Owner Comments:
One of the most amazing things about dinosaurs is the sheer degree of their astounding success as a group of animals. In both the Mesozoic Era and the current Cenozoic Era, dinosaurs have occupied almost every ecosystem on the planet, including those too harsh for most other forms of life, and have been able to find ecological niches in these inhospitable environments. Our next coin looks at one very famous modern dinosaur which calls Antarctica, one of the harshest ecosystems on our planet, home: The Emperor Penguin, species name Aptenodytes forsteri.
The Emperor Penguin is the largest living species of penguin, reaching up to 4 feet in height and with a weight range of 49 to 99 pounds. As for their coloration, you can see it on the coin, both for adults and babies. Emperor Penguins break two of the main rules of theropod dinosaurs; they have solid bones and males are heavier than females, but there are very good reasons for the breaking of these theropod rules among Emperor Penguins that we will come to later in this essay. Emperor Penguins also have some interesting adaptations which allow them to live in the coldest environment (sometimes -40 degrees Fahrenheit) of any known dinosaur species, both avian and non-avian. Most of the insulation is in the form of their dense feathers, which have muscles allowing the feathers to be held erect on land and flat against the bird’s body when swimming, allowing for efficient waterproofing and insulation. Emperor Penguins also have a layer of subdermal fat that can be up to 1.2 inches thick, allowing for another layer of insulation. It is this fat layer that gives penguins their characteristic and endearing waddle.
Emperor Penguins are also some of the most efficient thermoregulators in the animal kingdom and they can maintain their 102-degree Fahrenheit body temperature over a wide range of ambient temperatures without altering their metabolisms. This is one amazing and extreme example of how theropod dinosaurs are more efficient at thermoregulation than other endotherms like mammals. Emperor Penguins are also social dinosaurs, gathering in large flocks. These flocks form another defense against extreme cold as they will huddle closely together to share each other’s body heat and to protect all of the chicks.
Emperor Penguins are predators, feeding mostly on fish but they will also prey upon marine invertebrates such as krill and squid. When hunting, Emperor Penguins can make dives from between 160 to 3,000 feet deep and they can stay submerged for up to 18 minutes. The Emperor Penguin has further adaptations that allow it to deal with both extreme pressure and low oxygen levels. The solid bones give the penguin more heft when making these dives, allowing it to submerge and stay submerged. The solid skeleton of the Emperor Penguin also eliminates the possibility of mechanical barotrauma, which almost any other terrestrial vertebrate would suffer and likely die from if it dived to the depths that Emperor Penguins do when hunting.
Emperor Penguins can also reduce their heart rates to 15 to 20 beats per minute when diving and they can also shut down non-essential organs. These adaptations, along with highly efficient hemoglobin and myoglobin which can bind oxygen in extremely low concentrations, allow Emperor Penguins to keep functioning at oxygen levels that would cause unconsciousness and eventual death in almost any other animal.
Around three years of age, Emperor Penguins reach sexual maturity and begin breeding. Emperor Penguins are serially monogamous, meaning that they choose one mate per breeding season and stay faithful to that mate for that season only. They almost always choose a different mate each season. Males attract females with a courtship display which consists of them placing their heads on their chest and making their mating call for 1 or 2 seconds. Once a female shows interest, the male and female then stand face to face, with one extending its head and neck up and the other mirroring it; they both hold this posture for several minutes. Once in pairs, couples waddle around the colony together, with the female usually following the male. Once a bond is formed, the pair then bows to one another, solidifying the bond. Emperor Penguins begin the breeding process in the harsh Antarctic winter in the months of March and April.
By May or early June, the female has produced 1 egg. By this point, the female’s fat and energy reserves are almost exhausted and she returns to the sea to feed. The male then takes the egg, which is incubated by his brood pouch until the chick hatches 64 days later. Hatching can take up to three days. By the time the egg hatches, the male has not eaten for 115 days. This is the reason that it’s so important for the male to be larger than the female in this species and why they evolved this feature. Baby Emperor Penguins are semi-altricial and are born with only a thin layer of down. If the baby hatches before the mother returns, the father feeds it with crop milk like that produced by doves and flamingos. Once the female does return, she finds her mate by his distinct vocal call and takes over care of the baby so that he can return to the sea and feed. At between 45 and 50 days of age, a number of chicks form a group called a crèche, huddling together for warmth and protection while their parents depart for the sea to hunt. By early November, the chicks begin to fledge and begin feeding themselves by December or January.
The predator situation with Emperor Penguins is unusual for large theropods. Eggs, chicks and adults are preyed upon by the Southern Giant Petrel, a living nightmare of a polar dinosaur which bites holes in adult penguins and tears chunks of flesh out to feed on, leaving gaping, bloody wounds in the poor, still living penguin. Emperor Penguins are also preyed upon in more conventional ways by two mammals, which is unusual as mammals are usually not a major threat to large, predatory dinosaurs. These predators are the Leopard Seal and the Orca. If they make it to adulthood and they can avoid these predators, Emperor Penguins can live for up to 50 years.
Penguins are a fascinating modern dinosaur that have an important place in tracking the evolution of modern bird orders in the greater overall theropod family tree. As is mentioned earlier in this set, fossils are very rare in proportion to the amount of living things on the earth at any given time. It is estimated that only 1% of organisms ever fossilize and only 1% of those fossils are ever found. A long-standing debate in the study of dinosaurs is whether the huge evolutionary radiation of avians into modern orders began in the Cretaceous period or if it happened in the Paleogene, after the extinction of the other dinosaurs.
Waimanu is an extinct genus of Penguin from New Zealand that is from the early Paleocene with a temporal range between 60-58 million years ago. Waimanu shows that many of the unique adaptations found in modern penguins were present in the lineage as early as 6 million years after the Cretaceous-Paleogene Extinction. This tells us that the penguin lineage already existed as a differentiated and specialized family of theropods somewhere in the world in the Cretaceous period, and that the Penguin family was one of the theropod groups that made it across the boundary. These Cretaceous penguins were almost certainly not flightless yet as they did survive the extinction, but 6 million years is a blink of an eye in terms of evolution, so these Cretaceous penguins would have had to have exhibited many of the other distinct features of penguins to account for an animal like Waimanu so soon after the mass extinction.