Hakuseps imberis, Evans & Matsumoto, 2015

Evans, Susan E. & Matsumoto, Ryoko, 2015, An assemblage of lizards from the Early Cretaceous of Japan, Palaeontologia Electronica (London, England) 52 (4), pp. 1-36 : 18-28

Hakuseps imberis sp. nov.

Figure 13

zoobank.org/ 11AC5FFE-4BA8-4D27-B149-A326E5AF2921

Etymology. From imber, imberis (L) meaning a shower, in reference to the shape of the dentary which resembles that of an inverted shower-head.

Holotype. SBEI 2086 . An almost complete left dentary ( Figure 13 ).

Type locality and horizon. The Kaseki-Kabe, Shiramine, Hakusan city, Ishikawa Prefecture, Japan ( Figure 1 )

Referred material. None

Differential diagnosis. Small reptile (preserved dentary length 9.75 mm) that differs from all known squamates, living and extinct, in having dentary with alveolar margin ending abruptly roughly halfway along the bone and leaving thick, strongly curved, edentulous border between posteriormost tooth and coronoid facet; somewhat resembles Early Cretaceous Pachygenys spp. from China ( Gao and Cheng, 1999) and Japan ( Ikeda et al., 2015) in edentulous margin and in short dentary tooth row (10 tooth positions versus 8 in Pachygenys ), but differs in having heterodont dentition with unicuspid anterior teeth and bicuspid posterior teeth (versus homodont series of blunt-crowned teeth in Pachygenys ), dentary dorsal and ventral margins fused without suture to enclose

EVANS AND MATSUMOTO: JAPANESE FOSSIL LIZARDS

Meckelian fossa (versus deep fossa filled by separate splenial in Pachygenys ), and posterior edentulous region completely separated from tooth row (contiguous with it in Pachygenys ).

Material. SBEI 2086 (Li275) is a left dentary, originally preserved in labial view but prepared from the matrix to reveal its lingual aspect.

Description. The bone is divided into two parts of roughly equal length ( Figure 13 ). The alveolar (dental) margin is limited to the anterior half of the bone. It has a total of ten tooth positions, five of which bear complete teeth. The implantation is pleurodont, but the teeth protrude well above the labial wall of the jaw. The anteriormost tooth position lies immediately adjacent to the symphysis and is visible only in occlusal view ( Figure 13.7 ). The teeth are heterodont, unicuspid anteriorly, with a concave lingual surface flanked by weak mesial and distal crests, and distinctly bicuspid posteriorly, with a small divergent mesial cusp and a broader distal cusp. The tooth in the fifth position (third complete) is intermediate in crown morphology, essentially resembling the anterior teeth but bearing a slight protrusion on the mesial edge in the position occupied by the cuspule in more posterior teeth. The teeth also increase in basal diameter along the row, with the missing penultimate tooth represented by a gap that is more than twice the diameter of anterior teeth. The last tooth position is much smaller. Tooth replacement was lingual, replacement pits being present at the bases of the teeth in positions five and seven. The anterior tip of the bone narrows dorsoventrally, but maintains its width labiolingually to form a distinct symphysial surface. This surface is supported by a deep subdental ridge below which the Meckelian fossa opens for the short distance anteroventrally ( Figure 13.3–4 ). However, at the level of the sixth tooth position, the dorsal and ventral margins of the dentary fuse to fully enclose the Meckelian canal.

