Cranial and endocranial comparative anatomy of the Pleistocene glyptodonts from the Santiago Roth Collection

With their odd cranial features, glyptodonts, closely related to extant armadillos, are a highly diverse group of the South American megafauna. Doedicurus, Glyptodon, Panochthus, and Neosclerocalyptus were present in the “Pampean Formation” during the Pleistocene, and they are all exceptionally preserved in the Santiago Roth Collection, thus offering the possibility of investigating these four well-diversified genera. A total of 13 specimens (seven species) were analysed and compared in a qualitative/quantitative study of external cranial remains and endocranial reconstructions (i.e., braincase and associated cranial canals, and inner ears). We report on anatomical features that contribute to existing phylogenetic matrices; many of them are new potential synapomorphies supporting the current hypotheses regarding the evolutionary history of the Pleistocene glyptodonts. These include the anterior cranial shape, the position of the basicranium in respect to the whole cranium, the shape of the cranial roof, the position of the largest semicircular canal, and the inclination of the cerebrum. They may represent new shared-derived features among Glyptodon, Doedicurus, Neosclerocalyptus, and Panochthus. We also provide detailed comparative descriptions highlighting new potential convergences in respect to current phylogenies, concerning, for instance, the shape of the foramen magnum, the global shape of the cranium, orbital shape, cochlear position, and a strong protrusion of the zygomatic process of the squamosal. In light of these results, we discuss morphological transformations across phylogeny. The endocranial comparison brought insights on the phylogenetic patterns of cranial canal evolution.


Introduction
Glyptodonts are among the most emblematic representatives of the extinct South American megafauna.In the Pleistocene, they exhibited a relatively high diversity, before becoming extinct in the Early Holocene (Barnosky & Lindsey, 2010;Prado et al., 2015).Since the first classification works (e.g., Ameghino, 1897;Burmeister, 1866;Cuvier, 1798;Gray, 1869;Huxley, 1864;Owen, 1839a;Trouessart, 1897), the presence of osteoderms covering the whole body from head to tail represents an evident synapomorphy grouping the glyptodonts and the extant armadillos.In addition to several skeletal features, these gigantic herbivores, some weighing up estimated two tons (Vizcaíno et al., 2011), were distinguished by an immobility of the dorsal carapace and, more distinctly, by the acquisition of cranial features so derived that they were judged as the clade with the oddest anatomy of all mammals (Burmeister, 1874;Carlini & Zurita, 2010;Vizcaíno & Loughry, 2008).Based on molecular data, the hypothesis of their inclusion within the armadillos was reinforced with a phylogenetic position as the sistergroup of the clade Chlamyphorinae + Tolypeutinae (Delsuc, 2016;Mitchell et al., 2016).Their large size coupled with the presence of osteoderms led them to be among the most abundant mammals in the South American fossil record (e.g., Le Verger, 2023;Vizcaíno & Loughry, 2008).Pleistocene Glyptodontidae are mainly represented by four genera, Glyptodon Owen, 1839b, Doedicurus Burmeister, 1874, Neosclerocalyptus Paula Couto, 1957, and Panochthus Burmeister, 1866(e.g., Carlini & Scillato-Yané, 1999;Cuadrelli et al., 2019;Zurita et al., 2011a).
Although our knowledge of Pleistocene glyptodonts is being refined as a result of recent works, diagnostic elements to distinguish major clades are now unclear or poorly known.Although craniodental and skeletal characters are relatively well-represented in phylogenetic matrices for glyptodonts, morphological studies aiming at primary homology hypotheses among genera concern studies in only a few of them.For example, one of the most recent phylogenetic matrices at the evolutionary-scale of Pleistocene glyptodonts contains 20 craniodental characters of which only five show hypotheses of homologies among genera, i.e., less than 9% of the matrix (Núñez-Blasco et al., 2021).In addition, endocranial structures remain non-existent in the phylogenetic matrices to date, while several authors have emphasized Comparative Anatomy of the Pleistocene Glyptodonts their potential relevance for the phylogeny of glyptodonts (e.g., Le Verger et al., 2021;Tambusso & Fariña, 2015a;Tambusso et al., 2021).However, the discovery of diagnostic elements to differentiate or group Pleistocene glyptodont ideally requires a sufficiently complete amount of remains for comparison.
The Pleistocene Pampean Region of Argentina is rich in fossiliferous beds, first explored by Charles Darwin and Alcide D'Orbigny around 1830 and later by many others (e.g., Ameghino, 1881Ameghino, , 1908;;Cione & Tonni, 2005;Prado et al., 2021;Verzi et al., 2004).Among these fossil explorers is Santiago Roth, a Swiss-Argentinian palaeontologist who built up one of the largest collections from expeditions to the Pampean Region and supplied several Swiss, Danish, and Argentinian museums with specimens (i.e., MCGL; MHNG; MLP; PIMUZ; ZMK-see Abbreviations) (Sánchez-Villagra et al., 2023;Voglino et al., 2023).Santiago Roth prospected over a large part of the region, an area of more than 600,000 km2 (Fig. 1), during the late 19th and early 20th century.In accordance with the three stages that Ameghino (1881) grouped within the "Pampean formation", Santiago Roth defined the Inferior, Intermediate, and Superior Pampean, three units separated on the basis of their palaeontological content rather than their lithological differences (Ameghino, 1908).Nowadays, the Inferior Pampean unit comprises  Prado et al. (2021), andVoglino (2020).For each locality the proportion of each genus is indicated by the same color code as used in the tree.The numbered localities are: 1, San Lorenzo/Barranca San Lorenzo, Tonelero; 2, San Nicolás/Barranca San Nicolás, Tonelero; 3, Rosario/Barranca Rosario/Alverde près Rosario, Tonelero; 4, Arroyo de Cepeda; 5, Arroyo del Medio/Barranca del Arroyo del Medio; 6, Arroyo Pergamino; 7, Arroyo Pergo (locality lost or Arroyo Pergamino abbreviated).B Phylogeny of the studied glyptodonts following Nuñez-Blasco et al. (2021).The chronological scale is based on numerous works that have linked Roth's Pampean subdivisions with the stratigraphic Stages/Ages (see text).The nodes of the tree are not calibrated in time, but the stratigraphic extension of each species is indicated (see text for references).Bonae., Bonaerian; L., Lujanian; Sub., Subdivision; Sup., Superior roughly the majority of the Ensenadan, the Intermediate Pampean unit corresponds to the late Ensenadan and the Bonaerian, and the Superior Pampean to the Lujanian (see Cione & Tonni, 1995;Cione et al., 2015;Hansen, 2019;Prado et al., 2021;Voglino, 2020;Voglino et al., 2023), thus covering a large part of the Pleistocene (see Geological Settings).Through the Pampean Region, Santiago Roth collected a large number of fossils belonging to the extinct South American mammals, especially megafauna, including several Rodentia, Carnivora, Perissodactyla, and Cetacea and other artiodactyls as well as emblematic clades, such as toxodonts, gomphotheres, and macrauchenias (Aguirre-Fernández et al., 2022;Roth, 1889).However, the most abundant representatives belong to xenarthrans, including ground sloths and glyptodonts.These comprise more than half of the collection housed in the PIMUZ (Le Verger, 2023).The Pampean Region, and thus the Santiago Roth Collection, is crucial for the study of glyptodonts, as the cranial remains present in the collection cover most of the major Pleistocene glyptodont genera (Fig. 1).Despite the high quality of the collection with regard to the diversity of Pleistocene glyptodonts, according to our knowledge, the specimens present in European institutions were rarely studied (Le Verger, 2023;Schulthess, 1920).
We conducted a comparative description of the cranial anatomy of Pleistocene glyptodonts present in the Santiago Roth Collections housed in Europe.Our study focused on the external cranial anatomy, including the mandible, and the endocranial traits of the inner ear, braincase, and related cranial canals.In addition to address the first comparative description of mostly unpublished specimens, our study allows us to highlight the general endocranial and external traits of the skull among the major South American genera of Pleistocene glyptodonts and to discuss their relevance for the systematics of this clade.We address issues of palaeoecology and diversity preceding extinction during the Pleistocene of the Pampean Region.

