Palaehoplophorus meridionalis Ameghino, 1904

Ruiz, Laureano Raúl González, Reato, Agustina, Cano, Martín & Martínez, Oscar, 2017, Old and new specimens of a poorly known glyptodont from the Miocene of Patagonia and their biochronological implications, Acta Palaeontologica Polonica 62 (1), pp. 181-194 : 185-190

publication ID	https://doi.org/ 10.4202/app.00280.2016
persistent identifier	https://treatment.plazi.org/id/038F87E9-FFCE-917A-FCDE-F8B7D5AC33E6
treatment provided by	Felipe
scientific name	Palaehoplophorus meridionalis Ameghino, 1904
status

Treatment

Figs. 3–7 View Fig View Fig View Fig View Fig View Fig .

Type material: MACN A 11737 View Materials , caudal tube ( Fig. 4A View Fig ); MACN A 11137 View Materials , three fragments of 4, 2, and 2 articulated osteoderms and 12 disarticulated osteoderms of the dorsal carapace, and one osteoderm of the caudal ring ( Fig. 3 View Fig ) .

Nomenclatorial remarks: Ameghino (1904) in the original description mentioned as type material a caudal tube and osteoderms of the dorsal carapace, but described only the caudal tube (subsequently figured by Rovereto 1914: pl. 2: 3). The only evidence about the association of the type material (caudal tube plus osteoderms) is that they all were mentioned in the original description, and the osteoderms (MACN A 11137) are the only osteoderms assigned to Palaehoplophorus meridionalis in the collection. Accordingly, we suppose that they belong to the same individual or at least they are the osteoderms mentioned by Ameghino (1904) and collectively they should be considered as the holotype.

Type locality: Lower and middle levels of Río Fénix and Lago Blanco (formerly Laguna Blanca) ( Ameghino 1906).

Type horizon: Río Mayo Formation , middle–late Miocene.

Material.—MPM-PV 17410, 250 complete and 29 fragments of osteoderms, left half of the atlas, anterior portion of a caudal vertebra, medial and distal portion of right unla, right cuboid, right ectocuneiform, 1 st right ungual phalanx, 12 indeterminate postcranial fragments ( Figs. 5–7 View Fig View Fig View Fig ); from northern slope of Meseta de Guenguel (Santa Cruz Province), Río Mayo Formation. MACN A 11132, distal portion of the caudal tube ( Fig. 4B View Fig ) according to MACN database from “Rionegrense”. Although, the provenance of MACN A 11132 is lower and middle levels of Río Fénix and Lago Blanco ( Río Mayo Formation , late–middle Miocene) because some mammals from this area of old collections were labeled “Rionegrense” (see Ameghino 1904, 1906).

Emended diagnosis (of Ameghino 1904: 286–287).—Osteoderms of the dorsal carapace with the rosette pattern (similarly to Propalaehoplophorus , Neosclerocalyptus , and Glyptodon , and absent in Neuryurus , Doedicurus , and Panochthus ), with a circular or ellipsoidal flat central figure (concave in Palaehoplophorus antiquus , convex in Protoglyptodon sagradoi ), surrounded by one row of 8–12 angular peripheral figures (one of rounded figures in Aspidocalyptus castroi , two plus one incomplete in Palaehoplophorus antiquus , one of small plus one of larger figures in Palaehoplophoroides rothi ), defined by deep and narrow sulci (shallow and narrower in Glyptatelus , Propalaehoplophorus , and Neosclerocalyptus , wide and deeper in Glyptodon and Palaehoplophoroides rothi , obscurely defined in Palaehoplophorus antiquus and Protoglyptodon primiformis ). Cylindrical caudal tube (absent in Propalaehoplophorus and Glyptodon ) distally curved dorsally (straight in Palaehoplophorus antiquus , totally curved Palaehoplophoroides rothi ).Composedbyflatorslightlyconvex osteoderms (elevated cone-like in Palaehoplophoroides rothi ), without peripheral figures (with peripheral figures in Palaehoplophorus antiquus and Protoglyptodon ), separated by narrow sulci (wider in Protoglyptodon and Aspidocalyptus castroi ) with conspicuous and numerous foramina (more than 15). The distal portion is formed by 1–2 terminal osteoderms surrounded by a ring of 6–7 small osteoderms (absent in Palaehoplophorus antiquus ). The distal lateral osteoderms are the larger of the caudal tube (similar to Palaehoplophorus antiquus ) but the big terminal osteoderms (of Plohophorus , Lomaphorus , Neosclerocalyptus ) or the large excavated figures of Panochthus and Doedicurus are absent.