Half way along the bone, as preserved, the labial wall supporting the alveolar margin ends abruptly, creating a distinct step in the dorsal edge of the bone. This morphology is not the result of post-mortem damage, the bone surfaces are intact and smooth (unfacetted). The posterior half of the dentary is composed only of its cylindrical ventral portion, enclosing the Meckelian canal, the inferior alveolar nerve, and blood vessels. As a result, the dentary as a whole rather resembles a shower-head or a small hand brush. The "handle" curves posterodorsally but the posterior end of the bone is missing. The posterolingual wall is deeply incised. There is no trace of a splenial facet and this element was either absent or fully fused into the dentary. Immediately above the posteromedial incision, the rising dorsal edge of the bone bears a very shallow depression, flanked dorsolabially by a slight ridge. This depression may represent a weak coronoid facet, but this interpretation is tentative. Posteroventral to it, a vertical sheet of bone extends between the incised lingual wall of the dentary and the rounded labial one. This sheet appears to have a free ventral margin (although it cannot be fully prepared out from the matrix filling the Meckelian fossa as the walls are thin) and may represent an intramandibular septum, separating the Meckelian canal from the inferior alveolar canal laterally. The dorsomedial edge of the septum bears a facet, again possibly for part of the coronoid. The remaining postdentary bones (surangular, angular, prearticular), separately or conjoined, would have slotted into the back of the dentary, but they must have done so at a distinct angle to the horizontal given the strong curvature of the ventral dentary margin.

Four small nutrient foramina pierce the labial surface.

Affinities. This unusual dentary is attributed to the Squamata on the basis of tooth implantation and the general morphology of the anterior part of the jaw. However, it is unlike the dentary of any known lizard, with the partial exception of the roughly contemporaneous species Pachygenys thlastesa ( Gao and Cheng, 1999) ( Figure14.1–2 ). Pachygenys was based on two mandibles from Early Cretaceous deposits in Shandong Province, China. Recently, however, closely similar jaws were recovered from the Sasayama Group of Hyogo Prefecture, Japan ( Ikeda et al., 2015), dated as early Albian (112 Ma, Kusuhashi et al., 2013) and named Pachygenys adachii . As in Hakuseps imberis , the dentary of Pachygenys thlastesa is curved and has small number of teeth (eight) concentrated at the anterior end of the dentary. However, although the posterior region of the dentary of Pachygenys is also edentulous, the labial wall remains intact rather than being stepped ( Figure 14.1 ). Furthermore, below the tooth row, the lingually open Meckelian fossa is filled by a large free posteriorly deep splenial ( Figure 14.2 ). This splenial is pierced just posterior to the level of the last tooth by the anterior inferior alveolar foramen, behind which is the anterior mylohyoid foramen. Pachygenys also has blunt-crowned homodont teeth, unlike the heterodont dentition of Hakuseps with its strongly bicuspid posterior teeth. The two genera could be related, but given that both are represented only by partial mandibles, their phylogenetic position within Squamata is difficult to ascertain. Pachygenys has been referred to "scincomorphs" ( Gao and Cheng, 1999) or lacertoids ( Ikeda et al., 2015). Hakuseps imberis was not included in the phylogenetic analyses as it preserves too few codable characters.

Among extant lizards, some xantusiids have a short edentulous region behind the tooth row. However, this morphology more closely resembles the condition in Pachygenys thlastesa than Hakuseps imberis , and the tooth row is longer and the edentulous region shorter. Xantusiids also show the complete dentary enclosure of the Meckelian fossa seen in Hakuseps , but this feature occurs convergently in gekkotans and in some scincids, gymnophthalmids, and occasional members of other clades, and seems to be a way of strengthening the jaw against bending. An intramandibular septum that extends to the posterior end of the dentary (and has a free margin) has been considered an anguimorph synapomorphy associated with a reduced overlap of dentary and postdentary bones (e.g., Estes et al., 1988), although it can occur in other taxa (e.g., some chameleons, Estes et al., 1988). However, mesio-distally bicuspid teeth with lingual tooth replacement are more usually associated with lacertoids (notably teiids, gymnophthalmids, and lacertids), although bicuspidy can occur in other groups. In fossil lizards, it is recorded in the Early Cretaceous Meyasaurus spp . (= Ilerdaesaurus, Hoffstetter, 1966 ) from Spain (e.g., Richter, 1994; Evans and Barbadillo, 1997) and Britain ( Sweetman, 2009; Sweetman and Evans, 2011). Like Hakuseps , the anterior teeth in all Meyasaurus species are unicuspid and the posterior teeth bicuspid, but there the resemblance ends. Meyasaurus has variously been placed with teiids ( Evans and Barbadillo, 1997), anguimorphs ( Richter, 1994; Conrad, 2008; Bolet and Evans, 2011), cordyliforms ( Müller et al., 2011), or in an unresolved position amongst crown squamates ( Bolet and Evans, 2010). Bicuspidy has recently been reported in a second Spanish taxon, Pedrerasaurus latifrontalis ( Bolet and Evans, 2010) , in jaws (unnamed) that occur with Meyasaurus sp. in the Barremian Wessex Formation ( UK, Sweetman and Evans, 2011), and in another Tetori taxon (see below) with "normal" jaws. In all of these taxa, a small anterior cusp precedes a large posterior cusp, but the anterior cusp is divergent only in Hakuseps imberis , and none of the other taxa shares the atypical jaw morphology.

