Macrochorobates scalabrinii ( Moreno and Mercerat, 1891 )

Barasoain, Daniel, Tomassini, Rodrigo L, Quiñones, Sofía I, González-Ruiz, Laureano R, Bonini, Ricardo A & Zurita, Alfredo E, 2024, Evolutionary, taxonomical, and ecological traits of the Late Neogene armadillo Macrochorobates Scillato-Yané (Xenarthra: Cingulata), Zoological Journal of the Linnean Society (zlae 124) 202 (4), pp. 1-20 : 4-13

Macrochorobates scalabrinii ( Moreno and Mercerat, 1891)

(= Macrochorobates chapalmalensis Ameghino, 1908 new synonymy)

( Figs 2–7 ; Supporting Information, S3)

Type material:?MLP-PV articulated fragment of the pelvic shield ( Lydekker 1895: pl. XXXIII, fig. 6). This material ( Fig. 2A ) was published without a collection number and, according to Scillato-Yané (1982) and Mones (1986), it is not housed in the Museo de La Plata. We were unable to locate the type material .

Type locality and age: Valle de Santa María , Catamarca Province, Argentina. ‘Araucanian’, Late Miocene–Pliocene .

Material referred

Macrochorobates scalabrinii : CC529, almost complete articulated dorsal carapace; CRILAR-Pv-120, fixed and mobile osteoderms; CRILAR-Pv-420, fixed and mobile osteoderms; CRILAR-Pv-131, fixed and mobile osteoderms; FMNH-P14360, almost complete skull; FMNH-P14493, mandible; FMNH-P14510, cephalic shield fragment, nuchal osteoderms, almost complete articulated dorsal carapace including scapular shield, mobile bands, and pelvic shield, skull fragment including occipital area, cervical vertebrae, and distal left femur; FMNH-P14784, left hemi-mandible fragment; FMNH-P15435, skull fragment including parietal, posterior palatal, and basicranial area; FMNH-PM880, articulated dorsal carapace fragment including the last mobile band and pelvic shield; FMNH-PM1089, left hemi-mandible fragment, nuchal, mobile, and lateral osteoderms; IANIGLA-PV-120, articulated pelvic shield fragment; IBIGEO-P33, fixed osteoderm; IBIGEO-P37, fragmented mobile osteoderm; INGEO-PV-235, fixed osteoderm; JUY-P-0090, cephalic shield, fixed and mobile osteoderms; MACN PV 5345, fixed osteoderms; MACN PV 8134, left hemi-mandible fragment; MACN PV 8138, right hemi-mandible fragment; MACN PV 8144, right hemi-mandible fragment; MACN PV 8217, osteoderm fragments; MACN PV 8271, fragment of both hemi-mandibles; MACN PV 8283, left hemi-mandible fragment, mobile osteoderms; MMH-CH-84-04-56, mobile osteoderm; MMH-CH-84-04-66, mobile osteoderm; MMH-CH-85-04-113, fixed osteoderm; MMH-CH-87-7-6, mobile osteoderm; MMH-CH-87-7-69, mobile osteoderm; MMH-CH-88-6-6-6, fixed osteoderm; MMH-CH-88-6-13, fixed osteoderm; MMH-CH-88-6-15, fixed osteoderm; MMH-CH-10-4-66, mobile osteoderm; PULR-V-190, fragmented osteoderm; PULR-V-191, fragmented osteoderm; PULR-V-192, fixed osteoderm; PVSJ-652, mobile and fixed osteoderms, semi-mobile osteoderms of the scapular shield and semi-mobile osteoderms of the pelvic shield.

Materials previously referred to Macrochorobates chapalmalensis : MACN PV 5825 (originally defined as the holotype of this species), mobile and fixed osteoderms ; MACN PV 5908 , mobile osteoderm ; MACN PV 6482 , mobile and fixed osteoderms, right femur and tibia-fibula fragment ; MACN PV 7573 , palate fragment ; MACN PV 7889 , articulated dorsal carapace fragment including nuchal osteoderms, scapular shield bands, and mobile bands ; MACN PV 10267 , left hemi-mandible fragment ; MACN PV 10270 , mobile osteoderms ; MACN PV 16950 , mobile osteoderms; GHUNLPam 5066/5, fixed osteoderm; GHUNLPam 5976/1, mobile osteoderm; GHUNLPam 2291/55, mobile osteoderm; GHUNLPam 8198/96, fixed osteoderm .

