Crocodylian phylogeny

This is a follow-up to the last post, where I described 10 crocodylians. Again, the lengths of the branches of the cladogram don't mean anything. There you have it - 3 extant lineages, gharials, alligators and crocodiles.

10 crocodylians, scariest beasts around

Watching crocodylians, live or on TV, hits something deep in your gut (or maybe just my gut). Watching them move, stalk and pounce seems to activate some deep-seated flight instinct that says, "You'd better get out of here if you don't want to end up in someone's belly". I don't get this when I see a shark, but even a smallish gharial or caiman can induce alarm bells in my head (and gut, as it happens). But I can't stop watching - crocodylians have survived on Planet Earth for 220m years, since the Triassic period, and roughly as long as the dinosaurs, and as such, are inordinately interesting creatures. Why do they work so well?

That's not really a question I can answer in a post, or even a question that I'm actually qualified to answer. What's clear though, is that the basic crocodylian bodyplan has remained the same for a very long time, through a plethora of shapes and sizes - long snout, lots of teeth, long muscular tail, short legs, long body, semi-erect posture. Oh, and scales.

First, some phylogeny. In this post, I want to focus on members of the order Crocodylia (hence crocodylians - crocodilians include earlier species which placed in different orders). There are 3 extant lineages in this order, Gavialoidea, Alligatoroidea and Crocodyloidea. Each branch has the obvious candidates, and Alligatoroidea includes the caimans as well.

1. Rhamphosuchus

Rhamphosuchus ("beaked crocodile") lived from about 25m years ago in what is now the Indian sub-continent. It was a member of Gavialoidea, and was probably a relative of extant gharials, as can be seen from the beaked snout. The species is poorly known from fossils, but was probably between 15-18m long. The beak is indicative of a fish diet (although not exclusively). Adjacent image from Wikipedia.

Some recent work done has reinterpreted Rhamphosuchus as a member of Tomistoma, the taxon that includes false gharials. False gharials have the same thin beaked snouts as true gharials, but were thought to be members of the clade Crocodyloidea. This has now changed due to DNA analysis - false gharials are really members of Gavialoidea.

2. Gharial

Adjacent image from Laelaps, an excellent zoological blog well worth reading. Gharials are found on the Indian sub-continent, and are one of 2 extant species in Gavialoidea. The other is the false gharial (of course). The long thin snout is an evolutionary adaptation to facilitate a diet of small fish. They can be up to 6m in length. Gharials are currently endangered, and are being pushed to extinction as the sub-continent develops and grows in population. They are already extinct in Bhutan, Nepal and Myanmar, and are only found in very small numbers in Pakistan and in small numbers in India.

3. Pristichampsus

Pristichampsus belonged to a genus of entirely terrestrial crocodiles that preyed on land mammals. It was about 10m long, and lived about 6om years ago. It had long legs, and was well adapted to a running lifestyle, as it had hooves on its toes. Adjacent image from this University of Bristol website. Pristichampsus is thought to predate the split between Alligatoroidea and Crocodyloidea. It's not a member of Gavialoidea though.

4. Ceratosuchus

Ceratosuchus is thought to be a basal member of Alligatoroidea, and lived in the Palaeocene, maybe about 65m years ago. Adjacent image from Wikipedia. The main unusual feature of this creature is the 2 triangular plates on its skull, and indeed its name means "horned crocodile". Ceratosuchus lived in what is now North America.

5. Chinese alligator

There are 2 extant species of alligator, the Chinese alligator and the American alligator. The Chinese alligator is smaller, about 1.5m in length, and has an armoured belly, which is quite rare among crocodylians. What's left of their wild population can be found along the lower reaches of the Yangtze, and there are fewer than 200 wild individuals left. There are approximately 10,000 animals in captivity though. Adjacent image from danmex.org.

