Gobiderma pulchrum

Conrad, Jack L., Rieppel, Olivier, Gauthier, Jacques A. & Norell, Mark A., 2011, Osteology Of Gobiderma Pulchrum (Monstersauria, Lepidosauria, Reptilia), Bulletin of the American Museum of Natural History 2011 (362), pp. 1-88 : 69-75

Gobiderma pulchrum , Palaeosaniwa cana- densis, Estesia mongoliensis , and Heloderma-

tidae are united to the exclusion of other

anguimorphs based on three unambiguous

synapomorphies:

1. Presence of snout elongation anteriorly such that a rostrom is present anterior to the level of the anterior margin of the septomaxilla (char. 2, state 1; Conrad, 2008; Conrad et al., 2011).

2. Dentary excluded from the margin of the anterior inferior alveolar foramen (char. 183, state 1).

3. Presence of zygosphenes with dorsolaterally oriented articular facets (char. 235, state 1).

Monstersaurs more closely related to Helodermatidae than to Gobiderma pulchrum form a clade as evinced by the presence of five unambiguous synapomorphies:

1. Frontals with a trapezoidal outline in dorsal view (char. 57, state 1).

2. Absence of a pineal foramen (char. 77, state 3).

3. Absence of a transverse, midline, posterior margin to the parietal table (char. 82, state 1; Conrad, 2008).

4. Chevrons that attach anterior to the posteroventral margin of the centrum (char. 254, state 1).

5. Strongly sutured (rather than coossified or nonsutural) pelvic girdle elements (char. 284, state 1).

The principal trees of this analysis find various placements for UF 206579. It is variably recovered as the outgroup to Heloderma , as the sister group to Heloderma texana , as the sister group to Estesia mongoliensis , as part of a Necrosaurus clade (also including ‘‘ Saniwa ’’ feisti, Necrosaurus cayluxi , and, in some cases, ‘‘ Necrosaurus ’’ eucarinatus ) within Varaniformes, as the sister group of Saniwides mongoliensis within Varaniformes, as a proximal varanid outgroup, or as the sister group to Telmasaurus grangeri . The tree topologies recovering UF 206579 as a varaniform require that grooved dentary teeth arose independently within Varaniformes and Monstersauria.

DISCUSSION PHYLOGENETIC IMPLICATIONS

ANGUIMORPH INTERRELATIONSHIPS: A recent, combined-evidence, phylogenetic analysis of Anguimorpha revealed conflicting hypotheses of anguimorph interrelationships when results are compared between analyses of various data content and taxonomic sampling ( Conrad et al., 2011). Importantly, monstersaurs were found to be closely related to goannasaurs (monitor lizards, mosasaurs, and other fossil relatives) in morphological phylogenetic analyses. In molecular-based phylogenetic analyses and in their combined, global, phylogenetic analysis of anguimorphs, Conrad et al. (2011) found monstersaurs to be the basal radiation of a clade also containing Carusia intermedia , Restes rugosus , Xenosaurus , and anguids. However, when they deleted fossil taxa from their combined morphological/molecular data set, Conrad et al. (2011) found morphological and molecular data supporting a close relationship between monstersaurs and goannasaurs to the exclusion of other squamates.

Our phylogenetic analysis ( figs. 55 , 56 ) is in agreement with the results of the combined-evidence analysis presented by Conrad et al. (2011) in monstersaur membership and in suggesting that monstersaurs are closely related to anguioids. However, the present analysis differs in suggesting that shinisaurs also belong on that branch rather than with goannasaurs.

Fossils from Florida and Tennessee: Although the fossil dentary UF 206579 originally was suggested as a proximal outgroup to Heloderma and it possesses grooved teeth incipient to the Heloderma condition ( Bhullar and Smith, 2008), still it is not recovered as an unambiguous helodermatid or even monstersaur in the current analysis ( fig. 55 ). Indeed, it is one of the more labile taxa in the tree, along with ‘‘ Necrosaurus ’’ eucarinatus . Importantly, both of these taxa are known from very incomplete remains and this may contribute to the ambiguity regarding their phylogenetic placements in the current analysis.

