Sea lions are nested within the clade Pinnipedia. This carnivorous clade houses all seals, sea lions, and walruses. The earliest fossil pinnipeds were in the genus Enaliarctos, “bears of the sea.” These fossils, found in California, dated back 22.5 million years ago and are recognized as the origin for the recognized Otariidae family, or eared seals. Otariidae is further divided into 7 genera, including 5 genera of sea lions and 2 genera of fur seals. Each genus is unique in home range and physical characteristics. Sea lions are larger in size than fur seals, don’t have an underfur layer, have a different dental formula, and a wider penis bone, or baculum (Bonner, 1994).
Zalophus californianus), Galapagos sea lion (Zalophus wollebaeki), and Japanese sea lion (Zalophus japonicus). These species were previously regarded as subspecies of Zalophus californianus. Molecular research placed the common ancestor between the Galapagos sea lion and California sea lion to have lived about 2.5 million years ago (Wolf, Tautz, & Trillmich, 2004). All three species are sexually dimorphic in addition to having distinctly shaped skulls with a unique sagittal crest (Sakahira and Niimi, 2007). This feature is where the genus name “Zalophus” is derived. Translated from Greek, “za,” means an intensifying element, and “lophos,” means crest (Bonner, 1994). The two extant species have different breeding behaviors. Zalophus wollebaeki are non-migratory compared to its counterparts (Melin, Trillmich and Aurioles-Gamboa, 2017). Each species has similar pelage coloring as pups ranging from dark brown to blonde coloring (Jefferson et al., 2015). (Bonner, 1994; Jefferson, et al., 2015; Melin, et al., 2017; Sakahira and Niimi, 2007; Wolf, et al., 2004), includes three separate sea lion species that are found only in the northern Pacific Ocean: California sea lion (
In the genus Zalophus californianus) males are approximately 2.25 meters from nose to tail and can weigh up to 400 kilograms. Galapagos sea lions (Zalophus wollebaeki) are relatively smaller, weighing up to 250 kilograms. Japanese sea lions (Zalophus japonicas), through subfossil research, are thought to have weighed up to 500 kilograms and measure 2.5 meters in length (Jefferson et al,. 2015). All males have a robust neck, chest, and shoulders, tapering to an abdomen and hind limbs that are smaller in circumference. Males have a distinct sagittal crest on top of their skull. This bony crest starts developing around the age of five and can reach up to 4 cm in California sea lions. Until the sagittal crest begins forming, it is hard to distinguish juvenile males from females. Japanese sea lions had larger skulls with larger crests. Archeological research notes that the smallest adult male Japanese sea lion skull measured up in size to the largest California sea lion skull. Galapagos sea lion skulls are 10% shorter, narrower, and have a sagittal crest that is roughly 20 to 25% shorter (Jefferson et al,. 2015). Galapagos sea lion males have thicker and larger canine teeth relative to the females. Japanese sea lions had 6 instead of 5 upper post-canine teeth (Bonner, 1994). (Aurioles-Gamboa and Hernández-Camacho, 2015; Bonner, 1994; Jefferson, et al., 2015; Weise and Costa, 2007), all species are sexually dimorphic (Weise and Costa, 2007). Males are significantly larger than females; up to three to four times more massive and typically 1.2 times longer ( Aurioles-Gamboa and Hernández-Camacho, 2015). Mature California sea lion (
California sea lions females are on average 1.7 meters in length and up to 110 kilograms. Japanese sea lions are on average 1.4 meters in length but have no record of estimated weight. Mature female Galapagos sea lions are the smallest of the different species, ranging from 50 to 100 kilograms. Galapagos and California sea lion pups approximately weigh between 5 to 9 kilograms and are up to 80 cm in length. Little is known about the Japanese sea lion pups, but evidence suggests that at about 4 months of age, the pups were on average 65 cm and 9 kilograms (Jefferson et al,. 2015). The drastic difference in sizes between females and males plays an important role in their ability to hold oxygen stores, which determines diving ability. Males, who carry more muscle, are able to store a higher level of oxygen in blood and muscle, giving them the ability to dive deeper and longer (Weise and Costa, 2007). (Jefferson, et al., 2015; Weise and Costa, 2007)
Of the three pinnipedia to keep warm. Blubber can be up to four inches thick and is found only in the main body cavity of the animal. Besides insulation, blubber helps maintain a streamline body for effective swimming and dives (Bonner, 1994). (Bonner, 1994; Jefferson, et al., 2015)species, all share the same pelage coloration. Mature males have brown coats ranging from light brown to almost black and a light color variation around their muzzle. The only recorded difference in male pelage between the three species is that the Galapagos sea lions have light grey markings on their backs. In all species, female sea lions are tan to light brown in color. There is little research regarding Japanese sea lion pups, but pups of the living species are born with a dark-brown natal coat that is shed at around 6 months old. After this molt, pups obtain their juvenile coats with adult coloration (Jefferson et al,. 2015). Blubber, a layer of fatty tissue underneath the pelage, is important for all