6. Purussaurus

Purussaurus was a giant caiman found in South America in the Miocene, about 20m years ago (caimans are members of Alligatoroidea). Adjacent image from Tetrapod Zoology, and shows the scale of this animal - it was more than 15m in length, making it a very large crocodylian indeed, one of the largest to have ever existed. Darren Naish at Tet Zoo states that it was probably aquatic at that size, and would most likely have preyed on large mammals as well as other prey. His post on Purussaurus is here.

7. Spectacled caiman

The spectacled caiman is one of 5 extant species. All are found in Latin America. The difference between a caiman and an alligator lies in the septum between the nostrils - caimans have a bony one, alligators don't. The spectacled caiman is further distinguished by a bony ridge around the eye, which makes it look as if it is wearing spectacles. They grow to 2.5m in length, and are found from southern Mexico to Argentina. Adjacent image from US Geological Survey website.

8. Mekosuchus

Mekosuchus is a genus of crocodylians (4 species) that inhabited Australasia until quite recently, with remains discovered that are less than 4,000 years old. They were entirely terrestrial, and may well have been hunted to extinction by humans. One species, mekosuchus inexpectatus, was around 2m long, and had specialised back teeth that indicated a diet of molluscs. Adjacent image from Tetrapod Zoology, which has more information.

9. Baru

Crocodyloids of the genus Baru are thought to be mekosuchines, part of the same Australasian radiation. Adjacent image from Paul Willis's site - he does reconstructions of extinct crocodilians. As can be seen from the image (of a species called baru darrowi), baru mekosuchines had short broad snouts with long curved teeth. The fossils were found in Australia, and indicate that b. darrowi reached about 5m in length. It lived about 8m years ago, and is thought to have had a mostly terrestrial predatory lifestyle. According to this site, the first baru skull to be found had part of a marsupial lion's skull in its jaws.

10. Salt water crocodile

The largest crocodyloids (as well as crocodylians) alive today, salt water crocodiles are found in Australia and throughout South East Asia. They are ocean-going, and are up to 5m long. I have a video of a salt water crocodile underwater which I'm told was taken off Sipadan Island in Borneo, so they certainly get around. It is an ambush predator, and drowns its prey rather than tear it apart (although the famous "death roll" will rip off some flesh). There are documented cases of attacks on humans.

There are 13 species of crocodyloids extant today, across 2 genuses. The dwarf crocodile sits in its own genus, all the others are more closely related.


There are more interesting species of crocodylians I haven't yet discussed, although this post gives a quick run-through of the 3 main lineages and one of the extinct out-groups. Many so-called supercrocodile fossils discovered recently actually belong to the crocodylomorphs, a more basal group. More later perhaps. In the meantime, enjoy these beasties.

Cetacean phylogeny

This is a follow-up to the last post, where I described 10 cetacean ancestors and cousins. One (Indohyus) actually belongs to the order Raoellidae and not Cetacea. The image above is a graphical representation of the phylogenetic tree. Note that unlike a proper cladogram, the lengths of the branches don't mean anything (except maybe the limits of my skill with Visio...). Hopefully it gives a clearer idea of how all these interesting creatures are / were related to each other.

10 steps on the road to modern cetaceans

Whales (by which I mean both baleen and toothed whales, including dolphins, i.e. the taxonomic order Cetacea), besides being very impressive, magnificent and intelligent creatures, are pretty interesting from a zoological and evolutionary perspective. Prior to the late 1980s, there is little or no evidence of how whales evolved. There was no taxonomic tree linking land dwelling animals to completely marine cetaceans. Professors Hans Thewissen and Philip Gingerich changed all that. Working in Pakistan, they discovered many fossils of whale ancestors, and contributed a great deal to our understanding of the evolutionary chain that led from small, shore-dwelling deer-like ancestors to modern whales.

Among the major discoveries were that among extant animals today, whales are most closely related to hippos. Previously, it was thought that whales were descended from mesonychids, a group best described as carnivorous artiodactyls (even toed ungulates). It now appears that whales are descended from herbivorous artiodactyls (hippos are herbivorous artiodactyls). Also, whales evolved relatively quickly - within 8 million years. It is also possible to trace cetacean evolution from the beginning, just after cetacean ancestors began dipping their toes into the water, to today's massive, completely marine creatures.

