Eagles are large birds of prey that belong to the family Accipitridae. This family is part of the order Accipitriformes, which includes most diurnal birds of prey. So eagles belong to the clade Accipitriformes.
What is a clade?
A clade is a group of organisms that includes a common ancestor and all the descendants of that ancestor. More specifically, a clade is defined by shared derived characteristics that were inherited from the common ancestor. A clade can include organisms at any taxonomic rank, such as species, genus, family, order, class, etc.
Clades are a core concept in biological classification and phylogenetics. They allow biologists to understand the evolutionary relationships between organisms. Clades are nested within each other, with increasingly broad clades containing many smaller clades. For example, the clade of eagles contains many species clades, which in turn are part of the family clade Accipitridae.
The taxonomic classification of eagles
Here is the full taxonomic classification of eagles:
- Domain: Eukarya
- Kingdom: Animalia
- Phylum: Chordata
- Class: Aves
- Order: Accipitriformes
- Family: Accipitridae
- Genus: Examples include Aquila, Haliaeetus, and many others
- Species: Examples include Bald Eagle (Haliaeetus leucocephalus), Golden Eagle (Aquila chrysaetos), etc.
So in summary, eagles belong to the family Accipitridae, which falls under the order Accipitriformes. Therefore, the clade that contains eagles is Accipitriformes.
Characteristics of the Accipitriformes clade
Members of the Accipitriformes clade share many derived characteristics, such as:
- Powerful hooked beaks for tearing flesh
- Strong legs with large talons for grasping prey
- Excellent eyesight for detecting prey from afar
- Large wingspans to aid in soaring flight while hunting
- Carnivorous diet focused on small mammals, birds, reptiles, amphibians, fish, and carrion
In addition, most Accipitriformes have excellent aerial agility and speed to swiftly pursue and capture prey. Their brains and sensory capabilities are specifically adapted for hunting.
Evolutionary history
The Accipitriformes are believed to have evolved from early Cretaceous predatory birds about 100 million years ago. They underwent an adaptive radiation relatively early in their evolution, giving rise to many lineages specialized for particular niches and prey types.
The earliest known accipitriform is Eonanatus, from the Upper Cretaceous of China about 90 million years ago. It was a medium-sized predatory bird and already showed hallmarks of modern accipitriforms like an enlarged second toe claw and tapered wings.
By the Oligocene epoch about 30 million years ago, primitive representatives of most Accipitriformes families, including Accipitridae, had appeared. Most diversification into modern groups occurred throughout the Miocene.
Overall, both the fossil record and genetic evidence indicate accipitriforms have an ancient common origin, with ongoing adaptation into specialized raptors. Eagles evolved relatively late within this lineage, emerging in the Pliocene just 5 million years ago. But they are still firmly nested within the accipitriform clade.
Other families in the Accipitriformes order
In addition to Accipitridae, there are four other families included in the Accipitriformes order:
- Pandionidae – The osprey family, represented today only by one living species, the Osprey (Pandion haliaetus). This fish-eating specialist inhabits coastlines worldwide.
- Sagittariidae – The secretarybird family, including just one living species endemic to Africa, the Secretarybird (Sagittarius serpentarius). It has long legs for terrestrial hunting of small mammals and snakes.
- Cathartidae – The New World vultures, with seven species found in the Americas. Examples are the California Condor and Andean Condor.
- Pandionidae – The osprey family, represented today only by one living species, the Osprey (Pandion haliaetus). This fish-eating specialist inhabits coastlines worldwide.
There are also several extinct Accipitriformes families known only from the fossil record, such as Horusornithidae, Palaeociconiidae, and Pelargopodidae. All accipitriform families share the common ancestor that defines membership in the order.
Comparison with other bird groups
The Accipitriformes have a distinctive morphology and ecology compared to other major groups of predatory birds. For example:
- The Falconiformes (falcons, caracaras, etc.) are more specialized for speed and agility in the air, with elongated wings and tail for fast pursuit of avian prey.
- The Strigiformes (owls) are nocturnal hunters adapted for silent flight and acute hearing to capture small mammals and other prey at night.
- The Gruiformes (cranes, rails) are more herbivorous and omnivorous, wading in wetlands to feed.
The Accipitriformes have broader abilities as predators of live prey in diverse habitats. Their wings allow for soaring but also maneuverability in dense habitats. And their talons, beaks, and senses are adapted for violently dispatching a wide range of prey.
Conclusion
In summary, eagles belong to the Accipitridae family within the Accipitriformes order. The Accipitriformes originated at least 90 million years ago and underwent adaptive radiation into many ecologically diverse forms. All members share derived traits like hooked beaks, razor-sharp talons, keen eyesight, and aerial hunting capabilities. The Accipitridae specifically evolved to hunt small to medium-sized prey in a variety of habitats worldwide. Within this family, eagles represent a relatively recent Pliocene lineage of large, powerfully-built predators skilled at hunting diverse prey.