The Great Auk was a flightless seabird that stood about 75-85 cm (30-33 in) tall and weighed 5 kg (11 lb), making it the largest member of the alcid family. This penguin-like bird inhabited the North Atlantic coasts and islands until its extinction in the mid-19th century.

Often called the "original penguin" (the word penguin was first used for this bird), the Great Auk was a powerful swimmer that fed on fish and crustaceans. It nested in dense colonies on isolated rocky islands, where its inability to fly made it vulnerable to human exploitation.

The last known pair was killed on Eldey Island, Iceland, in 1844, while incubating an egg that was later crushed. The Great Auk's extinction marked one of the first clear cases of humans driving a species to extinction through overharvesting.

The Great Auk had several distinctive features:

• Size: 75-85 cm (30-33 in) tall, weighing about 5 kg (11 lb)
• Coloration: Black back and head, white belly
• Wings: Small and flipper-like, about 15 cm (6 in) long
• Bill: Large and hooked with white grooves
• Legs: Set far back for efficient swimming

In summer, adults developed a white patch over each eye and the beak developed more pronounced grooves. Their dense plumage and thick fat layer provided insulation in cold northern waters.

The Giant Orthocone was a massive straight-shelled cephalopod that dominated Ordovician seas 470-440 million years ago. Reaching lengths of 6-10 meters (20-33 feet), it was the largest known animal of its time and Earth's first apex predator.

These ancient mollusks were related to modern squid and nautiluses but lived in long, conical shells. They hunted by jet propulsion, filling their shell chambers with water then forcefully expelling it. Fossil evidence suggests they preyed on trilobites, early fish, and other marine invertebrates.

Orthocones went extinct during the Late Ordovician mass extinction event, but their evolutionary legacy continues in modern cephalopods. Their fossilized shells are prized by collectors for their impressive size and geometric beauty.

The Giant Orthocone had remarkable features:

• Size: 6-10 m (20-33 ft) long - largest Paleozoic predator
• Shell: Straight conical structure with buoyancy chambers
• Movement: Jet propulsion via hyponome (funnel)
• Tentacles: Multiple grasping arms near the mouth
• Eyes: Large and sophisticated for the time

Their shells grew in segments, with the animal living in the newest chamber. The siphuncle (a tube running through the chambers) allowed them to control buoyancy by adjusting gas and fluid levels.

Notable orthocone fossils include:

• Trenton Limestone: Exceptional specimens from New York
• Baltic Deposits: Well-preserved European examples
• Chinese Finds: Complete chambers showing growth

While complete shells are rare, fragments up to 3 meters long have been found. The largest specimens suggest some individuals may have reached 11 meters (36 ft) in length.