Protypotherium antiquum Ameghino, 1885

Fernández, Mercedes, Fernicola, Juan Carlos, Cerdeño, Esperanza & Reguero, Marcelo A., 2018, Identification of type materials of the species of Protypotherium Ameghino, 1885 and Patriarchus Ameghino, 1889 (Notoungulata: Interatheriidae) erected by Florentino Ameghino, Zootaxa 4387 (3), pp. 473-498 : 476-480

Protypotherium antiquum Ameghino, 1885

Lectotype (this contribution). ZMK 21/1877 (ex ZMK 208; Figs. 1 A–B ), right mandibular fragment with p4–m3 series.

Paralectotype (this contribution). A toothless fragmented mandible with its symphysis that has not been located.

Diagnosis ( Ameghino, 1885: 81–83). “[…] El fragmento de sínfisis de la mandíbula inferior que me sirvió de base para la fundación del género, es ancho y aplastado en sentido vertical, muy parecido a Typotherium en su parte cóncava interna, pero más aplastado en su parte inferior y con una depresión semilunar en la parte posterior de la sínfisis. El foramen mentale, situado en la parte sinfisaria, es un agujero elíptico, de unos 6 milímetros de diámetro mayor. Las dos ramas de la mandíbula están tan íntimamente unidas formando un solo hueso que en ninguna parte se ve ni el más mínimo rastro de sutura. La parte anterior está rota, pero todavía se distinguen en ella seis alvéolos horizontales en los que sin duda se implantaban seis incisivos. Al nivel del agujero mental, tiene la sínfisis 20 milímetros de ancho y 14 milímetros de alto. La pieza del señor Roth es un pedazo del lado derecho de la mandíbula inferior, con las cuatro últimas muelas y parte del alvéolo de otro molar anterior, de modo que el número de muelas era, por lo menos, de cinco en cada lado de la mandíbula inferior. Estas muelas eran sin raíces separadas, abiertas en la base y construidas sobre el mismo tipo general que las de Toxodon y Typotherium , con una capa de esmalte, que parece haber sido continua en algunas muelas, o a lo menos con no tantas interrupciones como en las muelas del género Toxodon y todas en serie continua muy apretadas entre sí. La primera muela existente, que corresponde al cuarto y último premolar, si la dentición fuera completa y normal, es más pequeña que las otras, dividida en dos partes desiguales, una anterior más grande y otra posterior bastante más pequeña; esta división es naturalmente producida por dos surcos perpendiculares opuestos, uno colocado sobre el lado interno y el otro sobre la esquina posteroexterna. Las dos muelas que siguen, primero y segundo verdadero molar, están divididas en dos partes o lóbulos más iguales, por dos surcos opuestos, uno interno, poco marcado y acompañado de una pequeña columna formada por la parte posterointerna del primer lóbulo, y el otro externo, más profundo y que forma en la corona un pliegue entrante parecido al que presentan las muelas de los caballos y varios otros mamíferos de órdenes distintos. La última muela, algo más grande que las demás, está dividida en tres partes o lóbulos formados por tres columnas en cada lado (externo e interno), separados por dos surcos. La corona de las muelas está bastante gastada y excavada en el centro, como las del género Typotherium . Parece que la rama ascendente empezaba a levantarse inmediatamente detrás de la última muela. […]”.

English translation. The fragment of mandibular symphysis used to found the genus is wide and vertically compressed, much similar to Typotherium in its internal concave face, but more compressed at its lower part and with a semilunate depression on its posterior end. The mental foramen is an elliptical opening of about 6 mm of diameter located in the symphyseal region. Both rami of the jaw are intimately fused into a single bone, without any trace of suture. The anterior part is broken, but there are six horizontal alveoli undoubtedly corresponding to six incisors. At the level of the mental foramen, the symphysis is 20 mm wide and 14 mm high. Roth’s specimen is a right mandibular ramus, with the last four cheek teeth and the broken alveolus of another anterior one, so that the number of cheek teeth was, at least, five on each side of the mandible. These teeth did not have separated roots, were open at the base and constructed on the same general way as those of Toxodon and Typotherium , with a layer of enamel that seems to have been continuous in some cheek teeth, or at least with less interruptions than in those of the genus Toxodon , and all implanted in a very tight, continuous series. The first cheek tooth, assuming a complete and normal dentition, would correspond to the fourth and last premolar; it is smaller than the molars, divided into two unequal parts, the anterior being rather larger than the posterior; this division is naturally produced by two opposite perpendicular grooves, one placed on the inner side and the other on the posteroexternal region. The first and second true molars are divided into two more equal parts or lobes by two opposite grooves, the internal is little marked and accompanied by a small column formed by the posterointernal part of the first lobe, and the external groove is deeper and forms an infolding in the crown similar to that of the cheek teeth of horses and several other mammals of different orders. The last molar, somewhat larger than the others, is divided into three parts or lobes formed by three columns at each side (external and internal), separated by two grooves. The crown of the molars is rather worn and excavated in the centre, such as those of the genus Typotherium . It seems that the ascending ramus was rising immediately behind the last molar.