Sampling
Specimens used in the present study are housed at the PIMUZ (Palaeontological collections of the Department of Paleontology, University of Zurich) and at the ZMK (Zoologisk Museum, København, Denmark, included in the Lausen Collection).We studied also glyptodonts housed at the MCGL (Musée Cantonal de Géologie Lausanne) and the MHNG (Museum d'Histoire Naturelle de Genève), but these were the same species as those stored at PIMUZ and ZMK, showed no significant intraspecific variation, and sometimes were much more fragmentary, thus, we do not report on them.Two almost complete skulls (= cranium + mandible), four incomplete crania, and five incomplete mandibles were examined from the PIMUZ collection (Table 1).We also studied three almost complete skulls of Glyptodon munizi, Neosclerocalyptus ornatus, and Panochthus intermedius at the ZMK (Table 1), including remains of Panochthus, which is crucial to cover most of the glyptodont diversity present in the Pleistocene.The total number of specimens (n = 13) from Roth collection corresponds to seven species of glyptodonts from the Pampean Region, including two unidentified glyptodonts at the specific level (Table 1see Le Verger, 2023, for taxonomic assessment).Digital data for a major part of our specimens from the PIMUZ were acquired using X-ray micro-computed tomography (μCT).Specimens were scanned at the Irchel Campus of the University of Zurich using Nikon XT H 225 ST.Three-dimensional reconstructions of the selected structures (see below) were performed using stacks of digital μCT images with MIMICS v. 23.0 software (3D Medical Image Processing Software, Materialize, Leuven, Belgium).In addition, the three specimens from the ZMK were acquired by surface scanning using an Artec Spider.The visualization of 3D models was also conducted with AVIZO v. 8.0.0 software (Visualization Sciences Group, Burlington, MA, USA).All the specimens μCT-scanned, or surface scanned will be available on MorphoMuseum for 3D models and on MorphoSource for μCT-scans (see dedicated part in the present volume).The list of μCTscanned and surface-scanned specimens is specified in Table 1.

Virtual reconstruction of endocranial regions
Endocranial anatomy has only recently been explored in glyptodonts, in particular the braincase (Tambusso & Fariña, 2015a, 2015b;Tambusso et al., 2023), inner ear (Tambusso et al., 2021), and tooth alveoli and cranial canals (Le Verger et al., 2021).These investigations have revealed a systematic and functional signal for Cingulata (Billet et al., 2015a(Billet et al., , 2015b;;Coutier et al., 2017;Tambusso & Fariña, 2015a, 2015b;Tambusso et al., 2021Tambusso et al., , 2023)).We reconstructed several endocranial elements of the neurocranium (Fig. 2) for three specimens: Doedicurus clavicaudatus (PIMUZ A/V 4148); Glyptodon munizi (PIMUZ A/V 461), and Neosclerocalyptus pseudornatus (PIMUZ A/V 439).We reconstructed the braincase while delineating the olfactory bulbs, cerebrum, and cerebellum in accordance with the work of Boscaini et al. (2020a) on Catonyx tarijensis Gervais & Ameghino, 1880, an extinct ground sloth.All the canals connecting with the braincase were reconstructed and identified following Le Verger et al. (2021), which allowed us to make the link with the analysis of the external anatomy through the opening Comparative Anatomy of the Pleistocene Glyptodonts of the canals by the cranial foramina (Fig. 2).Finally, we also reconstructed the inner ears of the same three specimens, comparing the anatomy of the bony labyrinth among some glyptodonts.Besides the value for taxonomy and systematics, the studied endocranial structures provide information on functional and palaeoecological aspects, particularly with respect to cerebral evolution, vascularization and innervation, and locomotion (e.g., Coutier et al., 2017, Schade et al., 2022).In our sample, at least one representative of Glyptodon (PIMUZ A/V 461), Doedicurus (PIMUZ A/V 4148), and Neosclerocalyptus (PIMUZ A/V 439), exhibits all these three endocranial parts complete.Information on Panochthus is taken from the work of Tambusso and Fariña (2015a) and Tambusso et al. (2021) on the species Panochthus tuberculatus Owen, 1845.

Measurements and estimations
To provide quantitative evaluation of our qualitative comparisons, we performed several measurements following numerous references regarding the cranial anatomy of glyptodonts (e.g., Núñez-Blasco et al., 2021;Tambusso & Fariña, 2015a) on the most complete specimens in our sample, plus several others (Fig. 2, Table 2).When specimens were incomplete, we produced estimates from complete specimens in the literature based on at least one comparable measurement.All measurements were made directly on the specimens using a Vernier Caliper with a precision of 0.05 mm and a Protractor.For the endocranial part, two linear measurements of the 3D braincase endocast, two linear and one new angular measurement of the inner ear (see Billet et al., 2012Billet et al., , 2015aBillet et al., , 2015b)), the total raw volume of the 3D braincase endocast, and the relative volumes (i.e., divided by the total raw volume) of the olfactory bulbs, cerebrum, and cerebellum were obtained using MIMICS v. 23.0 software (Table 2).

Taxonomical considerations and phylogenetic framework
The first identifications referring to the glyptodonts collected by Santiago Roth were provided by him at the end of the 19th century (Roth, 1889).Subsequently, Schulthess (1920) reviewed all the specimens in the PIMUZ Collection and made taxonomic corrections.Guth (1961) reassessed some specimens from this collection.Since then, no taxonomic update has been made except for a few isolated and unpublished notes.
As the assessment of the diversity of glyptodonts has changed considerably (e.g., Fernicola, 2008;Fernicola & Porpino, 2012;Zamorano & Brandoni, 2013), a taxonomic revision for the glyptodonts in our study was necessary (Le Verger, 2023).All the specimens of our sample were thus reassigned in accordance with this deferred work.Regarding the specimens from the ZMK, the three specimens are particularly complete     Verger (2023).
Because of the recent inclusion of glyptodonts within armadillos brought by both morphological and molecular phylogenetic studies (Delsuc et al., 2016;Gaudin & Wible, 2006;Mitchell et al., 2016), the taxonomic status of glyptodonts at a higher rank than genus is still subject to debate (see the discussion of Delsuc et al., 2016, andGaudin &Lyon, 2017).As the present study does not aim to resolve this issue, we have opted for a comparison at the generic level, where the monophyly of the groups is not debated.Regarding the phylogenetic context for glyptodonts, the literature is rich with studies that have addressed various questions about the evolutionary history of the clade.Some works address more broadly the position of glyptodonts within the Cingulata (e.g., Billet et al., 2011;Gaudin & Wible, 2006).Other studies have focused more specifically on the overall evolutionary history of the clade (e.g., Fernicola, 2008;Fernicola et al., 2018;Porpino et al., 2010) or on its diversity over a given period, such as the Pleistocene (Cuadrelli et al., 2020;Nuñez-Blasco et al., 2021;Zurita et al., 2013Zurita et al., , 2014)).Finally, some works focus more specifically on a clade within the glyptodonts (e.g., Zamorano & Brandoni, 2013;Zurita et al., 2017).In the present study, our interest is in a diversity of glyptodonts known only during the Pleistocene.Accordingly, here, the phylogeny used to discuss the anatomical traits (Fig. 1) is derived from Núñez-Blasco et al., (2021) and corresponds to the most parsimonious tree resulting from a cladistic analysis based on a widely used and reworked matrix of glyptodonts (Cuadrelli et al., 2020;Fernicola, 2008;Porpino et al., 2010;Zamorano & Brandoni, 2013;Zurita et al., 2013Zurita et al., , 2014Zurita et al., , 2017)).The updated matrix consists of 23 taxa and 57 characters of which 20 characters are from the skull (including teeth and mandibles) and includes all the species in our study except for Neosclerocalyptus gouldi and Neosclerocalyptus pseudornatus, which we added to the tree topology based on Zurita et al., (2013).Our purpose here is not to perform a new phylogenetic analysis but to have a phylogenetic framework to discuss the anatomical traits from our comparative analysis focused at the genus level.The homological hypotheses discussed based on this phylogenetic framework are also discussed in relation to one of the most recent alternative phylogenetic hypotheses of relationships among glyptodonts (see Fernicola et al., 2018).