The taxonomic sampling of the analysis provided by Bhullar and Smith (2008) constrained UF 206579 to be a nested helodermatid (sensu Conrad, 2008; Conrad et al., 2011). Certainly the presence of grooved dentary teeth, as well as some of the other characters described by Bhullar and Smith (2008) (and gestalt) would suggest that this is the proper placement of that taxon. However, the currently described remains simply cannot resolve the placement of UF 206579 with certainty (see above).

Similarly, fossil osteoderms recently described from Tennessee probably pertain to an unnamed helodermatid, but the remains are too incomplete to say much more than that (Mead et al., in press).

Estesia mongoliensis: Recently, Yi and Norell (2010) found Estesia mongoliensis to be a basal varaniform and reported on an analysis of 28 taxa coded for 389 characters that failed to recover a holophyletic Monstersauria. Instead, monstersaur monophyly was reportedly rejected, although the only support for this is a ‘‘polytomy between three species of Heloderma (Miocene-Recent, North America), Lowesaurus (Oligocene- Miocene, North America), and Eurheloderma (Eocene/Oligocene of Europe), and varaniforms’’ ( Yi and Norell, 2010: 191 A) rather than a topology actually rejecting monstersaur holophyly. Indeed, given the results of the current analysis ( figs. 55 , 56 ) and recent, extensive combined-evidence analyses supporting monstersaur holophyly ( Conrad et al., 2011; fig. 55 ), we feel that the result of Yi and Norell (2010) may have been caused by limited taxonomic sampling.

MONSTERAUR TOPOLOGY: The two extant monstersaur species are morphologically derived with numerous morphological specializations; they are transformed well beyond what might be considered plesiomorphic for either Anguioidea or Platynota (see data in Pregill et al., 1986; Nydam, 2000; Conrad, 2008; and Conrad et al., 2011). Monstersauria was distinct by the beginning of the Late Cretaceous as evinced by recovery of Primaderma nessovi as a basal monstersaur ( Nydam, 2000; Conrad, 2008; Conrad et al., 2011) and we interpret the similarities between Heloderma and Lanthanotus borneensis as convergences rather than shared derivation, as has been suggested by some analyses (e.g., Caldwell, 1999).

Results from the present analysis and those from the comparative analyses of Conrad et al. (2011) further highlight the importance of Gobiderma pulchrum . Gobiderma pulchrum is a basal monstersaur, falling outside a clade that includes the Cenozoic helodermatids and the Cretaceous taxon Estesia mongoliensis ( Norell and Gao, 1997; Gao and Norell, 1998; Conrad, 2008). As such, Gobiderma pulchrum is an important transitional form between helodermatids and the basal nonhelodermatid members of Monstersauria. Indeed, given the paucity of relatively completely known basal monstersaurs, the data represented by the new Gobiderma pulchrum specimens are invaluable.

MATURITY OF DESCRIBED SPECIMENS

The known Gobiderma pulchrum specimens are similar in overall size. The holotype skull has a craniobasal length of approximately 52 mm as preserved, that of IGM 3/55 is approximately 61 mm, and that of the partially disarticulated IGM 3/905 skull (lacking the snout tip) may be reconstructed as being between 56 and 60 mm long. The sacrum is disarticulated in the only specimen with preserved sacral vertebrae (IGM 3/905) ( figs. 45 , 47 , 48 ). This suggests the possibility that this relatively large specimen is a juvenile. However, the pelvis is completely fused in IGM 3/905. Moreover, the holotype represents a relatively small individual, but in that specimen (and all other available specimens), the braincase elements show some obliteration of the sutures and the supratemporal arch remains in nearly complete natural articulation. This suggests to us these are adult or late subadult specimens. Vertebrae preserved with IGM 3/59 ( fig. 22 ) and IGM 3/905 ( figs. 45 , 46 ) possess fused neural arches (indicating closure of the vertebral growth zones), further bolstering the hypothesis that these are adult individuals.

