Robiatherium
Temporal range: Middle Eocene
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Anoplotheriidae
Subfamily: Anoplotheriinae
Genus: Robiatherium
Sudre, 1988
Species:
R. cournovense
Binomial name
Robiatherium cournovense
Sudre, 1978
Synonyms

Robiatherium is an extinct genus of Paleogene artiodactyls containing one species R. cournovense. The genus name derives from the locality of Robiac in France where some of its fossil were described plus the Greek θήρ/therium meaning "beast" or "wild animal." It was known only from the middle Eocene and, like other anoplotheriids, was endemic to western Europe. The genus was erected by Jean Sudre in 1988 for a species originally attributed to the xiphodont genus Paraxiphodon in 1978. Robiatherium had dentitions typical of the subfamily Anoplotheriinae, differing from other genera by specific differences in the molars. It is one of the earliest-appearing anoplotheriine species in the fossil record as well as the earliest to have appeared in central Europe.

Taxonomy

In 1988, French palaeontologist Jean Sudre referenced an upper molar from the Robiac-Nord locality in France that he in 1969 listed as "Anoplotherioidea indet." He said that in 1978, he then defined the specimen to belong to the erected Paraxiphodon cournovense and interpreted it as a possible ancestor of P. teulonense. Based on fossil material from the locality of Le Bretou as well as older Quercy collections from the University of Montpellier, he determined recently that the species belonged not to the Xiphodontidae but the Anoplotheriinae subfamily of the Anoplotheriidae.[1][2][3]

Classification

Robiatherium belongs to the Anoplotheriidae, a Paleogene artiodactyl family endemic to western Europe that lived from the middle Eocene to the early Oligocene (~44 to 30 Ma, possible earliest record at ~48 Ma). The exact evolutionary origins and dispersals of the anoplotheriids are uncertain, but they exclusively resided within the continent when it was an archipelago that was isolated by seaway barriers from other regions such as Balkanatolia and the rest of eastern Eurasia. The Anoplotheriidae's relations with other members of the Artiodactyla are not well-resolved, with some determining it to be either a tylopod (which includes camelids and merycoidodonts of the Paleogene) or a close relative to the infraorder and some others believing that it may have been closer to the Ruminantia (which includes tragulids and other close Paleogene relatives).[4][5]

The Anoplotheriidae consists of two subfamilies, the Dacrytheriinae and Anoplotheriinae, the latter of which is the subfamily that Robiatherium belongs to. The Dacrytheriinae is the older subfamily of the two that first appeared in the middle Eocene (since the Mammal Paleogene zones unit MP13, possibly up to MP10), although some authors consider them to be a separate family in the form of the Dacrytheriidae.[6][7] Anoplotheriines made their first appearances by the late Eocene (MP15-MP16), or ~41-40 Ma, within western Europe with Duerotherium and Robiatherium. After a significant gap of anoplotheriines in MP17a-MP17b, the derived anoplotheriids Anoplotherium and Diplobune made their first appearances in western Europe by MP18, although their exact origins are unknown.[8]

Conducting studies focused on the phylogenetic relations within the Anoplotheriidae has proven difficult due to the general scarcity of fossil specimens of most genera.[8] The phylogenetic relations of the Anoplotheriidae as well as the Xiphodontidae, Mixtotheriidae, and Cainotheriidae have also been elusive due to the selenodont morphologies of the molars, which were convergent with tylopods or ruminants.[9] Some researchers considered the selenodont families Anoplotheriidae, Xiphodontidae, and Cainotheriidae to be within Tylopoda due to postcranial features that were similar to the tylopods from North America in the Paleogene.[10] Other researchers tie them as being more closely related to ruminants than tylopods based on dental morphology. Different phylogenetic analyses have produced different results for the "derived" selenodont Eocene European artiodactyl families, making it uncertain whether they were closer to the Tylopoda or Ruminantia.[11][12]

In an article published in 2019, Romain Weppe et al. conducted a phylogenetic analysis on the Cainotherioidea within the Artiodactyla based on mandibular and dental characteristics, specifically in terms of relationships with artiodactyls of the Paleogene. The results retrieved that the superfamily was closely related to the Mixtotheriidae and Anoplotheriidae. They determined that the Cainotheriidae, Robiacinidae, Anoplotheriidae, and Mixtotheriidae formed a clade that was the sister group to the Ruminantia while Tylopoda, along with the Amphimerycidae and Xiphodontidae split earlier in the tree.[12] The phylogenetic tree used for the journal and another published work about the cainotherioids is outlined below:[13]

