Question

Which of the following is the oldest living fossil?
A) Architeuthis
B) Neopilina
C) Nautilus
D) Limulus

Answer 1

We know that a living fossil is an entity that has remained intact from the beginning of geological time but has lost contact with its close relatives. The fossil species must be old compared to the time of the age of the extant clade to be considered a living fossil. Living fossils are mostly of species-poor lineages, although this is not always the case.

Complete answer:
Researchers use a clock to calculate the date a rock or fossil was created in order to determine its age. Radiometric dating techniques, which are dependent on the normal radioactive decay of some elements including potassium and carbon, are widely used by geologists to date ancient occurrences. There are unique features for fossils that belong to a certain period of time.

Now let us check the options one by one:
A) Architeuthis - It is a giant squid that belongs to the Architeuthidae family of deep-ocean squids. It can rise to enormous proportions, serving as an indicator of deep-sea gigantism: recent figures place the maximum size at about 12–13 m for females and 10 m for males, measured from the back fins to the tips of the two long tentacles.
B) Neopilina-The oldest living fossil is Neoplina. It has a single dome-shaped shell that is a limpet shell remnant. Related shells, known as limpets or chitons prior to their discovery, we’re also known. Neoplina is the representative of a new genus Monoplacophora because it had serially arranged muscle scars on the inner surface of its shell.
C) Nautilus - The nautilus is a pelagic marine mollusc belonging to the Nautilidae family of cephalopods. The nautilus is the only living member of the Nautilaceae superfamily and its smaller yet almost identical suborder, Nautilina. It consists of six living species divided into two genera, the most common of which is the Nautilus genus.
D) Limulus- The Atlantic horseshoe crab, also known as the American horseshoe crab, is a chelicerate arthropod that lives in the sea and in brackish waters. Horseshoe crabs are more closely associated with spiders, ticks, and scorpions than to crabs, despite their name.

Hence, the correct answer is option ‘B’ 'Neopilina', so “The oldest living fossil is neophilia”.

Note: Remember the unique features of each fossil which will help in getting the correct answers. If a specimen is over 10,000 years old, it is generally called a fossil. Each living fossil belongs to different families that helps in differentiating. The oldest fossils range in age from 3.48 billion to 4.1 billion years.