Prehistoric Animal Bit Like a Sabercat, Crunched Like a Bear

The skull of Kolponomos, with jaw muscles in red. From Tseng et al., 2016.
The virtual skull of Kolponomos, with jaw muscles in red. From Tseng et al., 2016.

Stroll through any museum hall well-stocked with fossil mammals and it’s tempting to look at the extinct beasts as variations on familiar themes. There’s a sloth, but bigger. There’s a camel, but smaller. I guess that weirdo in the corner looks something like a pig. We shove the remains of the extinct into expectations of the familiar even if the fit isn’t particularly good. And that’s a shame. Fossil mammals were stranger than we often give them credit for, and they often behaved in ways that no modern animal does. Just look at Kolponomos.

In the wide spread of the mammal family tree, Kolponomos was a carnivoran. That’s the group that includes cats, seals, bears, civets, and the dog snoring on the couch next to me as I write this. From there the phylogenetic haze sets in, however, with the 20 million-year-old Kolponomos fitting in somewhere around bears and their extinct relatives the bear-dogs, but not really belonging to either line. Regardless of which group can claim Kolponomos, however, what makes this beast so strange was the way it fed. This almost-bear bit like a sabertoothed cat, crunching mollusks in grizzly-like jaws studded with otterish teeth.

The idea that Kolponomos fed on shellfish has been around for a while. The mammal has been found in marine rocks from Oregon, Washington, and possibly Alaska, and the cheek teeth of these fossils show extreme wear from a diet of hard foods. In fact, Kolponomos so regularly dined on clams and mussels that the blocky crushing teeth are often “lakes” of softer dentine with the harder enamel fencing them in. Yet no one had tested this idea, nor how Kolponomos went about prying its food up from rocky shores. Now paleontologist  Jack Tseng and colleagues have finally looked Kolponomos in the mouth.

A restoration of Kolponomos by
A restoration of Kolponomos by Ken Kirkland.

From the anatomy of the shoreline mammal’s jaws, Tseng and coauthors expected that it shared a habit in common with saber-toothed cats. The front of the jaw in Kolponomos is deep and buttressed, giving it a prominent chin just like the famous sabercat Smilodon. In the cats this condition is thought to reflect an attack strategy of anchoring the head with the lower jaw and then using the leverage to drive the famous canines through their prey with a powerful contraction of neck muscles. Kolponomos was no sabertooth, but Tseng and coauthors thought that the mammal could have used the same strategy to detach mollusks from their beds.

To find out, Tseng and colleagues took a multi-pronged approach involving virtual models of Kolponomos, Smilodon, and five other carnivorans to examine bone stress during simulated bites and compare shape, adding examination of tooth wear patterns to see how the hypothesis held up. What they found was that Kolponomos fed like no mammal alive today.

Kolponomos bite sequence. Courtesy Jack Tseng.
Kolponomos bite sequence. Courtesy Jack Tseng.

Tseng and coauthors were on the mark with their Smilodon suspicion. Despite being distant relatives and feeding on entirely different prey, the lower jaws of both Kolponomos and Smilodon were extremely similar in their anatomy, shape, and response to anchor bite stress. The anchor bite was the key. More than that, the researchers found that even though the teeth of Kolponomos resemble those of sea otters the crushing portion of the extinct mammal’s jaw was actually much more like that of a bear in being stiffer but with less mechanical efficiency. Otters show the opposite condition, indicating that there’s more than one way for a carnivoran to be a shell-crusher as far as lower jaws are concerned. This makes the jaws of Kolponomos a multitool, the front strengthened for prying up shellfish and the back stiffened to crush through those defenses.

So if you were to visit coastal Washington about 20 million years ago, you might have seen something almost like a bear, but not quite like a bear, ambling along the rocky shorelines. Sniffing out a shellbed, the burly carnivore opens its jaws to jam its lower teeth into the colony of clams, biting and jerking its neck. The first shove doesn’t work, but the beast bites again and with another spasm the clam comes free with an audible pop and a little arc of spray as Kolponomos tosses its head back. There’s no hope for the bivalve now – with a swipe of its tongue the mammal shoves the snack to its cheek, and you can hear the shell give way beneath molars flattened through repetition. A quick swallow and the mammal’s snout is back in the shallows, ready to pry out another morsel as well as our preconceived notions about what fossil mammals were really like.


