Ankylopollexia

Rotatori, Filippo Maria, Moreno-Azanza, Miguel & Mateus, Octávio, 2020, New information on ornithopod dinosaurs from the Late Jurassic of Portugal, Acta Palaeontologica Polonica 65 (1), pp. 35-57 : 44-48

Ankylopollexia indet.

Figs. 5–8 .

Material.— ML 2042, isolated, almost complete scapula fromPraiadaPeralta; ML 452,twoassociatedvertebrae, ML 864, an isolated neural arch (not found in association with ML 452) from Praia de Porto das Barcas; ML 818, isolated dentary from Praia Vale Frades; ML 2206, isolated coracoids from Lourinhã coastline. All from Kimmeridgian– Tithonian of Lourinhã, Portugal.

Description.— Cranial skeleton: Dentary ( Fig. 5A ): The partial right dentary ML 818 is broken at both anterior and posterior extremities, measuring 150 mm in total length. The maximum depth is reached in the posterior extremity being 62 mm tall, while the anterior extremity is 49 mm tall. In general, the bone appears stout and compact, being heavily eroded towards the anterior-most part. The lateral surface is heavily eroded, although preservation of the coronoid process is fairly complete, missing just the dorsal-most end. The dorsal and ventral margins appear to be parallel to one another. The ventral surface is smooth, lacking a ventral flange (character 121: 0). The tooth row preserves ten, possibly eleven, distinguishable close-packed alveoli (character 136: 1). The tooth row, which ends medial to the coronoid process, is encased in a parapet-like shelf that is smoothly arched medially (character 122: 0). Two nutrient foramina are located on the marginal shelf of the tooth row (character 145: 0). Teeth are not preserved and the tooth-sockets do not show any interdental plates.

On the medial surface, dorsally to the Meckelian sulcus, a longitudinally striated surface extends almost to the anterior end of the specimen. Two other bones may have articulated against this surface: the splenial and the pre-articular. There is no difference in rugosity to distinguish these two areas.

On the lateral surface the coronoid process projects postero-laterally (characters 124: 1, 125: 1) with respect to the tooth-row and is inclined at about 30° to the horizontal. The contact with the surangular corresponds to the 4th alveolus counted from the coronoid process cranially, so it reaches further anteriorly than coronoid process.