External anatomical comparisons
Concerning the completeness, Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), Neosclerocalyptus pseudornatus (PIMUZ A/V 439), Neosclerocalyptus gouldi (ZMK 77/1888), as well as Panochthus intermedius (ZMK 66/1885) are the specimens with the best preservation.The whole crania of Glyptodon munizi (PIMUZ A/V 462) and Neosclerocalyptus ornatus (PIMUZ A/V 447) present a relatively large missing portion, mostly the zygomatic arches and the basicranium.Both of them are crushed, resulting in almost no visibility of the cranial sutures.For Doedicurus clavicaudatus (PIMUZ A/V 4148), only the neurocranium and anterior part of the left zygomatic arch including the maxillary with three Mf are preserved.

Dorsal view
In its general appearance, the cranium is rectangular with a length greater than the width for all glyptodonts (Table 2; for Doedicurinae see Núñez-Blasco et al., 2021); however, the incompleteness of the material does not allow a strict comparison of these cranial dimensions (Fig. 4).The main difference in our sample is the presence of ossified nasal cartilage in the three Neosclerocalyptus species compared to other glyptodonts.Neosclerocalyptus pseudornatus (PIMUZ A/V 439) shows two nasal bullae on each side of the cranium and a relatively more posterior position of the orbit than in Neosclerocalyptus ornatus (PIMUZ A/V 447) and Neosclerocalyptus gouldi (ZMK 77/1888; Fig. 4).Regardless of this feature, Neosclerocalyptus pseudornatus (PIMUZ A/V 439) exhibits a kite-like shape resulting from a nasal bone pointing anteriorly in a V-shape and a greater width at the level of the orbit than at the level of the zygomatic arches posterior margin.This general shape implies a reduced parieto-occipital area compared to the naso-frontal area in the dorsal view.In Neosclerocalyptus ornatus (PIMUZ A/V 447), Neosclerocalyptus gouldi (ZMK 77/1888), and Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), this reduction in width in the posterior part is not as pronounced, leading to an overall shape more comparable to an hourglass, although the postorbital constriction is more marked in Neosclerocalyptus pseudornatus (PIMUZ A/V 439).Doedicurus clavicaudatus (PIMUZ A/V 4148) cannot be compared to the other specimens with respect to the anterior part of the cranium, but it exhibits a laterally flattened neurocranium, suggesting  ) by the combination of a postorbital process and a frontal process of the jugal, both of which are strongly pronounced.The postorbital process is also present in Glyptodon but without a visible process emerging from the jugal (Fig. 4).In Panochthus intermedius (ZMK 66/1885), and in Doedicurus clavicaudatus (Nuñez-Blasco et al., 2021), the postorbital process is fully fused as a postorbital bar (Fig. 4).
Regarding the cranial roof, there is no major difference within glyptodonts, the parietal is less than half as short as the frontal and has a variable number of foramina for the rami temporales (see also Núñez-Blasco et al., 2021Zamorano et al., 2014a).The occiput inclination, however, is stronger in Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), a species for which the occipital condyles exhibit a more lateral position and anterolateral orientation than in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Panochthus intermedius (ZMK 66/1885).The latter two show relatively similar nuchal crests, with an anteriorly positioned occipital protuberance compared to Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) and Neosclerocalyptus species, except for Neosclerocalyptus ornatus (PIMUZ A/V 447; Fig. 4; see also Zurita et al., 2011b).

Lateral view
The anteroventral inclination of the naso-frontal area in relation to the parieto-occipital region is a highly variable feature among glyptodonts, with an angle of about   Blasco et al., 2021) and Neosclerocalyptus species (see also Zurita et al., 2008)  ), the premaxillary is more prominent and anteroventrally inclined (Fig. 5).

Ventral view
Concerning the anterior maxillary/premaxillary area, Neosclerocalyptus gouldi (ZMK 77/1888), Neosclerocalyptus ornatus (PIMUZ A/V 447), Neosclerocalyptus pseudornatus (PIMUZ A/V 439), and Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) do not exhibit the same enlarged and ventrally curved area as in Panochthus intermedius (ZMK 66/1885) and Doedicurus clavicaudatus (see Fig. 5 and ; for Doedicurinae, see Núñez-Blasco et al., 2021).The maxillary bone in the analysed Neosclerocalyptus species is laterally elongated compared to the other glyptodonts, a peculiarity underlined by the more posterior position of the orbit and the large additional ossified nasal cartilage on the snout (Fig. 6).In addition, the portion of the maxilla between the descending process of the zygomatic arch and the toothrow has a greater  (Zurita et al., 2011b) and Doedicurus clavicaudatus (PIMUZ A/V 4148) are subrectangular in cross section and anteroposteriorly elongated.In Doedicurus clavicaudatus (PIMUZ A/V 4148), the occipital condyle has nearly the same width as the foramen magnum, while all other genera show a smaller width of the condyle compared to the foramen magnum (Fig. 6 and ; Table 2).Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) exhibits the largest and most circular occipital condyle among the discussed species (Fig. 6).
The basioccipital and exoccipital in glyptodonts exhibit dozens of basilar tubercles.In Doedicurus clavicaudatus (PIMUZ A/V 4148), Panochthus intermedius (ZMK 66/1885), and Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), the basioccipital is fused with the exoccipital, exhibiting a broad and laterally elongated shape, compared to Neosclerocalyptus species, where this region is rather narrow and short.Doedicurus clavicaudatus (PIMUZ A/V 4148) exhibits the widest and shortest exoccipital compared to the cranial length, following by a laterally elongated and large foramen magnum (Figs. 6  and 7).

Occipital view
All genera analysed in the present study exhibit a prominent and well-pronounced "W-shaped" nuchal crest joining at the occipital protuberance.In all glyptodonts, the angle between both nuchal crests is larger than 90°, except for Neosclerocalyptus pseudornatus (PIMUZ A/V 439) with an angle of only about 90° (Fig. 7).In Doedicurus clavicaudatus (PIMUZ A/V 4148), the supraoccipital is subquadrangular with a concave surface, whereas other glyptodonts show a more subtriangular shape of the supraoccipital.Among Neosclerocalyptus species, Neosclerocalyptus ornatus (PIMUZ A/V 447) exhibits the largest laterally expanded supraoccipital.The foramen magnum is smaller and subcircular in Doedicurus clavicaudatus (PIMUZ A/V 4148) compared to the Neosclerocalyptus species.In the latter, the foramen magnum is subelliptic in cross section, expanding more laterally (see also Zurita et al., 2008).In Panochthus intermedius (ZMK 66/1885), the foramen magnum is circular in cross section, same as in other Panochthus (Zamorano et al., 2014a).Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) exhibits a strong elliptic foramen magnum.

