Midwestern Marine Mammals of the Pleistocene?

I was originally planning to use the title "Sperm Whales in Lake Erie?", but it just didn't work out quite right. It would stand out as one of the least likely titles possible though. As I'm alluding to, fossils of cetaceans and pinnipeds have actually been reported from the Pleistocene of...Michigan. And yes, I checked to make sure that none of the publications were published on April 1st.

Handley 1953 appears to be the first person to report these fossils to the scientific community, despite having a great deal of reservation about them. The first find was reported from 1861 but the specimen was never identified with a species, not specified as being from the surface or dug up, and was subsequently lost. A walrus (Odebenus) baculum (penis bone) was found outside of Gaylord, Michigan in a gravel pit with other bones in 1914 and was given to the University of Michigan. Handley himself examined three different alleged find reported in 1930. The first was a rib from Balaenoptera physalus (fin whale), found sitting vertically in loose sand of an "Arkona" age during a cellar excavation. A lumbar vertebrae and two ribs from a sperm whale (Physeter) were taken from a swamp, although exactly what formation it came from was not recorded. Another rib, this time from either a bowhead whale (Balaena) or possibly Eubalaena was found five feet down in Nipissing beach in Oscoda county. The anterior part of a walrus skull was found on Mackinac island in a beach deposit, but it may have had markings produced by humans on it.

Handley noted at the beginning that he only wanted to offer facts on the specimens and didn't make any conclusions. He did note specimens of marine mammals (including Balaena) from the Ottowa valley of Ontario and ended optimistically that more fossils may turn up in Michigan. Unfortunately none of the later publications are available to me, except Williams & Domning 2004 which seems to do a pretty thorough summary. The Ontario specimens are quite numerous (23 whales, 22 seals, 14+ walruses), have nearly complete specimens and are found in areas with preserved marine invertebrates - so it definitely appears that this area was part of the Champlain Sea. However, it would still take an unknown branch of the sea to explain the fossils. It did appear that occasionally large lakes in the Great Lake area (e.g. Lake Chicago) would flow into the Mississippi River drainage system and the Mohawk/Hudson (Larson and Schaetzl 2001), and it was proposed that this could have been another method for the whales to enter (Williams & Domning 2004). This still appears to have been hundreds of miles of swimming up river, and none of the authors speculated on whether or not the whales actually inhabited the areas or were just vagrants.

Or did people have a part to play? Several other authors have noted that it is strange for bones to show up totally unmodified by humans after being carried hundreds of miles and out of archaeological context. In 1988, radiocarbon dating was done and concluded that the bowhead whale was from 750 +/- 60 years before present, the fin whale was from 720 +/- 70 B.P. and possibly 190 years before present for the sperm whale (i.e. late 18th century?!). Were these not even fossils? While it appears there was some problem with the sperm whale date and the walruses weren't tested, it is clear that the only way the fossils could have gotten to their present location is by human transportation. But how did some end up several feet under the ground in Pleistocene deposits? Williams and Domning mention that a few authors that suggested a 19th/20th century hoax of some sort. Unless claiming bones were from incorrect strata was the thing to do back then in Michigan, I'm confused as to what exactly the motivation for a hoax would be. Saying that something is too irrational for a person to do isn't a very good argument, and I think any further investigation will likely be more a matter of anthropology than palaeontology.

It still is possible that a few cetaceans may have accidentally wandered into the Great Lakes or their precursors since there apparently were connections to the sea, but they didn't appear to have left us any evidence. Despite discussing Michigan's alleged marine mammals at length, Williams and Domning 2004 concentrate on a different subject: manatee fossils in inland North America. Part of a left rib was found in 1976 in Springfield Ohio was found to be identical to the West Indian manatee (Tricbecbus manatus) and was dated to about 2000 years before present (certainly not the Pleistocene). A radius and ulna were found on the Arkansas/Mississippi border in 1991 and was not dated. The authors conclude against any association with the Chesapeake Sea (which occurred much earlier) and conclude that the manatees most likely traveled up the river; this is notable because a 2001 source they used stated that they didn't go up the Mississippi despite living right near its mouth. After the events in Michigan, human transportation can't be fully ruled out, but it doesn't need to be.

It was widely reported in 2006 that a manatee actually swam over 700 miles up the Mississippi and subsequently died near Tennessee (north of the 2nd fossil find). Another manatee the same year set a northern record by making it up to Cape Cod. The idea of a freak occurrence getting fossilized seems remote, and it seems likely in the past their populations extended up considerably more northwards. Manatees seem prone to wandering, as Darren said a while back they had to have crossed the Atlantic at some point and may have made it all the way up to Europe (and Greenland) despite not being able to drink salt water. It seems that animals are more capable of turning up in bizarre places than we're readily willing to admit, but the idea of sperm whales in Lake Erie (and elephants in Australia) in historical times is really a bit much.

