A new cynodont from the Upper Triassic Los Colorados Formation (Argentina, South America) reveals a novel paleobiogeographic context for mammalian ancestors

Probainognathia is a derived lineage of cynodonts which encompass Mammalia as their crown-group. The rich record of probainognathians from the Carnian of Argentina contrasts with their Norian representation, with only one named species. Here we describe a new probainognathian, Tessellatia bonapartei gen. et sp. nov., from the Norian Los Colorados Formation of the Ischigualasto-Villa Unión Basin of Argentina. The new taxon, represented by a partial cranium with associated lower jaws, was analyzed through neutron and X-rays micro-tomography (μCT). The high-resolution neutron μCT data allowed the identification of a unique character combination, including features inaccessible through traditional techniques. We constructed the largest phylogenetic data matrix of non-mammalian cynodonts. The new species and its sister taxon, the Brazilian Therioherpeton cargnini, are recovered as probainognathians, closely related to Mammaliamorpha. We conducted the first quantitative paleobiogeographic analysis of non-mammalian cynodonts, focusing in probainognathians. The results indicate that Probainognathia and Mammaliamorpha originated in southwestern Gondwana (in the Brazilian Paraná Basin), which was an important center of diversification during the Triassic. Finally, the Chinese Lufeng Basin is identified as the ancestral area of Mammaliaformes. These new findings, besides adding to the knowledge of the poorly represented Norian cynodonts from the Los Colorados Formation, are significant to improve our understanding of probainognathian diversity, evolution, and paleobiogeographic history.


Introduction
Probainognathia (Synapsida: Cynodontia) is one of the two main clades of derived cynodonts (Eucynodontia), presently represented by Mammalia [1,2]. With the exception of the highly-specialized, herbivorous tritylodontids, non-mammaliaform probainognathians are mostly small-to medium-sized animalivorous forms. The oldest probainognathian remains are known from Middle Triassic deposits from Gondwana. After an initial diversi cation during the early Late Triassic (Carnian), basal (nonmammaliaform) probainognathians are also found in Norian, Rhaetian, and Jurassic-to-Cretaceous deposits [3]. The abundant Carnian record of the lineage in Argentina is in strong contrast with their poor Norian representation. Among the six Norian probainognathian species previously recognized from Gondwana, four were reported from Brazil, one from Argentina, and one from southern Africa (but see Supplementary Information); most of them only represented by a single or a few fragmentary specimens. This is in concordance with the general scarcity of cynodonts from Norian strata globally [3,4] (see Supplementary Information).
The Norian Los Colorados Formation of the Ischigualasto-Villa Unión Basin of Argentina is worldwide renowned for its vertebrate fossil record [5,6]. One of the youngest dicynodonts of Gondwana, Jachaleria colorata, is represented in the lower levels of the unit [7][8][9]. The upper levels of the Los Colorados Formation represent a different faunal assemblage [10] that have provided one of the oldest turtles [11,12]; basal and derived representatives of the crocodylian lineage [5,[13][14][15][16]; and a number of relatively well-represented dinosaurs [5,[17][18][19][20][21][22], key to the understanding of the rise of this group as it is the earliest assemblage where dinosaurs are dominant components of the ecosystem [23]. Non-mammaliaform cynodonts (NMC) are scarcely represented in this unit [14,24,25]. Only two partial skulls of Chaliminia musteloides [24,25] and a few fragmentary postcranial elements of an unnamed taxon [5,14,26] have been reported. They are among the oldest tritheledontids, a lineage of mainly Gondwanan cynodonts that have been proposed to be closely related to basal mammals [25,[27][28][29]. Renovated exploration efforts since 2014 in the Los Colorados Formation led to new ndings at the Parque Nacional Talampaya (La Rioja province, north-western Argentina), including ve cynodont specimens whose preliminary study suggests that at least three of them might represent previously unrecognized taxa [30]. Recent geochronological studies of the unit suggest that the richest and most renowned faunal assemblage ('La Esquina local fauna'), found in the upper levels of Los Colorados Formation, might be mid-Norian (~220-211Ma) in age [31,32].
Herein we describe a new species of derived NMC found in the upper levels of the Los Colorados Formation (Fig. 1) represented by a partial cranium with articulated lower jaws. The specimen was analyzed through neutron and X-rays micro-tomography (µCT). Although, only scarcely used to analyze fossil specimens, it has become clear that neutron µCT complements very well-with X-ray µCT and it allows circumventing some problems that might arise from the latter methodology depending on the characteristics of the fossil sample studied [33,34]. In addition, we constructed the most comprehensive data-matrix for non-mammalian cynodonts published to date, allowing us to analyze the phylogenetic relationships of the new species and the main hypotheses regarding the ancestry of mammaliaforms and their close relatives. We also present the rst quantitative paleobiogeographic analysis of nonmammalian cynodonts, focusing in probainognathians. Our results provide new insights on the understanding of the evolutionary and paleobiogeography history of Probainognathia. In particular, the new nding improves our knowledge on the diversity of the poorly represented Norian forms in the rich fauna of the Los Colorados Formation, north-western Argentina. Etymology. From the Latin tessella (each one of the tiles composing a mosaic), in reference to the combination of basal and derived features recognized in this taxon.

