Identify venomous and non-venomous snakes by their eyes, head shape, or belly scales…and you’ll be wrong

This post was inspired by a friend of mine who sent me a diagram proposing a simple rule to identify whether a snake is venomous or not. I’ve seen three of these simple rules shared on social media and all three are wrong.

The most popular rule normally consists of a diagram that looks like the one below, except that it claims that all venomous snakes have triangular heads and all non-venomous snakes have round heads.

Snake heads lie
This work by Eric Butler is licensed under a Creative Commons Attribution 4.0 International License.

Vipers (by which I mean any snake in the Viperidae, including rattlesnakes, copperheads, and water moccasins) do tend to have triangular heads, although the head shape changes in response to the amount of venom in the snake’s venom glands. But pythons and boas also have triangular heads because they eat large prey and have to have large heads. Meanwhile, round heads are found on many other species, including mambas, which are some of the most venomous snakes in the world, and coral snakes, which are also venomous.

The next most popular rule looks like this diagram, except it claims that venomous snakes all have slit-pupils and non-venomous snakes all have round pupils.

This work by Eric Butler is licensed under a Creative Commons Attribution 4.0 International License.

This is simply not a helpful characteristic. Slit-pupils and round pupils are both found in venomous and non-venomous snakes. In fact, while putting this article together I found a site claiming that all venomous snakes have slit-pupils and all non-venomous snakes have round pupils, no exceptions. It had a photo of a python (non-venomous) to illustrate slit-pupils. (Even if this characteristics worked more reliably it would require being quite close to the snake, and slit-pupil eyes with expanded pupils can look a lot like round-pupils.)

The last characteristic is whether the belly scales on the tail are in one or two rows. The claim is that venomous snakes have one row and non-venomous snakes have two rows.

Belly scales past anal plate in snakes
This work by Eric Butler is licensed under a Creative Commons Attribution 4.0 International License.

This characteristic (known as having a single anal plate or a divided one) is actually used by professional herpetologists and can be found in many field guides. However, while it can help identify what group of snakes a given snake belongs to it doesn’t tell you whether that group is venomous or not. Indeed, in a few snake species, individuals of the same species can vary in this characteristic.

What’s really going on here?

It turns out that all three of these characteristics are making the same mistake: they are taking characteristics that vary between the Viperidae and the Colubridae (or most colubrids) and attempting to use these to identify whether a snake is venomous or not.

In North America most venomous snakes (the rattlesnakes, cottonmouth/water moccasin, and copperhead) are vipers. Many other snakes are colubrids. This means that these shortcuts often seem to work in the United States. In South America there are some venomous colubrids and these rules wouldn’t work. In Africa, Asia, and Australia some of the most feared venomous snakes are elapids, including cobras, kraits, death adders, and mambas. Elapids and colubrids tend to match in the characteristics these shortcuts use.

However, even if you restrict your use of these rules to North America you run afoul of the coral snakes, venomous elapids found in the southern parts of the USA and into Central America.

The coral snake above has a small, non-triangular head, round pupils, and a divided anal plate. It also has distinctive, bright colors (although it has non-venomous mimics) and so you could learn to avoid those instead. But that won’t work in Central America, where some coral snake species are much duller in color.

What rules can you use?

Learn the venomous snakes in your area. Most snakes aren’t venomous (or aren’t venomous enough to harm humans) and so there’s normally a pretty short list of snakes to learn. For instance, where I live the venomous snake that people are most likely to run across is the copperhead. It has a distinctive pattern with only minor variations. Learning that pattern is far more effective than any of these rules, especially since the pattern will let you identify a snake that is visible only as a back half slithering away under cover.

Spiders Eating Bats and Fish

In honor of a recent presentation that I made at the North Carolina Museum of Natural Sciences Bugfest event I thought I would highlight two interesting articles relating to spiders. Both are from the open access journal PLoS ONE and so both are freely available to read to anyone with a working internet connection.

The first article is Bat Predation by Spiders by Martin Nyffeler and Mirjam Knörnschild. This topic is perhaps best introduced by the set of photos that accompanies the article.

