Carodnia feruglioi Simpson, 1935

Gelfo, Javier N., López, Guillermo M. & Bond, Mariano, 2024, New insights on the anatomy, paleobiology, and biostratigraphy of Xenungulata (Mammalia) from the Paleogene of South America, Palaeontologia Electronica (a 30) 27 (2), pp. 1-34 : 6-11

Carodnia feruglioi Simpson, 1935

Synonymy. Ctalecarodnia cabrerai Simpson, 1935a: 24 , figure 22. Carodnia cabrerai Paula Couto, 1952: 371 .

Holotype. MGP-PD 29046, mandible fragment with left m3.

Hypodigm. MGP-PD 29030a-c type of Ctalecarodnia cabrerai : MGP-PD 29030a, left p4; MPEF-PV 1872 , right dentary with m2–3 ; MPEF-PV 1873 , left dentary with p4 and part of m1 ; MPEF-PV 1874 , left dentary with m3 ; MGP-PD 29030 b, left m2? With broken trigonid, and MGP-PD 29030c, right m2? with broken trigonid ; MGP-PD 29030 d, a fragment of a cusp ; MGP-PD 29030 e, trigonid fragment of a left m1 ?; MGP-PD 29033 a, left i3 ?; MGP-PD 29033 b, mesial lobe of a left M2 ?; MGP-PD 29047 , isolated right I3 ; MLP-PV 34 -V-22-8: right m3, left and right p2–3 ; MLP-PV 34 -V-22-9, right p4 (originally assigned to Ctalecarodnia cabrerai ) ; UNPSJB-PV 680 , a fragment of mandible with left canine and roots of p2–3 ; UNPSJB-PV 680-1 , a fragment of mandible with right m1 ; UNPSJB-PV 680-2 , a fragment of the left mandible with anterior root of m3 ; UNPSJB-PV 680-3 , anterior root of a right m2 .

Remarks. We refer here to Carodnia feruglioi a left dentary with p4 and the mesial part of trigonid of the m1 (MPEF-PV 1873), a left dentary with m3 (MPEF-PV 1874,), and a right dentary with m2–3 (MPEF-PV 1872). These specimens were previously described as Carodnia cf. C. feruglioi and are probably of the same individual (Gelfo et al., 2008). They were found by Nestor Ronconi in levels of the Peñas Coloradas Formation, between Puerto Visser and Bahía Bustamante (45°17’19” S, 67°01’29” W) in Chubut province, Argentina. The main difference with materials previously assigned as C. feruglioi is the presence of a postcingulid, which projects from the distolabial side of the hypoconid to the labial cingulid, surrounding the hypoconulid. This feature was also present in the m3 of C. vieirai as mentioned by Paula Couto (1952) and wrongly mentioned as absent in Gelfo et al. (2008) but missing in C. feruglioi and apparently in C. inexpectans (see Antoine et al., 2015: figure 2). Since there are no wear facets present on the distal wall of the talonid in the m3, it can be inferred that there is no functional contact between the distal part of the M3 and the postcingulid of the m3 during the occlusion process. In most mammals, distal wear facets in the m3 are typically confined to the mesial part of the hypoconulid, the postcristid, and the hypocristid, rather than in the postcingulid of the m3 if it is present. Consequently, it is conceivable that the distal wall of the talonid in the m3 remains relatively unaffected by selective pressures associated with chewing, allowing for the passive accumulation of a certain degree of morphological variation, such as the presence or absence of the postcingulid. Based on these dental observations and the overall similitude observed among the three specimens (i.e., MPEF-PV 1872, 1873, 1874) and the holotype of C. feruglioi , we have confidently attributed them to this species.