Geographic and stratigraphic provenance and age: Buenos Aires Province: Cerro Azul (Late Miocene), Monte Hermoso (Early Pliocene), and Chapadmalal (Late Pliocene) formations ( Scillato-Yané 1980, 1982, Barasoain et al. 2018); La Pampa Province: Cerro Azul Formation (Late Miocene–Early Pliocene) ( Urrutia et al. 2008); Mendoza Province: Huayquerías (Late Miocene) and Tunuyán (Early Pliocene) formations ( Romano and Esteban 2019, Romano et al. 2023); San Juan Province: Las Flores (Late Miocene) and Loma de Las Tapias (Late Miocene) formations ( Contreras et al. 2013); La Rioja Province: Salicas (Late Miocene) and Toro Negro (Late Miocene) formations ( Barasoain et al. 2022b, Brandoni et al. 2023, Ruiz-Ramoni et al. 2023); Catamarca Province: Chiquimil (El Jarillal Member, Late Miocene) and Andalhuala (Late Miocene–Early Pliocene) formations ( Esteban et al. 2014); Tucumán Province: Tío Punco outcrops (Late Miocene–?Early Pliocene) ( Scillato-Yané 1982); Salta Province: Palo Pintado Formation (Late Miocene) ( Zimicz et al. 2018); Jujuy Province: Uquía (Late Pliocene), Maimará Formation (Late Miocene), and an unnominated formation (Pliocene) ( Scillato-Yané 1982, Quiñones et al. 2019); San Luis Province: Río Quinto Formation (Late Miocene) ( Strasser et al. 1998, Chiesa et al. 2019) (see Fig. 1 ).

Amended diagnosis: The same as the genus by monotype.

Descriptions and comparisons

Skull: Descriptions are based on the specimen FMNH-P14360 ( Fig. 3 ), an almost complete skull that includes the complete dental series, and the specimen FMNH-P15435 represented by a posterior fragment of skull that includes the distal ending of the palatine and the two last molariforms. The skull is elongated and larger than that of any extant Euphractinae , but considerably smaller (c. 10 cm) than that of the extinct Macroeuphractus .

In dorsal view ( Fig. 3A ), nasal bones widen toward the nasal aperture, resulting in a broad rostral region. This aspect is also observed, even more exacerbated, in Macroeuphractus , but not in other euphractines. The nasal aperture has a dorsoventrally compressed oval outline. The nasal bones are not projected over the nasal aperture, differing from most euphractines, including Macroeuphractus and Euphractus . The frontal bones are anteriorly projected between the maxillary and nasal bones with an arrow-point morphology, as in other euphractines such as Euphractus and Chaetophractus , while they are barely projected in non-euphractine armadillos. At the level of the anterior zygomatic process, there are two olfactory bulbs, much more developed than in Macroeuphractus and extant euphractines. The preserved part of the zygomatic processes infers a large and broad orbit, as occurs in other large-sized armadillos, such as Macroeuphractus and Vetelia , and the major orbital constraint is closer to the anterior zygomatic process. The cranial case is mostly flattened. The suture between the frontal and parietal bones is mostly straight, and the suture between parietals rises as an elevated sagittal crest. This represents a rare character among armadillos, only shared with Macroeuphractus outesi , in which the sagittal crest is wider but lower than in M. scalabrinii . In each parietal, there is a line of large neurovascular foramina extending parallel to the sagittal crest. The sagittal crest extends posteriorly until joining a thick nuchal crest, which is W-shaped as occurs in most Euphractinae , such as Euphractus and Macroeuphractus . The sutures between parietal and temporal bones are poorly defined, as in Euphractus and Macroeuphractus , while in other euphractines (i.e. Chaetophractus and Zaedyus ) they are well defined. The temporal fossa is enlarged, due to the posterior extent of the zygomatic squamosal process and a posterodorsal expansion of the parietals. The anteroposterior length of the parietals is approximately similar to that of the frontals; in extant euphractines the frontals are longer than the parietals, while in Macroeuphractus the parietals are longer than the frontal bones. The surface of the parietal area is rugose due to a series of scars for muscle attachment, which are far more developed than those of Euphractus , though not as much as those of Macroeuphractus .