Tseng, Z., Grohe´, Flynn, J. 2016. A unique feeding strategy of the extinct marine mammal Kolponomos: convergence on sabretooths and sea otters. Proceedings of the Royal Society B. doi: 10.1098/rspb.2016.0044

A Crushing Bite Gives Sea Otters Their Cute Mugs

A southern sea otter off Piedras Blancas, California. Photo by Brian Switek.
A southern sea otter off Piedras Blancas, California. Photo by Brian Switek.

All otters are adorable. That’s as much of a fact as the existence of gravity. But among the 13 or so living otter species, none generate as many “Aww”s as Enhydra lutris, the sea otter. These fuzzballs are so cute, in fact, that we often overlook their bad behavior. But what is it that sets them apart? There’s the dense coat of fur and their fastidious dining habits, of course, but they also look a bit different from most other otters. Sea otters have short, round faces compared to their relatives, and that’s all because of their specialist diet. To put it bluntly, I think a crushing bite has given sea otters an edge over their cute competition.

This epiphany came after reading a new paper by Texas A&M zoologists Lori Timm-Davis, Thomas DeWitt, and Christopher Marshall on the two major ways that otters feed. Some otters, like giant and North American river otters, primarily catch fish and other squirmy prey with their jaws, while otters such as Asian small-clawed otters and sea otters often nab mollusks, echinoderms, and other hardened prey with their dexterous hands before crushing through those exterior defenses with expanded cheek teeth. And given that there are trade offs between speed and power in any bite, Timm-Davis and colleagues expected that the differences between these two feeding styles would be visible in the shape of the otters’ skulls. With that in mind, they measured and estimated the bite mechanics for 150 otter skulls representing four different species, as well as parsing out three different populations of sea otters.

The skull of a southern sea otter at Año Nuevo State Park, California. Photo by Brian Switek.
The skull of a southern sea otter at Año Nuevo State Park, California. Photo by Brian Switek.

The otters generally met the researchers’ expectations. Giant and North American river otters, which subsist primarily on fish, have longer, narrower skulls capable of fast bites. Just the sort of setup for snapping at slippery and fast-moving prey. The Asian small-clawed and sea otters, which more often rely on plucking up slow-moving invertebrate morsels, have wider, shorter skulls and jaws, delivering a slower but more more powerful bite. Sea otters take this to the extreme, with wide, rounded cheek teeth best suited to pulverizing hard foods.

Not that all sea otters behave the same way, though. When Timm-Davis and coauthors looked at the differences between isolated Russian, northern, and southern sea otters they found that the skulls of each population clustered together in slightly different shapes. This appears to be because of diet. Northern and Russian sea otters diversify their diet a bit by eating more fish than their southern cousins, and this difference shows up in the anatomy of their jaws. Among other variations, the southern sea otters had about 19.1% more crushing surface on their cheek teeth – the better to mash up sea urchins with. These relatively recent changes reflect how quickly differences in diet can start to affect the shape of otter evolution.

For the most part, though, even sea otters with more cosmopolitan tastes still share the deep, short, and wide skull shape that distinguishes them from their lithe relatives. Sure, all that fur, the little nose, and oildrop eyes complete the package, but the mammal’s lutrine looks go down to the bone. Their cuteness comes from their ability to crush.


Timm-Davis, L., DeWitt, T., Marshall, C. 2015. Divergent skull morphology supports two trophic specializations in otters (Lutrinae). PLOS ONE. doi: 10.1371/journal.pone.0143236

Fossil “River Dolphin” Lived Out at Sea

The tale of how whales walked into the seas is one of the most celebrated in evolutionary biology. Even our own fossil backstory, of arboreal apes that eventually began to walk upright, seems relatively unimpressive compared to how little mammals that scampered along the beach on four legs began a transition that would result in oceanic leviathans. But the land-to-sea switch isn’t the only one whales have undergone.

Not all whales live in the ocean. River dolphins – long-snouted whales with tiny eyes – inhabit turbid freshwater streams in South America and Asia. For a time, before evolutionary biology began using molecular techniques, it was thought that all of these similar cetaceans belonged to a singular group, but, as it turns out, they represent different lineages that all independently gave up life in the seas for one in freshwater. Dolphins have done this over and over again in waterways around the globe for millions of years, and a newly-named prehistoric species from Panama adds a little more definition to the outline of when South America’s river dolphins made the switch.