The lot MLP-PV 34-V-22-8 belonging to a right m3 left and right p2–3, and MLP-PV 34-V-22-9 right p4 were first described by Cabrera (1935) but interpreting the p3 as P3, and the p4 as Ctalecarodnia cabrerai . Simpson (1967) partially illustrated these specimens correctly, and they were also discussed by Vera et al. (2020). However, the latter discussion was based on incomplete casts and several details of these specimens need to be highlighted considering their possible homologies. The main axis of the p2 runs mesiodistal with the protoconid as the main cusp with two main wear facets prcd-h and prcd-b ( Figure 3 A-C, G-I). The paracristid projects from it and bifurcates mesially in a strong precingulid which extends in a short portion labially and lingually. A strong distal cristid descends from the protoconid, up to a bifurcation which makes an inverted “Y” in the occlusal view ( Figure 3C, I ). There is a small bulge or thickening of the distal cristid at the bifurcation point. The short lingual portion of the cristid contacts an entoconid sensu Cabrera (1935). The more labial cristid, here interpreted as cristid obliqua, descends and reaches a high, but not too strong hypoconid at an angle of approximately 90° in labial view ( Figure 3C ). A postcingulid descends from the hypoconid to the lingual and labial sides. The hypoconulid is a small elevation with a strong wear facet (hd-mb) over the lingual postcingulid, with a soft facet pocgd-ml ( Figure 3A, C, I ). The p2 structure is comparatively more complex than the p2 of C. vieirai , where no cusp or cristid was identified by Paula Couto (1952) who just did a topographical description. In the p2 of C. vieirai , the protoconid is higher and more transversally compressed, the precingulid is less developed, the distal crest bifurcates in a short distolingual cristid with no entoconid associated, and a more distolabial cristid.

The p3 of MLP-PV 34-V-22-8 is more molarized with the protoconid as the main cusp but associated labially with a strong and a bit lower metaconid ( Figure 3 D-F, J-L). The paracristid could be interpreted as in p2 but there is an incipient paraconid? interrupting their continuity and from it, a mesial cristid contacts the precingulid ( Figure 3F ). Two small basins are delimited distally to the precingulid, the lingual one, which is also mesial to the base of the metaconid, is larger than the labial one. The mesial wear facets are well developed on the labial side (pacd-mb, prcgd-b, prcd-b, prcd-db) ( Figure 3L ). The talonid is also better defined than in p2, with a short cristid obliqua, and a large hypoconid, which in both teeth shows a clear hd-mb wear facet. A distal and straight cristid also descends from the protoconid lingually, ending in a small entoconid. The talonid basin is larger than the p2 delimited distally by a transverse postcingulid, which lingually seems to end in a small hypoconulid. This last cusp is close to the entoconid but separated from it by a short lingual opening of the talonid basin.

In contrast to the similar size of p2 and p 3 in Carodnia feruglioi and the features mentioned above, the p3 of C. vieirai is smaller than their p2 and differs in the absence of the metaconid and paraconid; also, the lingual distal cristid, is lees projected distally so the talonid basin present a wider lingual opening. Particularly, Paula Couto (1952) mentioned a variable present posterointernal cusp and a hypoconid, united by a smooth ridge.

The p4 (MLP-PV 34-V-22-9) was initially attributed to Ctalecarodnia cabrerai by Cabrera (1935), and it was comprehensively described by him and Vera et al. (2020). Hence, this discussion will focus on providing a few additional comments regarding its homologies. The cristid extending mesially from the metaconid, which does not contact the precingulid, as noted by Cabrera (1935), is here interpreted as the metacristid ( Figure 3 M-O) as those identified by Vera et al. (2020) in the p4 of MGP-PD 29030a. The protoconid and metaconid are well identified in the protolophid, which is the highest structure of the tooth. The hypolophid is low, transverse, and well differentiated from the postcingulid. The resemblance of this p4, as well as others assigned to C. feruglioi (see Vera et al., 2020) with the p4 of C. vieirai is stronger than those between p2–3. The primary distinctions lie in the labial extension of both the postcingulid and precingulid within the Itaboraian taxon. However, the degree of molarization is nearly identical in both species.

The m3 cusps identification for MLP-PV 34-V-22-8 mostly agrees here with those features referred to by Vera et al. (2020) for the holotype MGP-PD 29046. But, in contrast, the conulid placed mesiolingually to the hypoconid is here identified as plagioconulid ( Figure 3 P-R). In Carodnia feruglioi this cusp is not easily identified even in specimens with scarce wear, since the hypoconid developed a lingual wear facet (hd-l) very quickly. In these specimens, the plagioconulid was probably rapidly erased by wear and integrated into a single wear facet with the hypoconid. Despite this, the presence of plagioconulid seems to be an important derived feature in the m3 of C. feruglioi .

Assigned materials. MPEF-PV 564 right dentary with the trigonid of the m2; MPEF-PV 8165 right dentary with part of the canine, and premolars and molars alveoli.