SYSTEMATIC
Diagnosis. Same as for species.
Tessellatia bonapartei sp. nov. (Figure 2) Etymology. In honor to the late Dr. José F. Bonaparte, who worked unrelentingly to broaden our knowledge of Mesozoic ecosystems and described the rst cynodont remains from the Los Colorados Formation.
Holotype. PULR-V121, partial cranium, represented by the snout and orbital region, with articulated lower jaws.
Locality and horizon. Uppermost third of the Los Colorados Formation, Talampaya National Park, La Rioja Province, Argentina. The specimen was found in a massive-to parallel-laminated sandy mudstone interval locally interbedded with parallel-to rippled-laminated sandstone, representing deposition in a oodplain setting sporadically affected by sandy splays from the uvial channels. See Supplementary Information online for further details on the geological framework.
Diagnosis. (autapomorphies are marked with an asterisk). Small probainognathian with the anteorbital region notably longer than the height of the skull at the level of the anterior margin of the orbit. Alveolar margin of the maxilla sigmoidal, with its dorsal-most point at the level of the canine. Ventrally bowed secondary osseous palate with deep, narrow, lateral groove for the lower postcanines. Contribution of the palatine to the secondary palate relatively long, subequal to that of the maxilla. Masseteric fossa and low coronoid process posterior to the lower tooth row*. Angular process ventrally projected, well-developed, and semicircular in outline*. Horizontal ramus of the dentary comparatively low and lacking a welldeveloped platform lateral to the posterior postcanines. Broad groove between the lateral wall of the dentary and the postcanine alveoli*. Alveolar margin of the dentary anteriorly elevated. Posterior-most lower incisor smaller than the canines and postcanines. Large upper canine and small lower canine. Upper postcanine count larger (14) than the lower postcanines (7)