Spider species that were found to have killed bats included both web-building and hunting spiders (which do not make webs). Most of the hunting spiders recorded eating bats were tarantulas. In several cases the predator appears to have been a member of the genus Avicularia, an arboreal tarantula genus that could easily access locations in trees where bats sleep during the day. In India one of the arboreal Poecilotheria species was recorded eating a bat. In other cases the tarantulas were ground-pounders, such as a large Lasiodora, a genus that includes the Brazilian salmon pink bird-eater. Other hunting spiders also got in on the action. A huntsman spider in India was recorded killing a bat and a fishing spider was recorded stalking a bat pup in Indiana. In both of these latter cases the predation event appears to have be interrupted by the observer.

Obviously, since spiders don’t fly, it’s much easier for web-building spiders to eat a delicious bat. The main culprits were members of the genus Nephila, the golden silk orb-weavers, whose webs can span 1.5 meters (roughly five feet) and whose bodies are the largest of all the web-spinning spiders. Other web weavers included other nephilids and members of the Araneidae, another orb-weaving family. Most of these spiders spin large webs and are themselves large spiders. North American readers may be familiar with the genus Argiope, of which one species, A. aurantia, the black and yellow writing spider, is found across a large section of the continent. These spiders represent some of the smaller species known to catch bats in their webs.

The bats caught in webs also tended to be small, with small microbats (often subadult) being the most common. Larger bats are likely to break through a web when they hit it, which would prevent them from being captured by web-building spiders. The heaviest bat reported captured in this study was an adult that probably weighed 11g, while another specimen could have weighed somewhat more.

The question of whether bats are actively preyed upon by spiders is also raised in this study. In some cases a bat may run into a spider web and become entangled and die of dehydration, exhaustion, or exposure without any active attempts at predation by the spider that made the web. In some of the cases cited here the full predation sequence was observed (attack, kill, feeding) whereas in other cases only the feeding end of the sequence was involved, and in some of the web spider instances only entanglement was observed. Oddly, this includes all the Nephila clavipes records, which may mean that even smaller Nephila kill bats entirely incidentally, and gain nothing by capturing such large animals in their webs. Larger Nephila species were observed to actively kill and eat bats.

Overall, this study concludes that bat predation by spiders is probably infrequent. A bat must fail at multiple steps to be killed by a spider. First, it must fail to avoid the web, and bats appear to be pretty good at avoiding webs. Second, the bat must become entangled in the web, when a large majority of bat-web impacts probably result in a destroyed web and a bat with some spider silk stuck to it. Third, the bat must fail to escape from the web. Since bats can struggle against the web and potentially break free this may result in some number of very brief bat captures. Obviously, active predation by the spider can prevent the successful escape of the bat, as the bat can be envenomated and crippled beyond its ability to break free even before it dies.

Many of the bats captured in this study were young, which may suggest that inexperience (and lower body weight) play an important role in leading to bat capture by spiders. The authors also suggest that echolocation frequency and nearness to home may play a role, as some bats are thought to rely on memory, and not echolocation, when close to their roost.

Finally, the authors ask whether bats are at all important to spiders as prey. For some spider species, they conclude, bats are so large that a single rare bat capture can sustain the spider for an extended period of time.

The second article is Fish Predation by Semi-Aquatic Spiders: A Global Pattern by Martin Nyffeler and Bradley J. Pusey. Clearly Martin Nyffeler is as interested in spiders killing vertebrate prey as I am. Again, a photo montage of spider-induced carnage seems appropriate.

As with bat predation, spiders were more likely to engage in fish predation in warm areas of the world, although in this case “warm areas” included a much wider band around the equator, with the largest number of records of fish predation coming from the United States. Again, the only continent without records of spider predation on fish is Antarctica. The authors note that, for instance, a long study in Canada observing Dolomedes triton never observed this species catching fish, whereas a smaller amount of observation time in Florida observed this same species capturing fish multiple times. This may be biased by the greater presence of small fish in warmer areas.

The family Psiauridae was responsible for most of the fish captures by a wide margin – roughly 80% of all fish captures came from this family. The genus Dolomedes (common in North America) was one of the primary culprits, with Dolomedes triton (five out of six of the images above) being one of the species with the most records. This group of spiders hunts at the water’s surface, and attacks fish through the surface of the water after directly touching the fish. Fish are then dragged out of the water to be consumed, which the authors note is necessary for the spiders’ method of feeding to work and also gives the spider an advantage in holding on to potentially-struggling prey.