BASAL MONSTERSAURIAN MORPHOLOGY

Extant Heloderma have long been acknowledged for their morphological distinctiveness, including specializations associated with the presence of a specialized venomdelivery system (see, for example, Wiegmann, 1829; McDowell and Bogert, 1954; Rieppel, 1980a; and Pregill et al., 1986). They are the only extant lizards with an advanced venomdelivery system. Absence of a complete supratemporal arch and expansion of the jaw adductor musculature has led to comparisons with the enigmatic and derived varanid Lanthanotus borneensis (e.g., McDowell and Bogert, 1954), but this taxon has been demonstrated to be closer to Varanus than to Heloderma by numerous recent analyses ( Estes et al., 1988; Norell et al., 1992; Wu et al., 1996; Norell and Gao, 1997; Evans and Barbadillo, 1998; Gao and Norell, 1998; Lee, 1998; Caldwell, 1999; Evans and Barbadillo, 1999; Lee, 2000; Lee and Caldwell, 2000; Evans et al., 2005; Conrad, 2008; Norell et al., 2008; Conrad et al., 2011). Lesser-acknowledged peculiarities of the Heloderma skeleton include the absence of coracoid and scapular fenestrations and the relatively short pes.

Gobiderma pulchrum differs from Heloderma in having a tapering snout (compare figs. 3B, C , 4B, C , 5C, D , 7B , with 8B), a complete supratemporal arch ( figs. 3C , 5C , 7A, B versus 8A, B), large patches of pterygoid teeth ( figs. 4C , 5D , 7C , 17B , 43B, C versus 8C), a lack of grooved dentary teeth, and possession of an anterior coracoid fenestra and a relatively elongate pes. Estesia mongoliensis ( fig. 9B ) represents a fine morphological intermediate between Gobiderma pulchrum and Heloderma . Estesia mongoliensis retains the plesiomorphic features of a complete supratemporal arch and pterygoid tooth patches, but is similar to Heloderma in the shape of its skull and in the possession of grooved dentary teeth. Broader comparisons with nonmonstersaur anguimorphs, including the Cretaceous varaniform Telmasaurus grangeri , demonstrate that Gobiderma pulchrum exhibits the plesiomorphic condition with respect to Heloderma in all these characteristics.

Comparisons of Gobiderma pulchrum with extant Heloderma , shinisaurs, fossil varaniforms, and mosasaurs (such as Telmasaurus grangeri and Adriosaurus suessi ), and with anguioids (including Xenosaurus , Peltosaurus granulosus , and Gerrhonotus ), as well as the phylogenetic analysis suggest that basal monstersaurian apomorphies occurred in the skull while the postcranium remained relatively plesiomorphic. The monstersaurian apomorphies present in Gobiderma pulchrum (e.g., presence of a palatine flange of the maxilla and a pterygoid lappet of the quadrate) occur in the skull and lower jaw. The presence of an anterior coracoid emargination and absence of pedal foreshortening in Gobiderma pulchrum are plesiomorphic features.

One of the most conspicuous characteristics of modern Heloderma (as compared to other extant squamates) is its encrustation of mounded osteoderms, a condition distinct from all other extant squamates. Similar osteoderms are present in and often fuse to the skull bones of Gobiderma pulchrum as described above. However, the distribution of this characteristic indicates that it is not a monstersaur apomorphy, but that it characterizes a more inclusive node (see discussions in McDowell and Bogert, 1954; Sullivan, 1979; Conrad, 2008; and Conrad et al., 2011).

A REVISED DIAGNOSIS OF GOBIDERMA PULCHRUM

Borsuk-Białynicka (1984) offered separate generic and specific diagnoses for Gobiderma pulchrum . Her generic diagnosis (Borsuk- Białynicka, 1984: 39) reads as follows:

Medium-sized platynotan lizards about 5 cm of skull length. Sharp dentition with basal fluting. Lower teeth bigger than upper ones. External nares slightly retracted but not separating maxilla and nasal. Nasals paired. Subolfactory processes developed but weak. Postorbital joined to postfrontal from ventrolateral entering into the orbit. Parietal extended both laterally and posteriorly. Adductor musculature originating ventral on the parietal. Large alar process extending anteriorly. Small-plate osteodermal skull covering very strong, variable in ontogenesis with a tendency to eventually fuse into continuous although superficially sculptured layer. Rounded, perforated osteoderms of Heloderma type completely covering cheek region, supratemporal fossa and dorsal surfa of the orbit.

The specific diagnosis offered by Borsuk- Białynicka (1984: 41) is:

Skull subpentagonal in outline, its larger part posterior. Frontal paired but sometimes fusing with individual age. Posterolateral extensions of parietal close an angle of about 130 °. An angle between paroccipital processes is only slightly less than this. Number of tooth positions is 11 on maxilla, 4 on premaxilla, 10 on dentary. Osteodermal skull covering of small-plate type or variable (anterior to the orbit).