The prehistoric dolphin, described by Smithsonian Institution paleontologist Nick Pyenson and colleagues, didn’t actually live in a river. The geologic context in which it was found made it clear that this whale swam out in the open ocean off the Caribbean coast of Panama between 6.1 and 5.8 million years ago. But, at that time, this stretch of sea was not as it was now. The ocean was brimming with plankton and supported a much richer collection of creatures, possibly thanks to upwelling from the deep Pacific, and the dolphin snapped up fish in this highly-productive stretch of sea before the Panamanian Isthmus fully closed. Pyenson and coauthors drew from this fact to give the creature its name – Isthminia panamensis.

The skull of Isthminia. From Pyenson et al., 2015.
The skull of Isthminia. From Pyenson et al., 2015.

Relatively little of Isthminia was left in the rock. Just a skull, lower jaws, right shoulder blade, and two flipper bones. Much of the skeleton probably eroded away before it could be excavated in 2011. But enough remained to allow Pyenson and colleagues to outline how this dolphin lived and who it’s related to. While the size of the cetacean’s eyes and the wear on its teeth are most similar to open-ocean dolphins, the details of its anatomy indicate that it’s an ancient relative of today’s South American river dolphins in the genus Inia. In short, Isthminia was an early “river dolphin” that lived at sea.

Even though today’s river dolphins had marine ancestors, however, how Isthminia fits into this picture isn’t totally clear. Paleontologists have uncovered the first wave of river dolphin invasion in South America as occurring between 16 and 11 million years ago – a group called platanistids that later disappeared from this continent (but is represented by the Ganges River dolphin today). Isthminia could represent the beginnings of the second wave as dolphins became increasingly adapted to nearshore life towards the end of the Miocene, or, Pyenson and coauthors note, the dolphin could mark a reversal. In this case, an even earlier and as-yet-unknown group of dolphins threaded into South America’s rivers and, while most stayed, the ancestors of Isthminia went back to sea.

Regardless of which hypothesis turns out to be correct, there was no straight-line transition from the sea to the rivers. Just like the initial invasion of the water by whales was a tangle of different lineages that took to the water in disparate ways. Into the sea, to the rivers, and maybe even back again, fossil whales remind us that transcendent change is never as simple as it first seems.

To get a better look at the fossil, check out the Smithsonian X3D browser.


Pyenson, N., Vélez-Juarbe, J., Gutstein, C., Little, H., Vigil, D., O’Dea, A. 2015. Isthminia panamensis, a new fossil inioid (Mammalia, Cetacea) from the Chagres Formation of Panama nad the evolution of “river dolphins” in the Americas. PeerJ. doi: 10.7717/peerj.1227

Book in Brief: The Antarctic Dive Guide

I’m not going diving in the Antarctic anytime soon. I’ve averse to cold, I haven’t reupped by PADI certification since I was 16, and, frankly, I don’t have the cash to get there. But, all the same, I’m glad Princeton University Press sent me a copy of Lisa Eareckson Kelley’s The Antarctic Dive Guide.

The bulk of the book, as would be expected of a dive guide, is a listing of dive spots around Antarctica. Each includes a map, coordinates, a summary of what to expect from each site, and more. The overall impression is of a place meant for the hardest of the hardcore. Even some of the descriptions might be enough to make the reader want to pee their wetsuit. The description of Elephant Island warns that “Brash Ice can be a factor to be contended with, as the nearby glacier is very active”, and the Aitcho Islands profile advises “All dive sites have a very strong tidal current, which can sweep you out from land, away from your boat, and towards the center of the English Strait by as much as 1km.” Eep.

antarctic-dive-guideBut all of these frigid descriptions come with beautiful color photographs of sea cucumbers, seals, sea stars, salps, and an array of other marine organisms whose names don’t start with “s”. Far from being a saltwater tomb, the Southern Ocean is full of gloriously weird and colorful life. While I obviously can’t speak from experience, the guide does an admirable job of telling readers what sort of creatures to expect at each site and how to get the best photographs of them. The photos are enough to tempt a desert rat like myself to consider dipping a toe in the icy Antarctic waters.

Above all, though, one short section of the book caught my attention. Leopard seals are the Antarctic’s big, charismatic carnivores, and they have traditionally been cast as villains. Their bad reputation seemed to be earned when, in 2003, a leopard seal drowned marine biologist Kirsty Brown. Yet this was the only such death on record, and many divers have reported leopard seals as inquisitive more than aggressive.