The size of the fish captured was usually quite small. However, the spider was usually smaller. Fish were on average 2.2 times longer than the spider (unsurprising, given that fishes tend to possess longer body plans) and up to 4.5 times as heavy. Given my interest in catfish I do wish to note that one very small Ictalurus punctatus was reported as a prey item. Fish may also be made vulnerable by low oxygen levels (which drive fish towards the surface) and a tendency towards surface-feeding. The Gambusia mosquitofish seem especially vulnerable to being eaten by spiders.

Unlike spider predation on bats, spider predation on fish seems to be a normal (if often unobserved) behavior. Like predation on bats, a spider that successfully kills a fish can be expected to derive quite a lot of benefit from this kill.

Both of these papers noted something that should be, but isn’t always, obvious: many spiders are generalist predators with very simple means of determining whether something is prey or not. Prey specificity in spiders is probably normally quite low. For web-spinning spiders the rule is probably something like “what struggles without escaping is lunch”. Fish-eating spiders may have slightly more complex rules by which they determine that they can haul a struggling fish to shore but again things like estimated size are probably more important than taxonomic placement of potential prey.

Possibly more interesting in a general context, all of these events involve a smaller predator bringing down larger prey. Most predators do the opposite (a house cat, for instance, hunts mostly mouse-sized animals). The advantage that webs and venom give spiders is apparently sufficient to allow them to break the “rules” governing predator-prey size relationships. I’ll probably write more on that eventually but that will have to wait until I get time to do a full write up on what we know about Harpagornis moorei.


Catfish and the Lazarus Taxon Problem

Some time ago I mentioned the phenomenon of Lazarus taxa. For those who don’t remember, Lazarus taxa are taxa that are known from fossils that appear to disappear from the fossil record and then re-emerge (“from the dead”) significantly later. The concept gets tossed around a lot when discussing the possibility that groups thought to be extinct might still persist. One of the central questions in evaluating the odds of Lazarus taxa occurring is the completeness of the fossil record. Now, nothing I’m going to say is going to be surprising to a paleontologist, but the fossil record is, as far as completeness goes, pretty terrible. I’ve sometimes heard the fossil record compared to a TV show that is missing chunks. It’s probably more like five non-consecutive frames from an hour long show.

One of the clades that demonstrates this well, and that I happen to know about, is catfish. By catfish I mean the Siluriformes, a quite large group of mostly freshwater fish, some of whom don’t look very much like the “classic” catfish. Catfishes often have a heavy-duty first fin ray in their pectoral fins which happens to preserve well and is identifiable to major group. (This fin spine is meant to stab potential predators, as more than a few recreational anglers have found out.) Because of this catfish fossils are sometimes identifiable even in a severely fragmented state. This is good because fish bones are pretty lightweight compared to tetrapods and fish skeletons are easily scattered and the bones broken.

Diogo (2004) discusses a fossil from the catfish genus Corydoras dated to the Paleocene. Corydoras is a common modern genus, found not only as many species in South America but also as the “cory catfish” in pet stores across the world. The Paleocene period is just past the massive extinction event that brought the Mesozoic1 to a cataclysmic end. To give an idea how unlike our modern world the Paleocene was consider that mice, bears, and cats had not yet evolved, and that the ancestors of whales were walking on land at this time. And yet here’s a modern genus, Corydoras. Moreover, Corydoras is endowed with bony, armored plates that wrap around its body, making it potentially much more fossilizable than other fish (although it is a small fish). Given the success of the modern genus we might expect to find that the world is littered with Corydoras fossils. Instead, Diogo (and I have seen nothing more recent to suggest that new discoveries have changed the picture) notes that there are no other Corydoras fossils until, perhaps, recent sub-fossils. There’s a 56 million year fossil lacuna for this genus.

However, the story gets more interesting. Diogo was arguing for what now seems to be a seriously minority position about the age of the Siluriformes but what makes this an argument is that everyone is sure that we do not have the earliest Siluriformes in the fossil record. A short digression into geologic timelines (really just what I needed to teach myself to follow the arguments I was reading) is needed here. We live in a large era called the Cenozoic. The prior large era is the Mesozoic, known for dinosaurs. The Mesozoic is coarsely divided into three pieces: the Triassic (oldest), Jurassic (middle), and Cretaceous (most recent2). The Cretaceous is divided more finely into a number of periods which I can’t remember because only two have catfish fossils, the last two, the Campanian and the Maastrichtian. The Maastrichtian is the very last sliver of time before the disaster that closes out the whole Mesozoic.

