Bothriospondylus madagascariensis, Lydekker, 1895
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https://doi.org/10.5281/zenodo.4651066 |
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https://doi.org/10.5281/zenodo.15577092 |
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persistent identifier |
https://treatment.plazi.org/id/585787AF-FFA2-1A4A-895A-C758115681B2 |
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Felipe |
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Bothriospondylus madagascariensis |
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CARPUS
The carpus of
? Bothriospondylus madagascariensis
preserves five elements arranged in three rows (Fig. 2C). The five elements display a rugose surface, suggesting the presence of cartilage in life.
Proximal carpals
There are two proximal carpal elements.
The first (MNHN MAJ 289-2; Fig. 3 View FIG A-C) has a crescent-like shape (the “torus-like element” of Lavocat 1955b, c). The height is regular, but the element becomes thick medially. The distal surface is more flattened medially to contact the proximal surface of the larger element of the carpus (the “main bone” of Lavocat 1955b, c). It is placed antero-medially on this element (Fig. 2D). This bone is tentatively interpreted as the radiale (r), because of its contact with the radius.
The second proximal carpal (MNHN MAJ 289- 8; Fig. 3D, E, G View FIG ) is subcylindrical. It is inclined dorsolaterally. Its distal end is firmly fused with the posterior part of the proximal surface of the “main bone” ( Fig. 3E View FIG ; see below “distal carpals”). The suture between the two elements is only visible in posterior view of the “main bone”. This element is tentatively identified as the intermedium (i), because of contact with the radius and its posterolateral position to the radiale (Fig. 2D).
Distal carpals
There are four distal carpal elements.
The larger element of the carpus represents what Lavocat named the “main bone” ( Lavocat 1955b, c). This bone (MNHN MAJ 289-8; Fig. 3 View FIG D-G) has an elliptical outline in proximal view. It is taller proximodistally than any other carpal. The proximal surface is slightly convex if we except the fused intermedium (see above “proximal carpals”), and the distal surface bears two unequal shallow concavities (the medial being the largest) separated by a low osseous ridge. The anterolateral and posterior surfaces are pierced by foramina. The element is also pierced right through from the distal edge of the lateral surface to the lateral edge of the distal surface; this opening is of uncertain interpretation. In articulation, the distal surface of this “main bone” covers the proximal end of the first metacarpal (mcI) medially and the two adjacent distal carpals of smaller size laterally (which overlap the second and third metacarpals; Fig. 2C, D). This bone is identified as the distal carpal one (dc1) considering its position above the mcI. Its position relative to the two distal carpals suggests it is a composite element that is fused with one or two centrale(s) (dc1 + c), as already suggested by Lavocat (1955b, c). These two hypothetical centrales could thus represent a “centrale” row fused with the first distal carpal. According to this hypothesis, the “main bone” would represent a fusion between three different levels: the intermedium (proximal row, see above), the two centrale (“middle” row) and the first distal carpal (distal row). The “main bone” is thus identified here as “dc1 + c + i”.
The second distal carpal (MNHN MAJ 289-5e; Fig. 3H, I View FIG ) has a 8-shaped proximal outline that is oriented anteroposteriorly, with the anterior part smaller than the posterior one. This second distal element is placed on the posterior part of the proximal end of the second metacarpal (mcII) (Fig. 2D). It contacts the mcI laterally and extends its proximal surface laterally. Although it is unclear on the original specimen, the CT study of the manus reveals the absence of fusion between this element and the two first metacarpals. It is identified as the distal carpal 2 (dc2) according to its position.
The third distal element (MNHN MAJ 289-11; Fig. 3 View FIG J-M) is ovoid. Its medial surface is flattened to contact the dc2, and the distal one is slightly bevelled proximolaterally. The posterior surface is slightly convex and corresponds to the presumed contact with the fourth distal element (Figs 2D; 3K). In proximal view, a shallow groove extends anteroposteriorly on the posterior two thirds of the bone, while the anterior third displays a large depression which corresponds to the opening on the distal part of the anterolateral surface of the dc1 + c + i. This third distal element is located laterally to the dc2 and recovers the anteromedial part of the proximal end of the metacarpal III (mcIII) (Fig. 2D). It is identified as the distal carpal 3 (dc3).
Because it was not found in articulation, the position of the fourth element (MNHN MAJ 289-7; Fig. 3 View FIG N-Q) is unclear and subject to interpretation. Here, we postulate this element is astride the lateral part of the proximal end of the mcIII and the entire proximal surface of the metacarpal IV (mcIV) (Fig. 2D). This assumption is supported by a planar and circular surface on the medial surface of the bone, which could represent a contact with the posterior surface of the dc3 according to our interpretation (Figs 2D; 3N). So, we consider this element as the distal carpal 4 (dc4), even if it is also possible to consider it as the ulnare or a fusion between dc4 and ulnare. This bone is the second larger after the dc1 + c + i. It has a D-like outline in proximal view, with a plane anterior surface in our hypothesis. The proximal surface is convex while the distal one is plane to contact the proximal end of the mcIII and mcIV according to this orientation. It is pierced by a large foramen on the anterior surface.