References:

Handley Charles O., Jr. 1953. Marine mammals in Michigan Pleistocene beaches. Journal of
Mammalogy 34 (2), 252-253. (Under: General Notes)

Larson, Grahame and Schaetzl, Randall. 2001. Origin and Evolution of the Great Lakes. J. Great Lakes Res. 27(4):518–546

Williams, Michael E. and Domning, Daryl P. 2004. Pleistocene or post-Pleistocene manatees in the Mississippi and Ohio River Valleys. Marine Mammal Science 20 (1): 167-176.

A Geeky New Banner

On account of me not having used colored pencils in recent memory, I'm actually rather surprised at the quality of this. Well, the original looks much sharper and has a blue background (does my scanner not pick up blue?), but hey, it looks, uh, presentable? Now don't get me wrong, this is pretty far removed from those fancy, professional looking banners you might see at Scienceblogs or something. Instead of adding words to a picture, I definitely went for the more homemade look. Perhaps it is commentary on the very nature of this blog.

In the geeky spirit of this page, I might as well reveal the animals in the picture:


Top Row:

Dermophis sp.
A very strange looking lissamphibian (a caecilian) last seen here. A picture at Darren's post also provided inspiration.

Lissodelphis borealis
Previously mentioned here, this is from an image I never got permission to use. Well, I got it from the author, just not the publisher. The original still looks a little skinnier.

Hydrurga leptonyx
The Leopard Seal has not yet been mentioned on this blog. This is one of my favorites.


Middle Row:

Scutisorex somereni
The hero shrew! I felt I needed a nice nondescript small mammalian bust in this drawing for some reason. This species and its incredibly bizarre spine are discussed here.

Monjurosuchus sp.
My only extinct animal (a monjurusuchid choristodere) was discussed and drawn here. Ah, that appears to be the last time I used colored pencils.

Cathartes aura
The turkey vulture. Not outright mentioned, but cathartids are discussed here and here.

Fregata sp.
A generalized male frigatebird with what appears to be semi-inflated throat pouch. Discussed here.


Bottom Row:

Astronotus ocellatus
The Oscar or velvet cichlid. Not discussed (yet), but I did own a few in my childhood.

Leptoptilos crumeniferus
The Marabou stork. Mentioned a few times but not discussed (yet).

Cirroteuthis muelleri
A cirrate octopode, a group discussed here and mentioned sporadically.

Mesoplodon densirostris
The dense-beaked whale, owner of the most dense bone known (in the skull). This species wasn't discussed (yet), but potentially new mesoplodont whales were discussed here and here.

Rafetus swinhoei?, R. leloii?
The closest thing to a cryptid is this, the Hoan Kiem Lake turtle. Although it looks like some crude jumble, I can provide visual confirmation that this species really is that bizarre looking. Although not outright discussed, I previously exploited the bizarreness of softshell turtles for this post.

Smutsia temmincki
That bipedal pangolin mentioned here. And no, it probably shouldn't be in Manis.


Well, my spring break is coming to an unfortunate end.

The Surprisingly Predatory Sleeper Sharks

Sleeper sharks (Somniosus spp.) belong to the family Somniosidae in the order Squaliformes, so they're relatives of dogfish (Squalidae). The taxonomy of this genus has recently been given an overhaul by Yano et al. 2004, creating two sub-genera and re-establishing two other species. The sub-genus Rhinoscymnus is composed of two species: S. rostratus from the Mediterranean and North Atlantic and S. longus from the Pacific. They were formerly grouped into one species and are both under 1.4 m (4'7"), a calcified vertebral column, leaf-shaped denticles, and semi-oblique cusps in the lower jaw. For this blog post at least I'll be focusing on Somniosus (Somniosus) spp., the huge sleeper and Greenland sharks.

These sharks are identified by teeth with strongly oblique cusps in the lower jaw, hooked denticles, an uncalcified spine with an expanded notochord and much larger size. (Yano et al. 2004). It appears that sharks over 4 m (13 feet) are not uncommon, and the three species are widely cited as reaching 5-7 meters (16-23 feet) in total length (Yano et al. 2007). Using Table 1 from Yano et al. 2007, it can be calculated that a 7 meter Somniosus would weigh between 3500 and 3800 kg (~4 tons) and presumably rival the largest Carcharodon carcharias in size (my assumption, not theirs). These sharks can be differentiated from all other species by their range, S. microcephalus and S. pacificus are the only two species of shark known to live above the Arctic circle.

Yano et al. 2004 define three species defined by range and morphology: S. microcephalus from the Arctic and North Atlantic, S. pacificus from the North Pacific and S. antarcticus from the South Indo-Pacific and South Atlantic. A paper by Benz et al. which I unfortunately can't access, describes the first record of the subgenus from the Gulf of Mexico (note the distribution) and noted that there was no taxonomic character that could clearly identify each member of the group. The abstract didn't cast doubt on the existence of species, just some identification records. Oh, and apparently this video is the observation mentioned. Murray et al. 2008 note the rather similar morphology and supported the notion of S. microcephalus as a separate species. S. pacificus and S. antarcticus and a possibly distinct population from Taiwan did not appear to be separate species, but it is noted that more mtDNA analysis is needed to determine exactly what the status of them is. Curiously, Parin and Kotlyar 2007 note the capture of a small (1.4 m) shark showing characteristics (hook shaped denticles, number of turns in spiral valve) of the Somniosus subgenus from the southeastern Pacific that was not identifiable to any of the known species. Since sleeper sharks seem to be much more widespread in tropical (and very deep) waters than what was previously thought there's still probably a lot of work left to be done.

