Tetracentron hopkinsii

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Tetracentron hopkinsii
Temporal range: Ypresian
↓
Fossil leaf, Klondike Mountain Formation
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Trochodendrales
Family: Trochodendraceae
Genus: Tetracentron
Species:
†T. hopkinsii
Binomial name
†Tetracentron hopkinsii
Pigg et al, 2007

Tetracentron hopkinsii is an

Pentacentron sternhartae
.

Distribution and paleoenvironment

Tetracentron hopkinsii was initially described from two leaves, both recovered from the Early Eocene,

Acer species, Rosaceae species, Tsukada davidiifolia, and Ulmus okanaganensis are also present.[4]

The Allenby Formation preserves an upland temperate flora which was first interpreted as being distinctly

lacustrine shale as compression-impression fossils
.

Pigg et al noted in 2007 that one leaf assignable to Tetracentron had been found in the Klondike Mountain Formation of Republic, Washington, but was not complete enough to confidently attribute it to T. hopkinsii. The recovery of additional leaves deposited in the Stonerose Interpretive Center allowed Manchester et al to assign the Republic flora specimens to T. hopkinsii in 2018, expanding the confirmed distribution of the species.[3]

Taxonomy

Examination of the species was performed by Kathleen Pigg, Richard Dillhoff, Melanie DeVore and

patronym honoring Donald Q. Hopkins in recognition for his collecting efforts at both the One Mile Creek site and other sites in the Okanagan highlands floras.[2]

Along with the 2008 description of Tetracentron atlanticum from the Mid to Late Miocene of Iceland, Grímsson et al documented and figured Tetracentron pollen recovered from the Princeton Chert locality of the Allenby Formation.[6]

T. hopkinsii is one of between three and four trochodendraceous species that have been described from the Klondike Mountain Formation. Broadly circumscribed, three other species have been identified in the Republic flora,

Pentacentron sternhartae, and Trochodendron nastae. Additionally the species Trochodendron drachukii is known from related Kamloops group shales at the McAbee Fossil Beds near Cache Creek, British Columbia. Manchester et al 2018 noted that Tr. drachukii is likely the fruits of Tr. nastae, while Pe. sternhartae are likely the fruits of Te. hopkinsii. If fossils of the fruits and foliage in attachment are found, that would bring the species count down to three whole plant taxa.[3]

Description

The elliptical Tetracentron hopkinsii type specimen leaves have a length to width ratio of 1.3:1, being up to 9.5 cm (3.7 in) in length and up to 7.5 cm (3.0 in). The venation is

palmate with one thin midvein and two to three sets of lateral primaries which curve upwards towards the apex. The outermost set of lateral primaries are thin, branching off from the midvein at a 90° angle. Conversely the inter one to two sets of lateral primaries are thicker and arch towards the leaf apex.[2] The secondary veins which branch off the midvein are thin, and fork out from the midvein at 32°–40° angles before meeting secondaries from the lateral primaries and forming chevrons. The tertiary veins and quaternary veins are percurrent forking at 60° to 70° angles. The margin has regular teeth formed by a convex basal side and a convex apical side which may divide into a subtooth. A persistent gland is present in the tooth tip and which is supplied by a central vein and two converging lateral veins. The robust 4.3 cm (1.7 in) long petiole starts wide at its base, and gradually thins along its length before meeting the leaf in the center of the cordate leaf base.[2]

References

  1. ^
    doi:10.1139/E04-095
    .
  2. ^
    S2CID 86524324
    .
  3. ^
    S2CID 92201595
    .
  4. doi:10.1139/cjb-2012-0313
    .
  5. ^ Wolfe, J.A.; Tanai, T. (1987). "Systematics, Phylogeny, and Distribution of Acer (maples) in the Cenozoic of Western North America". Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and Mineralogy. 22 (1): 1–246.
  6. ^ Grímsson, F.; Denk, T.; Zetter, R. (2008), "Pollen, fruits, and leaves of Tetracentron (Trochodendraceae) from the Cainozoic of Iceland and western North America and their palaeobiogeographic implications", Grana, 73 (2)
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