Mandible
In all genera at the lateral view, toothrows exhibit a sigmoidal course with the posterior end of the toothrow being the most ventral part (Fig. 8).The most dorsal height of the toothrow is at the level of mf3 in    2).The angular process is concave and round in Neosclerocalyptus (Zurita, 2007), Doedicurinae (Núñez-Blasco et al., 2021), and Panochthus (Zamorano & Brandoni, 2013), contrary to the subtriangular shape of the angular process in Glyptodon.In lateral view, Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) also exhibits many tuberosities along the posterior margin of the angular process.The coronoid process and the condylar process have the same height in Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), contrary to the other compared genera, where the coronoid process is higher in lateral view (Fig. 8).The condylar process of all glyptodonts exhibits tuberosities at the anterior margin.

Inner ear
All described species display a poorly coiled cochlea, one with just 1.5 turns (Fig. 10).Specimens exhibit large semicircular canals in proportion to the cochlea and an overall relatively small size of the inner ear compared to the size of the cranium (see below).The semicircular canals in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) are more rounded than in the other species studied.In Glyptodon munizi (PIMUZ A/V 461) the semicircular canals exhibit an oval shape.In contrast with other glyptodonts, Doedicurus clavicaudatus (PIMUZ A/V 4148) shows a small lateral semicircular canal compared to the anterior and posterior semicircular canals.In this specimen, the anterior and posterior semicircular canals are equal in size, whereas in smaller glyptodonts, such as Glyptodon species (Fariña et al., 1998), the posterior semicircular canal is larger compared to the remaining semicircular canals (Fig. 10; Table 2).As a glyptodont closer in size to Doedicurus clavicaudatus than Glyptodon species (Fariña et al., 1998), Panochthus tuberculatus exhibits a larger lateral semicircular canal compared to the anterior semicircular canal (Tambusso et al., 2021).Neosclerocalyptus pseudornatus (PIMUZ A/V 439) shows similar sizes of all semicircular canals (Table 2).Regarding the relative position of each semicircular canal, Glyptodon munizi (PIMUZ A/V 461) shows a more acute angle dorsal to the crus commune between anterior and posterior semicircular canal than Doedicurus clavicaudatus (PIMUZ A/V 4148), Neosclerocalyptus pseudornatus (PIMUZ A/V 439; Fig. 10), and Panochthus tuberculatus (Tambusso et al., 2021; Table 2).The crus commune, formed by the merge of the anterior and posterior semicircular canals, is thinner in Doedicurus clavicaudatus (PIMUZ A/V 4148) than in the remaining glyptodonts.This result should be moderated as the crus commune appears relatively equivalent in size in all glyptodonts in the studies of Tambusso et al., (2021Tambusso et al., ( , 2023)), underlining a potential intraspecific variation of the crus commune thickness in Doedicurus.
The angle between posterior part of lateral and posterior semicircular canals in Glyptodon munizi (PIMUZ A/V 461) is smaller than in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439).In Neosclerocalyptus pseudornatus (PIMUZ A/V 439), these two semicircular canals only meet in the utricule, a feature also found in the Miocene glyptodont Pseudoplohophorus (Tambusso et al., 2021(Tambusso et al., , 2023)), whereas in the remaining species they already meet more anteriorly, forming the secondary common crus.Therefore, the anterior and lateral ampulla in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) are well-separated by a gap, formed by the more anterior connection of their ampulla, in comparison with the remaining species.

Braincase
The digital braincase of Doedicurus clavicaudatus (PIMUZ A/V 4148), Glyptodon munizi (PIMUZ A/V 461), and Neosclerocalyptus pseudornatus (PIMUZ A/V 439) are almost complete and well-preserved.The cerebellar hemispheres are more laterally expanded in the larger species Doedicurus clavicaudatus (PIMUZ A/V 4148), Panochthus tuberculatus (Tambusso & Fariña, 2015a), and Glyptodon munizi (PIMUZ A/V 461) compared to Neosclerocalyptus pseudornatus (PIMUZ A/V 439), leading to a more anteroposterior elongated cerebellum in the latter (Fig. 11), a feature also found in Pseudoplohophorus (Tambusso & Fariña, 2015a;Tambusso et al., 2023).In all specimens, the strongly pronounced vermis does not form any kind of posterior apex.The digital braincase of Neosclerocalyptus pseudornatus (PIMUZ A/V 439) exhibits a proportionally larger cerebellum compared to the other species, but also exhibits a similar size of the cerebrum, while having atrophied olfactory bulb compared to Doedicurus clavicaudatus (PIMUZ A/V 4148), Panochthus tuberculatus (Tambusso & Fariña, 2015a), and Glyptodon munizi (PIMUZ A/V 461).Like the cerebrum, in anterior view, the olfactory bulbs of Glyptodon munizi (PIMUZ A/V 461) are more dorsoventrally elongated than in Doedicurus clavicaudatus (PIMUZ A/V 4148), but both species exhibit the same frontal orientation of the olfactory bulbs.In Neosclerocalyptus pseudornatus (PIMUZ A/V 439), the olfactory bulbs are smaller than in the remaining species in relation to the braincase size, and are situated at the ventral edge of the cerebrum.The ventral position of the olfactory bulbs in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) implies a relatively larger longitudinal sulcus in the anterior view.Panochthus tuberculatus shows a similar relative size of olfactory bulbs (Tambusso & Fariña, 2015a) to Glyptodon munizi (PIMUZ A/V 461) and Doedicurus clavicaudatus (PIMUZ A/V 4148), situated at the ventral edge of the cerebrum, like in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) but more laterally oriented in dorsal view in the latter (Tambusso & Fariña, 2015a).In lateral view, with respect to the medulla oblongata, the cerebrum is slightly inclined ventrally in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) and Panochthus tuberculatus (Tambusso & Fariña, 2015a), inclined dorsally in Doedicurus clavicaudatus (PIMUZ A/V 4148), and even more inclined dorsally in Glyptodon munizi (PIMUZ A/V 461).In the latter, the mediolaterally oriented occipital gyrus at the border between the cerebrum and the cerebellum is more prominently concave than in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439), leading to a more pronounced transverse fissure in Glyptodon munizi (PIMUZ A/V 461).The cerebral hemispheres in dorsal view are separated by a strongly protruding medial part of the lateral gyrus, which is thinner and extends over the entire length of the cerebrum in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439) compared to Glyptodon munizi (PIMUZ A/V 461) and Panochthus tuberculatus (Tambusso & Fariña, 2015a).
For the latter, this part of the gyrus is more pronounced and only visible in the posterior and most anterior part of the cerebrum.In Glyptodon munizi (PIMUZ A/V 461), Panochthus tuberculatus (Tambusso & Fariña, 2015a), and Neosclerocalyptus pseudornatus (PIMUZ A/V 439), the lateral portion of the lateral gyrus is well-preserved and, on both hemispheres, anteroposteriorly directed and more pronounced compared to Doedicurus clavicaudatus (PIMUZ A/V 4148).The suprasylvian gyrus, situated laterally to the lateral gyri, is not prominent in all species.Glyptodon munizi (PIMUZ A/V 461) and Doedicurus clavicaudatus (PIMUZ A/V 4148) exhibit a defined temporal and pyriform lobe, whereas in Neosclerocalyptus pseudornatus (PIMUZ A/V 439), the two lobes are less protruding in lateral and dorsal views, which leads to a more quadrangular and narrower cerebrum in anterior view (Fig. 11).In this latter view, Doedicurus clavicaudatus (PIMUZ A/V 4148) exhibits a similar shape to that in Glyptodon munizi (PIMUZ A/V 461), with a less dorsoventral elongation of the cerebrum.Neosclerocalyptus pseudornatus (PIMUZ A/V 439) and Panochthus tuberculatus (Tambusso & Fariña, 2015a) show a prominent fissure between the olfactory gyrus and the pyriform lobe viewed from the dorsal side that is not as strongly visible in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Glyptodon munizi (PIMUZ A/V 461).The olfactory gyrus is anteroposteriorly elongated in Neosclerocalyptus pseudornatus (PIMUZ A/V 439).