1. Indohyus

Indohyus (adjacent image by Carl Buell, who is a fantastic natural history artist, and blogs under the name Olduvai George) is a member of an order called Raoellidae, closely related to the artiodactyls, that lived about 48 million years ago. Hans Thewissen published a paper at the end of 2007 advancing the theory that cetaceans and raoellids descend from a creature very much like Indohyus (but which lived at least 6 million years earlier). There are multiple strands of evidence - its heavy bones, which are an adaptation common to marine mammals, and basically provide ballast; isotopic analysis of the fossils also prove that Indohyus was semi-aquatic; and best of all, Indohyus has an involucrum, which is a thickened piece of bone in the inner ear that whales have (it aids hearing underwater). No other mammal group has an involucrum.

2. Pakicetus

Pakicetus, which lived 53m years ago (adjacent image again by Carl Buell), was discovered by in Pakistan in 1981. It is classified under its own family, Pakicetidae. Hans Thewissen found complete skeletons in 2001, with adaptations of the inner ear that are today unique to modern day whales. They were the earliest cetaceans, but they were not aquatic. Pakicetus lived much like Indohyus must have, wading along swampy shores looking for fish and small animals. Note that Pakicetus was already carnivorous. It was between 1 and 2 metres long, and looked very much like a large dog.

3. Ambulocetus

Ambulocetus, which lived 50m years ago, (adjacent image is a screen capture from the BBC natural history series Walking with Beasts) was the type species of its family, Ambulocetidae. It was up 5m long, and was for most purposes a large, furry crocodile. It hunted like a crocodile too, as an ambush predator, and could also walk on land, although not very well. It swam, unlike crocodiles, with an up and down motion of the spinal cord (as dolphins do today), and had vestigial hooves on its very large hind feet. It is hypothesized that they walked somewhat like sealions, pointing their hind feet laterally and waddling forward.

4. Kutchicetus

Kutchicetus, which lived 46m years ago (adjacent image again by Carl Buell, who has made something of a hobby of drawing ancient cetaceans), was a member of the family Remingtonocetidae. This family of cetaceans was characterised by their long snouts and broad tails, which made them slightly better adapted for marine life compared to the ambulocetids. Kutchicetus was small, about the same size as an otter, and probably had a similar lifestyle.

5. Rodhocetus

Rodhocetus (adjacent image from Science magazine) lived about 46m years ago too. It was a member of the family Protocetidae. This family displayed body plan features in common with today's whales, a long streamlined body, and some species may have had a tail fluke. However, they still retained large feet, which may have been webbed to aid swimming. Rodhocetus was about the same size as a sealion, and much the same shape. This family is heterogeneous, however, and is mainly characterised by large eyes set deep under the supraorbital bone. Remingtonocetids and ambulocetids had smaller eyes.

6. Dorudon

Dorudon belongs to the family Dorudontidae, from which the modern day whale families Mysticetes (baleen whales) and Odontocetes (toothed whales, including dolphins) descend. It lived about 38m years ago, and was about 5 metres long. It was fully aquatic (as can be inferred from where the fossils were found - not only in South Asia but also in Egypt and the US, so it had a wide range in the oceans of the day), although it retained small hind legs that were probably just stubs on the torso. Dorudon was toothed (baleen evolved later), and did not display any signs of echolocation apparatus, as modern day cetaceans do. The adjacent image is from Walking with Beasts.

7. Basilosaurus

Basilosaurus lived slightly later than Dorudon, from about 37m years ago. It was discovered in 1840, and was initially mistaken for a reptile, hence the dinosaur-sounding name. It was far larger than Dorudon, up to 18m in length (due to extremely elongated vertebra), and was fully aquatic as well. It also had small vestigial hind legs. Basilosaurus had a blowhole, which was located about halfway up its snout, which is further evidence of a fully aquatic lifestyle. Hans Thewissen has found the fossilised stomach contents of a Basilosaurus, which indicate that it ate fish, including sharks. The adjacent image is from Walking with Beasts.

