Weird Mississippian Plants of New Brunswick, Canada

Discoveries in a small borrow pit near Norton, New Brunswick, by Matt Stimson and Olivia King, both of whom are associated with the New Brunswick Museum of Natural History and working on their advanced geoscience degrees at Dalhousie University, have unearthed a treasure trove of “evolutionarily experimental” plants of Mississippian age. To date, a partial trunk and crown of likely Cladoxylalean affinity, a lycopsid similar to the enigmatic Valmerodendron, and Rhodea-type foliage are preserved in a tidal channel deposit along with a highly diverse trace-fossil (ichnofossil) assemblage. The assemblage comes from the Sanford Quarry, the rocks of which are assigned to the Albert Formation (Tournaisian; 359—347 Ma).

Cladoxylalean tree

The > 2 m tall specimen consists of a central axis with apical lateral branches. The basal, central axis is 0.4 m in diameter and 1.5 m in height and without evidence of lateral branches. There is an abrupt transition at 1.5 m to an interval of 0.5 m where there is a right-hand spiral arrangement of dense lateral branches which appear to continue to the tree terminus. There are at least 12 leaves (lateral branches) departing the trunk over a height of only 10 cm, with an estimated phyllotaxis of 2/12, an axial branch system that is anomalous with the Fibonacci spiral phyllotaxis found in modern plants. Hence, over the 0.5 distance from where the leaves/laterals are first found attached, nearly 60 lateral branches are retained towards the apex in a crown configuration.

The crown consists of leaves/lateral branches that depart the stem at moderate angles (~30̊ ) near the apex, but attain a near perpendicular orientation along the lower parts of the crown. Lateral axes are preserved for at least 1.5 m in total length. The diameter of the crown leaf/branch bases at the point of departure are 2 cm with the axis decreasing to a diameter of 1.5 cm shortly thereafter and tapering to 1 cm distally. All leaves/branches are devoid of secondary branching for a distance of at least 1.25 m, at which time alternates (?) depart in a perpendicular orientation. In the specimens currently in the collection, we have evidence of only four alternate laterals departing the branches before the specimen terminates at the edge of the rock. The ultimate “leafy” appendages are dichotomous branches. Unlike our concept of modern ferns with large laminate and pinnate megaphyllous leaves, the ultimate appendages that served this function in this tree are subdivided and millimeter-scale.

Lycopsids

Typical of Mississippian-aged wetland assemblages, the Sanford Quarry assemblage contains the genus Lepidodendropsis in a variety of preservational states. The spirally arranged leaf scars are vertically elongate with a raised ridge separating each attachment point. Leaf scars are small, only several millimeters in width and height, with the vascular trace positioned in the upper part of the spindle-shaped scar. Lepidodendropsis is reported from late Devonian to Mississippian-aged floras.

Recently, this very unusual lycopsid axis fragment exhibiting a leaf scar with aspects of both a “sigillarian” and “lepidophloios-style” morphology was found. The scars are distorted, likely a pre-fossilization taphonomic modification, and appear nearly equidimensional. Scars are ~3 cm in width and ~3 cm in height, with two elongated parichnos scars bounding what is likely the vascular bundle at the top.  The scar is reminiscent of Valmeryodendron from southern Illinois, a Visean-aged unit (347-331 Ma). Leaf scars in this younger lycopsid are described as quadrangular to hexagonal in shape, although these are small, attaining millimeter-scale dimensions on the holotype (Jennings, 1972). The scars exhibit a central vascular scar and a shallow groove at the top; there is no indication for the presence of parichnos. Hence, the New Brunswick plant also is enigmatic.

Pteridophyte & Pteridosperm-like foliage

Associated with the cladoxylalean tree and lycopsid axes are several different fimbriate and laminate leaves of either fern or seed-fern affinity. The following are a smattering of leaf types.