Related cranial canals
In Neosclerocalyptus pseudornatus (PIMUZ A/V 439), the posttemporal canal runs dorsally to the level of the internal auditory meatus from the outreaching flanks of the cerebellum.In Glyptodon munizi (PIMUZ A/V 461) and Doedicurus clavicaudatus (PIMUZ A/V 4148), the posttemporal canal emerges posteroventrally to the internal auditory meatus (Fig. 11).In all species, the ventral part of the posttemporal canal exhibits a downward trajectory.In lateral view, the posttemporal canal is oriented vertically in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439), in contrast to the more posterodorsal orientation in Glyptodon munizi (PIMUZ A/V 461).In anterior view, the descending branch of the posttemporal canal is directed outwards for Doedicurus clavicaudatus (PIMUZ A/V 4148) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439) whereas for Glyptodon munizi (PIMUZ A/V 461) this canal displays an inwards curvature (Fig. 11).
The posttemporal canal in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) exhibits a strong ventral curvature until the level of the oval canal.According to Wible and Gaudin (2004), this canal transmits the arteria diploëtica magna and the large vena diploëtica magna.Along the lateral side of all braincases, the posttemporal canal connects to a confluence area as described in Le  2021) described a region of confluence between the orbitotemporal canal, the canal for the capsuloparietal emissary vein, and the posttemporal canal, where the canals can no longer be distinguished from each other, a region welldefined in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Glyptodon munizi (PIMUZ A/V 461; Fig. 11).Glyptodon munizi (PIMUZ A/V 461) stands out concerning the course of the orbitotemporal canal, since it horizontally follows the lateral wall of the cranial roof until it connects to the optic canal, unlike in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) and Doedicurus clavicaudatus (PIMUZ A/V 4148) where the orbitotemporal canal provide a passage through the braincase.The orbitotemporal canal transmits the orbitotemporal artery and accompanying vein (e.g., MacPhee et al., 2021) and parts of the ramus superior of the stapedial artery (Wible & Gaudin, 2004).In Glyptodon munizi (PIMUZ A/V 461) and Doedicurus clavicaudatus (PIMUZ A/V 4148), the sphenorbital and optic canals are connected to the orbitotemporal canal.The connection with respect to the anterior end of the olfactory bulb is more anterior in Doedicurus clavicaudatus (PIMUZ A/V 4148) than in Glyptodon munizi (PIMUZ A/V 461).In lateral view, the sphenorbital canal is directed, with respect to the transverse plane, anteriorly in Glyptodon munizi (PIMUZ A/V 461), anteroventrally in Doedicurus clavicaudatus (PIMUZ A/V 4148) and even more ventrally in Neosclerocalyptus pseudornatus (PIMUZ A/V 439), this variation being perhaps correlated with the difference in orientation of the brain among the species.The distance in ventral view between the sphenorbital canal and the oval canal is especially larger in Doedicurus clavicaudatus (PIMUZ A/V 4148), following the observed trend of their overall larger canals.The sphenorbital canal transmits the ophthalmic and maxillary branches of the trigeminal nerve, oculomotor, trochlear, and abducens nerves, with accompanying veins, and a small branch of the maxillary artery which open in the sphenorbital fissure (Boscaini et al., 2020a;Le Verger et al., 2021;Wible & Gaudin, 2004).Moreover, in Doedicurus clavicaudatus (PIMUZ A/V 4148), the oval canal, which transmits the mandibular division of the trigeminal nerve (see for sloths Boscaini et al., 2020b), is directed more laterally in anterior view than in the remaining specimens.The optic canal opens externally at the optic foramen and connects to the encephalic cavity, located ventrally in the cerebrum.In Doedicurus clavicaudatus (PIMUZ A/V 4148), the two openings of the optic canal are closer together in anterior view than in Glyptodon munizi (PIMUZ A/V 461) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439), a trend that could potentially be an allometric effect, as inferred from a study on Dasypus (Le Verger et al., 2020).The optic nerve, the internal ophthalmic artery, and the internal ophthalmic vein are transmitted through the optic canal (Wible & Gaudin, 2004).The internal auditory meatus, bearing the facial and vestibulocochlear nerves (Boscaini et al., 2020b;Wible, 2010), are situated ventrally to the anterior part of the cerebellum in all species.The vestibulocochlear nerves split into the vestibular and cochlear nerve and open at the level of the inner ear region (Tambusso & Fariña, 2015a;Wible & Gaudin, 2004).In Neosclerocalyptus pseudornatus (PIMUZ A/V 439) and Doedicurus clavicaudatus (PIMUZ A/V 4148), the well-marked bifurcation of this canal into the vestibular and cochlear part can be observed (Fig. 11).

