Insectivores- primitive placentals

Insectivores- primitive placentals

These are animals under the phylum Chordate and within the class
mammalian. They are called insectivores due to the fact that they are
almost entirely insect eating animals. The Order insectivore includes
groups like shrews, hedgehogs, gymnures, tenrecs, otter shrews, moles,
desmans, solenodons and golden moles.
They are characterized by the by the traits that they are:
1. Among the smallest mammals.
2. Their senses of vision and touch are poor and thus compensated
by an outstanding sense of smell and hearing.

Insectivores are quite diverse with a genera of 65 and 439 species.
This abundance could be attributed to their diet of insects. They are
considered to be the most primitive of placentals, because their
morphological characters are considered to be primitive and common to
the earliest ancestors. These morphological characters include:
1. Pent dactyl, with generalized plantigrade locomotion.
2. Small braincase and a brain with smooth cerebral hemispheres.
3. Primitive dentition.
4. They tend to be small to medium in size.

The earliest known fossil within this Order is from the cretaceous
period, it was found somewhere in North America at about 100 million
years ago. Insectivores are of little or no economic importance. The
main thing that threatens their existence is the loss of habitat. This
is of importance because they are tropical species. They are found
throughout the world except for Australia, South America and Polar
Regions. In my assignment I will then look at the major issues coming
through, these include:
1. When did insectivores evolve?
2. Why they are considered primitive.
3. What is so special about the habitats they occupy?
4. What is their conservation status?

In trying to tackle this topic I will first look at their origin and
what has made them last for as long as they have. It is assumed that the
insectivores descended from one common ancestor, this is thought so
because they are the least evolved when one looks at their prevailing
morphology. They evolved during the cretaceous period at approximately
125 million years, insectivore mammals like purgatories evolved as tree
dwelling.
Now the second part of this would be to look at their distribution. As
mentioned above they have places which they inhibit, this could be due
to the fact that particular environments are favorable to them. The
resources and climate change within these areas are within coping range.
When one compares South America with other tropical areas that the
insectivores live in there is a dramatic difference in the climate one
region is very cold while the others are somewhat of average climate.

References:
1. www.ingentaconnect.com/content/
urban/161/2003/00000068/00000004/art00005
2. www.life.umd.edu/classroom/ bsci338m/Lectures/Insectivores.html
3. www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve
4. msc.bhsu.edu/biology/bsmith/mammlec9.html

Dlamini L.N
2449510@uwc.ac.za