Skull
The bones of the skull are fragmentary, including portions of the right premaxilla, maxillae, right nasal, frontals, lacrimals, palatines, and pterygoids (Fig. 2). Two elements are too incomplete to be con dently determined, but they might represent parts of the basisphenoid and prootic (Supplementary Figs. S3-4).
The skull is relatively high and in ated immediately anterior to the orbits, at the level of the lacrimals. The snout of Tessellatia is constricted posterior to the canines, resulting in a pin-shaped rostrum (Fig. 2e-f), a condition similar to that of Riograndia, Irajatherium, Pachygenelus monus, Prozostrodon, Pseudotherium, and Brasilitherium (but not Therioherpeton, Elliotherium, and Chaliminia) among derived non-tritylodontid probainognathians (NTP).
A remarkably large facial exposure of the lacrimal (Fig. 2b-c) is a distinctive feature of Tessellatia that, among probainognathians, is only recognized in some tritylodontids. Unlike in other probainognathians, Tessellatia shares with its sister-group Therioherpeton, some tritylodontids, and Morganucodon, a short lacrimal-frontal contact and frontals with short anterolateral projections.
Tessellatia is comparable to early-diverging probainognathians rather to relatively derived forms in the presence of an orbital process of the palatine excluded from the orbital wall and not contacting the frontal. Unlike in derived NTP, in which the secondary palate extends to the end of the tooth row or posterior to it, the osseous secondary palate of Tessellatia ends anteriorly to the antepenultimate upper postcanine (PC13; Fig. 2e-f). On the other hand, Tessellatia shares with some derived probainognathians (i.e., Chaliminia, Elliotherium, Irajatherium, and Pachygenelus), traditionally grouped in Tritheledontidae (see [25]), the presence of a ventrally bowed osseous secondary palate reaching the level of the crown of the upper postcanines ( Fig. 2b-c). In these forms, deep, narrow grooves are present medial to the upper tooth rows, posterior to the maxillae-palatines suture ( Fig. 2e-f).

Lower jaw
The dentary is relatively robust, high, and lateromedially wide ( Fig. 2b-c, h). Unique of Tessellatia is the presence of a broad groove between the lateral wall of the dentary and the postcanine alveoli (Fig. 2g). This groove starts at the posterior half of pc2 and ends laterally to the penultimate lower postcanine (pc6). The anterior region of the dentary is dorsally projected regarding the postcanine line in Tessellatia ( Fig. 2b-c, h) as well as in many derived NTP and the mammaliaform Morganucodon. The shape and development of the angular process of the dentary of Tessellatia distinguishes it from other taxa.

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The upper dentition is constituted by at least one incisor, one canine, and 14 postcanines (1+?I/1C/14PC) ( Fig. 2b-f). The lower dental formula is formed by at least one incisor preserved in position on the dentary and an isolated fragment of another, one canine, and seven postcanines (2+?i/1c/7pc) ( Fig. 2b-c, g-h). Incisors are small non-procumbent teeth ( Fig. 2b-h), unlike those of some tritheledontids (see [25]) such as Chaliminia, Pachygenelus, and Riograndia. The presence of a large upper canine (1.5 or more the mesiodistal length of the rst postcanine) in conjunction with a reduced lower one (the same mesiodistal length or less of the rst postcanine) (Fig. 2b-h) is only recorded in Tessellatia and Riograndia among NMC and shared with the early mammaliaform Morganucodon. On the other hand, in Prozostrodon, Pachygenelus, and Brasilodon as well as in more basal probainognathians (Trucidocynodon, Probainognathus, Lumkuia, Aleodon, and Chiniquodon), both the upper and lower canines are enlarged. Both lower and upper canines are reduced in Chaliminia. The general structure of the postcanines of Tessellatia ( Fig. 2i-j) is similar to those of tritheledontids (see [25]). A reduced number of lower postcanines (7) regarding the number of upper ones (14) is a distinctive feature of Tessellatia among NMC ( Fig. 2b-h). It is noteworthy that the lower tooth row is very short when compared to the upper one. The last lower postcanine (pc7) would have occluded approximately between PC8 and PC9. In this scenario, the last ve upper postcanines lacked a lower counterpart.