Discussion
Glyptodont diversity has been overestimated for the Pleistocene, and following several taxonomic revisions, some authors now suggest a decline in the Pleistocene glyptodont diversity probably due to several causes, related to the increase in body size, different latitudinal distribution of the genera, or the drastic climatic changes during this period (Cuadrelli et al., 2019(Cuadrelli et al., , 2020;;Vizcaíno et al., 2012;Zurita et al., 2016Zurita et al., , 2018)).The Pampean Region marks the ecoregion between the tropical and the temperate/arid ecosystems associated with a high productivity related to the Paleo-Parana River floods (Varela & Fariña, 2016;Varela et al., 2018), a region inhabited by the southern glyptodont taxa.Two radiations within the Comparative Anatomy of the Pleistocene Glyptodonts glyptodont have been identified (e.g., Nuñez-Blasco et al., 2021).One corresponds to the Hoplophorinae, a clade notably formed by the grouping of Panochthus and Neosclerocalyptus, two genera including eight species and four species during this period, respectively (Zamorano et al., 2021;Zurita et al., 2011b).The second correspond to the Glyptodontinae, which, during the Pleistocene, consisted only of the genus Glyptodon, restricted to South America, and the genus Glyptotherium Osborn, 1903, more widely distributed in North America and in northern South America (Zurita et al., 2018).In current phylogenies of Pleistocene glyptodonts, either Doedicurus is the sister group of the Hoplophorinae and the group they form is positioned as the sister group of the Glyptodontinae (Núñez-Blasco et al., 2021), or Doedicurus and Glyptodon form one clade and Neosclerocalyptus and Panochthus form another one (Fernicola et al., 2018).We base the following discussion of potential and optimized characters from our comparative analysis on these two phylogenetic hypotheses.
The most recent phylogenetic matrix used to address the evolutionary history of glyptodonts has 57 characters for 27 taxa and includes the four major Pleistocene glyptodont genera.Among the 57 characters, 20 are defined on the skull, including the dentition.Only five of these characters provide hypotheses of homologies among genera and not always in agreement with the topology obtained in the strict consensus (Fig. 12 and Nuñez-Blasco et al., 2021), implying that phylogeny at the scale of glyptodont genera is based mainly on postcranial material.We propose potential new cranial and endocranial characters to support different phylogenetic scenarios: 17 new characters could be defined based on the work we present (Fig. 12).In agreement with the monophyly of Hoplophorinae and the position as sister group of Doedicurus with the latter, supported in previous studies only by the presence of a pneumatization of the rostral region in Neosclerocalyptus and Panochthus (K2*) and the onset of labiolingual trilobulation at Mf2 in Neosclerocalyptus and Panochthus and Mf3 in Doedicurus, we propose seven new potential synapomorphies, five of which concern the general shape of the cranium (K1-K5), one corresponds to the lower dentition (K6), and one is defined by the inclination of the cerebrum (K14).Of these seven potential synapomorphies, six could also support the alternative phylogenetic hypothesis proposing closer relationship between the Glyptodon and Doedicurus (K1, K3-6, K14;Fernicola et al., 2018).Consequently, most of the potential external cranial characters studied here, and the unique character on the cerebrum, do not resolve between the phylogenetic hypothesis of Núñez-Blasco et al. (2021) and that of Fernicola et al. (2018).
Regarding other potential external cranial characters, we hypothesize on morphological convergences among glyptodonts, including the absence or presence of a curvature of the cranial roof (K9) and the descending process of the zygomatic arch (K10), grouping Doedicurus and Neosclerocalyptus each, and also supported by a subelliptic shape of the orbit (K11).Based on the trend of a more convergent orbit orientation in larger species such as Doedicurus, Panochthus and Glyptodon compared to Neosclerocalyptus, a diverse range of vision from a dominance of a monocular to binocular visual field in relation to size variation in Pleistocene glyptodonts is supported.This would mark a well-known allometric variation in mammals (Heesy, 2004(Heesy, , 2008)).Neosclerocalyptus exhibit a smaller and more posterior situated orbit in lateral view, probably due to the development of the prominent ossified nasal cartilage (Zurita et al., 2011b).Doedicurus also appear to have potential morphological convergences with the Panochthus, both clades sharing a strong protrusion of the zygomatic process of the squamosal (K7) and a circular shape of the foramen magnum (K8).The last two characters (K7 and K8) could be related to the allometric effect, since Doedicurus and Panochthus share a significantly larger body mass (~ 1400 kg up to ~ 2000 kg; Fariña, 1995;Fariña et al., 1998) than the small Neosclerocalyptus (~ 320 kg; Vizcaíno et al., 2011).In addition to the presence of an ossified nasal cartilage in Neosclerocalyptus, a strong impact of allometry was demonstrated in one extant armadillo species, Dasypus novemcinctus Linnaeus, 1758, leading to a protrusion of the zygomatic process of the squamosal and a modification of the shape of the foramen magnum (Le Verger et al., 2020).For these two traits, a potential correlation with size must be explored to evaluate if they are impacted by allometry or phylogenetic characters independent of size.The ossified nasal cartilage in Neosclerocalyptus species and the elongated nasal bone in Panochthus intermedius enlarges the snout area, and therefore, the position of the orbit is in the middle portion of the cranium.Pleistocene glyptodonts show great diversity in snout shape.This diversity has been associated with the respiratory and thermoregulatory functions of the nasal cavity in relation to the changing climatic cycles between glacial and interglacial that occurred during the Pleistocene (e.g., Rabassa & Coronato, 2009;Rabassa et al., 2005) and the potential low metabolic rate of glyptodonts (Vizcaíno et al., 2006), especially in the case of the Neosclerocalyptus (Zurita et al., 2011b), although this hypothesis is disputed (Fernicola et al., 2012).Our search for homology hypotheses was limited by the Neosclerocalyptus with the presence of the most unique external cranial traits, which may be closely linked to the presence of the prominent ossified nasal cartilage (Fernicola et al., 2012).This applies especially to Neosclerocalyptus pseudornatus, which shows most of the morphological differences in relation to the rest of the Neosclerocalyptus species.Anagenesis has been accepted concerning the evolution of the genus Neosclerocalyptus (e.g., Quiñones et al., 2020;Zurita et al., 2011b), but PIMUZ A/V 439 exhibits some unique characters which differ vastly from the remaining Neosclerocalyptus species and would mark a clear morphological differentiation between the early forms of the Ensenadan Stage and those from the Lujanian Stage.
The four Pleistocene glyptodontid genera, Doedicurus, Glyptodon, Panochthus, and Neosclerocalyptus, co-occurred in the "Pampean Formation" of Argentina, with ecological niche partitioning among them (e.g., De Melo-Franca et al., 2015;Domingo et al., 2012;Vizcaíno et al., 2011) and some of the characters mentioned above might be common morphological trait acquisitions related to the paleoenvironmental evolution of the region.For instance, Doedicurus clavicaudatus and Panochthus intermedius both inhabited the Pampean Region during the late Ensenadan/Bonaerian (see Table 1); these two genera show many common adaptational features related to the similar environmental conditions during the Bonaerian of the Pampean Region, a period that started with a great warming and suffered a severe cooling of the climate (Quattrocchio et al., 2008;Soibelzon, 2019).The acquisition of certain synapomorphies such as the round shape of the cranium in anterior view (K1) and the narial opening (K2) or the pneumatization of the rostral area (K2*) were notably hypothesized to be related to the cooling phases and the aridity of the climate during the Pleistocene (Fernicola et al., 2012;Zurita et al., 2011a), characters supporting the clade formed by Neosclerocalyptus and Panochthus.There may be an adaptive value for some of the new characters, as in the position of the head and the cranial roof, suggesting a larger area for muscle attachment (e.g., K3 and K5), related to wide muzzles and high hypsodonty index, typical features of bulk feeding in open environments (Vizcaíno et al., 2011).The hypothesis of a strong plasticity associated with dietary changes seems supported by the isotopic analyses on the diet of Glyptodon that showed a mixture of a C3 and C4 plant diet or a solely C3 plant diet, reflecting ecological plasticity (Cuadrelli et al., 2020;Domingo et al., 2012;Prado et al., 2011).However, the majority of other glyptodont genera have been interpreted as specialized (Vizcaíno et al., 2011) with the assignment of Doedicurus and Panochthus to bulkfeeders in open environments and Neosclerocalyptus to bulkfeeders in closer environments.The conspicuous trilobulation morphology observed in Glyptodon munizi is a synapomorphy of the genus (Cuadrelli et al., 2020;Zurita et al., 2013).Some of our characters such as those grouping Doedicurus and Panochthus may be the result of feeding strategy specializations and any hypothesis of synapomorphy should be considered with caution as the radiation of each genus occurred before the Pleistocene (Nuñez-Blasco et al., 2021;Zamorano et al., 2014b).
