Brachyplatystoma promagdalena, Lundberg, 2005

Lundberg, John G., 2005, Brachyplatystoma promagdalena, new species, a fossil goliath catfish (Siluriformes: Pimelodidae) from the Miocene of Colombia, South America, Neotropical Ichthyology 3 (4), pp. 597-605 : 599-601

Brachyplatystoma promagdalena , new species

Figs. 1a , 2a , 3 , 4a , 5a , 6a

Brachyplatystoma sp. Lundberg, 1997:78 (description, occurrence, fig, 5.7A, p. 78); Lundberg et al., 1998: 23 (listed); Lundberg, 1998:59 (listed); Gayet & Meunier, 2003: 507 (listed).

Holotype. IGM 183062 , a three-dimensional, partial but undistorted anterior section of the vertebral column, the Weberian complex, including first six centra, of which second through fourth are fused as the Weberian compound centrum ( Chardon, 1968), plus proximal ends of left fourth and fifth transverse processes. Maximum dimensions of specimen are: length 89.9 mm, width 50.2 mm, and depth 35.0 mm.An epoxy cast of the holotype, ANSP 180898, is deposited at the Department of Ichthyology , Academy of Natural Sciences, Philadelphia.

Locality and Geological Age. Miocene Villavieja Formation of the Honda Group in the southern end of the río Magdalena basin near the town of Villavieja, Huila Department, Colombia at approx. 3 o 5’N, 75 o 13’W (map in Guerrero, 1997, fig. 2.1, p. 16). The lowest part of the Villavieja Formation or “Fish Bed” from which the fossil came has been 40Ar/39Ar dated at 13.0- 12.8 Ma (Guerrero, 1997).

Diagnosis. An extinct species of Brachyplatystoma , subgenus Malacobagrus , distinguished by three uniquely autapomorphic features of the anterior vertebrae. 1) Fifth centrum with a prominent midventral expansion ( Figs. 1a , 2a , 3 , 4a , 5a ) that is coarsely sculptured with deep cavities and heavy ridges. This expansion is a central attachment site of the swim bladder; 2) Compound centrum with relatively prominent anterolateral processes before the ventral ends of the ossa suspensoria ( Figs. 1a , 2a , 3 , 4a ); 3) Compound centrum with low but clearly defined transverse ridge crossing its ventral surface in an anteriorly concave curve posterior to aortic canal foramen and anterolateral processes ( Figs. 2a , 3 , 4a , 5a ). This ridge is not to be mistaken as an intervertebral joint with the first centrum.

Brachyplatystoma filamentosum and B. capapretum of the subgenus Malacobagrus have moderately expanded attachment sites for the gas bladder on the fifth centrum with surface irregularities but not as coarsely rugose as in the new species ( Figs. 2b , 4b , 5b ). Other species of the subgenus Malacobagrus ( Figs. 2c , 4c , 5c ) plus B. vaillantii ( Figs. 2d , 4d , 5d ) and B. tigrinum have weaker anterolateral processes on the compound centrum, and a vaguely delimited ventral ridge on the compound centrum. Brachyplatystoma platynenum and B. juruense have prominently sharp and vertically elevated bony collars around the compound centrum.

Etymology. The name promagdalena is applied here as a noun in apposition to the neuter generic name Brachyplatystoma , and refers to the spatiotemporal provenance of the fossil species in central Colombia before the valley of the río Magdalena was formed by uplift of the Eastern Andes.

Description. Figs. 1a , 2a , 3 , 4a , 5a and 6a illustrate and identify the features described below. On its dorsal surface the Weberian complex has broken neural arch material flanking the neural canal beginning behind first centrum from the compound to sixth centra, and on the left side the proximal parts of the enlarged fourth transverse process and only the base of fifth transverse process. The ventral side is dominated by a wide first centrum, anteriorly broadened compound centrum with the anterior foramen of a long deeply embedded aortic canal within the compound, fifth and sixth centra, transverse ridge and paired ossa suspensoria, and broadly pitted gas bladder attachment site on the fifth centrum. The salient features of the left and right sides are the enlarged first centrum, anterolateral processes and ossa suspensoria of the compound centrum, followed by deeply vertical, smooth surfaces covered by a veneer of superficial ossification on the compound, fifth and sixth centra.

The first vertebra comprises a centrum only without neural arches, zygapophyses or transverse processes. The first centrum is coarsely sponge-like in texture; its articulation surface for the basioccipital is that of a typical vertebra, cardiform, slightly concave and surrounded by a thick, rugose rim; the central focus of growth rings on the anterior face is three times closer to dorsal rim than ventral rim. The joint between the first and compound centra is straight and nonsutural dorsally just anterior to the neural arches and transverse processes of the compound centrum, otherwise the joint is deeply and complexly sutural. The first centrum contributes a small laterally raised projection to each anterolateral process of the compound centrum.