To cut through these conflicting ideas, an array of contributors offer their perspectives on the seals and how to avoid injury at their jaws. A submerged diver usually doesn’t look like prey, for example, but a seal may mistake a diver walking to the edge of the ice for an overlarge penguin, the pinniped’s favored food. Even though relatively little is known about the beasts and their habits, the guide is clear that leopard seals are wild animals and even “friendly” seals that bring divers gifts of dead penguins should not be considered cuddly undersea buddies.

The sea can inspire and entrance. That doesn’t mean we can forget that it is wild. We may visit, but, despite being descendants of fishapods that swam through the water over 375 million years ago, the sea is not a place we’re adapted to in the least. The Antarctic Dive guide does an admirable job at balancing these perspectives, conveying the joys and the risks involved at entering such a beautiful, alien part of the world.

Sciencespeak: Whale Pump

Whales can poop almost anywhere they want. They have the entire ocean to relieve themselves in, so most of the planet can theoretically be their toilet. Yet, despite having a near-universal lavatory pass, cetaceans often relieve themselves near the surface. In the words of marine biologists Joe Roman and James McCarthy, many whales feed in the deeper tiers of the sea to then return to the surface and release “flocculent fecal plumes” – cetacean clouds that may create what Roman and McCarthy call a “whale pump“.

The researchers laid out their logic in a 2010 PLOS ONE paper. Our planet’s seas are constantly recycling themselves. Showers of marine snow send organic matter cascading down to the sea floor, and zooplankton excrete poop full of nitrogren, phosphorus, and iron in deep water as they go about their regular up-and-down migration through the water column. This is a downward “pump” of resources. But other organisms can also bring some of these elements back from the deep. Whales and other marine mammals, Roman and McCarthy hypothesized, replenish the surface waters with their excrement.

The researchers based their case on an array of cetacean observations. Whales must surface to breathe, the physiological consequences of diving and surfacing make it likely that marine mammals will let it all go near the surface, and observations of crappy clouds have shown that they dissipate through the water rather than sink. And even though whales sometimes feed in the upper portion of the sea, they often dive deeper to reach dense pockets of fish and invertebrates. These hard-to-reach resources are key to Roman and McCarthy’s proposal. Whales feed on deepwater prey that are taking up elements from far below. After a bit of digestion, the whales then jettison some of those elements in shallower waters and leave plankton to recycle the slightly-used nitrogen.

Seals and sea lions might do their share, too. If you’ve ever smelled a pinniped colony at the height of breeding season, you’ve probably cursed your sense of smell. What the blubbery mammals spill onto the shore can be washed back into the sea, emanating the ecological reek of seal-processed fish and squid returning nitrogen to the water.

A diagram of how the whale pump works. From Roman and McCarthy, 2010.
A diagram of how the whale pump works. From Roman and McCarthy, 2010.

It’s one thing to theorize from an armchair, though, and quite another to get out on a boat and collect some whale feces. That’s exactly what Roman and McCarthy did to further investigate their idea, taking 16 samples of billowy poops from the Gulf of Maine. All of the samples contained significantly more ammonium – a nitrogen-rich waste product – than the surrounding water. Based on these analyses, Roman and McCarthy suggested that whales could be responsible for dumping 2,3000 metric tons of nitrogen into the Gulf of Maine every year. The amount was probably even higher before commercial whaling tried to sate its hunger for the massive mammals.

And seagoing beasts may only be continuing a trend that was in place long before they took to the water. At this past weekend’s PaleoFest at the Burpee Museum of Natural History, paleontologist Ryosuke Motani pointed out that marine reptiles were doing the dive-and-surface shuffle hundreds of millions of years before the hoofed ancestors of whales were even a glimmer in natural selection’s eye. Some of these marine reptiles – such as the fish-like ichthyosaurs – were some of the first deep-divers, Motani pointed out, and they could have played an ecological role similar to what Roman and McCarthy have suggested for whales. So perhaps it’s too narrow to talk about “whale pumps” or “marine reptile pumps” feeding the seas. Those are just more academically-acceptable ways of talking about “poop pumps”.