We recorded differences in the studied endocranial structures among Glyptodon munizi, Neosclerocalyptus pseudornatus, Panochthus tuberculatus (Tambusso & Fariña, 2015a), and Doedicurus clavicaudatus.Overall, the braincase of Doedicurus clavicaudatus and Glyptodon munizi share more morphological similarities among the analysed braincase endocasts than with Neosclerocalyptus pseudornatus, supporting the phylogenetic hypothesis of Fernicola et al. (2018).First, regarding proportions of different braincase regions, the relative volume of the cerebellum is smaller in Doedicurus clavicaudatus compared to the other species (Table 2), implying a lesser development of the brain in this genus for sensory control of movement (Sultan & Glickstein, 2007).In Glyptodon munizi, the relative volume for the cerebrum, the cerebral neocortex involved in several perceptual and cognitive functions (Van Essen, 1979), is smaller than in Neosclerocalyptus pseudornatus and Doedicurus clavicaudatus (Table 2).Based on the analyses of Stankowich & Romero (2017), mammals living in open environments and with external antipredator defenses show reduced encephalization, since these defense strategies reduce the need of spending production and maintenance costs of cognitive abilities related to vigilance and predator recognition.These analyses are in accordance with our results on Glyptodon munizi showing a relative Fig. 12 Former and new potential phylogenetic characters for the relationships among the Pleistocene glyptodont genera from our comparative investigation.Shared morphological traits are defined as characters in the illustrated table and each homological or homoplasical hypothesis is illustrated on the schematic tree extracted from the strict consensus of Nuñez-Blasco et al. (2021) to address the evolutionary history of glyptodonts.For each evolutionary scenario, the anatomical regions involved are identified by a symbol from the cranium of Glyptodon munizi (PIMUZ A/V 461) in lateral view: a cranium for external morphological features, a cranium in transparency with teeth selected for dental characters, an isolated braincase endocast, an isolated and verticalized inner ear, and the neurocranial canals.The color follows the coding of each character.See Table 2 for  larger volume of the cerebellum and the smaller volume of the cerebrum while exhibiting an almost inexistant caudal tube (i.e., one or two distal ankylosed bony rings) in comparison with the remaining Pleistocene glyptodon genera (Cuadrelli et al., 2019), indicating a highly armored tail without weaponry.In accordance with the hypothesis of Stankowich & Romero (2017), the smaller volume of the cerebrum of Glyptodon munizi might be associated with a more passive defense mode than glyptodonts possessing tails with weaponry, such as Panochthus and Doedicurus.The major difference concerning the relative volumes of the different parts of the braincase can be found in the relative volume of the olfactory bulb.In Neosclerocalyptus pseudornatus, the olfactory bulbs accounts for only 2,4% of the contrary to the 7% in Glypotdon munizi and Doedicurus clavicaudatus in contrast with extant armadillos for which the olfactory bulbs are large compared to the total volume of the braincase endocast (Tambusso & Fariña, 2015a).In Neosclerocalyptus pseudornatus and Panochthus tuberculatus (Tambusso & Fariña, 2015a), the olfactory bulbs are more ventrally oriented as mentioned above.According to Tambusso and Fariña (2015a), this ventral orientation could be related to the great development of the paranasal sinuses dorsally to the olfactory bulbs and can be observed in other Hoplophorinae as well, such as Panochthus tuberculatus (Tambusso & Fariña, 2015a) and Neosclerocalyptus paskoensis (Fernicola et al., 2012).This smaller braincase in cingulates compared to that of extant sloths could be possibly linked to the earlier weaning age (Tambusso & Fariña, 2015a;Weisbecker & Goswami, 2010), the biological, ecological, and locomotory restrictions imposed by the carapace (Lovegrove, 2001), limited defense strategies due to the large body size and carapace (Tambusso & Fariña, 2015a), or the potential low metabolic rate (McNab, 1986(McNab, , 2008;;Vizcaíno et al., 2006).Tambusso and Fariña (2015a) hypothesized a possible link between larger body sizes and a relatively small brain in Pleistocene glyptodonts, a widespread trend among mammals (Burger et al., 2019;Ferreira et al., 2020).Although body size was not estimated in our study, a size gradient from smallest to largest genera appears from Neosclerocalyptus to Doedicurus (Fariña et al., 1998;Vizcaíno et al., 2011).Consequently, a nearly equivalent braincase endocast raw size between Glyptodon munizi and Doedicurus clavicaudatus suggest that the relative brain size of the latter is smaller than in other glyptodonts, supporting the hypothesis of Tambusso and Fariña (2015a).Although we mention aspects associated with the relative size of the brain and its units, we did not generate other characters than K14 for the braincase endocast, leaving room for further investigation of the variation of this part of the endocranium and its potential causes.
Besides the brain, for the endocranial anatomy, the potential relation between body mass and semicircular canal relative size observed for glyptodont might be in accordance with the allometric trend suggested by Billet et al. (2015a) for Xenarthra, especially for the relative reduction in size of the lateral semicircular canal when cranial size increase.However, Neosclerocalyptus pseudornatus in comparison with Glyptodon munizi does not fit clearly this allometric trend.The shape of the semicircular canals in xenarthrans has been hypothesized to be more strongly influenced by phylogeny than by allometry (Billet et al., 2015a).Unlike for extant sloths (Billet et al., 2012(Billet et al., , 2015a)), other xenarthrans including modern armadillos (Billet et al., 2015a) and extinct glyptodonts (Tambusso et al., 2021) show a low intraspecific variation of the bony labyrinth, which, according to Billet et al. (2012) and Hautier et al. (2014), is possibly related to the relaxation of functional constraints.Based on the shape of the inner ear of the analysed species, a clear difference between Glyptodon, Doedicurus, Neosclerocalyptus, and Panochthus was detected, the latter two showing a lateral semicircular canal as the largest or of similar size for all semicircular canals, respectively (K12).The trend of proportionally larger anterior and posterior semicircular canals compared to the lateral semicircular canal in larger species such as Doedicurus clavicaudatus compared to the small glyptodont Neosclerocalyptus pseudornatus is noteworthy, in particular because K12 supports the alternative phylogenetic hypothesis of Fernicola et al. (2018).According to Billet et al. (2015a), Xenarthra follow a general trend observed in primates and marsupials, where a more ventrally oriented cochlea is displayed in smaller xenarthrans.Our sample contradicts this general trend, with Doedicurus clavicaudatus and Panochthus tuberculatus (Tambusso et al., 2021) exhibiting the most ventrally oriented cochlea of our sample.
Finally, we compared the patterns of the cranial canals in relation to the braincase (Le Verger et al., 2021).Limited to the available data, in particular because of the lack of information about Panochthus, we found that a vertical orientation of the posttemporal canal in lateral view (K15) or a passage of the orbitotemporal canal inside the cranium (K16) could support the clade formed by Doedicurus, Neosclerocalyptus, and Panochthus (Fig. 12), on condition that this hypothesis be confirmed in the latter.These potential endocranial characters might, therefore, preferentially support the phylogenetic hypothesis of Nuñez-Blasco et al. (2021) than that of Fernicola et al. (2018).The circulatory pattern of the orbitotemporal canal appears to be similar between Pleistocene and Miocene glyptodonts (Le Verger et al., 2021), suggesting that Glyptodon show a derived pattern of this canal and not a variation due to gigantism.Size variation also does not Comparative Anatomy of the Pleistocene Glyptodonts seem to explain the convergence we found between Glyptodon and Neosclerocalyptus with respect to the distance between optic foramina, suggesting a strong derivation in Doedicurus.These last results remain to be confirmed while revealing the potential of cranial canals for the systematics of glyptodonts.
The completeness and taxonomic diversity of cranial remains collected by Santiago Roth enables potential studies to improve the understanding of evolution, phylogeny, and taxonomic revisions of glyptodonts of the Pampean Region during the Pleistocene.With this material, we provided novel data on the evolutionary morphology of glyptodonts and highlight the interest of endocranial structures for this purpose.Specifically, we highlighted the equivalent support of potential external cranial characters to two of the most recent evolutionary hypotheses concerning phylogenetic relationships among Pleistocene glyptodont genera and called for further evaluation of certain homological hypotheses, suspecting evolutionary convergences within glyptodonts.As a new insight, we suggested that some endocranial structures could provide answers in the debate opposing the current phylogenetic hypotheses of Pleistocene glyptodonts, encouraging their inclusion in future systematic work.The present work could serve as one of the bases for an extended study of the whole history of the clade.

