Tetrapod Zoology

No time for anything new (working on a book chapter and putting the finishing touches to the Tet Zoo book), so here’s this, from the archives. NOT properly updated, so please be aware that it’s more than four years old…

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There are three extant manatee species*: Trichechus inunguis of the Amazon Basin, T. manatus of the Gulf of Mexico, Caribbean and US Atlantic coast as far north as Virginia, and T. senegalensis of western Africa. So, how it is that they occur on opposite sides of the Atlantic? [West Indian manatee T. manatus shown here, from wikipedia. This one was photographed in Florida, not in the middle of the Atlantic].

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* Since this article was written, a fourth living manatee species has been named: the alleged dwarf, Amazonian species Trichechus pygmaeus [type specimen shown here]. The article naming this species does not yet exist in print (it was published online by primatologist Marc van Roosmalen in 2008 after its rejection from a major journal), and at the moment it does not appear likely that T. pygmaeus will be accepted as valid by other mammalogists (Daryl Domning is on record as stating that it is based on juvenile specimens of T. inunguis: see also the Tet Zoo comment here).

A very old idea explains manatee distribution thusly: as the Americas and the Old World rifted apart in distant geological times, the ancestral manatee species got separated and, presto, a vicariance event resulted in speciation. However, I’m sure I don’t need to tell you how absurd it is, today, to suggest this. The North Atlantic opened something like 100 million years ago, yet manatees (well, those of the extant genus Trichechus anyway) are probably less than 10 my old (there being questionable Trichechus fossils from the Pliocene).

Granted, there are sirenian workers who have, indeed, suggested that Atlantic rifting might explain manatee distribution… but, those workers were publishing their papers in the early years of the 20th century (Arldt 1907). Dispersal is clearly the only option: that is, yes, manatees simply must have crossed the Atlantic at some stage, and a quick check of the literature on manatee evolution reveals many references to this hypothesis [image below shows all modern sirenian species, by the excellent Pieter Arend Folkens (best known to me for the art you see in marine mammal books, but well known to Hollywood as the designer of the whales in Star Trek IV and Free Willy). I can't believe I've never blogged about Steller's sea cow].

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Based on a spurious idea about North Atlantic currents, Simpson (1932) thought that manatees migrated from east to west. However, the evidence clearly shows west to east to be more likely; the fossil trichechine phylogenetically closest to Trichechus (Mio-Pliocene Ribodon) is South American, and in fact all fossil trichechines are American; T. manatus and T. senegalensis are more like each other than either is to T. inunguis; the nematode parasites of T. senegalensis seem to be more specialised than the nematodes of T. manatus, and so on.

So, if manatees simply must have crossed the Atlantic to get to Africa, how did they do it? Well, they swam of course, and the really cool thing is that there are also reasons for thinking that this isn’t such a big deal: it is plausible, and in fact it’s supported by strange things that manatees have done in historical times.

Daryl Domning, world expert on sirenian evolution and history, published a paper on manatee evolution in Journal of Vertebrate Paleontology last year [note: I'm referring here to 2005]. In explaining the successful invasion of the African coast by American manatees, he brought in all of the arguments given above, but tied it together with data on Amazonian and Atlantic palaeocurrents. During the Pleistocene, the subtropical North Atlantic gyre was compressed, and a cold current ran along the Eurafrican coast as far south as the Gambia. Boekschoten & Best (1988) explained how this appears to have allowed Caribbean corals and certain molluscs to colonise the eastern Atlantic, and they speculated that manatees might also have used this route. Furthermore, it turns out that an ‘appreciable fraction’ of Amazon River water gets right across the Atlantic as far as Africa, so ‘manatees taking this route might even have access to relatively fresh water for a good part of the journey, if they rode in a large lens of Amazon water’ (Domning 2005, p. 699) [map below shows the distribution of the three living manatee species. In terms of distribution, the African species is the weird one. From wikipedia].