In lateral view ( Fig. 3B ), the skull profile is mostly straight with a subtle downward inclination of the rostral region as occurs in Macroeuphractus , while in most euphractines it has a sigmoidal profile (i.e. Zaedyus ) or a flat cranial case with a marked downward inclined rostral region (i.e. Euphractus ). The premaxillary bones are less vertically expanded than in Macroeuphractus , conferring a sharp appearance to the rostral region, similar to Euphractus . The infraorbital foramen is placed right at the basis of the anterior zygomatic process, a common character in Euphractinae , while in Tolypeutinae and Dasypodidae this foramen is placed in a more proximal position. The anterior root of the zygomatic process is robust and not laterally compressed as in Macroeuphractus . The lacrimal is dorsoventrally extended, as in Macrouphractus and Euphractus , while in other euphractines (i.e. Chaetophractus ) it is much reduced. The posterior root is also robust, and the squamosal process of the zygomatic is nearly horizontal, as in Macroeuphractus , while in Euphractus it is oriented downwards. Below the posterior root, the external auditory meatus is proportionately larger than in extant euphractines, resembling that of Macroeuphractus .

Viewed ventrally ( Fig. 3C ), the infraorbital foramen and the root of the anterior zygomatic process are placed at the level of the Mf6, as in Macroeuphractus and Euphractus . The palatal suture of the maxillary bones is mostly flat, while the suture of the palatines generates a slight crest, much less elevated than that of Macroeuphractus . The palatines are a bit more posteriorly extended than in Macroeuphractus , so that the choanae aperture is placed closer to the posterior zygomatic process, as occurs in Euphractus . The choanae aperture is concave and anteriorly projected, as in Macroeuphractus , while in extant euphractines it is triangular-shaped. The entopterygoid crests slightly deviate towards the external side as they distally extend, unlike in Macroeuphractus and Euphractus , in which they are straight. The ectotympanic and entotympanic are fused composing an ossified auditory bulla, which is proportionally larger than that of Macroeuphractus . The surface of the basioccipital is mostly flat, as in Euphractus and unlike in Macroeuphractus , which has a marked anteroposterior crest. The foramen magnum has a rounded outline and is little ventrally extended, differing from Macroeuphractus and Euphractus in which it has a triangular outline and is much expanded in ventral view. The occipital condyles have a similar inclined orientation to Macroeuphractus but with less ventral development, while in Euphractus they are placed in a more horizontal position.

In posterior view ( Fig. 3D ), the nuchal crest is less robust and posteriorly developed than in Macroeuphractus , but similar to that of Euphractus . In turn, the occipital condyles are proportionately larger than in Macroeuphractus and Euphractus , and the auditory meatus is more laterally projected.

Mandible: Descriptions are mainly based on the specimen FMNH-P14493 ( Fig.4A, B ),whichincludesbothpartiallycomplete hemi-mandibles preserving the complete dental series, although the following specimens were also considered: MACN PV 8134, MACN PV 8138, MACN PV 8144, MACN PV 8271, and MACN PV 8283 (here assigned to M. scalabrinii ; see: Scillato-Yané 1982).