Although many of the individual characteristics listed by Borsuk-Białynicka are shared by other taxa, the combination of character states described above diagnose Gobiderma pulchrum . Here, we emend this diagnosis by adding the following character states to the list: premaxillary nasal process is narrowest mediolaterally ( figs. 3B , 4B , 5C , 6B , 7B ), contrasting the condition in Heloderma and Estesia mongoliensis and most other non- Varanus anguimorphs); postfrontal and postorbital remain distinct (are unfused; figs. 6B , 7B , 19 , 25 ), contrasting the condition in Estesia mongoliensis ; Heloderma lacks a postorbital; postorbital extends posteriorly for almost the entire length of the supratemporal fenestra and approaches the supratemporal ( figs. 3B , 7B , 25A , 26 ; the only other monstersaur with a known postorbital, Estesia mongoliensis , has a relatively much shorter postorbital); posterior opening of the Vidian canal enclosed by the parabasisphenoid ( figs. 28C , 36A, B ; Heloderma and Estesia mongoliensis possess a posterior opening of the Vidian canal occurring at the parabasisphenoid-proötic suture); presence of an anterior coracoid emargination ( fig. 49 ; absent in Heloderma and unknown in other monstersaurs); obliteration of the pelvic sutures through bone intergrowth (the sutures remain visible and distinct in Heloderma and Palaeosaniwa canadensis [ Balsai, 2001]); and distal placement of lateral plantar tubercle on metatarsal V ( Heloderma possesses medial and lateral plantar tubercles on metatarsal V that possess an overlapping level; among anguimorphs, Lanthanotus and shinisaurs possess the condition seen in Gobiderma pulchrum ).

A DIVERSITY OF CARNIVOROUS CRETACEOUS GOBI LIZARDS

Cretaceous Gobi lizard diversity has been reviewed by several authors over the last three decades revealing a vast systematic and morphological array ( Borsuk-Białynicka, 1983, 1984, 1985, 1988, 1990, 1996; Borsuk- Białynicka and Moody, 1984; Borsuk- Białynicka and Alifanov, 1991; Norell et al., 1992; Alifanov, 1993, 1996, 2000; Gao and Hou, 1996; Norell and Gao, 1997; Gao and Norell, 2000; Conrad and Norell, 2006b, 2007; Norell et al., 2008). Indeed, the Cretaceous Gobi, particularly Djadokhta and similar deposits, is represented by a great number of species, including the three major dinosaurian clades (Ornithischia, Sauropodomorpha, and Theropoda; see, e.g., Makovicky and Norell, 2006; Ksepka and Norell, 2006, 2010; Turner et al., 2007 a, 2007b; Miles and Miles, 2009) as well as a diversity of mammals (see, e.g., Rougier et al., 2001; Wible et al., 2001; Wible et al., 2004), among other taxa (see Loope et al., 1998; Gao and Norell, 2000). Together, these fossils indicate the presence of thriving ecological communities with a broad taxonomic diversity despite xeric conditions.

Importantly, the Djadokhta Formation includes a variety of lizards that, given their similarities with extant forms and based on their dental morphology, are presumed to be capable of taking vertebrate prey. These include the relatively diminuitive gobiguanians ( Conrad and Norell, 2007) as well as several anguimorphs such as some goannasaurs ( Gilmore, 1943; Borsuk-Białynicka, 1984; Gao and Norell, 2000; Conrad, 2008; Norell et al., 2008), Gobiderma pulchrum (Borsuk- Białynicka, 1984; Gao and Norell, 2000), and Estesia mongoliensis ( Norell et al., 1992; Norell and Gao, 1997). Relatively small anguimorph taxa such as Aiolosaurus oriens and Ovoo gurvel might also have been capable of taking vertebrate prey; these taxa are larger than the tiny, extant monitors Varanus brevicauda and Varanus eremius , which are known to consume other lizards ( Pianka and Vitt, 2003). Shinisaurus crocodilurus is known to take larval amphibians and fishes in addition to invertebrate prey ( Ahl, 1930; Shen and Li, 1982; Sprackland, 1989).

