Wednesday, May 22, 2019

[Paleontology • 2019] Portunatasaurus krambergeri • A New Basal Mosasauroid from the Late Cretaceous of Croatia, with Comments on the Evolution of the Mosasauroid Forelimb


Portunatasaurus krambergeri
Mekarski, Japundžić, Krizmanić & Caldwell, 2019


ABSTRACT
A new genus and species of plesiopedal mosasauroid, Portunatasaurus krambergeri, from the Cenomanian–Turonian (Late Cretaceous) of Croatia is described. An articulated skeleton, representing an animal roughly a meter long was found in 2008 on the island of Dugi Otok. The specimen is articulated, in approximate life position, and is well represented from the anterior cervical series to the pelvis. Preserved elements include cervical and dorsal vertebrae, rib fragments, pelvic fragments, and an exquisitely preserved right forelimb. The taxon possesses plesiomorphic characters such as terrestrial limbs and an elongate body similar to that of basal mosasauroids such as Aigialosaurus or Komensaurus, but also shares derived characteristics with mosasaurine mosasaurids such as Mosasaurus. The articulated hand exhibits a unique anatomy that appears to be transitional in form between the terrestrially capable aigialosaurs and fully aquatic mosasaurines, including 10 ossified carpal elements (as in aigialosaurs), intermediately reduced pro- and epipodials, and a broad, flattened first metacarpal (as in mosasaurines). The new and unique limb anatomy contributes to a revised scenario of mosasauroid paddle evolution, whereby the abbreviation of the forelimb and the hydrofoil shape of the paddle evolves either earlier in the mosasaur lineage than previously thought or more times than previously considered. The presence of this new genus, the third and geologically youngest species of aigialosaur from Croatia, suggests an unrealized diversity and ecological importance of this family within the shallow, Late Cretaceous Tethys Sea.


FIGURE 2. The holotype of Portunatasaurus krambergeri, HPM 10807, housed in the Hrvatski prirodoslovni muzej (Croatian Natural History Museum), Zagreb, Croatia. 
A, composite interpretive outline showing the most complete skeleton reconstructed using combined data; B, photograph taken June 2008, shortly after discovery; C, photograph taken October 2008; D, photograph taken February 2011; E, photograph of specimen as currently preserved. Gray lines in A indicate impressions only. 

Abbreviations: c, cervical vertebra; co, coracoid; d, dorsal vertebra; lm, left mandibular ramus; pr, parietal ramus; pu, pubis; rm, right mandibular ramus; sc, scapula; st, sternal cartilage; tr, tracheal rings. Scale bars equal 10 cm.

SYSTEMATIC PALEONTOLOGY 

SQUAMATA Oppel, 1811 
ANGUIMORPHA Fürbringer, 1900 
PYTHONOMORPHA Cope, 1869 

MOSASAUROIDEA Camp, 1923 

PORTUNATASAURUS, gen. nov. 
Type Species:— Portunatasaurus krambergeri, sp. nov. 

Etymology:— After the island of Dugi Otok, Croatia, where the holotype was found. The ancient name connected with Dugi Otok is ‘Portunata,’ and ‘saurus’ in Latin means lizard

 PORTUNATASAURUS KRAMBERGERI, sp. nov.

 Etymology:— Specific name in honor of Dr. Dragutin Gorjanovic-Kramberger, great Croatian geologist, paleontologist, and ́ paleoanthropologist, university professor and director of the Geological and Palaeontological Department of the National Museum in Zagreb, in recognition of his contribution to the study of Late Cretaceous Adriatic marine lizards and for scientific achievements in the field of vertebrate paleontology in Croatia and worldwide.


FIGURE 6. Hypothetical scenario of forelimb evolution from terrestrial ancestors to mosasaurine mosasaurs.
 A, Varanus albigularis after University of Alberta Museum of Zoology 947; B, Aigialosaurus bucchichi after GBA 1901/002/0005; C, Carsosaurus marchesetti after MCSNT unnumbered; D, Portunatasaurus krambergeri after HPM 10807; E, Clidastes sp. after Carroll (1997); F, Mosasaurus conodon after Russell (1967); G, Plotosaurus bennisoni after Camp (1942).
 Color key: blue, humerus; orange, radius and ulna; green, carpal elements; pink, metacarpals; red, first metacarpal.

Life reconstruction of Portunatasaurus krambergeri, showing an intermediate stage of aquatic limb adaptation. The specimen is preserved in sediments deposited in a lagoon on the Adriatic-Dinaric Carbonate Platform and is inferred to be a shallow-water inhabitant.
artwork by Sydney Mohr.


Michelle Campbell Mekarski, Dražen Japundžić, Katarina Krizmanić and Michael W. Caldwell. 2019. Description of A New Basal Mosasauroid from the Late Cretaceous of Croatia, with Comments on the Evolution of the Mosasauroid Forelimb. Journal of Vertebrate Paleontology.  DOI: 10.1080/02724634.2019.1577872  

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