Platyphoca danica Koretsky, Rahmat et Peters, 2014

Koretsky, I., Rahmat, S. & Peters, N., 2014, Rare Late Miocene Seal Taxa (Carnivora, Phocidae) From The North Sea Basin, Vestnik Zoologii 48 (5), pp. 419-432 : 427-429

Platyphoca danica Koretsky, Rahmat et Peters , sp. n. (pl. 3, 2A–2B; table 2)

H o l o t y p e. Distal part of the left humerus (pl. 3, 2A–2B), GM1, Geological Museum, Copenhagen, Denmark. Cast in Museum MidtsØnderjyllands Museum, Gram Slot; number refers to collection number of original in Copenhagen.

T y p e l o c a l i t y. Skaerum MØlle , Jutland, Denmark (56.33°20' N, 8.35°21' E).

S t r a t i g r a p h i c a l r a n g e. Gram Formation, late Miocene (early-middle Tortonian, 8.0–11.5 ma).

Etymology. After Dania (Latinized, noun, feminine) — Denmark; danica (Latinized, adj.) — from Denmark.

D i a g n o s i s. Coronoid and olecranon fossae of humerus wide and shallow; extended more proximally than medial epicondyle, almost reaching distal part of deltoid crest; entepicondylar foramen large, with wide bridge over it; thin lateral epicondyle very elongated, but does not reach distal part of deltoid crest; medial epicondyle wide and flattened, its lateral border forming an oval that is oriented 45° to the bone’s axis.

D e s c r i p t i o n a n d c o m p a r i s o n. The humeral trochlea is very pronounced, especially the capitulum. The groove between the trochlea and capitulum (the middle of the internal crest of the humeral trochlear) is flattened near the floor of the coronoid fossa, unlike that in Monachinae (= arch-like) or Cystophorinae (= appearing wave-like over the coronoid fossa) ( Koretsky, Rahmat, 2013: fig. 3 ). The trochlea is higher and more prominent than in P. vulgaris (pl. 3, 1A–1B). The coronoid and olecranon fossae are so shallow (in contrast to P. vulgaris ) that they are barely outlined. They extend more proximal than the medial epicondyle and do not reach the distal part of the deltoid crest. The entepicondylar foramen is large, oval (in contrast to P. vulgaris ), with a broad and flat bridge over it. The lateral epicondyle is narrow, very elongated, and does not reach the distal part of the deltoid crest, but extends farther proximally than the medial epicondyle (as in P. vulgaris ). The medial epicondyle is oval (in contrast to P. vulgaris ) and forms a 45° angle with the bone’s axis. The distal epiphysis is narrower and thinner than in P. vulgaris . The entire bone is unusually flat, and slender. Collectively, these features lend a spatula-like appearance of the distal end of the humerus. The general appearance of the bone suggests that it belongs to the genus Platyphoca , as indicated above.

Discussion. Although a comparison with the humerus of P. vulgaris is limited due to the absence of the proximal part of the bone as well as by its origin from a different geological age, this Danish humerus is compatible with humeri of Platyphoca vulgaris in several anatomical characters and its size. At the same time, the preserved part of the humerus appears to bear enough distinctive characters to describe a new taxon.

Similar to Gryphoca , the unusual and rare taxon Platyphoca is known to researchers by name and was critically re-examined by Ray (1976) and Koretsky and Ray (2008). Despite the fragmentary representation of this species in Van Beneden’s original collection, the examination of additional fossil material from the Lee Creek Mine ( USA) shows the same very distinctive morphological features (such as spatula-like distal end of the humerus). The high affinity of this newly described humerus from Denmark with Platyphoca and the amount of similar fossil material from other parts of the world indicate that Platyphoca danica represents an identifiable species.

Figures

Plate 1. Fig. 1. Pontophoca sarmatica, right femur; Kishinev, Moldavia (Middle Miocene, middle Sarmatian); аfter Koretsky, Grigorescu (2002: fig. 3); USNM 214980: 1A — cranial; 1B — caudal view. Рис. 1. Pontophoca sarmatica, правая бедренная кость; Кишинев, Молдова (средний миоцен, средний сармат); по: Koretsky, Grigorescu (2002: рис. 3); USNM 214980: 1A — вид спереди; 1B — вид сзади.

Fig. 3. Gryphoca nordica sp. n., paratype, proximal part of right humerus (reversed); Gram, Jutland, Denmark. Clay pit of Gram Teglvaerk, Gram Formation (late Miocene, early-middle Tortonian, 8.0–11.5 ma); MSM 1404x1 (cast in Geological Museum, Copenhagen, Denmark): 3A — caudal; 3B — cranial; 3C — medial; 3D — lateral view. Abbreviations: ac — anconeal crest; rf — radial fossa; sg — spiral groove.

Fig. 2. Pontophoca jutlandica sp. n., holotype, incomplete right femur; Gram, Jutland, Denmark. Clay pit of Gram Teglvaerk, Gram Formation (late Miocene, early-middle Tortonian, 8.0–11.5 ma); MSM 1788: 2A — cranial; 2B — caudal view. Рис. 2. Pontophoca jutlandica sp. n., голотип, неполная правая бедренная кость; Грам, Ютландия, Дания. Карьер Грамского кирпичного завода, грамская свита (поздний миоцен, верхний-средний тортон, 8,0–11,5 млн лет назад); MSM 1788: 1A — вид спереди; 1B — вид сзади