Traditional chalicothere, Litolophus, moves to Arctocyon, a mesonychid
Traditionally considered a chalicothere,
(Fig 2) high-crested Litolophus (Fig 1) now nests in the large reptile tree (LRT, 2339 taxa) with Arctocyon, a high-crested mesonychid.
Don’t overlook the small split premaxillae in both taxa (Fig 1). That’s a rare trait.
Or is it a coincidence of taphonomy?
Figure 1. The mesonychid, Arcocyon, here compared to scale with Litolophus. These taxa are united by 4 premolars (blue) + 3 molars (green) along with a long list of other traits, including round hooves.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg?w=88″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg?w=300″ class=”size-full wp-image-95177″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg” alt=”Figure 1. The mesonychid, Arcocyon, here compared to scale with Litolophus. These taxa are united by 4 premolars (blue) + 3 molars (green) along with a long list of other traits, including round hooves.” width=”584″ height=”1996″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg?w=584&h=1996 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg?w=44&h=150 44w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg?w=88&h=300 88w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/arctocyon-skull588-1.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. The mesonychid, Arcocyon, here compared to scale with Litolophus. These taxa are united by 4 premolars (blue) + 3 molars (green) along with a long list of other traits, including round hooves. “Grangeria” is a plant genus and a synonym of Litolophus according to Radinsky 1964.
Arctocyon primaevus
(Blainville 1841, Gould and Rose 2014; YPM VP 021233; Paleocene, 60 mya; Fig 1) was long and widely considered a primitive plantigrade ungulate condylarth procreodi placental. In the LRT Arctocyon nests within the mesonychds not far from Sinonyx. Litolophus (below) is related.
Figure. 2. Chalicothere skulls to scale. Lophiodon is an outgroup closer to tapirs.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg?w=584″ class=”size-full wp-image-26713″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg” alt=”Figure. 2. Chalicothere skulls to scale. Lophiodon is an outgroup closer to tapirs.” width=”584″ height=”468″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg?w=584&h=468 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg?w=150&h=120 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg?w=300&h=240 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/05/chalicothere_skulls5881.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure. 2. Chalicothere skulls to scale. Lophiodon is an outgroup taxon. Note: Litolophus is different enough from chalicotheres to better nest with Arctocyon.
Grangeria gobiensis = Litolophus gobiensis
(Zdansky 1930, Colbert 1934; Early Eocene; Fig 1) is known from crushed materials of several individuals of various size referred by Radinsky 1964a to Litolophus (Fig 1) found in the same strata and formation. The incisors are large and square. The generic name is shared with a plant, so Grangeria is invalid as a current taxon name, but is retained in the LRT as a historical note while adding data not presented in Litolophus.
Litolophus gobiensis
(Radinsky 1964b, Bai, Wang and Meng 2010, 2011; Early Eocene; Fig 1) is traditionally considered an odd basal chalicothere with a slender premaxilla that curves ventrally and a very tall parietal crest (perhaps taphonomically rotated?). In the LRT this taxon is a sister to high-crested Arctocycon, a mesonychid. The hooves were small and round, not large and sharp.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
References
Blainville HM 1841. Osteographie et description iconographique des Mammiferes récentes et fossiles (Carnivores) 1, 2 Paris.
Bai B, Wang Y-Q and Meng J 2010. Early Eocene chalicothere Litolophus with hoof-like unguals. Journal of Vertebrate Paleontology 31(6):1387-1391.
Colbert EH 1934. Chalicotheres from Mongolia and China in the American Museum. Bulletin of the American Museum of Natural History 47(3):353–387.
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.
Radinsky LB 1964b. Notes on Eocene and Oligocene fossil localities in Inner Mongolia.
American Museum Novitates 2180: 1–11.
Zdansky 0 1930. ‘Die Alttertiaren Saugetiere Chinas nebst Stratigraphischen
Bemerkungen.’ Pal. Sinica, Ser. C, VI, fas. II, pp. 62-72, Pls. Iv, figs. 9-16, v, figs. 1-20.
Source: https://pterosaurheresies.wordpress.com/2025/11/15/traditional-chalicothere-litolophus-moves-to-arctocyon-a-mesonychid/
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