One of the most famous traits of the sleeper sharks is a parasitic infection frequently found in their eyes. Ommatokoita elongata is a copepod which has been found attached to the eyes of northern hemisphere sleeper/Greenland sharks (Benz et al. 2002) although I'm not sure about the southern hemisphere population. The cornea is smooth and apparently the ideal location for attachment (it doesn't have denticles), and there is typically one female specimen per eye (sometimes with larvae present) (Benz et al. 2002). It compromises the ability of the eye to form images, but not to detect light and it is believed that the sharks have no debilitations* (Benz et al. 2002.). Older articles and Wikipedia claim that the parasite is bioluminescent and acts as a fishing lure (making it mutualism, not parasitism) BUT Benz et al. 2002 continuously refer to them as parasites and it has been specifically stated that they are not bioluminescent.

*In another abstract I can't access, it is noted Greenland sharks in the St. Lawrence River do have a different pattern of behavior involving different intra- and interspecific aggression and predatory behavior.

The null idea of a fishing lure was also used to explain how the supposedly sluggish sleeper and Greenland sharks were able to catch the prey that they did. The paper that was the genesis of this post was Hoff and Morrice 2008 which documented bite wounds on elephant seals from sleeper sharks (S. antarcticus) . On account of the shark's blindness and apparent sluggishness, this seems to be quite remarkable. The bites* were not only found on juveniles and females, but on adult male elephant seals as well which were around the same length as the shark (judging from the size of the bite) (Hoff and Morrice 2008). This suggests that sleepers could be capable of successful predation and raises the possibility that other organisms found in the stomach of sleepers weren't just there as a result of scavenging. It is suggested that the sharks are capable of sneaking up on them using cryptic coloration (and possibly by gliding) and have a large buccal cavity which allows for suction feeding (Sigler et al. 2006). Even our speedy friend Lissodelphis wound up in the stomach of a sleeper shark, apparently from a living specimen. Since sleeper sharks travel towards the surface at night (Hulbert et al. 2006) and have been observed on the surface (Stokesbury 2005) I can't help but wonder if it sneaks up on sleeping cetaceans. Elephant seals may sleep while diving.

* There were also unidentified "conical" shark bites (not from sleepers or great whites) on male seals. Do the bites of the bluntnose sixgill (Hexanchus griseus) meet this description?

Of great interest to me is the fact that some very large cephalopods wound up inside sleeper sharks. In examinations of 36 sleeper shark stomachs in the Southern Ocean, all of them contained cephalopods - one of which was a large unknown cirrate. Cherel and Duhamel noted that sleeper sharks had a sperm whale-like diet; four of the gigantic squids I discussed earlier (Kondakovia, Taningia, Architeuthis and Mesonychoteuthis) were found in the stomachs of sleeper sharks. That's right, both the giant and colossal squid were eaten by this species. Incredibly, the average size of cephalopod prey eaten by the shark was slightly larger than that of the sperm whale. The authors do state that it is problematic exactly how sleeper sharks could prey on the giant cephalopods, and state that it is unknown if the giant and colossal squids were eaten while alive or scavenged. It is troubling for the ~4 meter animals in the study, but some of the largest sleepers presumably weighing around 4 tons would considerably outweigh the giant cephalopods.


I'm not trying to suggest that sleeper and Greenland sharks are unstoppable killing machines, certainly a lot of what they eat has been scavenged. It still seems that the predatory abilities of this species is much greater than what is expected, as demonstrated by attacks on similarly sized (or more massive?) elephant seals. Evidence for sharks 7 meters long is based on video evidence as far as I know, but it appears to be fairly strong. Such specimens comparable to the largest white sharks would be impressive predators, even if they are blind and sneak up on prey.

References:

Benz, George W. et al. 2002. Ocular lesions associated with attachment of the copepod Ommatokoita elongata (Lernaeopodidae: Siphonostomatoida) to corneas of Pacific sleeper sharks Somniosus pacificus captured off Alaska in Prince William Sound. J. Parasitol., 88(3), pp. 474–481

Benz, George W. et al. 2004. A second species of Arctic shark: Pacific sleeper shark Somniosus pacificus from Point Hope, Alaska. Polar Biol 27: 250–25

Cherel, Yves and Duhamel, Guy. 2004. Antarctic jaws: cephalopod prey of sharks in Kerguelen waters. Deep-Sea Research I 51 17–31

Hoff, John van den and Morrice, Margaret G. 2008. Sleeper shark (Somniosus antarcticus) and other bite wounds observed on southern elephant seals (Mirounga leonina) at Macquarie Island. Marine Mammal Science 24(1): 239–247

Hulbert, L. B. et al. 2006. Depth and movement behaviour of the Pacific sleeper shark in the north-east Pacific Ocean. Journal of Fish Biology 6, 406-425.

