Notiomastodon, Cabrera, 1929

Notiomastodon cf. N. platensis .

( Figs. 2C–I2 View Fig , 3A–D View Fig ).

Referred material

Lower third molars with fragmented roots and slight wear on first and second lophids that might belong to the same individual, since wear stages are very similar ( MHNG GEPI V-3473 and MHNG GEPI V-3475, Fig. 2C–D View Fig ), fragmented lower left third molar with no wear and no roots ( MHNG GEPI V-3478, Fig. 2E View Fig ), two upper third molars with fragmented roots and no wear that might belong to the same individual ( MHNG GEPI V-3474, Fig. 2F–G View Fig ), fragment of a left mandibular ramus with a third molar with advanced wear stage ( PIMUZ A/ V 4092, Fig. 2H View Fig 1–H View Fig 2 View Fig ), lower left third molar with advanced wear, roots and fragments of mandible ( PIMUZ A/ V 4161, Fig. 2 I View Fig 1–I View Fig 2 View Fig ), lower right third molar with intermediate wear and fragmented third pretrite ( MHNG GEPI V-3479, Fig. 3A View Fig ), lower left third molar with intermediate wear and fragmented at anterolingual bor- der ( MHNG GEPI V-3502, Fig. 3B View Fig ), fragmented upper left first molar with intermediate wear ( MHNG GEPI V-3491, Fig. 3C View Fig , and -3486), and fragmented lower right first molar missing part of the first lophid, with intermediate wear ( MHNG GEPI V-3480). Geographic data of the specimens are provided in Additional file 1.

Description and comparisons

All molars are bunodont with the characteristic double to simple trefoil wear pattern of Notiomastodon platensis (i.e., MHNG GEPI V-3502, -3491, -3486, and -3480). Te third molars are pentalophodont and have a variable distal cingulum, and those teeth with no wear or intermediate wear show a range from 57 to 64 cups, which is within the Notiomastodon ’s range of 35 to 82, as described in the literature ( Mothé et al., 2017c). For total length of the complete molars see Additional file 1.

Remarks

Isolated molars are the most common fossils of the South American proboscideans, but unfortunately they are not fully diagnostic for Notiomastodon and Cuvieronius when isolated and/or fragmented, since most features are variable and overlapping ( Mothé et al., 2017b). Te total number of cusps in complete and well-preserved third molars has been successfully used to differentiate both genera ( Mothé & Avilla, 2015; Mothé et al., 2017c). Cuvieronius hyodon presents third molars with a number of cusps ranging from 33 to 60, whereas in Notiomastodon , the number of cusps range between 35 and 82 (see Mothé et al., 2017c). As mentioned above, the complete third molars we are describing here show a range from 57 to 64 cusps, which is in the range of Notiomastodon . Te fragmentary nature of some specimens does not allow access to the complete number of cusps but, since the wear pattern on pretrites and postrites is complex (double–trefoil), it suggests that the number of cusps of some specimens might be higher (e.g., PIMUZ A/V 4092, 4161, MHNG GEPI V-3502). Te specimens reported herein are tentatively assigned to Notiomastodon cf. N. platensis .

Gomphotheriidae indet.

( Fig. 3E–O View Fig ).

Referred material

Five broken and incomplete teeth with extreme wear (PIMUZ A/V 4105, 4136, 4185, 4279), left distal humerus epiphysis (PIMUZ A/V 4159), left radius (MHNG GEPI V-3477), left femur (PIMUZ A/V 4158),?right patella (MHNG GEPI V-3490), right tibia (PIMUZ A/V 4160), right calcaneus (MHNG GEPI V-3505), navicular, right trapezoid,?metatarsal III and?metacarpal III (MHNG GEPI V-3494), and rib fragment (MHNG GEPI V-3499). Geographic data of the specimens are provided in Additional file 1.

Description and comparisons

PIMUZ A/V 4105 is a fragment of hemimandible with incomplete and fragmented crown of a m2, and an indeterminate tooth fragment in a poor state of preservation. Number PIMUZ A/V 4279 corresponds to an incomplete and extremely worn molar, possibly M2 or m2, and two other molariform fragments of indeterminate position. PIMUZ A/V 4185 is represented by three fragmented and isolated lophs, possibly from the same individual. Specimen PIMUZ A/V 4136 is a broken molar with extreme wear of indeterminate position ( Fig. 3E View Fig ). Postcranial appendicular elements are represented by a left distal epiphysis of a humerus (PIMUZ A/V 4159, Fig. 3F View Fig ), left radius of 567 mm in length missing the proximal epiphysis (MHNG GEPI V-3477, Fig. 3G View Fig ), complete left femur with a total length of 1045 mm (PIMUZ A/V 4158, Fig. 3I View Fig 1–I View Fig 2 View Fig ), diaphysis of a right tibia of 445 mm in length (PIMUZ A/V 4160, Fig. 3K View Fig ), a?right patella (MHNG GEPI V-3490, Fig. 3J View Fig ), a complete right calcaneus (MHNG GEPI V-3505, Fig. 3L View Fig 1–L View Fig 2 View Fig ), navicular, right trapezoid,?metatarsal III and?metacarpal III (MHNG GEPI V-3494, Fig. 3M View Fig 1–O View Fig ). A fragmented right rib is the sole element from the axial skeleton (MHNG GEPI V-3499, Fig. 3H View Fig ).

