Chandlera lacunosa R.A. SCOTT

Tiffney, Bruce H. & Manchester, Steven R., 2022, The Early Middle Eocene Wagon Bed Carpoflora Of Central Wyoming, U. S. A., Fossil Imprint 78 (1), pp. 51-79 : 54-56

Chandlera lacunosa R.A. SCOTT

Text-fig. 1g –n

M a t e r i a l. One specimen, USNM PAL 772340, preserved in translucent chalcedony.

D e s c r i p t i o n. Endocarp lozenge-like, elongateelliptic in face view ( Text-fig. 1g –h), narrowly elongateelliptic in lateral view ( Text-fig. 1i) with long, slightly convex, sides; narrowly elliptic in cross section (Textfig. 1k–n). 37 mm long, 18 mm wide and 12.5 mm thick; bilaterally symmetrical; the plane of symmetry running longitudinally, bisecting the width. Surface of endocarp smooth, with a very faint median longitudinal lineation. In cross section, a central reniform locule 7.5 mm wide by 3 mm high is present, surrounded by 6 smaller cavities on the dorsal and lateral flanks, ranging from nearly circular to more elliptic (2 × 2.5 mm to 3 × 4.5 mm), separated by 1–2 mm thick walls ( Text-fig. 1j, n). The endocarp wall is 3–4 mm thick. The translucent dorsal surface reveals that the endocarp cavities are longitudinally elongate, dorsal and lateral to the locule, and are linked in a network via transverse cross-cavities ( Text-fig. 1g, j). The ventral side of the endocarp, below the central locule, is infilled by chalcedony with only a hint of a pair of cavities. Both the apical and basal ends of the endocarp are marked by paired, round to elliptical concavities, separated by a median wall and an overhanging dorsal beak ( Text-fig. 1k–m). These concavities, or apertures, measure 3 × 5 mm at the apical end and 2.5 × 2.5 mm at the base. The apertures link to the network of elongate and cross cavities within the endocarp wall. Some of the cavities are filled with sand and clay while others remain empty ( Text-fig. 1m). No cellular structure is discernable.

D i s c u s s i o n. This fossil conforms closely to Chandlera lacunosa (tribe Tinosporeae , Menispermaceae ) first described by Scott (1954, 1956) and further detailed by Manchester (1994) from the middle Eocene Clarno flora of Oregon. The single specimen falls approximately in the middle of the size range of the Clarno specimens.We illustrate examples of well-preserved specimens from the Clarno Nut Beds for comparison ( Text-fig. 1o–r). The convex surface

g: Ventral view of semi-translucent endocarp, with faint silhouette of interconnected lacunae, reflected and transmitted light, uncoated. h, i: Dorsal and lateral views, micro-CT scan surface rendering. j: Virtual median longitudinal section in dorsi-ventral plane intercepting rows of lacunae within the endocarp wall. k: Apical, l: basal views, reflected light. m: Apical view, cf. (k), micro-CT scan surface rendering. n: Physical transverse section in the plane of saw cut seen in (g–j), reflected light. Note remains of curved locule in center and surrounding lacunae. o–r: Chandlera lacunosa from the type locality in the Clarno Formation of Oregon for comparison, surface and sectional views from micro-CT scanning. o: Transverse section showing central locule surrounded by endocarp with prominent lacunae, including a pair of ventral lacunae adjacent to the concave surface of the locule, UF225-33628 . p: Same specimen, surface rendering of the basal end with prominent pair of apertures and median groove. q: Oblique-ventral view of specimen fractured to show boat-shaped locule cast surrounded by fragmentary remains of the endocarp, UF225-6849 . r: Same specimen in virtual transverse section, showing lacunae surrounding the locule in arrangement similar to that of (n). Scale bars = 1 cm. Bar at (b) applies to (a–f); bar at (i) applies to (g–n) .

of the locule coincides with the endocarp dorsal surface. The presence of apical and basal paired apertures ( Text-fig. 1k–m) leading to six reticulated, dorsal-lateral, channels in the endocarp ( Text-fig. 1j) matches the condition in the Clarno specimens ( Text-fig. 1p, q). A physical transverse section of the Wagon Bed specimen intercepted some of these channels ( Text-fig. 1n), which are also seen in X-ray imagery, for example in virtual longitudinal section (Textfig. 1i). However, the Wagon Bed specimen does not clearly show the two ventral (condylar) lacunae seen in the Clarno specimens ( Text-fig. 1o, r). We interpret this as an artifact of preservation whereby chalcedony entered the basal and/or apical apertures and infilled these lacunae after the endocarp wall had disintegrated and been infilled with chalcedony forming the initial cast. A very faint medial hairline groove on the ventral surface (text-fig. 1h) resembles the median longitudinal line seen in the Clarno specimens ( Text-fig. 1p; Manchester 1994). The locule is not fully preserved, but appears to conform to the flattened, boat shaped, locule of Chandlera R.A.SCOTT ( Text-fig. 1q). The absence of cellular detail precludes further anatomical interpretation.

This is the first report of Chandlera beyond the Clarno Formation, extending its range to the Rocky Mountains in the middle Eocene. Endocarps of Menispermaceae are common in the Eocene of the Northern Hemisphere, and are generically diverse in the Clarno ( Manchester 1994), London Clay ( Chandler 1961), Messel ( Collinson et al. 2012) and Le Quesnoy ( Jacques and De Franceschi 2005) floras, among others. Today, the Tinosporeae are the most diverse tribe of the family and are pantropical with more temperate outliers ( Kessler 1993). Extant genera are readily distinguishable from each other on the basis of fruit morphology (e.g., Jacques 2009). Within the Tinosporeae , Scott (1954, 1956) suggested that extant Parabaena MIERS , a climbing vine of Indomalaysia, possessed the most similar living endocarp, although they differ greatly in size and sculpture ( Scott 1956, Jacques 2009). It is noteworthy that the family is dominated by vines and climbing shrubs, suggesting that the vegetation at the Wagon Bed locality offered a sufficiently forested environment for lianas.