LONCHODECTIDAE, Unwin, 2001

OF LONCHODECTIDAE

Nasoantorbital fenestra. Anterior border of nasoantorbital fenestra located above tooth pairs 13–14 is an apomorphy (autapomorphy?) of Lonchodraco according to Rigal et al. (2017). A nasoantorbital fenestra was indicated for the holotype of L. giganteus by Owen (1851a: pl. 31, fig. 2). However, Rodrigues and Kellner (2013) considered this opening as a breakage rather than an antorbital fenestra because it is not present on both sides. That interpretation is followed here.

Snout shape. The rounded anterior portion of premaxillae and dentaries is a diagnostic character of Lonchodraco giganteus according to Rodrigues and Kellner (2013). In Lonchodraco sp. from the Cenomanian Melovatka Formation of Volgograd Region, Russia, the snout is pointed ( Averianov and Kurochkin 2010: fig. 1). The snout shape is unknown in other lonchodectid taxa. This character could be an autapomorphy of L. giganteus .

Dorsoventrally flattened jaw tips. This is a diagnostic character of the Lonchodectidae , according to Unwin (2001). This character is present in L. giganteus ( Rodrigues and Kellner 2013) . In L. compressirostris , the tip of the rostrum likely was transversely compressed rather than dorsoventrally flattened. In Ikrandraco avatar , only the tip of the rostrum is dorsoventrally flattened. In Ikrandraco machaerorhynchus the tip of rostrum is unknown, but the tip of the mandible is flattened dorsoventrally. The taxonomic value of this character is not clear.

Alveolar margins divergence. Divergent alveolar margins of the anterior end of the upper and lower jaws is a diagnostic character of Lonchodraco giganteus ( Rodrigues and Kellner 2013) . According to these authors, L. machaerorhynchus differs from L. giganteus by “straight” alveolar margins in dorsal view ( Rodrigues and Kellner 2013: 28). “Parallel margins” is a more appropriate term in this case as diverging margins are also straight. This term was used in the original description of Ornithocheirus machaerorhynchus by Seeley (1870: 114). The state of this character is unknown for Ikrandraco avatar .

Palatal ridge. Longitudinal ridge on the palate was used for diagnosing the genus Lonchodectes ( Hooley 1914) . Unwin (2003: 179) formulated this character in the diagnosis of Lonchodectes as “a prominent, sharply ridged, median keel on the occlusal surface of the rostrum.” A deep palatal ridge is a diagnostic character of Lonchodraco , according to Rodrigues and Kellner (2013). The palatal ridge was indicated for L. giganteus ( Rodrigues and Kellner 2013: fig. 4D) although it is obscured by matrix. A deep palatal ridge was also cited as an autapomorphy of Lonchodraco (?) microdon by Rodrigues and Kellner (2013). This species is considered here to be a synonym of L. machaerorhynchus . In Lonchodectes compressirostris , the palatal ridge is confined to the posterior part of the palate apparently because of the great transverse narrowness of the anterior part of the snout. The palatal ridge is here considered to be a diagnostic character for the Lonchodectidae , while a short posteriorly located palatal ridge is diagnostic for Lonchodectes compressirostris .

Palatal surface shape. Palate between the elevation of the alveolar margins and the palatal ridge concave is a diagnostic character of Lonchodraco (?) microdon according to Rodrigues and Kellner (2013). However, the palatal surface is obscured by matrix in L. giganteus . In Lonchodectes compressirostris , the palatal surface between the palatal ridge and alveolar margins has a similar concave shape ( Owen 1851a: pl. 28, fig. 9). This character does not help to distinguish taxa within the Lonchodectidae .

Premaxillae dorsal margin. Rounded dorsal margin of premaxillae is a diagnostic character of Lonchodraco (?) microdon , according to Rodrigues and Kellner (2013). This character is redundant because it is correlative with the absence of a premaxillary crest in this taxon.