Remarks

Te state of preservation of the dental remains and the lack of diagnostic characters on the postcranial bones ( Mothé & Avilla, 2015), do not allow to classify these specimens beyond the family level. Tere are no detailed morphometric studies on postcranial elements of Cuvieronius and Notiomastodon that may demonstrate the taxonomic significance of postcranial features. Considering the known geographical distribution of Notiomastodon that includes the Pampean region ( Alberdi & Prado, 2022; Lucas, 2013; Mothé & Avilla, 2015; Mothé et al., 2017a, b, c), the assignment to this taxon is ultimately likely.

Artiodactyla ( Owen, 1848) .

Camelidae Gray, 1821

Lama Cuvier, 1800

Lama guanicoe ( Müller, 1776) .

( Fig. 4A View Fig 1–A View Fig 3 View Fig ).

Referred material

An almost complete mandible with both incomplete lower molar series and without coronoid and angular processes and condyle (PIMUZ A/V 4089). Geographic data of the specimens are provided in Additional file 1.

Description and comparisons

Te mandible is gracile, broken at the level of both coronoid and angular processes. Te dorsal and ventral margins of the horizontal ramus are almost parallel to each other. Te lingual surface of the horizontal ramus is flat and the labial side is slightly convex. Both rostral and caudal mental foramina are not observed due to embedded sediment on the bone surface. Tere are five incisors. Caniniforms are not preserved. Te dental formula shows the alveoli of premolars in the third and fourth positions as in Lama guanicoe and Hemiauchenia paradoxa ( Lynch et al., 2020) . Te right hemimandible has m1–m3, while the left preserving m1–m2 series, being broken at level of the anterior root of the m3 ( Fig. 4A View Fig 2 View Fig ). Occlusal length and width, respectively, are 13 mm and 10 mm in m1, 18 mm and 11 mm in m2, and 23 mm and 10 mm in m3. Te right m1–m3 series length is 54 mm. Tese selenodont molars are characterized by having well-developed anterior stylids or “Llama buttresses” (protostylids and parastylids), although on m3 these are weakly prominent labio-lingually. Te anterior fossa (trigonid fossa, Scherer et al., 2007) on m1 is not seen due to the advanced wear, making this specimen to correspond to an adult with "wear stage 4" in the classification of Breyer (1977). All fossae are closed, which is more typical of Camelidae than Cervidae (the latter group has the distal end of the anterior fossetid lingually opened) ( Fig. 4A View Fig 3 View Fig ). Te labial lophids are U-shaped (e.g., Gasparini et al., 2017; Scherer et al., 2007), and the second lobe of each molar is set off from the anterior lobe by a pronounced vertical and deep labial flexid. Te third lobe (hypoconulid) is smaller and oval in outline ( Fig. 4A View Fig 3 View Fig ).

Remarks

PIMUZ A/V 4089 displays many morphological characters consistent with South American Camelidae (see Lynch et al., 2020; Scherer, 2013). Te morphological and morphometric features reported above allow us to assign PIMUZ A/V 4089 to Lama guanicoe . Te fossil record of Lama is known since the Late Pleistocene deposits in Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Peru, and Uruguay ( Scherer, 2013; Tonni & Politis, 1980, and references therein). However, according to Wheeler (1995), the records of Lama from Ecuador and Colombia need confirmation. Lama has been widely recorded from Holocene deposits in the southern region of Argentina, although its record at different sites from the middle and lower Paraná River basin during this time has been questioned (see Politis et al., 2011).

Menegaz and Ortiz Jaureguizar (1995) reported the existence of a fossil Lama anatomically indistinguishable from L. guanicoe from Pleistocene deposits of the North Pampa (Buenos Aires Province), with dimensions similar to the range of Hemiauchenia . Lynch et al. (2020) reported a well-preserved South American Lamini partial skeleton from the Early Pleistocene of Argentina with a new cladistic analysis of the Camelinae subfamily. Tis specimen (PIMUZ A/V 4165) was also collected by Santiago Roth in the right cliff of the Paraná River, San Nicolás locality (Buenos Aires Province) ( Roth, 1889). According to the hypothesized phylogenetic position by Lynch et al. (2020), PIMUZ A/V 4165 is more closely related to L. guanicoe and Vicugna vicugna than to H. paradoxa . On the other hand, some morphological, morphometric and few molecular considerations on Lama taxonomy recognize the extinct Lama gracilis as a valid Lamini taxon of a gracile vicuña from the Late Pleistocene–Early Holocene of Patagonia and Tierra del Fuego ( Menegaz, 2000; Menegaz et al., 1989; Metcalf et al., 2016). Nevertheless, there is no consensus regarding the taxonomic status and phylogenetic context between the living and fossil camelids from South America (see Cajal et al., 2010; Cartajena et al., 2010; Miller, 1924; Stanley et al., 1994; Weinstock et al., 2009). Tus, these hypotheses must be tested by more molecular, morphological and morphometric studies.