Comparisons with Chaliminia musteloides
Chaliminia is the only named cynodont represented by cranial remains previously described from the Los Colorados Formation. It is represented by specimens of comparable size than Tessellatia. Hence, we deem it important to highlight some additional differences of the published specimens of Chaliminia (the holotype PVL 3857 and the referred specimen PULR 088) with the holotype of Tessellatia. Tessellatia has a proportionally longer snout when compared to the height of the skull at the level of the anterior margin of the orbit (Supplementary Table S3). When compared to the holotype of Chaliminia, Tessellatia has a comparatively slenderer dentary. On the other hand, the proportions of the horizontal ramus of the dentary are similar between Tessellatia and the referred specimen of Chaliminia (PULR 081) (Supplementary Table S4). However, it is important to take into account that the anterior end of the skull and lower jaws are missing in Tessellatia; a longer skull and dentary would mean a longer snout and a slenderer horizontal ramus of the dentary, accentuating the differences in these proportions with the specimens of Chaliminia.
In addition, Tessellatia (Fig. 2) differs from Chaliminia in the presence of a constriction in the snout posterior to the canines that results in a pin-shaped rostrum; a strongly concave posterior margin of the secondary palate; a notably short lower tooth row with the ascending coronoid process of the dentary well-posterior to the last lower postcanine, slightly sloping dorsally at the level of the orbits; the masseteric fossa does not reach the level of the last lower postcanine; a broad groove between the lateral wall of the dentary and the postcanine alveoli; and small non-procumbent lower incisors (Fig. 2). Tessellatia lacks the strong osseous platform lateral to the last lower postcanines observed in the holotype of Chaliminia. The lower canine of Tessellatia has approximately the same diameter than the rst lower postcanine, as measured at the upper portion of the root, whereas the lower canine of Chaliminia is markedly larger than the postcanines. Unlike the condition of Chaliminia, there is no lower post-canine diastema in Tessellatia.
Despite sharing the general morphology, there are some differences in the postcanine dentition between Tessellatia and Chaliminia. Unlike the convex labial and concave lingual surface of the upper postcanines of Tessellatia, in Chaliminia there is a central blunt crest separating mesial and distal depressions labially whereas the lingual surface is almost at. Contrary to what is observed in Tessellatia, the lower postcanines of Chaliminia are mesiodistally shorter than the upper ones. In Chaliminia, the lower postcanines show more conspicuous, higher distal accessory cusps, more closely placed to the main cusp than in Tessellatia.

Phylogenetic results
The parsimony analysis of 151 characters and 73 operational taxonomic units (OTUs) resulted in 29,304 most parsimonious trees (mpt) of 786 steps. The strict consensus is poorly resolved. There is a large polytomy including a wide array of taxa. A basal group of Cynodontia (represented by Late Permian forms), Epicynodontia, and Eucynodontia, as usually conceived [2,28,42], are not recovered. Only Cynognathia and a clade including some derived probainognathians are recovered by our analysis. Tritylodontidae, the only clade with a strong support, is nested among the latter group.
A second analysis excluding three wild-card taxa (i.e., Diegocanis, Charruodon, and Microconodon) retrieved 200 mpt of 782 steps, whose strict consensus is better resolved than with the complete dataset (Fig. 4). A basal group of Late Permian cynodonts is followed by Cynosaurus, a node that perhaps represents the Epicynodontia level. The next node is a large polytomy including several terminals. Traditional taxa of Probainognathia, such as Chiniquodon, Trucidocynodon, Ecteninion, Candelariodon, Probainognathus + Bonacynodon, and Aleodon cromptoni + Aleodon brachyrhamphus, are recovered as part of the mentioned polytomy that also includes basal members of Epicynodontia. Cynognathia and Tritylodondidae form monophyletic groups as in the complete analysis. This is not the case for Tritheledontidae whose members are found to belong to the Mammaliamorpha clade (as de ned by [43]), as stem-taxa to Tritylodontidae or to Mammaliaformes. According to this, Mammaliamorpha includes tritylodontids, mammaliaforms, and a number of derived probainognathians. Tessellatia is recovered as sister-group of the Brazilian Therioherpeton based on two unambiguous synapomorphies: axis of the posterior region of the maxillary tooth row directed towards the center of the subtemporal fossa (character 98:1) and transverse axis of crown strongly oblique to midline axis of the skull (character 114:1). The clade formed by Tessellatia + Therioherpeton is in a basal position among the reducedprobainognathian clade, as the sister-group to the group including Protheriodon and Mammaliamorpha. The clade Protheriodon + Mammaliamorpha is supported by two unambiguous synapomorphies: a relatively long secondary palate (character 48:1; which is shorter in Tessellatia and Therioherpeton) and snout longer than the temporal region (character 10:0; unknown in Tessellatia and shorter in Therioherpeton). The absence of the prefrontal and postorbital bones (character 4:1 and 6:2), a slender zygomatic arch (character 17:0), a moderate lateral expansion of the braincase (character 28:1), a reduced lower canine (character 96:1), and a unilateral postcanine occlusion without forming a consistent pattern between upper and lower teeth (character 99:1) are unambiguous synapomorphies of the clade formed by Tessellatia + Therioherpeton and Mammaliamorpha.
A traditional Probainognathia is portrayed in the majority rule consensus tree of the reduced, second analysis ( Supplementary Fig. S5). It shows a basal polytomy integrated by Candelariodon, a chiniquodontid clade (Chiniquodon + Aleodon), and a clade with remaining probainognathians, which includes a polytomy formed by three clades: (Bonacynodon + Probainognathus), (Trucidocynodon + Ecteninion), and the other probainognathians. In this topology, the placement of Lumkuia, the oldest and only basal Probainognathia from South Africa, is counterintuitive, and different to previous phylogenies in which it was recovered as the basal-most Probainognathia (e.g., [2,43]) or as the basal-most Eucynodontia, stem to Cynognathia and Probainognathia (e.g., [42]). In our majority rule tree, basal-most Probainognathia are represented by a group of largely South American Late Triassic taxa.

