A juvenile male northern elephant seal hauled out on a beach near Ano Nuevo in March, at the tail end of breeding season. Photo by author.
Introduction
Elephant seals are some of the most famous and conspicuous marine mammals along the California coast. Long before I had any interest in marine mammal paleontology, I went on a field trip to Ano Nuevo State Park while I was in fourth grade (1994 or so) during breeding season. I did not appreciate at the time the fact that the middle of their breeding season is, inexplicably, in January. Nevertheless, we braved the cold foggy coast and trudged off through the park with my class. I remember seeing thousands of elephant seals, so many in fact that we couldn't even approach the shoreline - the trails were all completely overrun by the seals. On a later visit while spending a weekend at the UC-operated Elkus Ranch (ironically right on Purisima Creek, the type section of the rock unit I've spent the last twenty years studying), it was summer time so just a few adult males were hauled out during their molting season, and we managed to get to the shoreline. That was in 1996 or 1997, and I had not returned to Ano Nuevo until this week - I went with my mom, who had wanted to go her entire life but was too busy running her private law practice in the 90s to go on our field trips. We had a great time - we saw about a hundred elephant seals (it was very, very early in the breeding season) including the first two newborn pups of the season, loads of females, juvenile males, and a handful of large males. We also saw plenty of sea birds, deer, and even a bobcat! Ano Nuevo and the elephant seals are a bit of a northern California institution - but it's only one of several rookeries. Piedras Blancas near Cambria is also quite well known, but much easier to get to since it's literally 100 feet off of Highway 1, as opposed to the ~1.5 mile hike within a state park, which requires purchasing a tour during breeding season. More rookeries are out on the channel islands, and in the past fifteen years, elephant seals established a new rookery at Point Reyes in Marin County. These big, charismatic, smelly, and incredibly loud pinnipeds are well-known to Californians, and loads of work has been done on their ecology, but their evolutionary significance and fossil record is critically underappreciated at best and poorly interpreted at worst. This blog serves to clarify some of the mistakes made in the past, summarize what we know and don't know about their evolutionary history and fossil record, and what we hope to learn in the future.
Photo of the earliest arrivals to the rookery at Ano Nuevo point in December 2024, with Ano Nuevo Island in the distance. Photo by author.
What we know about modern elephant seals
Distribution and Population Size: Modern elephant seals are grouped into two different species - the northern elephant seal, Mirounga angustirostris, and the southern elephant seal, Mirounga leonina. The northern elephant (100,000 individuals) seal is restricted to the eastern North Pacific, breeding in California (Ano Nuevo State Reserve, Point Reyes, Piedras Blancas, Morro Bay, Farallon Islands, the Channel Islands, and Islas Guadalupe, Benito del Este, and Cedros along the Baja California coastline. The foraging range of this species is notably large and unique to each sex: females tend to range far out to sea and generally at latitudes lower than ~55* N (e.g. south of the Alaskan panhandle) and as far west as 180* W (e.g. as far west as Adak island in the central Aleutians). Males, on the other hand, range further north, but for some reason, mostly skirt the coast and forage within 30 km of the edge of the continental shelf (Kienle et al., 2022).
World map showing the distribution of the Northern Elephant seal, Mirounga angustirostris. From NOAA.gov.
World map showing the distribution of the Southern Elephant seal, Mirounga leonina. From Wikimedia Commons.
Southern elephant seals (~700,000 individuals) have a circum-Antarctic distribution and three subpopulations; the Atlantic subpopulation is the largest (400,000), and chiefly breeds on South Georgia Island (the island that Shackleton sailed to in the makeshift sailboats after the Endurance broke apart in the ice - 2000 km due east of Tierra del Fuego), the Falklands, and the Valdes Peninsula in Argentina; the Indian Ocean subpopulation (200,000) mostly breeds in the Kerguelen Islands (southeast of Madagascar, but much closer to Antarctica), Crozet Islands, Marion and Prince Edward Islands, and Heard Island. The smallest subpopulation (75,000) breeds on islands south of Australia, Tasmania, and New Zealand - the subantarctic islands.
Migration: Elephant seals come onshore at least twice per year. In the case of northern elephant seals, males and females arrive in December and stay through to February/March (northern winter), the males generally showing up a couple of weeks earlier than the females to stake out harem territory. Males and females return to shore in a staggered fashion for molting (see below): juveniles and females from April to June, and males later, from July to August. This is nearly identical to southern elephant seals, with the breeding season shifted two months earlier, from late September to late November - the southern spring.
Elephant seals are not only physically very sexual dimorphic, but they are also behaviorally dimorphic: females predominantly forage out at sea whereas males, despite their larger body size and almost certain greater diving ability, stick close to the coast and dive shallowly. From Kienle et al. (2022).
Diving: Female elephant seals are incredible divers and can dive down 1.7 kilometers (about 1 mile) and for over two hours - similar in dive length to sperm whales and beaked whales. They tend to dive down to about 500 meters deep, into the mesopelagic or twilight zone - specifically, the "deep scattering layer", a depth where mesopelagic fish and cephalopods rise to at night to feed on plankton that sink to a lower depth at night - to feed directly on the plankton, or to hunt the various predators of planktivores, and even those that eat those predators. Northern elephant seal males tend to dive in shallower coastal waters and scrounge for epibenthic and demersal* fishes and cephalopods, though southern males conduct more pelagic dives. Southern elephant seals have been observed diving even deeper, down to 2.4 km. I was always surprised by the shallow depth of male diving - given that greater body size permits longer dive length, I always thought that the enormous bulk of males would confer greater diving depths. If the males and females were to swap foraging strategy, how much deeper could they go?
*benthic - living in the sediment; epibenthic - living on the seafloor; demersal - living just above the seafloor but not necessarily on it.
Surprisingly - or unsurprisingly when you consider diving depth - lanternfish (Myctophidae) represent some of the largest parts of an elephant seal's diet. Photo credit: David Wrobel.
Prey: Normally when we think about pinnipeds, we naturally assume they feed mostly on fish - and visions of sea lions swallowing steelhead salmon or mackerel come to mind (there is a famous video on social media of a recreational fisherman, almost certainly in Baja, with a prized dolphin/mahi mahi that he is posing with - and while the camera is filming, a sea lion hops up onto the back of the boat and carries it off into the depths). Elephant seals, at least the females, completely bypass all of these familiar fish and head straight for deeper waters - surprisingly, the majority of fish eaten by elephant seals are myctophid fish - the lanternfish! These are Myctophiform fish (e.g. anglerfish) with bioluminescent photophores behind their gills. These fish constitute up to 65% of all biomass of deep sea fish. Otherwise, elephant seals are also voracious predators of cephalopods.
A pair of adult male elephant seals fighting on the beach at Ano Nuevo, California. This image shows only a tasteful volume of blood. Photo credit: A. Friedlander.
A closer shot of two males fighting in the surf. Photo credit: Mike L. Baird.
