Taubateia paraiba, Malabarba & Lundberg, 2007

Malabarba, Maria Claudia & Lundberg, John G., 2007, A fossil loricariid catfish (Siluriformes: Loricarioidea) from the Taubaté Basin, eastern Brazil, Neotropical Ichthyology 5 (3), pp. 263-270 : 264-267

Taubateia paraiba , new species

Figs. 2-5

Holotype. DGM 17 -P, a ventral impression of the anterior part of the fish including neurocranium and first vertebrae articulated, ventral skull length 54.5 mm.

Locality and geological age. Late Oligocene to Early Miocene shales from the Tremembé Formation, Taubaté Basin, cropping out near Tremembé county (22º 50’ S, 45º 52’ W), São Paulo State, Brazil .

Diagnosis. As for the genus.

Description. The description is necessarily limited to the ventral view of the head skeleton and anterior vertebrae.

Neurocranium. The neurocranium is roughly triangular in outline shape, narrow anteriorly and greatly expanded across the occipital region. The arrangement and shapes of cranial bones resemble those of other loricariids, and show typical loricariid features, such as: vertical projection in the anterior end of mesethmoid; the reduced mesethmoid cornua, triangular shaped and expanded lateral ethmoids, a compound pterotic posteriorly expanded.

The mesethmoid is a triangular bone, anteriorly narrow and pointed, and expanded posteriorly. It is flattened with lateral expansions (crest of Py-Daniel, 1997) incorporated into the main body of the bone, as occurs in the depressed species. It presents the typical pair of greatly reduced and rounded anterolateral cornua, each with a shallow concavity in the center and a few grooves in the cornua base. The anterior edge of the mesethmoid is smooth with a small median cleft between the cornua. A moderately developed rounded disk (condyle) projects ventrally from the mesethmoid behind the cornua; there are no signs of concave facets on the disk but two depressions are present laterally. Based on the good preservation of this specimen, particularly the mesethmoid region, we may assume that these facets did not exist. The mesethmoid disk has a subterminal position, not contacting the anterior margin of the mesethmoid and would not be visible in a dorsal view. Posteriorly, the mesethmoid meets the prevomer in a V-shaped suture.

The prevomer has the shape of an elongated diamond with small lateral wings contacting the mesethmoid and the lateral ethmoid. The anterior end is moderately developed as a pointed spike that deeply interdigitates with the mesethmoid. Its posterior end is an elongate spine that extends between a pair of parasphenoid spikes.

The paired lateral ethmoids are large and triangular with the posterolateral corner expanded. The lateral ethmoid anterior border is straight and bears an anterolateral articular facet for the palatine. The lateral ethmoid expands posteriorly to form a distinct lateroposterior process at the anterior margin of the orbit. A low ridge, rounded in cross-section, extends longitudinally near the lateral ethmoid margin from the palatine articular facet to the posterior border to terminate at an ovoid condyle that would presumably articulate with dorsal surface of the metapterygoid. According to Py-Daniel (1997:38), regardless of the extent of contact between lateral ethmoid and metapterygoid, the posterior end of the lateral ethmoid is always involved via a condyle or suture. The state of preservation does not allow us to determine the structure of the nasal capsules.

The parasphenoid lies flat on the ventral midline between the prevomer anteriorly to basioccipital posteriorly. Anteriorly the parasphenoid forms a wide and slightly raised ridge separating the lateral ethmoids; posteriorly its margin is gently curved laterally below the orbitosphenoid, and expanded, forming small lateral wings in contact with the prootics. The posterior margin of the parasphenoid strongly interdigitates with the basioccipital across the ventral midline.

The basioccipital is laterally sutured with the prootic and exoccipital. Its lateral process contacting with the mesial end of the ossified transcapular (Baudelot’s) ligament of the posttemporal-supracleitrum that continues laterally forming a wall sutured to the exoccipital and pterotic. In a developmental study of the skeleton of the loricariid Ancistrus cf. triradiatus, Geerinckx et al. (2007) show that the ossification of the transcapular ligament arises from two sources: medially from the basioccipital (our “basioccipital lateral process”) and laterally from the pterotic-supracleithrum (our ossified transcapular ligament).

The orbitosphenoid is nearly retangular in form with concave lateral margins. It is sutured to the lateral ethmoid anteriorly, and with the prootic posteriorly. Despite the large expansion of the lateral ethmoid posterior border, the orbitosphenoid does not follow this enlargement, and the anterior (with the lateral ethmoid) and the posterior (with prootic) sutures remain with similar lengths.