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And the trump card? Domning (2005) suggested that purported manatee strandings made on the coasts of the North Atlantic in historical times may really have been genuine. Animals alleged to have been manatees have been reported from the shores of Greenland (1780), Scotland (1801 and 1837) and France (1782). Though we should remain sceptical about these accounts, it’s not implausible that they were genuine. Domning cites a radio-tracked Florida manatee that, in 1995, got as far as Rhode Island [UPDATE: in 2008, a manatee turned up in Sesuit Harbour, Cape Cod, Massachusetts (the individual - 'Dennis' - is shown below). It was captured and was going to be taken to Florida, but died during transit, perhaps because it was already too chilled. Some sources say that manatees are now turning up fairly regularly (every one or two years) off the Rhode Island or Massachusetts coasts].

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Here’s another spin on this. A long-standing mystery in the cryptozoological literature has been the purported presence of manatees on St. Helena, in the South Atlantic (not too far south: St. Helena is at the same latitude as Bolivia, Angola, or northern Madagascar). Nobody’s ever really known what these animals were – were they really manatees, or were they actually seals of some kind? The several descriptions provided sound to me like those of pinnipeds: mostly sea lions, and indeed most authors have concluded that this is what the animals were. After reviewing the mystery, Shuker (1995) left the case open, however. While, previously, there were good reasons for doubting the idea that manatees might ever have gotten to St. Helena, our new understanding of manatee dispersal at least renders this idea a remote possibility: in other words, it probably is just about conceivable that manatees could have gotten to St. Helena after all. But I’m speculating to the extreme.

Oh – and if, on hearing about an Atlantic crossing made by manatees you thought of this…

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… well: shame on you.

For previous Tet Zoo articles on sirenians see…

Multiple new species of large, living mammal (part II)

Refs – -

Arldt, T. 1907. Zur Atlantisfrage. Naturwissenschaftliche Wochenschift 22, 673-679.

Boekschoten, G. J. & Best, M. B. 1988. Fossil and recent shallow water corals from the Atlantic islands off western Africa. Zoologische Mededelingen 62, 99-112.

DOMNING, D. (2005). FOSSIL SIRENIA OF THE WEST ATLANTIC AND CARIBBEAN REGION. VII. PLEISTOCENE TRICHECHUS MANATUS LINNAEUS, 1758 Journal of Vertebrate Paleontology, 25 (3), 685-701 DOI: 10.1671/0272-4634(2005)025[0685:FSOTWA]2.0.CO;2

Simpson, G. S. 1932. Fossil Sirenia of Florida and the evolution of the Sirenia. American Museum of Natural History Bulletin 59, 419-503.

Shuker, K. P. N. 1995. The saga of the St. Helena sirenians. Animals & Men 4, 12-16.

Comments

#1 David Marjanović
May 10, 2010

Simpson, G. S. 1932. Fossil Sirenia of the Floria

“Of the Floria”? ~:-|
#2 Darren Naish
May 10, 2010

Hmm… Hold on.
#3 TheBrummell
May 10, 2010

So, what about the two other species illustrated by Folkens? I know Steller’s Sea Cow was exterminated in historical times, something like the mid-1800s, right? Its distribution was northern Pacific, has there been discussion of how they got there? And what are Dugongs, where did / do they live, and are they extinct? I’ve seen (and heard) the name from time to time, but I know basically nothing about them. I guess I’ll risk massive procrastination and dive into Wikipedia…
#4 Sili
May 10, 2010

I can’t believe I’ve never blogged about Steller’s sea cow

Well, it does look rather like a giant leech …
#5 Jorge Velez-Juarbe
May 10, 2010