Probainognathian paleobiogeography
A Bayesian Binary Markov Chain Monte Carlo (BBM) analysis of 100,000 cycles and 100 chains was performed, including nine a priori determined areas of provenance (Supplementary Table S1) and allowing the maximum number of areas per node. The study was based on the probainognathian clade as shown in the majority rule consensus tree ( Supplementary Fig. S5) obtained from the analysis of the pruned dataset (70 OTUs, 151 characters). Additionally, we performed a Hausdorf's [44] manual optimization of Probainognathia, Mammaliamorpha, and Trityldontidae nodes (Supplementary Tables  S5-8).
The results (Fig. 5) indicate that the paleobiogeographic history of probainognathians was dominated by dispersions (22 events) and sympatric speciation events (18 events), followed by vicariances (13 events) and with a single extinction event. Probainognathia originated in Brazil (87.29%) and this was followed by a large and relatively quick increase in the diversity. This diversi cation event included the origin of Mammaliamorpha in this region (97.31%). Hausdorf's optimization indicates the same results for Probainognathia and Mammaliamorpha nodes (Supplementary Tables S5-6).
According to our results, mammaliamorphs thrived in Brazil and experimented a few dispersions to Argentina (2 events), China (1 event), and North America (1 event). It is in China where the origin of Mammaliaformes is expected (52.03%). However, it must be noted that we did not include Gondwanodon and Tikitherium, from the Late Carnian-Early Norian Tiki Formation (Madhya Pradesh, India), in our analysis as they are both represented by an isolated tooth which is even incompletely preserved in the case of Gondwanodon [45][46][47]. Although never tested phylogenetically, Gondwanodon has been considered to be closely related to Morganucodon [48,49]. Tikitherium, originally interpreted to be related to Morganucodon, is now regarded as a docodontan, more closely related to the Rhaetian Delsatia and Woutersia from France [50]. The Tiki Formation records the only faunal assemblage from the Triassic of Gondwana featuring remains of mammaliaforms (in fact, the oldest record of the group) and the early recognition of two mammaliaforms with clearly different tooth patterns suggests an undocumented worldwide evolution of this group. By the end of the Norian, dispersion events from Brazil to South Africa are identi ed. In this latter region, they diversi ed and dispersed to China (1 event) and North America (1 event). The origin of Tritylodontidae is inferred to have occurred in South Africa (28.44%), whilst Hausdorf's optimization indicates that the origin of this group occurred in China (Supplementary Table  S7).

