Answer:
As the animals die, they get covered in layers. The lowest being the oldest. The difference is showing us a direct link between the two fossils. This means that the longer-spined sea urchins existed before the shorter-spined sea urchins. And evolved to have shorter spines rather than long ones.
Explanation:
Answer:
Gene mutations provide new alleles, making these mutations the ultimate source of variation. A gene mutation is an alteration in the DNA nucleotide sequence, producing an alternate sequence, termed an allele. Mutations occur at random, and can be beneficial, neutral, or harmful.
Explanation:
The correct answer is an apocrine gland.
The apocrine gland is a type of exocrine glands with a specific kind of secretion by membrane budding. The apical portion of the secretory cell of the apocrine gland pinches off, enters the lumen and loses part of its cytoplasm. The example of the apocrine gland is the sweat gland.
Answer:
d.The wing-assisted incline running theory postulates that wings were initially used to maintain balance while climbing up slopes.
Explanation:
Two theories were given to explain the origin of avian flight. The top-down theory suggested that the birds' ancestors were tree dwelling species. They took help of wings to glide from tree to tree in order to avoid predator or catch prey. The bottom up theory suggested that the birds' ancestors were ground dwelling species. They took help of wings to maintain a balance and provide a lift for efficient running.
Wing-assisted incline running was a mixture of both the above theories and gave a balanced view point. According to it, birds' ancestors used wings to maintain a balance while running up inclined slopes. The wings helped them to save energy while scaling slopes and eventually a flight mechanism was also developed.
The beginning of the Cambrian Period is marked by the evolution of hard body parts such as calcium carbonate shells. ... These body parts fossilize more easily than soft tissues, and thus the fossil record becomes much more complete after their appearance.