Steller’s sea cow (Hydrodamalis gigas) and other hydrodamalines (Dusisiren spp. & Hydrodamalis spp.) likely evolved from a halitheriine dugongid similar to Metaxytherium arctodites from the Middle Miocene of Baja California and California (Aranda-Manteca et al., 1994). Other species of Metaxytherium are known from the Mediterranean, Western Atlantic and Caribbean (WAC) regions (they seem to have originated in the WAC during the Oligocene). Getting to the eastern Pacific from the Caribbean was no problem (and the most likely route) as the Central American seaway was open until about 2 million years ago. Hydrodamalines show an increase in body size, reduction and eventual loss of dentition (algae are not as hard to chew as seagrasses), and in Hydrodamalis modification of forelimbs.
Dugongs (Dugong dugon) are the last remnant of a much more diverse group (the Dugonginae), they are now found in the Indo-Pacific region, but its fossil relatives are found in the Indian, Mediterranean, Eastern Pacific, Western Atlantic and Caribbean regions. As for the evolutionary history of modern dugong, an undescribed skull (very similar to D. dugon) from the Pleistocene of Florida (unfortunately in private hands), seems to indicate that their common ancestor lived between the WAC and Eastern Pacific, being split into two populations by the rise of the isthmus of Panama, one leading to modern dugong the other to the extinct Florida critter.
#6 Riggy
May 10, 2010

Have you ever heard (or seen) about the Florida sea monster video? Well a man videotape alot footage of the creature at different times. What’s interesting is that the animal is real, let alone looks a sea cow but with seal like features (to give you an idea of what it looks if you haven’t seen it, it looks a manatee with the head of a leapard seal and a trident tail, buts not fake).

Here’s one sample of it for people who are curious:http://www.youtube.com/index?desktop_uri=%2F&gl=US#/watch?client=mv-google&tspv=v1&v=GtFyv8vAhtY
#7 Frank
May 10, 2010

The distribution is wrong… The West Indian Manatee goes way down in Brazil, as south as Pernambuco. Trust me, I live there…

In fact, one of the most notable conservation projects in Brasil is Projeto Peixe-Boi (‘Manatee Project’), which is located in Itamaracá, Pernambuco.
#8 Anthony Docimo
May 10, 2010

an excellent repost (with updated notes within)…and a nice Huge Manatee to boot.

thank you.
#9 Cameron
May 10, 2010

Riggy #6:

Here’s a working link

There’s nothing in the video that suggests a cryptid, it’s probably this individual manatee. Classic Phylogenetic Roulette.
#10 AD
May 10, 2010

Neat post. I am going to comment on a mere tangental point. The ice-age compression of the N Atlantic subtropic gyre circulation and an associated cold current going equatorward all the way to Gambia I can understand. However how would this help Caribbean corals get to the eastern Atlantic? The “bottom” of the NA subtropical gyre is defined by the north equatorial current flowing west. although there is the (relatively weak) north equatorial countercurrent flowing east, that does not really follow from a statement about the equatorward eastern boundary current.

Nonetheless, the Atlantic equatorial currents are weird- look at Pacific currents for a better idea of what surface ocean circulation *should* look like- and they may have been even weirder during a Pleistocene compression of the subtropics. Maybe there was a strong equatorial countercurrent moving animals west to east?
#11 shiva
May 10, 2010

“Well, it does look rather like a giant leech … ”

That reconstruction of Steller’s sea cow made me think of the reports of some (Scottish and Norwegian, IIRC?) lake monsters that described them as resembling gigantic slugs/worms/leeches.

What are the “rings” round it? just skin wrinkles, or something else? They (as well as the smallness and odd shape of the head) are a major contributing factor to making it look like a monster annelid.

As for that “Florida sea monster” video, IMO it’s a manatee with a tail damaged by a boat propellor (possibly when it was much younger), much as the “sawback monster” of the Amazon was a boto with a propellor-damaged dorsal fin.
#12 Zach Miller
May 10, 2010

I await the full-length post about the Stellar Sea Cow, Darren.
#13 neil
May 10, 2010

All this raises the question Darren – did you have a tip off on the Mediterranean Gray Whale story? Because, I have to say, it kind of makes manatees bobbing across the Atlantic seem um, a little less impressive.
#14 Hai~Ren
May 11, 2010

The gray whale in Israel is such an incredible story. As much as I want to believe that this might be a survivor from the long-extinct Atlantic population, I think it would probably be more likely that this whale has seriously wandered a long way from the Pacific.