Murray, Brent William et al. 2008. Mitochondrial cytochrome b variation in sleeper sharks
(Squaliformes: Somniosidae). Mar Biol 153:1015–1022

Parin, N. V. and Kotlyar, A. N. 2007. On Finding of Shark of the Genus Somniosus (Squalidae) at the Submarine Ridge of Nazca (Southeastern Pacific). Journal of Ichthyology, Vol. 47, No. 8, pp. 669–672.

Sigler, M. F. et al. 2006. Diet of Pacific sleeper shark, a potential Steller sea lion predator, in the north-east Pacific Ocean. Journal of Fish Biology 69, 392–405

Stokesbury, Michael J. W. et al. 2005. Movement and environmental preferences of Greenland sharks (Somniosus microcephalus) electronically tagged in the St. Lawrence Estuary, Canada. Marine Biology 148 (1): 159-165.

Yano, Kazunari et al. 2004. A review of the systematics of the sleeper shark genus Somniosus with redescriptions of Somniosus (Somniosus) antarcticus and Somniosus (Rhinoscymnus) longus (Squaliformes: Somniosidae). Ichthyological Research. 51: 360-373.

Yano, Kazunari et al. 2007. Distribution, reproduction and feeding of the Greenland shark Somniosus (Somniosus) microcephalus, with notes on two other sleeper sharks, Somniosus (Somniosus) pacificus and Somniosus (Somniosus) antarcticus. Journal of Fish Biology 70, 374–390

Aquatic Stem-Group Synapsids?

Simply put, the stem-group synapsids are a fascinating group that has been incredibly overlooked by popular culture. We are synapsids, but it seems like the only stem-group species widely known is the early Permian pelycosaur Dimetrodon. As the Permian progressed, synapsids diversified into many groups ranging from carnivores to herbivores, the size of a rat to species over a ton. After the end-Permian extinction wiped out most groups and the archosaurs became the dominant land animals, a group of cynodonts evolved into us crown-group synapsids (mammals). While not as "spectacular" as the dinosaurs, archosaurs and other diapsids, they are relevant to our own evolution - and they're fairly bizarre looking to boot. Stem-group synapsids are unfamiliar enough that they're not even blessed with a halfway decent common name. They've been called "mammal-like reptiles", but this is deceptive since they didn't evolve from reptiles and don't have any of their derived characters. Some of the proposed names include "Protomammals", "Paramammals" and "Stem-Mammals"(a discussion is here), but the one I chose for the title is still the best in my opinion.

I've wanted to blog on this, dare I say, exotic group for some time, but it just never really worked out. When it was nebulously suggested that some marine cryptids were "transitional animal(s) with reptilian and mammalian characteristics" (ahem...), this got me wondering if any of these early mammal relatives took to the water. While mammals have evolved numerous semi and fully aquatic forms, earlier synapsids did not evolve fully marine forms. This certainly makes the notion of a living marine one pretty dang bizarre. So, how aquatic did stem-group synapsids manage to become?

Germain and Laurin 2005 studied the microstructure of extinct and extant amniotes at the mid-diaphyseal level in order to determine lifestyle (terrestrial, amphibious or aquatic). One taxa studied was Ophiacodon, a pelycosaur of the family Ophiacodontidae (which includes some of the earliest known amniotes). Their model predicted an aquatic lifestyle for this species, which others predicted from morphology and the fact that it was found with fish and amphibians or even marine deposits. However, the authors note that the limbs of this species show no adaptations to an aquatic lifestyle and due to the lack of animals at its size, clustering in the study could be considered ambiguous. This paper appears to be a warmup of sorts, the authors intend to determine the lifestyle of early amniotes (they obviously plump for an amphibious one) but only used three fossil species to do so! As early an amniote as Ophiacodon is, it is still probably far too derived to be of any use. Perhaps studying fossils like Casineria would be of more use. Hopefully with future studies the lifestyle of Ophiacodon would be made more clear, oh yeah, and determine how early amniotes lived.

Ophiacodon, from here (no copyright). Since this is a rather common species, we can assume this reconstruction is fairly accurate. Superficially it doesn't seem to have any features of an aquatic creature. The snout is noted as being long and narrow with a lot of teeth, and would be characteristic of a piscivore if it wasn't so high. It could be possible for bone density and microstructure to be artifacts of some other lifestyle. Still, if it was found in those deposits, I guess it could have hung around the water a little...