Breeding Behavior and Harems: Males arrive at the rookeries first, females tend to give birth once per year, and returning females give birth to their pups within two weeks of returning to the rookery. Elephant seals have coordinated estrus, and estrus* begins a few days before the pup is fully weaned. Males arrive on the rookery beaches first, a few days to about a week before the females (generally always sandy beaches; many pinniped species are, surprisingly, substrate specific, with most preferring hauling out on rocks, sand, or ice). The males pick out where they think the most females are going to come ashore, picking out territory to defend. As the males await the arrival of the females, male contenders will invade the territories and the males will fight for control. Combat is preceded by vocalizations. Relatively small or weak males are often simply chased off by the dominant male, and only males that are of similar or exceeding body size will commit to a fight. Males get to prime breeding (and fighting) age at about 8-10 years. Elephant seal combat is violent and often quite bloody, and provided you're visiting at the right time, it's not difficult to see males engaging in combat stained in blood (my childhood trips to Ano Nuevo were quite eye opening!). The males take up a distinctive posture where their hindflippers and posterior trunk are on the beach and they raise their neck and anterior trunk off the beach, including their foreflippers - they will body slam each other in the chest (a bit like frat guys) and will start to just clobber each other by striking with their open mouths; loud vocalizations are made between strikes. A thickened zone of skin forms a leathery 'chest shield' that is cracked and fissured, protecting males somewhat from strikes - though not really protecting the head or face; occasionally males will bite the other's proboscis and there are video
clips of the tips of probosces just torn to shreds (admittedly a bit
hard to watch). Defeated males will leave the territory, and successful males will have to rest for several hours after just a few minutes of exertion. Dominant males rule harems that consist of about 40 females on average but can be as many as 300; given that males generally only have about 2-3 years at their prime (9-12 years), the most successful males might sire around 500 offspring; they tend to die within a year or two of their reproductive prime (maximum age of 14). Most males will never mate - less than 30% of male M. leonina in the Falkland Islands mate, and out of those, 90% were dominant "beachmasters".
*Humans, for the uninitiated, have continuous estrus with a menstrual cycle instead - we're the odd ones out - we share this with a few other primates, bats, a shrew, and a mouse. We, and these other species, also have concealed ovulation: there are no obvious physical (e.g. color changes) or behavioral cues (e.g. vocalizations) indicating females are ovulating.
Freshly erupted permanent teeth with the highly reduced milk teeth (black arrows) of a juvenile elephant seal. From Abbott and Verstraete (2005).
Weaning and Tooth Eruption: Weaning takes approximately four weeks. Pups are born at a mass of about 40 kg and a length of about 1.2 meters (4'); they gain approximately 9 kg per day until at weaning they weigh 140-180 kg. Like nervous penguin chicks on an iceberg hesitating to dip their toes, elephant seal pups hang around on the beach for about two weeks after weaning before they slip into the ocean. Male pups become heavier at weaning, and on average, take an extra day to become weaned. The milk teeth are highly reduced (much more so than in sea lions and fur seals) and shaped a bit like tadpoles, with a spherical crown and a long, tail-like root, and tiny - only a few millimeters in length. These teeth are generally shed shortly after birth. Permanent canines erupt about ten days after birth, followed by the first molar, and then the incisors and premolars.
A rather cranky elephant seal undergoing a catastrophic molt. Image from Friends of the Elephant Seal.
An immature male elephant seal undergoing a catastrophic molt. Photographed by yours truly at the Piedras Blancas rookery near San Simeon, CA.
A closer look at that catastrophic molt. Photographed by yours truly at the Piedras Blancas rookery near San Simeon, CA.
Molting: Elephant seals undergo a catastrophic molt, where the hair and epidermis (somewhat fused at a layer called the stratum corneum) are molted in big sheets once per year, very different from the more gradual molting of hair/fur in land mammals. Like other "hair seals"*, elephant seals do not possess underfur (aka "fur" - shorter, finer hairs forming a dense insulating layer) - in other words, they only possess guard hairs. Molting and regrowth of the epidermis is faster when the skin is hotter, and so elephant seals fast during this time, getting nice and toasty in the summer sun. In northern elephant seals, this happens from about April to August, with the females first and the males second; in the southern species, it happens only about 2-3 months after, but generally at the same time in males and females so that there is a much longer time period between molting and breeding (eight months, versus only three months in northern elephant seals). The catastrophic molt mostly occurs in a few other phocids, in monk seals and at least harp seals; in otariids (fur seals and sea lions), individual hairs are shed peacemeal over a longer time period as in land mammals (think about the spring/summer when your dog or cat is blowing its coat).
*It is commonly stated that true seals, aka "hair seals" (Phocidae) don't possess underfur, but several species actually do; monk seals, and elephant seals, lack underfur, but several phocines - northern earless seals - possess underfur.
An elephant seal pup cools off by tossing beach sand onto its back. Photographed by yours truly at the Piedras Blancas rookery near San Simeon, CA.
Conservation, Near Extinction, and Genetic Bottleneck: Elephant seals have been hunted extensively for their blubber, which can be rendered down into oil. The population of Northern elephant seals may have been winnowed down to only about 20-40 individuals, and by 1884, they were so rare that they were considered extinct. In 1892, a group of nine individuals were found still living on Guadalupe Island off of Baja California by a Smithsonian Institution scientific expedition; nearly all of them were killed and the animal's skeletons (and presumably skins) were collected for the museum. Surprisingly, the population rebounded, and by the early 1920s both the government of Mexico and the United States issued laws that protected the species (the former is quite surprising as Mexico had just emerged from their decade-long revolution). The current population has rebounded to over 200,000 individuals at present and in California continues to grow at a rate of about 6% per year; for comparison, there are only about around 10,000 sea otters that have rebounded from a similarly small population (and may be at carrying capacity now), and about 250,000-300,000 California sea lions (also possibly at carrying capacity). Several of the California rookeries had never been used prior to hunting, with elephant seals showing up at Ano Nuevo in the 1950s (first pup born in 1960) and the San Simeon rookery simply didn't exist until 1990. Owing to the small population size, there is a documented genetic bottleneck for this species as the small population resorted to inbreeding. This loss of genetic diversity manifests as increased homozygosity (identical, rather than varying alleles for a particular gene), and there is some evidence that this has impacted the fitness of these seals - including affecting diving performance and decreased reproductive success in comparison to the less extremely hunted southern elephant seals. While a few rookeries of southern elephant seals were lost during the late 19th century (Tasmania, Saint Helena island, and Juan Fernandez island) and never recovered, the population has never experienced a bottleneck (though I cannot easily find an estimate of the minimum population size).
An incredible shot of an adult male southern elephant seal with scientist for scale. Photo credit: Nico Lubcker.
Body Size, Dimorphism, and Sexual Selection: Elephant seals are not only the largest of all pinnipeds, they're also the largest members of the Carnivora - living or extinct. Male elephant seals far exceed the body mass of the modern walrus Odobenus rosmarus, which attains a mass of 800-1700 kilograms (and up to a maximum of 2300 kg) - northern elephant seals are typically 1500-2500 kg, frequently exceeding 3000 kg, and the even more extremely large southern elephant seal males grow to 1500 to 3500 kg, with the largest tipping the scales at 5000 kg. Females of both species are similar in size and most frequently grow to around 350-900 kg. The rather extreme size of the males would confer a supreme advantage
for deep diving with a greater supply of oxygenated blood - yet, at
least in the northern species, the deep diving is performed only by the
females, which are considerably smaller individuals. On average, males weigh up to two to ten times the mass of females - and are some of the most extremely sexually dimorphic species, similar to species of otariids like the northern fur seal (Callorhinus ursinus). This extreme body size increase therefore is purely a result of dimorphism - itself driven by sexual selection in elephant seals. In addition to differences in body mass, male elephant seals have very large canines (absolutely and proportionally), a thickened layer of hide-like epidermis on the chest and neck (a leathery shield to absorb damage from fighting other males), and of course the distinctive proboscis (see below).