Roman, J., McCarthy, J. 2010. The whale pump: marine mammals enhance primary productivity in a coastal basin. PLOS ONE. doi: 10.1371/journal.pone.0013255

Acoustic Fats, Ear Trumpets, and How Whales Hear

Up until a few days ago, I had never heard a blue whale. I wasn’t even aware they made sounds that my primate ears could pick up. But, thanks to Australian Antarctic Division researchers, I was able to listen to the massive mammal for the first time:

It’s an incredibly soothing sound. Certainly moreso than Jeff Bridges and his singing bowls. But I’m probably not hearing the blue whale’s “song” as it’s meant to be heard. My ears are all wrong.

I take in sounds through my ear canal. But modern whales are weird. As their four-legged ancestors slipped into the sea and took up permanent residence there, evolution granted whales an entirely different way of hearing that relies on “acoustic fats” that help transmit sounds to a specialized “ear trumpet” on the skull.

But when did whales evolve this alternative auditory apparatus? To answer that question, National Museum of Natural History researchers Maya Yamato and Nicholas Pyenson looked to fetal whales and fossils to determine when whales started listening through acoustic funnels.

Yamato and Pyenson scrutinized 56 fetal whales collected during the heyday of 20th century commercial whaling, as well as specimens saved by the Smithsonian from bycatch and strandings. This sample encompassed ten different living whale lineages, which was critical because of differences in the way the two main groups of modern whales listen to the sea.

Toothed whales – odontocetes – have acoustic funnels that are oriented forward and connect to acoustic fat in the jaw. This is probably because a forward-facing ear is essential to accurately reading returning pings from echolocation. But some baleen whales – mysticetes – have acoustic funnels oriented more toward the side. By studying the early development of the ear trumpets in each of these lineages, Yamato and Pyenson were able to outline how this common structure diverged amongst the whales.

In both toothed and baleen whales, Yamato and Pyenson found, the acoustic funnel starts out as a forward-facing, V-shaped structure made by the malleus and goniale bones of the ear. As toothed whales grow, the acoustic funnel extends forward from the bones to the acoustic soft tissues, but, among some baleen whales, the acoustic funnel shifts to the side. Why this happened isn’t entirely clear, but it may have something to do with baleen whales communicating with low-frequency sounds over long distances and no longer needing the forward-directed hearing of their echolocating cousins.

Since the acoustic funnel starts off the same way in both toothed and baleen whales, Yamato and Pyenson hypothesize, the feature must have been present in the last common ancestor of both, around 34 million years ago. And the fossil record bears this out. Adult specimens of fossil baleen whales such as Aetiocetus and Albertocetus have forward-oriented ear funnels. This means that head-on hearing was probably the default state for both baleen and toothed whales, only later modified by humpbacks, minkes, and their relatives. Sadly for me, though, this means that even if I could learn to speak whale, I wouldn’t be able to properly understand a whale without some pretty drastic modifications to my head.


Yamato, M., Pyenson, N. 2015. Early development and orientation of the acoustic funnel provides insight into the evolution of sound reception pathways in cetaceans. PLOS ONE. doi: 10.1371/journal.pone.0118582

Basilosaurus the Bone-Crusher

Bite force is all the rage lately. This year alone paleontologists have published new bite force estimates for the largest rodent of all time and a prehistoric crocodylian heavyweight. And in the pages of PLOS ONE, Eric Snively, Julia Fahlke, and Robert Welsh have brought another superlative chomper to attention – the early whale Basilosaurus.

The inspiration for the study came from damaged bones. In 2012 Fahlke published a paper on a set of busted whale skulls from the 38-36 million year old strata of Egypt. Each of the four were from juveniles of a whale called Dorudon – a sinuous, fully-aquatic whale that still had differentiated teeth for gripping and shearing – and they all bore bite marks that matched the size and spacing of teeth belonging to the similar, but much larger, Basilosaurus. The bigger whales were grabbing the young Dorudon by the skulls, sometimes repositioning their prey before a final crunch.

The ancient toothmarks offered compelling evidence that, much like today’s orcas, Basilosaurus was a whale that ate other whales. But as a check on its biting power, Snively, Fahlke, and Welsh turned to an engineering technique called finite element analysis to run Basilosaurus through some virtual chomping.

Working from a skull belonging to a beautifully-complete specimen of Basilosaurus isis found in Egypt, the researchers found that the whale could bite with a force of over 3,600 pounds at the position of its upper third premolar. As suggested by Fahlke, this was the part of the mouth Basilosaurus used to crack open little Dorudon skulls and the estimated force is more than sufficient to penetrate through skin, muscle, and bone. And while the figure is undoubtedly influenced by the size of Basilosaurus, as Andy Farke points out, this is still the highest bite force yet estimated for a mammal.