A jaw morphology somewhat similar to that of Hakuseps imberis , with the posterior half dentary being much shallower than the anterior half, and having a strong upward curvature, is found in some scolecophidian snakes (e.g., Leptotyphlops dulcis, Kley, 2014 ). However, without further material, this strange squamate remains an enigma. The sharp pointed teeth suggest a diet of small invertebrates, but their unusual arrangement (and the overall shape of the jaw) implies a specialised feeding strategy. In the absence of the maxilla and premaxilla, however, it is difficult to understand how the jaws might have been used.

SQUAMATA Oppel, 1811

Family indet. Morphotype A

Figure 15

Material. Within the Shiramine lizard collection there are several maxillae and dentaries with bicuspid teeth, notably SBEI 1501 (Li191) and 1525 (Li193), a right and left maxilla respectively ( Figure 15.1–4 ); SBEI 197 (Li8) and 808 (Li92) ( Figure 15.5–10 ), both left dentaries; and SBEI 1487 (Li190), a right dentary. In all, the accessory cusp is smaller and less divergent than the corresponding cusp of Hakuseps imberis .

Description. SBEI 1501 (Li191) and SBEI 1525 (Li 199) both represent the anterior maxilla. SBEI 1525 is a left maxilla, 4.7 mm long, with 10 tooth positions ( Figure 15.1–2 ). The last four preserved teeth are bicuspid (from tooth position five or six). Although the dorsal margin of the premaxillary process is oblique, the anterior tip is recurved. SBEI 1501 ( Figure15.3–4 ) is a right maxilla, 2.6 mm long, that preserves 12 tooth positions. The anterior teeth are damaged but the posterior ones (from tooth position 8) are bicuspid. The anterior narial margin of the bone is smoothly oblique, with no step or angulation between ventral and posterior components. In this respect it resembles the maxilla of Asagaolacerta tricuspidens , but is less than half of its size. It is possible that this maxilla originally bore a recurved tip like that of SBEI 1525.

SBEI 808 (Li92) is a shallow left dentary, preserved in two pieces, both in labial view ( Figure15.5–10 ). The reconstructed length is ~ 7.9 mm, with a posterior depth of ~ 1.6 mm. The bone tapers at the symphysis, and there are six large labial neurovascular foramina. Fourteen teeth are preserved with at least 10 empty tooth positions, more than twice the number in Hakuseps imberis . The dorsal margin of the dentary is scalloped, with the edge expanding slightly at the base of each tooth. There is also some cementum around the tooth bases. Most of the tooth crowns are preserved and they are visibly bicuspid with a small anterior cusp and a large posterior one ( Figure 15.9–10 ). The second preserved tooth, which is probably the fourth or fifth in position (allowing for at least two small symphysial tooth positions), is already bicuspid. The teeth are quite long and narrow in labial view (exposed height/width 1.9). SBEI 808 is supplemented by two smaller specimens, SBEI 197 (Li8) and SBEI 1487 (Li190) (not illustrated), with similar teeth.