A male and female northern elephant seal, showing the sheer difference in body size. Photo credit: Phillip Colla.
Sexual dimorphism is a result of sexual selection, where one sex is rather choosy and the other sex is obligated to perform some ridiculous task or appear a certain way; frequently, the females are the choosy ones (guarding their unfertilized eggs until only the most exceptional male , and the males are the showy or violent ones. The basic idea is that the more spectacular the male's size, display structures, or behavior (whether singing or fighting or something else), it serves as a signal of how good the male's genes are and hence chances of delivering successful offspring to the female. The most absurd examples of sexual selection familiar to the reader are likely to be seen in birds like birds of paradise or peacocks where the males have to do these highly choreographed dance routines and grow spectacularly delicate and long feathers - at the risk of being more easily caught by predators in the case of male peacocks and the ungainly, rather heavy train of feathers. Most species of birds breed with the male performing some dance or song and/or growing temporary breeding plumage, and competing with other males - sometimes the males all gather in the same area and stake out small patches of territory called "leks". Elephant seals of course use a more extreme version of this, harem breeding - a form of polygyny - one male mating with multiple females. Females are so choosy that perhaps less than 2% of males will successfully mate. You can imagine that from an ancestral population, even just a slight preference among females for larger males could rapidly cause an increase in male body size. The apparent speed at which sexual dimorphism can evolve has led to an idea called runaway selection or "Fisherian runaway". A major concern in the study of sexual selection is what happens when the selection of a structure interferes with the fitness/survival of a male (e.g. interfering with natural selection itself) - and similarly, what other factors might stop sexual selection from going in an even more extreme direction. In the case of elephant seals, I expect that maximum body size of the males is probably strongly controlled by prey availability, with the richer southern ocean ecosystem permitting southern males to grow even larger than their northern relatives.
Growth of the proboscis in male southern elephant seals. From the Elephant Seal Research Group.
Species differences in the proboscis of northern elephant seals (Mirounga angustirostris, A) and southern elephant seals (Mirounga leonina, B). From Briggs and Morejohn (1976).
Proboscis and communication: Perhaps the most unusual feature of elephant seals is the strange trunk-like proboscis of males that lends the species its common name. The proboscis itself has the hemispherical "1st bump" and the trunk-like "2nd bump" - which will be informally referred to here as the dorsal knob and the trunk hereafter. There is a deep crease between the knob and trunk, and the trunk becomes much more inflated in mature males. Photogrammetric study of the proboscis indicates that it grows allometrically - becoming exaggerated during later growth. The size of the proboscis may be correlated with elevated testosterone levels, as it is retracted during times when testosterone levels decrease. The proboscis acts as a resonating chamber and significantly increases the length and volume of the 'vocal tract', with males producing sounds that are considerably lower in pitch based on the size of that volume - with deeper pitch signalling greater maturity, and likely, superior genes. The northern elephant seal has a longer proboscis than the southern species.
The skull of a male northern elephant seal, Mirounga angustirostris, on display at the Ano Nuevo visitor center. Photo by author.
Skull Anatomy and Dentition: The most distinctive feature of the skull of Mirounga is the broad prenarial shelf and cavernous narial fossa. The prenarial shelf is a bony platform below the soft tissues of the nose and proboscis resulting from the expansion of the narial fossa and the posterior migration of the nasal bones and the edge; there is a broad, shallow trough on the dorsal side of the rostrum, accommodating the rather cavernous nasal cavity. A similar prenarial shelf occurs in the middle Miocene pinniped Allodesmus, and whether or not it also possessed a proboscis has been a matter of debate.
The tiny postcanine teeth of a southern elephant seal, Mirounga leonina. Photo by author.
The canines are quite large in male elephant seals, more comparable to the proportions seen in sea lions and extinct walruses rather than other phocids - a consequence of polygyny and sexual selection. The cheek teeth of male and female elephant seals are all proportionally tiny, single rooted, and have small blunt button-like crowns that wear away rapidly during growth, and only juveniles have recognizable crowns. The crowns are quite variable, but sometimes have multiple low conical cusps.
Several differences in skull anatomy are evident between Mirounga leonina and Mirounga angustirostris; the most obvious, evident in the species names, the northern elephant seal has a narrower rostrum than the southern species, though it is a subtle difference. In M. leonina, the posteriormost tooth socket is positioned slightly further posteriorly and in-line with the infraorbital foramen rather than just anterior to it as in M. angustirostris. The posterior end of the palate, where the internal choanae are present, is wider and shallower in M. leonina than the more deeply incised margin in M. angustirostris. Briggs and Morejohn (1976) further reported some slight statistical differences in skull proportions between the two species, though none of these would necessarily be useful for phylogenetic study. These authors further find evidence of a greater degree of sexual dimorphism in M. leonina, though it's perhaps unsurprising as the males of this species get much larger in size. Teeth of Mirounga angustirostris tend to have a higher degree of teeth with bilobate tooth roots, as well as a slightly higher frequency of teeth with multiple cusps than in Mirounga leonina (Briggs and Morejohn, 1976).
One of the only elephant seal skeletal mounts in the world - northern elephant seal, Mirounga angustirostris, on display at California Academy of Sciences in 2019; the skeleton has moved somewhat in the past five years. Photo by author.
A Brief Glossary of Clade Names
Phocidae: family including all earless seals.
Phocinae: subfamily including all northern seals - harbor, harp, bearded, hooded, etc. (minus northern elephant seal).
Monachinae: subfamily including all southern seals - including the elephant seals. This subfamily includes three 'tribes':
Monachini: the monk seals proper, formerly just three species of Monachus, but the Caribbean and Hawaiian monk seals have recently been split off into their own genus, Neomonachus. An unnecessary taxonomic development, in my opinion.
Miroungini: elephant seals in the genus Mirounga and their extinct allies. Formerly included "Callophoca", but now just includes the unnamed Waipunga seal.
Lobodontini: the Antarctic seals, including the leopard seal (Hydrurga), weddell seal (Leptonychotes), ross seal (Ommatophoca), and the crabeater seal (Lobodon).
Cystophorinae: a now-disused (see below) subfamilial grouping of Mirounga and the hooded seal, Cystophora cristata.
The Cystophorinae - a Monophyletic Group of trunk-nosed Seals?
The Cystophorinae are a traditional grouping of three species: the Hooded seal, Cystophora cristata, from the Arctic, and the two species of elephant seals. This grouping is largely a pre-phylogenetic idea, and was based chiefly on the shared presence of some rather distinctive facial features - the large proboscis of Mirounga spp., and a somewhat similar but shorter proboscis in male hooded seals (also adorned with a dorsal knob and transverse crease). Hooded seals are one of the most bizarre of all modern pinnipeds: they inflate not only the dorsal fleshy knob, but also have a spectacularly expandable and elastic septum between their nasal passages which they can inflate like a bladder out of one of their nostrils - forming a fantastically disgusting blood red balloon which the ladies are apparently quite attracted to. This is the most bizarre sexually selected structure amongst pinnipeds, and quite possibly ALL marine mammals - yes, even weirder than the tusk of the narwhal or the strange tusks of beaked whales.
A male hooded seal (Cystophora cristata) with its bladder and elephant seal-like proboscis inflated. Photo from Critter Science.