Gobiguania is a clade composed of six species ( Anchaurosaurus gilmorei , Ctenomastax parva , Saichangurvel davidsonae , Temujinia ellisoni , and Zapsosaurus sceliphros ) of relatively small-bodied lizards. Because of their convergent similarities to modern crotaphytids (e.g., dentition, habitat choice, general proportions; Gao and Hou, 1995; Gao and Norell, 2000; Conrad and Norell, 2007), it is speculated they were capable of taking vertebrate prey (including mammals, in addition to other lizards), as are modern crotaphytids ( McAllister and Trauth, 1982; Pianka and Vitt, 2003).

Telmasaurus grangeri is the largest varaniform known from diagnostic remains in the Djadokhta localities, with a femur length of approximately 48.5 mm (AMNH FR 6643) and a total parietal length of approximately 23.5 mm (AMNH FR 6645) (suggesting a skull length of perhaps 55–70 mm based on general comparisons with complete anguimorph skulls, especially varaniforms). This is slightly larger than the smaller of the two known Djadokhta monstersaurs, Gobiderma pulchrum . Gobiderma pulchrum (IGM 3/905) has a femur length of 38.3 mm and a skull length of approximately 60 mm (see above). Estesia mongoliensis possesses a skull length of approximately 122.5 mm.

The lizard fauna of the Djadokhta is unusually rich, and the presence of several large-bodied forms is especially striking. However, a similarly xeric environment to the Cretaceous Gobi is present in the desert of modern Australia where there are at least six cooccurring species of Varanus ( Farlow and Pianka, 2000; Pianka and Vitt, 2003). Even the smallest of these species, ( Varanus brevicauda ; the smallest known varanid) is known to take relatively large prey items, including other lizards ( Pianka and Vitt, 2003). Additionally, the two extant species of Heloderma share a narrow distributional overlap in northwestern Mexico. Perhaps something similar occurred in the Late Cretaceous of the Gobi, with the various types of lizards preying upon one another with theropod dinosaurs representing the apex predators.

Two features considered to be characteristic of modern Heloderma (grooved teeth associated with venom delivery and mounded osteoderms) uniformly cooccur in all known Helodermatidae , but have a dissociated distribution within the Djadokhta monstersaurs. Estesia mongoliensis possesses grooved teeth and apparently lacks osteodermal encrustation. By contrast, Gobiderma pulchrum possesses domed osteoderms, but lacks grooved teeth. Domed osteoderms may be plesiomorphic for a clade that is more inclusive than Monstersauria (Conrad, 2008; Conrad et al., 2011); thus, their presence in Gobiderma pulchrum and many helodermatids may be a retention of a plesiomorphic character state rather than a monstersaur innovation. Estesia mongoliensis is the earliest monstersaur known to have grooved dentary teeth. The plesiomorphic condition for the Estesia mongoliensis – Helodermatidae clade is to possess osteoderms and grooved teeth, with the loss of osteoderms a derived state in Estesia mongoliensis .

The selective pressures that would have led to the loss of osteoderms in Estesia mongoliensis are unknown. Given the hypothesis that Estesia mongoliensis was a predator of reptile nests ( Norell et al., 1992) like modern Heloderma and many Varanus ( Bogert and Del Campo, 1956; Pianka and Vitt, 2003), one might expect osteoderms to be important defensive structures (although no Varanus possesses monstersaur-style dermal armor). Development of a venom-delivery system might have been a defensive innovation rendering passive defensive structures less critical; that is, in this case, the best defense may have been a good offense. Despite the presence of much larger reptiles with impressive offensive weaponry (e.g., dromaeosaurid theropods with enlarged pedal unguals and serrated teeth), it may be that Estesia mongoliensis had no serious predators. Lacking the ability to threaten animals with an advanced venom-delivery system, coeval Gobiderma pulchrum relied on plesiomorphic defensive structures and strategies. Additional data might shed light on this evolutionary story; certainly, the currently available evidence appears inadequate to provide a definitive understanding of the ecological complexities in this ecosystem.

