Aumelasia gabineaudi: This tiny Eocene addition solves three basal artiodactyl problems in the LRT

There is no Wikipedia page
or Aumelasia (Figs 1, 2). No diagram of the skull and skeleton appears in the original and only description of Sudre 1979. Only molar pix.

Figure 1. Aumelasia skull. Colors added here.

That seems strange
because this priceless gift to paleontology is represented online by only a single fan photo of a complete and articulated fossil housed in the Senckenberg Museum of Frankfurt (Figs 1, 2). Discovered in a Middle Eocene European lagerstätten, Aumelaisa preserves internal organs and its last meal(s). Given this extraordinary fossil, Aumelasia really should be better studied by now, more than 40 years after its one and only dental description.

Figure 2. Aumelasia skeleton on display. Colors added here. Note the deltopectoral crest and the protruding pubis.

Sudre 1979
focused on and illustrated only the molar cusps of Aumelasia. From those few clues, and prior to the era of software assisted phylogenetic analysis, Sudre was able to place Aumelasia more or less close to Diacodexis.

For 140 years
Diacodexis (Cope 1882) has been. and still is the ‘go-to’ basal artiodactyl. Unfortunately it is known from remains so incomplete it will not be able to enter the LRT. So perfectly preserved Aumelasia (Fig 2) comes along as a welcome addition.

Here
in the large reptile tree (LRT, 2051 taxa, subset Fig 4) tiny Middle Eocene Aumelasia nests with massive Miocene Homalodotherium (Fig 3). The two are identical in most regards. The exceptions/differences are obvious and explained below.

Yesterday
massive Homalodotherium (Fig 3) nested alone as the basalmost artiodactyl in the LRT. That brought up three problems: it was too large, too derived and appeared too late. Tiny, plesiomorphic and earlier Aumelasia (Fig. 3) solves all three problems.

Figure 3. Tiny Aumelasia joins these relatives of giant Homalodotherium. Having a smaller basalmost artiodactyl, or pre-artiodactyl, is a better fit for small descendants, like Cainostherium, at the base of pigs.

Aumelasia ancestors include much larger oreodonts,
like 1.3m Merycoidodon (Fig 3), much larger mesonychids, like 2m Mesonyx, and much larger phenacodonts, like 1.5m Phenacodus in the LRT (subset Fig 4).

That means, once again,
phylogenetic miniaturization produced new tiny taxa characterized by novel structures appearing at the genesis of new clades in the LRT. Such new traits (including a temporary small size due to neotony and precocious maturation) introduced adaptations favoring or permitting survival in local conditions.

Figure 4. Subset of the LRT focusing on terrestrial and herbivorous placentals (= pantodonts + phenacodonts). Aumelasia nests with Homaloldotherium as the last common ancestor of the Artiodactyla.

Aumelasia gabineaudi
(Sudre 1979. Middle Eocene, 42cm long) was originally described as a basal artiodactyl based on its dention. Here it nests as a tiny relative of Homalotherium, which nests basal to artiodactyls in the LRT (subset Fig 4). Distinct from its larger sister (Fig 3) the tibia of Aumelasia (Fig 2) is not markedly shorter than the femur in this smaller taxon. The deltopectoral crest is likewise not as prominent. Those derived traits evolved in later, larger Homalotherium, a dead-end taxon leaving no other known descendants.

Homalodotherium cunninghami
(Huxley 1870; 2m in length; Miocene) was originally considered a notoungulate, but here descends from the oreodont Merycoidodon and nests at the base of the Artiodactyla as a late survivor evolving in its own way apart from other and extant artiodactyls. The clawed manus was digitigrade. The clawed pes was plantigrade. A pair of clavicles oddly reappears in this taxon and its ancestor and sister in the LRT, Aumelasia.

The sisterhood of Aumelasia with Homalodotherium
appears to be a novel hypothesis of interrelationships. If not, please send a citation so I can promote it here.

References
Sudre J 1980. Aumelasia gabineaudi n.g. n.sp. nouveau Dichobunidae (Artiodactyla, Mammalia) du gisement d’Aumelas (Hérault) d’âge Lutétien terminal. Palaeovertebrata, Mémoire Jubilaire R. Lavocat 9:197–211.

wiki/Dichobunidae