Dr. Marcelo Carvalho
is a researcher in the Department of Biology at the Ribeirão
Preto campus of the Universidade de São Paulo in Brazil.
He is also a Research Associate of the Department of Ichthyology
at the American Museum of Natural History. He studies the
anatomy and systematics of sharks and rays, both fossil
and recent, in order to better understand which species exist
or have existed, their characters and evolutionary relationships,
and how they have evolved over time.
Marcelo grew up in Rio de Janeiro, Brazil, surrounded by
a rich local biodiversity. He fell in love with nature at
an early age, with a particular interest in fishes. His curiosity
was encouraged by his family through numerous camping and
fishing trips. Marcelo studied biology at St. Ursula University
in Rio, concentrating on zoology, marine biology, and botany.
Brazil's wealth of biodiversity increased Marcelo's interest
in anatomy as a way of studying the historical relationships
between species and encouraged him to pursue a career in
systematics and taxonomy.
While in college, Marcelo met some fishermen from a village
near Rio, who caught mako sharks that they sold to local
markets. Marcelo accompanied them on their fishing trips.
In return for beers, the fishermen would give Marcelo the
sharks' heads. Back in the lab, Marcelo dissected the shark
heads and studied the anatomy of their skulls and muscles,
and the patterns of their nerves and veins.
At about this time, Marcelo began an internship at another
university, where he further pursued his studies of shark
anatomy, including shark systematics, or the study of the
evolutionary relationships between sharks. He also started
to focus on stingrays and electric rays at this point in
his career. In 1992, he applied for and was awarded a fellowship
by the Brazilian government that allowed him to travel to
the United States to work on a Ph.D. in the systematics of
electric rays, in AMNH's Department of Ichthyology. After
successfully completing his Ph.D. in 1999, Marcelo continued
to work at the Museum as a postdoctoral research fellow,
where he collaborated with curator Dr. John Maisey in the
Division of Paleontology. In 2001, he ended this assignment
to move into an in-house Research Associate position back
in Ichthyology, a relationship he continues
today from Brazil.
One of Marcelo's
current research interests is the systematic relationships
of freshwater stingrays, with a focus on the relationships
among different genera of stingrays: their diversity and
how the different species are related in evolutionary terms.
He received a four-year grant at the Universidade de São
establish a research laboratory and advise students. The
grant also allows him to continue research on the evolution
of rays—both fossil and living—with a particular focus on
a family of freshwater stingrays that occur only in South
American rivers. During his fellowship
in the Museum's Division of Paleontology, Marcelo
studied fossil stingrays from extinct freshwater lakes in
Wyoming and extinct coral reefs in Italy. He then started
to compare the characters of these extinct fossil species
to the characters of stingray species still alive today,
such as Potamotrygonidae.
By studying the form, or anatomy, of these animals, Marcelo
is building a picture of their evolutionary relationships.
The characters in stingrays that most often elucidate relationships
between genera are found in their skeletal anatomy, sensory
pore pattern, and muscles. A fossil provides a preserved
two-dimensional skeletal pattern that contains valuable anatomical
information. This is a difficult process because stingrays
are anatomically conservative, that is, there is not a great
deal of variation in the anatomies of different species.
When Marcelo manages to find a character that unites two
groups of stingrays, it is an important finding. For example,
in one study, Marcelo found that the cartilaginous support
for the pectoral fins of two genera of Australian stingrays
are derived, or unique. In other words, only those two stingray
genera have this particular character in common. In evolutionary
terms, they are more closely related to each other than to
any other genera.
A large part of Marcelo's work, and the topic of his dissertation,
focuses on the systematics of electric rays. There are some
fifty described species of electric rays all over the world.
However, the systematics of electric rays is in a state of
chaos, needing much work. Since working with the Museum,
Marcelo has discovered some twelve new species of electric
rays. In addition, Marcelo is producing a complete study
of the fossil rays from Monte Bolca. These
rays existed during the Eocene (52 million years ago) in
a coral reef environment in what is now northeastern Italy.
It is one of the richest localities for fossil rays in the
"Most people tend to think of elasmobranchs (sharks and
rays) as primitive animals, or a lower form of vertebrates,"
Marcelo reflects. "There is an unfortunate assumption that
these animals are not as advanced as bony fishes or more
recent animals, simply because they have existed for somewhere
between 420 million and 450 million years. The more we examine
their anatomy, however, the more we find that elasmobranchs
are actually very specialized animals. For example, the particular
calcification of their skeletal cartilage is an evolutionary
novelty, rather than a primitive or unevolved character.
Their longevity is proof of their evolutionary success."
Little is known about elasmobranchs, not only in terms of
taxonomy and biology, but also in terms of their biomedical
potential. There are only about a dozen people in the entire
world who study the taxonomy and systematics of these animals.
Marcelo refutes the common attitude toward sharks that they
are terrifying predators of the sea that should be eliminated;
instead he is a great advocate for the view that sharks and
rays are very important to humans. There remains a wealth
of information that we have yet to learn about them.