Premaxillary crest. The premaxillary crest is a diagnostic character of Lonchodraco giganteus , according to Rodrigues and Kellner (2013). The absence of a premaxillary crest is a diagnostic character of Lonchodraco (?) microdon , according to Rodrigues and Kellner (2013). According to Rigal et al. (2017), there is no evidence of a premaxillary crest in L. giganteus . In the absence of a definition what constitutes a premaxillary crest it is a matter of opinion to describe the condition seen in L. giganteus as a premaxillary crest or tall premaxilla. In contrast with the mandibular crest, the premaxillary crest has no evident transverse constriction in relation to the rest of the premaxilla. The premaxillary crest is also absent in Lonchodectes and Ikrandraco . Here the premaxillary crest is considered a diagnostic character for the genus Lonchodraco .

Odontoid process. Rigal et al. (2017) diagnosed Lonchodraco as having a triangular dorsally directed perforate process at the symphysis extending two to three millimeters above the dental border. This structure corresponds to an odontoid process present in some pterodactyloids ( Martill 2014; Kellner et al. 2019a; Pêgas et al. 2019). As this character has a wider distribution, it cannot be diagnostic for Lonchodraco .

Mandibular groove. A deep, V-shaped median sulcus on the occlusal surface of the mandibular symphysis is a diagnostic feature of Lonchodectes according to Unwin (2003). Wide mandibular groove is an autapomorphy of Lonchodraco machaerorhynchus , according to Rodrigues and Kellner (2013). A deep mandibular groove is present in Lonchodraco giganteus , but its details are obscured by matrix ( Rodrigues and Kellner 2013). A distinctly wider mandibular groove is present in the anterior mandible fragment NHMUK R2269 from the Cambridge Greensand, referred to Lonchodectes microdon by Unwin (2001: fig. 11F) and not mentioned by Rodrigues and Kellner (2013). The mandible is unknown for Lonchodectes compressirostris , but this taxon might not have the mandibular groove because of a strongly transversely narrow snout and short palatal ridge confined to the posterior part of the palate. In Ikrandraco avatar the presence of a mandibular groove cannot be established because of the flattened preservation. This character is a possible synapomorphy for the Lonchodectidae .

Mandibular crest. The mandibular crest is a diagnostic character of Lonchodraco , according to Rodrigues and Kellner (2013). Short, low, blade-like dentary crest is an autapomorphy of Lonchodraco giganteus ( Rodrigues and Kellner 2013) . Deep dentary crest is an autapomorphy of Lonchodraco machaerorhynchus ( Rodrigues and Kellner 2013) . However, according to my observation, there is no significant difference in the relative dorsoventral depth of the mandibular crest between these two taxa. Rodrigues and Kellner (2013) also noted that L. giganteus differs from anhanguerids in that the mandibular crest does not start at the tip of the mandible. Indeed, the dorsoventrally low mandibular crest in L. giganteus starts some distance posterior to the anterior margin of the mandible and does not increase in depth for some distance. A similar low mandibular crest in the anterior portion of the mandible is present in Lonchodraco microdon (NHMUK R2269) . Rodrigues and Kellner (2013) considered Lonchodectes compressirostris to lack the mandibular crest based on the erroneous interpretation of the anterior rostrum fragment as a fragment of the mandibular symphysis. A mandibular crest is currently unknown for that taxon. A very prominent mandibular crest is present in Ikrandraco . The mandibular crest is presently considered as a diagnostic character for the Lonchodectidae (unknown in Lonchodectes ).

Ventral margin of mandible posterior to mandibular crest. The ventral margin of mandible posterior to the mandibular crest ascending in lateral view is an autapomorphy of Lonchodraco machaerorhynchus , according to Rodrigues and Kellner (2013). See the next character for discussion.

Ventral depression of mandible. Ventral depression located posterior to the mandibular crest is an autapomorphy of Lonchodraco machaerorhynchus according to Rodrigues and Kellner (2013). Seeley (1870) considered a peculiar posterior margin of the mandibular crest of the holotype of Ornithocheirus machaerorhynchus (CAMSM B54855) as the angular facet, a feature differentiating this taxon from the other pterodactyloids known at that time. In Pteranodon , the angular comes close to the mandibular symphysis but contacts the dentary dorsally, not posteriorly ( Bennett 2001: fig. 22B). Rodrigues and Kellner (2013) interpreted this margin as the posterior surface of the mandibular crest. They proposed two autapomorphies for this taxon based on this interpretation: ventral depression located posteriorly to the dentary crest and ventral margin of the mandible posterior to the dental crest ascending in lateral view. However, this surface is likely the broken surface, and the mandibular crest was continuing posteriorly. This is supported by the ventral margin of the mandibular crest, which deepens posteriorly and probably attained the maximum depth in the missing posterior part.

