Gaultia ragei ( Sullivan et al., 2012 ) Sullivan et al., 2012

Čerňanský, Andrej, Smith, Richard, Smith, Thierry & Folie, Annelise, 2024, Timing of intercontinental faunal migrations: Anguimorph lizards from the earliest Eocene (MP 7) of Dormaal, Belgium, Zoological Journal of the Linnean Society 201 (4), pp. 1-25 : 3-11

Gaultia ragei ( Sullivan et al., 2012) comb. nov.

( Figs 1–6 )

Zoobank LSID: urn:lsid:zoobank.org:act:DDA313D5-2D77-43B8-9896-C22E43FA7B32 .

1962 Anguidae proche de Melanosaurus — Hecht and Hoffstetter: 6–8.

1978 cf. Melanosaurus — Godinot et al. 1978: 1273.

1983 Melanosaurus ? sp.— Estes: 146.

1990 Melanosaurini indéterminé— Augé: 169, 170, fig. 6.

1990 Glyptosauriné indéterminé— Augé: 169.

2005 Placosaurus indét.— Augé: 203, figs 139, 142, 143.

2006 cf. Paraplacosauriops quercyi — Augé and Sullivan (in part): 135, fig. 4.

2012? Placosaurus ragei — Sullivan et al.: 630, figs 2, 3.

Holotype: IRSNB R 263 (formerly DO 2 in Augé 2005), a nearly complete left dentary ( Fig. 1 ; Sullivan et al. 2012: fig. 2).

Previously referred material: IRSNB R 112, incomplete left maxilla ( Augé 1990: fig. 6); IRSNB R 264, incomplete parietal missing the left posterior corner and distal portions of the supratemporal processes ( Sullivan et al. 2012: fig. 3); and IRSNB R 265, cephalic osteoderm ( Sullivan et al. 2012: not figured).

Newly referred material: IRSNB R 478, IRSNB R 479, IRSNB R 480, three maxillae; IRSNB R 481, right frontal; IRSNB R 392, fused frontals; IRSNB R 266, medial part of a right frontal; IRSNB R 482, mid- and right portion of the parietal table; IRSNB R 483, left dentary without anterior end; IRSNB R 484, anterior portion of the left dentary; IRSNB R 485, posterior region of the left dentary.

Type locality and horizon: Dormaal, Flemish Brabant, eastern Belgium, Dormaal Member, Tienen Formation, Landen Group, earliest Eocene (MP 7).

Taxonomic comment: Since Hecht and Hoffstetter (1962), the Dormaal glytosaurid taxon has been questionably considered as Melanosaurus or Placosaurus based on a dentary and a parietal, and was eventually allocated to the new species? Placosaurus ragei ( Sullivan et al. 2012) . However, the current taxonomy of species of Placosaurus is based on the morphology of the frontal. The newly referred frontal differs from that of the European Placosaurus (see: Sullivan and Augé 2006: figs 1, 3, Čerňanský et al. 2023b) and is similar to that of the North American Gaultia Smith, 2009 ( Smith 2009: fig. 18D, E), sharing features such as apically flat osteoderms (not thick as in Placosaurus , and not bulbous as in, e.g. Glyptosaurus , Helodermoides , and Stenoplacosaurus ) and presence of chevron-shaped osteoderms.

Revised diagnosis: A species of Gaultia that is similar to Ga. silvaticus but differs from it by (i) slightly laterally narrower frontal; (ii) presence of additional shields between the anterior one and chevron shields; and (iii) a different arrangement of shields in the posterior region—larger shields, less fragmented. It can be distinguished from Sullivanosaurus gallicus by the following combination of features: (i) frontal of Ga. ragei is narrower compared to Su. gallicus ; (ii) frontal of Ga. ragei possesses fewer osteodermal shields in the posterior portion—three instead of four. The second row anterior to that possesses two osteoderms vs. three; (iii) the shape of osteoderms—the osteoderms of the first posterior row are hexagonal in Ga. ragei but distinctly elongate, roughly trapezoidal in Su. gallicus ; (iv) the first anterior central shield in Ga. ragei reaches much further anteriorly vs. only slightly further anteriorly than the lateral shield; and (v) the first central shield in Ga. ragei is laterally larger than the lateral shield vs. a narrower central shield in Su. gallicus .