Hooded seals are otherwise quite beautiful - they have black and white speckled hair in both males and females, and the juveniles have light yellowy hair on their bellies and darker gray on their back. Altogether this coloration is quite odd given their proclivity for mating on sea ice, as the adult coloration is what you would expect for a seal mating on a rocky beach - and, is surprisingly similar to the speckled coloration of harbor seals. The skulls of hooded and elephant seals are admittedly quite similar at first glance - they have a large narial cavity and a bit of a prenarial shelf like Mirounga, and simplified peg-like teeth that are mostly double rooted or bilobate. However, these generalizations are also true in the gray seal, Halichoerus grypus, to a lesser degree; indeed, gray seals have a bit of a large schnoz - though unlike hooded and elephant seals, it is 'erect' and does not droop over the edge of the snout. The eye sockets of the skull of hooded seals are similarly quite large, resulting in widely expanded zygomatic arches, like Mirounga, and the skull is overall quite wide and stout, with a wide, short palate.
The skull of the hooded seal - superficially resembling elephant seals in some regards. Photo credit: DG Huckaby.
However, the similarities end around the eye sockets. One feature in which Cystophora resembles the northern seals (Phocinae) is that the mastoid process of the squamosal bone is visible in dorsal view, whereas it is obscured in most of the southern seals, including the elephant seals. The posterior lacerate foramen - a large fissure in the basicranium just behind the tympanic bulla/petrosal - is quite large, similar to other northern phocids, whereas in Mirounga, it is proportionally small and similar to the Antarctic seals. Further, the middle ear ossicles, atlas and axis vertebrae, and throughout the fore- and hindlimbs are much more similar to other phocines than to elephant seals. Predictably, during the 1990s, molecular phylogenetic analyses of phocids strongly demonstrated that hooded seals are in fact northern species (consistent with their Arctic distribution) and have no relation to the elephant seals (King, 1966). Even the first phylogenetic analyses of pinnipeds based on morphology and fossils supported this result (Berta and Wyss, 1994; Bininda-Emonds and Russell, 1996); the only studies in recent years to find any phylogenetic support "Cystophorinae" have all been published from Irina Koretsky's working group and have relied on much smaller datasets (e.g. Koretsky and Rahmat, 2013: 48 characters); these datasets essentially need to 1) ignore molecular data altogether and 2) ignore a fair amount of morphological characters as well. More recent morphological phylogenetic analyses (e.g. Berta et al., 2015; Rule et al., 2020A, 2020B)
A northern or southern origin for elephant seals?
A southern hemisphere origin for the elephant seal was originally, albeit briefly, proposed by Davies in 1958. He suggested that elephant seals may have had a continuous distribution along the eastern Pacific margin as a single species during the Pleistocene, and then separated by warming of equatorial waters after the end of the last glaciation. This argument was based purely on biogeography and was not informed by any fossils. However, Davies (1958) accepted the Cystophorinae without question - not unusual for the time, as King (1966) was really the first to suggest the subfamily was paraphyletic. Still, Davies hypothesized a southern origin for Mirounga. When King (1966) recommended discarding the "Cystophorinae", she did not discuss the evolutionary history of elephant seals further.
Burns and Fay (1970) concluded that the skulls of elephant seals were more similar to the Antarctic seals (Lobodontini) than to the monk seals (Monachus and now, Neomonachus). Hendey (1972) later argued that given that elephant seals are so specialized, they make more sense to be allied with the anatomically diverse Lobodontini rather than monk seals - a conclusion that eventually was borne out by molecular data a couple of decades later. Hendey further pointed out the strange breeding season for the northern Elephant seal - during the northern winter and southern summer - further indicated a southern origin. Hendey reiterated the 'vicariance' hypothesis of Davies (1958), with a continuous population fragmented by Holocene equatorial warming. As for timing, they cite a personal communication from Charles Repenning, who apparently told Hendey of an early Pleistocene elephant seal record from California - leading him to propose a Pliocene arrival of elephant seals in the northern hemisphere. However, this record was omitted by Repenning and Tedford (1977), and it is unclear if Repenning had in mind the San Diego Formation 'tusks' or the skull from the much younger San Pedro Sand.
A male elephant seal vocalizing in the balmy December water of the Pacific at Ano Nuevo. Photo by author.
Briggs (1974) reported on the dental anatomy of elephant seals, and disagreed with Hendey, who apparently also concluded the simplified peg-like teeth of Mirounga were useless for interpreting their evolutionary heritage. Briggs outlined how there were some dental differences between the two species, and how the dentition shows evidence of being simplified from a monachine ancestor with double-rooted, multicuspate teeth. He concluded that the southern hemisphere origin hypothesis was at best "equivocal" - but also raised the possibility of a future analysis incorporating many different points of morphological data that could sort it out.
Yours truly holding the incredible skull of a southern elephant seal, Mirounga leonina, at the Otago Museum, back in 2013 during my Ph.D. Photo probably taken by Nic Rawlence (but possibly Felix Marx).
Briggs and Morejohn (1976) published a series of observations on the skulls of elephant seals, and identified a number of features that distinguish the two species. They did their best to synthesize what was known at the time - admittedly not very much - and came out strongly in favor of a northern hemisphere origin. They confirmed that the skulls of the northern species are narrower, rightfully earning the species name angustirostris - which, admittedly, is hard to imagine when you hold a skull of an adult male northern elephant seal - "how could this thing get any larger, or wider? It's already enormous!" was my second thought (my first thought was "oh shit this is way heavier than I expected" coinciding with a grunt). They identified a greater degree of sexual dimorphism in the skull proportions of Mirounga leonina - which is not surprising given that this is the species with greater body size dimorphism, and so the males should be expected to have even more elaborated skull features relative to the northern species. Many of the differences between the skulls of the two species - most obvious in males - are a result of foreshortening of the skull in Mirounga leonina. Further, they noted that the skulls of male M. leonina do not mature to the same extent in M. angustirostris - many of the sutures do not fully knit together and close. This parallels the lesser degree of development of the proboscis in M. leonina; it's as if despite their much larger size, many of the secondary sex characteristics do not develop as extremely as in M. angustirostris. In the dentition, Briggs and Morejohn highlighted that the cheek teeth of M. angustirostris frequently show some evidence of double-rootedness, and never in M. leonina. Further, teeth of M. angustirostris tend to have more cusps than M. leonina - and in the context of dental simplification in pinnipeds, would suggest a more plesimorphic status for the northern species. Ultimately, Briggs and Morejohn (1976) argued from dental evidence, skull differences, and greater sexual dimorphism that Mirounga angustirostris was more primitive, suggesting that Mirounga leonina is a newcomer to the Antarctic rather than the other way around - with the Pliocene San Diego Formation canines (see below) being "inseparable" from modern M. angustirostris as a central argument. They did, however, note that this hypothesis is tentative and required further fossil evidence to test. Curiously, they accepted the conclusions of Judith King that the Cystophorinae is not a real grouping, and argued that from developmental traits, the ancestors of Mirounga likely evolved from a monk seal-like (e.g. Monachus) ancestor somewhere in the tropics, as the natal coat of elephant seals is very dark, otherwise only like Monachus (also seen in the bearded seal, which is the earliest diverging species of northern seal).
The conclusions of Briggs and Morejohn were followed and left unchallenged until the 1990s. However, Muizon (1982), inferring an ancestor-descendant relationship between Callophoca and Mirounga (see below), hypothesized that Mirounga had an Atlantic origin rather than north Pacific or Antarctic origin, with Callophoca dispersing through the then-open Central American Seaway and evolving into ancestral Mirounga in the eastern Pacific. Bininda-Emonds and Russell (1996) concluded from their phylogenetic analysis that Mirounga likely had a southern hemisphere origin, largely agreeing with Hendey (1972) but ignoring Callophoca altogether.
