Wednesday, August 21, 2019

[Paleontology • 2019] Keresdrakon vilsoni • A New Toothless Pterosaur (Pterodactyloidea) from Southern Brazil with Insights Into the Paleoecology of A Cretaceous Desert

Keresdrakon vilsoni

 Kellner, Weinschütz, Holgado, Bantim & Sayão, 2019

  The first pterosaur bone bed from Brazil was reported in 2014 at the outskirts of the town Cruzeiro do Oeste, Paraná State, in the Southern region of the country. Here named 'cemitério dos pterossauros' site, these outcrops were referred to the Goio-Erê Formation (Turonian-Campanian) of the Caiuá Group (Bauru Basin) and revealed the presence of hundreds of isolated or partially articulated elements of the tapejarine pterosaur Caiuajara and fewer amounts of a theropod dinosaur. Here we present a new tapejaromorph flying reptile from this site, Keresdrakon vilsoni gen. et sp. nov., which shows a unique blunt ridge on the dorsal surface of the posterior end of the dentary. Morphological and osteohistological features indicate that all recovered individuals represent late juveniles or sub-adults. This site shows the first direct evidence of sympatry in Pterosauria. The two distinct flying reptiles coexisted with a theropod dinosaur, providing a rare glimpse of a paleobiological community from a Cretaceous desert.

Key words: Paleoecology; Pterosauria; Pterodactyloidea; Keresdrakon vilsoni; Paraná; Cretaceous

Figure 3: Holotype of Keresdrakon vilsoni gen. et sp. nov. (CP.V 2069). Skull and lower jaw are presented in right lateral view.

Abbreviations: cra - skull, cv - cervical vertebra, fe - femur, gas - gastralia, hu - humerus, man - mandible, q - quadrate, ra - radius, ri - ribs, sca - scapula, st - sternum, ti - tíbia; l - left, r - right. Scale bar = 100mm.


TAPEJAROMORHA Andres et al. 2014

Keresdrakon gen. nov.

Etymology: A combination of Keres, death-spirits who personified violent death in Greek mythology and are associated to doom and/or plunder; and drakon, which is the Ancient Greek word for dragon or huge serpent.

Type species: Keresdrakon vilsoni, type by monotypy.

Keresdrakon vilsoni gen. et sp. nov.

Etymology. In honor to Mr. Vilson Greinert, a volunteer who dedicated hundreds of hours preparing most of the specimens from 'cemitério dos pterossauros' site housed in CENPALEO and in the town of Cruzeiro do Oeste.

Figure 1 Map showing the location of the 'cemitério dos pterossauros' site in Cruzeiro do Oeste (red arrow), Paraná State, southern Brazil. (a) The outcrops of the Bauru Basin (light grey) in Brazil, (b) detail of the Bauru basin with the Rio Paraná (light green), Goio-Erê (light blue), Santo Anastácio (grey) formations, and the Bauru Group (dark grey), and (c) stratigraphic chart showing the relations of the former, including the underlying Serra Geral Formation (green).

Type locality, horizon and age. 'cemitério dos pterossauros' site (53° 03′ 53,4″W; 23° 45′ 34,5″S - contra Langer et al. 2019), Cruzeiro do Oeste, Paraná State, Brazil; Bauru Basin, Caiuá Group, Goio-Erê Formation Cretaceous (Milani et al. 2007, Basilici et al. 2012, Batezelli 2015).

Diagnosis. Azhdarchoid pterodactyloid with the following autapomorphies: short blunt ridge on the dorsal surface of the posterior end of the dentary; foramen on the ventral surface at the anterior half of the proximal articulation of the first phalanx of digit IV; and foramen on lateral surface of the ischium.

The new species can be further distinguished from other azhdarchoid pterosaurs by the following combination of characters: dorsal margin of the premaxillae above the nasoantorbital fenestra rounded; sagittal groove on the dorsal surface of the premaxillae above the nasoantorbital fenestra; ridge on the medial surface of the splenial; ventral bar of the nasoantorbital fenestra thick; lateral pneumatic foramen on mid-cervical vertebra large; and strongly asymmetrical sternal articulation of the coracoid.

Figure 10: Time-calibrated phylogenetic tree showing the relationships of Keresdrakon vilsoni gen. et sp. nov. within the Pterodactyloidea. Intermittent bars show uncertain temporal range. Letters in intermittent bars indicate controversial age hypotheses of the Goio-Erê Formation: (a) Albian-Aptian; (b) Turonian-Campanian. Outgroup relationships are not shown (see Holgado et al. 2019 - Supplementary Information for further details). Stratigraphic chart modified from Cohen et al. (2013).

Figure 16: Sample (CP.V 2374) from bonebed C of Figure 2, showing two caudal vertebrae from Vespersaurus paranaensis (a), the diaphysis of a large first phalanx of manual digit IV of Keresdrakon vilsoni gen. et sp. nov. (b), and bones of Caiuajara dobruskii (c), separated by the white line. 
Abbreviations: cdr - caudal vertebrae, ph1d4 - first phalanx of manual digit IV. Scale bar = 100mm.


Figure 17: Reconstruction of the paleoenvironment showing the possible interaction of the vertebrate fauna recovered from the 'cemitério dos pterossauros' site. Artwork by Maurilio Oliveira.

The coexistence of fossil vertebrates, including pterosaurs, are hard to be proven in the fossil record, specially cases of sympatry. Regarding pterosaurs, there must have been several places along deep time where closely related species might have overlapped and shared similar geographic distribution. The challenge is to find direct evidences of this. The 'cemitério dos pterossauros' site represents the co-occurrence of distinct pterosaur species in the same bone beds, showing that Keresdrakon and Caiuajara were coeval. This site also shows that the dinosaur Vespersaurus paranaensis shared this ancient desert environment with these two flying reptiles. While Caiuajara, despite being small and therefore potentially having a more fragile skeleton, by far outnumber the other taxa and is one of the few examples in the fossil record that might argue for gregarious behavior in pterosaurs, Keresdrakon vilsoni was scarcer and apparently represents a species with solitary behavior. We advocate that both specialized in different feeding items of this most likely depauperate environment. Caiuajara is regarded as being frugivorous and Keresdrakon might have been an opportunistic predator or a scavenger feeding at small animals or carcasses such as that of Vespersaurus. The latter might have made a living by hunting individuals of Caiuajara dobruskii that were abundant. All three were part of a paleobiological community that existed in this region during part of the Cretaceous.

As has been pointed out before (Kellner 2012), the outcrops in the region of Cruzeiro do Oeste, more specifically deposits from the Caiuá Group as the Goio-Erê formation, might turn out to become the `Brazilian Mongolia´ in terms of fossil vertebrates. The hundreds of fossils from two pterosaur species and one theropod dinosaur, as well as the occurrence of a lizard, endorse this potential. It is also likely that the future might show additional taxonomic groups like mammals and other reptiles. More fieldwork and careful collection of specimens might contribute to a better understanding of the ecosystem of ancient Cretaceous deserts that, despite its general depauperate conditions, had areas where life could prosper.

Alexander W.A. Kellner, Luiz C. Weinschütz, Borja Holgado, Renan A. M. Bantim and Juliana M. Sayão. 2019. A New Toothless Pterosaur (Pterodactyloidea) from Southern Brazil with Insights Into the Paleoecology of A Cretaceous Desert. Anais da Academia Brasileira de Ciências. [An. Acad. Bras. Ciênc.] 91; supl. 2.  DOI: 10.1590/0001-3765201920190768 


No comments:

Post a Comment