The mandible of M. scalabrinii is larger than that of any extant euphractine, but smaller (∼ 10 cm) than that of the extinct Macroeuphractus . The dentary is robust compared with Euphractus , but is less massive and more stylized than in Macroeuphractus . The angle between the horizontal and vertical ramus is obtuse (c. 120°). The horizontal ramus is approximately twice as long as the vertical ramus, as in Euphractus , while in Macroeuphractus the vertical ramus approximately represents two-thirds of the horizontal ramus length. Towards the proximal extreme (also in MACN PV 8283, previously assigned to M. chapalmalensis ), the dentary becomes slightly thinner, although not as much as in extant armadillos. The maximum width of the horizontal ramus is placed at the level of the mf5, as in M. chapalmalensis . On the labial side, the mental foramen is placed at the horizontal ramus between the mf2 and 3. On the lingual side, the mandibular foramen is not preserved, as this area is damaged in both hemi-mandibles. The angular process is placed slightly above the occlusal surface, as is typical in euphractine representatives. The angular process has a huge surface and its ventral edge is in continuity with that of the horizontal ramus, as occurs in Euphractus but different from that of Macroeuphractus in which it protrudes from the vertical ramus. The coronoid process is placed above the level of the condylar process as observed in all euphractines. The surface of the vertical ramus bears huge scars for muscle attachment. The mandibular symphysis is not fully fused, a typical characteristic of all armadillos.

Molariforms: Descriptions are based on the specimens FMNH-P14360 (cranium) and FMNH-P14493, MACN PV 8134, MACN PV 8138, MACN PV 8144, MACN PV 8271, and MACN PV 8283 (mandibles). Both upper and lower series are composed of 10 molariforms, while the dental formula is 9/ 10 in Euphractus and 8/ 8 in Macroeuphractus . Contrary to most armadillos, M. scalabrinii shows dental differentiation, including notable variations in size and disposition and shape of the alveolar contour.

In the upper series ( Fig. 3C ), the Mf1 is placed in the premaxilla and there is absence of the toothless spout generally developed in armadillos ( Thenius 1989). This condition has also been reported for Macroeuphractus and Vetelia ( Vizcaíno and Iuliis 2003, Barasoain et al. 2021a). All molariforms have an ovate alveolar contour and ‘chisel-shaped’ occlusal surface. Both proximal and distal wear facets are flat, and the crest between them is sharp and placed close to the anterior side of the molariform. The main axis of Mf1 to Mf3 is oblique to the main axis of the dental series, while it is parallel in Mf4 to Mf10. The Mf1 is separated from the Mf2 by a small diastema, as occurs in Macroeuphractus . The largest molariform is the Mf2, followed by the Mf5, and the smallest are Mf9 and Mf10. In Macroeuphractus , the Mf2, which is the largest, adopts the shape of a caniniform, with a notable insertion that broadens the rostral region, while the Mf5 is the second largest molariform. Although in M. scalabrinii the Mf2 is not so extremely developed as a caniniform, it also denotes a pronounced insertion easily differentiated from the rest of the molariforms. The Mf8 to Mf 10 are placed past the root of the anterior zygomatic process.

The lower series ( Fig. 4C ) shows greater differentiation in the morphology of the molariforms than the upper series. Molariforms have a ‘chisel-shaped’ occlusal surface, with both proximal and distal wear facets flat and a sharp crest between them, similar to the upper series molariforms. The alveolar contour is crescent-shaped in mf1 to mf5 and ovate in mf6 to mf10. The mf1 and mf2 are much smaller than the other molariforms and are placed closer to the anterior ending of the dentary in comparison with other euphractines. Similar morphology is observed in MACN PV 8283 (previously assigned to M. chapalmalensis ; see: Scillato-Yané 1982). Because the lower series is positioned forward with respect to the upper series, the small anterior molariforms (mf1 and mf2) occlude directly on the premaxilla; the mf1 also occludes on the premaxilla in Euphractus and Chaetophractus . The mf3 is the largest, reaching the size of the Mf2; it is followed by the mf6, mf7, and mf8. The last molariform (mf10) is reduced, although not as much as mf1 and mf2, and it is hidden by the vertical ramus of the hemi-mandible in lateral view. In Macroeuphractus , mf1 is the smallest and mf2 is the largest. In other euphractines, dental series do not show these differences in molariform size.

