Candelariodon barberenai Oliveira, Schultz, Soares, and Rodrigues, 2011
|
publication ID |
https://doi.org/ 10.4202/app.00344.2017 |
|
persistent identifier |
https://treatment.plazi.org/id/71324253-FFAC-FFEA-889A-8E48FD9B49BD |
|
treatment provided by |
Felipe |
|
scientific name |
Candelariodon barberenai Oliveira, Schultz, Soares, and Rodrigues, 2011 |
| status |
|
Candelariodon barberenai Oliveira, Schultz, Soares, and Rodrigues, 2011
Figs. 2 View Fig , 3A View Fig , 4 View Fig , 5A View Fig .
Holotype: MMACR PV-0001 - T, almost complete left branch and anterior half of the right branch of the dentary, fused at the symphysis, bearing partial dentition, and an isolated posterior lower left postcanine tooth ( Oliveira et al. 2011; Figs. 2 View Fig , 3 View Fig ).
Type locality: ~ 20 km south of Candelária city, Pinheiro (or Pinheiros) region, Rio Grande do Sul, Brazil ( Fig. 1 View Fig ).
Type horizon: Dinodontosaurus AZ of the Pinheros-Chiniquá Sequence, Santa Maria Supersequence, late Ladinian–early Carnian.
Emended diagnosis.— Probainognathian cynodont with the following combination of features (autapomorphies marked with an asterisk): tall horizontal ramus of the dentary and coronoid process; no angular process; fused mandibular symphysis; lower incisor alveolar level positioned above the level of the postcanine crowns; last lower incisor with strongly posteriorly curved crown; large lower canine without serrated edges; pc2–3 with large cusp a, tiny cusp b, small cusp c, accessory cusp g, faint lingual cingulum, and absence of cusp d*; pc2–4 transversely broader at distal half of the crown than mesially; posterior postcanines (pc5–8) mesiodistally longer than preceding ones; pc5 with continuous lingual cingulum, bearing accessory cusp g and at least cusps a, c, and d*; posterior postcanines with large, slightly posteriorly curved cusp a, small cusp b, cusp c larger than b, cusp d, accessory cusp e, and with non-continuous cingulum, absence of cusp g*.
Description.— Dentary: The dentary has a tall horizontal ramus and well-developed coronoid and articular processes ( Fig. 2 View Fig ). The horizontal ramus has an almost straight ventral edge, parallel to the alveolar line. It is slightly convex dorsoventrally and about three times taller than the crown height of pc 4 in lateral view. Hence, the horizontal ramus is relatively stout as usually found in probainognathians (e.g., Probainognathus jenseni, PVL 4445; Bonacynodon schultzi , MCT-1716-R; Prozostrodon brasiliensis , UFRGS- PV-248-T, Fig. 3B View Fig ; Botucaraitherium belarminoi , MMACR- PV-003-T; Riograndia guaibensis , UFRGS-PV-0596-T). It differs from the low horizontal ramus of Protheriodon estudianti (UFRGS-PV-0962-T), Santacruzgnathus abdalai (UFRGS-PV-1121-T), and Brasilitherium riograndensis (UFRGS-PV-1043-T; Fig. 3C View Fig ). A large mental foramen is observed at mid-height below pc2 and there are other small foramina nearby. The coronoid process is tall, with its dorsal edge broken off and the anterior margin wider at its base. It presents a large masseteric fossa on its lateral surface that extends anteriorly to about the level of the pc5 ( Figs. 2A View Fig , 3A View Fig ), as observed in most probainognathians ( Hopson and Kitching 2001). The articular process of the dentary extends far posteriorly, but it is not completely preserved. Its ventral edge projects posterodorsally with the posteriormost tip positioned above the postcanine level, lacking an angular process, as in Prozostrodon , Brasilitherium , and some early mammaliaforms, such as Haramiyavia ( Luo et al. 2015) . Medially, the postdentary trough is reduced and at the inflection of the coronoid process there is no clear evidence of a facet or remnant of coronoid bone.
The straight ventral border of the dentary bends abruptly anteriorly at the level of pc1, forming an angle of ~140° and delimiting the posteroventral edge of symphysis ( Fig. 2A View Fig ). It is anterodorsally to posteroventrally inclined, being about twice as long as wide. There is no evidence of suture at the symphysis, indicating that both dentaries are fused, which is the condition in most non-prozostrodontian cynodonts ( Hopson and Kitching 2001; Abdala 2007). The anterodorsal development of the dentary places the alveolar edge of incisors and canine above the level of the tip of postcanine crowns. This condition is also seen in Prozostrodon ( Fig. 3B View Fig ), Brasilitherium ( Fig. 3C View Fig ), and, to a lesser degree, in Microconodon and Dromatherium ( Simpson 1926; Sues 2001). In Botucaraitherium , this portion is partially broken but the canine seems to be positioned in a higher position than the postcanine line.
