Earless seal

Earless seals, called phocids or true seals, form one of the three main groups in the seal lineage, Pinnipedia. They belong to the family Phocidae and are sometimes referred to as crawling seals to set them apart from fur seals and sea lions, which are in the family Otariidae. These seals inhabit oceans in both hemispheres and, aside from the more tropical monk seals, are largely found in polar, subpolar, and temperate regions. The Baikal seal is the only species that lives exclusively in freshwater. The earliest known fossil of an earless seal, *Noriphoca gaudini*, comes from the late Oligocene or earliest Miocene of Italy. Other early phocid fossils date to the mid-Miocene, around 15 million years ago, in the north Atlantic. For a long time, many researchers thought phocids evolved separately from otariids and odobenids, descending from otter-like animals like *Potamotherium* that lived in European freshwater lakes. However, recent evidence strongly points to a single common ancestor for all pinnipeds, possibly *Enaliarctos*, which is most closely related to mustelids and bears. It was once believed that monk seals and elephant seals first entered the Pacific through open straits between North and South America, with Antarctic true seals taking the same route or traveling down Africa’s west coast. Now, scientists think monk seals, elephant seals, and Antarctic seals all evolved in the southern hemisphere and likely spread to their current ranges from more southern latitudes. In the 1980s and 1990s, morphological phylogenetic analysis of phocids led to new ideas about how the various genera are related. More recent molecular studies have confirmed that the two phocid subfamilies, Phocinae and Monachinae, are each monophyletic. Monachinae, known as the “southern” seals, includes three tribes: Lobodontini, Miroungini, and Monachini. The four Antarctic genera—*Hydrurga*, *Leptonychotes*, *Lobodon*, and *Ommatophoca*—belong to Lobodontini. The tribe Miroungini consists of elephant seals, while monk seals (*Monachus* and *Neomonachus*) are in Monachini. The subfamily Phocinae, or “northern” seals, also has three tribes: Erignathini (containing *Erignathus*), Cystophorini (containing *Cystophora*), and Phocini (all other phocines). More recently, five species were split off from *Phoca*, creating three additional genera. Alternatively, the three monachine tribes have been treated as separate families, with elephant seals and Antarctic seals considered more closely related to the phocines. Adult phocids range in size from the ringed seal, at 1.17 meters (3.8 feet) long and 45 kilograms (99 pounds), to the southern elephant seal, the largest member of the order Carnivora, reaching 5.8 meters (19 feet) and 4,000 kilograms (8,800 pounds). Phocids have fewer teeth than land-based carnivores but still have strong canines; some species lack molars entirely. Their dental formula is 2–3.1.4.0–2 over 1–2.1.4.0–2. While otariids are known for speed and agility, phocids are built for efficient, energy-saving movement. This lets most phocids travel far from land to find food, whereas otariids depend on rich upwelling zones near breeding sites. Phocids swim by moving their bodies side to side; their front flippers mainly steer, while their hind flippers provide propulsion underwater. Their streamlined bodies make them better long-distance swimmers than otariids, but unlike fur seals, their hind flippers are attached to the pelvis and cannot rotate forward for walking. This makes them clumsy on land, forcing them to wriggle using their front flippers and abdominal muscles. Phocid respiratory and circulatory systems are adapted for deep diving, allowing them to stay underwater for long periods. When a seal dives, air is pushed from the lungs into the upper respiratory passages, where gases cannot easily enter the bloodstream, protecting the seal from decompression sickness. The middle ear is lined with blood sinuses that inflate during a dive, helping to maintain steady pressure. Phocid bodies are more specialized for aquatic life than otariids, as seen in their ear holes (instead of external ears), retractable nipples, internal testicles, and an internal penile sheath. They can also divert blood flow to a smooth layer of blubber beneath the skin to help regulate body temperature. Unlike otariids, phocine seals do not bark to communicate. Instead, they slap the water and grunt, and a few species have been observed clapping at each other underwater. One study in *Animal Behaviour* reported that seals use rhythmic percussive signaling, or clapping, in both aggressive interactions and display behavior. Monachine seals, on the other hand, are well known for vocalizing. Elephant seals often call out on land, with males roaring to establish dominance and identify themselves. Weddell and leopard seals are famous for their underwater singing. Because their front flippers are short and their rear flippers cannot rotate, true seals cannot walk on land like sea lions. Instead, they bounce forward in a motion called galumphing; polar explorer Edward Wilson described it as lolloping. It is also referred to as worm-style locomotion. Phocids spend most of their time at sea but return to land or pack ice to breed and give birth. Pregnant females forage for long periods at sea, building up fat reserves, and then return to the breeding site to use that stored energy to nurse their pups.