Axial skeleton: Dorsal vertebrae and neural arch ( Figs. 6 , 7 ): ML 452 are two partially distorted and fractured associated vertebrae, while ML 864 is a broken and isolated neural arch, which preserves both postzygapophyses and one prezygapophysis. The two vertebrae ML 452 were found in association and therefore are interpreted to represent the same individual, while ML 864 is a second individual recovered from a different locality but comparable in size. Compared to the axial series of Camptosaurus dispar and Mantellisaurus atherfieldensis, ML 864 is most likely located at the 6–8 th position of the dorsal series, while ML 452 are located after the 10th but before the 16th position of the dorsal series ( Gilmore 1909; Norman 1986). The preserved centra are stout ranging 60–65 mm and consistently sub cylindrical in shape as in Ankylopollexia (Norman 2004), slightly amphicoelous with the anterior facet slightly bigger than the posterior (anterior facet height 60 mm, 65 mm; anterior width 65 mm, 73 mm; posterior height 60 mm, 73 mm; posterior width 75 mm, 70 mm). The slight amphicoelous condition indicates a close proximity to the sacrum. On the ventral surface, a slight constriction forms a smooth keel. The lateral surfaces of the centrum are longitudinally convex, showing the presence of small vascular foramina. The neural canal is fully open in both articulated vertebrae, being sub-circular in shape. Dorsally, two clearly distinguishable prezygapophysis are arranged in an angle of 45° with respect to one another, as in other iguanodontians (Norman 2004). Posterolateral to the prezygapophyses, the stout transverse processes originate, strongly inflecting dorsally in the partial neural arch. The associated vertebrae ML 452 show a strong lateroventral inflection on the left lateral side and a weaker dorsolateral inflection on the right side. The similar orientation of the transverse processes caused by the same diagenetic alteration further supports the association of these two specimens. Similar cases are reported by Janensch (1955) describing bone beds of Dysalotosaurs. Nevertheless, it is here noted that in Ornithopoda, the transverse processes generally are not directed ventrally, therefore it is suggested the lateral left side has been affected by taphonomical processes more than the right one. The right transverse processes show an inclination which goes from weakly anterodorsal to nearly sub-horizontal, in the case of the most incomplete vertebrae of the pair. Comparing with other taxa ( Gilmore 1909; Norman 1980, 1986; Carpenter and Wilson 2008; Carpenter and Lamanna 2015; Carpenter and Galton 2018) we note that this degree of inclination is consistent with undistorted specimens. Therefore, it is suggested that the right side has not been strongly affected by taphonomy, the inclination being different on the right lateral side a genuine character to discriminate the position of the vertebrae along the vertebral column. The different inclination of the transverse processes indicates that ML 864 is more cranially positioned than ML 452 vertebrae. This interpretation is corroborated also by the position of the parapophyses with respect to the diapophyses, being on two well separated planes in ML 864 and almost on the same one in ML 452 vertebrae, reflecting the general trend within Iguanodontia (Norman 2004). The neural spines rise immediately posterior to the prezygapophyses, with an anterior lamina encased by two lateral grooves, as in Camptosaurus , Mantellisaurus atherfieldensis , Iguanodon bernissartensis , and other ankylopollexians ( Gilmore 1909; Norman 1980, 1986, 2004). In the most-complete vertebra of the sample, the neural spine is highly elevated with respect to the centrum as in other ankylopollexians, while dryosaurids have comparatively lower spines ( Galton 1981). The overall shape of the neural spine is rectangular, a characteristic shared both by ML 452 and 864 individuals and different from the condition shown by Camptosaurus dispar and C. aphanoecetes ( Gilmore 1909; Carpenter and Wilson 2008) but similar to that of Mantellisaurus atherfieldensis . Moderately deep grooves for the attachment of ossified tendons are visible on the apical-most part of the neural spine. Posteriorly, the postzygapophyses originate from the base of the neural spine.

A 1 B C D E F A dia par 2 dia par par dia par par dia par par dia dia I J K L G H dia dia par dia dia dia par par par par

Appendicular skeleton: Coracoid ( Fig. 8A ): The left coracoid ML 2206 is complete with the marginal sides slightly eroded. It is sub-rectangular in shape, bowed medio-laterally, and measures 130 mm in antero-posterior length and 108 mm in dorsoventral width. The dorsal margin is straight, while the ventral margin is deeply arched. The scapular surface is slightly concave and relegated to the dorsal-most part of the coracoid, while the glenoid surface is wider and slightly convex. Ventrally, the glenoid deflects abruptly, forming with the bowed ventral margin a conspicuous labrum. The coracoid foramen is dorsally located and totally enclosed on the lateral surface. On the medial surface, instead, it is open along the scapula-coracoid suture as in Camptosaurus , Iguanodon , Mantellisaurus , and derived iguanodontians ( Gilmore 1909; Norman 1980, 1986). With derived iguanodontians it also shares the width/length ratio falling between 70–100% ( Dieudonné et al. 2016). The sternal process is wide and broad, a plesiomorphic condition within Ornithopoda ( Weishampel et al. 2003).