Description.— Dorsal carapace (anterior region): Fixed osteoderms (MPM-PV 17410), small sized ( Table 1), quadrangular, rectangular, trapezoidal or pentagonal osteoderms

Fig. 5A View Fig ). They have a large circular, sub-circular or ellipsoidal central figure, which occupies most of the dorsal surface of the osteoderm, and is surrounded by foramina. The peripheral figures are reduced, especially the lateral and posterior figures. Ventrally the osteoderms are flat or slightly convex.

Movable and semi-movable osteoderms (MPM-PV 17410), rectangular, quadrangular or exceptionally trapezoidal osteoderms. The movable osteoderms ( Fig. 5C View Fig ), larger than the semi-movable osteoderms ( Fig. 5B View Fig ; Table 1), have beveled sagittal section due to the opposite antero-dorsal and postero-ventral articular surfaces ( Fig. 5C View Fig 2 View Fig ). In a single row, movable osteoderms are placed laterally close to the lateral margin of the carapace, then internally the semi-movable osteoderms, and finally the fixed osteoderms, going from postero-ventral articular surface oblique (= movable) in the movable osteoderms to posterior perpendicular (= fixed) articulations in the semi-movable and fixed osteoderms, keeping the semi-movable osteoderms a reduced antero-dorsal articular surface oblique. Those are incomplete movable rows of osteoderms that are placed ventrally at the antero-lateral region that become fixed to the dorsal region of the carapace. Both movable as semi-movable osteoderms have a circular central figure surrounded lateral and posteriorly with foramina, while peripheral figures are absent in movable osteoderms and reduced in semi-movable osteoderms. Ventrally are slightly concave, especially in the posteriormost region.

Dorsal carapace (middle region): Fixed osteoderms (MPM-PV 17410), the anteriormost osteoderms are generally rectangular or pentagonal, and the posteriormost ones quadrangular, pentagonal or hexagonal. Osteoderms progressively increase in size from the anterior to posterior ( Table 1). The anteriormost osteoderms have circular or elliptical central figure with the major axis coincident with the antero-posterior axis of the carapace ( Fig. 5D View Fig ), and the posteriormost osteoderms have a circular central figure ( Fig. 5E View Fig ). From the anteriormost to the posteriormost and from the lateral to the dorsal region of the carapace, the peripheral figures progressively increase size; in the anteriormost osteoderms the lateral figures are reduced or absent and in posteriormost osteoderms all (anterior, laterals and posterior) have 8–12 peripheral figures, but where there are more than ten, usually two of them are much smaller. In the intersections of the sulci there are well developed foramina. Accessory peripheral figures are in general absent. Ventrally the osteoderms are flat or slightly convex.

Lateral margin osteoderms (MPM-PV 17410), rectangular osteoderms with sharp ends ( Fig. 5F View Fig ) have an ellipsoidal central figure anteriorly that is laterally surrounded by a row of small foramina, and by poorly defined and generally reduced peripheral figures. The anterior margin presents a perpendicular articular surface while the posterior is sharp and does not articulate with any other osteoderm. The ventral surfaces are slightly concave or convex.

Dorsal carapace (posterior region): Fixed osteoderms ( MACN A 11137 View Materials , type; MPM-PV 17410 ), quadrangular, pentagonal, or hexagonal osteoderms, some could be rectangular with the major axis perpendicular or parallel to the antero-posterior axis of the carapace, generally of large sizes ( Figs. 3A–N View Fig , 5G, H View Fig ; Table 1). Fixed osteoderms have a circular central figure that becomes an ellipse posteriorly with the major axis transversal to the antero-posterior axis of the carapace, usually surrounded by 8–11 peripheral figures, and with foramina at the intersections of the sulci that delimit the figures. The presence of more than one or two accessory peripheral figures in the anterior or posterior region (outside of the row surrounding the central figure) is common, in some cases forming a complete anterior and/ or posterior row of up to six figures. Towards the margins of the carapace fixed osteoderms become smaller but keep the described pattern. Generally, they are ventrally concave .

Posterior margin osteoderms (MPM-PV 17410), qadrangular osteoderms that become posteriorly thinner ( Fig. 5I View Fig ). They have a circular or sub-circular central figure contacting the posterior margin of the osteoderm and surrounded by foramina. They have an anterior roughened region, followed posteriorly by a region with three peripheral figures, and occasionally an accessory latero-anterior figure. They have no lateral or posterior peripheral figures. Foramina that are located at the intersections of the sulci that delimit the figures are larger. Posterior margin osteoderms are ventrally concave.

