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The postcranial skeleton of Boreogomphodon (Cynodontia: Traversodontidae) from the Upper Triassic of North Carolina, USA and the comparison with other traversodontids - PubMed

  • ️Sun Jan 01 2017

The postcranial skeleton of Boreogomphodon (Cynodontia: Traversodontidae) from the Upper Triassic of North Carolina, USA and the comparison with other traversodontids

Jun Liu et al. PeerJ. 2017.

Abstract

Postcranial remains of Boreogomphodon from the Upper Triassic of North Carolina are described and compared to those of other known traversodontid cynodonts. The postcranial skeleton of Boreogomphodon is characterized by four sacral ribs, simple ribs lacking costal plates, the extension of the scapular neck below the acromion process, a short scapular facet on the procoracoid, a concave anterior margin of the procoracoid, humerus entepicondyle with smooth corner, and the presence of a fifth distal carpal. Four types of ribs are identified among traversodontids: 'normal' form, tubercular rib, costal plate, and Y-shaped rib. Fossorial behavior is suggested for traversodontids with elaborate costal plates. Within Traversodontidae, the procoracoid is relatively small; the anterior process of the iliac blade extends anteroventrally to different degrees in different taxa, which facilitates retraction of the femur; and the limb bones show allometric growth in terms of length and width.

Keywords: Boreogomphodon; Cynodontia; Postcranial skeleton; Traversodontidae.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Boreogomphodon (NCSM 20711), cervical vertebrae and ribs 2 to 5 in lateral view.

Abbreviations: 2–5, cervical 2–5; d, dentary; cl, clavicle; cr, cervical rib; ns, neural spine; pp, posterior process. Scale bar equals 1 cm.

Figure 2
Figure 2. Boreogomphodon (NCSM 20698), anterior dorsal vertebrae and ribs.

In (A) ventral and (B) ventrolateral views, the anterior is right; posterior dorsal vertebrae in (C) dorsal, (D) left lateral and (E) ventral views, the anterior is left. Two parts form a continue series. Scale bars equal 1 cm.

Figure 3
Figure 3. Boreogomphodon (NCSM 20698), posterior dorsal, sacral and anterior caudal vertebrae and ribs.

In (A) ventrolateral and (B) ventral views; the left ischium in lateral view. Anterior is right. Abbreviations: dr, dorsal rib; poz, postzygapophysis; prez, prezygapophysis; sr, sacral rib; sv, sacral vertebra. Scale bar equals 5 mm.

Figure 4
Figure 4. Boreogomphodon, shoulder girdles.

(A) NCSM 20711 mainly in ventral view. NCSM 20698, left scapula in (B) lateral, (C) posterior, and (D) medial views; (E) right procoracoid in lateral view. Abbreviations: acr, acromion; ar, anterior ridge; bi, fossa for origin of biceps muscle; C, clavicle; cb, fossa for origin of coracobrachialis muscle; cc, concavity for articulation with medial end of clavicle; COR, coracoid; d-t min, insertion for deltoideus plus teres minor muscle complex; f prc, procoracoid foramen; H, humerus; IC, interclavicle; lr, lateral ridge; pr, posterior ridge; PRC, procoracoid; prc (cor), procoracoid articular surface for coracoid; prc (s), procoracoid articular surface for scapula; S, scapula; spc, fossa for supracoracoideus muscle. Scale bars equal 5 mm.

Figure 5
Figure 5. Boreogomphodon, humeri.

Right humerus (NCSM 20698) in (A) ventral, (B) anterior (lateral), (C) dorsal, and (D), posterior (medial) views; distal part of left humerus (NCSM 21370) in (E) ventral, (F) distal, and (G) dorsal views. Abbreviations: bi gr, bicipital groove; cp, capitulum; d c, deltopectoral crest; ec, ectepicondyle; en, entepicondyle; f en, entepicondylar foramen; g t, greater tuberosity; h, humeral head; l t, lesser tuberosity; sc f, supracondylar flange; th, trochlea. Scale bar equals 1 cm.

Figure 6
Figure 6. Boreogomphodon, forelimbs.

Left forelimb (NCSM 21370), (A) manus in plantar view, ulna and radius in posterior view; (B) carpus and metacarpus in plantar view; (C) ulna and radius in anterior view; (D) carpus in dorsal view. Right forelimb (NCSM 20698), (E) manus in plantar view, ulna and radius in posterior view; (F) a few digitals in dorsal view, it continues with digits in (E). Abbreviations: c, centrale; dc, distal carpal; i, intermedium; mc, metacarpal; paf, proximal articular facet; pc, proximal centrale; R, radius; U, ulna; r, radiale; u, ulnare. Digits in Roman numbers. Scale bars equal 5 mm.

Figure 7
Figure 7. Boreogomphodon (NCSM 20698), ischium and hindlimb.