Scapula ( Fig. 8B ): ML 2042 is an incomplete and eroded scapula measuring 440 mm, missing the distal-most part of the blade and being partially eroded in the proximal end. The missing part is estimated to be not more than 10% of the total length of the whole scapular blade. The preserved dorsal and ventral margins appear to be parallel and progressively converging towards the distal part of the blade as seen in Mantellisaurus atherfieldensis and Iguanodon bernissartensis ( Norman 1980, 1986), differently from the condition exhibited by Camptosaurus dispar , C. aphanoecetes , and C. prestwichii ( Gilmore 1909; Carpenter and Wilson 2008; McDonald 2011; Carpenter and Lamanna 2015), which display a strong distal expansion towards the middle of the blade. The scapular blade is dorsoventrally bowed as in Mantellisaurus atherfieldensis and Iguanodon bernissartensis ( Norman 1980, 1986). The proximal part flares gently, being concave on the lateral surface. The acromion process is slightly rounded and forwardly directed, the underlying coracoid suture is straight and ventrally deflects into the glenoid. Contrarily to Camptosaurus dispar , C. aphanoecetes , and C. prestwichii but similar to Mantellisaurus atherfieldensis, ML 2042 does not possess high protuberances corresponding to the acromion process and glenoid ( Gilmore 1909; Norman 1980, 1986; Carpenter and Wilson 2008; McDonald 2011; Carpenter and Lamanna 2015).

Remarks.— Cranial skeleton: Dentary: ML 818 shares with other ankylopollexians, such as Camptosaurus spp. , Mantellisaurus atherfieldensis , Theiophytalia kerri , Iguanodon bernissartensis , and Kukufeldia tilgatensis , parallel margins of the dentary, closed packed alveoli, and a highly emarginated parapet-like structure which constrains the tooth row ( Gilmore 1909; Norman 1980, 1986; Brill and Carpenter 2006; McDonald et al. 2010a). These characters suggest an ankylopollexian affinity for ML 818. However, it differs from thesetaxainhavingamorestronglyinclinedcoronoidprocess, a condition shared with dryosaurids and Tenontosaurus spp. ( Galton 1983; Thomas 2015). Furthermore, ML 818 has a dentary/surangular contact placed further anterior to the coronoid process as in basal taxa: Hypsilophodon foxii , Dryosaurus altus , Dysalotosaurus lettowvorbecki , and Tenontosaurus sp. ( Galton 1974, 1983; Thomas 2015). This condition is different from other akylopollexians such as Camptosaurus spp. , Mantellisaurus atherfieldensis , Theiophytalia kerri , Iguanodon bernissartensis , and Kukufeldia tilgatensis in which the dentary/surangular contact is placed on the same axis or immediately posterior to the coronoid process in a nearly perpendicular fashion ( Gilmore 1909; Norman 2004; Brill and Carpenter 2006; McDonald et al. 2010a).

Axial skeleton: Dorsal vertebrae and neural arch: Ankylopollexians (and ornithopods in general) display a conservative axial skeleton during their evolutionary history, thus a taxonomic attribution of isolated material is problematic. The dorsal vertebrae ML 452 and the partial dorsal neural arch ML 864 are noteworthy in terms of size, they are bigger than most of the material recovered from the Lourinhã Formation, although it is comparable in size with Camptosaurus sp. dorsal vertebrae from the Morrison Formation, in particular USNM 4282 ( Gilmore 1909) and the specimen discussed in Carpenter and Galton (2018: fig. 19G). The holotype of Draconyx loureiroi is a mature individual ( Waskow and Mateus 2017), the caudal centra preserved ranges 46–58 mm in length, being sensibly smaller than the ones presented here ( Mateus and Antunes 2001). The general size proportions also closely resemble the ones of Mantellisaurus atherfieldensis and Hippodraco scutodens ( Norman 1986; McDonald et al. 2010b). Both ML 452 and ML 864 share with Mantellisaurus atherfieldensis , Hippodraco scutodens , Iguanodon bernissartensis , Barilium dawsoni , and Hypselospinus fittoni ( Norman 1980, 1986, 2011, 2015; McDonald et al. 2010b) the antero-posterior stout proportions, the rectangular shape of the neural spine, and its ratio with respect to the centrum; while Camptosaurus dispar shows a paddle like structure towards the dorsal-most part of the spine and generally slender proportions ( Fig. 7 ). Both ML 452 and ML 864 display a more developed neural spine with respect to the transverse processes as in Mantellisaurus atherfieldensis , Iguanodon bernissartensis , Barilium dawsoni , and Hypselospinus fittoni ( Norman 1980, 1986, 2011, 2015); while in Camptosaurus dispar specimens it is less developed ( Gilmore 1909; Norman 2004; Carpenter and Wilson 2008; Carpenter and Galton 2018). Herein, ML 452 and ML 864 are conservatively assigned to Ankylopollexia, although the antero-posterior extension of the neural spine and its rectangular shape, its development respect to centrum and transverse processes, suggests a possible affinity to Styracosterna.