METACARPALS
The mcI-III (mcI: MNHN MAJ 289-5a,c; mcII: MNHN MAJ 289-5b; mcIII: MNHN MAJ 289-6; Fig. 4A, B View FIG ) were found in articulation. Although the mcIV-V (mcIV: MNHN MAJ 289-9a; mcV: MNHN MAJ 289-9b; Fig. 4C, D View FIG ) were found separated from the first three, there is no doubt about the tubular arrangement of the manus. McII is heightened relative to the mcIII, but in natural position the proximal articular surfaces of these two bones should be on the same level while the shift between the two first metacarpals is natural according to the position of the dc2 (Figs 2A, B; 4A). The metacarpals are gracile and present a subvertical orientation in a digitigrade posture, as observable in many neosauropods and Mamenchisaurus youngi Pi, Ouyang & Ye, 1996 or Lapparentosaurus Bonaparte, 1986 ( Ogier 1975; Ouyang & Ye 2002). They contact each other proximally and distally with small articular surfaces (Fig. 2A, B), as usually observed in sauropods ( Apesteguía 2005). McI-IV are of equivalent size, nevertheless the first is slightly smaller as in all non macronarian sauropods ( Wilson 2002) and Camarasaurus lewisi Jensen, 1988 ( McIntosh et al. 1996a). The distal part of the fifth metacarpal is broken, and it is thus impossible to determine if this element is really smaller than the mcIV as in Ferganasaurus Alifanov & Averianov, 2003 . The proximal articular surface of the first metacarpal is subrectangular but those of other metacarpals are subtriangular ( Fig. 4E View FIG ). The distal surfaces of metacarpals I-IV are subrectangular and divided in two condyles. Both the proximal and distal articular surfaces are perpendicular to the longitudinal axis of diaphyses. The articular surfaces for the phalanges extend on the anterior face of the distal end of the metacarpals, in contrast to Brachiosaurus Riggs, 1903 , in which these surfaces become restricted to distal surface ( Janensch 1922, 1961). Like in Shunosaurus Dong, Zhou & Zhang, 1983 ( Zhang 1988) , Lapparentosaurus ( Ogier 1975) , and Camarasaurus Cope, 1877 ( Osborn 1904) , this peculiar morphology allows the phalanges to articulate at approximately 90° (Fig. 2A, B). This suggests a highest mobility with a possibility of flexor movements contrary to the single, rigid, block-like structure postulated by Bonnan (2003).
PHALANGES
Only five phalanges belonging to the digits I to III have been collected ( Fig. 4 View FIG F-J). The first phalanx of the digit I (I-1; MNHN MAJ 289-5d; Fig. 4H View FIG ) is longer proximodistally than transversely and of rectangular shape, contrary to the first phalanx broader transversely than proximodistally in other sauropods ( Upchurch 1998; Wilson & Sereno 1998; Wilson 2002; Upchurch et al. 2004). The proximal articular surface is twisted laterally relatively to the whole phalanx. This morphology confers to the phalanx a laterally inclined position relatively to the shaft of the first metacarpal, and a divergent arrangement to other phalanges (Fig. 2A). Although there is no collateral fossa, this phalanx I-1 displays a strong concavity on the lateral surface of the distal end. In distal view, the articular surface is rectangular, contrary to Lapparentosaurus and some other sauropods where this surface is trapezoid. The first phalanges of digit II and III (II-1, MNHN MAJ 289-4a and III-1, MNHN MAJ 289-1; respectively Fig. 4I View FIG and Fig. 4J View FIG ) are wider than long and their distal articular surfaces extend dorsally and ventrally. The ungual of digit I (I-2 or pollex, MNHN MAJ 289-10; Fig. 4F, G View FIG ) is relatively conical and slightly curved ventrally in lateral view. It only displays a slight longitudinal groove on its lateral surface. Its proximal surface is transversely slightly compressed and presents two articular facets (the medial one is the larger). Following the twist of phalanx I-1, the pollex is also slightly inclined laterally, leading its lateroventral edge to contact the ground (Fig. 2A). The ungual of digit II (II-2, MNHN MAJ 289-4b; Fig. 4I View FIG ) is very reduced, wider than longer, and naillike. As in sauropods, digit II (and probably digit III) has two phalanges ( Upchurch 1998; Wilson & Sereno 1998; Wilson 2002; Upchurch et al. 2004). This lead us to consider the following phalangeal formula: 2-2-2?-?-?.
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.
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