CONCLUSIONS

Fossil material from the Gobi Desert continues to offer new information about the origin and evolution of various squamate groups as well as increasing their known diversity ( Gao and Norell, 2000; Conrad and Norell, 2006a, 2006b; Norell et al., 2008). The basal monstersaur Gobiderma pulchrum is pivotal for understanding the early evolution of monstersaurs and the derived extant squamate group Heloderma . The new material described above and reexamination of the fossils originally described by Borsuk-Białynicka (1984) allow rediagnosis of Gobiderma pulchrum and a more complete reconstruction of the animal as a whole ( fig. 56 ). Among Cretaceous varaniforms and monstersaurs, only Gobiderma pulchrum , Palaeosaniwa canadensis , and Telmasaurus grangeri are known from relatively complete skulls and associated postcrania. The postcranial remains of Palaeosaniwa canadensis are, apparently, less complete than those of Gobiderma pulchrum and still await formal description (but see Balsai, 2001), making the documentation of the Gobiderma pulchrum postcranium all the more influential for understanding character polarities within Anguimorpha.

Gobiderma pulchrum and Palaeosaniwa canadensis are the most proximal helodermatid outgroups ( figs. 55 , 56 ) and lack grooved dentition. That Gobiderma pulchrum cooccurred with a larger and more helodermatidlike monstersaur is significant because it offers an opportunity to further investigate the Djadokhta fauna. As with modern communities wherein lizards are a conspicuous part of the fauna, it is likely that some prey partitioning existed. Gobiderma pulchrum , the relatively smaller monstersaur, may have been taking small prey items while the broad-snouted, larger-bodied, and perhaps venomous Estesia mongoliensis might have had a broader range of potential prey items.

In conclusion, Gobiderma pulchrum represents an important transitional form linking basal monstersaurs with the more derived Helodermatidae and its proximal outgroups. Further discovery of Gobiderma pulchrum and other Gobi lizards may offer greater understanding of their diversity, the Djadokhta communities, and offer opportunities to the understand mosaic evolution.

Figures

Fig. 55. Combined-evidence analysis as performed for the present study (2214 equally short trees recovered). Here we present both the Adams consensus and the reduced strict consensus. Note that the overall tree topology is the same in both cases and that only species-level terminals were used in each analysis, but that some have been collapsed into their containing clades here for brevity, but highlighting monstersaurian species that were included. Taxa pruned from the trees for the reduced strict consensus are joined to the tree by gray lines. Tree length for each principal tree 5 8888 steps; consistency index excluding uninformative characters 5 0.3945; retention index 5 0.5012.

Fig. 56. Monstersaurs interrelationships as presented in figure 55 presented as a temporally calibrated cladogram including biogeographic data and scaled thumbnail images of some of the relevant taxa. Gray vertical bars indicate time spans covered by the associated paleomaps. Note that the map for Primaderma nessovi represents a 94 Ma reconstruction; that for the remaining Cretaceous monstersaurs (e.g., Gobiderma pulchrum) represents a 66 Ma reconstruction; the Eocene map is a 50.2 Ma reconstruction; the Oligocene-Miocene map is a 14 Ma reconstruction, and the Holocene map represents the presented continents in their current distribution. Maps based on Scotese (1991, 2003) and Scotese et al. (1988).

Fig. 45. Incomplete postcranial skeleton of Gobiderma pulchrum (IGM 3/905), mostly in left lateral view. This partly articulated specimen includes most of a skull (see figs. 6, 12, 23, 24, 26, 33B–D, 35, 36B, 40A–C), 22 presacral vertebrae with some associated ribs, both sacrals, and two proximal caudal vertebrae as well as a right scapulocoracoid, an incomplete left manus, a complete pelvis, and most of both hind limbs.

Fig. 47. Pelvic girdle and associated structures in Gobiderma pulchrum (IGM 3/905).

Fig. 48. Second sacral vertebra and the first two caudal vertebrae in Gobiderma pulchrum (IGM 3/905) in ventral view.

Fig. 22. Partially articulated incomplete skeleton of Gobiderma pulchrum (IGM 3/59), including a partial skull, mandibles, osteoderms, and axial column.

Fig. 46. Disarticulated presacral vertebrae from Gobiderma pulchrum (IGM 3/905). A. Vertebra near the preserved scapulocoracoid in anterior view. B. Two vertebrae located near the partial ribcage displaying left lateral and ventral views. Note the absence of a strong precondylar constriction in the vertebrae and the presence of zygosphene-zygantra articular surfaces.

Fig. 3. Gobiderma pulchrum, holotype skull with lower jaws (ZPAL MgR III/64). Skull and left mandible in A, left lateral, B, dorsal, and C, ventral views. Right mandible in D, lateral and E, medial views.

