Phocidae GEN. & SP. INDET.
- Dataset
- Colonization of the ancient southern oceans by small-sized Phocidae: new evidence from Australia
- Rank
- FAMILY
Classification
- kingdom
- Animalia
- phylum
- Chordata
- class
- Mammalia
- order
- Carnivora
- family
- Phocidae
description
NMV P 41759 (Fig. 7) represents the anterior portion of the body of a sacrum, with partially incomplete sacral wings. The cranial articular surface and sacral crests are missing. Identified as a phocid due to sacral wings that are orientated dorsoventrally and laterally flared. Referral to Phocini can be excluded as the sacral wings are not orientated anteriorly [e. g. Phoca vitulina Linnaeus, 1758 NMV P 27683 and Pagophilus groenlandicus (Erxleben, 1777) USNM 21532]. The dorsoventral orientation of the sacral wings is consistent across all other phocids. The promontory appears to be ovoid in shape (rather than spherical), but this may be due to the incomplete preservation of the dorsal surface. In dorsal view, the sacral foramina appear to be anteroposteriorly elongated. The auricular surface of the sacral wing appears to be concave and forms a fossa. This auricular fossa is present in most phocids and odobenids, but not in otariids. NMV P 160433 (Figs 8 – 10) represents an articulated thoracic vertebral column, with eight thoracic vertebrae, four right and two left ribs preserved. The preserved thoracic vertebrae represent T 7 – T 14, based on the identification of the fifth vertebra from the anterior end of the column (T 11) as the anticlinal vertebra. Overall, the column is better preserved on the right lateral side, with the posterior vertebrae being the most complete. The column is eroded on the left posterolateral side. Most of T 7 and T 8 are missing. Both T 9 and T 12 are missing a large portion of the body on the left side. The spinous processes of all vertebrae, except T 11 and T 12, are not preserved, with T 11 being the most complete. T 11 (the anticlinal vertebrae) and T 14 are the most complete vertebrae. While the entire column is articulated, it is contorted both mediolaterally and dorsoventrally relative to anatomical position. Descriptions and comparisons will be from the more complete right side and limited to pre-anticlinal (T 7 – T 10, Fig. 10 A – C), anticlinal (T 11, Fig. 10 D) and post-anticlinal (T 12 – T 14, Fig. 10 E – F). The ribs of T 9 and T 10 are in articulation (Fig. 10 A), with the heads situated within the anterior costal fovea and the posterior costal fovea (Fig. 10 C). Due to dorsal displacement of the ribs, the tubercles are not articulated with the costal fovea of the transverse process. The tubercle is not preserved on rib 9. The transverse processes of T 8 – T 10 are laterally separated from the anterior articular processes, supporting their identification as pre-anticlinal. On the transverse process, the mamillary process (preserved on T 9) is clearly reduced, and the accessory process (preserved on T 10) is underdeveloped, when contrasted to thoracic vertebrae later in the series. The posterior articular process on T 7 – T 10 faces ventrally. The anticlinal vertebra (T 11) has an anterior articular process that contacts the anteromedial border of the mamillary process (Fig. 10 B). The mamillary process projects anteriorly (Fig. 10 D). As the section of the transverse process posterior to the transverse fovea is not preserved, the condition of the accessory process is unknown. A rib is articulated to the anterior costal fovea, and the body of T 10 appears to be missing a posterior costal fovea (Fig. 10 C). The anterior and posterior borders of the spinous process are nearly vertical. The posterior articular process faces ventrolaterally. The anterior articular process for the postanticlinal vertebrae (T 12 – T 14) are dorsomedially facing. This results in the anterior portion being more open than the more anterior thoracic vertebrae. The mammillary process becomes more developed moving down the column, with little separation from the anterior articular process in T 13 and T 14. None of the post-anticlinal vertebrae have ribs articulated or preserved. While the transverse fovea is