8. Janjucetus

Janjucetus was an early baleen whale that lived about 25 million years ago, and therefore a member of the order Mysticetes. It had not yet evolved baleen, as you can see from the image (also by Carl Buell, via Carl Zimmer's blog, The Loom). Despite not having any baleen, Janjucetus had acquired some features of modern day baleen whales, such as lower jawbones that were no longer fused at the front. It was about 3.5m long. It was a fierce creature, hunting much like today's leopard seals, a swift ambush predator that would strip flesh from bone.

9. Aetiocetus

Aetiocetus was the first baleen whale (and therefore a member of Mysticetes) found with baleen. It also had teeth, but displayed troughs in the palate bone which in modern day baleen whales hold vascular tissue that supplies blood to the roots of the baleen plates. The adjacent image is from National Geographic, via Edward T. Babinski, who has written a great deal on whale evolution on his website.

10. Squalodon

Squalodon lived between 15m and 30m years ago. It was a member of Odontocetes, which encompasses today's toothed whales. Other than its teeth, which resembled those of a shark's, it was very similar morphologically to today's dolphins, and also displays the first evidence of echolocation apparatus hat we know of. Squalodon had the beginnings of a melon-shaped forehead, which is how modern day whales amplify and direct their clicks. The adjacent image is from museumkennis.nl.


There are many more species known in the family Archaocetes, that is, all cetaceans except Odontocetes and Mysticetes. We now know of about 30 species, most from greatly detailed fossils. Of ancient Odontocetes and Mysticetes, we know of at least another 20 species. Resolving the evolutionary history of the cetaceans is a great triumph for science. Unfortunately, an even greater challenge now presents itself - how to conserve the extant species of cetaceans?

11. Yangtze river dolphin and northern right whales

In 2007, a search by the Chinese government of the Yangtze River for several baiji (image on the left from the Guardian), or Yangtze River dolphins, to fill a long-hoped for nature sanctuary found precisely zero specimens. The baiji has not been seen in the wild since about 2005, and there are no specimens in captivity. The baiji is for all intents and purposes extinct, and the same fate may befall other freshwater dolphins, particularly the Ganges dolphin and the Amazon dolphin. The northern right whale may also go extinct, as there are fewer than 300 individuals left in the North Atlantic. Part of the reason why these whales have been reduced to so few is that the North Pacific population was decimated by large illegal catches by the Soviet Union's whaling fleet in the 1960s.

With several countries beginning whaling again - Norway, Iceland and Japan so far - these whales may never recover. Vote against whaling - no one needs to eat whales, and particularly in Japan, to waste whale meat. Vote for conservation, otherwise interesting and magnificent animals such as river dolphins will disappear. There is no time to waste.

10 members of Proboscidea

Elephants are incredible creatures. They are probably as intelligent as dolphins, and communicate in a similar way, using infrasound (low frequency sound waves) instead of ultrasonic clicks. Unlike dolphins and other members of the order Cetacea however, there are only 3 species extant today. In no particular order, 10 interesting members of the order that elephants belong to - Proboscidea:

1. Gomphotherium

This elephant ancestor lived during the Miocene and Pliocene. It is considered to be a member of the gomphotheres, a group of proboscids directly ancestral to mammoths and modern day elephants. It stood about 3m tall, and had 4 tusks, two upper incisors and 2 lower incisors. Conjecture has it that Gomphotherium used the bottom tusks to dig up aquatic vegetation.

2. Platybelodon

This is another gomphothere. The upper two tusks were reasonably small compared to the size of the animal, and were probably used for defensive purposes. The bottom 2 tusks were fused, forming a kind of shovel, which helped the animal dig up more solid vegetation than aquatic plants. It also let the animal scrape bark off trees, as modern-day elephants do. Platybelodon lived during the Miocene.

