Earth history and evolution
In classical mythology, the cypress tree is associated with death, the underworld and eternity. Indeed, the family to which cypresses belong, is an ancient lineage of conifers, and a new study of their evolution affords a unique insight into a turbulent era in Earth's history. During the geological era known as the Mesozoic, the continental crust was concentrated in a single huge landmass, the supercontinent Pangea. Pangea began to break up about 150 million years ago, and the fragments drifted apart, eventually giving rise to the disposition of continents we know today. The progressive break-up of such a large landmass meant that existing groups of plant and animal species were split apart, and the descendant lineages then evolved in isolation from each other.
Dating divergence with the molecular clock
"Fossils show that the cypress family is a very ancient group of plants," says LMU biologist Professor Susanne Renner, who is also Director of the Munich Botanic Garden. "We therefore suspected that it might be possible to follow their evolutionary history back to the period before the break-up of Pangea, as long as the many episodes of climate change and associated extinctions had not obscured things too much." Renner and her research group therefore set out to reconstruct the cypress family tree, based on the comparison of specific gene sequences from 122 species belonging to 32 genera reflecting the family's worldwide distribution. In order to date divergence events, they applied the concept of the molecular clock.
The idea is based on a simple principle. When two lineages diverge from a common ancestor, each accumulates genetic substitutions independent from the other. To a first approximation, the number of unique substitutions provides a measure of the time that has elapsed since a species diverged from its sister species. By comparing the spectra of genetic changes found in different lineages and calibrating the amount of change with fossils, one can therefore reconstruct a group's history.
Evolutionary dead ends
"Over the past 15 years, these molecular methods, in combination with new fossil finds, have revolutionized the study of biogeography, the branch of biology concerned with understanding the distribution patterns of animal and plant species," says Renner. Some groups have turned out to be surprisingly young in evolutionary terms, others much older than people had assumed.
The new study confirms that cypresses represent a very old plant family. Their origins can be traced back to Pangea, and the evolutionary divergence of the northern and southern subfamilies of cypresses actually reflects the break-up of Pangea about 153 million years ago. As fragmentation progressed and ancestral lineages were separated from each other, new lineages were established and followed separate evolutionary trajectories. The Cupressaceae is the first plant family whose evolutionary history gives us such a detailed picture of the break-up of a supercontinent.
- A new evolutionary history of primatesThu, 17 Mar 2011, 18:04:55 EDT
- Oxygen-free early oceans likely delayed rise of life on planetMon, 10 Jan 2011, 16:10:36 EST
- Martian history: Finding a common denominator with Earth'sTue, 20 Nov 2012, 21:03:33 EST
- Fool's gold gives scientists priceless insight into Earth's evolutionFri, 22 Jul 2011, 14:35:24 EDT
- Northern conifers youngest of the speciesThu, 4 Oct 2012, 16:05:11 EDT
- Cypress Trees Saw Rupturing of Earth's Supercontinentsfrom Live ScienceFri, 4 May 2012, 15:00:29 EDT
- Earth history and evolution: Cypress tree distribution reflects the breakup of Pangaeafrom Science DailyThu, 3 May 2012, 13:20:31 EDT
- Earth history and evolutionfrom PhysorgThu, 3 May 2012, 11:30:45 EDT
Latest Science NewsletterGet the latest and most popular science news articles of the week in your Inbox! It's free!
Check out our next project, Biology.Net
From other science news sites
Popular science news articles
- Printing artificial bone
- Artificial sweetener a potential treatment for Parkinson's disease
- Testosterone improves verbal learning and memory in postmenopausal women
- Submarine springs reveal how coral reefs respond to ocean acidification
- Jet stream changes cause climatically exceptional Greenland Ice Sheet melt
- Even with defects, graphene is strongest material in the world
- Detection of the cosmic gamma ray horizon: Measures all the light in the universe since the Big Bang
- Genetic engineering alters mosquitoes' sense of smell
- Allosaurus fed more like a falcon than a crocodile, new study finds
- 'Popcorn' particle pathways promise better lithium-ion batteries