One of the most fascinating taxa suggested to be somewhat aquatic is Lystrosaurus, a herbivorous dicynodont genus which straddled the Permian and Triassic. This means that the genus survived an event which killed off 70% of terrestrial vertebrate families, although a few species did not locally survive (Botha & Smith 2007). A few (probably carnivorous) therocephalian genera also straddled the barrier but with nowhere near the abundance of Lystrosaurus (Botha & Smith 2007). It has been noted that the genus did not have elongated neural spines and an expanded chest with thick ribs compared to other genera; it was previously suggested that these features indicated enlarged lungs which helped them survive the extinction event (Botha & Smith 2007). Earlier workers suggested that Lystrosaurus had adaptations for burrowing and finds in scratch-digger burrows confirm this; presumably this could have aided their survival (Botha & Smith 2007). Germain and Laurin 2005 also studied this genera (the third was Pachypleurosaurus) and cautiously inferred that it was amphibious, and noted that fossorial activities have not been accounted for. However, they also suggested that a fossorial and amphibious lifestyle are not incompatible. The star-nosed mole (Condylura cristata) is less fossorial than other moles and an excellent swimmer (Petersen and Yates 1980), although given the vastly different sizes and niches I don't know how comparable the two are. Ray et al. 2005 also studied bone microstructure and noted cortical thickness (especially in the humerus) which could suggest either swimming or digging. However, there was some bone structure (medullary spongiosa) which is typical of semi to fully aquatic animals. Since Botha and Smith reference this paper and still suggest it was fossorial, I'd suggest the latter explanation is still the most plausible. While some features may suggest an aquatic nature, with everything taken into account it seems weakly supported. Perhaps like the thick-tailed opossum they spent some time in the water, but were in that apparent "semi-semi-aquatic" category.

L. murrayi from Wikipedia commons.

By now it seems pretty hopeless that there's a synapsid out there clearly demonstrating the traits of a semi-aquatic animal. Enter: the primitive cynodont Procynosuchus. It was a primitive member of the group (which gave rise to modern mammals) and lived in the upper Permian, and presumably went extinct in the P-Tr event. Kemp 1980 notes that Procynosuchus shows a suit of characters not found in any modern animals, and several unique to other therapsids as well. The zygapophyses (articular process) on the vertebrae are normally oriented (vertical) until the lumbar region where there is a sudden switch to a near-horizontal orientation. It appears that this allows for a great deal of lateral movement which was otherwise restricted in the other vertebrae. The tail had well-developed haemal arches and was also apparently flexible. Since this would not appear to help terrestrial locomotion at all, these features point to lateral anguilliform movement comparable to crocodilians and monitor lizards. Flattening of leg bones and well developed muscles suggest that it may have been used in locomotion. Oddly, the hindlimbs were capable of an erect gait when the forelimbs could only attain a sprawling gait. It is possible that it could attain two different gaits, also like a crocodilian.

Unfortunately, according to an article referenced at Palaeos (Hopson 1991) one author thought that all the traits thought to be related to a semi-aquatic lifestyle were artifacts of preservation. It's very hard discussing something that I don't have access to, were there other skeletons not showing traits? The flattening of the hindlimb bones and ribs could possibly be due to preservation, but really, all those other traits? I haven't seen any more discussion of this, and it seems like Kemp's analysis still stands (or is at least better known).


To answer my initial question: maybe? Presumably all of the taxa mentioned here interacted with water on some basis, but how adapted the first two are just isn't clear. I think that a skeleton getting deformed in a way that makes functional sense as an aquatic species is a bit hard to buy, and Procynosuchus seems to be the most aquatically adapted stem-group synapsid. The absence of many aquatically adapted species like the diapsids (and mammals) is conspicuous, and there really doesn't seem to be any anatomical reason for a whole radiation of animals to be incapable of adapting in such a way. Perhaps a few otter-like taxa will be found in the future, but I'm doubting any turtle mimics or long-necked whatzits.

Addendum:

Thanks to Christopher Taylor for pointing this out. Castorocauda lutrasimilis was a mid-Jurassic species often incorrectly called a mammal. It was a docodontan mammaliaform, which places it outside of Mammalia and makes it a stem-group synapsid. Confusingly, the term "mammal-like reptile" does not appear to be used for mammaliaformes and my replacement term was a bit more inclusive than I realized. Oh, and as far as adaptation goes it is supported by both skeletal and soft evidence and I have not seen any voices of dissent.



References:

Botha, Jennifer and Smith, Roger M. H. 2007. Lystrosaurus species composition across the Permo–Triassic boundary in the Karoo Basin of South Africa. Lethaia. 40, pp. 125-137.

Germain, Damien and Laurin, Michel. 2005. Microanatomy of the radius and lifestyle in amniotes (Vertebrata, Tetrapoda). Zoologica Scripta, 34, 4, July 2005, pp335–350

Kemp, T. S. 1980. The Primitive Cynodont Procynosuchus: Structure, Function and Evolution of the Postcranial Skeleton. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, Vol. 288, No. 1027, pp. 217-258.

Petersen, Karen E. and Yates, Terry L. 1980. Condylura cristata. Mammalian Species, No. 129, pp. 1-4.

Ray, Sanghamitry et al. 2005. Lystrosaurus murrayi (Therapsida, Dicynodontia): Bone histology, growth and lifestyle adaptations. Palaeontology, Vol. 48, Part 6, pp. 1169–1185

Those Magnificent Frigatebirds

Female Fregata magnificens from the Wikipedia Commons.

