Question

There is some evidence that pharyngeal slits occur in certain species of echinoderms that appear early in the fossil record. If confirmed, what do these data suggest? a. Echinoderms are chordates. b. Pharyngeal slits were present in the earliest echinoderms and lost later. c. Some lineages of echinoderms are more closely related to chordates than others. d. Pharyngeal slits should not be used as a trait in phylogenetic analysis.

Short answer

Based on the information given and evaluation of the four suggestions, the most likely outcomes are (b) Pharyngeal slits were present in the earliest echinoderms and lost later, and (c) Some lineages of echinoderms are more closely related to chordates than others due to the presence of pharyngeal slits.

Step-by-step solution

Understand the Terminologies

In order to answer this question, we must first understand the key terms involved: - Echinoderms: A group of marine animals that include starfish, sea urchins, and their relatives. They have a unique water vascular system and usually exhibit radial symmetry. - Chordates: Animals that possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some point during their development. This group includes vertebrates like humans, as well as invertebrates like tunicates and lancelets. - Pharyngeal slits: Openings in the pharynx (the part of the throat behind the mouth and nasal cavity) that allow water to exit the body without passing through the digestive system. These are a characteristic feature of chordates. - Phylogenetic analysis: A method used to understand the evolutionary relationships between different organisms based on their shared inherited traits or characteristics.

Evaluate Each Suggestion

Now let's evaluate each of the suggestions given: a. Echinoderms are chordates: Although echinoderms possess pharyngeal slits, other important chordate characteristics like the notochord, dorsal hollow nerve cord, and post-anal tail are absent in echinoderms. Thus, it cannot be concluded that echinoderms are chordates based solely on the presence of pharyngeal slits. b. Pharyngeal slits were present in the earliest echinoderms and lost later: If pharyngeal slits are found in early echinoderm fossils, it suggests that this trait was present in the common ancestor of echinoderms and was lost over time in some lineages. This is a reasonable suggestion. c. Some lineages of echinoderms are more closely related to chordates than others: The presence of pharyngeal slits in some early echinoderms species may indicate a closer evolutionary relationship between these particular species and chordates, compared to other echinoderm species without pharyngeal slits. This is also a reasonable suggestion. d. Pharyngeal slits should not be used as a trait in phylogenetic analysis: Pharyngeal slits are an important chordate characteristic, and their presence or absence in different animals can still provide valuable information for phylogenetic analysis. However, they should be considered alongside other traits to form a more accurate representation of evolutionary relationships.

Determine the Most Likely Outcome

Based on the information given and the evaluation of the four suggestions, we can conclude that suggestions (b) and (c) are the most likely outcomes. It is possible that pharyngeal slits were present in the earliest echinoderms and lost later in some lineages (b), and that some lineages of echinoderms are more closely related to chordates than other species due to the presence of pharyngeal slits (c). Using pharyngeal slits as a trait in phylogenetic analysis can still be valuable when considered along with other important traits in analyzing evolutionary relationships.

Key concepts

Echinoderms

Echinoderms are fascinating marine animals known for their unique features. They belong to the phylum Echinodermata, which includes creatures such as starfish, sea urchins, and sand dollars. One of the most distinctive traits of echinoderms is their radial symmetry, meaning their body parts are arranged around a central axis. This is different from the bilateral symmetry found in many other animal groups, where the left and right sides are mirror images.

Another crucial characteristic of echinoderms is their water vascular system. This system serves multiple functions, including movement, food and waste transportation, and respiration. Echinoderms move using tube feet, which are part of this system, allowing them to navigate their aquatic environment efficiently. Additionally, echinoderms undergo a remarkable process called regeneration, enabling them to regrow lost parts like arms or spines. This adaptation is particularly helpful in environments where they face predators or harsh conditions.

In the study of evolutionary biology, echinoderms are intriguing for their fossil record and evolutionary history. They appear early in the fossil record, giving scientists insights into the development of complex life forms in marine settings.

Chordates

Chordates are a diverse group of animals characterized by specific features present at some stage in their life cycle. The hallmark traits of chordates include a notochord, a flexible rod supporting the body; a dorsal hollow nerve cord, which eventually develops into the central nervous system in many species; pharyngeal slits; and a post-anal tail.

These features have evolved into various forms among chordates, leading to an array of species from invertebrates like tunicates and lancelets to more complex vertebrates, including mammals, birds, reptiles, amphibians, and fish. The notochord in vertebrates is often replaced by a backbone as they develop, providing structural support and enabling more complex movements.

Chordates not only include well-known animals like humans but also less familiar ones, making their study important for understanding a broad range of life forms. In phylogenetic studies, chordates are essential for piecing together how diverse animal lineages are related, showcasing the evolutionary narrative that links aquatic and terrestrial life.

Pharyngeal Slits

Pharyngeal slits are an interesting feature found in the pharynx, the part of the throat behind the mouth and nasal cavity in chordates. They are openings that were likely evolved to support feeding and respiration in aquatic environments. In fish, these slits provide a pathway for water from the mouth to exit, bypassing the digestive system, allowing efficient breathing through gills.

While invertebrate chordates may retain these structures into adulthood, in many vertebrate species, pharyngeal slits are present only during embryonic development. They later evolve into different structures, such as parts of the ear and throat in mammals, including humans. Their presence in embryos reveals important aspects of evolutionary development, showing how different species share common ancestry.

Recognizing the significance of pharyngeal slits in phylogenetic analysis can aid in understanding evolutionary relationships among species. When combined with other traits, they provide valuable information about how lineages like echinoderms and chordates might be interconnected evolutionarily. It emphasizes the complexity and shared history of life on Earth, highlighting the intricate web of evolutionary progress.