Description of newly referred material

Maxilla: Three incomplete right maxillae were recovered. The specimen IRSNB R 478 ( Fig. 2A–F ) is better preserved, only its anterior portion forming the forked premaxillary process is broken off. Its maximum anteroposterior length is 23.7 mm. The specimen IRSNB R 480 ( Fig. 2K, L ) represents only the posterior region, whereas the specimen IRSNB R 479 ( Fig. 2G–J ) is a partly preserved mid-portion of the maxilla. IRSNB R 478 possesses 16 tooth positions (four teeth are still attached in the posterior region), IRSNB R 479 has nine (six teeth are preserved), and IRSNB R 480 has seven tooth positions (five and a half teeth are still preserved). The facial (nasal) process of the maxilla is fairly preserved in IRSNB R 478, forming a high, almost perpendicular wall to the subdental shelf ( Fig. 2A–F ). On its external surface, irregular osteoderms are preserved, the largest of which is the second one from the anterior tip of the bone ( Fig. 2A ). They are irregular in shape, some of them being roughly polygonal. They are sculptured with tubercles and divided by sulci. Ventrally, the labial face of the maxilla is pierced by eight supralabial foramina. They gradually increase in size posteriorly, where the posteriormost is located at the level of the sixth tooth position (counted from posterior). The facial process itself has an irregular shape. Its dorsal margin is wavy, roughly M-shaped. It has two peaks, of which the anterior one is smaller and slightly bent medially. The posterior peak of the facial process is larger, rising more-or-less straight dorsally. The posterior margin of this peak slopes distinctly ventrally and therefore gradually decreases in size posteriorly. Its end is stepped.

In medial view, the posterodorsal portion of the facial process (the posterior peak) broadly overlaps the prefrontal—the large and rough articulation surface is still clearly visible ( Fig. 2B ). In the posterior ventral corner, there is an articulation for the lacrimal ( Fig. 2E ). The smooth medial surface of the facial process bears two depressions: a large, elliptical one anteriorly [its dorsal portion bears a foramen–ethmoidal foramen sensu Conrad (2004); Fig. 2E ] and a smaller, longitudinal one posteriorly [posterior depression sensu Evans (2008); the medial recess for the nasal sac sensu Ledesma and Scarpetta (2018)]. They are separated from each other by an anteroventrally to posterodorsally oriented ridge. The supradental shelf dorsal surface is straight ( Fig. 2B ), but its anterior section is broken off. The shelf itself expands medially, reaching its maximum at the level of the sixth tooth position (counted from posterior). Here, the contact with the palatine is present ( Fig. 2F ). All specimens bear the posterior opening of the superior alveolar canal ( Fig. 2D–F, J, L ). It is anteroposteriorly large, elliptical, and located at the level of the fifth tooth position (counted from posterior) in IRSNB R 480 and third tooth position in IRSNB R 479 (note, however, that the posterior portion in this specimen is broken off and the real number of the posterior teeth is unknown). The posterolateral margin of IRSNB R 478 ( Fig. 2F ) and IRSNB R 480 ( Fig. 2L ) is formed by a rounded lip of bone that, posteriorly, presents a deep facet for the jugal.

Remarks

The tuberculate sculpture of osteoderms ( Fig. 2A, G ) represents a synapomorphy of glyptosaurids ( Camp 1923, Gilmore 1928, Sullivan 1979, 2019, Estes 1983, Gauthier et al. 2012, Čerňanský et al. 2023b). A division of osteodermal cover of the facial process indicates that the maxillae belong to Glyptosaurinae rather than ‘Melanosaurinae’ (although it lacks the well-defined hexagonal osteoderms, see below). Additional specimens are described here as Gaultia ragei on the basis of tooth morphology (including the holotype IRSNB R 263; Fig. 1 , see: Sullivan et al. 2012: fig: 2) and size, all coming from the same locality of Dormaal, Belgium. Note that the osteodermal division on the lateral side of the maxilla is very atypical for Glyptosaurinae , lacking the well-defined hexagonal osteoderms. This might support the association of these elements with the frontal bones ( Fig. 3 ) presenting also the same atypical osteodermal division (the pattern of osteoderm shapes; see below).