Eurodexis russelli

Dichobune leporina

Amphimeryx murinus

Xiphodon castrense

Tylopoda

Paratoceras coatesi

Eotylopus reedi

Ruminantia

Parvitragulus priscus

Lophiomeryx chalaniati

Archaeomeryx optatus

Mixtotheriidae

Mixtotherium cuspidatum

Anoplotheriidae

Anoplotherium latipes

Dacrytherium ovinum

Cainotherioidea
Robiacinidae

Robiacina lavergnesis

Robiacina minuta

Robiacina quercyi

Cainotheriidae

Palembertina deplasi

Oxacroninae

Paroxacron bergeri

Paroxacron valdense

Oxacron courtoisii

Cainotheriinae

Cainotherium laticurvatum

Caenomeryx

Caenomeryx filholi

Caenomeryx procommunis

Plesiomeryx

Plesiomeryx cadurcensis

Plesiomeryx huerzeleri

In 2022, Weppe created a phylogenetic analysis in his academic thesis regarding Paleogene artiodactyl lineages, focusing most specifically on the endemic European families. The phylogenetic tree, according to Weppe, is the first to conduct phylogenetic affinities of all anoplotheriid genera, although not all individual species were included. He found that the Anoplotheriidae, Mixtotheriidae, and Cainotherioidea form a clade based on synapomorphic dental traits (traits thought to have originated from their most recent common ancestor). The result, Weppe mentioned, matches up with previous phylogenetic analyses on the Cainotherioidea with other endemic European Paleogene artiodactyls that support the families as a clade. As a result, he argued that the proposed superfamily Anoplotherioidea, composing of the Anoplotheriidae and Xiphodontidae as proposed by Alan W. Gentry and Hooker in 1988, is invalid due to the polyphyly of the lineages in the phylogenetic analysis. However, the Xiphodontidae was still found to compose part of a wider clade with the three other groups. He said that Ephelcomenus, Duerotherium, and Robiatherium compose a clade of the Anoplotheriidae.[9][14]

Description

The dental formula of the Anoplotheriidae is 3.1.4.33.1.4.3 for a total of 44 teeth, consistent with the primitive dental formula for early-middle Paleogene placental mammals.[15][16] Anoplotheriids have selenodont or bunoselenodont premolars and molars made for folivorous/browsing diets, consistent with environment trends in the late Eocene of Europe. The canines of the Anoplotheriidae are premolariform in shape, meaning that the canines are overall undifferentiated from other teeth like incisors. The lower premolars of the family are piercing and elongated. The upper molars are bunoselenodont in form while the lower molars have selenodont labial cuspids and bunodont lingual cuspids. The subfamily Anoplotheriinae differs from the Dacrytheriinae by the lower molars lacking a third cusp between the metaconid and entoconid as well as molariform premolars with crescent-shaped paraconules.[5]

Robiatherium in particular is diagnosed specifically in terms of its dentition. It has trapezoidal upper molars that increase in size from M1 to M3. Their protocone cusps are in a middle position and subconical. Robiatherium also lacks postparaconule ridges. The labial sides of the paracone and metacone cusps of the upper molars are concave and lack ridges, the labial sides of the styles forming W-shaped ectolophs. The dental characteristics of Robiatherium, especially the ectoloph shapes of the molars, are somewhat reminiscent of the Xiphodontidae but are most similar to the Anoplotheriinae.[1][6]

Robiatherium is also diagnosed as being a small-sized anoplotheriine.[1][6] It does not have any direct size or weight estimates, but Miguel-Ángel Cuesta and Ainara Badiola discussed size comparisons of anoplotheriines. They observed that Robiatherium was smaller than Duerotherium, which itself was smaller than Ephelcomenus, Anoplotherium, and most Diplobune species.[8]

Palaeoecology

Palaeogeography of Europe and Asia during the middle Eocene with possible artiodactyl and perissodactyl dispersal routes.

For much of the Eocene, a hothouse climate with humid, tropical environments with consistently high precipitations prevailed. Modern mammalian orders including the Perissodactyla, Artiodactyla, and Primates (or the suborder Euprimates) appeared already by the early Eocene, diversifying rapidly and developing dentitions specialized for folivory. The omnivorous forms mostly either switched to folivorous diets or went extinct by the middle Eocene (47 - 37 Ma) along with the archaic "condylarths". By the late Eocene (approx. 37 - 33 Ma), most of the ungulate form dentitions shifted from bunodont cusps to cutting ridges (i.e. lophs) for folivorous diets.[17][18]

