Terranectes magnus, Rahmat & Koretsky & Osborne & Alford, 2017

Rahmat, S. J., Koretsky, I. A., Osborne, J. E. & Alford, A. A., 2017, New Miocene Monachinae From The Western Shore Of The Chesapeake Bay (Maryland, Usa), Vestnik Zoologii (Vestn. Zool.) 51 (3), pp. 221-242 : 228-233

Terranectes magnus sp. n. ( figs 4–11 ; tables 1–5 ).

urn:lsid:zoobank.org:act:F3B7C135-ECE1-4741-A428-32AAC14FC95A

Etymology. Magnus (Latin, “big”)

Holotype. CMM-V-4710 , proximal half of the left humerus. Collected by J. Osborne and A. Alford, between September 2011 and September 2012.

Type locality. Site # PQ-BH9812, Southampton County, Virginia near the North Carolina border .

Geological age and d i s t r i bution. Upper Miocene, Chesapeake Group, Eastover Formation (7.0–6.0 Ma) and St. Marys Formation (10.0–8.0 Ma).

Referred specimens. In addition to the holotype, the following specimens were found in southern Virginia near the North Carolina border :

Skull fragment: CMM-V-4680; Atlas: CMM-V-4677; Cervical vertebra: CMM-V-4676; Ulna: CMM-V-4707; Innominata: CMM-V-4704, CMM-V-4705, CMM-V-4708; Femur: CMM-V-4706; Tibia: CMM-V-4702; Thoracic vertebrae: CMM-V-4675, CMM-V-4685; Sacra: CMM-V-4681, CMM-V-4703.

Diagnosis. Seals of large size. Posterior border of glenoid fossa of skull thicker than anterior; postglenoid foramen located at end of postglenoid groove; shallow, wide depression between meatal tube and postglenoid foramen.

Humerus: proximal part of deltoid crest located lower than head and lesser tubercle; lesser tubercle oval, flattened; extends higher than head and distal part of deltoid crest; ratio of head’s width to its height is 1.09; deltoid crest strongly developed, short, terminates at middle of diaphysis; greater width of deltoid crest located on its proximal part; deltoid tuberosity hardly noticeable; in lateral view, deltoid crest flattened and oval.

Femur: narrowest width of diaphysis located at middle of bone; condyles relatively large, and placed wide apart; greatest distance between condyles 17.3 mm.

Description — s k u l l, fig. 4 , E. Only the glenoid fossa with partial squamosal is preserved.The glenoid fossa measures 20.5 mm anteroposteriorly and 26 mm transversely. Its posterior border is thicker than the anterior and forms a deep postglenoid groove in the tympanic bone. A postglenoid foramen is located at the end of the postglenoid groove. We consider the presence of this foramen to be a primitive condition in Phocidae , in contrast to the opinion of Wyss and Flynn (1993). This foramen is present and large in terrestrial carnivorans ( Koretsky and Holec, 2002). The postglenoid process itself is located 2 mm in front of the meatal tube. Between the meatal tube and the postglenoid foramen is a shallow, wide depression (in contrast to the groove in Devinophoca ) in the tympanic bone. This depression is parallel to the meatal tube and floored by the tympanic bone. The suprameatal fossa is present.

Vertebrae: The vertebral column in Monachinae has the formula C7, T15, L5, S3–4, Ca1–12. The transverse processes on thoracic vertebrae are present from T11 to T15. The neural spines are high and pointed on the first five vertebrae, but get progressively smaller and more posteriorly inclined.

C e r v i c a l v e r t e b r a e: figs 4 , J–L. The bodies (centra) are oval in coronal sections (primitive condition) as in Phocinae , not round as in other Monachinae . The ventral surfaces have a median keel in all except the atlas. The transverse processes are at right angles to the median plane and are directed slightly ventrally, and not divided into two branches as in other Monachinae . Compared with sea lions, the cervical transverse processes of seals are narrower, reflecting less complexity of the longus colli muscle. The spinous processes are also less developed.

Atlas: fig. 4 , H–I. The atlas (C1) is delicately built, measuring 120 mm in width and 43 mm in dorsoventral height. Its dorsal and ventral tubercles are well marked. The vertebral arch is oval, with a larger anterior radius than posterior. The transverse process is wide; cranially the transverse process is expanded and directed vertically, whereas overall it is inclined caudo-laterally ( Koretsky, 2001, table 13). The intervertebral foramen is large, measuring 8.6 mm in diameter caudally, whereas cranially it forms an enormous depression (21.0 mm wide mediolaterally, 17.5 mm anteroposteriorly and 20.3 mm high).The alar notch is not present, in contrast to land carnivores.