A simulated Basilosaurus bite on a Dorudon skull. From Fahlke, 2012.
A simulated Basilosaurus bite on a Dorudon skull. From Fahlke, 2012.

Basilosaurus didn’t go right for a killing stroke, though. Some of the Dorudon skulls hint at initial capture with the conical, canine-like teeth at the front of the jaw first, and the researchers found that Basilosaurus could grip victims with over 2,300 pounds of force. With prey in place, Basilosaurus could then toss it back further along the jaw for a deadly shear bite. Crocodylians sometimes do the same with turtles and other hard-shelled prey, nabbing them with pointed teeth before obliterating their victims’ defenses with a back-tooth bite.

All that biting power allowed Basilosaurus to effectively dismantle large prey. The skulls of dead Dorudon and Basilosaurus teeth worn from scraping against bone attest to that grisly fact. And as Snively, Fahlke, and Welsh note, that Basilosaurus was capable of such shattering bites also fits with the picture of the whale as a consummate hunter.

The highest bite forces known – whether recorded from live animals or estimated from bones – belong to active predators, including carnivores like saltwater crocodiles, spotted hyenas, great white sharks, and Tyrannosaurus. Sure, powerful bites might let them take advantage of carrion from time to time, but the ability to deliver devastating chomps is also a critical skill for predators who must quickly disable their victims. What was true for spotted hyenas was likely true for Basilosaurus, making the ancient mammal one of the most frightening whales of all time.


Fahlke, J. 2012. Bite marks revisited – evidence for middle-to-late Eocene Basilosaurus isis predation on Dorudon atrox (both Cetacea, Basilosauridae). Palaeontologia Electronica. 16 (2), 1-16.

Snively, E., Fahlke, J., Welsh, R. 2015. Bone-breaking bite force of Basilosaurus isis (Mammalia, Cetacea) from the Late Eocene of Egypt estimated by finite element analysis. PLOS ONE. doi: 10.1371/journal.pone.0118380

Why an Ichthyosaur Looks Like a Dolphin

Textbooks aren’t known for their originality. They build on the basics, and often include the same standard examples from one generation of students to the next. (I haven’t checked, but I wouldn’t be surprised if the fox terrier clone is still creeping somewhere.) That’s why ichthyosaurs are a textbook staple.

Mesozoic “fish lizards”, ichthyosaurs were marine reptiles that independently became adapted to a life at sea around 200 million years before dolphins. Despite their distance from the oceanic mammals in both time and evolutionary history, though, ichthyosaurs look enough like dolphins for the two to be practically inseparable in textbooks. They’re a striking example of convergent evolution – two lineages independently evolving extremely similar anatomy from different starting points.

A Jurassic ichthyosaur on display at the Royal Ontario Museum. Photo by Brian Switek.
A Jurassic ichthyosaur on display at the Royal Ontario Museum. Photo by Brian Switek.

But how similar are the two, exactly? An Opthalmosaurus looks kind of like a bottlenose dolphin, sure, but stopping at superficial similarities isn’t very scientific. Here’s where a new Biology Letters study by National Museum of Natural History paleontologist Neil Kelley and U.C. Davis’ Ryosuke Motani offers an opportunity to see whether such resemblances are only skin deep.

Kelley and Motani focused on skulls of marine tetrapods – descendants of the four-legged vertebrates that crawled out of the swamps over 360 million years ago. They’re an ideal group for such comparisons because all of them – from seals to turtles to whales – had terrestrial ancestors that eventually took on life in the seas. By combining skull, jaw, and tooth measurements from 69 living species with data on what they actually eat, Kelley and Motani were able to pick out how form relates to feeding.

How skull (top) and tooth (bottom) shapes group marine tetrapods together. From Kelley and Motani, 2015.
How skull (top) and tooth (bottom) shapes group marine tetrapods together. From Kelley and Motani, 2015.

As it turns out, skull anatomy is a fairly good predictor of feeding style regardless of ancestry. For example, herbivores like the marine iguana, green sea turtle have short skulls with larger areas of attachment for powerful jaws muscles to crop and crush vegetation. Species that snatch up fish and squid, on the other hand, tend to have longer, toothier snouts better-suited to “snap feeding” and swallowing prey whole. Apex predators such as the saltwater crocodile, leopard seal, and orca fell in-between, characterized by elongated jaws and relatively deep skulls that give them the power to tear apart larger prey.