Femur: The specimen FMNH-P14510 is represented by a distal fragment, broken at the beginning of the third trochanter. The general morphology does not differ significantly from that of the specimen MACN PV 6482 ( Fig. 5A 1–D1 ) previously assigned to M. chapalmalensis by Scillato-Yané (1982), and also resembles that of other euphractines, such as Euphractus and Chaetophractus , although it is more robust. In Macrochorobates , the distal epiphysis preserves both internal and external condyles; the internal condyle is larger and more distally extended than the external condyle. In MACN PV 6482, the medial epicondyle is extended as an enlarged process, while it is absent in extant euphractines; in FMNH-P14510 this area is damaged and its presence cannot be confirmed. The lateral epicondyle in both specimens is larger and more laterally expanded than in extant euphractines. The greater trochanter projects slightly higher than the femoral head, which is hemispherical and bounded by the neck and a trochanteric fossa. On the medial margin, the lesser trochanter is well developed, compressed antero-posteriorly and prolonged distally to the level of the third trochanter. Notably, the third trochanter is placed closer to the distal epiphysis than in the extant euphractines. According to Copploe et al. (2015), those armadillos with higher body mass (i.e. Priodontes ) have a more distal third trochanter to compensate for tensile (bending) stresses on the lateral cortex of the femoral shaft. The body mass estimated on the basis of the material MACN PV 6482 gives a value of ~ 8.946 kg for M. scalabrini .

Tibio-fibula: The specimen MACN PV 6482 ( Fig. 5A 2–D2 ), previously assigned to M. chapalmalensis by Scillato-Yané (1982), preserves the complete tibia and distal part of the fibula. At the proximal end of the tibia, the medial facet for the femoral condyle is slightly concave; it has a thick diaphysis along the proximal half due to the presence of a prominent tibial crest that ends distally in the malleolus, as occurs in Euphractus . The fibula only has part of the diaphysis and the anterior crest, which ends in an acute process. On the distal epiphysis of the tibia, the facet for the talus is subdivided into two parts, the medial one being wider and the lateral one ending posteriorly in a triangular downward-pointing process. The fibula has an ellipsoidal facet for the calcaneus and the lateral malleolus. Tibia and fibula are fused by the epiphyses as in all Cingulata ( Burmeister 1870 –74, Scillato-Yané 1982, McDonald and Naples 2007).

Cephalic shield: The specimen FMNH-P14510 includes a fragment of the cephalic shield with eight articulated osteoderms ( Fig. 6A ). The shape of these osteoderms is more variable than those of the dorsal carapace, ranging from sub-quadrangular to hexagonal. The size of cephalic osteoderms is approximately similar to those fixed osteoderms of the dorsal carapace, as in Macroeuphractus and Euphractus , while in other euphractines (i.e. Chaetophractus , Zaedyus , and Paleuphractus ) the cephalic shield is composed of smaller and more numerous osteoderms. Their dorsal surface does not have a well-developed ornamentation pattern, although in some cases an elevated central figure that resembles those of fixed osteoderms from the dorsal carapace can be distinguished (see below).

Nuchal osteoderms: These osteoderms are associated with the specimens FMNH-P14510 ( Fig. 6B ) and MACN PV 7889. They are divided into an articular and an ornamented portion, and their general morphology is similar to that of mobile osteoderms from the dorsal carapace (see below), although substantially smaller; the main difference is that nuchal osteoderms become progressively wider towards the posterior margin, while osteoderms of the mobile bands maintain a constant width along their entire length. In Macroeuphractus and Euphractus , nuchal osteoderms do not get wider towards the posterior margin. The articular surface is flat, while the ornamented portion includes a central figure, which is much less elevated than that of mobile osteoderms from the dorsal carapace. These osteoderms are present in most Chlamyphoridae and Dasypodidae , composing one or two nuchal bands that are not attached to either the cephalic shield or dorsal carapace.

