Sulidae Gannets and Boobies

The extant species of the Sulidae are exclusively marine birds, which plunge-dive to capture fish or squid. All Paleogene fossils of the taxon were recorded from European fossil sites and mainly consist of fragmentary remains of uncertain affinities.

Masillastega rectirostris Mayr, 2002 from Messel is known from an isolated skull and was only tentatively identified as a stem group representative of the Sulidae (Mayr 2002c). M. rectirostris has a long, straight beak, which is deep in its proximal part and which, in contrast to the conical beak of extant Sulidae, has a slightly hooked tip (Fig. 7.2). The narial openings are strongly ossified. The dorsal surfaces of the mandibular rami are very wide mediolaterally and the tip of the mandible is truncated in lateral view. M. rectirostris shares with crown group Sulidae a deep

Masillastega Fossil
Fig. 7.2 Skull of Masillastega rectirostris Mayr, 2002 (?Sulidae) from the middle Eocene of Messel (holotype, Palaeontological Institute of Bonn University, Bonn, Germany, IPB 140b). Coated with ammonium chloride. (Photo by Sven Tränkner)

upper beak and mandible, which both bear numerous impressions of blood vessels, and the presence of a deeply excavated dorsal tympanic recess. If its assignment to the Sulidae can be confirmed by future specimens, the species indicates that stem lineage representatives of the taxon also occurred in limnic environments.

Eostega lebedinskyi Lambrecht, 1929 is based on an incomplete mandible from marine (Paratethyan) and putatively middle Eocene deposits of Romania, and was assumed to be closely related to extant Suloidea by Lambrecht (1929b). It was referred to the Sulidae by Mlikovsky (2002, 2007), but this assignment was due to overall similarity rather than unambiguous derived similarities. Mlikovsky (2007) further synonymized Masillastega with Eostega, an action whose validity needs to be evaluated by direct comparison of the specimens.

Prophalacrocorax ronzoni (Gervais, 1849) from the early Oligocene (MP 21; Mlikovsky 2002) lacustrine deposits of Ronzon in France is based on a fragmentary pelvis. The species was originally described as a merganser ("Mergus ronzoni"), i.e., a representative of the Anseriformes, but was transferred to the Sulidae by Milne-Edwards (1867-1871) ("Sula ronzoni"). It was then assigned to the taxon Prophalacrocorax by Harrison (1975a), who considered it to be a species of the Phalacrocoracidae. Without more material, its affinities probably cannot be determined (see also Olson 1985).

Empheresula arvernensis (Milne-Edwards, 1867) from the late Oligocene (MP 30; Mlikovsky 2002) lacustrine deposits of Gannat in France is also only known from an incomplete pelvis and a referred sternum (Milne-Edwards 1867-1871). As first noted by Olson (1985), the sternum of this species differs from that of crown group Sulidae in the presence of four incisions in the caudal margin. Its assignment to the Sulidae also needs to be established with additional material.

Remains of sulids were further reported from late Oligocene marine sediments of southern Germany (Darga et al. 1999, distal end of a humerus).

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