Affinities. Given that these bicuspid jaw remains are generally smaller than the jaws of Asagaolacerta tricuspidens , one possibility is that they represent juveniles of that taxon. Ontogenetic variation in cusp number is known to occur in some modern lizards (e.g., lacertids, Barahona and Green, 1997), and variation can also occur along the tooth row. However, although none of the bicuspid jaws is complete, SBEI 808 has at least 24 tooth positions, almost double the number found in Asagaolacerta tricuspidens , and none is tricuspid. This high tooth count also rules out relationships with Hakuseps imberis and suggests the second kind of bicuspid jaws may represent a distinct lizard taxon, intermediate in size between Kuroyuriella mikikoi and Asagaolacerta tricuspidens .

As noted above, mesio-distal bicuspidy is relatively rare in Mesozoic lizards. The dentition of this second bicuspid Japanese lizard differs from the condition in Meyasaurus in which the anterior dentary teeth are unicuspid and become bicuspid halfway along the tooth row. SBEI 808 shows bicuspidy in anterior dentary teeth (from at least tooth position four). The dentary of Pedrerasaurus latifrontalis is poorly known but, as in the Japanese lizard, it is relatively shallow and bicuspid teeth were present more anteriorly in the tooth row than in Meyasaurus spp . ( Bolet and Evans, 2010). In the maxilla, both have unicuspid anterior teeth, with bicuspidy occurring at about tooth position 8-9 in Pedrerasaurus latifrontalis and at 5-6 in the Japanese lizard. However, without more complete specimens, it would be premature to attach a name to any of these bicuspid jaws as they cannot be diagnosed with assurance.

SQUAMATA Oppel, 1811

Family indet. Morphotype B

Figure 16

Material. SBEI 827 (Li100) is a small right mandible separated into its dentary and postdentary components ( Figure 16 ). The dentary is 4.5 mm long as preserved but is missing the symphysial region and posterior margin (estimated original total length ~ 5.7 mm). The postdentary complex is 4.8 mm long, giving an overall original jaw length of ~ 10.5 mm. The specimen is delicate and is held together by a preservative that obscures some of the detail but which cannot be removed without risk of damage.

Description. The dentary bears at least 15 small, closely-packed unicuspid pleurodont teeth ( Figure 16.3–4 ). Allowing for the missing symphysial region, there may originally have been about 20 teeth. These teeth are slightly spatulate lingually but taper abruptly into small pointed tips (SEM not possible due to the fragility of the specimen and preservative covering). Where visible anteriorly, the subdental ridge is deep and there is a narrow gutter between the tooth bases and the edge of the ridge. The Meckelian fossa seems to be closed anteriorly by the dentary alone but behind this closure, a long splenial obscures the rest of the fossa. The splenial is slightly disarticulated and has been displaced anteromedially, probably by about four tooth positions. It is narrow anteriorly and deepens posteriorly, but a dorsal embayment at the posterior end appears to be real. By comparison with modern lizards, this embayment probably originally underlay the coronoid region. The dentary extends behind the tooth row, expanding dorsally into a large coronoid process that would have covered at least part of the lateral surface of the coronoid bone. Seen in lateral view ( Figure 16.1–2 ), and allowing for preservational artefact, the dentary shows a marked anterior to posterior increase in height.

The postdentary bones appear, at first, to be co-ossified, with a deep anterior notch between dorsal and ventral processes ( Figure 16.5–10 ). However, although the surangular and articular/ prearticular are fused, the narrow angular is separate and has disarticulated labially so that it forms the lower margin of the apparent notch. A thin fragment of bone anterior to this notch may be part of the posterior process of the dentary. The surangular is shallow and bears lateral facets for the dentary, and angular and medial facets for the coronoid. Along its lateral face is a low surangular crest marking the ventral limit of the superficial adductor muscle mass. Even allowing for some distortion, the postdentary bones at their anterior margin are much shallower than the posterior part of the dentary, and a large coronoid presumably filled part of the gap between them. The surangular has a tongue-like anterior extension but this flange is short and is unlikely to have penetrated the Meckelian fossa of the dentary to any significant degree. Medially, the surangular and articular/ prearticular enclose a small shallow posterior adductor fossa. The articular surface for the quadrate is small, broad, and almost vertical, suggesting that the quadrate was oriented at an oblique angle to the rest of the skull. There is no evidence of a retroarticular process but, if thin, this process may have broken off without leaving an obvious edge.