Dorsal carapace: Descriptions of the dorsal carapace ( Figs 6 , 7 ) are mainly based on two specimens. FMNH-P14510 ( Fig. 6 C, D ) is the most complete carapace reported for the genus and includes an almost complete dorsal carapace with the caudal area of the pelvic shield broken. FMNH-PM880 includes part of the last mobile band and the caudal area of the pelvic shield. Other specimens are CC529 , which includes the scapular and mobile bands, but lacks most parts of the pelvic shield; MACN PV 5345 , isolated pelvic osteoderms; and MACN PV 8283 , isolated mobile osteoderms. The comparative analyses involving relatively complete dorsal carapaces show no differences between the materials assigned to both species (see above). The general anatomy does not differ from materials previously assigned to M. chapalmalensis (i.e. MACN PV 7889 ; see Fig. 7 ).

The dorsal carapace of M. scalabrinii is composed of a scapular shield, mobile bands, and a pelvic shield ( Fig. 6C, D ). The carapace borders are serrated due to the presence of pointed osteoderms, as is typical in euphractine armadillos. The general morphology is elongated and stylized, more than Macroeuphractus and other euphractines. This is due to the presence of a smaller number of osteoderms per row (c. 20) than in Macroeuphractus and Euphractus (c. 30). In lateral view, the dorsal profile is more convex than in Macroeuphractus and Euphractus , and the maximum convexity area is placed closer to the anterior notch. In FMNH-P14510 the scapular shield is much higher (c. 9 cm) than the pelvic shield (c. 5 cm).

The scapular shield is composed of four rows of osteoderms, and it is much reduced compared to the pelvic shield, which is composed of six or seven rows. A similar morphology is present in Macroeuphractus and Euphractus , while in other euphractines (i.e. Chaetophractus and Zaedyus ) the scapular shield is much more developed. The first row is composed of osteoderms that resemble nuchal osteoderms, with an articular portion that articulates with the nuchal band. The osteoderms of the last row are substantially longer than regular fixed osteoderms, showing an intermediate morphology between fixed and mobile osteoderms. This feature is also present in most euphractines, including Macroeuphractus and Euphractus . This character is observed in both FMNH-P14510 and MACN PV 7889.

The mobile portion of the carapace is composed of six mobile bands in the specimen FMNH-P14510, similar to the specimen CC529 described by Castellanos (1947). In turn, carapaces described by Scillato-Yané (1982) have five mobile bands. Similar differences occur in extant armadillos, which show great intraspecific variation in the number of mobile bands. While not complete, the specimen MACN PV 7889 shows at least five mobile bands.

The pelvic shield is much larger than the scapular shield, composed of eight rows of osteoderms. Osteoderms of this shield are slightly larger than those of the scapular shield, and those of the first row have an articular portion that articulates with the last mobile band. In the more dorsal area, there is an anteroposterior line of four modified osteoderms presenting a cavity at the beginning of the central figure. This morphology is related to glandular areas, by comparison with extant euphractines ( Scillato-Yané 1982). The caudal notch is much reduced compared to extant euphractines, and the osteoderms of the caudal borders develop spine-like morphologies.

Fixed osteoderms: These osteoderms ( Fig. 6E ) are longer than wide, with a variable contour from sub-rectangular to pentagonal. The ornamentation pattern is composed of a large, central figure surrounded, both laterally and anteriorly, by a set of five to eight peripheral figures. The central figure is elongated and reaches the posterior margin of the osteoderm, with the extreme usually extending beyond it and deviate towards the external lateral margin of the osteoderm. The central figure is more elevated than the peripheral figures, and its height progressively increases towards its distal extreme. Some osteoderms can develop a remarkable keel, while in others the central figure is rounded, contrary to mobile osteoderms, which always develop a more or less pronounced keel. The central figure is delimited by a main sulcus, in which there are small dorsal foramina. Peripheral figures are slightly convex and develop very irregular sizes and shapes (from oval to polygonal). These figures are delimited by minor sulci, in which there are no foramina. At the posterior margin of the osteoderms there is a single row of four to seven piliferous foramina. Small foramina are usually placed along the osteoderm laterals, especially at the external ones. These features are observable in all specimens (see Figs 6E , 7B ).