Land-based connections to the north of the developing Atlantic Ocean were interrupted around 53 Ma, meaning that North America and Greenland were no longer well-connected to western Europe. From the early Eocene up until the Grande Coupure extinction event (56 Ma - 33.9 Ma), the western Eurasian continent was separated into three landmasses, the former two of which were isolated by seaways: western Europe (an archipelago), Balkanatolia, and eastern Eurasia (Balkanatolia was in between the Paratethys Sea of the north and the Neotethys Ocean of the south).[4] The Holarctic mammalian faunas of western Europe were therefore mostly isolated from other continents including Greenland, Africa, and eastern Eurasia, allowing for endemism to occur within western Europe.[18] The European mammals of the late Eocene (MP17 - MP20) were mostly descendants of endemic middle Eocene groups as a result.[19]

Robiatherium is known only from MP16 localities of southern France, contemporary with dacrytheriines and the Iberian anoplotheriine Duerotherium. Robiatherium is the earliest-known anoplotheriine to have appeared in central Europe, but it and other anoplotheriines are not present in any MP17 locality, making the evolutionary history of anoplotheriines not fully known.[20][8][5] The locality of Robiac indicates that Robiatherium coexisted with similar mammal faunas such as the herpetotheriids Peratherium and Amphiperatherium, apatotherian Heterohyus, hyaenodonts Paroxyaena and Cynohyaenodon, miacids Paramiacis and Quercygale, palaeotheres (Palaeotherium, Plagiolophus, Anchilophus), lophiodont Lophiodon, cebochoerids Cebochoerus and Acotherulum, choeropotamid Choeropotamus, dichobunid Mouillacitherium, robiacinid Robiacina, xiphodonts (Xiphodon, Dichodon, and Haplomeryx), amphimerycid Amphimeryx, and other anoplotheriids Catodontherium and Dacrytherium.[20]