Frigatebirds are pretty high up there on animals I'd like to see some day. Two of the five species have been seen in New England, but encounters are so rare that I'll probably have to bother going elsewhere, sigh. Prior posts documenting my taste in art and fascination with Big Animals makes the appeal of these dark, angular and somewhat monster-y birds fairly obvious. Superficiality aside, these are some very impressive animals.

The five living species of Fregata are classified as Pelecaniformes in the family Fregatidae, although beyond that things have been rather murky. These aren't "core Pelecaniformes" (darters, gannets, cormorants), but frigatebirds may be a sister group to a clade containing the core plus pelicans and tropicbirds (Kennedy & Spencer 2004). All of these groups have four toes joined by webbing, a gular sac and pre-landing vocalizations, and like all major groups their monophyly has been questioned. My previous blogging on bird phylogeny taught me that large-scale relations between groups right now is, well, a bit confusing. Focusing in a bit, it is worth pointing out that until the early 20th century there were only two species of frigatebird: the small and distinctive F. ariel (the lesser/least frigatebird) and F. aquila. The latter species was split into four superficially similar species, possibly grouped into two pairs of similar species (F. minor/F. andrewsi and F. magnificens/F. aquila) according to Kennedy and Spencer. Interestingly all the species appear to have diverged as recently as 1.5 million years ago despite having a fossil record that goes back 50 million years (Kennedy and Spencer 2004).

The first possible member of the family is Volgavis marina from the Uppermost Maastrichtian (presumably around 65 mya) of Eastern Russia (Buffetaut et al. 2002). However, another paper (which I can't find) apparently considered it a graculavid charadriomorph and the fact that Kennedy and Spencer don't mention it is worth something too. The early Eocene of Wyoming has the first definite frigatebirds: Limnofregata azygosternon (first described in 1977) and L. hasegawai (2005). L. azygosternon was the smaller species with a proportionally shorter bill and proportionally larger tibiotarsus; the size range between the species and tibiotarsus proportions are reminiscent of modern Fregata (Olson and Matsuko 2005). All the specimens of L. azygosternon seem to be very consistently sized, so it is unlikely that this early genus had the same sexual dimorphism (with larger females) as Fregata. Despite being small, the feet of this genus could still be theoretically used as paddles; coupled with the lack of dimorphism this group seems reminiscent of gulls from the genus Larus. Presumably there are other anatomical features that the authors didn't explicitly mention. Aside from Quaternary remains, this snapshot in time is all we know about the evolution of frigatebirds. So what did this group do in their impressive ~50 million year ghost lineage? Olson and Matsuko speculated that cooling in the mid-Eocene and the evolution of gulls in the Late Oligocene put the frigatebirds into their current tropical, pelagic niche. I haven't seen more than 5 species of Fregata listed anywhere, so presumably the Quaternary species were the same (or very similar to) the modern ones.

During the course of their nebulous evolutionary history, frigatebirds became some of the most impressive fliers known. The great frigatebird (F. minor) has been known to spend as much as 12 days on the wing (Weimerskirch et al. 2004) although there is no evidence they (or any other birds) can actually sleep on the wing (Rattenborg 2006). Albatrosses, for comparison, also spend most of their lives on the wing but they have been known to sleep floating on the sea (Rattenborg 2006). It isn't clear if frigatebirds actually can land on the surface of the water. Mahoney 1984 got some frigatebirds wet and set them on water; it turned out that only half of the males (10% less massive than females) managed to take off, and with great difficulty at that. Since the studied frigatebirds could still fly wet when thrown into the air, Mahoney concluded that the short legs with vestigial webbing and the wingspan (2-2.4 m or 6'6" to 7'10") constrained the birds from taking off in water. Food that isn't stolen from other birds (kleptoparasitism) and fisheries is taken through surface dipping (well, not flying fish) (Calixto-Alberran and Osorno 2000). Feeding from a medium that may not be escapable is certainly a testament to the flying abilities of frigatebirds. Exactly how frigatebirds spent their time on the wing was a mystery until quite recently (2003) when it turned out that they moved in a succession of climbs and descents powered by thermals (generally used by land birds) at both day and night and can fly as high as 2,500 meters (8200 feet) (Weimerskirch et al. 2003). Since feeding opportunities are limited in unproductive waters, frigatebirds don't spend much time near the surface of the water (which is probably for the best). Weimerskirch et al. 2003 further notes that frigatebirds weight only 1.2-1.5 kg (2.6 to 3.3 lbs) and even with narrow wings still have the lowest wing-loading of any bird species*. This, coupled with the longest period of parental care of any bird species and a very long life expectancy (30+ years) are further examples of their adaptations to tropical and unproductive waters.

*I wonder if any pterosaurs came close. Quetzalcoatlus is occasionally estimated as (insanely) low as 50-100 kilograms, but Mark Witton compellingly tells us why this is not so. Oh yes, and I'm convinced many modern day "pterosaur" sightings are of our friends, the frigatebirds (and turkey vultures, and pelicans, et cetera).

