Wednesday, March 14, 2018

[Paleontology • 2018] Late Maastrichtian Pterosaurs from North Africa and Mass Extinction of Pterosauria at the Cretaceous-Paleogene Boundary


Size disparity of late Maastrichtian pterosaurs. 
Maastrichtian pterosaurs are larger than coeval birds in both marine (blue) and terrestrial/freshwater (orange) ecosystems. 

in Longrich, Martill & Andres, 2018.

Abstract
Pterosaurs were the first vertebrates to evolve powered flight and the largest animals to ever take wing. The pterosaurs persisted for over 150 million years before disappearing at the end of the Cretaceous, but the patterns of and processes driving their extinction remain unclear. Only a single family, Azhdarchidae, is definitively known from the late Maastrichtian, suggesting a gradual decline in diversity in the Late Cretaceous, with the Cretaceous–Paleogene (K-Pg) extinction eliminating a few late-surviving species. However, this apparent pattern may simply reflect poor sampling of fossils. Here, we describe a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. With 3 families and at least 7 species present, the assemblage represents the most diverse known Late Cretaceous pterosaur assemblage and dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families—Pteranodontidae, Nyctosauridae, and Azhdarchidae—persisted into the late Maastrichtian. Late Maastrichtian pterosaurs show increased niche occupation relative to earlier, Santonian-Campanian faunas and successfully outcompeted birds at large sizes. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary.


Fig 20. Size disparity of late Maastrichtian pterosaurs and birds. Maastrichtian pterosaurs are larger than coeval birds in both marine (blue) and terrestrial/freshwater (orange) ecosystems. Wingspan estimates for pterosaurs are from S2 Data. Wingspans for terrestrial birds were made using estimated masses from Longrich et al. [2011] and the equation for passeriformes from Norberg [1981] or from reconstructions based on fossils [Dyke, et al 2002; Agnolín, et al 2017].

Systematic paleontology

The fauna comprises a minimum of 7 species, including 1 species of Pteranodontidae, 3 species of Nyctosauridae, and 3 species of Azhdarchidae.

Archosauria Cope, 1869
Pterosauria Kaup, 1834

Pterodactyloidea Plieninger, 1901
Ornithocheiroidea sensu Kellner, 2003 
Pteranodontoidea sensu Kellner, 2003 

Pteranodontia sensu Unwin, 2003 

• Pteranodontidae Marsh, 1876

Tethydraco regalis gen. et sp. nov.

Etymology. The genus derives from Tethys, in reference to the Tethys Sea, and the Latin draco, “dragon.” The species name is derived from the Latin regalis, “royal.”

Holotype. FSAC-OB 1, left humerus (Figs 2 and 3).

Diagnosis. Pteranodontid with a deltopectoral crest that is small and proximally placed, terminating just past the end of the ulnar crest; a very broad, triangular distal end of the humerus; an ectepicondyle with a prominent dorsal projection; and an entepicondyle that is enlarged and proximally extended. The ulna is proportionately short and broad, with a massively expanded proximal end.
Horizon and locality. Middle Couche III; Sidi Daoui, Khouribga Province, Morocco.


Some of the Moroccan pterosaur fossils.
Top: the mandible (lower jaw) of Alcione elainus, a small pterosaur newly described in this paper.
Bottom: part of the ulna (forearm bone) from a giant pterosaur, tentatively identified as Arambourgiania.

Note the different scales - the mandible is less than 20 cm long, while the ulna is more than 40 cm long; Arambourgiania would have had a wingspan more than three times that of Alcione

• Nyctosauridae Nicholson and Lyddekker 1889

Alcione elainus gen. et sp. nov.

Etymology. The genus name is from Alcyone of Greek mythology, who was turned into a seabird, and the species name is from the Greek elaino, “to stray or wander.”

Holotype. FSAC-OB 2 (Fig 6), partial skeleton including humerus, sternum, scapulocoracoid, and femur.

Diagnosis. Small nyctosaur. The scapula and coracoid are subequal in length. The humerus is short and robust, with a strongly expanded proximal end; proximal pneumatic fossa and foramen are absent. The deltopectoral crest is positioned proximally, close to the head of humerus, with strong constriction at midlength producing an exaggerated hatchet shape and an acutely pointed distal prong. It has a very large, proximally positioned supracondylar process. The entepicondyle is hypertrophied and distally projecting. The antebrachium and metacarpal IV are short and robust. The femur is short and robust.
Type locality. Middle Couche III; Sidi Daoui, Khouribga Province, Morocco.


 Simurghia robusta gen. et sp. nov.

Etymology. The genus name refers to the Simurgh, a flying beast from Persian mythology. The species name is from the Latin robusta, “robust.”

Holotype. FSAC-OB 7 (Fig 10).

Diagnosis. Large nyctosaurid, with a humerus that is approximately 165 mm long. The deltopectoral crest is proportionately short and broad, but the apex is strongly expanded with a strongly convex apical margin giving it a fan shape. The ventral pillar is shifted to the proximal margin of the deltopectoral crest. The humeral shaft is proportionately robust and distally expanded. The supracondylar process is hypertrophied and triangular.
Locality and horizon. Middle Couche III, Sidi Daoui, Khouribga Province, Morocco.


Barbaridactylus grandis gen. et sp. nov.

Etymology. The genus name refers to North Africa’s Barbary Coast region and the Greek dactylo, “finger.” The species name is from the Latin grandis, “great.”

Holotype. FSAC-OB 232 (Fig 11), associated skeleton including left humerus, radius and ulna, right femur, left scapulocoracoid, partial right mandible.

Diagnosis. Large nyctosaurid, with a humerus that is up to 225 mm long. The humerus is slender, with the deltopectoral crest well distal to the humeral head. The deltopectoral crest is short, broad, and subrectangular, with weak constriction; warping of the deltopectoral crest is weakly developed. The humeral head has large ventral pneumatic fossa and foramen/foramina. Small pneumatic foramina are proximal to the lateral condyle. The bones of the antebrachium are slender—130% of the humerus’s length. The femur is 85% of the humerus’s length, with a slender shaft and a moderately developed greater trochanter.
Locality and horizon. Middle Couche III, Sidi Daoui, Khouribga Province, Morocco.


Azhdarchoidea Kellner 2003
Neoazhdarchia Kellner 2003 

• Azhdarchidae Nessov 1984

Phosphatodraco mauritanicus Pereda-Suberbiola et al. 2003 
- Azhdarchidae aff. Quetzalcoatlus
- Sidi Chennane Azhdarchid


Nicholas R. Longrich, David M. Martill and Brian Andres. 2018. Late Maastrichtian Pterosaurs from North Africa and Mass Extinction of Pterosauria at the Cretaceous-Paleogene Boundary. PLoS Biol. 16(3): e2001663.  DOI: 10.1371/journal.pbio.2001663
Pterosaurs went out with a bang, not a whimper http://phy.so/440144378 via @physorg_com

  

Author summary: Pterosaurs were winged cousins of the dinosaurs and lived from around 200 million years ago to 66 million years ago, when the last pterosaurs disappeared during the Cretaceous-Paleogene extinction that wiped out the dinosaurs. The pterosaurs are thought to have declined in diversity before their final extinction, suggesting that gradual processes played a major role in their demise. However, pterosaur fossils are very rare, and thus, it is unclear whether pterosaurs were really low in diversity at this time or whether these patterns merely result from a paucity of fossils. We describe new pterosaur fossils from the end of the Cretaceous in Morocco, including as many as 7 species. They represent 3 different families and show a large range of variation in size and skeletal proportions, suggesting that they occupied a wide range of ecological niches.

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