3. African elephants

The African elephants are members of the genus Loxodonta, and there are thought to be 2 extant species, the African bush elephant (familiar to everyone) and the African forest elephant, a smaller species that inhabits the African jungles, has more toenails, and shorter tusks. There are probably around 10,000 elephants of both species left in the wild.

4. Mastodons

Mastodons were members of the genus Mammut (no, not mammoths, although we'll come to those). Although some species were furry like woolly mammoths, they had larger heads and differently shaped teeth compared to mammoths, and had a differently curved spine. Their tusks were up to 5m long, and they may possibly have been hunted to extinction by humans in North America 4 million years ago.

5. Mammoths

Mammoths were members of the genus Mammuthus (confusing? Yes, I know). They survived till relatively recently, up to 4,500 years ago. Some species were up to 5m at the shoulder, and there were some furry ones (see, for example, woolly mammoth). They have been found to be more closely related to Asian elephants than to African elephants. They lived mostly in the northern hemisphere, and some examples have been preserved in permafrost till excavated by scientists (and the occasional hungry hunter). Pygmy woolly mammoths were found to have lived on several islands off the coast of California and in Siberia.

6. Asian elephants

Asian elephants belong to a genus all their own, Elephas. They split from the African elephant lineage about 5 million years ago in North Africa, and then migrated across to East Asia and the sub-continent. There are several extant subspecies, the most famous one living in India and Sri Lanka. There are also populations in Malaysia, Thailand, Indonesia and Vietnam. The Chinese one however, is extinct.

7. Palaeomastodon

Palaeomastodon was a member of an eponymous genus. It lived about 38 million years ago, and was fairly small at 1 to 2m. They had 2 short tusks in the upper jaws, and flat broad protruding teeth (not quite tusks) in the lower (also protruding) jaws to scoop swamp vegetation out of the water. It did have a trunk, although it was short and probably not as flexible as those of later proboscids.

8. Moeritherium

This is an extremely basal member of Proboscidea, so basal, in fact, that it doesn't have a trunk. It lived about 50m years ago, and is regarded as the common ancestor for all members of Proboscidea so far discovered. As with many of the others it was a swamp creature than subsisted on vegetation. It looked like a tapir, and was less than a metre high. It already had slightly protruding incisors on both the upper and lower jaws, the forerunners of tusks.

9. Stegodon

Stegodon is another proboscid that may have survived into historical times. A dwarf species was present on the island of Flores (part of Indonesia) till about 12,000 years ago. The first member of the genus however stood about 4m high, and had straight tusks that were up to 10m long. These tusks were so close together that the trunk would not have been able to hang down between them, and must have been been supported by them. Intriguingly, some may still survive today.

10. Anancus

As with most of the creatures described here, Anancus refers to both a genus and the first discovered member of that genus. This proboscid died out around the same time as the mastodons did, and looked very much like modern day elephants, and was about 4m high. However, it had shorter legs and much longer tusks in proportion to its size. These tusks jutted out straight ahead, and helped the animal push trees and shrubs over in its forest habitat.


While googling around for images for this post, I discovered a creationist website claiming to "disprove" evolution using elephants as an example. The counterproof was photographic evidence of the stegodont-like elephants in Nepal (and a page that claimed that mammoths were not extinct, but showed a rather rheumatic Asian elephant). How sad - there are so many pieces of evidence to support the existence of evolution, but some people still insist in sticking their heads into the ground and denying reality. Why? Aren't these creatures amazing enough to admire without bringing ideology (I won't dignify such claptrap with the word "religion") into it?

I don't like to end on that sour note, so I'll add one more fantastic proboscid:

11. Deinotherium

According to Wikipedia, the 3rd largest land mammal to have existed - up to 5m tall and 12 tonnes in weight. It also lived during the Miocene and the Pleistocene, and had recurved tusks in the lower jaw and no tusks in the upper jaw. The shape of the tusks is puzzling - what did the animal use them for? Digging for roots is a possibility, but the animal's size and weight suggests that it also used its lower jaw as a bark stripper, or a bulldozer to push trees down.