Fig. 2
Fig. 2 Illustrations of the measurements defined in the present work on a skull of Glyptodon munizi (A-F; PIMUZ A/V 461) and selected endocranial structures on a cranium of Neosclerocalyptus pseudornatus (G-I; PIMUZ A/V 439).Cranium in lateral (A), anterior (B), dorsal (D), and ventral (E) views.Mandible in occlusal (C) and lateral (F) views.Endocranial structures are represented by an isolated and verticalized inner ear (G), an isolated braincase in dorsal view (H), and a cranium in transparency and in lateral view (I), showing the inner ear (yellow), braincase (pink), and associated neurocranial canals (red).See Table 2 for measurement definitions

Fig. 3
Fig. 3 Plate of the most complete studied crania in anterior view and their associated schematic drawings housed at PIMUZ and ZMK of Pleistocene glyptodonts of the Pampean Region collected by Santiago Roth.iof, infraorbital foramen; no, narial opening; on, orbital notch; onc, ossified nasal cartilage; zpm, descending process of the zygomatic arch

Fig. 4
Fig. 4 Plate of the most complete studied crania in dorsal view and their associated schematic drawings housed at PIMUZ and ZMK of Pleistocene glyptodonts of the Pampean Region collected by Santiago Roth.nc, nuchal crest; onc, ossified nasal cartilage; pb, postorbital bar; ppj, postorbital process of jugal; sc, sagittal crest 150° in Panochthus intermedius (ZMK 66/1885) and about 160°-170° in Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), 170° in Neosclerocalyptus ornatus (PIMUZ A/V 447) and Neosclerocalyptus gouldi (ZMK 77/1888) and up to 180° in Neosclerocalyptus pseudornatus (PIMUZ A/V 439), without the consideration of the ossified nasal cartilage (Fig.5).While Neosclerocalyptus species show a reduced inclined nasal, in Panochthus intermedius (ZMK 66/1885), the nasal is elongated and strongly anteroventrally inclined.Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) shows the same anteroposterior inclination of the nasal, but with a less prominent elongation of the frontal.In Neosclerocalyptus pseudornatus (PIMUZ A/V 439), the unique well-developed ossified nasal cartilages exhibit an anteroposteriorly inclined point-like structure at the anterior tip.The diverse forms of the ossified nasal cartilages of Neosclerocalyptus species are inclined anteroventrally, forming an angle of about 150° with the naso-frontal area in Neosclerocalyptus pseudornatus (PIMUZ A/V 439), contrary to the inclination of Neosclerocalyptus ornatus (PIMUZ A/V 447) and Neosclerocalyptus gouldi (ZMK 77/1888) of about 160° due to the higher pneumatization of the paranasal sinuses(Zurita et al., 2011b).Regarding the posterior inclination of the parieto-occipital region of the cranium in relation to the upper toothrow, in Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) and Doedicurus clavicaudatus (PIMUZ A/V 4148), the area is inclined upwards, differing from the subparallel course of the parieto-occipital area observed in Neosclerocalyptus pseudornatus (PIMUZ A/V 439) and the downwards inclination of the parieto-occipital region of Panochthus intermedius (ZMK 66/1885), Neosclerocalyptus gouldi (ZMK 77/1888), and Neosclerocalyptus ornatus (PIMUZ A/V 447).This inclination of the parieto-occipital area results in a general convex shape of the cranial roof in the latter three species and in different positions of the basicranium with respect to the dorsal margin of the orbit among the different genera.The basicranium has a more dorsal position relatively to the toothrow in Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) and Doedicurus clavicaudatus (PIMUZ A/V 4148) in contrast to Neosclerocalyptus species, where the basicranium lies below the horizontal level of the dorsal margin of the orbit (Fig.5).An intermediate position of the basicranium can be found in Panochthus intermedius (ZMK 66/1885).Consequently, the palate is dorsoventrally elongated in Doedicurus clavicaudatus (PIMUZ A/V 4148) and Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885).Subsequentially, the zygomatic process of the squamosal inclines in an anteroventral direction in Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885), Panochthus intermedius (ZMK 66/1885), and Doedicurus clavicaudatus (Núñez-Blasco et al., 2021), whereas Neosclerocalyptus gouldi (ZMK 77/1888) and Neosclerocalyptus pseudornatus (PIMUZ A/V 439) exhibit a more horizontal course of the zygomatic process of the squamosal.The zygomatic arch is high and more dorsoventrally elongated in the latter two species, in contrast to the remaining species in which the zygomatic process of the squamosal is thinner dorsoventrally and more anteroposteriorly elongated.The orbit has a middle position in the length of the cranium in Neosclerocalyptus species and Panochthus intermedius (ZMK 66/1885).In Doedicurus clavicaudatus (Núñez-Blasco et al., 2021) and Glyptodon munizi (PIMUZ A/V 461 and ZMK 69/1885) the orbit has a more anterior position than in Neosclerocalyptus and Panochthus; Neosclerocalyptus species

Fig. 5
Fig. 5 Plate of the most complete studied crania in lateral view and their associated schematic drawings housed at PIMUZ and ZMK of Pleistocene glyptodonts of the Pampean Region collected by Santiago Roth.nfa, nasal-frontal area; on, orbital notch; onc, ossified nasal cartilage; pal, palatine; poa, parietal-occipital area; za, zygomatic arch; zpm, descending process of the zygomatic arch

Fig. 7
Fig. 7 Plate of the most complete studied crania in occipital view and their associated schematic drawings housed at PIMUZ and ZMK of Pleistocene glyptodonts of the Pampean Region collected by Santiago Roth.fm, foramen magnum; nc, nuchal crest; oc, occipital condyle; sc, sagittal crest; za, zygomatic arch; zpm, descending process of the zygomatic arch

Fig. 8
Fig.8Plate of the most complete studied mandible in lateral view and their associated schematic drawings housed at PIMUZ and ZMK of Pleistocene glyptodonts of the Pampean Region collected by Santiago Roth.an, angular process; ar, ascending ramus; con, condylar process; cor, coronoid process; hr, horizontal ramus; pda, pre-dentary area

Fig. 9
Fig. 9 Plate of the most complete studied mandible in occlusal view and their associated schematic drawings housed at PIMUZ and ZMK of Pleistocene glyptodonts of the Pampean Region collected by Santiago Roth.con, condylar process; cor, coronoid process; mf1-8, lower molariforms

Fig. 11
Fig.11Plate of the reconstructed braincase (blue-olfactory bulbs; pink-cerebrum and brain stem (pons + medulla oblongata); purplecerebellum) and associated canals (red) including Doedicurus clavicaudatus, Glyptodon munizi, and Neosclerocalyptus pseudornatus.iam, internal auditory meatus; lg, lateral gyrus; ls, longitudinal sulcus; me, medulla oblongata; og, occipital gyrus; olg, olfactory gyrus; opt, optic canal; otc, orbitotemporal canal; ovc, oval canal; pl, pyriform lobe; ptc, post temporal canal; rt, rami temporales; sg, suprasylvian gyrus; soc, sphenorbital canal; tl, temporal lobe; ve, vermis Fig. 12Former and new potential phylogenetic characters for the relationships among the Pleistocene glyptodont genera from our comparative investigation.Shared morphological traits are defined as characters in the illustrated table and each homological or homoplasical hypothesis is illustrated on the schematic tree extracted from the strict consensus ofNuñez-Blasco et al. (2021)  to address the evolutionary history of glyptodonts.For each evolutionary scenario, the anatomical regions involved are identified by a symbol from the cranium of Glyptodon munizi (PIMUZ A/V 461) in lateral view: a cranium for external morphological features, a cranium in transparency with teeth selected for dental characters, an isolated braincase endocast, an isolated and verticalized inner ear, and the neurocranial canals.The color follows the coding of each character.See Table2for measurement abbreviations.Symbol: *, from Nuñez-Blasco et al. (2021).D, Doedicurus; G, Glyptodon; K, character; N, Neosclerocalyptus; P, Panochthus (See figure on next page.)

Table 1
List of specimens from the Roth Collection housed at PIMUZ and ZMK and associated information *, CT-scan available; **, Surface

scan available Specimen-reference Institutional N°Roth N°Locality-age-anatomical part
Table 2 for measurement definitions

Mandibular Measurement- Estimation PIMUZ A/V 461 - PIMUZ A/V 439 PIMUZ A/V 437 ZMK 77/1888 ZMK 66/1885
Gaudin & Wible, 2006)see below).The rami temporales observed in all species open in the cranial roof in various foramina (e.g.,Gaudin & Wible, 2006), marking auxilliary canals from the main braincase canals for the vascularization of temporalis muscles, here, emerging mainly from the orbitotemporal canal (Fig.11; see Le Verger et al., 2021 for more details in glyptodonts, and MacPhee et al., 2021 for different origins of rami temporales in mammals).The largest glyptodont, Doedicurus clavicaudatus (PIMUZ A/V 4148), exhibits a high density and broad canals of the rami temporales in contrast to the remaining species.