The very earliest catfish fossil comes from the Campanian in Argentina but skip forward just briefly in time to the Maastrichtian and catfish fossils are found in Bolivia (de Muizon et al., 1983; Gayet et al., 2001), India (Cione & Prasad, 2002), Niger (possibly, I cannot find the original description, just a mention in Cione & Prasad [2002]), the western United States (possibly, the species Vorhisia is not unanimously agreed to be a siluriform, Frizzel & Koenig, 1973), and Spain (Pena & Soler-Gijon, 1996, possibly not actually Maastrichtian but just beyond, the authors place the fossil on the border between the Maastrichtian and the following era). Also importantly, even within just the undisputed (as far as I know) Bolivian finds at least two major catfish clades are present. de Muizon et al. identify these two clades as the families Ictaluridae and Ariidae. Even if these exact assignments were to be disputed it seems unlikely that the total diversity of catfish at this site will be reduced. What this means is that the snapshot we have of early catfish is a diverse, widespread clade. Clades don’t start this way. Clades start as small, localized groups with low diversity. They then spread and diversify. It’s a bit like looking through a photo album and finding that the earliest photo you have of someone who you are researching is a photo of them holding their first child. You know they are not a child themselves but you also don’t know quite how old this makes them. All you know is that the beginning is further back.

I won’t get into the (long, complex) debate about when the first catfish swam the rivers of Earth (and the first catfish probably did swim in rivers, not lakes) but what we know is that the Siluriformes have a significant ghost lineage, the name for a lineage that is unrepresented in the fossil record. When we discuss things like Lazarus taxa we should be aware just how many creatures we know existed during times in which they did not leave fossil records.

Perhaps fittingly, since the last Lazarus taxa article discussed the coelacanth, there are particular biases against bony fish in the fossil record. Becker et al. (2009) discuss our friend Vorhisia and the other osteichthyan fish found in that time and region. They also discuss why the fossil record for Cretaceous fish is so poor. They list four things that bias the fossil record against bony fish.

  1. Fish skeletons are lightly built and fall apart easily. Many are from small animals. The bones can be destroyed easily and what is collected are frequently only a few more durable parts of the skeleton (like teeth).
  2. Fish bones are often hard to identify because a lot of basic work remains to be done. Perhaps someone has already found a Jurassic catfish, which would be a major find, but can’t identify it as such because the work comparing catfish skeletons to other fish skeletons hasn’t been done and so this person can’t determine what they have.
  3. Bias in collection and research. Basically, nobody cares about fish. People grab the big stuff and prioritize that when they do research. Fish bones may get left in the ground or in a file drawer instead of being described.
  4. In the specific area Becker et al. described the rock type was also not a good one for preserving fish.

Now, there are examples where it would be hard to claim that the fossil record is simply too patchy to show the continued existence of a taxon. For instance, the (unfortunately frequent) claims that pterosaurs or plesiosaurs have made it into the modern era require that entire lineages of large creatures with very distinctive bones have made it millions of years without leaving fossils. However, individual species seem quite capable of dodging fossilization for extensive periods of time.


Becker, M. A., Chamberlain Jr., J. A., Robb, A. J., Terry Jr., D. O., & Garb, M. P. (2009). Osteichthyans from the Fairpoint Member of the Fox Hills Formation (Maastrichtian), Meade County, South Dakota, USA. Cretaceous Research, 30(4), 1031–1040.

Cione, A. L., & Prasad, G. V. R. (2002). The Oldest Known Catfish (Teleostei:Siluriformes) from Asia (India, Late Cretaceous). Journal of Paleontology, 76(1), 190–193.

Diogo, R. (2004). Phylogeny, origin and biogeography of catfishes: support for a Pangean origin of “modern teleosts” and reexamination of some Mesozoic Pangean connections between the Gondwanan and Laurasian supercontinents. Animal Biology, 54(4), 331–351.