Morphology, Molecules, and Mirounga
Prior to the development of cladistics, paleontologists frequently assessed relationships and biogeographic history from a sort of 'gestalt' perspective - mentally chalking up anatomical features and degrees of relatedness. Muizon (1982) published a landmark early study of phocid seal evolution and assembled what Ewan Fordyce later called "intuitive cladograms" - based on a mental assessment of character states rather than a computer-aided analysis. These sorts of evaluations of the data are certainly testable using more modern methods, but the lack of computer-aided analysis makes them non-repeatable. Regardless of how it was assembled, the phylogeny is remarkably, if not eerily similar to modern cladograms derived from molecular data: monk seals (Monachus) are placed at the base of the monachines, with elephant seals branching off before a grouping of Antarctic seals (Muizon has the sister taxon relationships of the Antarctic seals wrong with respect to molecular data, but I would have made the same conclusions). It was in this paper that the tribe Miroungini was named, and Muizon included within it Callophoca along with Mirounga (see below).
An early morphological cladistic analysis of phocids by Wyss (1988), using only 39 characters, resulted in a pretty unusual evolutionary hypothesis for the family - that large-bodied monachine seals were basal to the smaller phocines. This hypothesis relied strongly on the trend of neoteny and decreased body size in the northern seals - and while the controversial phylogeny did not stand the test of time (both subfamilies have rather old origins, well back into the Miocene, corroborated by molecular phylogeny), this and a followup study did have some important thinking about the evolution of northern seals that is still accurate.
Bininda-Emonds and Russell (1996) published the first detailed cladistic analysis of true seal relationships based only on morphological data. Although the precise species-level placement of some seals differs from molecular analyses, in general the broader results echo that of molecular cladistic analyses, especially concerning the Cystophorinae. These authors found that many of the features, aside from the convergent rostral features associated with the enlarged narial fossa and proboscis, are instead broadly distributed amongst phocids and that Cystophora and Mirounga both occupy relatively basal positions in the Phocinae and Monachinae.
Numerous molecular phylogenetic analyses published in the late 1990s and 2000s confirmed that the Cystophorinae is a paraphyletic (fake) grouping, and that Mirounga is a monachine, diverging after the Monachini but basal to the Lobodontini. Fyler et al. (2005) is a prominent example, and highlighted here owing to its honorable attempt to interpret the biogeographical history of the Monachinae. Fyler et al. (2005) noted the historical assertion (but in reality unproven) of a link between Callophoca and Mirounga would support a north Atlantic to Pacific dispersal of early elephant seals through the Central American Seaway, though they noted that a simple dispersal of Mirounga from the South Pacific to the North Pacific during the Pleistocene would also be supported - one of the first molecular analyses to (gently) crack the foundation of the Briggs and Morejohn (1976) hypothesis.
Evidence of paleontological baggage: the legacy of Callophoca on interpreting elephant seal evolution rears its ugly head here yet again, leading Fyler et al. (2005) to highlight the North Atlantic rather than southern ocean as the origin of the Mirounga + lobodontin clade. From Fyler et al. (2005).
In their landmark analysis of pinniped biogeography, Demere et al. (2003) interpreted Mirounga as a southern lineage with a northern dispersal over the equator. They acknowledged problems with this hypothesis including the absence of Callophoca-like fossils from the Pisco Formation of Peru and absence of fossils of Mirounga that were older than the late Pleistocene. As you will see in the next section, Callophoca may not have anything to do with elephant seals and is likely a red herring.
Virtually all later molecular analyses continued to support placement of Mirounga within the Monachinae, diverging after Monachus but before the Lobodontini; I won't cite them all here in order to keep this "brief", but I'll note some of the findings from the more relevant studies. Fulton and Strobeck (2010) is one such example, and they conducted a molecular clock analysis, finding that the two species of Mirounga split sometime in the Pliocene or earliest Pleistocene. This is, in my opinion, far too old - as it happens, these authors used the Peruvian fossil seal Acrophoca as the fossil calibration point for the elephant seal-lobodontin clade; Acrophoca now appears to be completely basal to the elephant seals, so use of a more appropriate fossil calibration will likely provide a much, much more recent divergence (middle Pleistocene is where I'd put my money - but, more on that below). Other molecular analyses have focused on the reduction in genetic diversity in elephant seals driven by their near-extinction, with northern elephant seals losing considerable mitochondrial DNA diversity (Weber et al., 2000). While there is considerable molecular evidence of a genetic bottleneck, it doesn't seem to have had much of an effect on the actual fitness of elephant seals (Hoffman et al., 2024).
Is Callophoca/Sarcodectes from the Lee Creek Mine a Pliocene elephant seal ancestor?
One of the stubbornly persistent ideas regarding the evolution of elephant seals is that the extinct phocid seal Callophoca represents an extinct elephant seal relative. Callophoca obscura is a large seal from Pliocene rocks of the North Atlantic, having originally been reported in the 1870s by Pierre-Josephe Van Beneden, a prominent Belgian paleontologist who named the Pliocene walrus Alachtherium cretsii and a boat-load of fossil baleen whales. His work on fossil baleen whales is noteworthy, daresay infamous, for simultaneously 1) not designating holotype specimens, 2) assembling chimeric groupings of non-associated fossils to base his species on, and 3) re-naming many of these completely different names just a decade or so later. His work on fossil pinnipeds was generally more careful, however, and pinniped workers have benefited for a long time from the much more stable taxonomy of Pliocene seals and walruses from the North Atlantic. That is not to say that the taxonomy is much less confusing or much more useful; many of the type specimens have been the subject of debate over how diagnostic they are, and most of the seals are based on postcranial bones like the humerus. Callophoca obscura is one such example, and based on a somewhat damaged humerus measuring about 15 cm (about six inches) from the Pliocene strata of Antwerp, where most of the Pliocene Belgian marine mammal fossils originated. A second species named by Van Beneden, Mesotaria ambigua, is based on a much better preserved and larger ~22 cm long humerus (about one foot). These were interpreted as the female and male "morphotypes" of the same species (respectively); though both Callophoca obscura and Mesotaria ambigua were named in the same publication, Callophoca was named on an earlier page, so the 'female morph' got taxonomic priority (Koretsky and Ray, 2008). A large number of additional fossils of Callophoca obscura were reported from the Lee Creek Mine in North Carolina, originating from the lower Pliocene Yorktown Formation, and catalogued into Smithsonian collections. These include hundreds of specimens such as mandibles, isolated teeth, skull fragments, scapulae, humeri, radii, ulnae, pelves, sacra, femora, tibiae, and fibulae - all described (however briefly) by Koretsky and Ray (2008). One spectacular specimen is a partial skull including the rostrum, palate, and much of the basicranium, USNM 475486. These specimens are for the most part all isolated elements, which is a problem, given that the type material from Belgium are humeri. The Callophoca material in general seems to be the largest morph in the Yorktown Formation, so there is some rational basis for tentatively referring the largest postcranial bones from this locality all to this taxon.
Some of the fossils referred to Callophoca by Koretsky and Ray (2008) were coded into a phylogenetic analysis by Berta et al. (2015) in their reassessment of the Italian monachine Pliophoca etrusca. In this analysis, they found that the Lee Creek Mine Callophoca was a very early diverging lineage, diverging even before the true monk seals (Monachus + Neomonachus) - and not at all forming any sort of a sister taxon relationship with elephant seals.
