Question

fill in the blanks:Turtles and tortoises have an upper shell that is modified Rib cage tortoise have a heavier and more dome-shaped sheel then tortoise do this top shell is called the plastron​

Answer 1

Answer:

true is the answer

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Answer 2

Explanation:

The most obvious feature of any tortoise is the shell. This is the tortoises primary defence mechanism against would-be predators. The shell has remained almost unaltered by two hundred million years of evolution. The shell is basically an extension of the rib cage, which unlike most vertebrates is housed on the “outside” rather than inside the body.

The shell is made up of two halves, the underneath known as the plastron and the top known as the carapace. Both parts are fused together at the sides by a “bridge”.

The whole shell of the tortoise is made up of numerous small bones which are covered by separate plates of keratin called scutes. As a tortoise grows, extra layers of keratin are added underneath the existing layer, causing “growth rings”. Contrary to popular belief, a tortoise cannot be accurately aged by counting these rings. However they can tell us approximately how many spurts of growth the tortoise has had, thus we could also gauge what type of seasonal changes the tortoise has in its natural environment. Abundant vegetation means more food, which relates to more growth. Sparse vegetation due to extreme climatic conditions would mean little food, leading to little or no keratin growth.

Very old tortoises often have extremely worn scutes, giving their shells an alost completely smooth appearance.

The scutes of the carapace are split into five categories;

The Nuchal – the scute directly above the head

The Supracaudal – the scute directly above the tail

The Vertebrals – a single line of scutes which run centrally from the head to the tail

The Costals – run parallel to, and at either side of, the Vertebrals

The Marginals – flank the Costals and attach to the “bridge”

The Marginal scutes have a large influence on the overall shape of a tortoise’s shell. In some species, most noticeably Testudo Marginata, the Marginal scutes are extremely flared.

The scutes of the plastron are also separately categorised, of which there are two scutes in each category. Starting from the head moving down to the tail we have;

The Gular

The Humeral

The Pectoral

The Abdominal

The Femoral

The Anal

Some tortoises have a flexible “hinge” on their plastron which they can use for extra protection from predators by clamping the carapace and plastron firmly shut. Some females of other species have a much less flexible plastron, but nevertheless flexible enough to move slightly to aid her egg laying duties.

The skeleton of a tortoise is made up of two parts; the exoskeleton (carapace and plastron) and the endoskeleton (internal bones). The endoskeleton consists of two main groups; the appendicular skeleton (limb bones and girdles) and the axial skeleton (ribs, vertebrae and skull).