The exoccipitals are a small pair of bones limited anteriorly by the prootic and mesially by the basioccipital. Posteriorly, the exoccipital remains limited by the basioccipital lateral process and transcapular ligament. The exoccipital is pierced by the two foramina for the glossopharyngeal and vagus nerves, near its posterior border.

The prootic forms the ventrolateral floor of the neurocranium posterior to the orbitosphenoid. It is a large bone sutured posteriorly to the basioccipital, exoccipital and pterotic. A circular notch is present in the anterolateral border of the prootic representing the trigeminofacial foramen. Almost in the center of the bone there is a smaller foramen presumably for the hyomandibular branch of the facial nerve.

Generally in loricariids the sphenotic is a paired bone mostly developed and visible on the dorsal side of neurocranium. However, in DGM 17-P a portion of this bone is preserved in a ventral view, displaying its anterior suture to the frontal and the spine projected from its lateral border. Some odontode marks can be observed along the sutures and lateral border of the sphenotic. Even a few odontodes are preserved scattered in the sediment.

The paired pterotics are broad compound bones (pterotic + supracleithrum) forming most of the posterolateral part of the skull. Each pterotic is greatly expanded and squarish in shape with the lateral margin nearly straight. The ventral surface of the pterotic bears a strong ridge for pectoral girdle articulation. Posteriorly it is closely associated but not fused with the transverse processes of complex vertebrae. The ventral aspect of Taubateia shows the transverse process of the Weberian compound centrum surrounding the swimbladder.

Weberian apparatus and anterior axial skeleton. The Weberian complex centrum is almost square and relatively short, not much longer than the seventh centrum. It is fused to the basioccipital anteriorly and sutured to the sixth vertebrae centrum posteriorly. The transverse process and the complex centrum form nearly a 70º angle, being slightly ventrally directed. The distal tip of the transverse process of the Weberian complex centrum is in contact with the pterotic with about the same width than the shaft. It is distally rounded (not pointed) and cancellous.

In addition to the vertebrae incorporated into the Weberian apparatus, vertebral centra six through nine are preserved. The sixth centrum has a large pair of ventrolaterally placed facets for articulation with the first pair of ribs. The aortic groove runs open and delimited by laminar bone from the complex centrum to at least the vertebra centrum 9.

Etymology. The specific name paraiba (a noun in apposition) refers to the modern river Paraíba do Sul, which crosses the geological basin where the fossil was collected; gender feminine.

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Figures

Fig. 2. Taubateia paraiba, DGM 17-P, holotype. Shale slab with fossil impression from the Tremembé Formation, Taubaté Basin (a) and the cast in latex (b).

Fig. 3. Comparison between an interpretative drawing of Taubateia paraiba (a) and a Hypostomus sp. neurocranium (b), both in ventral view. Abbreviations: acm, articular condyle for metapterygoid; af, articular facet for rib on v6; ag, aortic groove; bl, basioccipital lateral process; bo, basioccipital; cc, Weberian complex centrum; ex, exoccipital; exf, exoccipital foramina; fr, frontal; le, lateral ethmoid; ler, lateral ethmoid ridge for metapterygoid; me, mesethmoid; md, mesethmoid disk; os, orbitosphenoid; pr, prootic; ps, parasphenoid; pt, pterotic-supracleithrum; rb, rib; sp, sphenotic?; trl, transcapular ligament; tvp, transverse process of the Weberian compound centrum; v6, sixth vertebrae.

Fig. 4. Taubateia paraiba, most anterior part of the neurocranium showing mesethmoid features: a, original fossil impression sprinkled with ammonium chloride; b, cast in latex sprinkled with ammonium chloride. Abbreviations: ac, mesethmoid anterior cornua; mc, mesethmoid crest; md, mesethmoid disk; me, mesethmoid; mmc, mesethmoid median cleft.

Fig. 5. Taubateia paraiba, posterior region of the neurocranium and first vertebrae articulated: a, fossil sprinkled with ammonium chloride; b, interpretativedrawing.Abbreviations: af,articular facet forrib on v6; ag, aorticgroove; bl, basioccipital lateral process; bo, basioccipital; cc, Weberian complex centrum; ex, exoccipital; exf, exoccipital foramina; hbf, hyomandibular branch of facial nerve foramen; pr, prootic; pt, pterotic-supracleithrum; tgf, trigeminofacial foramen; v6, sixth vertebrae.