Mobile osteoderms: These osteoderms ( Fig. 6F ) are rectangular, much longer than wide, and divided into an articular and ornamented portion, separated by a short and rough transitional area. The articular portion is flat and smooth and represents less than one third of the osteoderm total length. The ornamented portion includes an elongated central figure that extends from the transitional area to the posterior margin. As in fixed osteoderms, it is much deviated towards the external lateral margin. Its height progressively increases along its length, giving rise to a marked keel, more developed than that of fixed osteoderms. The main sulcus that delimits the central figure is much shallower than in fixed osteoderms, and contains a minor number of dorsal foramina, which are mainly placed along the proximal half of the sulcus. At each lateral of the central figure there is an undivided and elongated peripheral figure, extending in parallel. These figures are slightly convex and lower than the central figure; in some osteoderms there are barely distinguishable grooves dividing the lateral peripheral figures. At the posterior margin of the osteoderms, there is a single row of four to seven piliferous foramina. Additionally, foramina can be placed along either lateral margin of the osteoderm, being more numerous at the external ones. These features are observable in all specimens (see Figs 6F , 7C ).

Phylogenetic affinities

The cladistic analysis resulted in a single most-parsimonious tree ( Fig. 8 ). All armadillos ( Dasypodidae and Chlamyphoridae ) compose a monophyletic group supported by the synapomorphies 29[1], 36[0], 38[1], and 56[1]. In turn, they are split into two major clades: Dasypodidae and Chlamyphoridae . This basal dichotomy is in concordance with phylogenetic analyses based on molecular data and previous analyses that also considered morphological information ( Gaudin and Wible 2006, Delsuc et al. 2012, 2016, Gibb et al. 2016, Mitchell et al. 2016, Barasoain et al. 2021a).

Dasypodidae are supported by the synapomorphies 4[1], 6[1], 8[1], 14[1], 30[1], 42[0], 57[2], and 65[0]. Within Dasypodidae , Plesiodasypus colombianus is the sister-taxon of two sub-clades, one of them composed of Anadasypus hondanus + Anadasypus aequatorianus (synapomorphy 62[1]) and the other by Propraopus sulcatus as sister-group of Dasypus bellus + Dasypus novemcinctus (synapomorphy 15[1]).

Chlamyphoridae are supported by the synapomorphies 4[2], 6[0], 8[0], 30[0], and 42[1]. Chlamyphoridae contain two main clades.ThefirstoneincludesTolypeutinaeand‘Chlaymphorinae’ armadillos and is supported by the synapomorphies 23[0], 51[3], 52[0], and 65[2]. This first clade is divided into two clades. One of them groups the Tolypeutini and is supported by the synapomorphy 40[0], with Pedrolypeutes praecursor as sister-group of the extant Tolypeutes matacus + Tolypeutes tricinctus (synapomorphies 28[1] and 32[0]). The other includes Priodontini and ‘Chlamyphorinae’ and is supported by the synapomorphies 22[1], 37[0], 39[0], and 57[1]. Priodontini are supported by the synapomorphies 53[1] and 61[1]; they include Priodontes maximus + Cabassous tatouay (synapomorphy 14[2]) as sister-group of Vetelia perforata + Vetelia ghandii (synapomorphies 25[1] and 26[2]). ‘Chlamyphorinae’, supported by the synapomorphies 10[1] and 35[0], include the extinct fairy armadillo Chlamydophractus dimartinoi as sister-group of the extant Calyptophractus retusus + Chlamyphorus truncatus (synapomorphies 19[0] and 33[0]); although ‘Chlamyphorinae’ are not a natural grouping but a monophyletic clade within Tolypeutinae , this result is consistent with molecular data that suggest that fairy armadillos had a common ancestor with Tolypeutinae ( Delsuc et al. 2012, 2016).