Otariidae. Sea lions have an external ear pinna that covers their ear canal. All sea lions have a fusiform body shape equipped with two front and hind flippers. The hind flippers have five digits, each equipped with a claw at the end. The first toe, or hallux, is longer and wider than all the other toes (Jefferson et al,. 2015). Eared seals, Otariidae, are also known for their ability to rotate their hind flippers underneath their body for locomotion that resembles “walking” on land. All sea lions have vibrissae, or whiskers, on their muzzle. This sensory adaptation, which contains a powerful follicle-sinus complex, is responsible for picking up hydrodynamic trails of their prey. Hydrodynamic trails are vibrations caused by movement in the water. Compared to terrestrial animals, their vibrissae are approximately three times bigger (Gläser et al., 2011). Sea lions also have large eyes that have dichromatic color vision that aids in their ability to see above and below the water (Griebel and Schmid, 1992). (Gläser, et al., 2011; Griebel and Schmid, 1992; Jefferson, et al., 2015)species are eared seals
Mating systems are similar among all species in the Zalphus species. Males hold and defend small territories of land and shallow water. California sea lions hold these territories for up to 45 days during the breeding season. During this time males rely on fat built up from non-breeding season foraging to guard of their territory (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Females come to the rookeries, or cobblestone shorelines, to give birth to pups. Approximately 27 days after giving birth, they return to estrus (Jefferson et al., 2015). Female sea lions are social and tend to ignore territory boundaries set by males (Bonner, 1994). When females are present, males will vocalize more with boisterous roars. They also use these vocalizations, along with aggression such as biting and flipper slapping when in contact with another male. It is the females that actively seek out and end mating sessions (Bonner, 1994). Female California sea lions gather in small “milling” groups in which they roll around in substrate and mount each other and nearby males. These group disperse after a small handful of females successfully mates with a bull male (Jefferson et al., 2015). Galapagos sea lions, on the other hand, mate in the water (Trillmich, 2015). (Bonner, 1994; Jefferson, et al., 2015; Melin, et al., 2017; Trillmich, 2015)
All Otariidae, averaging 2.5 years (Villegas-Amtmann et al., 2017). Breeding and pupping season takes place during “garua,” or the cool season of mist and drizzle. When pupping, mothers follow a pattern on local Galapagos islands, starting at Fernandina in the early season and shifting towards the island of Española later on (Bonner, 1994). In both species, sexual maturity is reached around 5 years of age. Females tend to have their first pup at age 6 (Aurioles-Gamboa and Hernández-Camacho, 2015). (Aurioles-Gamboa and Hernández-Camacho, 2015; Bonner, 1994; Jeglinski, et al., 2012; Villegas-Amtmann, et al., 2017)species mate within two weeks of giving birth to a pup. California sea lions have an 11-month gestation period and give birth to a single pup in rookeries (Aurioles-Gamboa and Hernández-Camacho, 2015). Breeding and pupping season falls between early May until late July. Mothers stay in the area until August to raise their pup and breed again. Pups are initially fully dependent on their mother’s milk, but start foraging around 7 months. By implementing foraging in addition to suckling, pups can learn needed skills while being supported by milk (Jeglinski et al., 2015). Some pups continue to suckle up to 3 years of age. To be considered a juvenile, a pup molts its prenatal coat at about 5 months and replaces it with adult pelage. Galapagos sea lions, on the other hand, are recorded to be one of the longest lactating mammals within the family
Pinnipedia species, unlike cetaceans, Cetacea, have flexible necks, which increases versatility when swimming. Sea lions are able to swim up to 40 kph but average about 17 kph (Riedman, 1990). species have been observed hunting together using their swift swimming and speed to isolate prey (Bonner, 1994). Sea lions have the ability to “porpoise,” or leap out of water similar to that of a school of dolphins. This ability increases their distance traveled as there is less drag in air than water. Sea lions, Otariidae, have the ability to “walk” on land by rotating their hind flippers underneath their body (Riedman, 1990). (Bonner, 1994; Friedman and Leftwich, 2014; Riedman, 1990)species are agile when swimming to travel and catch prey. Unlike most aquatic mammals who use their tails for propulsion, sea lions use their fore flippers for forward movement. Using a flapping motion, they are able to move forward. Each flap is followed by a long glide, which is benefited by their fusiform body. To navigate and maneuver, sea lions manipulate their hind flippers (Friedman and Leftwich, 2014).
