Results and discussion

The species appears to be assignable to Rhinelepinae based on its low, wide parasphenoid—a synapomorphy of this subfamily (Armbruster, Reference Armbruster1998, character 20:1; Armbruster, Reference Armbruster2004, character 106:1; the parasphenoid of †Taubateia has a break just anterior of its contact with the basioccipital [Fig. 2.4, dashed line]). The parasphenoid typically has lateral projections anterior of the basioccipital (Fig. 2, LPP; the processes are broader in †Taubateia); the width just posterior to these processes is approximately half or greater than the width of the main body of the basioccipital in rhinelepines, but much less than half in hypostomines. In addition, the portion of the parasphenoid just anterior to the lateral processes is almost flush with the surrounding bones in rhinelepines but is greatly raised in hypostomines. Some Hypoptopomatinae and Loricariinae have widened parasphenoids that do not form a tall ridge, but the anatomy is significantly different (Fig. 3.2, 3.4). Some loricariines also have flat skulls with wider, flatter parasphenoids (Fig. 3.4), but their skulls are generally narrow and lack the other synapomorphies between †Taubateia and Rhinelepis Agassiz in Spix and Agassiz, Reference Spix and Agassiz1829.

Figure 2. Ventral views of the medial bones and lateral ethomoids of the neurocrania of: (1) Hypostomus luteus (Godoy, Reference Godoy1980), MCP 12809; (2) Pseudorinelepis genibarbus (Valenciennes in Cuvier and Valenciennes, Reference Cuvier and Valenciennes1840), UF 162115; (3) Rhinelepis aspera Spix and Agassiz, Reference Spix and Agassiz1829, AMNH 58332; (4) †Taubateia paraiba Malabarba and Lundberg, Reference Malabarba and Lundberg2007, DGM 17-P; dashed line indicates a break in the parasphenoid. BO = basioccipital; LE = lateral ethmoid; LPM = lateral process of mesethmoid; LPP = lateral process of parasphenoid; ME = mesethmoid; PF = palatine facet; PS = parasphenoid; V = vomer. Scale bars = 1 cm.

Figure 3. Comparative ventral-view cranial CT scans of representative loricariids (not to scale): (1) Hypostomus luteus (Godoy, Reference Godoy1980), MCP 12809; (2) Otocinclus vittatus Regan, Reference Regan1904, ANSP 174732, (3) Pseudorinelepis genibarbus (Valenciennes in Cuvier and Valenciennes, Reference Cuvier and Valenciennes1840), UF 162115, (4) Planiloricaria cryptodon (Isbrücker, Reference Isbrücker1971), ANSP 191512. APT = anterior process of compound pterotic; ME = mesethmoid; PF = prootic foramina; PS = parasphenoid; V = vomer.

Although we have not assessed the character fully across loricariids, the mesethmoid is very wide at its base (over twice as wide as the narrowest portion) in the Rhinelepinae (Figs. 1.1, 2.2, 2.3, 3.3) as well as in †Taubateia (Figs. 1.2, 1.4, 2.4). The mesethmoid generally has lateral flaps located on its dorsal surface (Fig. 2, LPM). Normally, the flap ends anterior to the palatine condyle of the lateral ethmoid. In Rhinelepinae, the processes continue posteriorly and contact the dorsal wall of the palatine roughly halfway or greater from the lateral midpoint of the condyle, leaving a small gap between the lateral process and the main body of the mesethmoid, producing a roughly triangular bone (Fig. 2.2–2.4; the palatine facet is unclear on †Taubateia but the lateral processes of the mesethmoid are extended). Most other loricariids have a much narrower mesethmoid (base less than twice the width of the narrowest portion) with a lateral process that does not extend to the palatine facet, resulting in a bone that is mainly rectangular posterior to the flared anterior portion; Figs. 2.1, 3.1, 3.2, 3.4). We did find a similar state in Rineloricaria rupestris (Schultz, Reference Schultz1944); however, the process was sutured to the lateral ethmoid in Rineloricaria rupestris (versus just contacting) and the mesethmoid was much more elongate in Rineloricaria rupestris, with the greatest width only about twice the width of the narrowest. †Taubateia is also much larger than any known Rineloricaria sp. and overall cranial shape is a poor fit.

Although we have not examined this character across Loricariidae, there is an unusual feature of the fossil impression of †Taubateia: evidence of a two-part flat ridge across the prootic and orbitosphenoid bones and located within the orbit (outlined in Fig. 1.3, 1.4). This structure is visible on the CT scan of Rhinelepis, but to get a better view of it, we made a resin, three-dimensional print of the Rhinelepis neurocranium and pressed it into a substance called Model Magic (Crayola, Easton, Pennsylvania, USA). Model Magic is a lightweight, foam-like material that can hold impressions and hardens to keep its form. The imprint of the Rhinelepis skull is very similar to that of †Taubateia (Fig. 1.3, 1.4) in dimensions and depth of the impression of structures and the synapormorphies mentioned. We have not observed this ridge in any other loricariid. Also, the strong concavities on either side of the vomer that are present in most loricariids (Fig. 3.1, 3.3), but are much shallower in both Rhinelepis and †Taubateia, are noteworthy (Fig. 1.1, 1.2). The neurocrania of Rhinelepis and †Taubateia are comparatively flatter than in other rhinelepines, which is likely one feature that allowed for the excellent preservation of †Taubateia.