Sacrum: fig. 5 , D–F. The sacrum consists of 4 fused vertebrae as in other seals (cystophorines and phocines) with an absolute length of 169.5 mm; the greatest width of the wing is 148.0 mm. The sacral promontory is almost flat and not pronounced. However, the ala is thick and the anterior surface of the first centrum is higher than the wings of the sacrum (as in Mirounga and monachines, but in contrast to cystophorines and phocines, where the ala is on the same level as the centrum; Antoniuk, 1979; Koretsky, 2001). The maximum width across the wings is 87.3 % of the length of the sacrum, which according to Antoniuk (1979) is a monachine character. Thin, slender, and well-defined transverse processes are present on S2. Also on S2 is a well-defined mammillo-articular process (intermediate sacral crest) and a long spinous process that does not extend caudally. S3 shows a shorter spinous process that extends caudally with a less developed mammillo-articular process. The median sacral crest, which is formed by the spinous processes, is not fused. All spinous processes are almost the same size. The body of the sacrum is long and slender.

Humerus: fig. 6 , D–G; table 1 .The proximal part of the deltoid crest is located below the lesser tubercle and the humeral head. The deltoid crest is not strongly developed, relatively short, and very well outlined. The deltoid crest is only slightly wider proximally and terminates abruptly in the middle of the bone. In lateral view, the deltoid crest is visibly flattened and oval in outline. The deltoid tuberosity is hardly noticeable. The lesser tubercle is oval and flattened, extending higher than the head and distal part of the deltoid crest. The intertubercular groove is wide and slightly concave. The head is large and oval, compressed craniocaudally. The musculospiral groove is well expressed.

Innominate: figs 7 , 8 , A, G, I, J; table 3 . The ilium is thick and flattened for the insertion of the gluteus medius m., which abducts and extends the femur ( Piérard, 1971). The iliac crest is slightly averted and not excavated on its ventral surface as in other Monachinae and Cystophorinae (similar to Terranectes parvus ). The iliopectineal eminence for insertion of the psoas minor m. (flexing lumbar vertebral column during caterpillar-like terrestrial locomotion; Muizon and Hendey, 1980; Muizon, 1981 c) is wide and very well pronounced ( fig. 7 , C–D).

The pectineal line is visible. On the ventral side of the ilium, anterior to the iliopectineal eminence, one insertion is present for three muscles (psoas major m., quadratus lumborum m., and psoas minor m.) that aid in flexing the hip joint and rotating the thigh outward ( Miller et al., 1964; Muizon, 1981 c). These muscles (psoas minor and major, and quadratus lumborum) work together with the iliacus m. to flex the vertebral column in a vertical plane when acting jointly to facilitate locomotion on land. However, when acting alternately they flex the column in a horizontal plane and this movement is used for swimming. The iliac tuberosity ( fig. 7 , C–D) on the ventral side of the ilium is rounded, large (in contrast to T. parvus ), and turned anteriorly (for insertion of the psoas major and iliacus m.).

The iliacus m. does not rotate the thigh outward as in other terrestrial mammals (as the psoas major m. does not insert on the femur). This is one of the major synapomorphies of phocids ( Muizon, 1981, 1981 c; Miller et al., 1964). This tuberosity is generally welldeveloped in Phocinae and less developed in Monachinae (a primitive character).

The caudal dorsal iliac spine (figs, 7, C–D, 8) is big, thick (similar to T. parvus ), and has a flattened surface laterally, but is turned medially. On the medial side of the wing is a deep and long auricular fossa for articulation with the sacrum. The edges of the acetabulum are raised slightly above the plane surface (similar to T. parvus ) of the bone. The acetabulum is circular, with a deep and well-marked acetabular notch. Anterior to the acetabulum is a big, shallow, and wide depression for the origin of the rectus femoris m. ( Koretsky and Rahmat, 2013, fig. 8 ). The incomplete pubis is flattened, and most of the ischium is not preserved.

Femur: fig. 9 , E–F; table 4 . The minimum width of the diaphysis is located at the midpoint in the length of the bone. The supracondylar fossa, located above the lateral condyle, is shallow and wide. The condyles are relatively big and widely spaced.

Tibia: fig. 10 , D–F; table 5 . The two condyles are weakly concave on their anterior surface, large, and oval. The intercondyloid eminences are weak and rise only slightly above the lateral borders of the condyles, and especially above the medial border of the medial condyle. The borders of the condyles are well developed. The popliteal notch is shallow and wide, but well-marked. The tibial crest is rounded in a dorsomedial direction. The tibial tuberosity is flattened, well-marked, triangular, and extends along the axis of the bone. The muscular groove is flat and narrow; and the distal end of the bone is missing.