Geographic and stratigraphic provenance. Both specimens come from the Peñas Coloradas Formation, Rio Chico Group sensu Raigemborn et al. (2010), in Chubut province. MPEF-PV 564 was found by F.J. Goin in the outcrops located 5 km south of El Gauchito farm (45º13’53.8” S, 67º09’01.9” W). MPEF-PV 8165 was found by one of the authors ( JNG) at Bajo Palangana, in a level of red sands partially covered by a fraction of whitish gray conglomerate sands, with a significant degree of weathering at 45º33’28.2” S, 67º17’43.1” W ( Figures S1–S 2 in Appendix 1) .

Description and comparisons. MPEF-PV 8165 is a fragmentary right jaw more robust than MPEF-PV 564 ( Table 1). It was found in several associated pieces that fit together, plus a more posterior portion with remains of the coronoid crest and distal edge of the m3 alveolus (reconstructed in Figure 4 A-C). The rest of the jaw is preserved in two parts, conserved the base of the canine and roots of p1–m2. The canine is transversely fractured practically at the height of the tooth’s neck ( Figure 4A, C ). The preserved section is rounded (19.24 mm x 17 mm), and three layers of dentine can be observed ( Figure 5 ). While this resembles the different layers of dentin such as hard orthodentine, orthodentine, osteodentine, and vasodentine identified in Xenarthra (Kalthoff, 2011), a microstructural analysis would be necessary to further deepen these types of comparisons. The innermost layer, no more than 0.6 mm wide, surrounds a wide pulp cavity (3.50 mm in diameter) and is only differentiated from the middle layer by its more yellowish coloration. The middle layer is the most homogeneous, compact, and wide (4.56 mm) and is easily differentiated from the outermost portion of dentine by what appears to be a line of fragility. The outermost part does not exceed 1.76 mm in thickness and is well differentiated from the middle layer, and in it, a structure of concentric rings is observed towards the outermost portion. There is practically no preserved enamel, except for a thin layer on some of its edges. Strong vertical striations are observed in the outer part, which also shapes the bony contour of the alveolus. In the canine of Carodnia vieirai , the enamel is thin and corrugated, so, likely, the dentine crenulations observed in this specimen (MPEF-PV 8165) had a similar layer of enamel, which is not preserved. While the direct observation of specimen UNPSJB-PV 680 has failed to verify the presence of the finely grooved enamel layer described for its canine ( Vera et al., 2020), it is still probable that this layer was present as observed in C. vieirai . Therefore, the observed grooves in UNPSJB-PV 680 are more likely to be associated with the outer layer of dentine, as reported in the present jaw.

Posterior to the canine there are seven alveoli in the first portion of the dentary, interpreted here as those of p1 (with a single root), and p2–4, (each of two roots). Our loci interpretation as p1–4, rests in what is observed in Carodnia vieirai , where p1 is small and single-rooted, ( Figure 4C ). In the occlusal view, the inter-alveolar space between mesial and distal roots of the same premolar is mesiodistally longer than between the alveoli of successive teeth. The labial face of the premolar series is broken.

The preserved portion of the symphysis is large and robust. The upper surface is labiolingually concave and the lower flat. A small foramen opens mesially, like in Carodnia vieirai (DGM 333- M, see Paula Couto, 1952). The more mesial part is missing, and it extends backward distal to the p3 locus. Paula Couto (1952) described for Carodnia vieirai a similar symphysis but in contrast, extended up to the posterior border of p 4 in the type specimen DGM 333-M. We could not directly check this specimen, but in another jaw assigned by him to C. vieirai (cast AMNH 49848 of DGM 334-M) the symphysis extends to the distal part of p3 as in MPEF-PV 8165 (see also Paula Couto, 1952: plate 37: 1). This last criterion seems to have been followed by (Muizon et al., 2015) when they coded this character for Carodnia in their matrix. Three oval mental foramina are present below the position of the distal root of p2, p4, and m1 as described for MPEF-PV 564. A rounded fourth smaller foramen is present between the canine and p1, likely corresponding to the one described for C. vieirai beneath the p1 (Paula Couto, 1952). Another similarly rounded foramen is present in the ventral side of the symphysis (see Figure S3 and 3D image available at http://morphobank.org/permalink/?P5193). A small mental foramen was previously mentioned by Paula Couto (1952) for C. vieirai , but positioned on the posterior part of the lower border of the symphysis, beneath the canine, rather than medially as observed in MPEF-PV 8165. Towards the distal portion of the MPEF-PV 8165 dentary, two additional smaller foramina are situated beneath the positions of the m2 roots ( Figure 4A ). The first is almost vertically aligned with the mental foramina, while the second is located below it but more anteriorly.