Frontal: The right frontal IRSNB R 481 is almost completely preserved, only the posterolateral corner is partly broken off ( Fig. 3A–D ). It is laterally narrow and robustly built. The bone is anteroposteriorly long (its maximum anteroposterior length is 19.7 mm), roughly triangular—the posterolateral corner expands into a short process. This lateral expansion starts at about the half length of the bone. At the posterior end, the bone is widest (the maximum width here is 6.9 mm; note, however, that as the posterolateral process is partly damaged, the original width of this region was slightly larger).The lateral margin of the bone is slightly concave medially, so the bone is the narrowest at around mid-orbit (the minimal width here is 4.4 mm). Anteriorly, the frontal extends into a long and pointed anteromedial (nasal) process. The dorsal surface of its anterolateral side is exposed, bearing weak longitudinal grooves and ridges forming the articulating surface for the nasal ( Fig. 3A, B ). The external surface of the frontal is almost fully covered by sculptured osteodermal shields. The sculpture is formed by small rounded discrete tubercles that are regularly and densely arranged. In the anterior section, tubercles are arranged in anteromedially to posterolaterally oriented parallel rows extending anteriorly from the centre. This most likely indicates an ossification centre. The osteodermal shields are of various irregular, polygonal (rhomboidal, pentagonal, hexagonal) to roughly oval or ovoid shape. In the anterior portion, there is a large, first anterior central shield that is ovoid in shape. Posterolaterally to this, a lateral shield is present. It is wing-shaped, with an anterolaterally protruding lateral section. However, it reaches anteriorly less than half of the first central shield. The posteromedial margin is V-shaped. Medially to this, two small second and third central shields are present. They probably continued to the left frontal. If so (estimating its mirror symmetry), they would be more-or-less hexagonal. Posteriorly, two single mediolaterally elongated and chevron-shaped shields are located in a row. They cover the mid-portion of the frontal (where the frontal is the narrowest) and expand medially, probably having contact in the midline with those on the left frontal. In the case of the second chevron shield (the most posterior one), however, one additional small triangular (if they continue to the left frontal, estimating its mirror symmetry, it was rhomboidal) shield is present posteriomedially to the second chevron one. Note, however, that it is not clear whether the groove separating it from the next posterior pentagonal osteoderm is a sulcus or a break (in such case, it would be a part of this pentagonal osteoderm). This posterior large pentagonal shield is one of two pentagonal shields that form a row posterior to the two chevron ones. In the posteriormost portion of the frontal, close to the straight contact with parietal, a row of three, anteroposteriorly slightly elongate, roughly hexagonal shields, is present (the lateral one is missing).

In lateral view ( Fig. 3D ), a large, wedge shaped and rugose facet for the prefrontal is located in the anterior region, laterally to the frontal cranial crest ( Fig. 3C ). On the lateral side of the posterolateral process, a slightly narrow facet for the postfrontal is clearly visible. Prefrontal and postfrontal were not in contact, so they did not fully exclude the frontal from the orbital border.

In ventral view ( Fig.3C ), a large and robust frontal cranial crest can be observed. In its anterior portion, it extends ventrally into a rather well-defined and rounded prefrontal (=subolfactory) process (its end is slightly damaged) that achieves a maximum depth of 3.7 mm below the dorsal surface of the bone. The anterior portion of the frontal cranial crest, anterior to the subolfactory process, forms a sharp, medially directed ridge. The anteromedial margin of this crest is thin and sharp. Posteriorly, it widens, gradually diminishing dorsally and extending to the posterolateral process of the frontal. On the lateral side of the crest, a foramen is visible ( Fig. 3C, D ).

