Question

Design experiment on macroevolution. Needs to have a species that splits into two, or a species that changes into another species over a given time

Include 3 parts:

1. Experimental design.
2. Results.
3. Conclusions

Answer 1

experiment on macroevolution

The term "macroevolution" refers to a change of an evolutionary nature in a species. A species that splits into two, or a species that changes into another species over a given time are examples of macroevolution. These changes can be a result of species selection, independent evolution (also called vicariance), historical constraints or developmental constraints.

Species selected for macroevolution experiment :- Dimetrodon ( which comes under the classification: Pelycosauria ,Dimetrodon is a large quadrupedal animal with a sprawling posture like a modern crocodile, but unlike a modern crocodile, had a tall, narrow skull with huge canine teeth and a single opening on each side behind the eyes that marked it as a mammal-like reptile. Its most conspicuous feature is a tall ‘sail’ projecting from its back. The sail was composed of skin supported internally by greatly elongated bony spines growing from the tops of the vertebrae. )


Experimental design.

The experiment which consists of several process such as

1. species selection
2. independent evolution (also called vicariance)
3. historical constraints or developmental constraints.
• background of the species
• testing the species
• observing, comparing and analyzing fossils.


Lets check the "evolution of Dimetrodon to mammals"

Dimetrodon was a quadrupedal, sail-backed synapsid. Most Dimetrodon species ranged in length from 1.7 to 4.6 metres (6 to 15 ft) and are estimated to have weighed between 28 and 250 kilograms (60 and 550 lb)

The evolution of dimetrodon in to mammals are happend over the few years. lets looks into how they evolve from demetrodon,what are the changes occured in demetrodon over certain period of past.

Results.

Skull

A single large opening on either side of the back of the skull links Dimetrodon with mammals and distinguishes.

The skull of Dimetrodon is tall and compressed laterally, or side-to-side. The eye sockets are positioned high and far back in the skull. Behind each eye socket is a single hole called an infratemporal fenestra.

Teeth

The size of the teeth varies greatly along the length of the jaws, lending Dimetrodon its name, which means "two measures of tooth" Dimetrodon and other closely related sphenacodontids, and help distinguish them from other early synapsids.

several Dimetrodon species started developing serrations on their teeth and increasing in size. For instance, D. limbatus had enamel serrations that helped it cut through flesh (which were similar to the serrations that can be found on Secodontosaurus). The second largest species, D. grandis, has denticle serrations similar to those of sharks and theropod dinosaurs, making its teeth even more specialized for slicing through flesh. This study demonstrates that, as Dimetrodon's prey grew larger, the various species responded by evolving into larger sizes and developing ever-sharper teeth.

Nasal cavity

On the inner surface of the nasal section of skull are ridges called nasoturbinals, which may have supported cartilage that increased the area of the olfactory epithelium, the layer of tissue that detects odors. The nasal cavity of Dimetrodon is transitional between those of early land vertebrates and mammals.

Jaw joint and ear

Dimetrodon has a ridge in the back of the jaw called the reflected lamina. The reflected lamina is found on the articular bone, which connects to the quadrate bone of the skull to form the jaw joint. In later mammal ancestors, the articular and quadrate separated from the jaw joint while the articular developed into the malleus bone of the middle ear. The reflected lamina became part of a ring called the tympanic annulus that supports the ear drum in all living mammals.

Tail

The tail of Dimetrodon makes up a large portion of its total body length and includes around 50 caudal vertebrae. Tails were missing or incomplete in the first described skeletons of Dimetrodon; the only caudal vertebrae known were the eleven closest to the hip. Since these first few caudal vertebrae narrow rapidly as they progress farther from the hip, many paleontologists in the late nineteenth and early twentieth centuries thought that Dimetrodon had a very short tail. It was not until 1927 that a largely complete tail of Dimetrodon was described.

Sail

The sail of Dimetrodon is formed by elongated neural spines projecting from the vertebrae. Each spine varies in cross-sectional shape from its base to its tip in what is known as "dimetrodont" differentiation. Near the vertebra body, the spine cross section is laterally compressed into a rectangular shape, and closer to the tip.A cross section of the spine of one specimen of Dimetrodon giganhomogenes is rectangular in shape but preserves figure-eight shaped rings close to its center, indicating that the shape of spines may change as individuals age.The microscopic anatomy of each spine varies from base to tip, indicating where it was embedded in the muscles of the back and where it was exposed as part of a sail. The lower or proximal portion of the spine has a rough surface that would have served as an anchoring point for the epaxial muscles of the back.

specimens of Dimetrodon preserve deformed areas of the neural spines that appear to be healed-over fractures. The cortical bone that grew over these breaks is highly vascularized, suggesting that soft tissue must have been present on the sail to supply the site with blood vessels. Their crookedness suggests that soft tissue may not have extended all the way to the tips of the spines, meaning that the sail's webbing may not have been as extensive as it is commonly imagined.

Skin
Dimetrodon also may have had large scutes on the underside of its tail and belly, as other synapsids did.Evidence from the varanopid Ascendonanus suggests that some early synapsids may have had squamate-like scales.However, recent studies have recovered varanopids as taxonomically closer to diapsid reptiles.


Conclusions

Changes over the parts of dimetradon under several condition they evolved into various species.as all over the result they closely related to mammals.