Mandibles and teeth of Callophoca obscura. From Koretsky and Ray (2008).
However, in recent years there have been several calls made for a more conservative approach to be made using isolated postcranial bones as the foundation for type specimens of phocid seals. A number of studies took a step back from the taxonomic work by Koretsky et al. and pointed out that the anatomy of postcranial bones is not diagnostic to the species level, broadly painting a picture that the taxonomic framework for Callophoca - and most Atlantic basin phocid seals - is likely to be overly confident; e.g. precise but not accurate (Berta et al., 2015; Dewaele et al., 2018; Churchill and Uhen, 2019; Rule et al., 2024). More specifically, Koretsky and others use a working method called the "ecomorphotype hypothesis" (Koretsky, 2001) which posits that seals have a maximum of about five or six different "ecomorphotypes" in the modern fauna or extinct assemblages, and that each "ecomorphotype" has a specific suite of anatomical characters that define the mandibule, humerus, and femur, permitting suites of isolated bones to be cobbled together into species-level collections. This working method was born out of necessity, given the poor state of most of the phocid seal fossil record outside the Pacific Basin. However, it seems as though it was probably a scientific mirage as statistical analyses have failed to support the "ecomorphotype hypothesis" (Churchill and Uhen, 2019; Rule et al., 2024). Earlier, Berta et al. (2015) suggested that Callophoca obscura, and Mesotaria ambigua, were both nomina dubia. Additionally, it's possible, if not likely, that material assigned to Pliophoca by Koretsky and Ray (2008) actually includes fossils that represent the same morph as their Callophoca (Berta et al., 2015).
Comparison of the type humerus of Callophoca obscura (left), Mesotaria ambigua (right), and the more recently described Sarcodectes magnus (middle). From Rule et al. (2020A).
Dewaele et al. (2018) reevaluated the species of phocids from the Miocene and Pliocene of the North Atlantic, declaring several Miocene species from Calvert Cliffs as nomina dubia but ultimately upholding Callophoca obscura - but reidentifying all specimens that are not humeri, and therefore directly comparable with the type material - as indeterminate monachines. Critically, virtually the entire fossil record of Phocidae (excluding fossils from Peru) in general is represented by isolated bones, and as a result, most of the type specimens that species are founded upon are also isolated bones. There are also perilously few skulls.*
*The fossil record of "otarioids" - the walruses, sea lions, fur seals, and the desmatophocids - as well as the early-diverging enaliarctine pinnipeds - has a high number of partial skeletons, and complete skulls. The fossil record from California, Oregon, Baja, and Japan is very different from the Atlantic.
Rule et al. (2020A) redescribed the skull mentioned above, USNM 475486, and also reported a new specimen, USNM 534034, which is an exception to the rule when it comes to isolated bones - includes a partial skeleton
including a fragmentary skull, fragmentary vertebrae, scapula, nearly
complete humerus, partial ulna and radius, metacarpals, rib fragments,
and sternebrae. These authors named this taxon Sarcodectes magnus - meaning flesh biter, inspired by the unusually large and sharp cheek teeth - but, how could they do that if these fossils had earlier been assigned to Callophoca obscura? These authors went a step further than prior calls for more conservative treatment of phocid type specimens and flat out declared the type humerus of Callophoca obscura to be nondiagnostic. Rather than declaring it a nomen dubium, they restricted the name to this lectotype humerus - if you recall, this is the smaller 'female morph' according to Koretsky and Ray (2008), the male morph being represented by the completely preserved humerus of Mesotaria ambigua - so, what about this taxon? After all, if Callophoca obscura is truly a nomen dubium owing to incompleteness, the humerus of Mesotaria ambigua is virtually complete, and is certainly more diagnostic (diagnostic enough, however, is a different question). Rule et al. (2020A) point out that the type specimen is just an isolated humerus and propose that it is non-diagnostic, and highlight two key differences in the humerus of their new specimen with Mesotaria ambigua: 1) the Lee Creek specimen has virtually no olecranon fossa (a pit on the posterior side of the humerus for the olecranon process of the ulna to fit into with the elbow is straightened out) and 2) a slightly thickern medial entepicondyle (a bump on the elbow end of the humerus, on the medial side). These are admittedly fairly minor differences to my eye, and for all the prior comments published on the need for quantitative approaches in phocid taxonomy, none was presented here. Will Sarcodectes stand the test of time - or will it end up as Mesotaria magnus, or even synonymized with Mesotaria ambigua? Quantitative study is needed.
Phylogenetic relationships of the monachine seals, showing a distant relationship between Sarcodectes ("formerly" Callophoca) and the elephant seals. From Rule et al. (2020A).
This interesting taxonomic story is, however, a bit of an aside to the real point here. However, given that the treatment of Callophoca as an extinct Pliocene ancestor of elephant seals for fifty years (Hendey, 1972) and how it has been uncritically cited even in more recent phylogenetic and biogeographic analyses (see above), the dissection of the tortured taxonomic history of Callophoca was a relevant red herring to outline here. Ultimately, material referred to Callophoca at one time or another has been included into phylogenetic analyses by Berta et al. (2015) and Rule et al. (2020A, 2020B), who have all found the material to plot nowhere near elephant seals on a cladogram and instead, support recognition of the Callophoca-Sarcodectes morph as some sort of early diverging monachine basal to modern Monachus. This shouldn't really come as any surprise, because aside from some presumed humeral features, the skull, dentition, and mandible of the Callophoca-Sarcodectes morph have little in common with Mirounga: there's no prenarial shelf, the teeth are multicuspate and all of them are double-rooted, and the mandible is gracile and shallow. This seems to be a case of a paleontological "wag the dog" scenario.
The modern view of momachine seal evolution and biogeography, showing a southern hemisphere origin of the elephant seals. From Rule et al. (2020B).
A Pliocene elephant seal from the San Diego Formation?
One of the only northern hemisphere fossils older than the Pleistocene identified in the literature as an elephant seal is a set of canines and other teeth mentioned offhand in a 1975 review of the North Pacific phocid fossil record by Larry Barnes and Ed Mitchell. This specimen, LACM 28432 , was briefly outlined as "scraps of postcranial bones and teeth from the Pliocene rocks of the San Diego Formation...may contain material referable to Mirounga." and "Also relevant is the final identification of the Pliocene scraps, especially two large canine teeth" (Barnes and Mitchell, 1975:41). In 2012, I visited the Natural History Museum of Los Angeles and Larry Barnes showed me the specimen - "it's an older specimen!" he remarked, and happily retrieved it from the collections, impressed that I had picked up on the reference. LACM 28432 includes two relatively short upper canines with deep longitudinal grooves, and a handful of isolated but single rooted cheek teeth that were highly worn and lacked recognizable tooth crowns. One of the canines was sawn open and polished in cross-section. After examining the specimen for a few minutes, I recognized that it possessed one very obvious feature of walruses: a thick core of globular dentine. This feature is only known from odobenine walruses - the walruses with elongate upper tusks. However, the tusks are quite short and stubby - unlike most named species of odobenines. Dusignathine walruses do not have any globular dentine, so the specimen cannot be identified as Dusignathus seftoni - a species of short-tusked walrus from the San Diego Formation with similarly sized tusks (and is confirmed to lack globular dentine by CT scan). The specimen also cannot be Mirounga, as elephant seal canines have isolated globules of dentine but not a thick core of globular dentine like walruses (Ray, 1975); their canines further differ from LACM 28432 in being evenly curved, rather than having a nearly straight root with a rectangular, wide open pulp cavity and pronounced curvature present only near the gumline and crown. Rather than representing a Pliocene elephant seal, this specimen probably represents a Protodobenus-like or Ontocetus-like walrus with short tusks (Boessenecker, 2013; Boessenecker and Churchill, 2016).