Fig. 4. Gobiderma pulchrum (IGM 3/55) skull with lower jaws in A, left lateral, B, dorsal, and C, ventral views.

Fig. 5. High-resolution X-ray computed tomography scans of Gobiderma pulchrum (IGM 3/55) with matrix rendered invisible in A, right lateral, B, left lateral, C, dorsal, and D, ventral views.

Fig. 7. Reconstructed skull and mandibles of Gobiderma pulchrum based on all available specimens. A. Skull and mandible in left lateral view. Skull in B, dorsal and C, ventral views. D. Mandible in medial view. E. Skull in posterior views. Note that the entire skull and mandible are known through comparison of available material.

Fig. 17. Selected parasagittal HRXCT slices through the skull and mandible of Gobiderma pulchrum, (IGM 3/55). A. Parasagittal slice 157 is through the left side of the specimen. B. Parasagittal slice 197 is very near the midline.

Fig. 43. Selected transverse HRXCT slices through the right mandible of IGM 3/55 illustrating the morphology of adductor fossa near the level of the coronoid. A. Section 324, illustrating the anterior part of the adductor fossa (af) occuring lateral to the coronoid eminence and laterally bounded narrowly by the surangular. The jugal, with it a pronounced ventral flange lies dorsolateral to the coronoid. B. A slightly more posterior secion (334) with greater development of the adductor fossa, more deeply invading the coronoid and with a greater surangular contribution to its lateral margin. C. Section 344, illustrating the mediolateral shape of the adductor fossa near the posterior terminus of the coronoid eminence. D. Section 354, just beind the levelof the coronoid eminence, where the adductor fossa occurs primarily on the medial mandibular surface.

Fig. 9. Reconstructions of three monstersaurs in left lateral view. A. Primaderma nessovi (modified after Cifelli and Nydam, 1995, and Nydam, 2000); B, Estesia mongoliensis (modified after Norell et al., 1992, and Norell and Gao, 1997); C, Eurheloderma gallicum (Hoffstetter, 1957). Scale bars 5 10 mm.

Fig. 6. Gobiderma pulchrum, (IGM 3/905) skull with lower jaws. A. Snout and orbital portions in right lateral and B, dorsal views. C. Braincase and right jaw suspensorium in posterior view. Partial right mandible in D, lateral and E, medial views.

Fig. 19. Nearly complete skull and left mandible of Gobiderma pulchrum (ZPAL MgR III/66) in A, left lateral view, B, dorsal view, and C, ventral view. The right mandible is shown in D, lateral and E, medial views.

Fig. 25. Selected frontal HRXCT slices through the dorsal part of the cranial portion of the skull in Gobiderma pulchrum (IGM 3/55), illustrating details of the parietal and the supratemporal arch. A. Frontal slice 58 shows the contacts between the postfrontal and parietal, between the suprafrontal and parietal, the frontoparietal suture, and the pineal foramen. B. Frontal slice 66 illustrates the contacts between postfrontal, postorbital, and squamosal, and the pineal fossa.

Fig. 26. Gobiderma pulcrhum (IGM 3/905), ventral view of the left jaw suspensorium and surrounding structures.

Fig. 28. Selected transverse HRXCT slices through the skull of Gobiderma pulchrum (IGM 3/55) at the level of the anterior part of the cranial portion. Sections A. near the base of the basipterygoid processes; B. just posterior to the dorsum sella; C. at the level of the posterior opening of the Vidian canal.

Fig. 36. The braincases of selected monstersaurs. A. Reconstructed braincase of Gobiderma pulchrum in left lateral view primarily based on ZPAL MgR III/64, ZPAL MgR III/65, IGM 3/905, and IGM 3/55. B. Braincase of IGM 3/905 in left lateral view. C. Reconstruction of the braincase of Estesia mongoliensis in left lateral view (modified after Norell et al., 1992, and Norell and Gao, 1997). D. Braincase of Heloderma horridum in left lateral view (based on comparisons among AMNH R 64128, Boulenger, 1891, the Deep Scaly Project, 2007, and Evans, 2008). Note that reconstructed areas are represented by semiopaque shadows.

Fig. 49. A. Photograph and B, drawing of the right scapulocoracoid of Gobiderma pulchrum (IGM 3/ 905) in lateral view. Unknown/incomplete portions are represented by semiopaque, gray shadows in the drawing (B.).