The posterior portion of the dentary is fractured distally to the m2, leaving only the ventral edge of the jaw visible at the m3 locus. In this cross-section of the jaw, a relatively large mandibular canal is present at the base. However, at the level of m1, the diameter of the canal is smaller, and in a more central position. The mandibular canal cannot be followed to the back of the jaw since it is broken. The last dentary segment, which bears the distal alveolus of the m3, does not have direct contact with the anterior part.

MPEF-PV 564 represents a fragmentary right jaw, retaining solely the trigonid of m2 and a fragment of the mesial root of m3 ( Figure 4 D-F). The jaw is broken anterior to the p3, preserving only a severely damaged distal portion of the symphysis. Moving distally along the dentary, a small segment of the coronoid crest is visible on the labial side. Unlike Carodnia vieirai (DGM-333 and DGM-334) and Carodnia inexpectans (Antoine et al., 2015) , the extensive damage in the distal part of the jaw hinders the possibility of identifying the anterior foramen of the coronoid canal. In contrast to the alveoli surfaces of the distal root of m2 and m3, those of p3–m1 are broken and eroded, not preserving the real upper margin of the bone. The dentary is robust, with a convex ventral profile below the m2–3 and a straight one mesially. At the m1 position, a small portion of the ventral margin of the dentary is missing. Three mental foramina occur in the mandible, each one located, respectively, below the position of the distal root of p2, the p4 as in Carodnia vieirai (Paula Couto, 1952) , and another one under the m1. The mesial fragment of the m2 preserves the trigonid with a clear transverse protolophid with a wear facet that runs through the length of the lophid and slopes distally. Despite the protoconid and the metaconid being almost integrated into the protolophid, they still retain a rounded external surface, making them easily identified in occlusal view. The mesial part of the trigonid is short and there is no trace of paraconid. A blunt paracristid descends abruptly from the mesial border of the protoconid to the base of the tooth and then runs lingually. A precingulid runs from the lingual side mesial to the protoconid base, up to the metaconid but not reaching the labial margin. The precingulid is undulated, thinner and lower on the lingual side, and thicker and higher near the metaconid.

Figures

FIGURE 1. Map showing the locations of the localities where the described materials came from.

FIGURE 2. Stratigraphy Synthesis: Left: Bajo Palangana with three columns representing on the sides two alternative interpretations of the Rio Chico Group, based on Vera and Krause (2020) and Raigemborn et al. (2010); in the center “fossil content and guide banks,” summarize the descriptions of Brandmayr (1932), Bordas (1935), Simpson (1935a), Feruglio (1949), and personal observations. Meters above sea level and meters above the “Banco Negro Superior”: BNS. Banco Negro Inferior: BNI. Right: Lower levels at Cerro Redondo, left column levels described by Brandmayr (1932) and Simpson (1935a); on the right: our interpretation based on Raigemborn et al. (2010).

FIGURE 3. Carodnia feruglioi: MLP-PV 34-V-22-8 left p2 in (A) lingual, (B) labial, and (C) occlusal views; left p3 in (D) lingual, (E) labial, and (F) occlusal views; right p2 in (G) labial, (H) lingual, and (I) occlusal views; right p3 in (J) labial, (K) lingual, and (L) occlusal views; MLP-PV 34-V-22-9 right p4 (first assigned to Ctalecarodnia cabrerai) in (M) labial, (N) lingual, and (O) occlusal views; MLP-PV 34-V-22-8 right m3 in (P) labial, (Q) lingual, and (R) occlusal views. Wear facets are hd-mb: hypoconulid-mesiobuccal, pacd-mb: paraconid-mesiobuccal, prcgd-b: precingulid-buccal, prcd-h: protoconid-horizontal, prcd-b: protoconid-buccal, prcd-db: protoconid-distobuccal, pocgd-ml: postcingulid-mesiolabial. Approximate scale 5 mm.

FIGURE 4. Carodnia feruglioi: MPEF-PV 8165 right jaw fragment in (A) labial, (B) lingual, and (C) occlusal views. MPEF-PV 564 right jaw fragment in (D) labial, (E) lingual, and (F) occlusal views. r: roots of different preserved dental loci. Scale 50 mm.

FIGURE 5. Carodnia feruglioi: MPEF-PV 8165 right canine cross-section.