This is a bit of a problem for interpreting the fossil record of elephant seals, because Barnes and Mitchell (1975) concluded, however briefly, that elephant seals probably had a northern hemisphere origin, and indicated that the biogeographic hypothesis outlined by Davies (1958) needed to be revised. Many subsequent studies took this at face value (e.g. Briggs and Morejohn, 1976), without the fossils in question ever being properly described or published. Nevertheless, just like the onslaught of molecular studies demonstrated that the "Cystophorinae" were a paraphyletic grouping, these analyses firmly placed elephant seals as monachines and with a likely southern hemisphere origin.
What I did find surprising was that such a fragmentary specimen that had been misidentified and then never actually published had such a disproportionate effect on the conclusions made by marine mammalogists for literally decades. In the future, we need to do better, and base biogeographic hypotheses on fossils that have been formally described and identified in the peer review literature, rather than relying on untested assertions passed around the "old boy's club".
The Waipunga Seal
When I arrived in New Zealand in 2012, I was supposed to be focused on eomysticetid whales but I brought with me a deep craving for studying fossil pinnipeds I inherited from my work here on the Pacific coast when I was a master's student. I was aware of a handful of specimens from New Zealand, three key ones to be specific: 1) the holotype skull of a Pleistocene sea lion, Neophoca palatina, named by British mammalogist Judith King in 1983; 2) a Pliocene or Pleistocene jaw of Ommatophoca, described by Judith King in 1973; and 3) the "Waipunga" fragments, a handful (literally) of skull fragments with associated teeth discovered in the early 20th century (no date) by railway workers. The Waipunga specimen had never been properly described. Sometime in 2012 I learned that my colleague Morgan Churchill, then still a PhD student at U. Wyoming, would be visiting New Zealand for an East Asia and Pacific Summer Institutes grant. Ahead of this visit, Ewan and I took out on loan both the Neophoca palatina holotype as well as the "Waipunga" fragments. I had seen some images of the fragments on the GNS website (GNS is Geological and Nuclear Sciences, essentially the NZ equivalent of the US Geological Survey). The teeth looked very interesting to me. Sadly, the skull had more or less been exploded to smithereens, as it was found in a block of rock and promptly smashed with a pickaxe. According to Dr. J.A. Berry, a surgeon and naturalist in Napier, NZ who studied the specimen in the early 20th century, "an argument ensued as to whether the find was really a fossil skull or not and it was shattered to pieces with a pickaxe, when a number of two-rooted teeth were exposed". Though allegedly complete originally, now only three large chunks of bone and two teeth (plus other fragments) survived, kept by Mr. Henry Hill. The specimen was given to Berry had, like Neophoca palatina, been studied by Berry in the 1930s and 1940s. When we received the specimen on loan, it also came with perhaps 40 or 50 pages of Berry's handwritten notes - written in longhand, in pencil, and indecipherable to my eyes (and Ewan's for that matter). Judith King wrote in her 1973 paper on a specimen of Ommatophoca that "To Dr. Berry goes the credit for recognising the jaw as that of Ommatophoca, but unfortunately his manuscripts are not in a state to be used as they stand..." I wonder if Dr. King had as much difficulty reading the handwritten notes as we had! Unfortunately, we were unable to extract further locality information or a collection date. Dr. Berry was a Captain in the Medical Corps during the first world war (in NZ, this is the war that folks refer to as "the war"; ANZACs fought in World War II, but the first world war is what really culturally shook and simultaneously defined modern New Zealand). Berry was appointed superintendent of Napier Hospital in 1921, and presumably the specimen was loaned to him at some point after.
The fragments of the Waipunga seal (Miroungini indet.) from the Pliocene-Pleistocene of New Zealand. From Boessenecker and Churchill (2016).
Indeed, when the specimen arrived, Morgan and I puzzled over it extensively; the cheek teeth were very simplified - the enamel was very thin, with a simple, bumbous central cusp and an accessory cusp on either side - more closely resembling an elephant seal than any other phocid seal (and was quite obviously not from a sea lion). The cheek teeth were also double rooted - unlike elephant seals, but similar to fossil and modern monk seals (in the broad sense, including the Antarctic seals). Several skull fragments were also present - though we couldn't easily make sense out of them; did we have parts of both the left and right side? There were three key fragments: one was the roof of the canine socket, and was very clearly the right half of the rostrum; a chunk of the toothrow with a single tooth at first appeared to represent the opposite side, since the teeth typically slant forwards in pinnipeds. However, if from the left side, the tooth socket just behind the preserved tooth is smaller - which is unusual; typically, the premolars get larger from front to back, rather than being larger anteriorly. Further, if placed on the right, it did seem to likely fit below the dorsal edge of the rostral fragment, albeit with an imperfect fit. A third fragment looked like it could be a fragment of the basicranium - I thought maybe a chunk of the squamosal at first. It had a small hole with a blind end, and a tubular vertical hole on one fractured end.
At some point, regrettably months after Morgan had visited, I looked at the Waipunga fragments with a fresh set of eyes and realized that the third fragment, and the second fragment, were both bits of the tooth row - and, for that matter, all from the right side. While the first fragment had the roof of the canine socket, the second fragment had part of the first premolar (P1) socket, part of the P2, the entire P3, and the fracture that separated the second and third fragments had gone right through the P4 socket - leaving just a sliver of it on each fragment. The one blind hole on the third fragment? That was the socket for the small, single rooted first molar (M1); a small spur on the back end was the base of the zygomatic arch, and a small groove was even present for the jugal bone. Everything clicked now: the angle of the cheek teeth was a false lead that had confused me at first, but it was now obvious that this seal had unusually oriented teeth. The teeth are further unusual in having three cusps and relatively simple in shape - features only seen in Mirounga amongst modern (and fossil) phocids. Further, the small M1 alveolus of the Waipunga seal indicates a much smaller molar - also shared with Mirounga. Lastly, the dorsal edge of the maxilla lacks any sort of obvious articulation with the nasal bones and is long and shallow, with a medial surface for the premaxilla, suggesting the premaxilla was completely within the narial fossa, perhaps having a prenarial shelf. This is mostly based on the fact that there is no evidence of the posterior end of the nares being any further forward than the P4 or P3, whereas the nasal bones in most modern monachines terminate around the level of the P1 or P2. The condition in the Waipunga specimen is approximately equivalent to what we see in a modern female Mirounga - though the maxilla is arguably steeper. This suggested to us that the Waipunga seal likely had a large narial fossa and prenarial shelf, like modern elephant seals (and possibly, even a proboscis). However, owing to the extremely fragmentary makes this speculative, and discovery of new specimens from New Zealand (or elsewhere) are really needed.
