Archeoptreyx is the connecting link between Aves & Reptiles .& it is extinct....whereas others exists as living fosdils...

Living Fossils

Living fossils are organisms that have remained relatively unchanged over millions of years and can be considered ancient in terms of evolutionary history. They provide valuable insight into the evolution and adaptation of species. Among the given options, the correct answer is option 'B', Archaeopteryx.

Explanation

1. Sphenodon

Sphenodon, also known as tuatara, is a reptile native to New Zealand. It is often referred to as a living fossil because it represents an ancient lineage of reptiles that existed during the time of dinosaurs. Sphenodon is the only surviving member of the order Rhynchocephalia, which was once more diverse and widespread. It has several primitive characteristics, such as a diapsid skull, a cloaca, and a third eye on the top of its head.

2. Archaeopteryx

Archaeopteryx is an extinct bird-like dinosaur that lived about 150 million years ago during the Late Jurassic period. It is considered a transitional fossil between feathered dinosaurs and modern birds. Archaeopteryx had both reptilian and avian features, such as feathers, wings, teeth, and a bony tail. Although it is not a living organism, it is an important link in the evolutionary history of birds.

3. Peripatus

Peripatus, also known as velvet worms, are a group of small invertebrates found in tropical and subtropical regions. They are considered living fossils because they have changed very little over the past 500 million years. Peripatus have several primitive characteristics, such as a segmented body, paired legs on each segment, and the ability to produce adhesive secretions to capture prey.

4. King Crab

King crabs are decapod crustaceans that belong to the family Lithodidae. While they have been around for millions of years, they are not considered living fossils. King crabs have undergone significant evolutionary changes over time, and their morphology and behavior have adapted to their specific marine environments. They are known for their large size, spiny exoskeleton, and powerful claws.

Therefore, the correct answer is option 'B', Archaeopteryx, as it is an extinct organism rather than a living fossil.