Interactions between sea lions are typically seen during breeding seasons, mother/pup interactions, and in haul out areas. During non-breeding season, Zalophus californianus is considered migratory, as they leave the nesting grounds and travel all along the western coast of North American (Aurioles-Gamboa and Hernández-Camacho, 2015). Zalophus wollebaeki are non-migratory and stay close to their haul out site (Trillmich, 2015). (Aurioles-Gamboa and Hernández-Camacho, 2015; Riedman, 1990; Trillmich, 2015)species are colonial with small to moderate-sized groupings (Riedman, 1990).
Species in the genus Otariidae and Obodenidae families, are oval in diameter and can reach up to 20 centimeters in length. The whiskers help the sea lions follow prey in the water and help sense their environment when foraging (Milne and Grant, 2014, Gläser et al., 2011). (Gläser, et al., 2011; Griebel and Schmid, 1992; Jefferson, et al., 2015; Milne and Grant, 2014; Schusterman, et al., 1972; Weise and Costa, 2007)rely heavily on vocalization and touch for communication. Vocalization comes in the form of roars, growls, and barks. Barks, which are only presented by mature males, occurs when defending territories and while the male is moving its head from side to side. When alarmed, all sea lions might present a “shriek-like” bark. Growls, an aggressive communication that is low-frequency, is used when the animal is angered or startled (Jefferson et at., 2015). Sea lions also have the ability to communicate underwater through a series of clicks. Using their ears, sea lions are able to perceive sounds within a frequency range between 250 to 64,000 hertz underwater (Schusterman, Billiet, and Nixon, 1972). Another important form of communication is through touch. Mothers and pups touch noses and rely on smell to recognize each other after being separated (Weise and Costa, 2007). Perception for sea lions is also heightened with sensitive whiskers and eyes. Their large dichromatic eyes give the animal the ability to see above and below the water. species are able to depict shades of green and blue from grey. This ability to distinguish the 3 colors is thought to be a physical adaptation based on their aquatic habitat (Griebel and Schmid, 1992). species are equipped with highly sensitive vibrissae that helps with detection of vibrations in the water. With 38 whiskers on each side of their face, the vibrissae are three times the size of terrestrial mammals and have ten times more nerve receptors. The vibrissae hair, shared by other species in the
Merluccius productus), Northern anchovies (Engraulis mordax), salmon (Oncorhynchus spp.), rockfish (Sebastes spp.), Pacific jack mackerel (Trachurus symmetricus), sardines (Sardina spp.), and flatfish (Pleuronectiformes spp.) (Bonner, 1994, Merlin, Trillmich, and Aurioles-Gamboa, 2017, Reidman, 1990). Galapagos sea lions (Zalophus wollebaeki) rely heavily on Sardines as a food source (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Japanese sea lions (Zalophus japonicus) prefer yellowtail (Seriola lalandi), but also ate sardines and squid. When foraging, common cephalopods that are caught include red octopus (Octopus rubescens) and market squid (Doryteuthis opalescens) (Bonner, 1994, Merlin, Trillmich, and Aurioles-Gamboa, 2017, Reidman, 1990). Pinnipeds are equipped with specialized cone-shaped teeth that allow for better grip on slippery prey, like fish and squid. Prey is most commonly consumed whole. In the case that the prey is too large, the animal will eat it in bite-size chunks with minimal chewing (Reidman, 1990). (Bonner, 1994; Melin, et al., 2017; Riedman, 1990)species are natural predators to a plethora of smaller marine animals. Diet is different throughout the year and can be greatly affected by El Niño events. These events, which causes a warming of oceanic waters, make a nutrient-poor zone that decreases the populations of prey for sea lions (Merlin, Trillmich, and Aurioles-Gamboa, 2017). Diets for the species includes a variety of schooling fish, cephalopods, and some small sharks. A diet of fish include Pacific hake (
Zalophus californianus) were once prey for bald eagles (Haliaeetus leucocephalus) prior to the population of eagles’ disappearing from California (Aurioles-Gamboa & Hernández-Camacho, 2015). In their marine habitat, apex predators such as the orcas (Orcinus orca), and requiem sharks prey (Carcharhinidae) on sea lions. The flexibility of the necks, which allows for quick maneuvering when swimming, can make sea lions hard prey to catch (Reidman, 1990). Humans are considered predators to all species and are responsible for the extinction of Japanese sea lions (Zalophus japonicus) due to overhunting (Jefferson et al., 2015). (Aurioles-Gamboa and Hernández-Camacho, 2015; Jefferson, et al., 2015; Riedman, 1990)species are preyed upon both on land and in the water. When hauled out, sea lions are easy prey due to slow locomotion on land. Sea lions evade terrestrial predators by hauling out on islands or near water to have easy escape routes. California sea lion pup (
