Early spiny plants diversity in the late Eocene subtropical woodlands_of central_Tibet

1. • Xinwen Zhang
PhD student
Paleoecology Research Group,
Xishuangbanna Tropical Botanical Garden,
Chinese Academy of Sciences
• Research interest
Evolution of Grasses in Tibetan Plateau
Self Introduction

2. Rapid Eocene diversification of spiny plants in subtropical
woodlands of of central Tibet
Xinwen Zhang
2021.12
Xishuangbanna Tropical
Botanical Garden, CAS

3. Contents
1. Introduction
2. Geological Setting
3. Material and Result
4. Discussion
5. Conclusion

4. Plant functional traits
• Plant characters that impact plant
survival, growth, or reproduction;
• Have significant influence on
ecosystem processes.
The aerial roots of Ficus Sharp spines on the tree trunk
1. Introduction

5. • Sharp projections on the surface of plants;
• Specialized plant organs;
• Mainly associated with defense against
vertebrate herbivores.
1. Introduction-Spinescence
Main types of spinescence: prickle,
thorn, stipule
Triston et al., 2016; Burns et al., 2013
The density of plant
spines is related to
herbivores.

6. Triston et al., 2016
Phylogeny of woody spiny species in southern Africa
Spiny species:
Lack of fossil records
hindered our understanding
of the evolutionary history
of this functional trait.
1. Introduction-Spinescence

7. 2. Geological Setting
• Tibetan Plateau (TP)
“Third Pole”
“Roof of the world”
• Lunpola Basin
Bangong-Nujiang Suture Zone;
Core area of the TP;
A natural laboratory for
studying the evolution of life.
Locality of the Lunpola Basin, central Tibetan Plateau
Spicer et al., 2020

8. Rowley & Currie, 2006; Fang et al., 2020; Su et al., 2019
Oxygen isotope: the elevation of lunpola
basin reached 4000 m at 35 Ma
Palm fossils reveal a younger Tibetan plateau
2. Geological Setting
Age of Dayu flora: ~39 Ma

9. The fossil sites (red stars) from the middle member of the
Niubao Formation, Lunpola Basin, central Tibetan Plateau.
DY, Dayu flora; XD, Xiede flora
Fossil spines
2. Geological Setting

10. 3. Material and Result
Prickle Thorn
Morphological classification of spines

11. Fossil spines: seven morphotypes
A, B prickle; C~G thorn (Bar=1cm)
3. Material and Result
The accumulation curve of woody spiny
eudicots in Eurasia
• The rich diversity of spiny plants in
central Tibet during the late Eocene.
• Woody spiny species in Eurasia have
accumulated rapidly since the Eocene.
Phylogenetic analyses of spiny plants

12. Grass phytoliths
Herbaceous fossils
• Numerous well-preserved herbaceous fossils
were found in the same sediments.
3. Material and Result

13. 3. Material and Result
• Paleoenvironmental reconstructions:
Climate-Leaf Analysis Multivariate Program
(CLAMP)
• H = 2.6 ~ 2.7 km
The elevational changes of central Tibet in different
geological periods
Fossil leaves from the same sediments

14. 3. Material and Result
• Paleotopography (~39 Ma): a central valley
bounded by twin mountain ranges (the Gangdese
and the Qiangtang highlands to the south and
north).
• Palaeovegetation prediction:
Atmosphere-Ocean General Circulation Model
(AOGCM), HadCM3BL-M2.1aD; 0.5×0.5° resolution.

15. 3. Material and Result

16. 4. Discussion
• An early diversification of spiny plants in
the Tibetan region, ~24 million years earlier
than similar transformations took place in
Africa.
Triston et al., 2016
Spiny plants in Africa have diversified
rapidly since the Miocene
• This flora bears the richest diversity of
spiny plants known among Cenozoic
floras worldwide.

17. 4. Discussion • Central Tibet hosted an open landscape
during the late Eocene: a woodland.
African woodland
Spiny plants appear to be most abundant
in open canopy communities.
Triston et al., 2016
Woodland:
A tree-rich community with an open
canopy and grassy understory.

18. • A deep East-West trending valley existed in
what is now the central Tibetan Plateau for
more much of the Palaeogene.
• The valley bottom being at an elevation of
~1500m at 47Ma and ~2600–2700m at ~39Ma.
4. Discussion
Su et al., 2021; Spicer et al., 2020
Paleogene plate tectonics in central and southern Tibet
Central Tibet
Jianglang flora: 47Ma
H = ~1500m
Central Tibet
Dayu flora: ~39Ma
H = ~2600–2700m

19. 4. Discussion
Cenozoic Global Reference benthic foraminifer carbon and oxygen Isotope Dataset
(CENOGRID) from ocean drilling core sites spanning the past 66 million years.
Westerhold et al., 2020
• Global cooling
Global climate began its
transition from a ‘warm
house’ to a ‘cool house’
and eventually an
icehouse condition.

20. 4. Discussion
Changes of Marine and continental patterns
from the Eocene to the Oligocene
Sun er al., 2017
• Water constraints promote the emergence
of open vegetation.
The retreat of the Neotethys during Paleogene
resulted in the reduction of the amount of water
vapor that passed into the then shallowing valley,
which, together with a growing Himalaya, led to
increasingly dry Neogene environmental
conditions across the Tibet and central Asia.

21. Paleogene mammal fossil records on the
Tibetan Plateau
Deng et al., 2019
• Herbivorous mammals in Tibet became
increasingly diversified from the Paleogene
to the Neogene. This may promote the
diversification of spiny plants.
4. Discussion
Blue curve: The cumulative number of
mammalian herbivore species in central Asia

22. As predation pressure increases,
plants produce longer spines.
4. Discussion
Triston et al., 2016; Young et al., 2003
The rapid accumulation of spiny plants in
Africa since the middle Miocene closely
matched the arrival of bovids.
• Mammalian herbivores influence the length,
density, and distribution of plant spines.

23. 4. Discussion
Bakker et al., 2016; Answer et al., 2012
• Large animals have the capacity to create
open ecosystems by reducing woody
biomass.
Species-rich megaherbivore communities can
effectively reduce woody vegetation coverage
by 15%–95%.
Herbivores reduce the height of woody plants.

24. 1. The plant fossils reported here record the beginnings of vegetation opening-up
under a drying climate as the modern Tibetan Plateau began to form from the late
Eocene onwards, and the observed spinescence marks the early development of
defence mechanisms against large herbivore feeding pressure in the region.
2. In the late Eocene climate changes in central Tibet, driven by the onset of global
cooling and regional tectonism, resulted in changes in vegetation that allowed
increased access by large herbivores. This in turn led to further opening-up of the
landscape favouring further diversification of herbivorous mammals and spiny plants.
3. This string of climate/plant/animal interactions long pre-dated the middle Miocene
arrival of herbivorous mammals (especially bovids) in Africa where similarly linked
evolutionary feedback processes took place some 24 million years later.
5. Conclusion

25. Thanks!