Either that, or whales have learned how to teleport.
#15 John Harshman
May 11, 2010

Speaking as a molecular systematist, I’m appalled that there is only a single Genbank entry for Steller’s sea cow, a partial cytochrome b sequence. Can’t we do better than this? It comes from Ozawa et al. 1997. Phylogenetic position of mammoth and Steller’s sea cow within Tethytheria demonstrated by mitochondrial DNA sequences. J. Mol. Evol. 44:406-413.

And all it established is that there’s a trichotomy among Steller’s, manatee, and dugong, presumably meaning a soft polytomy. Oh, and using the typical 2%/my, it finds this divergence to be 22my.

Hey, why haven’t you ever written on Steller’s sea cow? Where are the rumors of a relict population? Too far from the Pacific for Nessie to travel? And are there any decent preserved specimens?
#16 John Scanlon FCD
May 11, 2010

I’d go with the ‘teleport’ suggestion. As it says in the BBC story,

“Over a lifetime, a gray whale migrates the equivalent distance of a return trip to the moon.”

The writers of the current Dr Who series had prior knowledge of these space-travelling whales, which proves it’s all true.
#17 Dartian
May 11, 2010

John H.:

Hey, why haven’t you ever written on Steller’s sea cow?

Because he’s so lazy, that’s why.

And are there any decent preserved specimens?

There are a few complete, or near-complete, skeletons in museums around the world.

And W. T. F.?! A grey whale in the Mediterranean?! For realz?

John S.:

As it says in the BBC story

From the same story:

It would also have had to swim a circuitous route to reach the Mediterranean, perhaps taking the extremely unlikely course of swimming up a major swimming canal that links the Pacific and Atlantic. That raises the possibility that the whale did not swim into the Mediterranean Sea alone, but is part of a population that has recolonised parts of the Atlantic Ocean, and the Mediterranean Sea that links to it.

Don’t ask me what a ‘major swimming canal’ is – do they perhaps mean the Panama Canal? Anyway, it seems that the experts consulted by the BBC are assuming that the whale (or whales) came from the west and crossed the Atlantic. Why could it not as well have come from the east, across the Indian Ocean? (Does anyone know if a whale could pass through the Suez Canal unnoticed, or indeed pass through it at all?)

Hoping that this incident might indicate grey whale recolonisation of the Atlantic is, unfortunately, a wee bit premature methinks.
#18 Nahan Myers
May 11, 2010

Speaking of trans-oceanic transport, my daughter thinks she spotted an amphisbaenian in Hawaii: scales, eyeless, tail and head shape identical, grey and fast, nipped a hole in her fishnet and escaped. She also found something red and worm-like, but with a backbone; a caecilian? It’s her first day there. Would these have come in potted plants?
#19 Andreas Johansson
May 11, 2010

Is the “hole” in T. manatus distribution in the north-central Gulf of Mexico accurate, and if so is it known what causes it?
#20 Yashca
May 11, 2010

“Animals alleged to have been manatees have been reported from the shores of Greenland (1780), Scotland (1801 and 1837) and France (1782).”

Are these records from a book or something? They sound like a good read.
#21 David Marjanović
May 11, 2010

Is the “hole” in T. manatus distribution in the north-central Gulf of Mexico accurate, and if so is it known what causes it?

The mud from the Mississippi delta?
#22 Andreas Johansson
May 11, 2010

Seems unlikely the Mississippi would keep them away if the Orinoco and the Amazon do not?
#23 Sili
May 11, 2010

Don’t ask me what a ‘major swimming canal’ is – do they perhaps mean the Panama Canal?

I imagine it’s some sort of shared migration route/gyre/stream. I think someone would have noticed a whale in the Panama Canal – you know, with the sluices an’ all.
#24 Hai~Ren
May 11, 2010

Is that where the Gulf of Mexico “dead zone” is located? Looks like it.
#25 Jorge Velez-Juarbe
May 11, 2010

Manatees were present in the Pleistocene (or latter) in the Ohio and Mississippi rivers, and are still rarely found in the area where the “hole” is.