Appendicular skeleton: Coracoid: The isolated coracoid ML 2206 possesses a short and broad sternal process, a typical basal condition within Ornithischia . It shares with ankylopollexians, basal ornithopods (non-dryomorphans) and neornithischians, a width/length ratio between 70–100% It shares with dryomorphans, Anabisetia saldivai , and Muttaburrasurus langdoni an open coracoid foramen along the scapula-coracoid suture. The size of ML 2206 is greatly bigger than dryosaurids and other neornithischians ( Galton 1974; Norman et al. 2004; Hübner 2018), while it is comparable with ankylopollexians ( Gilmore 1909; Norman 1980, 1986; Carpenter and Wilson 2008; Carpenter and Lamanna 2015; Carpenter and Galton 2018). The coracoid ML 2206 does not present any distinguishable characters with respect to the variability shown by other ankylopollexians present in the Late Jurassic, such as Camptosaurus sp. ( Dodson 1980; Carpenter and Wilson 2008; Carpenter and Lamanna 2015).

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glenoid

Scapula: ML 2042 shows characters which are widespread among Ankylopollexia, although they hint to more derived affinities. It is differentiated from Camptosaurus dispar , C. prestwichii , and dryosaurids in having the dorsal margin of the scapular blade convex and slender proportions of the proximal end with respect to the scapular blade. ML 2042 shares with Barilium dawsoni , Hippodraco scutodens , Hypselospinus fittoni , Iguanacolossus fortis , Mantellisaurus atherfieldensis , Iguanodon bernissartensis , and more derived Hadrosauriformes the general bowed outline of the scapular blade ( Norman 1980, 1986, 2011, 2015; Horner et al. 2004; McDonald et al. 2010a, b). The scapular blade in C. prestwichii , M. atherfieldensis , Hypselospinus fittoni , and I. bernissartensis displays a concave proximal end ( Norman 1980, 1986, 2015; Carpenter and Wilson 2008; McDonald 2011). The acromion process is rounded, different from C. dispar , but similar to C. aphanoecetes , M. atherfieldensis , Iguanodon bernissartensis , and Hypselospinus fittoni ( Gilmore 1909; Norman 1980, 1986, 2015; Carpenter and Wilson 2008; McDonald 2011). The ventral and dorsal margins, being sub-parallel towards the middle of the blade, resemble the condition seen in M. atherfieldensis , I. bernissartensis , and other derived styracosternans (Norman 2004) but differ from C. dispar , C. aphanoecetes , and C. prestwichii which have the ventral margin slightly diverging from the mid-blade or immediately distal to the mid-blade ( Gilmore 1909; Carpenter and Wilson 2008; McDonald 2011). Carpenter and Lamanna (2015) lumped the once considered oldest styracosternan “ Uteodon ” aphanoecetes and “ Cumnoria ” prestwichii into the genus Camptosaurus . This lumping has great implications for the attribution of ML 2042 to Styracosterna, since some of the characters considered diagnostic present in the scapular blade (i.e., dorsal scapular margin convex, rounded acromion process) are now ambiguously widespread among Ankylopollexia. ML 2042 is here conservatively considered Ankylopollexia, although the presence of a dorsoventrally bow of the scapular blade, sub-parallel ventral and dorsal margins at mid-blade, and a generally rounded acromion indicates a possible attribution to Styracosterna.