Splenial: The right and left splenials are preserved on each ramus. It is a laminar bone that covers the entire Meckelian groove. It extends parallel to the ventral edge of the dentary and reaches the mandibular symphysis ( Fig. 2C View Fig ), where it contacts its counterpart. The splenials are as developed as in Prozostrodon and other non-prozostrodontian probainognathians, being slightly dorsoventrally taller than in Brasilitherium and Riograndia .
Incisors: The lower incisor number is unknown in Candelariodon . The last left incisor is the only preserved Fig. 2A View Fig ). It is small in comparison to the canine and positioned next to it, without diastema. The crown is sub-conical, strongly curved posteriorly, with a thick layer of enamel. The distal edge seems to form a distal ridge of enamel. There is a small wear facet on the labial surface of the tip. The curved crown, with a strongly convex labial surface and ridged distal edge, is a morphology also seen in Prozostrodon .
Canine: Both canines are poorly preserved. The right canine only preserves the root and the left one less than half of the crown ( Fig. 2A, B View Fig ). They are the largest teeth, oval in cross section, being about two times longer than width. There is no evidence of serrated edges. The preserved portion of the left canine has a concave distal edge, indicating a posteriorly curved crown, as is seen in Prozostrodon ( Fig. 3B View Fig ). There is a diastema between canine and postcanines, being slightly longer on the right side as evidenced by the loss of the right pc1 (but not the left pc1; see below).
Postcanine teeth: There are empty alveoli for the right pc1, pc4–7 and left pc6–8. Complete to fairly complete tooth crowns are represented in the right pc2–3 and left pc1–5, plus an isolated tooth laying on the lateral surface of the coronoid process of the dentary, here interpreted as a posterior left lower postcanine (see below) ( Figs. 2A, B View Fig , 4 View Fig , 5 View Fig ).
The postcanine tooth rows slightly diverge posteriorly and the last tooth is placed medial of the anterior base of the coronoid process ( Fig. 2C View Fig ). As indicated by alveolar dimensions, the postcanine teeth increase in size gradually to the rear. The right dentary is incomplete and only has seven tooth positions, with the position for pc8 only partially preserved. The right pc1 alveolus is small in comparison to the left one and is positioned very close to anterior wall of pc2 alveolus ( Fig. 4 View Fig ). This condition together with the fact that the right canine-postcanine diastema is longer than the left one suggests that the anterior postcanines were lost during ontogeny, increasing the size of the diastema, as seen in some prozostrodontians (e.g., Prozostrodon , Brasilodon , Sinoconodon ) and some gomphodonts (e.g., Diademodon , Exaeretodon ) ( Hopson 1971; Crompton and Luo 1993; Luo et al. 2004; Martinelli and Bonaparte 2011). Differences between the right and left postcanine tooth rows are common in eucynodonts. For example, in Prozostrodon (Fig. 6C) the left pc1 is absent and there is a substantial discrepancy in size between the large left and small right pc2.
The left pc1 is the smallest of the series. The crown is badly preserved, hampering the recognition of discrete cusps. However, it seems simpler and transversely narrower than pc2 ( Fig. 4B–D View Fig ).
The left pc2 crown is also broken but the crown shape can be discerned on the right one. The right pc2 has a prominent cusp a, with its tip broken off, followed by a reduce cusp c, which is slightly labially displaced ( Fig. 4A View Fig ). There is an evidence of a sharp mesial edge that seems to indicate the presence of a reduced cusp b. In addition, there is an evidence of a small distolingual cusp, which is interpreted as cusp g (following Crompton 1974). Due to the position of cusps c and g, the distal half of the crown is transversely wider than the mesial half. Such morphology is seen in middle postcanine teeth of sub-adult individuals of Brasilitherium (e.g., UFRGS-PV-603-T; Fig. 5C View Fig ). In Prozostrodon there is also an accessory cusp on the distolingual corner of the crown of the anteriormost teeth, but due to the presence of other accessory cusps on the mesiolingual edge, the crown width is more homogeneous. Because the lingual cingular cusps are almost similar in size, the identification of a putative cusp g is not possible in Prozostrodon ( Fig. 5B View Fig ). Moreover, the anterior postcanine teeth of Prozostrodon have a cusp b, although very reduced, and the main cusp a is less bulbous and slightly posteriorly curved (Fig. 6C).