Williams, M. E. & D. P. Domning. 2004. Pleistocene or post-Pleistocene manatees in the Mississippi and Ohio river valleys. Marine Mammal Science 20(1):167-176.
#26 Pavel Volkov
May 11, 2010

And in Hans Christian Andersen’s tale “The Great Sea Serpent” (about the trans-Atlantic cable joining Europe and America) the old sea cow is mentioned. How do you think, who was this animal? Its sirenian origin is clear – it is not mixed with seals and whales (also heroes of the story). And sea cow (“vacca marina”) may be seen on old Medieval maps of Atlantic Ocean near long-necked “Physeterus”, giant crayfishes, tusked whales and horned “sea devils”.
#27 Craig York
May 11, 2010

You posted the image, and I should be ashamed?! harumph.

Like some others here, I’d love to see you writing on Stellars’ Sea Cow-and if you could work in some informed
speculation on his mysterious “Sea Ape”, well, bonus, as
the kids say.
#28 Andreas Johansson
May 11, 2010

@Jorge Velez-Juarbe:
Thank you.
#29 Nathan Myers
May 11, 2010

The Orinoco and Amazon are not so choked with fertilizer as the Mississippi is. The hole in the range corresponds to the resulting oxygen-depleted region of the gulf. No vertebrates live there, but cnidarians can.
#30 Jerzy
May 11, 2010

BTW, Walker’s Mammals of the World says that Dugong historically occured in the east Mediterranean sea. Anybody knows more?

Walker’s is actually full of interesting historical data about mammals – eg. Barbary Macaques in Spain and France. I never saw some of them supported/refuted elsewhere. Sometimes I don’t know what to make of it.
#31 AD
May 11, 2010

And speaking of possibly using paleocurrents to get from here to there:
Mammals primarily colonized Madagascar during the Paleogene when currents flowed opposite to how they flow today:
http://www.nature.com/nature/journal/v463/n7281/abs/nature08706.html
#32 Monado, FCD
May 11, 2010

Riggy and Cameron, I notice that the split tail of the manatee in question is not symmetrical. It looks to me as if those splits were cut by a slightly curved propeller.
#33 Adam F
May 11, 2010

Manatees breathe air, they shouldn’t need oxygenated water. My bet is on temperature: in the winter manatees need warm water to survive-even in central Florida they are stuck hanging out in warm springs and power plant outflows. In the summer they do range north on the coasts, but mostly don’t bother swimming too far. Assuming they start from overwintering points at some latitude crossing mid to lower Florida and Texas/Mexico, you can see the range extends about the same distance north, representing seasonal swimming distance. The central Gulf just doesn’t have a southern overwintering spot nearby.

Now someone who knows more about Brazil should explain why their range doesn’t extend further south.
#34 Nathan Myers
May 11, 2010

By the way, I have read that manatees are a major threat to otherwise threatened sea-grass range around Florida.
#35 Nathan Myers
May 11, 2010

The plants that manatees live on might not be able to grow around the Mississippi outflow any more. I wonder about herbicide concentration and sensitivity.
#36 Dartian
May 12, 2010

Jerzy:

Walker’s Mammals of the World says that Dugong historically occured in the east Mediterranean sea. Anybody knows more?

There appears to be at least one recent-ish record. Boudouresque & Verlaque (2002) incidentally cite Por (1978), who says that a dugong has once been observed along the Mediterranean coast of Israel. Apparently (I haven’t seen the original source), Por thought that this individual was a genuine vagrant that had swam through the Suez Canal; if that is true, then aquatic megafauna too might have the potential to become Lessepsian migrants…

References:

Boudouresque, C.F. & Verlaque, M. 2002. Biological pollution in the Mediterranean Sea: invasive versus introduced macrophytes. Marine Pollution Bulletin 44, 32-38.

Por, F.D. 1978. Lessepsian Migrations: The Influx of Red Sea Biota into the Mediterranean by Way of the Suez Canal, Springer, Berlin.
#37 Dartian
May 12, 2010

Myself:

Does anyone know if a whale could pass through the Suez Canal unnoticed, or indeed pass through it at all?