Discussion
There is a profuse Triassic record of cynodonts in the Ischigualasto-Villa Union Basin of Argentina, particularly remarkable in the Carnian Chañares and Ischigualasto formations [51,52]. American assemblages because it is numerically dominated by large taxa (e.g., sauropodomorphs), with only a few known specimens of the rare small-sized cynodonts present (see Supplementary Information). On the other hand, small cynodonts are diverse and/or abundant in the Caturrita and Quebrada del Barro formations [8,53].
Contrasting with the limited record of Probainognathia (and cynodonts) of the Los Colorados Formation, the Late Carnian-Norian record of the Santa Maria and Caturrita formations (Brazil) shows a burst of diversity of small derived probainognathians with at least eight species [4]. In fact, the Brazilian record of the group provides most of the information regarding Probainognathia during that time in the world. A second, very important pulse of diversi cation of this lineage is clearly headed by mammaliamorphs mostly from the early Jurassic. In this case, tritylodontids make the great difference because extreme modi cations of the skull, dentition and, together with early mammaliaforms (i.e., Morganucodon and allies), of the postcranium. Tritylodontids were also abundant and diverse, with a cosmopolitan distribution, and the only cynodont lineage of this time reaching comparatively large body sizes.
Basal and derived probainognathians are recognized during the Carnian, including some relatively earlydiverging forms that attained the largest body-masses of the Triassic representatives of the clade (e.g., Chiniquodon, Trucidocynodon; [51,54]). During the Norian, only small-sized probainognathians are represented. This scenario suggests that the Carnian-Norian transition represented a pivotal moment for the diversity and ecology of cynodonts in general and probainognathians in particular, probably related to the Carnian Pluvial Episode [55].
According to our phylogenetic results (Fig. 4), the two taxa from Los Colorados are not closely related. Tessellatia is an early-diverging taxon whereas the comparatively more crownward positioned Chaliminia is more closely related to tritylodontids than to mammaliaforms. The calibrated phylogeny together with the quantitative paleobiogeographic analysis of probainognathians (Fig. 5) presented here point to two major diversi cation events. One of them took place during the Middle Triassic and the earliest Late Triassic and included the origin of Mammaliamorpha. The second occurred in the latest Rhaetian and is represented by the origin of tritylodontids and closely allied forms. According to our results, the Norian is marked by an almost absence of diversi cation events. It is by mid-Norian times that the origin of Mammaliaformes would have occurred; however, mammaliaforms are not recognized until the latest Triassic and Jurassic. The results of our analysis imply long ghost-lineages for many taxa, including Tessellatia, suggesting a still unrecorded history of Probainognathia.
Dispersion events from Brazil during the Carnian-earliest Norian were restricted to Argentina whereas during the late-Norian-Rhaetian dispersions are from Brazil to South Africa. This suggests that, during these two time-lapses, barriers or favorable conditions to dispersion were alternatively in place in Argentina and South Africa preventing or encouraging dispersions from Brazil. It is also interesting to note that the three dispersion events from Brazil to Argentina represented by Tessellatia, Chaliminia, and Pseudotherium were not followed by diversi cations. These results highlight the importance of improving the knowledge on Norian probainognathians.
Our study reveals a new species of a probainognathian cynodont, adding to the poorly known cynodont diversity from the rich Norian faunal assemblage of the Los Colorados Formation. The phylogenetic evaluation of Tessellatia through the most comprehensive non-mammalian cynodonts data-matrix assembled to date together with the rst quantitative paleobiogeographic analysis of probainognathians highlight a previously unrecognized evolutionary and biogeographic history.