Ulna: fig. 11 , A–C; table 2 . The medial aspect of the bone is slightly concave. The olecranon is long and slender, sharply connected to the proximal half of the bone. A prominent protuberance of the rugosity for insertion of the brachialis m. is present on the medial surface. On the lateral aspect, the fossa for insertion of the abductor pollicis longus m. is deep. Caudal to the articular surface on the lateral aspect is a shallow, wide, and long depression. On the bone’s radial aspect, the coronoid process noticeably protrudes forward over the radial notch, which is deep and long. On the lateral aspect, the interosseous crest is swollen, forming an oval prominence that protrudes considerably. The head is not preserved.

Figures

Fig. 4. Atlas and skull. Atlas (C1) of Leptophoca lenis from Maryland, USA (USNM 411889) in A — dorsal; B — ventral; C — caudal and D — cranial views. Skull fragment of Terranectes magnus (CMM-V-4680) in E — lateral view; and T. parvus (CMM-V-4679) in F — lateral and G, medial views. Atlas of T. magnus (CMM- V-4677) in H — cranial and I — caudal views. Cervical vertebra of T. magnus (CMM-V-4676) in J, ventral; K — dorsal, and L — caudal views.

Fig. 5. Sacrum. Sacrum of Leptophoca lenis from Maryland, USA (USNM 23231) in A — dorsal; B — ventral and C — cranial views.Sacrum of Terranectes magnus (CMM-V-4703) in D — lateral; E — ventral, and F — medial views.

Fig. 6. Humeri. Left humerus of Leptophoca lenis from Maryland, USA (USNM 412115) in A — medial; B — cranial; and C — caudal views. Incomplete left humeri of Terranectes magnus (holotype, CMM-V-4710) in D — medial; E — lateral; F — caudal and G — cranial views; and T. parvus (CMM-V-4688) in H — medial; I — cranial and J — caudal views. Scale bars equal 5 cm/2 inches.

Fig. 7. Modern and fossil innominate bones. Left innominate of Leptophoca lenis from Maryland, USA (USNM 263648) in A — lateral (reversed) and B — medial views. Innominate of Recent Phoca vitulina (CMM-O-399, L. and R.) in C — lateral and D — medial views.

Fig. 8. Fossil innominata. Innominate bones in lateral view: A — Terranectes magnus (L., incomplete, CMM- V-4708); B — Terranectes parvus (L., incomplete, CMM-V-4683); C — Homiphoca capensis (L., incomplete, South African Museum PQ-L30236; Muizon and Hendey 1980, fig. 12); D — Callophoca obscura (Ơ, incomplete, USNM 425886, from Lee Creek Mine, USA; Koretsky and Ray 2008, fig. 33); E — Acrophoca longirostris (L., incomplete, SAS 563; Muizon 1981a, pl.11, fig. 1); F — Piscophoca pacifica (R., SAS 682; Muizon 1981a, pl.5, fig.1). In medial view: G — T. magnus (L., incomplete, CMM-V-4708) and H — T. parvus (L., incomplete, CMM-V-4683). T. magnus (L., incomplete, CMM-V-4708) in I — cranial and J — caudal views. T. parvus (L., incomplete, CMM-V-4683) in K — caudal and L — cranial views.

Fig. 9. Femora. Femora of Leptophoca in dorsal views. L. amphiatlantica: A — male, (R., reversed; USNM 23227) from Maryland, USA; B — female, (L., USNM 3211926) from Maryland, USA; C — Male, (L., MAB 2129) from Liessel, southeastern Netherlands; D — L. lenis (R., reversed; USNM 263648) from Maryland, USA. Incomplete femur of Terranectes magnus (CMMV-4706) in E — dorsal and F — ventral views. T. parvus femur (holotype, CMM-V-4709) in G — dorsal; H — ventral and I — lateral views.

Fig. 10. Tibiae. Right tibia of Leptophoca lenis from Mary- land, USA (USNM 175578) in A — caudal; B — cranial; and C — proximal views. Incomplete L. tibia of Terranectes magnus (CMM-V-4702) in D — cranial; E — caudal and F — proximal views; and incomplete R. T. parvus tibia (CMM-V-4778) in G — caudal; H — cranial and I — proxi- mal views.