Affinities. In tooth number and the presence of a coronoid process, SBEI 827 resembles the jaws of Kuroyuriella mikikoi , but the jaw shape is completely different (anterior/posterior height difference), the coronoid process is larger and broader, the splenial is deeper, and the angular is shallower. The tightly packed pleurodont teeth, partial dentary closure of the Meckelian fossa, posterior extension of the dentary, co-ossification of the surangular and articular/prearticular, and small size of the adductor fossa are features shared with extant gekkotans, and this jaw was tentatively attributed to that group in a previous review ( Evans and Manabe, 2000). However, gekkotans generally have larger numbers of teeth; do not have a large dentary coronoid process; lose or reduce the splenial; and lose a free angular in all except some eublepharids. Gekkotans are rare in the Mesozoic fossil record. The earliest recorded taxon is Hoburogekko suchanovi from Höovor (Aptian-Albian) in Mongolia ( Alifanov 1989, 1990; Daza et al., 2012, 2014), but the associated dentary lacks postdentary bones and has a fully open Meckelian fossa. Another possible stemgekkotan (as yet unnamed) was described ( Conrad and Norell, 2006) from Öösh, Mongolia (Berriasian to Albian, Andres and Norell, 2005; Berriasian to Barremian, Turner et al., 2007). Like the Tetori specimen, it has a large splenial covering a largely open Meckelian fossa and a small angular, but it lacks a dentary coronoid process and the surangular and articular/prearticular are not fused. The Late Cretaceous Gobekko ( Borsuk-Białynicka, 1990; Daza et al., 2013) has a very poorly preserved jaw making comparison difficult.

Many characters of SBEI 827 (fusion or partial fusion of postdentary bones, partial closure of the Meckelian fossa by the dentary, posterior extension of the dentary, reduced angular) occur in individual members of other squamate clades including pleurodont iguanians, scincids, cordyliforms, xantusiids, gymnophthalmids, and xenosaurs (Evans, 2008). A subset of these clades share other features of SBEI 827, notably the well-developed dentary coronoid process (scincids, cordyliforms, and xantusiids), the small adductor fossa (scincids, xenosaurs, gerrhosaurid cordyliforms), and a sublingual gutter (xantusiids, cordyliforms), but in xantusiids the adductor fossa is large and the Meckelian fossa is usually closed by the dentary and a co-ossified splenial.

Myrmecodaptria microphagosa Gao and Norell, 2000 is an enigmatic Late Cretaceous Gobi lizard currently represented by a single skull. Gao and Norell (2000) referred it to Gekkota, but it lacks gekkotan characters and subsequent phylogenetic analyses have not supported this attribution ( Conrad and Norell, 2006; Conrad, 2008; Gauthier et al., 2012; Daza et al., 2014). Conrad (2008) placed it on the stem of Autarchoglossa (scincomorphs + anguimorphs, sensu Estes et al., 1988), whereas Gauthier et al. (2012) sited it on the scincid stem, and our analyses recover it in the same position - usually in a clade with Carusia ( Figure 6 ). SBEI 827 resembles Myrmecodaptria ( Figure 17.1–2 ), in having a jaw that deepens strongly from anterior to posterior, as well as a large dentary coronoid process, a large splenial, fusion of the postdentary bones, the near vertical orientation of the articular surface for the quadrate, and a posterior extension of the dentary. Some of these features are also present in Carusia intermedia ( Borsuk-Białynicka, 1985) , although the jaw shape is markedly different. The jaw of Myrmecodaptria microphagosa does have a retroarticular process, apparently absent in the Japanese jaw. Both fossils show some resemblance in jaw morphology (posterior deepening, large dentary coronoid process, nearvertical articular surface) to the rare living burrower, Dibamus spp .