Micro-tomography
The small size and delicate bones make it impossible to remove the hard rock matrix without damaging the specimens and losing important information. In order to overcome this issue, PULR-V121 was analyzed through X-ray micro-tomography in YPF Tecnología S.A. (Y-TEC, Ensenada, Buenos Aires, Argentina) using the Bruker SkyScan 1173 instrument. The equipment was set up to 100kV and 80µA. A total of 900 images of the specimen were captured through a 360° tomography (rotation step 0.4°) with an exposure time of 250ms with two frames averaged. The experimental design resulted in a 40.01µm pixel size. The tomographic reconstruction was then produced with the software NRecon v. 1.6.9.8. Although obtaining acceptable results, the resolution was not ideal. Regrettably, the reconstructed images proved to be di cult to interpret, as bone and matrix were in some regions indistinguishable from each other. We acknowledged that this issue was probably technique-related due to the presence of ferruginous material in the sediment. Hence, we decided to perform a preliminary neutron-tomography at the RA-6 facility (Comisión Nacional de Energía Atómica, San Carlos de Bariloche, Argentina). Considering the promissory results obtained and the hypothesis that this specimen may represent a previously unregistered taxon of the very poorly represented mammalian ancestors in the late Late Triassic of Argentina, we performed a neutron tomography with the highest possible spatial resolution at the ANTARES instrument [56,57] in the Forschungs-Neutronenquelle Heinz Maier-Leibnitz Zentrum (FRM II, Garching, Germany).
The specimen did not show previous radioactivity before introducing it directly to the reactor hall at ANTARES instrument. For the neutron tomography, PULR-V121 was wrapped in aluminum foil together with two additional specimens from the same stratigraphic levels (PULR-V222 and PULR-V223) to maximize the available beam-time. The package was placed in a 5cm long slot of an aluminum cylinder.
A small aluminum plate was xed to the cylinder using aluminum tape to act as a oor. This stabilized the specimens during the tomography and allowed to place them as close as possible to the detector (Supplementary Fig. S1). At ANTARES, a collimation ratio of L/D=500 was used. The Andor Neo sCMOS detector was equipped with a 100mm Zeiss Milvus f2.0 lens which allowed us to obtain high resolution images, with a 19.74µm pixel size. We performed a standard (white-beam), 360° tomography employing who also generated the 3D model of PULR-V121. Approximately two weeks after the neutron tomography, PULR-V121 showed a very low decay ratio and was possible to remove it from the reactor hall.

Phylogenetic analysis
We put together a data matrix combining those of Liu and Olsen [42] and Ruta et al. [28] considering the subsequent modi cations to both of them as well as modifying or deleting some of the characters and character states. We also added new characters and included the new specimen PULR-V121 as well as other relevant taxa. As a result, a comprehensive data matrix including 73 taxa and 151 characters was produced. Previous scorings were revised, and corrections implemented (Supplementary Appendix S1).
A rst analysis was produced after the complete data matrix. After the recognition of three wild-card taxa (i.e., Diegocanis, Charruodon, and Microconodon), we pruned them from the matrix and performed a second analysis considering only the 70 remaining taxa. TNT 1.5 software program [63, 64] was used for searching of most parsimonious trees. Routine used was the command xmult=level 10, that produce 14 autoconstrained replications; each replication with random sectorial searches, drifting (36 iters) and fusing (10 round), nding best score 1 time; followed by bb (bbreak) command that perform branchswapping (tree bisection reconnection) using pre-existing trees. Characters were unordered and equally weighted.    Tessellatia bonapartei holotype specimen (PULR-V121). Neutron tomography image of a transversal cross-section of the cranium showing the ossi ed maxillary canal.

Figure 4
Equal length calibrated, strict consensus tree of the pruned data matrix.

Supplementary Files
This is a list of supplementary les associated with this preprint. Click to download. GaetanoetalSupplementaryInformation.docx GaetanoetalSupplemetaryAppendixS1Anotatedphylogeneticdatamatrix.nex