Sea lions play an ecological role of being a predator, prey, and competitor to many species. They help keep prey populations in check and also provide for larger apex predators. Pinnipeds are parasite hosts. Parasites include nematodes, tapeworms, and hookworms. Between the prey/predator relationship and being a host to parasites, sea lions transfer nutrients and energy in the marine environment and keep it running smoothly (Bonner, 1994). (Bonner, 1994)
The three species in the genus Zalophus japonicus) are extinct with the last known sighting of 50 to 60 animals in 1951. Factors that greatly contributed to their extinction included capturing the animals to be sold into the circus trade and being slaughtered by soldiers and angered fisherman (Lowry, 2017). California sea lions (Zalophus californianus) are of least concern. They have a stable population of about 180,000 mature individuals and are expected to keep growing (Aurioles-Gamboa and Hernádes-Camacho, 2015). Galapagos sea lions (Zalophus wollebaeki) are endangered. There are between 9,200-10,600 mature individuals living in the wild. Population trends for this species are decreasing(Trillmich, 2015). Prior to the 20th-century, many sea lion populations were harmed from extensive predation by humans. However, protective measures are being taken to protect all populations. On the Galapagos islands, tourism is heavily monitored to reduce disturbances to wild populations. Fishing is controled by National Park authorities (Trillmich, 2015). California sea lions are protected in the United States and in Mexico through governmental laws such as the U.S. Marine Mammal Protection Act of 1972 (Aurioles-Gamboa and Hernádes-Camacho, 2015). Stranded pups are a common site as mothers abandon their young for many reasons. If found, along with any other injured marine mammal, rehabilitation centers will take them in and help them recover. Once healthy, sea lions are reintroduced back into the wild. If for any reason, due to health or physical issues, the animal is deemed unreleasable, they are taken in by a zoo/aquarium and cared for throughout the rest of their life (Corkeron, 2017). (Aurioles-Gamboa and Hernández-Camacho, 2015; Corkeron, 2017; Lowry, 2017; Trillmich, 2015)have different conservation statuses. Japanese sea lions (
The earliest fossil evidence of sea lions dates back about 22.5 million years ago from the Miocene period. This fossil, named Enaliarctos or “bear of the sea,” was a collection of two incomplete skull fragments and carnassial teeth. The teeth, which were more rounded than normal, had similar characteristics to terrestrial bear and showed evolutionary changes to aid in the aquatic environment. A complete skeleton, named Enaliarctos mealsi, is considered the oldest and most primitive pinniped specimen and shows records of evolutionary changes that contribute to modern pinnipeds. Features including a broad olecranon process suggests that the animal’s forearm muscles originated more from the humorous and greatly resembled terrestrial bears (Berta, Ray and Wyss, 1989). The complete fossil documents evolutionary change associated with aquatic movement. Three additional fossils from the Miocene period were found in Maryland and Virginia. The three fossils represent the rise of Desmatophocidae, which are now extinct, walruses Odobenidae, and sea lions and fur seals Otariidae. Galapagos sea lions, Zalophus wollebaeki, arrived in the in the Galapagos Islands in the late Pliocene/early Pleistocene time period. They utilized the East Pacific Corridor pathway to reach the Southern Hemisphere (Schramm et al., 2009). No information was found of how Japanese sea lions arrived on the coast of Japan. Modern day skeletal structures of Otariidae, which includes Zalophus, displays enlarged vertebrae and scapula to support the heavily muscled body (Bonner, 1994). (Berta, et al., 1989; Bonner, 1994; Schramm, et al., 2009)
Karyn Orth (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
makes seasonal movements between breeding and wintering grounds
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
having more than one female as a mate at one time
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
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