Alveolar parapet. Alveoli placed in an elevation in relation to the palate and the dorsal margin of the mandible is a diagnostic character of the Lonchodectidae according to Unwin (2001, 2003), or an autapomorphy of Lonchodraco , according to Rodrigues and Kellner (2013). This character is present in Lonchodectes compressirostris (contra Rodrigues and Kellner 2013). Here it is considered a diagnostic character of the Lonchodectidae .

Raised margins of alveoli. Unwin (2001) considered dental alveoli with margins that are raised into a low collar so that the teeth appear to be “pedicellate,” as a character diagnostic for the Lonchodectidae . Later he formulated this character as “alveoli with margins raised into a low collar” ( Unwin 2003: 179). According to Rigal et al. (2017), the teeth set in raised alveoli, separated by a C-shaped depression, is a diagnostic character for Lonchodraco , a view, which is followed here.

Size of alveoli. Comparatively small alveoli (up to 4 mm in diameter) in the anterior portions of the upper and lower jaws is a diagnostic character of the Lonchodectidae or Lonchodraco , according to Unwin (2001, 2003) and Rodrigues and Kellner (2013), respectively. Small alveoli are present also in Lonchodectes compressirostris and Ikrandraco avatar . This character is considered here diagnostic for the Lonchodectidae .

Size variation of alveoli. Teeth “uniform in size” was cited in the original diagnosis of Lonchodectes ( Hooley 1914: 535) . “Subequal sized” alveoli are diagnostic for Lonchodectes , according to Unwin (2003: 179). Alveoli of the anterior portions of the upper and lower jaws without significant variation in size is a diagnostic character of Lonchodraco according to Rodrigues and Kellner (2013). The teeth do not vary in size in Ikrandraco avatar . The same condition was likely present in Lonchodectes compressirostris , although the tip of the snout is unknown in this taxon. The size variation of alveoli is considered here diagnostic for the Lonchodectidae .

Spacing between alveoli. Spacing between alveoli roughly equivalent to their diameters is a diagnostic character of Lonchodraco according to Rodrigues and Kellner (2013). Spacing between alveoli larger than their diameters is an autapomorphy of Lonchodraco (?) microdon according to Rodrigues and Kellner (2013). The latter character contradicts the generic diagnosis of Lonchodraco . In Ikrandraco avatar and I. machaerorhynchus , the spaces between the alveoli are of variable size, some are similar in length with the alveoli, whereas others are larger. Here this character is considered diagnostic for the genus Lonchodraco .

The number of alveoli per 3 cm. Approximately six alveoli per 3 cm of jaw margin is an autapomorphy of Lonchodraco giganteus , according to Rodrigues and Kellner (2013). About 4.5 alveoli per 3 cm of jaw margin is an autapomorphy of Lonchodraco machaerorhynchus and, at the same time, is a diagnostic character for Lonchodraco (?) microdon , according to Rodrigues and Kellner (2013). In Ikrandraco avatar , the average number of alveoli per 3 cm is 3.8 for dentary. Rigal et al. (2017) considered tooth count per 3 cm a not taxonomically reliable character because it varies ontogenetically. This could be well true, but the size difference between the holotypes of L. giganteus and I. machaerorhynchus is not significant, and both likely belong to adult individuals. However, the spacing of teeth is markedly different between these two taxa, being denser in L. giganteus . Here these characters are considered diagnostic for the genera Lonchodraco and Ikrandraco .

Tooth shape. “More or less laterally compressed teeth” is a diagnostic feature of the genus Lonchodectes according to Hooley (1914: 535). According to Unwin (2003), in Lonchodectes , the teeth have constricted bases. Rigal et al. (2017) diagnosed Lonchodraco as having short, conical teeth that are gently recurved labially. However, in most of the lonchodectid specimens, the teeth are not preserved, and the diagnostic value of these characters cannot be evaluated.