At present, two living species of wild Lamini Camelidae have been recognized, L. guanicoe and V. vicugna , which are restricted to environments with arid to semi-arid conditions from the north-central area of the Andes and Patagonia (8º S to 55º S), and also between altitudes that range from sea level to 4000 m ( Baldi et al., 2008; Franklin, 1982; Lichtenstein et al., 2008; Wheeler, 1995).

Hemiauchenia Gervais & Ameghino, 1880 Hemiauchenia paradoxa Gervais & Ameghino, 1880 ( Fig. 4B View Fig 1–B View Fig 6 View Fig ).

Referred material

Anterior region of the skull and left maxilla with P3–M3, left hemimandible with three pair of lower incisors and p3–m3 from the same individual (PIMUZ A/V 4287). Geographic data of the specimens are provided in Additional file 1.

Description and comparisons

Cranial remains including fragmented premaxilla and part of the maxilla preserved up to the area of the infraorbital foramen, with right I3 and a caniniform

( Fig. 4B View Fig 3 View Fig ). Te left maxilla shows the P3–M3 series with slight wear and M3 erupting. Both fossetids in M3 are opened ( Fig. 4B View Fig 2 View Fig ). Te occlusal length of the molar series is 82 mm. PIMUZ A/V 4287 corresponds to a young-adult camelid ( Breyer, 1977). Te left hemimandible has three lower incisors (i1–i3) on both sides, a caniniform (that is separated from the incisors by a diastema), and p3–m3 series ( Fig. 4B–B View Fig 6 View Fig ). Te occlusal length of the molar series is 105 mm. Te lingual surface of the horizontal ramus is flat and the labial side is slightly convex

( Fig. 4B4 View Fig ). Both rostral and caudal mental foramina are observed in labial view of the hemimandible. Te former is located distally to the caniniform ( Fig. 4B View Fig 5 View Fig ). Te left caniniform is preserved and both m3. Te p3–m2 series has labial U-shaped lophids with closed fossae ( Gasparini et al., 2017; Scherer et al., 2007). Te second lobe of each cheek tooth is set off from the anterior lobe by a deep labial flexid. Te third lobe (hypoconulid) is smaller and oval in outline. Te anterior stylids (protostylids and parastylids) of lower molars are not observable because the teeth are partially inside their alveoli. All dental fossae are closed, with the exception of those in m3, showing both fossetids mesiodistally opened. PIMUZ A/V 4287 corresponds to a young-adult individual with permanent dentition already erupted but almost no wear ("wear stage 1" following Breyer, 1977).

Remarks

Hemiauchenia represents one of the largest Lamini camelids that inhabited South America during the Late Pliocene to Pleistocene ( Gasparini et al., 2017; Scherer, 2013). It is known from outcrops mostly of Argentina and Uruguay (Cione & Tonni, 1999; Cione et al., 1999, 2015; Gasparini et al., 2017; Menegaz & Ortiz-Jaureguizar, 1995; Ubilla, 2004; Ubilla & Perea, 1999). In contrast, Palaeolama , has been reported from Early Pleistocene deposits of Bolivia ( MacFadden & Shockey, 1997; Marshall et al., 1984), and Late Pleistocene deposits of Bolivia, Brazil, Chile, Ecuador, Paraguay, Peru and Venezuela ( Carrillo-Briceño, 2015; Cartelle et al., 1989; Marshall et al., 1984; Scherer, 2013).

López-Aranguren (1930) synonymized H. paradoxa to Hemiauchenia major , and Cabrera (1932, 1935) and Rusconi (1931) attributed the former taxon to Palaeolama weddelli . Later investigations revalidated H. paradoxa , although included in another genus: Palaeolama (see Hoffstetter, 1952). Webb (1974) and Scherer (2013) considered both Hemiauchenia and Palaeolama as valid taxa, but suggested that H. paradoxa is restricted to Argentina and H. major to northeastern Brazil. Nevertheless, some authors considered that the Brazilian forms correspond to Palaeolama major ( Bergqvist, 1993; Cartelle et al., 1989; Guérin et al., 1990; Souza-Cunha, 1966). Some taxonomic studies suggested that morphological differences between H. paradoxa and P. major do not support a taxonomic separation, but rather indicate intraspecific variations ( Cartelle, 1992, 1999). However, more recently Scherer (2009, 2013) supported the taxonomic validity of both genera for South America, with the recognition of at least three Palaeolama species: P. weddelli , P. major , and P. hoffstetteri . In contrast, H. paradoxa is considered the only valid species for this genus.