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. 2016 Aug 31;3(8):160333.
doi: 10.1098/rsos.160333. eCollection 2016 Aug.

A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants

Elizabeth Martin-Silverstone  1 , Mark P Witton  2 , Victoria M Arbour  3 , Philip J Currie  4
Affiliations

A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants

Elizabeth Martin-Silverstone et al. R Soc Open Sci. .

Abstract

Pterosaur fossils from the Campanian-Maastrichtian of North America have been reported from the continental interior, but few have been described from the west coast. The first pterosaur from the Campanian Northumberland Formation (Nanaimo Group) of Hornby Island, British Columbia, is represented here by a humerus, dorsal vertebrae (including three fused notarial vertebrae), and other fragments. The elements have features typical of Azhdarchoidea, an identification consistent with dominance of this group in the latest Cretaceous. The new material is significant for its size and ontogenetic stage: the humerus and vertebrae indicate a wingspan of ca 1.5 m, but histological sections and bone fusions indicate the individual was approaching maturity at time of death. Pterosaurs of this size are exceedingly rare in Upper Cretaceous strata, a phenomenon commonly attributed to smaller pterosaurs becoming extinct in the Late Cretaceous as part of a reduction in pterosaur diversity and disparity. The absence of small juveniles of large species-which must have existed-in the fossil record is evidence of a preservational bias against small pterosaurs in the Late Cretaceous, and caution should be applied to any interpretation of latest Cretaceous pterosaur diversity and success.

Keywords: Azhdarchoidea; British Columbia; Campanian; Late Cretaceous; Northumberland Formation; pterosaur.

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Figures

Figure 1.
Figure 1.
Locality data for RBCM.EH.2009.019.0001, and condition before preparation. (a) Location of Vancouver Island in British Columbia, Canada; (b) location of Hornby Island off the east coast of Vancouver Island; (c) extent of Northumberland Formation and location of Collishaw Point, where RBCM.EH.2009.019.0001A was recovered; (d) RBCM.EH.2009.019.0001 as preserved within a carbonate nodule. (a–c) after Arbour & Currie [9] and (d), photograph by Sandy McLachlan.
Figure 2.
Figure 2.
Photographs and interpretative drawings of RBCM.EH.2009.019.0001, element A, a left humerus, in (a,b) dorsal, (c,d) ventral, (e,f) proximal and (g,h) distal aspect. Shading denotes preserved bone cortex (white); weathered bone (light grey) and matrix (dark grey).
Figure 3.
Figure 3.
Photographs and interpretative drawings of RBCM.EH.2009.019.0001 vertebral material. (a–h) Element C, fragment of notarium in (a,b), lateral; (c,d), dorsal; (e,f), ventral and (g,h), anterior aspect; (i–l) element D, partial dorsal vertebra in (i,j), dorsal and (k,l) posterior aspect; (m–p), element G, probable vertebral process, posterior(?) and (o,p), anterior(?) aspect; and (q–t) element E, two associated dorsal vertebrae in (q,r), dorsal and (s,t), anterior aspect (c, centrum; nc, neural canal; ns, neural spine; tp, transverse process). Approximate junctions between vertebrae of element C are indicated by dotted lines.
Figure 4.
Figure 4.
Photographs of unidentified material of RBCM.EH.2009.019.0001, mostly comprising internal moulds of a long bone. (a) element B; (b,c) element H in lateral(?) and anterior(?) aspect; (d) element F.
Figure 5.
Figure 5.
Histology of RBCM.EH.2009.019.0001A, left humerus, transverse cut through distal diaphysis. (a) Entire thin section in cross polarized light; (b) detail of cortical bone showing differentiation of highly vascularized reticular inner regions, and relatively avascular outer layer with laminar vascular canals, normal light, (c) detail of thickened and reworked endosteal region, thought to represent the base of a trabeculum or pneumatic structure, and possible evidence of zonal growth ((i) photograph in normal light; (ii) as (i) but superimposed with interpretative line drawing of major features). For clarity, only select features are labelled (bc, bladed calcite cement; CVC, circumferential vascular canals; end, endosteal lamella; Hav, Haversian system; LAG, line of arrested growth; m, medullary cavity; ma, sediment matrix; po, primary osteon; ravc, region of radial vascular canals; rvc; reticular vascular canals; so, secondary osteon; vc, vascular canal).
Figure 6.
Figure 6.
Speculative restoration of a 1.4 m wingspan azhdarchid, representing the atypically diminutive Late Cretaceous azhdarchoid specimen RBCM.EH.2009.019.0001, against a modern housecat (ca 300 mm tall at shoulder). All other Campanian and Maastrichtian azhdarchids are famous for being much larger, the biggest being as tall as giraffes and, even at their smallest, comparable in size to the largest extant flying birds. The pterosaur is restored here with anatomical characteristics and body proportions predicted for neoazhdarchian and azhdarchid azhdarchoid pterosaurs [30,42].
See this image and copyright information in PMC

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