The nearly complete frontal IRSNB R 392 ( Fig. 3F–J ) is a large and unpaired element, missing only the anterior end and posterior corner, both on the right side. On the anterior edge of the dorsal surface, a small and clearly visible area is present for the articulation with the nasal ( Fig. 3F, G ). In the anterior and mid-section, the frontal bears traces of the original midline suture on both ventral and dorsal surfaces (more visible, however, in ventral view). The maximum anteroposterior length of the frontal is 20 mm. Overall, the bone is laterally wide, although a weak constriction can be seen in the mid-orbital region. At this level, the width of the bone is 9 mm. The lateral margins of the frontal are slightly concave medially and the whole bone gradually widens posteriorly. This lateral expansion starts at about the half length of the bone. The posterior region is expanded into short posterolateral processes (only the left one is preserved). The maximum width of the preserved element here is 12.8 mm. Note, however, that the right posterior portion of the bone is broken off and estimated width of the complete element in this region, based on the left half, was 16 mm. The external surface is covered by sculptured osteodermal shields that are completely fused to the underlying bone. The sculpture is formed by small, rounded, discrete tubercles. Although some divisions of the osteoderms are visible, they are not as clear as on the specimen IRSNB R 481. There is a hint of chevrons in the mid-region ( Fig. 3F, G ). In the posterior region, there are clear divisions of osteodermal armour to at least three osteoderms on the left side. The first two left (the two most lateral ones: osteoderms 2 and 3 on Fig. 3G ) appear to be rectangular (or polygonal, their shape is unclear, especially at their anterior borders). Potentially, a hint of ‘radiating’ tubercles might be present, but overall, the division pattern is not recognizable.

In ventral view ( Fig. 3H ), large and robust frontal cranial crests are visible. Their anterior portions are ventrally expanded forming well-defined and rounded prefrontal (=subolfactory) processes—the end of the left one is slightly damaged. The anteromedial margins of the crests are thin and sharp, whereas they are wide posteriorly. The anterior portion of the frontal crest, anterior to the subolfactory process, is less deep, forming a well-visible, medially directed ridge. The right and left branches gradually diminish anteriorly, although they appear to join in the anterior mid-line.

In lateral view ( Fig. 3I ), in the anterior region, lateral to the frontal crest (including its lateral surface), a large wedge-shaped facet for the prefrontal is located. In the posterior region, there is a narrower facet for the postfrontal. Prefrontal and postfrontal were probably not in contact, and did not exclude the frontal from the orbital border. The posterior margin forms a contact with the parietal.

Remarks

This frontal was briefly described by Hecht and Hoffstetter (1962) but never figured. Recently, it was figured and discussed by Sullivan (2019: fig. 2) and identified as indeterminate ‘melanosaurine’. According to Sullivan (2019), this specimen bears the frontoparietal scale impression typically present in ‘melanosaurines’ and appears to be similar to that of Placosauriops Kuhn, 1940a . This frontal is, however, problematic, because the exact division pattern of osteodermal cover is difficult to define. Moreover, when studied in detail, the osteoderm morphology differs from that of Placosauriops (see: Meszoley et al. 1978, Smith et al. 2018): there is a complex division of osteodermal cover in the posterior region and traces of chevrons, and maybe a hint of ‘radiating’ tubercles, indicate typical features of Gaultia . So both frontals IRSNB R 392 and R 481 share an apomorphy (chevrons). The unclear division deserves a comment here. As documented in extant Pseudopus Merrem, 1820 , sulci separating osteodermal cover are difficult to observe in large adults due to stronger ossification (Klembera et al. 2017: fig. 17C). This is probably the case of the frontal IRSNB R 392, which is almost completely fused (note that traces of the fusion are still visible). We regard IRSNB R 392 and R 481 as both belonging to Gaultia ragei , the differences in size, shape, and degree of fusion all being attributable to the greater maturity of R 392. In both specimens, the lateral expansion (posterolateral process) starts at about the half length of the bone. A fusion of the frontals in mature adult individuals is also documented in Gaultia ( Smith 2009) , as well as in Sullivanosaurus ( Čerňanský et al. 2023b) and other glyptosaurids in which either fused or separate frontals can be found (Sullivan 1979). This can be seen in anguids as well. In adult specimens of extant Pseudopus , the frontal shields may fuse together (Klembera et al. 2017) and in extinct Pseudopus pannonicus ( Kormos 1911) , the frontals are firmly coalesced ( Roček 2019). Another interesting feature is an orbital margin, which can be slightly different between younger and mature individuals. In P. apodus , it is markedly concave in juvenile specimens in contrast to an almost convex margin in adults ( Klembara et al. 2017: fig. 31A, B). The more convex orbital margin is present also in a single left frontal of Gaultia silvaticus if compared to fused, larger frontals of this species ( Smith 2009: fig. 18D, E). The same appears to be true for Sullivanosaurus ( Čerňanský et al. 2023b: figs 2A, 3A). This is probably related to the presence of larger eyes (and thus larger orbits) in juvenile lizards relative to the skull size, as it is also observed in, e.g. lacertids ( Čerňanský and Syromyatnikova 2019: fig. 31J).