Male Great Frigatebird (F. minor) from Wikipedia Commons. I tend to only look at pictures on Wikipedia, I hope I'm not posting exactly the same information...

The sexual dimorphism in frigatebirds is a bit, well, confusing to me. As stated before, males are considerably less massive than females, yet for some reason they have those balloon-like gular pouches used for display. In a nice free article, Dearborne et al. note that uneven parental care and extra-pair fertilizations expected with a dimorphic male don't occur in frigatebirds. There was, however, a greater number of males so presumably this skewed operational sex ratio was the cause of the gular pouches and display behavior. But what about the size? Schreiber and Schreiber note than many of the characteristics seen with larger females in other birds (polyandrous mating, males using agility to attract mates, maintenance of pair bond) are not seen here and they couldn't quite reach a conclusion. The idea that the different sizes (and wing loading) allow the genders to have a sort of ecological segregation. I haven't seen any followups to this, and since dimorphism in boobies is also unexplained, I'm guessing this is still an open mystery. Well, unless there's something I missed.


Oh, and I accidentally left the Guinness Book of Animal Facts and Feats in Maine, dangit. I do recall some passages about frigatebirds reaching tremendous speeds (in storms) and....a claim that they are used as some sort of homing bird on some tropical islands. Wow.

As far as conservation is concerned, the great frigatebird (F. minor), magnificent frigatebird (F. magnificens) and Lesser frigatebird (F. ariel) are all least concern and have at least a couple hundred thousand representatives. The Ascension frigatebird (F. aquila) breeds on only one island with invasive cats and is classified as vulnerable with a downwards population trend. The Christmas island frigatebird (F. andrewsi) also breeds on only one island but is critically endangered with a downwards trend.

Maybe I'll end on a happier note next time.

-Cameron

References:

Buffetaut, Eric et al. 2002. A fossil feather from the Upper Cretaceous of Kras (Slovenia). C. R. Palevol 1, 705–710.

Calixto-Alberran, Itzia and Osorno, Jose-Luis. 2000. The diet of the magnificent frigatebird during chick rearing. The Condor 102:569-576.

Dearborne, Donald C. et al. 2001. Behavioral Ecology Vol. 12 No. 6: 746–752. Available: Here (for free)

Kennedy, Martyn and Spencer, Hamish G. 2004. Phylogenies of the Frigatebirds (Fregatidae) and Tropicbirds (Phaethonidae), two divergent groups of the traditional order Pelecaniformes, inferred from mitochondrial DNA sequences. Molecular Phylogenetics and Evolution 31, 31–38

Rattenborg, Neils C. 2006. Do birds sleep in flight? Naturwissenschaften, 93: 413–425

Mahoney, Sheila A. 1984. Plumage Wettability of Aquatic Birds. The Auk, Vol. 101, No. 1., pp. 181-185.

Olson, Storrs L. and Matsuoka, Hiroshige. 2005. New specimens of the early Eocene frigatebird Limnofregata (Pelecaniformes: Fregatidae), with the description of a new species. Zootaxa 1046: 1–15.

Schreiber, Elizabeth Ann and Schreiber, Ralph W. 1988. Great Frigatebird Size Dimorphism on Two Central Pacific Atolls. The Condor, Vol. 90, No. 1., pp. 90-99.

Weimerskirch, Henri et al. 2003. Frigatebirds ride high on thermals. Nature Vol. 421, p. 333-334.

Weimerskirch, Henri et al. 2004. Foraging strategy of a top predator in tropical waters: great frigatebirds in the Mozambique Channel. Marine Ecology Progress Series, Vol. 275: 297–308. Available: Here (for free).

Matamata

© 2006 Shawn Mallan, used with permission. Also available here

When I was using this as my desktop background, the various people overlooking my shoulder struggled to identify this animal. If the image had just extended a little more upwards I'm sure nobody would be guessing that this was a frog or lizard of some sort. This picture from the Wikipedia commons is equally as "mean" and strange looking:

If this seems vaguely familiar, I've done something similar in this post which also featured a creature with a snorkel-like snout, large lips, a wide mouth and slightly raised eyes. That animal was the trionychid (softshell turtle) Amyda, to which the matamata is not related. Turtles can be broadly classified into cryptodires (e.g. trionychids) that can retract their necks strait in and pleurodires (e.g. the matamata) which have to bend it sideways to retract. Pleurodires currently live only in the Southern Hemisphere, the matamata lives in the Amazon and Orinoco river systems as well as Trinidad (Lemell et al. 2002). The matamata is known as Chelus fimbriatus and is nestled in the family Chelidae (Krenz et al. 2005) and appears to be most closely related to the toad-headed turtles, Phrynops (Seddon et al. 1997) which it somewhat resembles. While not necessarily very interesting from a phylogenetic standpoint, it does have some fascinating morphology.