Two other disarticulated elements in the Shiramine collection also resemble bones in Myrmecodaptria microphagosa and are of comparable size to SBEI 827. SBEI 2407 (LI304: Figure 17.4 ) is an almost complete left maxilla preserved in labial view (3.35 mm along the alveolar margin). It preserves only six sharp unicuspid teeth but has spaces for up to 18 others. The premaxillary process is oblique but, as preserved, the facial process extends anterodorsally creating an overhang that partially closes the narial opening. This arrangement could be a preservational artefact, but closely resembles the same region in Myrmecodaptria microphagosa (Gao and Norrell, 2000, Figure 17.1 ). In SBEI 2407, the posterior margin of the facial process inclines gradually to form a deep orbital process. Only at the end of the bone is there a sharp step. The maxilla probably formed most of the ventral orbital margin in this lizard with much of the jugal hidden in lateral view by the deep maxilla.

SBEI 1803 (Li253, Figure 17.5 ) is an almost complete median frontal (~ 2 mm across the preserved anterior margin, and 1.3 mm between the orbits). There is no trace of a midline suture and the facets for adjacent bones are well formed, suggesting maturity despite the very small size. The dorsal surface bears weak tuberculate sculpture. Small shelves on the anterior margins are probably the edges of the nasal facets. Prefrontal facets extend along the anterolateral margins of the bone for almost two-thirds of its preserved length, although it is not clear how much of the bone has been lost posteriorly. The bone is embedded in matrix and the small size limits preparation. However, exposure of the ventrolateral edges shows that the subolfactory crests (cristae cranii) extended medially as well as ventrally, although it is not clear how far. Asagaolacerta tricuspidens , Kuroyuriella mikikoi , and Sakurasaurus shokawensis all have paired frontals, and their larger size precludes their paired condition being a juvenile feature. SBEI 1803 is also too small for either the long-bodied Kaganaias hakusanensis or the borioteiioid Kuwajimalla kagaensis , but again it resembles the frontal of Myrmecodaptria microphagosa and could pertain to Shiramine morphotype B.

Whether these elements belong to a single taxon, and whether that taxon is related to Mymecodaptria, remains speculative pending recovery of more complete material.

SQUAMATA Oppel, 1811

Family indet. Morphotype C

Figure 18

Material. Many of the other isolated lizard maxillae and dentaries in the Shiramine collection can be attributed to Sakurasaurus , which is the most common lizard taxon at this locality. However, SBEI 1277 (Li177) is the posterior end of a deep (2.25 mm) left dentary preserved in labial view and bearing seven teeth with spaces for 4–5 others ( Figure 18 ).

Description. The jaw is characterised by a deep posterior incisure that extends anteriorly below the end of the tooth row, and in having teeth that are very small in relation to the height of the jaw (tooth height/jaw height 0.08-0.11 v. 0.21-0.34 in other small Tetori lizards). It does not match any of the named Shiramine taxa, and seems to represent yet another squamate morphotype, but is too fragmentary for further identification. In the deep posterior incisure, it resembles some of the "scincomorph" dentaries described by Ikeda and Saegusa (2013) from the Sasayama Group, but the teeth of the Tetori lizard are relatively much smaller.

SQUAMATA Oppel, 1811

Family indet.

In addition to the two partial postcranial skeletons that may pertain to Asagaolacerta tricuspidens , the Shiramine material includes further isolated postcranial elements. A large proportion of the vertebrae can be attributed to the long-bodied Kaganaias hakusanensis ( Evans et al., 2006) , but smaller ones include: SBEI 292 (Li157), the anterior part of an autotomous caudal vertebra; SBEI 831 (Li104), a procoelous vertebra with a rounded condyle and no zygosphenes; and SBEI 833 (Li106), a fragmentary vertebra with small zygapophyses and a more dorsoventrally depressed condyle. These vertebrae are difficult to attribute but presumably belong to one or more of the small lizards described above.