Finally, it is worth mentioning that the Indeterminate ‘Melanosaurini’ IRSNB R 266, also from Dormaal and representing the medial part of a right frontal described by Sullivan et al. (2012: fig. 4), appears to share similar morphology to the specimen describe here as well. Therefore this specimen could potentially be also included in the material attributed to Gaultia ragei .

Parietal: The parietal IRSNB R 482 is incomplete—the anterior, mostly central and right sides are preserved ( Fig. 4 ). The left part is only partly preserved, whereas the posterior portion, including supratemporal processes, is completely broken off. A network of sulci marks the boundaries of osteodermal shields that cover the dorsal surface of the bone. The largest is the interparietal one, which is trapezoidal in shape. In the posterior section of the shield, the bone is pierced by the parietal foramen. Other osteoderms are smaller and of various size and shape, generally being more rounded than those of the frontal ( Fig. 3 ). The lateral portion of the bone is smooth, lacks osteodermal covering, and some lateral osteoderms are partly peeled off. This surface is pierced by small foramina accompanied by anterolaterally (in the anterior portion) or posterolaterally (in the posterior portion) running grooves. The anterolateral process is robust and well expanded laterally. Its end is rounded and blunt. Ventrally, at the base of the process, a wedge cut from the anterolateral margin of the parietal is present and forms the articulation facet with the postfrontal. The facet is mainly visible in lateral and ventral views ( Fig. 4B, C ). In ventral view, it forms a triangular blunt imprint on the anterolateral process. In this view, a strongly developed sharp parietal cranial crest is developed. It separates the supratemporal fossa (containing a muscular surface) from the cranial vault. The crest is low at the level between the frontoparietal suture and the parietal foramen. Posteriorly, it grows markedly in depth and further forms a large (although not distinctly ventrally protruding), mediolaterally compressed ventral process. Its end is blunt and well preserved (only the posterior small portion is partly damaged—note, however, that the preservation of this process is exceptional since the process is broken in most specimens of glyptosaurine isolated parietals). The muscular surface in the supratemporal fossa is broad. Its mediolateral width is slightly larger than the width between the cranial crest and the median line of the parietal at the level of the parietal foramen. The parietal foramen is clearly visible, having a dorsoposterior-anteroventral orientation. The elliptical secondary pit is located posteriorly to the foramen (its presence is caused by the ‘pineal-related cartilage’ immediately underlying the bone; see: Smith et al. 2018). It is lens-shaped, anteroposteriorly elongated, and mediolaterally compressed. It is bordered by a sharp bony lamina. Its anterior tip is well ventrally protruded to form a lip of bone. The posterior tip is connected to a ridge that shortly diminishes in height posteriorly. The frontoparietal suture is more-or-less straight, only slightly interdigitated.

Remarks

The parietal is associated on the basis of size and osteoderm morphology. Indeed, the size of the parietal IRSNB R 482 matches very well with the frontal IRSNB R 392 ( Fig. 3A, B ). In both cases, the osteoderms also appear to match.

