Wednesday, August 31, 2016

[Paleontology • 2016] A Small Azhdarchoid Pterosaur from the latest Cretaceous, the Age of Flying Giants

a group of Hornby azhdarchoids on shore-living Campanian bird nests.


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: pterosaur, Azhdarchoidea, Late Cretaceous, Campanian, British Columbia, Northumberland Formation

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.  DOI: 10.1098/rsos.160333 

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. 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.
 DOI: 10.1098/rsos.160333

. Systematic palaeontology

Pterosauria Kaup, 1834 
Pterodactyloidea Plieninger, 1901 

Azhdarchoidea Nessov, 1984 (sensu Unwin)
Neoazhdarchia Unwin, 2003 

?Azhdarchidae Nessov, 1984 


Elizabeth Martin-Silverstone, Mark P. Witton, Victoria M. Arbour and Philip J. Currie. 2016. A Small Azhdarchoid Pterosaur from the latest Cretaceous, the Age of Flying Giants.   Royal Society Open Access. 3, 160333.  DOI: 10.1098/rsos.160333

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