Arctocyon and Deltatherium are now mesonychids in the LRT

High-crested
Arctocyon  and Deltatherium (Fig 1) nested with similar marsupial carnivores = creodonts in the large reptile tree (LRT, 2320 taxa) until yesterday. Now these two taxa nest within the similarly high-crested placental mesonychids, an herbivorous clade anchored by Mesonyx (Fig 1) with worn down tooth crowns evidence of its plant-based diet.

Mesonychids are pre-oreodonts in the LRT and therefore pre-artiodactyls.

Despite those long canines,
mesonychids nest within the Phenacodontidae = Ungulata in the LRT. So their canines were not for killing, but for show and interpersonal fights, as in fanged deer, hippos, Astrapotherium and Coryphodon. Those high cranial crests were jaw muscle anchors on sometimes very narrow skulls.

Figure 1. The mesonychids revisited, this time with the addition of Arctocyon and Deltatherium. ” data-image-caption=”

Figure 1. The mesonychids revisited, this time with the addition of Arctocyon and Deltatherium.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/mesonychidsjuly2_scale588-2.jpg?w=111″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/mesonychidsjuly2_scale588-2.jpg?w=380″ tabindex=”0″ role=”button” class=”size-full wp-image-87283″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/mesonychidsjuly2_scale588-2.jpg” alt=”Figure 1. The mesonychids revisited, this time with the addition of Arctocyon and Deltatherium.” width=”584″ height=”1573″ />

Figure 1. The mesonychids revisited, this time with the addition of Arctocyon and Deltatherium.

Mesonychids have always been
a troublesome clade for paleontologists. The LRT is one way to clear that up by minimizing taxon exclusion, a perennial problem in paleontology. The other way is to toss out all deep time genomics = molecule studies.

According to Wikipedia – Mesonychia,
“Once considered a sister-taxon to artiodactyls, recent evidence now suggests no close connection to any living mammal. Mesonychid taxonomy has long been disputed and they have captured popular imagination as “wolves on hooves”, animals that combine features of both ungulates and carnivores. Skulls and teeth have similar features to early whales, and the family was long thought to be the ancestors of cetaceans.”

Currently in the LRT mesonychids (Fig 1) are a monophyletic extinct clade within Ungulata, very basal to the first artiodatyls.

Figure 2. Tetraclaenodon skull in 3 views. Colors added here. Zygomatic arch and jaw joint restored.

A note about little Tetraclaenodon
(Figs 1, 2) and the phylogenetic mess well-meaning scientists have created by deep time molecule studies that too often recover untenable results, but get published and widely accepted anyway.

The LRT checks their work in a trait-based analysis that includes fossil taxa.

Figure 3. The origin of ungulates in the LRT occurs between Vulpavus and Phenacodus, perhaps at Conoryctes, for which no post-crania is available to check for hooves. ” data-image-caption=”

Figure 3. The origin of ungulates in the LRT occurs between Vulpavus and Phenacodus, perhaps at Conoryctes, for which no post-crania is available to check for hooves.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/ungulate_origins588.jpg?w=172″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/ungulate_origins588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87299″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/ungulate_origins588.jpg” alt=”Figure 3. The origin of ungulates in the LRT occurs between Vulpavus and Phenacodus, perhaps at Conoryctes, for which no post-crania is available to check for hooves.” width=”584″ height=”1021″ />

Figure 3. The origin of ungulates in the LRT occurs between Vulpavus and Phenacodus, perhaps at Conoryctes, for which no post-crania is available to check for hooves.

Kondrashov and Lucas 2012 wrote:
“Tetraclaenodon is the most primitive and oldest genus of the family Phenacodontidae and is very important for assessing the phylogenetic relationships of the family.

Currently in the LRT, Phenacodus (Fig 3) and members of two other clades are more primitive. Tetraclaenodon (Figs 1, 2) nests within the Mesonychidae (Fig 1).