The compound centrum is about 2.6 times the dorsolateral length of the first centrum. The anterior end of the compound centrum carries the bases of the paired fourth transverse processes, paired anterolateral processes in front of and adjacent to lower ends of the ossa supensoria, and wide aortic canal foramen followed posteriorly by a curved raised ridge (not to be confused with an intervertebral joint). The aortic canal anterior foramen is asymmetrically placed to the right side and flanked on its right by a small pit. Each os suspensorium runs from below the proximal end of the fourth transverse process anteroventrally to the anterolateral process. Paired shallow channels for the postcardinal veins course obliquely along the dorsal sides of their respective os suspensorium; the right cardinal vein channel is about twice the diameter of the left reflecting an asymmetry of the size of these major blood vessels that is common in Siluriformes . The fourth transverse process is horizontal, flat except for a shallow concavity near the neural arch, and lacks prominent transverse crests. The dorsal surface of fourth transverse process has spongy or finely trabeculated texture; the ventral surface is covered with dense, smooth veneer of superficial ossification like that of the adjacent centra. Proximally the anterolateral limb of the fourth transverse process forms a wide, flat-roofed trough above the os suspensorium (trough occupied by the tripus in articulated skeletons but missing from fossil); trough terminating distally at an abrupt distal expansion. The posterior limb of the fourth transverse process arises behind base of the os suspensorium, projects posterolaterally about 45 o off longitudinal axis, and is thickened reflecting the development of the bony gas bladder platform. The compound centrum has a flattened ventral surface; its ventrolateral corners abruptly curve dorsad. The joint between the compound and fifth centra is deeply and complexly sutural across ventral midline in front of the expanded gas bladder attachment site, then laterally abutting and scarcely suturing along vertical sides of centra.

The fifth centrum is longer than the combined lengths of the first and compound centra. The much expanded ventromedian gas bladder attachment site contains five large, irregular pits and several smaller pits separated by heavy walls and ridges. The sides of the fifth centrum are laterally compressed and dorsally constricted above the gas bladder attachment site. The proximalmost part of the fifth transverse process forms a horizontal shelf in line with the fourth transverse process. The fifth and sixth centra greatly compressed along their shallow sutural joint. The sixth centrum, like the fifth, is compressed and has vertical sidewalls; its transverse process and posterior end are broken.

Figures

Fig. 1. Weberian complexes in dorsal view of the fossil and modern Brachyplatystoma species, a, B. promagdalena, IGM183062, b, B. filamentosum, DU F1052, from the ríoApure, Venezuela; c, B. rousseauxii, DU F1078, from the río Apure, Venezuela; d, B. vaillantii, DU F1034, from the río Apure, Venezuela. Scale bars equal to 1 cm.Abbreviations:ALP, anterolateral processes; ALTP4, anterior limb of fourth transverse process; C1-CC, First centrum-compound centrum joint; MVE, midventral expansion on fifth centrum; NA, neural arch; NC, neural canal; NS4, neural spine of fourth vertebra; PLTP4, posterior limb of fourth transverse process; SBN, spongy bone, TP4C, crests on fourth transverse process, TP5, fifth transverse process; TP6, sixth transverse process.

Fig. 2. Weberian complexes in ventral view of the fossil and modern Brachyplatystoma species, a, B. promagdalena, IGM183062, b, B. filamentosum, DU F1052, c, B. rousseauxii, DU F1078, d, B. vaillantii, DU F1034. Scale bars equal to 1 cm.Abbreviations as in Fig. 1 plus: AACF, aortic canal anterior foramen; C1, first centrum; C7, seventh centrum; C5-C6, fifth centrum- sixth centrum joint; CC-C5, compound centrum- fifth centrum joint; OS, os suspensorium; PACF, aortic canal posterior foramen; PGB, gas bladder platform; TR, transverse ridge; TRP, tripus.

Fig. 3. Weberian complex of the fossil Brachyplatystoma promagdalena, IGM183062; a, ventral view, b, right lateral view. Abbreviations as in Figs. 1 and 2.

Fig. 4. Weberian complex in left lateral view of the fossil and modern Brachyplatystoma species, a. B. promagdalena, IGM183062, b. B. filamentosum, DU F1052, c. B. rousseauxii, DU F1078, d. B. vaillantii, DU F1034. Scale bars equal to 1 cm. Abbreviations as in Figs. 1 and 2 plus: NS5, neural spine of fifth vertebra; NS6, neural spine of sixth vertebra.

Fig. 5. Weberian complex in right lateral view of the fossil and modern Brachyplatystoma species, a. B. promagdalena, IGM183062, b. B. filamentosum, DU F1052, c. B. rousseauxii, DU F1078, d. B. vaillantii, DU F1034. Scale bars equal to 1 cm. Abbreviations as in Figs. 1, 2 and 4.

Fig. 6. Weberian complexes in anterior view of the fossil and modern Brachyplatystoma species, a, B. promagdalena, IGM183062, b, B. filamentosum, DU F1052, c, B. rousseauxii, DU F1078, d, B. vaillantii, DU F1034. Scale bars equal to 1 cm. Abbreviations as in Figs. 1 and 2 plus: C1F, central focus of growth rings; TP4T, trough below fourth transverse process.