Despite diverging far back in the prehistoric past, creatures as distantly-related as iguanas and dugongs have evolved similar skull shapes to cope with similar diets. And with this proof-of-concept in place, the same technique can be applied to the fossil record. Paleontologists will able to investigate the similarities, and differences, between ichthyosaurs and dolphins, and perhaps even gauge how marine reptiles like different species of mosasaur may have been able to coexist by picking different items off the marine menu. There are plenty of prehistoric secrets embodied by evolution’s greatest hits.


Kelley, N., Motani, R. 2015. Trophic convergence drives morphological convergence in marine tetrapods. Biology Letters. doi: 10.1098/rsbl.2014.0709

Science Word of the Day: Super-weaner

There are some technical terms that make me think “Hah, that’s funny”, but not actually laugh out loud. That’s how this weekly feature got started. But thanks to intellectual neoteny that has let me maintain a juvenile sense of humor, I can’t help but giggle at some science words. “Super-weaner” is one of them.

I first heard the word during a trip to California’s Año Nuevo State Park. Scores of plump northern elephant seals haul out there every winter to breed, and since I arrived relatively early in the season, the stink emanating off the shore wasn’t too bad yet. A few mother elephant seals had even birthed their pups, which led the park ranger leading our tour to introduce us to “weaners” and “super-weaners”.

At first I thought the ranger was making a joke. It sounded like he was calling the pups “wieners”. Made sense to me. The pups looked like sausages wrapped in buns of blubber.

Of course, this wasn’t what the ranger meant. He was talking about how seals nurse. Weaners, not wieners. The higher echelon of my brain quickly scolded the baser part, and I learned the difference between the standard elephant seal pup and a super-weaner.

Mother elephant seals usually feed their pups for about twenty eight days. That might not seem like very long, but their milk is about 55% fat. That’s richer than heavy whipping cream, straight from the nipple. And given the thirst of their pups, mother elephant seals quickly become diminished. Already starting off depleted from a pre-birth fast, female elephant seals lose about half their body fat while nursing their offspring. After nearly a month of giving their pup everything, they need to return to the sea to feed. The 300 pound pup, now having to fend for itself, is a “weaner”.

But some pups still want more. There’s almost always another mother on the beach with a new baby, and some weaners badger and nag them to get more milk. Male pups are especially persistent, and, as Joanne Reiter and colleagues once wrote, “exceptionally large weaners are always males.”

Get lost, weaner. Illustrations of female elephant seals rejecting a pushy pup. From Reiter et al., 1978.
Get lost, weaner. Illustrations of female elephant seals rejecting a pushy pup. From Reiter et al., 1978.

It doesn’t always work. Most mothers don’t take kindly to alien weaners prodding them for milk. A swift bite sends most interlopers on their way, and the whole harem of females might join in if the weaner screams in protest. But, for reasons unknown to us, some mothers will let the intruding pups nurse. These pushy pups are super-weaners, and they certainly look the part. After supping on extra milk, super-weaners can weigh 600 pounds.

Not all super-weaners gain their edge through theft, though. There is a safer way for pups to become so bulbous. Some pups will be adopted by a second female while they’re still nursing or immediately after. They don’t have to try to “steal” milk, but can simply enjoy the largesse. Reiter and colleagues gave these super-weaners the extra title “double-mother sucklers”.

A few early season super-weaners inchwormed across the crowded beach during my December visit. They could still live large, at least for a little while. Little did they know that they would be cut off in March. At the cusp of spring all the mothers have typically vacated the beach, leaving the pups alone save for the beachmasters and adolescent males that spar in the shallows. So, with no one else to turn to, the pups do the logical thing to stay comfortable. They pile next to and on top of each other to bask in the sun. These, as you may have guessed, are weaner pods.


Costa, D., Le Boeug, J., Huntley, A., Ortiz, C. 1986. The energetics of lactation in the northern elephant seal, Mirounga angustirostris. Journal of the Zoological Society of London. 209: 21-33.

Reiter, J., Stinson, N., Le Boeuf, B. 1978. Northern elephant seal development: The transition from weaning to nutritional independence. Behavioral Ecology and Sociobiology. 3: 337-367.

Riedman, M., Le Boeuf, B. 1982. Mother-pup separation and adoption in northern elephant seals. Behavioral Ecology and Sociobiology. 11: 203-215.