“The newly described skeleton belonged to a lightly built terrestrial mammal that could use trees for shelter. The structure of the ulna, manus, femur, crus, and pes corresponds to that of a typical terrestrial mammal, while morphological features such as the low greater tubercle of the humerus, long deltopectoral crest, pronounced lateral supracondylar crest, and hemispherical capitulum indicate some scansorial adaptations of Tetraclaenodon. The postcranial skeleton of Tetraclaenodon does not exhibit the cursorial adaptations seen in later phenacodontids and early perissodactyls.

Currently in the LRT, perissodactyls are derived from the early artiodactyls. The outgroup taxa for Phenacodus and the rest of the Ungulata are smaller, slinky, arboreal Vulpavus species (Fig 3) with claws, not hooves.

Phylogenetic analysis did not recover monophyletic “Phenacodontidae”; instead, phenacodontids formed a series of sister taxa to the Altungulata clade. Tetraclaenodon is the basal-most member of the “Phenacodontidae” + Altungulata clade.”

Currently in the LRT, Phenacodus and Conoryctes (Fig 3) nest at the base of a monophyletic clade, Ungulata = Phenacodontidae.

According to Wikipedia – Phenacodus,
“The middle toe was the largest, and the weight of the body was mainly supported on this and the two adjoining digits, which appear to have been encased in hooves,”

See those early hooves in figure 3.

According to Wikipedia – Ungulate,
“Euungulata (“true ungulates”), which primarily consists of large mammals with hooves. Once part of the clade “Ungulata” along with the clade Paenungulata, “Ungulata” has since been determined to be a polyphyletic and thereby invalid clade based on molecular data: Euungulata within the clade Laurasiatheria while Paenungulata has been reclassified to a distant clade Afrotheria.”

The trait-based LRT does not confirm = refutes the invalid molecule clades ‘Laurasia’ and ‘Afrotheria‘, neither of which include fossil taxa, both of which recover untenable results.

According to Wikipedia – Altungulata
“is an invalid clade (mirorder) of ungulate mammals comprising the perissodactyls, hyracoids, and tethytheres (sirenians, proboscideans, and related extinct taxa). The name “Altungulata”, introduced by Prothero & Schoch 1989 and revised by McKenna & Bell 1997, was erected as an alternative because the updated concept of “Pantomesaxonia” was regarded too deviant from the original concept. Both names are still in use, and, to add to the confusion, various authors assign different ranks to the involved taxa.”

So, there is ‘confusion’ even within the ranks. Build your own trait-based analysis to see for yourself how taxa are related to one another.

Deltatherium fundaminis
(Cope 1881, middle Paleocene 60 mya, 14 cm skull length, cat-sized, AMNH 16610) this former creodont and former tillodont nests with Arctocyon within the Mesonyx clade. Wikipedia reports, “its relatives are far from clear.” The large cranial crest anchored large jaw muscles.

Arctocyon primaevus
(Blainville 1841, Gould and Rose 2014; YPM VP 021233; Paleocene, 60 mya) was long and widely considered a primitive plantigrade ungulate condylarth procreodi. In the LRT Arctocyon nests within the mesonychds not far from Sinonyx.

Here’s yet another chapter in the housekeeping process
as learning and experience accumulate during this homeschooling process. Apologies for the earlier errors. Corrections, once noted, will always be implemented.

Thank you for your readership.

References
Blainville HM 1841. Osteographie et description iconographique des Mammiferes récentes et fossiles (Carnivores) 1, 2 Paris.
Cope ED 1881. Mammalia of the lower Eocene beds. American Naturalist 15:337-338.
Gould FDH and Rose KD 2014. Gnathic and postcranial skeleton of the largest known arctocyonid ‘condylarth’ Arctocyon mumak (Mammalia, Procreodi) and ecomorphological diversity in Procreodi. Journal of Vertebrate Paleontology 34(5):1180-1202.
Kondrashov P and Lucas SG 2012. Nearly Complete Skeleton of Tetraclaenodon (Mammalia, Phenacodontidae) from the Early Paleocene of New Mexico: Morpho-Functional Analysis. Journal of Paleontology 66(1):25–43.

wiki/Arctocyon
wiki/Deltatherium
wiki/Tetraclaenodon
wiki/Mesonychidae