Question

Mammals and birds are both endothermic. Which statement is true? a. They both inherited this trait from a common ancestor. b. Birds are more closely related to mammals than to reptiles. c. Endothermy arose independently in these two lineages. d. All reptiles are ectothermic.

Short answer

Option c – "Endothermy arose independently in these two lineages" – is the correct statement. Mammals and birds evolved endothermy individually in their respective lineages, rather than inheriting it from a common ancestor.

Step-by-step solution

Read and Understand Options

Begin by carefully reading each of the four provided statements regarding mammals, birds, and endothermy.

Evaluate Option a

Option a states, "They both inherited this trait from a common ancestor." While mammals and birds are both endothermic, we need to consider their evolutionary history to determine if this statement is true.

Evaluate Option b

Option b states, "Birds are more closely related to mammals than to reptiles." To evaluate the accuracy of this statement, we must examine the evolutionary relationships between these groups.

Evaluate Option c

Option c states, "Endothermy arose independently in these two lineages." This statement suggests that endothermy was not inherited from a common ancestor but evolved separately in mammals and birds.

Evaluate Option d

Option d states, "All reptiles are ectothermic." To determine the validity of this statement, we must consider whether or not all reptiles are indeed ectothermic.

Review the Evolutionary Relationships

By understanding the evolutionary tree of organisms, we can conclude that birds are more closely related to reptiles (specifically dinosaurs) than to mammals. Birds are actually considered a group within the reptiles, and they share many common characteristics (such as scales, amniotic eggs, and certain skeletal features) with other reptilian lineages. Mammals, on the other hand, are a separate group of animals with their own unique features (such as hair, mammary glands, and a unique jaw structure).

Determine the Correct Statement

Based on the evolutionary relationships between mammals, birds, and reptiles, we can conclude that option c – "Endothermy arose independently in these two lineages" – best explains the fact that both mammals and birds are endothermic, as they did not inherit this trait from a common ancestor but evolved it individually in their respective lineages.

Key concepts

Mammalian Traits

Mammals are a fascinating group of endothermic vertebrates characterized by a range of unique traits. One defining feature is the presence of mammary glands, which produce milk to nourish their young. This ensures a healthy start for the offspring. Another distinct trait is the presence of hair or fur on their bodies, which helps maintain body temperature, a crucial aspect of endothermy.
Furthermore, mammals possess a unique jaw structure and three middle ear bones that aid in efficient chewing and acute hearing. Their diverse limb structures allow them to adapt to various environments, be it terrestrial, aquatic, or aerial.
Collectively, these traits define mammals and set them apart from other groups like reptiles and birds.

Avian Evolution

The evolution of birds, or avian evolution, is an intriguing journey from their reptilian ancestors. Birds are known for their feathers, a feature that provides insulation and enables flight, although not all birds are capable of flying. The evolution of flight is thought to have been a major driver in avian evolution.
Birds also have a lightweight skeleton, with fused bones that provide the necessary strength for flight without the accompanying weight. Their respiratory system is highly efficient, allowing them to meet the high oxygen demands of flight through a unique air sac system.
Their endothermy is another fascinating aspect, as it enables them to maintain a stable body temperature, vital for survival in diverse climates. Avian evolution highlights how birds adapted from their ancestors and became a highly successful and diverse group of vertebrates.

Reptile Characteristics

Reptiles are central to discussions about evolution due to their diverse characteristics. Unlike mammals and birds, most reptiles are ectothermic, meaning they rely on external heat sources to regulate their body temperature. However, this group displays vast diversity in other characteristics.
Reptiles commonly exhibit scales, which help reduce water loss, critical for survival in arid environments. They also lay amniotic eggs, providing extra protection and a self-contained aquatic environment for the developing embryo.
Reptiles, like snakes, lizards, crocodiles, and turtles, share these fundamental traits. Yet, within the group of reptiles, birds stand out as an exception with their endothermic metabolism and adaptations for flight. Understanding reptiles' characteristics enhances our comprehension of broader evolutionary patterns among vertebrates.

Independent Evolution

The concept of independent evolution, particularly regarding endothermy, is a captivating topic in evolutionary biology. For both mammals and birds, endothermy arose independently, a phenomenon known as convergent evolution.
In mammals, endothermy allowed for increased metabolic rates, more active lifestyles, and survival in varied environments. In birds, coupled with the demands of flight, endothermy allowed for high levels of activity and adaptability.
These independent evolutionary paths demonstrate how different lineages can develop similar traits in response to comparable environmental pressures. This concept is fundamental to understanding why dissimilar groups like mammals and birds share the trait of endothermy despite their distinct ancestral backgrounds.

Evolutionary Lineage

Understanding evolutionary lineages reveals how various traits evolved over time. In evolutionary history, birds and mammals took different paths from a common ancestor, leading to their distinct groups today.
Birds evolved from theropod dinosaurs, a group within reptiles. This lineage gives them traits such as feathers and a high level of care for their young. On the other hand, mammals emerged from synapsid ancestors, developing their unique traits like hair and mammary glands.
Both lineages showcase remarkable adaptations such as endothermy, providing insights into the dynamics of evolution. These evolutionary lineages tell us that while birds and mammals share certain lifestyle traits, the paths they followed to acquire these traits were distinct, highlighting the diversity of evolution's course.