References

  1. 1 2 3 Sudre, Jean (1978). "Le gisement du Bretou (Phosphorites du Quercy, Tarn-et-Garonne, France) et sa faune des vertebres de l'Eocene superieur: 7. Artiodactyles". Palaeontographica. Abteilung A, Paläozoologie, Stratigraphie. 205: 129–254.
  2. Sudre, Jean (1969). "Les gisements de Robiac (Eocène supérieur) et leurs faunes de Mammifères". Palaeovertebrata. 2: 95–156.
  3. Sudre, Jean (1978). Les artiodactyles de l'Eocène moyen et supérieur d'Europe occidentale: systématique et évolution. Vol. 7. Mémoires et Travaux de l'Institut de Montpellier.
  4. 1 2 Licht, Alexis; Métais, Grégoire; Coster, Pauline; İbilioğlu, Deniz; Ocakoğlu, Faruk; Westerweel, Jan; Mueller, Megan; Campbell, Clay; Mattingly, Spencer; Wood, Melissa C.; Beard, K. Christopher (2022). "Balkanatolia: The insular mammalian biogeographic province that partly paved the way to the Grande Coupure". Earth-Science Reviews. 226: 103929. Bibcode:2022ESRv..22603929L. doi:10.1016/j.earscirev.2022.103929.
  5. 1 2 3 Badiola, Ainara; De Vicuña, Nahia Jiménez; Perales-Gogenola, Leire; Gómez-Olivencia, Asier (2023). "First clear evidence of Anoplotherium (Mammalia, Artiodactyla) in the Iberian Peninsula: an update on the Iberian anoplotheriines". The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology. doi:10.1002/ar.25238. PMID 37221992. S2CID 258864256.
  6. 1 2 3 Erfurt, Jörg; Métais, Grégoire (2007). "Endemic European Paleogene Artiodactyls". In Prothero, Donald R.; Foss, Scott E. (eds.). The Evolution of Artiodactyls. Johns Hopkins University Press. pp. 59–84.
  7. Orliac, Maeva; Gilissen, Emmanuel (2012). "Virtual endocranial cast of earliest Eocene Diacodexis (Artiodactyla, Mammalia) and morphological diversity of early artiodactyl brains". Proceedings of the Royal Society B. 279 (1743): 3670–3677. doi:10.1098/rspb.2012.1156. PMC 3415922. PMID 22764165.
  8. 1 2 3 4 Cuesta, Miguel-Ángel; Badiola, Ainara (2009). "Duerotherium sudrei gen. et sp. nov., a New Anoplotheriine Artiodactyl from the Middle Eocene of the Iberian Peninsula". Journal of Vertebrate Paleontology. 29 (1): 303–308. Bibcode:2009JVPal..29..303C. doi:10.1671/039.029.0110. JSTOR 20491092. S2CID 55546022.
  9. 1 2 Weppe, Romain (2022). Déclin des artiodactyles endémiques européens, autopsie d'une extinction (Thesis) (in French). University of Montpellier.
  10. Hooker, Jerry J. (2007). "Bipedal browsing adaptations of the unusual Late Eocene–earliest Oligocene tylopod Anoplotherium (Artiodactyla, Mammalia)". Zoological Journal of the Linnean Society. 151 (3): 609–659. doi:10.1111/j.1096-3642.2007.00352.x.
  11. Luccisano, Vincent; Sudre, Jean; Lihoreau, Fabrice (2020). "Revision of the Eocene artiodactyls (Mammalia, Placentalia) from Aumelas and Saint-Martin-de-Londres (Montpellier limestones, Hérault, France) questions the early European artiodactyl radiation". Journal of Systematic Palaeontology. 18 (19): 1631–1656. Bibcode:2020JSPal..18.1631L. doi:10.1080/14772019.2020.1799253. S2CID 221468663.
  12. 1 2 Weppe, Romain; Blondel, Cécile; Vianey-Liaud, Monique; Escarguel, Gilles; Pélissié, Thierry; Antoine, Pierre-Olivier; Orliac, Maëva Judith (2020). "Cainotheriidae (Mammalia, Artiodactyla) from Dams (Quercy, SW France): phylogenetic relationships and evolution around the Eocene–Oligocene transition (MP19–MP21)" (PDF). Journal of Systematic Palaeontology. 18 (7): 541–572. Bibcode:2020JSPal..18..541W. doi:10.1080/14772019.2019.1645754. S2CID 202026238.
  13. Weppe, Romain; Blondel, Cécile; Vianey-Liaud, Monique; Pélissié, Thierry; Orliac, Maëva Judith (2020). "A new Cainotherioidea (Mammalia, Artiodactyla) from Palembert (Quercy, SW France): Phylogenetic relationships and evolutionary history of the dental pattern of Cainotheriidae". Palaeontologia Electronica (23(3):a54). doi:10.26879/1081. S2CID 229490410.
  14. Gentry, Alan W.; Hooker, Jerry J. (1988). "The phylogeny of the Artiodactyla". The Phylogeny and Classification of the Tetrapods: Volume 2: Mammals (The Systematics Association Special Volume, No. 35B). Oxford University Press. pp. 235–272.
  15. von Zittel, Karl Alfred (1925). Schlosser, Max (ed.). Text-Book of Paleontology. Volume III. Mammalia. Macmillan and Co. Limited. pp. 179–180.
  16. Lihoreau, Fabrice; Boisserie, Jean-Renaud; Viriot, Laurent; Brunet, Michel (2006). "Anthracothere dental anatomy reveals a late Miocene Chado-Libyan bioprovince". Proceedings of the National Academy of Sciences. 103 (23): 8763–8767. Bibcode:2006PNAS..103.8763L. doi:10.1073/pnas.0603126103. PMC 1482652. PMID 16723392.
  17. Eronen, Jussi T.; Janis, Christine M.; Chamberlain, Charles Page; Mulch, Andreas (2015). "Mountain uplift explains differences in Palaeogene patterns of mammalian evolution and extinction between North America and Europe". Proceedings of the Royal Society B. 282 (1809). doi:10.1098/rspb.2015.0136. PMC 4590438. PMID 26041349.
  18. 1 2 Maitre, Elodie (2014). "Western European middle Eocene to early Oligocene Chiroptera: systematics, phylogeny and palaeoecology based on new material from the Quercy (France)". Swiss Journal of Palaeontology. 133 (2): 141–242. doi:10.1007/s13358-014-0069-3. S2CID 84066785.
  19. Badiola, Ainara; Perales-Gogenola, Leire; Astibia, Humberto; Suberbiola, Xabier Pereda (2022). "A synthesis of Eocene equoids (Perissodactyla, Mammalia) from the Iberian Peninsula: new signs of endemism". Historical Biology. 34 (8): 1623–1631. Bibcode:2022HBio...34.1623B. doi:10.1080/08912963.2022.2060098. S2CID 248164842.
  20. 1 2 Aguilar, Jean-Pierre; Legendre, Serge; Michaux, Jacques (1997). "Synthèses et tableaux de corrélations". Actes du Congrès Bio-chroM'97. Mémoires et Travaux de l'EPHE Institut de Montpellier 21 (in French). École Pratique des Hautes Études-Sciences de la Vie et de la Terre, Montpellier. pp. 769–850.
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