The second main clade within Chlamyphoridae is composed ofthesubfamilyEuphractinae, supportedbythesynapomorphies 13[0], 18[0], 23[1], 34[1], 41[0], and 51[1]. This is divided into two main subclades, represented by the tribes Eutatini and Euphractini tribes. Eutatini , supported by the synapomorphies 24[0],31[2],44[1], and 45[0],includethespecies Eutatusseguini as sister-group of Chasicotatus ameghinoi + Chasicotatus peiranoi (synapomorphy 48[0]). Euphractini , the most diverse, are supported by the synapomorphies 50[1] and 65[1]. The clade that clusters Prozaedyus proximus + Prozaedyus scillatoyanei (synapomorphies 12[0] and 17[1]) appears as the sister-group of the remaining diversity, which branch sequentially as follows: Zaedyus pichiy , Chaetophractus villosus + Chaetophractus vellerosus (synapomorphy 28[0]), Proeuphractus limpidus , Paleuphractus argentinus + Euphractus sexcinctus (synapomorphy 43[0]), Chorobates villosissimus + Chorobates recens (synapomorphy 60[1]), and internally placed, a clade including Macroeuphractus outesi as sister-group of Macrochorobates scalabrinii . The sisterrelationship between Macroeuphractus and Macrochorobates is supported by the synapomorphies 3[0], 10[2], 20[0], and 25[0], suggesting a close affinity between them, in concordance with the analysis of Carlini and Scillato-Yané (1996).

Figures

Figure 1. Map of Argentina showing the geographic and stratigraphical distribution of the genus Macrochorobates.

Figure 2. Type materials of the Macrochorobates species.A, fragment of dorsal carapace of M. scalabrinii (MLP-PV-lost-, from Lydekker 1895: pl. XXXIII); B, fragment of dorsal carapace of M. chapalmalensis (MACN PV 8283). Scale bars represent 20 mm.

Figure 3. Macrochorobates scalabrinii skull.A1–D1, specimen FMNH P14360 and A2–D2, schematic drawing. In: A, dorsal view; B, right lateral view; C, ventral (occlusal) view; and D, posterior view. Abbreviations: am, auditory meatus; as, alisphenoid; bo, basioccipital; bs, basisphenoid; ca, choanae; ec, ectotympanic; en, endotympanic; eo, exoccipital; fm, foramen magnum; fr, frontal; if, infraorbital foramen; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; nc, nuchal crest; oc, occipital condyle; pa, parietal; pal, palatine; pe, petrosal; pmx, premaxilla; pp, paracondylar process; pt, pterygoid; sc, sagittal crest; sq, squamosal; so, supraoccipital.Scale bars equal to 20 mm. Artwork by P.Cuaranta.

Figure 4. Macrochorobates scalabrinii mandible, corresponding to the specimen FMNH P14360.In: A, labial view; B, medial view; C, occlusal view. Abbreviations: ap, angular process; cp, coronoid process; cop, condylar process; mf1–10, molariforms.Scale bars equal to 20 mm.

Figure 5. 1, femur and 2, tibia-fibula of Macrochorobates scalabrinii (MACN PV 6482). In: A, posterior view; B, anterior view; C, lateral view; and D, medial view.Abbreviations: Fh, femoral head; Gt, greater trochanter; Lc, lateral condyle; Lt, lesser trochanter; Mc, medial condyle; Me, medial epicondyle; Tt, third trochanter; Mm, medial malleolus; Lm, lateral malleolus Scale bars equal to 20 mm.

Figure 6. Macrochorobates scalabrinii armor, corresponding to the specimen FMNH P14510. A, cephalic shield; B, nuchal osteoderms; C, dorsal carapace in dorsal view; D, dorsal carapace in lateral view; E, fixed osteoderms; F, mobile osteoderms. Scale bars equal to 20 mm.

Figure 7. Armor elements corresponding to the specimen MACN PV 7889, previously assigned to Macrochorobates chapalmalensis. A, dorsal carapace in dorsal view; B, fixed osteoderms; C, mobile osteoderms. Scale bars equal to 20 mm.

Figure 8. Most Parsimonious Tree resulting from the phylogenetic analysis and support values.Numbers above each branch indicate Bootstrap and Jack-knifing support, respectively. Numbers below each branch indicate absolute and relative Bremer support, respectively. Rectangles indicate the temporal distribution of taxa.