Kloster and Gnaedinger—Agathoxylon wood anatomy from La Matilde Formation, Argentina


553


Holotype.—4506 B.S.I.P. from Mandro, Rajmahal Hills, Bihar, India (Jurassic).


Description.—Wood fragments found in situ of 95cm in dia- meter, and a trunk of 1.20m long and 30cm in diameter were studied. These materials come from the Barda Blanca locality of the Gran Bajo de San Julián sector and Bajo El Puma locality of the central and south-western sector (Figs. 1, 2). The description is based on specimen CTES-PB 10649, although examination of the other specimens supports it. Secondary xylem is pycnoxylic with distinct growth ring boundaries, and the transition from early wood to late wood is gradual. In TS, the tracheids are quadrangular-rectangular and irregular in shape. The radial diameter of the tracheids is 59 μm(45–82 μm) and the tangential is 50 μm (30–75 μm). The average number of tracheids separat- ing the rays is 10, with a range of 3–26 tracheids. The rays are displayed in a continuous way through the section (Fig. 5.1). In RLS, the wood secondary type (tracheid radial pitting) is arau- carian (100% of the contiguous pits are araucarioid). In the early wood, pits are bordered, uniseriate, flattened (16% [10–20%]), biseriate, hexagonal, and alternate (53% [46–60%]), and occa- sionally triseriate or bi-triseriate, hexagonal, and alternate (3% [2.5–3%]); in addition, they are uniseriate, with biseriate por- tions (30% [27–33%]), flattened and hexagonal, alternate (17% [15–19%]) and opposite in a single pair (11% [9–13%]) or in a several pairs (2% [1–3%]). In the late wood, pits are bordered, uniseriate and flattened. The size of the pits is 15–30 μm×15 μm. The pits present a central circular aperture, which measures 6–7.5 μm (Figs. 4.3, 4.4, 5.2, 5.3). Cross-fields show an arau- carioid type arrangement, with 2–6 araucarioid pits, measuring 11 μm with a circular aperture of 4 μm, whose frequency range is 3–4, arranged in groups or in horizontal rows. In some mar- ginal cross-fields, 9–12 pits can be observed (Figs. 4.5, 5.4). In TLS, the radial system is homogeneous with homocellular rays, uniseriate, of 1–8, 12 cells in height, with an average of 4–5 cells. The central cells are ovoidal and measure 15– 30 μm×22–30 μm in width by height, respectively. Tracheids are observed with resins associated with the rays, which in radial and tangential section form the typical biconcave plates or “resin plates” (Fig. 5.5).


Materials.—Gran Bajo de San Julián sector: Barda Blanca: CTES-PB 10649 (CTES-PMP 2328-2329); CTES-PB10665 (CTES-PMP 2321 a, b, c), CTES-PB 14239 (CTES-PMP 3538 a, b, c); CTES-PB 14240 (CTES-PMP 3539 a, b, c); Center and south western sector, Bajo El Puma: CTES-PB 14206 (CTES- PMP 3530 a, b, c); CTES-PB 14207 (CTES-PMP 3531 a, b, c).


Remarks.—After comparison with species of the genera Araucarioxylon and Dadoxylon, the specimen from the La Matilde Formation was determined to be Agathoxylon santa- lense (Sah and Jain) n. comb. This species was erected by Sah and Jain (1964) as Dadoxylon santalense and is characterized by araucarian wood types with mostly uniseriate, sometimes biseriate, alternate, flattened, and hexagonal radial pitting; cross-fields with 2–6 pits arranged in an araucarioid pattern, usually four, with the aperture as big as the border and rays of 1– 10 cells in height; and resin tracheids present, associated with the rays (Table 3).


Table 2. Quantitative data of the anatomical characteristics examined type radial pitting (contiguity) araucarioid. M-M (m)= Minimum-Maximum (mean). Agathoxylon agathioides A1= CTES-PB 10659; A2= CTES-PB 10647; A3=CTES-PB 14236; A4= CTES-PB 10703; A5= CTES-PB 10702; A6= CTES-PB 12036; Agathoxylon santalense B1= CTES-PB 10649; B2= CTES-PB 14239; B3= CTES-PB 10665; Agathoxylon termieri C1= CTES-PB 10693; C2= CTES-PB 10696; C3= CTES-PB 10675; C4= CTES-PB 12043; C5= CTES-PB 12041; Agathoxylon santacruzense D= CTES-PB 12012.


Characters Specimens Radial pitting (in percentage) Shape Circular Seriation


Hexagonal Flattened 1-seriate 2 seriate 3 seriate


Cross-field Rays


Arrangement in multiseriate Alternate Opposite Minimum


Number of pits Maximum


Ray height (number of cells)


63 67 61 69 60 60 60–69 70 67 69 67–70 (63)


36 33 39 31 40 40 31–40 30 33 31 30–33 (36.5)


51 49 52 48 55 54.7 48–55 29 28 31 28–31 63 (51)


48 50 46 51 43.5 44 43–51 68 70.5 66 66–70 35 (48)


(68) (31) (29) (68)


0.5 1


9.6 4 2


6 7 6 2 1


2 6


8 10 2


6 8


0.5 1.3 0.4–2 (1)


2 6


7


9 2


6 7


8 2


6 6 3


90 96 92 90 91 92 90–96 85 86 84 84–86 93 (92)


(85)


2 6


2 6


2 6


2 5


Occasional maximum —— 810 — 88–10 —— 8 Frequency range Mean


5 (6.8)


Minimum Maximum


1 1 2 2 2 2 1–21 2 22 16 20 21 18 20 16–22 8 2 9 10 1–2 1 8–10 12 3 12 2 1 2 10 14 14 Occasional maximum 37 — 40 —— 28 28–40 12 12 15 12–15 —— 19 — 20


1.8 1 11.6 16 19.5 20


2 2 10 2


5–68 8 8


4–55 7 A1 A2 A3 A4 A5 A6


M-M (m) B1 B2 B3


M-M (m) C1 C2 C3 C4 C5


M-M (m) D


100 100 100 100 100 100


66 25


9


67 32


1.5 3 1.5–32 1 (2.5)


93


66 69 75 32 30 23 2


1


4–10 15 14 16 15 77 5 (8)


95 94 93 6


68 2 7 29


30.4 63.5 1–2 7.5 93–95 92 6.4 8


2 — 222 7 — 8


4–64–64–64–64–64–64–62–42–42–42–43–43–44 — 3–43–46–8 6–84 5


10 —— 10 7


6 5 6


6.5 14 20


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