I had a look at the vagrant cetacean records from the Mediterranean, and circumstantial evidence suggests that the Indo-Pacific humpback dolphin Sousa chinensis is another large marine mammal species that has occasionally succeeded in passing through the Suez Canal. This dolphin has been observed a couple of times along the Mediterranean coasts of Egypt and Israel, respectively – that is, in the extreme southeastern corner of the Mediterranean Sea.

I am not suggesting that this is the most likely way that the grey whale got into the Mediterranean, and nor do I wish to exaggerate the importance of this ‘trans-Suez’ marine mammal dispersal route. But since dolphins and dugongs apparently sometimes pass through the canal from the Red Sea to the Mediterranean, maybe it’s not out of the question that a larger whale could do the same?
#38 Jerzy
May 12, 2010

Walker referred to ancient presence – presumably long before construction of the Suez Canal!
#39 Jerzy
May 12, 2010

In Walker’s: ‘Kingdon (1971) indicated that this species was present historically in the eastern Mediterranean sea.’

Who knows. Maybe prehistorically it was possible for Dugong to cross via some temporary waterway. Wikipedia mentions, incredibly, attempts to dig the canal in Ancient Egyptian times on the site of current Suez Canal. Also, maybe Nile shifted the course, or todays hypersaline lake was temporary a narrow sea channel?
#40 Dartian
May 14, 2010

Jerzy:

In Walker’s: ‘Kingdon (1971) indicated that this species was present historically in the eastern Mediterranean sea.’

I had a look at Kingdon’s book (it’s volume 1 of his awesome series East African Mammals: An Atlas of Evolution in Africa, in case anyone is interested). He does indeed make the claim that Dugong dugon used to live in the Mediterranean in Ancient times, but he does not back that up with any solid references. His sirenian chapter also includes a distribution map in which the entire Mediterranean Sea is shown as dugong territory! Pending further evidence, I would treat Kingdon’s claims regarding Mediterranean dugongs with considerable scepticism.

attempts to dig the canal in Ancient Egyptian times on the site of current Suez Canal

Heh, they mention that in Asterix and Cleopatra, so it must be true!
#41 David Marjanović
May 16, 2010

Wikipedia mentions, incredibly, attempts to dig the canal in Ancient Egyptian times on the site of current Suez Canal.

“Incredibly”? All you need is a huge workforce, and the Egyptians had that. The canal was dug several times, the last time under Persian rule.

It never lasted very long, because the sand isn’t stable.

There’s no evidence for a natural seaway having ever existed in that region.
#42 Jorge Velez-Juarbe
May 17, 2010

His sirenian chapter also includes a distribution map in which the entire Mediterranean Sea is shown as dugong territory!

To my knowledge, Dugong dugon was never a permanent inhabitant of the Mediterranean, of course I’m not ruling out vagrants. There hasn’t been dugongids in that region since the extinction of Metaxytherium subapenninum about 3 million years ago.
#43 Manatees
May 28, 2010

Looks like Russ got his 10 minutes of fame (and for a really, really stupid thing. Almost as stupid as balloonboy daddy.
#44 Dino
June 6, 2010

The distribution is wrong for the Amazonian Manatee, it lives deep within Peru too.
#45 Christopher Sellars
November 22, 2010

As Dino commented, the distribution is wrong for the amazonian manatee, nearly all the rivers in eastern Bolivia contain manatees, even in the San Pablo/San Julian river just 200kms north of Santa cruz de la Sierra. I have swum alongside them in the river Mamore. Manatees have never been considered “edible” in Bolivia unlike in Brazil. Coincidentally, after living 30 years in eastern Bolivia, I now live in Vila Velha, Ilha de Itamaracá,Pernambuco just 2 km from the IBAMA manatee investigation centre, and yes, the west indian manatee is found all along the coastline here, and even farther south in the states of Alagoas and Sergipe. cheers, Chris.