, and the Finnish agent participle constructions may in fact derive from similar constructions in Baltic languages, e.g. Lithuanian tėvo perkamas automobilis or automobilis (yra) tėvo perkamas.
Notable is the unmistakable resemblance between the Baltic and Finnic verbal suffixes, and the fact that -mV is missing in both Estonian and Mordvinic, despite being two very close relatives of Finnish.
[27] Even if the ending derives from Proto-Uralic and not the Baltic languages, the transition from a passive to ergative construction is very common and has been observed in Indo-Aryan, Salish, and Polynesian.
North Saami veaiki, Finnish vaski ‘copper, bronze’, Hungarian vas, and Nganasan basa ‘iron’).
[31] Examples of vocabulary correspondences between the modern Uralic languages are provided in the list of comparisons at the Finnish Wikipedia.