Bairdia chaotianensis Zazzali, 2015

Zazzali, Sindbad, Crasquin, Sylvie, Deconinck, Jean-François & Feng, Qinglai, 2015, Biodiversity across the Guadalupian-Lopingian Boundary: first results on the ostracod (Crustacea) fauna, Chaotian section (Sichuan Province, South China), Geodiversitas 37 (3), pp. 283-313 : 292-294

Bairdia chaotianensis Zazzali , n. sp.

( Fig. 6D, E ; 18 )

TYPE MATERIAL. — Holotype: one complete carapace (P6M3613; Fig. 6D ); paratype: one complete carapace (P6M3614; Fig. 6E ).

ETYMOLOGY. — From the Chaotian section, Type locality.

MATERIAL EXAMINED. —24 complete carapaces and 35 isolated valves. DIMENSIONS. — L= 694-1160 µm; H= 322-631 µm. Holotype: L= 1050 µm; H= 557 µm. Paratype: L= 914 µm; H= 459 µm ( Fig. 18 ).

TYPE HORIZON. — Sample 11 CHAO 172, “Limestone Unit” (L3), Maokou Formation, Middle Capitanian, Middle Permian.

TYPE LOCALITY. — Chaotian section (30°23.713N- 106°49.615E), Sichuan Province, P. R. China.

OCCURRENCES. — Chaotian section, Sichuan Province, China, Maokou and Wujiaping Formations, Middle Capitanian-basal Wuchiapingian, Middle-Late Permian (samples: 11 CHAO 173, 11 CHAO 172, 11 CHAO 170, 11 CHAO 169, 11 CHAO 168, 11 CHAO 167, 11 CHAO 166, 11 CHAO 165, 11 CHAO 164, 11 CHAO 151, 11 CHAO 87, 11 CHAO 88, 11 CHAO 92, see Table 1).

DIAGNOSIS. — A species of Bairdia with elongated carapace, AB and BP with small radius of curvature, hinge line located below DB; both valves present a more or less expressed shoulder with a crest at the top, parallel to the hinge line.

DESCRIPTION

Overlap: absent at DB, narrow to absent at AB, PB and PVB, narrow at AVB and distinct at ADB, PDB and VB.

DB broadly convex at right lateral view. Hinge line located below DB; presence of more or less expressed shoulder at DB of both valves with a crest at the top, parallel to the hinge line; shoulder and crest extend from DB to PDB at RV and from ADB to PDB at LV.

RV: ADB significantly concave at its median part. AB with small radius of curvature. AB maximum convexity slightly above mid-H. AVB gently convex to nearly straight.VB faintly curved (convex) to nearly straight. PVB in the lengthening of VB. PB with a smaller radius of curvature than anterior one. PB pointed near or slightly below mid-H. PDB more slightly concave than anterior one.

LV: ADB more slightly concave the RV one. AB with small radius of curvature. AB maximum convexity at mid-H. AVB gently convex to nearly straight. VB faintly curved (convex) to nearly straight. PVB gently curved. PB with a smaller radius of curvature than anterior one. PB pointed near or slightly below mid-H. PDB more slightly concave than RV one.

Greatest L slightly above mid-H. Greatest H slightly anterior to mid-L.

In dorsal view, lateral outlines asymmetrically convex, with a maximum of W at mid-L and mid-H. RV slightly to significantly wider than LV.

L/H=0.5.

REMARKS

Within Wuchiapingian specimens some intraspecific variations are observed. Some specimens present slightly higher valves, wider carapaces and, at LV more prominent DB shoulder and crest than at RV. More or less faint angles could be observed at RV between DB and upper half of PDB and ADB. Some differences could also be noticed between Capitanian and Wuchiapingian specimens. Capitanian ones show more rounded valves, with a RV significantly wider than LV, and a more marked mid-dorsal crest on shoulder’s top. Wuchiapingian specimens are, proportionally, slightly longer, DB is also longer. DB of Wuchiapingian specimens is about the half of L and about the third of L for Capitanian ones.

The presence of DB shoulder and crest on each valve distinguishes B. chaotianensis Zazzali , n. sp. from all the other close species. Bairdia chaotianensis Zazzali , n. sp. could be compared to B. sp. 9 sensu Cordell (1952) from the Late Pennsylvanian (Late Carboniferous) of Missouri ( USA; Cordell 1952) by its general lateral RV shape.It differs here by the absence of overlap at DB, more concave ADB and PDB and by more rounded sides in dorsal view. Bairdia chaotianensis Zazzali , n. sp. is also close to Orthobairdia oklahomensis (Harlton, 1927) (in Melnyk & Maddocks 1988b) from the Late Pennsylvanian (Late Carboniferous) of Texas ( USA) by RV general lateral outline. It differs here by a PDB more concave at RV, the absence of DB overlap, and a longer posterior end. B. chaotianensis Zazzali , n. sp. differs here from B. urodeloformis Chen, 1987 (in Crasquin et al. 2010) from latest Permian of Meishan section, Zhejiang province, China, by its PB and AB smaller radius of curvature. It differs also here by an arched DB, an ADB deeply concave in right lateral view and a maximum of overlapping located at VB.

Internal characters could not be observed due to the infilling and preservation.

Figures

FIG. 6. — Ostracods from Guadalupian-Lopingian boundary interval in South China: A-C, Ceratobairdia? ambigua Ishizaki, 1964; A, P6M3610, 11CHAO88; B, P6M3611, 11CHAO88; C, P6M3612, 11CHAO88; D, E, Bairdia chaotianensis Zazzali, n. sp.; D, holotype, P6M3613, 11CHAO172; E, paratype, P6M3614, 11CHAO88;F, Bairdia sp.1, P6M3615, sample 11CHAO173;G, Bairdia sp.2,P6M3616, sample 11CHAO173;H, I, Bairdia sp.3;H, P6M3617,sample 11CHAO171; I, P6M3618, sample 11CHAO171; J, Bairdia sp. 4, P6M3619, sample 11CHAO172; K, Bairdia sp. 5, P6M3620, sample 11CHAO171; L, Bairdia sp. 6, P6M3621, sample 11CHAO171;M, Bairdia sp. 7, P6M3622, sample 11CHAO171;N, O, Bairdia sp.8; N, P6M3623, sample 11CHAO170; O, P6M3624,sample 11CHAO165. All photographs represent complete carapaces in right lateral view, except F in left lateral view. Scale bar: 100 μm.

FIG. 18. — Height-length diagram of Bairdia chaotianensis Zazzali, n. sp.