Fig. 11. Ulnae. Incomplete L. ulna of Terranectes magnus (CMM-V-4707) in A — lateral; B — medial and C — cranial views. Incomplete L. immature ulna of T. parvus (CMM-V-4690) in D — lateral; E — medial and F — cranial views. Scale bar equals 5 cm / 2 inches.

Tables

Table 1. Measurements of humeri, mm

Characters	n	Leptophoca lenis		Terranectes
		M	OR	magnus	parvus
Absolute length	5	122.4	111.0–129.0	–	–
Lenght of deltoid crest	5	75.6	62.0–82.0	81	–
Height of head	5	25.0	19.5–28.0	32.5	–
Height of trochlea	8	17.6	15.0-19.0	–	28.1
Width of head	5	28.2	22.5–31.0	43.8	–
Width of deltoid crest	2	20.5	17.0–24.0	39.4	35.2
Width of distal epiphysis	9	37.3	35.0–42.0	–	55.9
Width of proximal epiphysis	5	35.7	33.5–38.0	63	–
Width of trochlea distally	9	20.0	18.0–23.0	–	27.2
Width of trochlea, frontal view	8	17.6	15.0–20.0	–	37.2
Transverse width of diaphysis	9	15.9	14.0–17.5	34.0	26.9
Trickness of proximal epiphysis	4	34.8	32.5–38.0	62.2	–
Trickness of medial condyle	10	17.8	15.0–21.0	–	33.3
Trickness of lateral condyle	8	16.8	13.0–20.5	–	20.2
Diameter of diaphysis with deltoid crest	8

Table 3. Measurements of innominata, mm

Characters	Leptophoca lenis			Terranectes
	n	M	OR	magnus	parvus
Lenght from center of acetabulum to iliac crest	6	73.8	66.0–83.0	64.2	62.2
Width of level of iliac crest	5	59.4	52.0–76.0	71.7	67.8

Table 4. Measurements of femora, mm

Characters	Leptophoca						Terranectes
	lenis			amphiatlantica			magnus	parvus
	n	M	OR	n	M	OR
Absolute length	2	–	119.0–120.0	2	107.1	96.0–118.3	–	109.4
Medial length	2	–	109.0–112.0	1	109.5	–	–	109.4
Lateral length	6	104.8 101.5–112.0		2	102.0	95.4–109.4	–	98.2
Length of medial condyle	2	–	21.5–22.0	1	19.7	–	–	23
Length of lateral condyle	5	22.9	21.0–24.5	2	19.6	19.4–19.8	31.1	28.3
Length of greater trochanter	4	33.3	28.5–37.0	3	28.8	27.1–30.5	–	37.1
Intertrochanter length	8	44.0	42.0–48.0	3	43.8	38.0–48.8	–	25.1
Height of head	2	–	23.5–25.5	2	18.7	18.3–19.0	–	22.8
Height of articular area of patella surface	6	23.8	23.5–24.0	2	21.5	20.0–23.0	27.8	24.2
Width of poximal epiphysis	8	53.9	51.0–59.0	3	54.8	47.1–59.2	–	58.3
Width of distal epiphysis	4	53,3	54.0–62.0	2	52.4	46.0–58.8	–	64.6
Width of condyles	3	50.7	45.0–54.5	2	47.0	43.0–51.0	–	59.4
Width of greater trochanter	7	18.8	16.5–22.5	3	19.7	18.3–20.5	–	25.2
Width of head	7	20.5	18.0–23.5	2	20.5	18.0–23.0	–	21.5
Width of diaphysis	9	28.1	26.0–35.0	2	27.3	23.7–30.9	45.1	35.9
Anteposterior trickness of diaphysis	9	15.2	14.0–17.0	3	16.0	15.5–16.5	23.5	22.6
Trickness of medial condyle	3	27.3	27.0–27.5	1	30.0	–	–	18.4
Trickness of lateral condyle	8	28.3	27.0–31.5	2	28.7	26.4–31.0	27.9	22.6
Distance between condyles	8	14.3	13.0–17.5	2	15.1	14.3–15.8	–	11.7
Diameter of neck	9	16.2	14.5–18.0	3	17.7	16.3–18.9	–	22.6

Table 5. Measurements of tibiae, mm

Characters	Leptophoca lenis			Terranectes
	n	M	OR	magnus	parvus
Width of proximal epiphysis	16	46.3	44.0–58.0	67.3	50.9
Lenght of proximal epephysis	7	28.3	25.0–33.0	44.5	34.7

Table 2. Measurements of ulnae, mm

Characters	Terranectes
	magnus parvus
Width of trochlear notch proximally	15.4	13.5
Width of notch distally	13.9	12.5
Maximal width of middle part of diaphysis	28.7	19.9