Date:
April 16, 2015
Source:
Smithsonian
Summary:
Scientists synthesized
decades of scientific discoveries to illuminate the common and unique
patterns driving the extraordinary transitions that whales, dolphins,
seals and other species underwent as they moved from land to sea.
Drawing on recent breakthroughs in diverse fields such as paleontology,
molecular biology and conservation ecology, their findings offer a
comprehensive look at how life in the ocean has responded to
environmental change from the Triassic to the Anthropocene.
___________________________________________________
Modern dolphins
(pictured) and extinct marine reptiles called ichthyosaurs descended
from distinct terrestrial species, but independently converged on
an extremely similar fish-like body plan although they were separated
in time by more than 50 million years. In April 2015, a team of
Smithsonian scientists synthesized decades of scientific discoveries to
illuminate the common and unique patterns driving the extraordinary
transitions that whales, dolphins, seals and other species underwent as
they moved from land to sea, offering a comprehensive look at how life
in the ocean has responded to environmental change from the Triassic to
the Anthropocene. Credit: Courtesy of NOAA
For more
than 250 million years, four-limbed land animals known as tetrapods have
repeatedly conquered the Earth's oceans. These creatures--such as
plesiosaurs, penguins and sea turtles--descended from separate groups of
terrestrial vertebrates that convergently evolved to thrive in aquatic
environments.
In a new scientific review, a team of Smithsonian scientists
synthesized decades of scientific discoveries to illuminate the common
and unique patterns driving the extraordinary transitions that whales,
dolphins, seals and other species underwent as they moved from land to
sea. Drawing on recent breakthroughs in diverse fields such as
paleontology, molecular biology and conservation ecology, their findings
offer a comprehensive look at how life in the ocean has responded to
environmental change over time. The paper also highlights how
evolutionary history informs an understanding of the impact of human
activities on marine species today. More information is available in the
April 17 issue of Science.
Marine tetrapods represent a diverse group of living and extinct
species of mammals, reptiles, amphibians and birds that all play--or
played--a critical role as large ocean predators in marine ecosystems.
The repeated transitions between land and sea have driven innovation,
convergence and diversification against a backdrop of changing marine
ecosystems and mass extinctions dating back to the Triassic period. In
this way, they provide ideal models for testing hypotheses about the
evolution of species over long periods of time. Modern species of marine
tetrapods now face a suite of human-driven impacts to their
environment, including climate change, habitat degradation, ship
collisions and underwater noise.
"We know from the fossil record that previous times of profound
change in the oceans were important turning points in the evolutionary
history of marine species," said Neil Kelley, a Peter Buck post-doctoral
researcher in the National Museum of Natural History's department of
paleobiology and lead author in the study. "Today's oceans continue to
change, largely from human activities. This paper provides the
evolutionary context for understanding how living species of marine
predators will evolve and adapt to life in the Anthropocene."
Recent investigations in the fossil record have provided new insight
into the evolution of traits that allowed marine tetrapods to thrive in
the sea. In some cases, similar anatomy evolved among lineages that
adapted to marine lifestyles. For example, modern dolphins and extinct
marine reptiles called ichthyosaurs descended from distinct terrestrial
species, but independently converged on an extremely similar fish-like
body plan although they were separated in time by more than 50 million
years.
The repeated transformation of legs adapted for walking on land
into fins is another classic example of convergent evolution. Species
ranging from seals to mosasaurs independently developed streamlined
forelimbs as they transitioned from living on land to the ocean,
allowing them to move quickly and efficiently in the water. This
transformation may have been achieved by parallel changes at the genome
level.
"Land to sea transitions have happened dozens of times among
reptiles, mammals and birds, across major mass extinctions," said
Nicholas Pyenson, the museum's curator of fossil marine mammals. "You
often get similar looking results but convergence is more than skin
deep. It can be seen on a broad range of scales, from molecules to food
webs, over hundreds of millions of years."
In the case of deep divers such as beaked whales and seals, these
species have independently evolved to have positively charged
oxygen-binding proteins called myoglobin in their muscles, allowing them
to survive underwater for long periods of time. Scientists also have
found identical genetic sequences in different marine species, such as
whales, seals and sea cows. Whether these invisible molecular
similarities account for larger-scale visible patterns of convergent
evolution, or whether convergent anatomy follows different genetic
pathways in different groups, remains an important open question to be
tackled as genomic sequences become available for more species.
Not all adaptations observed in marine tetrapods can be attributed to
convergent evolution. For instance, as baleen whales evolved to live
underwater, they developed a unique filter-feeding system that depends
on hair-like plates instead of teeth. In contrast, toothed whales
evolved to catch and feed on prey by emitting calls and using
echolocation, a kind of sonar, to process the echoes from these noises
and detect objects in the sea.
Kelley and Pyenson synthesized research from existing studies and
referenced the Smithsonian's paleobiology collections during the course
of their research. They intend that this comprehensive review will
encourage future collaboration between researchers across scientific
fields and lead to new insights about evolutionary biology, paleontology
and marine conservation.
Story Source:
The above story is based on
materials provided by
Smithsonian.
Note: Materials may be edited for content and length.
Journal Reference:
- Neil P. Kelley, Nicholas D. Pyenson. Evolutionary innovation and ecology in marine tetrapods from the Triassic to the Anthropocene. Science, 2015 DOI: 10.1126/science.aaa3716
Smithsonian.
"Repeated marine predator evolution tracks changes in ancient and
Anthropocene oceans." ScienceDaily. ScienceDaily, 16 April 2015.
<
www.sciencedaily.com/releases/2015/04/150416145547.htm>.