Virtual microanatomy and histology

The micro-CT scans of the frontals and parietal revealed a very similar pattern of the internal microanatomy in terms of a vascular network and spongiosis ( Fig. 5 ). There is a large and complex meshwork of numerous cavities. They are irregular, bubble-shaped, and some are interconnected. The bone appears to be less compact in both axial and coronal sections [in comparison to Ophisaurus holeci ( Georgalis and Scheyer 2021) , Ophisaurus spinari ( Syromyatnikova et al. 2022) , and Pseudopus pannonicus ( Loréal et al. 2023) ] and slightly resembles another European glyptosaurid Sullivanosaurus ( Čerňanský et al. 2023b: fig. 3E). In the IRSNB R 392 frontal, traces of a complex firm suture can be visible ( Fig. 5C ). Note that the finer histological details, such as growth marks and cell lacunae of the bone, are not visible.

Dentary: Three left dentaries are preserved. The best preserved one, IRSNB R 483, is only missing the anteriormost end with the symphysis and most of the angular process ( Fig. 6A–E ). The maximum anteroposterior length of the preserved portion is 30.2 mm. It bears 15 tooth positions (seven teeth and half of two others are still attached to the bone). The bone gradually widens posteriorly in lateral and medial views. The lateral surface of the dentary is laterally convex, except at the anterior region. In dorsal view ( Fig. 6C ), from the level of the 10th tooth position (counted from posterior), the bone is slightly rotated dorsolaterally. Thus, its lateral surface is partly visible when the dentary is viewed in dorsal view. The lateral surface of the bone is smooth, being pierced in the mid-region by four labial foramina ( Fig. 6A ). The last posterior foramen is located at the level of the fourth tooth position (counted from posterior). In the dorsal posterior region of the bone, there is a wedge-shaped depression forming the articulation surface for the anterolateral process of the coronoid. The dentary is slender rather than robust, being straight in dorsal view, except the anteriormost section, which appears to be slightly bent medially (note that only the beginning of the anterior portion is preserved, and the anterior end is broken off). The dentary has a slightly dorsally concave appearance in medial view, although the ventral margin of the bone seems to be fairly straight ( Fig. 6D ). This latter margin bears a facet for the splenial reaching the level of the ninth tooth position anteriorly. The Meckelian canal is fully open, although narrow in the anterior and mid-section, being exposed ventrally rather than medially. Posteriorly, the Meckelian canal gradually widens, being open medially. The alveolar canal is large, ventromedially oriented, and separated from the Meckelian canal by the intramandibular septum ( Fig. 6E ). The posteroventral margin of the intramandibular septum extends to a distinct posterior spine that does not fuse to the internal surface of the dentary and is divided from the wall of the dentary by a distinct groove. The Meckelian canal is roofed by a distinctly dorsally convex subdental shelf [dental crest sensu Georgalis et al. (2021)], which is reduced to a smooth sloping, slightly rounded border. Its ventral section slightly expands into a lip of bone that partly overlaps the dorsal portion of the Meckelian canal. On the dorsal section, there is no dental sulcus. In the posterior region, the shelf is interrupted by a notch—it forms the dorsal and anterior border of the anterior inferior alveolar foramen. In IRSNB R 484, the splenial spine is preserved ( Fig. 6G ). The foramen is located at the level of the sixth tooth position (its anterior margin is located at the level between the sixth and seventh tooth position, counted posteriorly). Further posteriorly, the subdental shelf (or crest) is dorsally elevated ( Fig. 6B, D ). It distinctly narrows to form a thin, sharp crest. Note, however, that it is partly damaged. Posteroventrally to this crest, an articulation for the anteromedial process of the coronoid is located, reaching the level of the fourth tooth position (counted from posterior). The bone ends posteriorly in three processes. The coronoid process is short, forming only a small projection ( Fig. 6A, B, D ). It is well defined, separated by a coronoid incisure. The surangular process is large and roughly triangular in shape. It is well projected posteriorly. Only the root portion of the angular process is preserved, but the rest is broken off.

The anterior portion of the dentary, including a symphyseal region, is preserved in the specimen IRSNB R 484 ( Fig. 6F–I ). This dentary narrows anteriorly in medial view. Its anterior end is distinctly bent medially in dorsal view ( Fig. 6H ). The symphysis is well developed, being rectangular in shape. This region is slightly elevated relative to the shelf. The ventral section of the symphysis is pierced by the Meckelian canal. The specimen IRSNB R 485 represents the posterior region of the dentary. It bears seven tooth positions (three and half teeth are still attached).