Figures

Fig. 5. Cranial material of Ankylopollexia indet. from the Lourinhã municipality, Portugal, Lourinhã Formation, Kimmeridgian–Tithonian. Dentary ML 818, in medial (A1, A5), lateral (A2, A6), and dorsal (A3, A7) views, detail of the dentary/surangular contact (A4, A8).

Fig. 6. Dorsal vertebrae Ankylopollexia indet. from the Lourinhã municipality, Portugal, Lourinhã Formation, Kimmeridgian–Tithonian. A. Partial neural arch, ML 864 in anterior (A1), posterior (A2), lateral (A3), and dorsal (A4) views. B, C. Dorsal vertebrae, ML 452a, complete (B) and ML 452b, incomplete (C) specimens, in anterior (B1, C1), posterior (B2, C2), lateral (B3, C3), dorsal (B4, C4), and ventral (digitally modified) (B5, C5) views.

Fig. 7. Comparative dorsal vertebrae table of selected Ankylopollexians from the Late Jurassic and Early Cretaceous. A, B. Ankylopollexia indet. Lourinhã municipality, Portugal, Lourinhã Formation, Kimmeridgian–Tithonian. A. ML 452 in lateral view (A1, A2). B. ML 864 in right lateral view. C. “Uteodon” SHN.LPP 015 in left lateral view; Praia da corva, Torres Vedras Municipality, Portugal, Lourinhã Formation (Kimmeridgian–Tithonian). D. “Uteodon” aphanoecetes CM 11337 in left lateral view; East end of Carnegie Quarry at Dinosaur National Monument, Uintah County, Utah (USA), Morrison Formation (Kimmeridgian–Tithonian). E. Camptosaurus dispar (unnumbered specimen) in left lateral view; Bone Cabin Quarry, Wyoming USA), Morrison Formation (Kimmeridgian–Tithonian). F. “Cumnoria” prestwichii OUM. J.3303 in lateral view; Oxford, UK, Kimmeridge Clay Formation (Kimmeridgian–Tithonian). G. Hippodraco scutodens UMNH VP 20208 in left lateral view; Andrew’s Site, Grand County, Utah; Upper Yellow Cat Memberof the Cedar Mountain Formation (upper Barremian–lowermost Aptian). H. Iguanacolossus fortis UMNH VP 20205 in right lateral view; Don’s Ridge, Grand County, Utah, Lower Yellow Cat Member, Cedar Mountain Formation (?lower Barremian). I. Mantellisaurus atherfieldensis IRSNB 1551 in left lateral view; Isle of Wight, Wessex Formation (Barremian). J. Barilium dawsoni NHMUK R798 in left lateral view; Shornden, East Sussex, UK, Wadhurst Clay Formation (Valanginian). K. Hypselospinus fittoni NHMUK R604 in lateral view; Shornden Quarry, Hastings, UK, Wadhurst Clay Formation (Valanginian). L. Iguanodon bernissartensis IRSNB “Individu S” in left lateral view; Bernissart, Belgium, Sainte Barbe Clays Formation Barremian). Abbreviations: dia, diapophysis; par, parapophysis. Scale bars 100 mm. Re-drawn from: C, Escaso 2014: fig. 6.5; D, Carpenter and Wilson 2008: fig. 11; E, Carpenter and Galton 2018: fig. 22D; F, Galton and Powell 1980: fig. 4; G, McDonald 2010b: fig. 27; H, McDonald 2010b: fig. 10;, Norman 1980: fig. 37; J, Norman 2011: fig. 4; K, Norman 2015: fig. 22; L, Norman 1980: fig. 31).

Fig. 8. Ankylopollexian appendicular skeleton from the Lourinhã municipality, Portugal, Lourinhã Formation, Kimmeridgian–Tithonian. Coracoid ML 2206 (A), scapula ML 2042 (B), in lateral (A1, B1) and medial (A2, B2) views.