It appears that the post-cranial skeleton of Chelus has yet to be described in its entirety (see here). The carapace of this species has sub-pyramidal knobs that makes it superficially similar to that of the (cryptodire) alligator snapping turtle Macrochelys; see this drawing by Haeckel (they're above and below the giant tortoise). Chelus is noted as being a poor swimmer that typically walks on the bottom of shallow waterways (Davidson 2001). Sexual dimorphism is limited to a concave plastron and long, thick tail in males and a flat plastron and smaller tail in females (Davidson 2001). With a reported carapace length of up to 45 cm and a length of up to 15 kg (by Wikipedia), this species is roughly the size of the snapping turtle Chelydra. The cervical vertebrae are noted as being "extremely long" and are apparently longer than the carapace (Gaffney 1977). I haven't heard or seen if the neck and head can actually be retracted into the shell.

The head of the matamata has received quite a bit more attention. The projections on the head are highly innervated extensions of skin and there appear to be veins associated with the ear that transmit vibrations; both have been viewed as analogous to a lateral line system (Winokur 1977). I unfortunately can't access this article, but the abstract tells me that the snout has erectile tissue but is immobile. Since trionchids are noted as being unique for drawing in water with their snout, apparently Chelus uses its snorkel more conventionally. Then there's the skull...

Eugene Gaffney colorfully describes it as "riddled with automorphies and looks as if it has been run over by a truck" (Gaffney 1977). The extremely flattened cranium has been compared to trionychids like Chitra (Lemell et al. 2002) - coincidentally I once confused the two. Chelus is a specialized suction feeder, and Lemell et al. discuss the kinematics and unique morphology involved. The hyoid apparatus is typically large in aquatic feeding vertebrates, but in Chelus it is among the largest in turtles and allows for a suction force comparable to Chitra. The mouth can open up to 80 ° and there is a missing cartilago transiliens, both of which appear to be unique situations for turtles. The presence of "cheeks", a reduced tongue, and an esophagus that can expand to four times its original volume are all related to the suction feeding as well. During suction the water just can't pass through like a fish, it has to flow back out but it does so after the prey is encased within the jaws. The Austaliasian pleurodire Chelodina is also capable of suction (and also has an incredibly long neck), but kinematically it appears to everything much faster (e.g. moving prey at 280 cm s–1 vs 80, maximum gape in 20 ms vs 60). Compared to other suction feeding vertebrates (fish and salamanders) the opening phase was very fast, but the closing phase took longer. Oh yes, and Chelus is able to capture prey without pressure waves, probably due to the unique shape of its skull.

Not exactly the most academic of sources, but it is fun to see them in action. Look for the slow motion replays at the end.

Curiously, Gaffney 1977 said that only one species of Chelus is "usually recognized", which made me wonder if there were some alleged other species out there. As Wikipedia tells us, this species has undergone some horribly confusing taxonomy, so perhaps it is a reference to that. There were also a couple fossil species, C. lewisi and C. colombrianus, from the Miocene that have a marked different pattern to the carapace (Villanueva 1988). The lowlands of the Lake Maracaibo basin in Venezuela have a lot of endemics, and it is reported that another extant species of Chelus may be among them (Scharegel 2007). Unfortunately it referenced a personal communication, so we can't tell exactly what unique characters this population/species may have. Villanueva pointed out that some characteristics of the carapace didn't have very obvious selective pressures, so perhaps if this is distant enough it can shed light on that. Even if it doesn't, it still highlights the fascinating diversity of South America that has still yet to be well understood.


Spring break already, weird. Well I'm going to attempt to clean up around town and maybe vote tomorrow. Who knows what will come next...

-Cameron



References:

Davidson, B. 2001. "Chelus fimbriatus" (On-line), Animal Diversity Web. Accessed March 03, 2008. Available: Here

Gaffney, Eugene S. 1977. The Side-Necked Turtle Family Chelidae: A Theory of Relationships Using Shared Derived Characters. American Museum Novitiates, Number 2620, pp. 1-28. Available here (for free)

Krenz, James G. et al. 2005. Molecular phylogenetics and evolution of turtles. Molecular Phylogenetics and Evolution 37, 178–191

Lemell, Patrick et al. 2002. Feeding patterns of Chelus fimbriatus (Pleurodira: Chelidae). The Journal of Experimental Biology 205, 1495–1506. Available here (for free)

Seddon, Jennifer M. et al. 1997. Phylogenetic Relationships of Chelid Turtles (Pleurodira: Chelidae). Molecular Phylogenetics and Evolution Vol. 7, No. 1, pp. 55–61.

Scharegel, Walter F. et al. 2007. A New Aquatic Snake (Colubridae: Pseuoerix) from the Lake Maracaibo basin, Northwestern Venezuela: A Relic of the past course of the Orinoco River. Herpetologica, 63(2), 2007, 236–244.

Villanueva, Jean Bocquentin. 1988. On the Turtle Chelus lewisi (Testudinata, Pleurodira). Journal of Herpetology, Vol. 22, No. 3. pp. 343-344.

Winokur, Robert M. 1977. The Integumentary Tentacles of the Snake Erpeton tentaculatum: Structure, Function, Evolution. Herpetologica, Vol. 33, No. 2.