All these characters are also present on the holotype, the left dentary IRSNB R 263 ( Fig. 1 ; Sullivan et al. 2012: fig. 2), which is nearly complete .

Dentition: The tooth implantation is pleurodont. Teeth are not tightly packed—large gaps are present between them. The teeth are heterodont—in the anterior section of the tooth row, they are smaller and obtusely pointed. More posteriorly, the teeth become gradually anteroposteriorly larger and blunter. The tooth crowns of the posteriormost teeth have a square appearance in lingual view ( Fig. 6B, J, K ). The mesiodistal cutting edges are present (although less distinct than in the jaws of Glyptosauridae indet. from the French Early Eocene Cos locality; see: Čerňanský et al. 2023b: fig. 5). The apicobasal striations are well developed on the lingual side, being restricted on the tooth crown. The labial sides of the tooth crowns are more-or-less smooth. Note, however, that striations can be present on the labial side in some individual teeth, although such striae are not as pronounced as those on the lingual side. Nonetheless, it cannot be excluded that the smooth surface of most of the teeth is caused by poor preservation. In anterior or posterior view, the tooth necks are slightly swollen lingually. The tooth bases are pierced by small elliptical resorption pits.

Remarks

The Glyptosauridae described here from Dormaal, Belgium strongly resembles that of the earliest Eocene North American Gaultia silvaticus Smith, 2009 (biozone Wa-0, Willwood Formation in Wyoming; Smith 2009: fig. 18). Both share apomorphies (flatosteodermsandchevron-shapedosteoderms). Moreover, tubercles are arranged in anteromedially to posterolaterally oriented parallel rows, extending anteriorly from the centre; the dentitions of both American and European forms are also very similar. This is not surprising. In fact, half of the North American mammal taxa are close to Dormaal mammals ( Gingerich and Smith 2006; see Discussion).

Figures

Figure 1. Gaultia ragei comb. nov. from the earliest Eocene of Dormaal.The holotypic left dentary IRSNB R 263 in A, lateral; B, medial; C, ventromedial; and D, dorsal views (all micro-CT visualizations).

Figure 2. Gaultia ragei comb. nov. from the earliest Eocene of Dormaal.Right maxillae: IRSNB R 478 in A, lateral; B, medial with detail of teeth in ventromedial; C, ventral; D, dorsal; E, dorsomedial; and F, posterodorsomedial views. IRSNB R 479 in G, lateral; H, medial; I, ventral; and J, dorsal. IRSNB R 480 in K, lateral with detail of teeth in ventrolateral; L, medial with detail of teeth in ventromedial views (all micro-CT visualizations except of tooth details).

Figure 3. Gaultia ragei comb. nov. from the earliest Eocene of Dormaal.Right frontal IRSNB R 481 (A–E) and fused frontals IRSNB R 392 (F–J) in A, F, dorsal (photographs); B, G, dorsal; C, H, ventral; D, I, lateral; E, J, anterior views (all micro-CT visualizations, except A and F).

Figure 4. Gaultia ragei comb. nov. from the earliest Eocene of Dormaal.The parietal IRSNB R 482 in A, dorsal; B, ventral; C, lateral; D, anteroventrolateral; and E, anteroventral views (all micro-CT visualizations).

Figure 5. Gaultia ragei comb. nov. from the earliest Eocene of Dormaal.Axial section of right frontal IRSNB R 481 (A) and fused frontals IRSNB R 392 (C) and parietal IRSNB R 482 (E) at the mid-level of the dorsoventral thickness; B, D, coronal section at the level of the frontal cranial crests; F, coronal section at the level of the parietal foramen (all from the CT scans).

Figure 6. Gaultia ragei comb. nov. from the earliest Eocene of Dormaal.Left dentaries:IRSNB R 483 in A, lateral; B, medial with detail of teeth; C, dorsal; D, ventromedial and E, posterior views.IRSNB R 484 in F, lateral; G, medial H, dorsal; and I, ventromedial views.IRSNB R 485 in J, lateral with detail of teeth in dorsal; K, medial with detail of teeth in dorsomedial views (all micro-CT visualizations except of tooth details).