Comments. Ameghino (1885: 81–83) described Protypotherium antiquum based on two partial mandibular fragments. One of them is a rolled and shattered, toothless fragmented mandible with its symphysis, which Ameghino (1885: 83) recognised to have been used to name the genus and species in a faunal list of a collection catalogue in 1882. However, as already mentioned (see Historical Background), those names are nomina nuda as acknowledged by him years later (e.g., Ameghino, 1887a). The other specimen was collected in the cliffs of Paraná River (Entre Ríos Province) by Santiago Roth, probably during an excursion in 1881, and later borrowed by Ameghino for its study and the description of all the dental characteristics of the species ( Ameghino 1885, 1889). It involves a right mandibular ramus with broken alveolus of p3 and complete p4–m3. As the nomenclatural act that made available the name P. antiquum took place in 1885 when Ameghino described both specimens, they are here recognised as the syntypes of the species.

There are no comments on the type material of P. antiquum in Ameghino’s catalogue and neither in Mones (1986). Regarding the toothless symphysis, it should be housed at the MLP, because this institution bought Ameghino’s collection in 1886, unless Ameghino had deviated the specimen to his posterior personal collection; in such a case, it should be in MACN-A. However, this syntype could not be located in any of these institutions or in ZMK and, unfortunately, it has not been identified in any of the available photographs taken from AMNH, FM and YPM. Nevertheless, we cannot reject the hypothesis that it could be located in another foreigner institution (see Vizcaíno et al. 2013); further searching will corroborate or refute this.

In the case of Roth’s specimen, it was further described by Ameghino (1887a, 1889) and even illustrated in his Atlas ( Ameghino 1889, plate 15: fig.1); this illustration is herein reproduced in Figures 1 C–D . Roth kept this specimen until he sold it to Dr. V. Lausen, a wealthy Danish citizen settled in Buenos Aires, who sent it to the Zoological Museum, Quaternary Zoology Collections-V, Lausen Collection, University of Copenhagen in Denmark, being housed there since the 25th of November of 1887 (B. E. Kramer, pers. comm. to M. Fernández; M. Reguero’s pers. obs.). This specimen has a label handwritten by Roth with the following information: “ Protypotherium antiquum Amegh. Delta-Egnen , Entre Ríos. Original Roth (37.), Laussen. 25.11.87. 208*”. Original Roth (37.) refers to the number in Roth’s catalogue, and 208 refers to an older catalogue number of Museum of Zoology in Copenhagen (ZMK 208). However, nowadays this material is catalogued as ZMK 21/1887 ( Figs. 1 A–B ). Two casts of ZMK 21/1877 were fortunately kept in MLP and MACN-A: MLP 97-XI-20-1, a complete cast, and MACN-A 1288 ( Figs. 1 E–F ), a cast of the tooth row.

Before this contribution, there were two mentions regarding the type specimen of P. antiquum , with different interpretations: Schmidt (2013) considered the missing toothless symphysis to be the holotype, whereas Luna (2015) stated the partial mandible ZMK 21/1887 as such. Although Ameghino (1885) recognised that the missing toothless symphysis was the object that he used to name P. antiquum in 1882 (nomen nudum), it is true that the taxonomic conception of P. antiquum as well as all of its diagnostic dental features (e.g., p4–m3 rootless, with two continuous and opposite, labial and lingual sulci that separates well-delimited trigonid and talonid; tooth row in a very tight continuous series; p4 smaller than m1–3, with the trigonid longer and wider than the talonid; m1–2 larger than premolars, with talonid longer than trigonid, and labial sulcus deeper than the lingual one; m3 larger than the other cheek teeth, with its talonid with two, labial and lingual, distal grooves that delimit a third lobe) were established based on ZMK 21/1887. At the same time, these characteristics were used later by Ameghino to include and contrast the remaining species within the Genus Protypotherium . Therefore, we designate ZMK 21/1887 as the lectotype of P. antiquum and, consequently, the remaining syntype becomes the paralectotype (ICZN 2000: Art. 73.2.2).

Chronological and geographical distribution of the type specimen. Huayquerian SALMA, Entre Ríos Province.

Figures

FIGURE 1. Protypotherium antiquum, lectotype ZMK 21/1877, right mandibular fragment with p4-m3, in labial (A) and occlusal (B) views; reproductions of figures 1 (C) and 1a (D) from Ameghino (1889, plate 15); and MACN-A 1288, cast of lectotype, inlabial (E) and occlusal(F)views. Protypotherium australe, MACN-A 1338, cast of theholotype, in occlusalview (G). Protypotherium praerutilum, holotype MACN-A 1081, incomplete skull, in ventral (H) and dorsal (I) views; holotype MACN-A 1082, incomplete mandible, in lateral (J) and occlusal (K) views; reproductions of figures 6 (L) and 6a (M) from Ameghino (1889, plate 14); reproductions of figures 7 (N) and 7a (O) from Ameghino (1889, plate 14). Scale bar = 10 mm.