In addition to the vertebrae, the most common postcranial elements are osteoderms (e.g., SBEI 200-226, 247-255, 276, 556, 559-61, 563, 565, 568-69, 571-79, 807, 811-813, 819, 839-841, 857, 865-883, 893-899, 1218-1220, 1230, 1280-81, 1296-97, 1299-1300, 1509, 1523, 1516-17, 1539, 1544, 1547, 1560, 1564, 1580, 1584, 1586, 1594,1599, 1634, 1640, 1648, 1671-73, 1694, 1715, 1723, 1728, 1731, 1741, 1804-1806), preserved either individually or in groups. These osteoderms are all of the same type. They are rectangular and broadly resemble the osteoderms of paramacellodid lizards (e.g., Paramacellodus spp ., Becklesius spp ., Sharovisaurus karatauensis, Mimobecklesisaurus gansuensis from the Late Jurassic and Early Cretaceous of Europe (e.g., Guimarota, Portugal; Purbeck Limestone Group of England: Hoffstetter, 1966; Estes, 1983; Broschinski, 2000; Evans, personal observation); Asia (e.g., Transbaikalian Russia: Averianov and Fayngertz, 2001; Averianov and Skutschas, 1999; Kazakhstan: Hecht and Hecht, 1984; China: Li, 1985); and North America (e.g., Morrison Formation: Evans and Chure,1998). However, the Tetori osteoderms are too large to belong to any of the lizard taxa described herein and none of the lizard specimens from the Tetori deposits preserves osteoderms in association with other skeletal material. They therefore remain something of a mystery.

Figures

FIGURE 1. Map showing the location of the Kaseki-Kabe fossil site, Ishikawa Prefecture.

FIGURE 6. The phylogenetic position of Kuroyuriella mikikoi gen. et sp. nov. as recovered by analyses run with Implied Weighting (k=7), and character ordering. 1, no backbone constraint; 2, backbone constraint tree based on the molecular trees of Wiens et al. (2010) and Pyron et al. (2013). Only the scincoid section of each tree is shown as in all analyses with equally weighted taxa, Kuroyuriella lies in the stem-squamate position shown in Figure 5.

FIGURE 13. Hakuseps imberis gen. et sp. nov., holotype left dentary, SBEI 2086. 1–2, labial view; 3–4, lingual view; 5–6, occlusal view; and 7, ventral view. For abbreviations, see Material and Methods.

FIGURE 14. Comparison of Pachygenys thlastesa (Gao and Cheng, 1999) and Hakuseps imberis gen. et sp. nov. Labial and lingual views respectively of 1-2, Pachygenys thlastesa (redrawn from Gao and Cheng, 1999), 3-4, Hakuseps imberis gen. et sp. nov.

FIGURE 15. Shiramine Morphotype A, bicuspid dentition. 1–2, left maxilla, SBEI 1525 in labial view; 3–4, right maxilla, SBEI 1501, in labial view; 5–10, left dentary, SBEI 808, in two parts, in labial view, with 5–6, symphysial region, 7– 8, posterior dentary, and 9–10, detail of bicuspid teeth.

FIGURE 16. Shiramine Morphotype B, right mandible SBEI 827. 1–2, dentary in labial view; 3–4, dentary and associated splenial in lingual view; 5–11, postdentary bones in 5–6 dorsomedial view; 7, ventral view; 8, dorsal view; 9, medial view; and 10, posterior view of articular surface. For abbreviations, see Material and Methods.

FIGURE 17. Comparison of Shiramine Morphotype B and Myrmecodaptria microphagosa (Gao and Norell, 2000) from the Late Cretaceous of Mongolia. 1-2, left lateral and dorsal views respectively of the skull of Myrmecodaptria microphagosa, redrawn from Gao and Norell (2000). Scale bar equals 5mm; 3, dentary of morphotype B, SBEI 827, labial view; 4, isolated left maxilla, SBEI 2407, in labial view; 5, isolated median frontal, SBEI 1803, in dorsal view.

FIGURE 18. Shiramine Morphotype C, SBEI 1277, posterior region of a left dentary in 1–2, labial view.