Both right and left pc3 of Candelariodon are well preserved. They have a pattern similar to pc2 but with accentuated features ( Figs. 4 View Fig , 5 View Fig ). The main cusp a is large, with a strongly convex mesial edge that descends to a very small cusp b, lingually located. The distal edge of cusp a is shorter than the mesial one and almost straight. It contacts the mesial edge of cusp c, without defining a conspicuous (“carnassial”) notch. The cusp c is considerably larger than cusp b and labially displaced. The distolingual accessory cusp g is slightly smaller than cusp c, but considerably larger than cusp b. In the left pc3 there is a distal accessory cusp ( Fig. 4B View Fig ) that is not seen in the right pc3. This distal accessory cusp is not interpreted as the cusp d based on the morphology seen in pc5 (see below). Between the distal accessory cusp and cusp g there is a “v” shaped notch, deeper than the one between accessory cusp and cusp c. One of the most conspicuous features of the pc3 is the presence of a faint, continuous cingulum connecting cusps b and g ( Figs. 4B View Fig , 5A View Fig ). There are two tiny notches at mid-length of the cingulum that do not define discrete crenulations or cusps. In occlusal view, pc3 has a width/length ratio of 0.7.
The pc4 has a large cusp a and small cusp c. The cusp b and accessory distolingual cusp g are not seen ( Figs. 4B View Fig , 5A View Fig ). However, this tooth has the same width/length ratio (= 0.69) as pc3. The lack of cusp g could be the result of breakage or perhaps due to wear (food processing and not tooth-to-tooth occlusion) on the crown. Based on the fact that the cusp g is smaller in the following teeth (i.e., pc5 and isolated posterior tooth, which have more sectorial shape), a less developed cusp g should be expected in pc4 than in pc3. A distal accessory cusp and cusp d is not discerned in pc4. In this postcanine, the lingual cingulum is better developed on the more mesial portion of the crown.
The pc5 is badly preserved with most of its mesiolabial portion broken off ( Figs. 4B–D View Fig , 5A View Fig 2 View Fig , A 3 View Fig ). Based on the preserved portion and the size of the alveolus, it is considered a mesiodistally larger and transversely narrower tooth than pc4–3. Oliveira et al. (2011) considered the crown of pc5 as having two mesiodistal rows of four cusps each. They considered the labial row to be made up of cusps b’, a’, c’, d’, and the lingual row of cusps b”, a”, c”, d”, separated by a mesiodistally oriented groove. That morphology was found fairly similar to the condition seen in the probainognathian Aleodon brachyramphus ( Oliveira et al. 2011) , which is characterized by having a row of sectorial labial cusps (homologous to the sectorial cusps of other probainognathians) and a broad lingual cingulum (i.e., cingular platform, sometimes with evident crenulations or tiny cusps), much more developed than in other known probainognathians (UMZC T906; Crompton 1955; Abdala and Giannini 2002). As shown in Figs. 4 View Fig , 5 View Fig , it is evident that most of the mesiolabial region of the crown is broken off. This is evident by the lack of the enamel layer that is continuous in the other parts of the crown, as also seen in the remaining postcanine teeth, and the eroded surface. Therefore, the bulk of cusp a and the entire cusp b are not preserved. Nonetheless, the notch between the distal ridge of cusp a and the mesial ridge of cusp c is still present ( Figs. 4B View Fig , 5A View Fig 3 View Fig ) and also adds supports to our interpretation. The cusp c is slightly labial, as in the remaining postcanine teeth, and smaller than the supposed size of cusp a. Distally, there is another cusp in line with cup c that is considered as cusp d. In addition, the pc5 has the accessory distolingual cusp g, which is present in previous teeth. Consequently, the morphology of pc5 is more complex than that of the preceding teeth, and it indicates that a discrete cusp d first appears in the pc5. Thus, the cusp interpreted as d in pc2–4 by Oliveira et al. (2011) is here considered as the accessory distolingual cusp g, which is kept all along the postcanine teeth (in pc1 and pc4 it is not observed due to preservation).
The pc5 also has a continuous cingulum, more transversely developed than that seen in pc3. It forms a shallow concavity between the main cusps a and c and its elevated lingual edge ( Fig. 5A View Fig 2 View Fig , A 3 View Fig ). Along the cingulum, at least two worn cusps are evidenced. This cingulum, however, is not comparable with the labial platform seen in the middle and posterior postcanine teeth of Aleodon , which form a large lingual platform (UMZC T906, NHMUK-PV-R-9390; Crompton 1955). A continuous lingual cingulum is observed in Prozostrodon , Botucaraitherium , Brasilodon , and some tritheledontids ( Pachygenelus , Diarthrognathus ; Gow 1980). In Prozostrodon the lingual cingulum bears up to nine tiny, discrete cusps ( Bonaparte and Barberena 2001) ( Figs. 5 View Fig , 6). That number is smaller in Botucaraitherium ( Soares et al. 2014) and Brasilodon ( Bonaparte et al. 2005) .
