Protypotherium compressidens Ameghino, 1891b

Fernández, Mercedes, Fernicola, Juan C. & Cerdeño, Esperanza, 2023, Systematic revision of the species of Protypotherium (Notoungulata: Interatheriidae) from the Santa Cruz Formation (Early-Middle Miocene), Argentinian Patagonia: a new phylogenetic hypothesis for the Interatheriidae, Zoological Journal of the Linnean Society 199 (2), pp. 417-444 : 432

Protypotherium compressidens Ameghino, 1891b

( Figs 5 , 6 , 8E–K ; Supporting Information, Table S2) 1891b Protypotherium compressidens Ameghino , p. 292 (original description).

Holotype: MACN-A 4029 ( Fig. 8E ), less maxillary fragment with P3–M3, and MACN-A 4030 ( Fig. 8F ), less mandibular fragment with p4 (talonid)–m3, of the same individual (see Fernández et al. 2018), Early–Middle Miocene , SCF, Santa Cruz Province ( Argentina).

Referred materials: MACN-A 41-55 lot b.f, less mandibular fragment with poorly preserved p3–4 (trigonid); MACN-A 3867 ( Fig. 8G ), right mandibular fragment with dp1–2–p3–4 (trigonid); MACN-A 9716–9732?g ( Fig. 8H ), right mandibular fragment with m1 (talonid)–3; MPM-PV 19761 ( Fig. 8I ), right maxillary fragment with M1–2; MPM-PV 19781 ( Fig. 8J ), right mandibular fragment with p2–m1; and MPM-PV 19782 ( Fig. 8K ), less maxillary fragment with P2–M3.

Extended diagnosis: Protypotherium compressidens differs from Pr. antiquum , Pr. australe , Pr. praerutilum , Pr. columnifer , Pr. claudum , Pr. minutum , and Pr. colloncurensis by narrower cheek teeth, even more noticeable in P2–M3; from Pr. antiquum by the talonid of m3 without a labial groove; from Pr. colloncurensis and Pr. columnifer by the talonid of p2–4 sub-triangular in outline; from Pr. claudum by having p2–3 with a distinctive entoflexid; from Pr. colloncurensis by a descending process of the maxilla with a moderate development; from Pr. praerutilum by having a larger size; from Pr. minutum and Pr. distinctum by less cement covering the cheek teeth, the P2–4 with an entoflexus located in a more distal position that is slightly less expanded, M1–3 with straighter ectolophs, and infraorbital foramen above premolars; from Pr. columnifer by the talonid of p4 narrower than the trigonid; and from Pr. antiquum by the talonid of m3 without its labial groove.

Geographic and stratigraphic provenance: Santa Cruz Province ( Argentina), SCF, Early–Middle Miocene , Santacrucian SALMA.

Measurements: Supporting Information, Table S2.

Remarks: The ratio between the width and length of each upper molar (R W/L) of Pr. compressidens (holotype plus referred materials) for M1 and M2 is <0.5, whereas it is ≥ 0.55 in Pr. australe and Pr. praerutilum , and for M3 (with enlarged distal lobe), R W/L ≤ 0.42, whereas it is ≥ 0.47 in Pr. australe and Pr. praerutilum . The scaưer diagrams for M1 ( Fig. 5A ) and M2 ( Fig. 6A ) show the separation of these species in terms of the length and width of M1–2. A similar condition is observed in m1 and m2: R L/W ≤ 0.41 in Pr. compressidens , whereas it is ≥ 0.47 in Pr. australe and Pr. praerutilum , and in m3 (with enlarged talonid), R W/L ≤ 0.33 for Pr. compressidens , whereas it is ≥ 0.35 for Pr. australe and Pr. praerutilum .

Figures

Figure 5. Scaưer diagram of the Santacrucian species of Protypotherium (except for Pr.claudum). A, Length vs.width of M1. B, Length vs. width of m1. Abbreviations: L, length; W, width.

Figure 6. Scaưer diagram of the Santacrucian species of Protypotherium (except for Pr.claudum). A, Length vs. width of M2. B, Length vs. width of m2. Abbreviations: L, length; W, width.

Figure 8. Protypotherium praerutilum, in occlusal view.A, MACN-A 4044, incomplete palate. Protypotherium claudum, in occlusal view. B, MACN-A 551, right mandibular fragment with p2 (alveolus)–p3–m2; (C) MLP 73-VII-6-4 d, less mandibular fragment with p2 (broken)–m2 (trigonid); (D) MPEF-PV 1394, incomplete mandible with less i1–dp1–p2–p4, and right i1 and dp1–p2–m3. Protypotherium compressidens, in occlusal view. E, MACN-A 4029, less maxillary fragment with P3–M3; (F) MACN-A 4030, less mandibular fragment with p4 (talonid)–m3; (G) MACN-A 3867, right mandibular fragment with dp1–2–p3–4 (trigonid); (H) MACN-A 9716–9732?g, right mandibular fragment with m1 (talonid)–3; (I) MPM-PV 19761, right maxillary fragment with M1–2; (J) MPM-PV 19781, right mandibular fragment with p2–m1; (K) MPM-PV 19782, less maxillary fragment with P2–M3. Abbreviation: ’, indicates broken tooth. Scale bar = 10 mm.