present on T 13, it is completely absent on T 14 (Fig. 10 E). The accessory process is complete on both T 13 and T 14, but is relatively larger on T 13 (Fig. 10 F). The accessory processes of both these vertebrae appear to be bifurcated, with a lateral and posterior facing tubercle. In ventral view, the posterior end of the body appears to be narrower than the anterior end. The posterior articular processes of the post-anticlinal thoracic vertebrae are ventrolaterally facing. Several differences between representatives of Otariidae (Arctocephalus NMVC 33579 and Callorhinus USNM 49439) and Phocidae (Phoca NMV C 27683 and Neomonachus USNM 22543) support referral of NMV P 160433 to Phocidae. The accessory process of the post-anticlinal thoracic vertebrae is elongate, ‘ pronged’ and well separated from the transverse process, similar to Phoca. This contrasts with the thin and reduced accessory process seen in otariids, such as Arctocephalus Cuvier, 1826 and Callorhinus Gray, 1859. Lastly, the vertical condition of the spinous process on the anticlinal vertebrae of NMV P 160433 appears to be most similar to phocids (NMV C 27683, USNM 22543), which have a much steeper angle than otariids (NMV C 33579, USNM 49439) and odobenids (USNM 396932), which have a shallower angle. MONACHINAE GRAY, 1869
materials_examined
Referred specimens: NMV P 42523, metatarsal V, collected by J. Dixon; NMV P 215759, metatarsal V, collected by D. Rawlings, 2002 (Fig. 5). NMV P 240711, partial interorbital region of cranium, collected by B. S. J. Francischelli, 2013 (Fig. 6). NMV P 41759 partial sacrum collected by C. Macrae, 1980 (Fig. 7). NMV P 160433 eight articulated thoracic vertebrae and five ribs, collected by T. Flannery c. 1975 (Figs 8 – 10). D e s c r i p t i o n: N M V P 2 1 5 7 5 9 a n d N M V P 4 2 5 2 3 (Fig. 5) are both identified as fifth metatarsals due to the irregular, asymmetrical, transversely flattened proximal end. NMV P 215759 is a left metatarsal V and NMV P 42523 is a right metatarsal V, both lacking the distal articular surfaces (Fig. 5). The absence of the distal articular surface may represent an immature condition. However, the majority of postcrania of mature phocids (based on cranial fusion and dental eruption) is usually unfused (pers. obsv.). Both specimens are identified as pinnipeds, based on a dorsoventrally expanded proximal end [e. g. Monachus monachus (Hermann, 1779) NHMUK 1958.11.26.1, Phoca sp. NHMUK 1951.3.2.3 and Arctocephalus sp. NMV C 33579]. Both NMV P 215759 and NMV P 42523 are referred to Phocidae due to the shaft being more rounded (not dorsoventrally flattened) proximally approaching the base and having a plantar tubercle that (in dorsal view) is less than 90 ° proximal from the proximal – distal plane. The lateral surface of the proximal end is mostly orientated laterally (similar to phocids, e. g. Hydrurga leptonyx NMV C 23614 or Homiphoca capensis: Hendey 1972), thus differing from the otariid condition (Arctocephalus sp. NMV C 33579) where the lateral surface of the base is deflected to face proximally. A slight depression on the medial surface of the base, directly medial to the plantar tubercle, is present in both specimens. In addition, there is a shallow fossa present on the lateral surface of the proximal end on the ventral side for both specimens. NMV P 42523 is larger than NMV P 215759 (Supporting Information, Appendix S 2) and has a more ventrally developed proximal end. NMV P 240711 (Fig. 6) is the interorbital region of a phocid cranium. The nasal bones are inserted medially between the frontal bones, and the lack of a supraorbital process is diagnostic for Phocidae (King, 1983 a). The posterior extent of the nasal bone is preserved, along with an anterior section of the frontals. A small portion of cribriform plate and nasal turbinates of the ethmoid are preserved on the posteroventral surface; with a small section of the lateral interorbital region preserved on the dorsolateral surface of the frontal bone (Fig. 6). The interorbital region must have been narrow relative to most other phocids (excluding phocins), based on the posterior tapering of the frontal bones.