(A) hindlimb; (B) left ischium in lateral view; (C) left femur in ventral view, left tibia and left fibula in posterior views; (D) right pes in plantar view. Abbreviation: as, astragalus; ca, calcaneum; cu, cuboid; ecc, ectocuneiform; enc, entocuneiform; FE, femur; FI, fibula; if, intertrochanter fossa; mec, mesocuneiform; mit, minor trochanter; mjt, major trochanter; mt1∼mt4, metatarsal 1∼4; n, navicular; p2, second phalange; st, sustentaculum tali; tc, tuber calcis; TI, tibia. Digits in Roman numbers. Scale bars equal 1 cm.

Figure 8
Figure 8. Different types of ribs in Traversodontidae.

(A) type I, Exaeretodon argentinus (PVL2554); (B) type II, Protuberm cabralensis (UFRGS PV1010T); (C) type III, Pascualgnathus polanskii (MLP 65-VI-18-2); (D) type IV, Masetognathus pascuali (PVL 5443); (E) Scalenodon angustifrons (NHMUK R9391). Scale bars equal 1 cm.

Figure 9
Figure 9. Interclavicles and clavicles.

Exaeretodon argentinus (PVL 2467): (A) right clavicle in ventral view; (B) interclavicle and left clavicle in dorsal view; Massetognathus pascuali (PVL 4613): interclavicle and clavicles in (C) dorsal and (D) ventral views. Scale bars equal 1 cm.

Figure 10
Figure 10. Scapulocoracoids of various cynodonts.

Cynognathus (NHMUK 2571) in (A) lateral and (B) medial views; Diademodon (UMZ T 502) in (C) lateral and (D) medial views; Pascualgnathus (MLP 65-VI–18-1) in (E) lateral view; Boreogomphodon (NCSM 20698) in (F) lateral view; Andescynodon mendozensis (PVL 4428) in (G) lateral view; Exaeretodon argentinus (PVL 2554) in (H) lateral view; Luangwa (OUMNH TSK 121) in (I) lateral and (J) medial views; Massetognathus pascuali (PVL 4613) in (K) lateral and (L) medial views; Menadon besairiei (FMNH PR 2444) in (M) lateral and (N) medial views; Traversodon (GPIT RE 1069) in (O) lateral and (P) medial views. Scale bars equal 1 cm. (M, N, O, P image credit: Christian F. Kammerer).

Figure 11
Figure 11. Traversodontid left humeri in ventral view.

(A) Andescynodon mendozensis (PVL 3894); (B) Pascualgnathus polanskii (MLP65-VI-18-1); (C) Luangwa drysdalli (OUMNH TSK121); (D) Boreogomphodon (NCSM 20698); (E) Massetognathus pascuali (PVL 4241); (F) Exaeretodon argentinus (PVL 2467). (B, D, E) are reflected as left side. Scale bars equal 1 cm.

Figure 12
Figure 12. Regression of various width to humeral length (L).

(A) the proximal width (PW), (B) the distal width (DW), (C) the sum of humeral shaft minimum width in dorsoventral and anteroposterior directions (S1 + S2).

Figure 13
Figure 13. Right ulnae of traversodontids in lateral view.

(A) Boreogomphodon (NCSM 20698); (B) Andescynodon (PVL 3890); (C) Pascualgnathus polanskii (MLP 65-VI-18-1); (D) Massetognathus pascuali (PVL 5444); (E) Exaeretodon argentinus (PVL 2467). (A, E) are reflected as right side. All scale bars equal to 1 cm.

Figure 14
Figure 14. Pelvises in lateral view.

(A) Scalenodon angustifrons (NHMUK R 9391 = TR 8); (B) Pascualgnathus polanskii (MLP 65-VI-18-1); (C) Andescynodon mendozensis (PVL 3894); (D) Luangwa drysdalli (OUMNH TSK121); (E) Menadon besairiei (FMNH PR 2444); (F) Massetognathus pascuali (PVL 4442); (G, H) Exaeretodon argentinus (PVL2554). (A, H) are reflected from right side. (I) a trirachodontid (NMQR 3521) right ilium. All scale bars equal to 1 cm.

Figure 15
Figure 15. Femora of traversodontids.

Pascualgnathus polanskii (MLP 65-VI-18-1), right side in (A) anterior and (B) posterior views; Scalenodon angustifrons (NHMUK R9391 = TR 8), left side in (C) anterior view; Luangwa drysdalli (OUMNH TSK121), left side in (D) anterior view; Andescynodon mendozensis (PVL 3894), left side in (E) anterior and (F) posterior views; Traversodon stahleckeri (GPIT RE 1069), right side in (G) anterior and (H) posterior views; Massetognathus pascuali (PVL no number), right side in (I) anterior and (J) posterior views; Exaeretodon argentinus (PVL 2554), left side in (K) anterior and (L) posterior views. All scale bars equal to 1 cm.

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Grants and funding

This study was supported by Chinese Academy of Sciences (XDPB 0501), Columbia University through a Faculty Fellowship, and IRG-China/South Africa Research Cooperation Programme (CS08-L02/95449). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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