As consequence, the changes along the postcanine tooth row of Candelariodon are gradual, within a “triconodont-like” pattern, contrary to the original proposal of Oliveira et al. (2011) that recognized a drastic change of morphology only in pc5.
The isolated tooth was originally considered as an upper postcanine tooth ( Oliveira et al. 2011), by comparing with gomphodonts ( Diademodon and Andescynodon ) and based on the original interpretation of pc5 that made difficult the allocation of a more sectorial tooth at the rear of the tooth series. We interpreted here this tooth as a posterior left postcanine that should have occupied one of the three last empty alveoli. This tooth is more sectorial (i.e., it is mesiodistally longer and transversely narrower) than the remaining ones ( Fig. 5A View Fig 1 View Fig ), as seen in some other prozostrodontians, such as Prozostrodon ( Fig. 5B View Fig ) and Brasilitherium ( Fig. 5C View Fig ). The crown of this isolated tooth of Candelariodon has a sectorial crest with main cusp a followed by cusps c and d, this latter being slightly lingually dislocated. Just lingual to the base of cusp d there is a small bulge that would be a remnant of the accessory distolingual cusp, present in more anterior teeth. The cusp a has a rounded tip and its main axis is posterodorsally inclined. The cusp b is small and low in position ( Fig. 5A View Fig 1 View Fig ). Lingually to it, there are two accessory cingular cusps, being the more mesial cusp e, as large as cusp b, and the other one relatively smaller. Differing from the pc5, the cingulum is not lingually complete, being restricted to the mesiolingual corner of the crown. This postcanine tooth has a single root, differing from the constricted root pattern seen in most, but not all (e.g., Pachygenelus ; Gow 1980), prozostrodontians ( Hopson and Kitching 2001; Liu and Olsen 2010).
There is no positive evidence to consider this isolated tooth as an upper postcanine. The changes in tooth crown morphology along the row are similar to that observed in Brasilitherium (e.g., UFRGS-PV-603-T; Bonaparte et al. 2003). Importantly, in Prozostrodon and Botucaraitherium the cuspidated cingulum is maintained in the last teeth, a condition not seen in Candelariodon .
The distribution of enamel on the postcanine teeth of Candelariodon is noteworthy. The external walls of the crown exhibit a thick layer of enamel with a yellowish coloration, but the inner walls of the cusps and cingulum have a whitish coloration, suggesting the lack of enamel or the presence of a very thin layer. This enamel pattern is clearly seen in both right and left pc3, left pc4–5, and the isolated tooth. Particularly the enamel, if present, is extremely thin in the lingual portion of the crown-root boundary of the isolated tooth, where the cingulum is absent.
Clear evidence of wear is seen in the left pc3, having apical wear on the main cusp a, and the left pc4, with an oval wear facet on the labial surface of cusp c ( Figs. 4C View Fig , 5A View Fig 2 View Fig , A 3 View Fig ).
→ Fig. 6. Comparisons of postcanine teeth among selected eucynodonts. A. Brasilitherium riograndensis Bonaparte, Martinelli, Schultz, and Rubert, 2003 (UFRGS-PV-603- T) from the Late Triassic of Rio Grande do Sul, Brazil ; left postcanines. B. Candelariodon barberenai Oliveira, Schultz, Soares, and Rodrigues, 2011 (holotype, MMACR PV-0001 - T) from the Middle–Late Triassic of Rio Grande do Sul, Brazil ; isolated left posterior postcanine (B 1) and left pc1–5. C. Prozostrodon brasiliensis (Barberena, Bonaparte, and Teixeira, 1987) (holotype, UFRGS-PV-248- T) from the Late Triassic of Rio Grande do Sul, Brazil ; left (C 1) and right (C 2) postcanine rows. D. Botucaraitherium belarminoi Soares, Martinelli, and Oliveira, 2014 (holotype, MMACR-PV-003- T) from the Late Triassic of Rio Grande do Sul, Brazil ; last left postcanines. E. Thrinaxodon liorhinus Seeley, 1894 (NHMUK-PV-R3731) from the Early Triassic of South Africa ; left postcanine row. All teeth are in lingual view. The dashed line in pc5 represents the shape of cusp a. The dotted line indicates the point where postcanine teeth change their morphology radically. Abbreviations : apc, alveolus of postcanine tooth; pc, postcanine tooth .
Stratigraphic and geographic range.— Dinodontosaurus AZ of the Pinheros-Chiniquá Sequence, Santa Maria Supersequence, late Ladinian–early Carnian, Middle–Late Triassic. Pinheiro region, Rio Grande do Sul, Brazil.
| T |
Tavera, Department of Geology and Geophysics |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.