The age of the specimen at first was a bit challenging to pin down. All I had to go on was 1) it was collected from near the Waipunga railway station and 2) by virtue of it being found by railway workers, almost certainly came from within a few meters of the railway itself. The approximate location was quite clearly identifiable as being well within the Esk Formation - though it took a bit of effort to demonstrate this, and to find old enough maps that even showed the location of Waipunga Station. Based on the fact that the Petane Formation or Petane Group, which includes the Esk Formation (or possibly Esk Member), is no older than the local Nukumaruan stage, the maximum age for the fossil is 2.4 Ma - earliest Pleistocene. The minimum age is provided by the extinction of a species of plankton, the dextral (right-coiling) form of the foraminifer Globorotalia crassiformis near the top of the Esk Formation, giving a minimum age of 2.1 Ma.
We identified the Waipunga specimen not to the genus Mirounga - the backwards pointing teeth with double roots precludes that - but to the tribe Miroungini. Though fragmentary, this specimen represented the first tangible fossil evidence of an seal with ancestral elephant seal-like anatomy from the southern hemisphere - suggesting a southern hemisphere origin of the group rather than a northern origin. In concert with the 1) paraphyly of the "Cystophorinae", 2) the lack of any association between Callophoca/Sarcodectes and elephant seals, and 3) the reidentification of the San Diego Formation teeth as a walrus, this specimen helps erase the likelihood of a northern hemisphere origin for elephant seals - finally bringing fossil and molecular evidence back in line.
The Genuine Pleistocene Fossil Record of Mirounga
In recent years a number of genuine fossils clearly identifiable as Mirounga have emerged from Chile and the USA. The earliest of these to be reported is a partial skull of Mirounga from the early late Pleistocene Palos Verdes Sand of the Palos Verdes Peninsula in Los Angeles - one of the only Pleistocene marine mammal fossil localities along the west coast. The specimen was briefly mentioned by Miller (1971) in a large faunal list of Pleistocene mammals from the Los Angeles Basin. I've seen the specimen (briefly) and it is a large male skull, quite clearly representing Mirounga - though whether it is closer to M. angustirostris or M. leonina is a separate and unanswered question. The specimen was cited briefly in the annotated faunal list reported by Miller (1971), and it remains unpublished.
Some additional specimens were reported in conference abstracts by Meredith Rivin, from late(?) Pleistocene strata of Orange County, and are in the collections of the LACM/Cooper Center. I saw one of these in 2013, and can confirm the identification. These specimens have only been reported in a conference abstract for the 2014 Secondary Adaptations of Tetrapods meeting (Rivin, 2014).
A Medieval-aged Mirounga leonina from... Indiana?
Though not a fossil, I'd be remiss if I didn't outline one of the most bizarre tales that can be told by a fossil pinniped. Valenzuela-Toro et al. (2020) report a very odd specimen with a very odd history - a partial skull of an elephant seal from 30 feet below the ground surface, collected from near the bank of the Wabash River in Lafayette, Indiana. The specimen was collected in 1965 during the construction of a building, and consists of a right maxilla with the canine, and it did not appear to be fossilized, being rather light and fragile like archaeological bone. The identity of the specimen was uncertain, but after correspondence back and forth between several different non-pinniped specialists, it was tentatively identified as an elephant seal. Eventually, infamous marine mammal paleontologist Ed Mitchell (then still a Ph.D. student at UC Berkeley) was contacted, and he confirmed the identification and suggested that comparisons might need to be made with Mirounga leonina. At some point, the skull was molded and casted, and then a sample prepared for radiocarbon dating (14C). However, virtually the entire bone and tooth were ground up into dust for the dating, so the only record of the specimen now are the plaster casts made.
The ~1200 year old southern elephant seal (Mirounga leonina) from... Indiana. One of the most puzzling "fossil" records of any pinniped. From Valenzuela-Toro et al. (2020).
Valenzuela-Toro et al. (2020) reported this specimen formally for the first time, and identified it as Mirounga leonina based on some of the features reported by Briggs and Morejohn (1976) including the wider rostrum, and posteriormost upper tooth (M1) being located at the level of the infraorbital foramen (a large hole below the eye socket that transmits the infraorbital nerve), rather than anterior to it in Mirounga angustirostris. They also reported the results of the radiocarbon date - analyzed in 1972 or 1973 at UT Austin. They report a date of 1260 ybp (years before present), +/- 90 years; in other words, a date of about 760 AD. This pre-dates the development of the "moundbuilders" of Cahokia by over 200 years, and dates to the "late Woodland" period in the midwest. Further south, this approximates the fall of the Teotihuacano "civilization", and across the Atlantic, fits between the Battle of Tours (where Charles Martel halted the Arab invasion of Europe in 1730) and the crowning of Charlemagne in 800.
Accepting that the specimen was collected from that location, Valenzuela-Toro et al. (2020) propose that the specimen most likely represents one of two scenarios: either a southern elephant seal crossed the equator and swam way up the Mississippi River during the early Medieval period ("late Antiquity" using modern historical-archaeological terms), or it made it to the coast someplace and its bones were traded northwards into modern day Indiana. Trading has been the explanation for Holocene whale bones in Michigan. Just two centuries later, Native American trade networks brought obsidian sourced from Yellowstone in modern day Wyoming all the way to Cahokia in Illinois.
I took a read through the documentation provided by the authors substantiating the unusual locality - and there's no mention of the name of the collector or the exact location or collection date, which admittedly are problems. However, the statement that it had been collected from about 30 feet down at a construction site is awfully specific - and, made within a year of collection. So, I'm hesitant to dismiss that as an incorrectly stated locality. That's very different from some fossil records I've tossed out of analyses before because the locality was "unknown but somewhere in ___ county/province". The specimen does very much seem to have come out of a specific hole in the ground in Indiana, and short of some collector moonlighting as a construction worker who happened to have a 1200 year old elephant seal skull from an archaeological site bringing it to work and accidentally dropping it into the pit - that seems to be a bit more of a stretch than a vagrant elephant seal crossing the equator and getting buried in a river so far from home. After all, southern elephant seals have been sighted all over the northern hemisphere, and cross the equator surprisingly often. This one is truly a weird story, but any other explanations are either weirder or would require someone to have deliberately placed it there in the 1960s, a la Piltdown Man. That's not to say that deliberate or accidental 'contamination' doesn't happen; in coastal South Carolina, fossil collectors occasionally find orange-tan teeth of Paleocene species of sharks that are quite distinct from the black, shiny Miocene-Pliocene shark teeth usually found - these are Moroccan teeth, either fallen off of necklaces, or bought by the pound from tourist shops and dispersed onto Myrtle Beach for kids to find.
Future Directions
We know quite a lot about the anatomy, behavior, population dynamics, and finally the phylogenetic relationships of elephant seals - but perilously little about their evolution and fossil record. That can be remedied quite quickly by getting several known fossils published finally - including unpublished skulls from the Pleistocene of California known since the early 1970s.
Secondly, we desperately need to investigate middle and early Pleistocene rock units more closely - both here along the Pacific coast of California and Baja California, but also along the coast of South America. Even places like the Kerguelen Islands (south Indian Ocean) have produced Pliocene cetacean fossils, although underwater - perhaps there are terrace deposits on some of the larger islands in the southern ocean that might produce some fossil elephant seals (e.g. South Georgia in the South Atlantic), unless they've been completely eroded away. Any further fossils, wherever they come from, can potentially answer questions like "how far back in time does each species go?" and "were there ever any extinct species of elephant seals?" or "when did elephant seals evolve to be gigantic?" and "when did that silly trunk evolve?" Right now, these are all very basic questions we don't have any answers for, other than "a few hundred thousand years", "maybe?" and "at least a few hundred thousand years ago but possibly much earlier" in that order (which is not very satisfying).
References
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