Rhadinorhinina

Rhadinorhines
Temporal range: Middle Eocene,
Skull of Fossendorhinus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Order: Perissodactyla
Family: †Brontotheriidae
Subfamily: †Brontotheriinae
Tribe: †Brontotheriini
Subtribe: †Rhadinorhinina
Osborn, 1929
Genera

Rhadinorhines (subtribe Rhadinorhinina) were a group, or clade, of derived (advanced) brontotheres. Rhadinorhines were small to intermediate-sized brontotheres, known only from the Middle Eocene (Uintan) of western North America.

Description

Jaw of Metarhinus

Rhadinorhines are known only from cranial fossils (skulls, jaws, and teeth).[2][3] They were small to intermediate-sized brontotheres[2] that share a single securely identified apomorphy (shared evolved trait): that the premaxillomaxillary rostrum (the snout of the animal, below the nasal incision) does not deepen ventrally (towards the underside).[2] This trait is also seen in the more distantly related Dolichorhinus hyognathus, though is in that case treated as a case of convergent evolution.[2]

Classification

History, systematics, and phylogenetics

Fossendorhinus diploconus was the first rhadinorhine to be described, by Henry Fairfield Osborn in 1895, under the name "Telmatotherium diploconum".[4] In 1929, Osborn named the brontothere subfamily "Rhadinorhininae" to encompass only the genus Rhadinorhinus, which per Osborn's taxonomy included the two species R. abbotti and R. diploconus (formerly T. diploconum).[4] Osborn placed the genus Metarhinus in a separate subfamily, "Dolichorhininae", alongside the genera Dolichorhinus, Mesatirhinus, and Sphenocoelus.[4]

Rhadinorhinus is today considered a junior synonym of Metarhinus.[2] In a major 2008 brontothere monograph, Matthew C. Mihlbachler transferred "R". diploconus to the distinct genus Fossendorhinus.[2] In a phylogenetic analysis performed for the monograph, Mihlbachler recovered a small clade containing Metarhinus and Fossendorhinus. Mihlbachler referred to this clade as Rhadinorhinina, having reranked "Rhadinorhininae" to the status of a subtribe to fit with his larger-scale systematic revision of the brontotheres.[2] Rhadinorhinina was not recovered as a clade in a 2016 analysis by Mihlbachler and Thomas A. Deméré,[3] but recovered again in a 2021 analysis by Mihlbachler and Donald Prothero.[5] The cladograms below show brontothere classification per the primary strict reduced consensus tree from Mihlbachler's 2008 analysis,[2] and the reduced strict consensus tree from the 2021 analysis by Mihlbachler and Prothero:[5]

Etymology

The name Rhadinorhinina is derived from the now invalid genus Rhadinorhinus[4] (=Metarhinus).[2] Rhadinorhinus means "slender nose", from the Greek ῥαδινός (rhadinós, "slender") and ῥινος (rhinos, "nose").[4] Members of the Rhadinorhinina are informally referred to as "rhadinorhines".[4]

Evolutionary history and paleobiogeography

The two known rhadinorhine genera, Fossendorhinus and Metarhinus, are known only from the Uintan land mammal age[1] of the western United States.[2] Metarhinus is known from Wyoming, Utah, and California,[2][3] from deposits of early to middle Uintan age (Ui1–Ui2).[1] Fossendorhinus is known from the middle Uintan (mid-to-late Ui2)[1] of Utah.[2]

Notes

  1. ↑ The fossil range follows North American land mammal age correlations (with precise dates) from Hodnett et al. (2022).[1]

References

  1. 1 2 3 4 Hodnett, John-Paul M.; Welsh, Edward T.; Santucci, Vincent L.; Tweet, Justin S. (2022). "A Middle Eocene brontothere (Mammalia; Perissodactyla; Brontotheriidae) from Yellowstone National Park, Wyoming". FOSSIL RECORD 8. New Mexico Museum of Natural History and Science. p. 211.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 Mihlbachler, Matthew C. (2008). "Species Taxonomy, Phylogeny, and Biogeography of the Brontotheriidae (Mammalia: Perissodactyla)". Bulletin of the American Museum of Natural History. 2008 (311). doi:10.1206/0003-0090(2008)501[1:STPABO]2.0.CO;2.
  3. 1 2 3 Mihlbachler, Matthew C.; Deméré, Thomas A. (2010). "Phylogenetic status of Metarhinus pater (Brontotheriidae: Perissodactyla) from Southern California and species variation in Metarhinus from the middle Eocene of North America". Journal of Vertebrate Paleontology. 30 (4): 1229–1244. doi:10.1080/02724634.2010.483568. ISSN 0272-4634.
  4. 1 2 3 4 5 6 Osborn, Henry F. (1929). The Titanotheres of Ancient Wyoming, Dakota, and Nebraska, Volume 1. Department of the Interior, U.S. Geological Survey. pp. 156, 248.
  5. 1 2 3 Mihlbachler, Matthew C.; Prothero, Donald R. (2021). "Eocene (Duchesnean and earliest Chadronian) brontotheres (Brontotheriidae), Protitanops curryi and cf. Parvicornus occidentalis, from West Texas and Mexico". Palaeontologia Electronica. 24 (3): a35. doi:10.26879/944.
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