Frizzell, D. L., & Koenig, J. W. (1973). Upper Cretaceous Ostariophysine (Vorhisia) Redescribed from Unique Association of Utricular and Lagenar Otoliths (Lapillus and Asteriscus). Copeia, 1973(4), 692–698.

Gayet, Mireille; Marshall, Larry G.; Sempere, Thierry; Meunier, François J.; Cappetta, Henri; Rage, J.-C. (2001). Middle Maastrichtian vertebrates (fishes, amphibians, dinosaurs and other reptiles, mammals) from Pajcha Pata (Bolivia). Biostratigraphic, palaeoecologic and palaeobiogeographic implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 169(1–2), 39–68.

de Muizon, C., Gayet, M., Lavenu, A., Marshall, L. G., Sigé, B., & Villaroel, C. (1983). Late Cretaceous vertebrates, including mammals,from Tiupampa, Southcentral Bolivia. Geobios, 16(6), 747–753.

Pena, A. D. E. L. A., & Soler-Gijon, R. (1996). The first siluriform fish from the Cretaceous-Tertiary interval of Eurasia. Lethaia, 29(1), 85–86.

Is the Coelacanth Special?

I assume everyone knows what a coelacanth is, or at least I did until WordPress suggested I had meant to write “complacent” instead, but just in case you are one of the few who missed the largest sarcopterygian1 discovery of the 20th century the story is as follows.

In the early 1930s scientists knew of a group of ancient, lobe-finned fishes2 thought to be either the ancestors of tetrapods or closely related to them, known as the coelacanths. These fishes were thought to have gone extinct prior to the beginning of the Paleogene, either slightly before or during the extinction that ended the age of dinosaurs. However, in 1938 a scientist in South Africa received a strange fish from a local fisherman that proved (after some investigation) to be a coelacanth. This species is now known to science as Latimeria chalumnae after the scientist who first found it (Marjorie Courtney-Latimer) and the river mouth it was found near (the Chalumna).

The coelacanth is one of the best examples of a Lazarus taxon around – a name applied to species that have disappeared from the fossil record only to reappear later with a substantial gap between its apparent extinction and its reappearance. Because of this it frequently gets co-opted as evidence that many other supposedly-extinct animals might still live among us, normally (it is claimed) as semi-mythical monsters. It’s hard to run across stories of living dinosaurs in the jungles of Africa, living pterosaurs in New Guinea, Gigantopithecus in North America, or plesiosaurs in Scottish lakes without someone invoking the coelacanth as evidence that pretty much any animal from the past might still be around. In fact, this particular post was inspired by watching “Expedition Mungo” on Animal Planet claim that the coelacanth was a good reason to suspect that the Triassic archosaur Postosuchus was behind the semi-legendary “ghbali” of Liberia3. So does the coelacanth herald a new world in which creatures from the past come back like sequels to movies from my childhood? Or is the coelacanth special, a once-off discovery?

A few things to note: there are actually two coelacanths. In 1999 a second species of coelacanth was discovered in Indonesia. This species received the name Latimeria menadoensis. Moreover, the total number of coelacanth specimens known to science is tiny. In 2005 Inoue et al. reported that L. chalumnae was represented by “more than 200 specimens” and that L. menadoensis was represented by only two specimens4. Moreover, there was a 14-year gap between the initial discovery of Latimeria and the discovery of a second specimen.

So how could we figure out what the discovery of the coelacanth means for other potential Lazarus taxa? Ideally we would want to know what Latimeria (and its precursors) have been doing since the K-Pg extinction event.

This is what we do know. Inoue et al. (2005) estimated the divergence time between the two Latimeria species using the mitochondrial genomes of the two species. The short take-home on the study is that they estimate that the two Latimerias split 40-30 million years ago, which is right around the time India collided with Eurasia. Indeed, Inoue et al. believe that this event is what split an African/Eurasian coastal population into two reproductively-isolated populations. This is also a remarkably long period of separation for two species in the same genus (although genera are pretty arbitrary – mammalogists tend to erect lots of genera for their special snowflakes whereas entomologists tend to pack species into genera like genera are being rationed). In fact, Inoue et al. point out that some prior studies had even suggested that the two Latimeria species might need to be synonymized because the differences between the species were so small.