Caudal carapace (caudal rings): Osteoderms from the 1 st proximal row ( MACN A 11137 View Materials , type), pentagonal osteoderms, with concave anterior margin concave in frontal view), two perpendicular lateral articular surfaces, and two perpendicular posterior articular surfaces ( Fig. 3O View Fig ). The posterior articular surfaces are at an oblique angle between them forming a vertex pointing posteriorly. A sub-circular central figure contacts the posterior margin of the osteoderm, with five very small anterior peripheral figures, and four foramina at the intersections of the sulci that delimits the figures. The ventral surface is concave .

Movable osteoderms from a proximal row (MPM-PV 17410), these pentagonal osteoderms have a large, oblique, antero-dorsal articular surface that covers ca. 40% of the surface and tubercle-like projections in the anterior margin ( Fig. 5J View Fig ). An intermediate region with 3–4 foramina and three peripheral figures is followed by an ellipsoidal central figure with its major axis transverse to the carapace surrounded by a row of foramina. The lateral and posterior articular surfaces are perpendicular. Two obliquely oriented, posterior articular surfaces form a vertex pointing posteriorly. The ventral surface is flat or slightly concave.

Fixed osteoderms from a distal row (MPM-PV 17410), two adjacent osteoderms of the proximal row articulate rigidly with one osteoderm of the distal row ( Fig. 5K View Fig ). These osteoderms are pentagonal with two anterior, obliquely oriented, perpendicular articular surfaces, forming an anteriorly oriented vertex. The lateral and posterior articular surfaces are perpendicular. These osteoderms have a sub-circular central figure reaching the posterior margin, and surrounded posteriorly and laterally by a row of foramina; they typically have no peripheral anterior figures (exceptionally they can have one). The ventral surface is slightly concave.

Caudal carapace (caudal tube): MACN A 11737 View Materials (type), the caudal tube is mostly cylindrical but somewhat depressed at its anterior and posterior portion (taphonomic deformation?) it is slightly narrowed and curves dorsally at its distal portion ( Fig. 4A View Fig ). The total length is 38.2 cm, the dorso-ventral diameter decreases from the anterior (10.6 cm) to the posterior region (6.86 cm) and the transverse diameter increases from the anterior (7.8 cm) to the middle region 9.1 cm), and decreases to the posterior region (8.7 cm). The caudal tube is made of osteoderms arranged in rings anteriorly that become disordered distally. The osteoderms from the 1 st ring have an antero-dorsal articular surface. The osteoderms of the caudal tube have a rough dorsal surface without surface sculpturing, unlike the osteoderms from the carapace (i.e., figures, sulci), and are separated by sulci in which are located several foramina (ca. 15). Posteriorly, lateral osteoderms are larger than osteoderms in dorsal or ventral positions. Distally, a ring of seven osteoderms plus two terminal osteoderms “close” the caudal tube .

MACN A 11132 View Materials , represented by a distal portion of caudal tube, has a length of 8.7 cm, and an antero-posterior and dorso-ventral diameters in the preserved region of 6.2 cm and 7.3 cm, respectively ( Fig. 4B View Fig ). The osteoderm pattern is the same as the type ( MACN A 11737 View Materials ), although distally a ring of six osteoderms and one terminal osteoderm “close” the caudal tube .

Osteoderms from indeterminate region: Semi-movable osteoderms (MPM-PV 17410), pentagonal osteoderms ( Fig. 5L View Fig ). The larger pentagonal osteoderms have a large circular, sub-circular or elliptical central figure surrounded laterally and posteriorly by foramina, with no peripheral figures. The antero-dorsal articular surface has small tubercle-like projections in the anterior margin. In lateral view the antero-dorsal articular surface is slightly concave, and the transition between the osteoderm surface and the dorsal articulation is abrupt. The smaller pentagonal osteoderms have a reduced circular, sub-circular or ellipsoidal central figure and foramina, with no peripheral figures and the antero-dorsal articular surface is smaller. Osteoderms are ventrally flat or slightly convex. These osteoderms could belong to a nuchal band placed between the dorsal carapace and cephalic shield or to an anterior caudal ring, but they do not belong to the typical semi-movable osteoderms of the antero-lateral region of the dorsal carapace or to the typical caudal ring osteoderms.