Rhinelepis was described by Armbruster (Reference Armbruster2004) as lacking an anterior process of the compound pterotic; however, an extremely short anterior process is present in the CT scan (Fig. 1.1). In addition, the anterior edge of the compound pterotic lies nearly at a right angle to the long axis of the body. †Taubateia has a normal anterior process of the compound pterotic causing the anterior margin of the bone to be at an ~45° angle to the long axis of the body (Fig. 1.2). In addition, the transverse process of the Weberian apparatus is well-separated from the compound pterotic in Rhinelepis and only slightly separated from the compound pterotic in †Taubateia, and the anterior end of the mesethmoid is wider in Rhinelepis than in †Taubateia. Unique to †Taubateia is the shape of the posterior end of the parasphenoid, which tapers to the basioccipital posterior to broad lateral processes (Fig. 2.4). In other rhinelepines, the posterior end of the parasphenoid is approximately parallel with the sagittal plane posterior to the narrow, more pointed lateral processes (Fig. 2.2, 2.3). Based on these differences, we choose to continue recognizing †Taubateia as a distinct and valid genus in Rhinelepinae, which is nonetheless more closely related to Rhinelepis than to Pogonopoma Regan, Reference Regan1904 or Pseudorinelepis Bleeker, Reference Bleeker1862.

The morphological similarity of †Taubateia to Rhinelepis suggests that the two are sister taxa or perhaps chronospecies and that Rhinelepinae has changed little in the last 20–30 Myr. This is likely true for other loricarioids as well. †Corydoras revelatus Cockerell, Reference Cockerell1925 (Callichthyidae) is a fossil species from the late Paleocene Mais Gordo Formation of Argentina (~58.5 Ma) that differs little from living Corydoras spp. (Lundberg et al. Reference Lundberg, Marshall, Guerrero, Horton, Malabarba, Wesselingh, Malabarba, Reis, Vari, Lucena and Lucena1998, Reference Lundberg, Sullivan, Rodiles-Hernández and Hendrickson2007; Reis, Reference Reis1998). Characiform fish fossils found with †Taubateia in the Tremembé Formation are also considered congeners with living taxa, including †Brycon avus Woodward, Reference Woodward1898, †Lignobrycon ligniticus (Woodward, Reference Woodward1898), and †Cyphocharax mosesi Travassos and Santos, Reference Travassos and Santos1955, whereas †Megacheirodon unicus (Travassos and Santos, Reference Travassos and Santos1955) is considered sister to the extant taxa Serrapinus Malabarba, Reference Malabarba, Malabarba, Reis, Vari, Lucena and Lucena1998b and Spintherobolus Eigenmann, Reference Eigenmann1911 of the Cheirodontinae (Malabarba, Reference Malabarba1998a, Reference Malabarba, Malabarba, Reis, Vari, Lucena and Lucenac). The extant pimelodid catfish genus Steindachneridion Eigenmann and Eigenmann, Reference Eigenmann and Eigenmann1919 also has two extinct species in the Taubaté Basin (Bogan and Agnolín, Reference Bogan and Agnolín2019).

Using a molecular clock, Roxo et al. (Reference Roxo, Ochoa, Sabaj, Lujan, Covain, Silva, Melo, Albert, Chang, Foresti and Alfaro2019) found that Rhinelepinae was one of the earliest branching lineages of the Loricariidae (~47 Ma), and they suggested that many of the loricariid genera were already present by the late Oligocene or early Miocene. Roxo et al. (Reference Roxo, Ochoa, Sabaj, Lujan, Covain, Silva, Melo, Albert, Chang, Foresti and Alfaro2019) used two calibration points: the calculated age of Siluriformes from other studies (Lundberg, Reference Lundberg and Goldblatt1993; Sullivan et al., Reference Sullivan, Lundberg and Hardman2006; Lundberg et al., Reference Lundberg, Sullivan, Rodiles-Hernández and Hendrickson2007) and the outgroup fossil †Corydoras revelatus. Although †Taubateia should be more thoroughly compared across loricariids, particularly species still found in the same region today, the genus is best recognized as a member of the Rhinelepinae based on the evidence provided. With the current assignment of †Taubateia to the Rhinelepinae as well as the recent identification of Acanthicus by Bogan and Agnolín (Reference Bogan and Agnolín2020), there are now two internal Loricariidae calibration points available for future molecular dating analyses.