So what’s going on? Another clue is in how much further back Inoue et al’s divergence time is from other studies. Instead of assuming a mutation rate from studies in other species they calculated it using the split between the Actinopterygii and Sarcopterygii as a calibration point5. The results they got suggest that Latimeria has had a relatively unchanging genome for a long, long time.

This is not entirely surprising. L. chalumnae is ovoviviparous (Smith et al., 1975) and found in water around 200 m deep (Fricke et al. 1991) where it appears to move largely by passive drifting. It appears that Latimeria is a slow-growing, slow-living, slow-reproducing species. These things tend to mitigate against rapid speciation.

So if the modern Latimeria spp. are slow-living fish of deeper (although not truly deep) water what have then been doing since the K-Pg extinction? Probably living right where they are. Modern coelacanths are nocturnal and have eyes adapted to low-light conditions (Yokayama et al. 1999) suggesting either a long period as nocturnal animals or a long period as deep-sea animals, or both. What this also means is that coelacanths are probably in a long, drawn-out process of going extinct. At one point coelacanths were a speciose group found in a variety of habitats. Now they are a clade with only two species found in a single habitat type. While it is possible that coelacanths could rebound and become a species-rich group again I think they’ve probably missed the boat on that. If in 40-30 million years coelacanths can barely split into distinguishable species it seems unlikely that in the next 10 million years they will suddenly evolve into a multiplicity of forms and take back the seas from the actinopterygians. (Mind you, the other possibility is that coelacanths are under strong stabilizing selection that keeps them from diverging significantly. This would suggest that coelacanths have inhabited a habitat that has experienced little to no change in millions of years, which again suggests that they aren’t really cut out for the rest of the world.)

A lot of this suggests that the main reason coelacanths are such an amazing Lazarus taxon is that they’ve spent a lot of the “age of mammals” in an environment of very poor fossilization where their unchanging body plans still serve them well. It is likely that if we had coelacanths from the age of coelacanth peak diversity to compare our modern Latimeria to we would find that Latimeria is a strange, deep-water offshoot of the main coelacanth branch. It just happens to be the branch that dodged the meteor 66 million years ago as well.

So are you about to find a dinosaur deep in the African jungles? Well, yes. Dinosaurs are remarkably abundant with over 10,000 extant species…oh, wait, you didn’t mean birds. Then no (probably). Theoretically a mountain or rainforest species could dodge fossilization in the same way that Latimeria did but terrestrial environments haven’t been nearly as static as the ocean. The world has warmed, cooled, dried, and, uh, wettened in ways that have had enormous impacts on terrestrial ecosystems but these same changes probably did little to the 200 m depths Latimeria prefers. The odds that a Mesozoic holdover is hanging out in a rainforest waiting to be re-discovered seems low.

But wait! It gets worse! You see, Latimeria is the sort of thing that is hard to find anyway. (Oh, and just in case you forgot, 1938 is a long time ago. Marjorie Courtney-Latimer, the coelacanth’s discoverer, died at age 97, and also died before I graduated college. We’ve yet to top the coelacanth.)

This lovely graph is a graph showing how fast we’ve been discovering fishes. Really, this is a graph using data from FishBase to attempt to determine when species were discovered. Two caveats: FishBase doesn’t include every species (although it tries) and I’m using the date associated with the description as the discovery date because that’s something I can slice out of the dataset with a few lines of code. Third bonus caveat: FishBase is sometimes wrong. However, all of this is small potatoes compared to the size of the dataset. There’s a lot of data here and so the occasional mistake or omission probably doesn’t change much.

What this graph shows is that we are still discovering fish pretty rapidly. While it might look like there’s a rapid leveling-off very recently (which would indicate that either we have collectively become terrible at finding new fish species or that we found them all) that’s an artifact of the data. Instead, we are, if anything, accelerating our rate of finding species. For comparison, the data for birds (which I had somewhere and can’t find) has pretty much flatlined. We’re basically done.

Here’s why this matters: if we are still discovering fish like crazy then we probably have a lot left to discover. The less we have already found the more likely it is that another big discovery awaits. Latimeria is in a group that we haven’t discovered much of (although in 78 years we haven’t outdone Latimeria) whereas many of the creatures people wish to support via Lazarus taxa are in groups that we know much, much more about. Someone will discover a new bacterium this year (or month, or week). Someone will discover a new beetle. Large mammals? We’re pretty much done with those, and the ones we “discover” tend to be things we knew about but didn’t realize they were different from something we’d already described.