Axial skeleton (vertebral column): Atlas (MPM-PV 17410), the dorsal arch (= neural arch) has a greater antero-posterior diameter (23.1 mm) than the ventral arch (= center) (15.2 mm). The vertebral foramen (= neural canal) has a dorso-ventral diameter of 27.4 mm and although only the left half of the atlas is preserved, the outline of the vertebral foramen indicates the ventral half is wider than the dorsal half. In anterior view ( Fig. 6A View Fig ), the major axis of the prezygapophysis is concave and dorso-ventrally oriented (25.1 mm × 18.0 mm), and the anterior intervertebral foramen is situated dorsally and internally. In posterior view ( Fig. 6A View Fig 2 View Fig ), the postzygapophysis with its concave major axis transversally oriented (13.4 mm × 22.2 mm); the vertebroarterial foramen is dorsally located in the midline. The ventral arch has an internal tuberosity (= tubercle) where the odontoid process of the axis articulates. In lateral view and externally ( Fig. 6A View Fig 3 View Fig ), only the base of the transverse process is preserved (23.2 mm × 9.0 mm), dorsally the intervertebral foramen is located within the alar foramen, and ventral to the transverse process another opening of the alar foramen could be observed.

Caudal vertebra (MPM-PV 17410), has preserved the anterior portion of the vertebral body (= centrum) and a portion of the transverse processes ( Fig. 6B View Fig 1 View Fig ). The anterior intervertebral articular surface has a dorso-ventral diameter of 37.1 mm and a transverse diameter of 54.2 mm. The preserved portion of the transverse processes are long (73.0 mm) and wide (22.4 mm), expanding even more distally (25.3 mm), while directed downward and forward slightly, which is the morphology of the first free caudal vertebrae.

Appendicular skeleton (anterior member): Right ulna (MPM-PV 17410), most of the proximal extremity (= olecranon) of the ulna is missing; only the anconeal process was preserved ( Fig. 7A View Fig ). Medially, the ulna has a large and wide trochlear notch (= semilunar notch, sigmoid cavity), a developed coronoid process for the articulation with the humerus, and the smaller radial notch (= fossa lunar) for the proximal articulation with the radius, all of them transverse to the longitudinal axis of the ulna. The diaphysis of the ulna is a straight, compressed triangular prism with a sharp and long interosseous crest. At the distal extremity there is a small styloid process, a large semicircular facet for the articulation with the cuneiform, an anterior facet from the contact with the radius, and a posterior smaller and rounded facet for the articulation with the pisiform. From the coronoid process to the styloid process the unla is 77.3 mm long and has a transverse diameter of 31.1 mm (not completely preserved).

Appendicular skeleton (posterior limb): Right cuboid (MPM-PV 17410), a pyramidal shape bone with a base of 38.5 mm and 21.4 mm height, having four articular facets and a posterior tuberosity. In the internal lateral position the navicular facet is triangular ( Fig. 7B View Fig 1 View Fig ). Dorso-laterally, a semi-circular facet for the articulation with the calcaneum ( Fig. 7B View Fig 3 View Fig ). Facets for articulation with the 4 th and 5 th metatarsal are situated antero-ventrally ( Fig. 7B View Fig 2 View Fig ); the facet for the 4 th metatarsal is larger (22.4 mm × 13.0 mm) than the facet for the 5 th metatarsal (15.8 mm × 9.8 mm). Separated from the cuboid’s body by a neck is a triangular plantar tuberosity.

Right ectocuneiform (MPM-PV 17410), the triangular ectocuneiform has a posteriorly oriented, rounded apex, with a base that measures is 28.8 mm, 35.2 mm height and 12.4 mm thickness. The smaller proximal articular facet (26.5 mm × 17.0 mm) is slightly concave, for articulation with the navicular ( Fig. 7C View Fig 1 View Fig ). The larger distal articular facet (33.8 mm × 31.2 mm) occupies the entire surface of the bone and articulates with the 3 rd and 4 th metatarsal ( Fig. 7C View Fig 3 View Fig ). A small facet (10.9 mm × 8.7 mm) at right angle to the distal facet for the 4 th metatarsal contacts internally the cuboid and/or the 4 th metatarsal ( Fig. 7C View Fig 4 View Fig ); another small facet (5.9 mm × 7.5 mm) at right angle of the distal facet of the 3 rd metatarsal internally contacts the 2 nd metatarsal ( Fig. 7C View Fig 2 View Fig ).

Right 1st ungual phalanx (MPM-PV 17410), has a proximal, concave, transversely oriented facet for the 2 nd phalanx. Ventrally, the ungual crest (= tubercle) possesses a sub-ungual foramen in the center and a smaller foramen in the external margin ( Fig. 7D View Fig 2 View Fig ). Distally, the ungual process is compressed and internally curved ( Fig. 7D View Fig 1 View Fig ). The antero-posterior length is 29.6 mm and the transverse diameter at the base is 24.1 mm.

Stratigraphic and geographic range.—Middle–late Miocene; Patagonia, Argentina.