But it gets better/worse! What if we split fish by depth? After all, Latimeria is, as I’ve noted, not very easy to get ahold of. Here I’ve split all fish species into one of three categories: shallow water fish (fish whose deepest depth range in FishBase is less than Latimeria chalumnae‘s shallow depth range of 150 m), deep water fish (L. chalumnae range or deeper), and medium depth fish who straddle these other ranges. Sure enough, there’s a real trend where deeper water fish are less well known.

Latimeria chalumnae (at least) is also a fairly large fish, close to the size of an adult human. If we split the available fish by size (smaller than L. menadoensis at 140 cm and larger) we see that larger fish are better known than smaller ones. Latimeria chalumnae was discovered right at the end of the age of describing big fish. Latimeria mendoensis was discovered ridiculously late, although since Latimeria was already known the Lazarus-ness of L. menadoensis‘s discovery is significantly less.

So what does this mean? It means, I think, that referencing the coelacanth as if it shows that some other creature from the depths of deep time is about to reappear is probably pretty wrong-headed. The coelacanth seems to be a pretty special case for the following reasons:

  1. First, the coelacanth lineage had to tail off into oblivion slowly. It’s not the only example of this by far (off the top of my head, temnospondyls closed down the party at the end of the Triassic but left a few loners at the bar drinking until the end of the Cretaceous) but there are other models as well, including catastrophic extinction over a short time. Without this the group in question is either numerous, and easily found already, or extinct.
  2. Second, the coelacanth lineage had to go somewhere where it was unlikely to fossilize. Not too hard, since fossilization is hard, but it’s a hoop to jump through. Shallow, inland waters wouldn’t have worked at all.
  3. Third, the coelacanths had to go somewhere where the world stood still for millions of years. The world just doesn’t do this. When India slammed into Eurasia’s underbelly and blasted the Himalayas skyward coelacanths noticed that there was a bit too much silt and the populations on either side of India lost contact. For animals on land, freshwater, or in the shallow coastlines this event was probably a good bit more dramatic6. If they had failed to do this one of two things would have happened: 1) they would have died 2) they would have changed and wouldn’t be the rediscovery of an ancient fish as much as the discovery of a weird fish that, eventually, we would find was related to a group we thought had died out.
  4. Fourth – and this one is really important – coelacanths had to end up somewhere where they were fundamentally hard to find. When people invoke the coelacanth to say that ancient creatures could remain undiscovered this undiscovered bit is pretty key. Coelacanths are still pretty hard to find. They may have small population sizes, they may just be hard to catch, but it really, really helps (as the graphs above show) that they are deeper-water fish. Not only are they deeper-water fish but the Indian Ocean is probably a better place to hide from scientists than, say, the North Atlantic. Coelacanths are the sort of fish that we would expect to have trouble finding regardless of their “living fossil” status.

In short, I tend to believe that the coelacanth rolled a lot of sixes. Coelacanths really are special. Almost any other path through their history would have either ended their lineage before humans could have discovered them or made them either common or known from ancient (historical) times. It’s not impossible that another species could pull off something similar, but only because adding up probabilities doesn’t generally get you to “impossible”.



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Inoue, J. G., Miya, M., Venkatesh, B., & Nishida, M. (2005). The mitochondrial genome of Indonesian coelacanth Latimeria menadoensis (Sarcopterygii: Coelacanthiformes) and divergence time estimation between the two coelacanths. Gene, 349, 227–235.

Smith, C. L., Rand, C. S., Schaeffer, B., & Atz, J. W. (1975). Latimeria, the Living Coelacanth, Is Ovoviviparous. Science, 190(4219), 1105 LP-1106. Retrieved from

Yokoyama, S., Zhang, H., Radlwimmer, F. B., & Blow, N. S. (1999). Adaptive Evolution of Color Vision of the Comoran Coelacanth (Latimeria chalumnae). Proceedings of the National Academy of Sciences of the United States of America, 96(11), 6279–6284. Retrieved from