Saturday, May 24, 2008


As this post indicates, oscars (Astronotus ocellatus) are held in fairly high regard by me, banner-worthy in fact. I've owned two as pets (thus far) and I have fond memories of them eating a Siamese fighting fish, breaking heaters, flopping around outside the tank, getting scared by earthworms and so forth. Having owned goldfish previously, I was amazed that fish could be so active, intelligent and destructive.

A. ocellatus from the Wikipedia commons

A. ocellatus is a member of the enormous family Cichlidae and is a member of the Neotropical radiation comprising over 407 species (Musilova et al. 2008). The subfamily Astronotinae is regarded as being a sister group to most of the Neotropical radiation (Lopez-Fernandez et al. 2005) and is composed of only three genera. Unfortunately, it doesn't seem that any species aside from A. ocellatus is very well known. Chaetobranchus consists of two species specialized for planktivory; C. semifasciatus has a superficially oscar-like appearance and coloration but specimens attributed to C. flavescens look remarkably different (see here). The Guide to South American Cichlidae notes particular resemblance to the genus Acaronia, a member of a different (and more derived) subfamily. I can't help but wonder if Chaetobranchus is paraphyletic or if C. flavescens reverted to a more ancestral coloration and body shape. Chaetobranchopsis is a closely related genus with two species that are even more rarely discussed. Fishbase indicates that C. australis is non-predatory and likely and micro- and planktophagous feeder and C. orbicularis is probably a filter feeder. Unfortunately, I can't talk much more about these species without rampant speculation.

Then there's the other oscar A. crassipinnis which is mainly distinguished by an overall darker coloration, different position of light and dark bars and different scale and fin ray count. Kullander mentions that the syntypes are either from A. ocellatus or some other species. Astronotus ocellatus is distinguished by having multiple ocelli near the dorsal and caudal fin, although this feature does not show up in every specimen (A. crassipinnis and C. semifasciatus also have a single ocelli) and is believed to be anomalous (Winemiller 1990). Since oscars and similar relatives are large, slow-moving fish they have large fins and the ocelli appear to be an eye mimic that dissuades fin-nipping piranhas from feeding on them (Winemiller 1990).

I recall one instance of a broken heater raised the temperature in an aquarium to perilous levels and forced one of my oscars to attempt breathing air. Astronotus ocellatus is actually one of the most hypoxia tolerant fish in the Amazon, capable of tolerating 6 hours of anoxia at 28 degrees C (82 F) (Almeida-Val et al. 2000). Chippari-Gomes et al. studied A. crassipinnis (and another cichlid less hypoxia tolerant) and noted that higher glycogen concentration in the liver and muscles were partially responsible for maintaining metabolism in very low oxygen. Almeida-Val et al. discovered that while smaller fish are typically better at dealing with hypoxia, the anaerobic potential of oscars actually increases with growth. Sloman et al. 2006 investigated the matter further and noted that the younger animals tended to stay in oxygen deficient waters longer than the adults, likely since they would be more vulnerable to predators on the water surface. Smaller individuals will also remain fairly active in hypoxic waters (likely searching for areas with higher oxygen levels) whereas larger individuals will limit their activities to suppress their metabolism - although aggression levels are not affected until very low oxygen levels (this is also rather atypical). Chippari-Gomez et al. theorize that the hypoxia tolerance of A. crassipinnis allows it to exploit a larger ecological scope than other species (this is undoubtedly applies to A. ocellatus as well); Sloman et al. point out the little is known about the distribution of the fish in the wild and that the ecological context of their remarkable hypoxia and anoxia tolerance needs investigating.

There's a great deal of information on the web about Astronotus ocellatus: ADW is always a good source, Fishbase is a must and there's even a forum.

My lack of output thus far was due to me getting rather tied up on some very long posts which should hopefully make it out sometime this summer. Stay tuned...



Almeida-Val, V.M.F. et al. 2000. Scaling effects on hypoxia tolerance in the Amazon fish Astronotus ocellatus (Perciformes: Cichlidae): contribution of tissue enzyme levels. Comparative Biochemistry and Physiology Part B 125, 219–226.

Chippari-Gomes, A. R. et al. 2005. Metabolic adjustments in two Amazonian cichlids exposed
to hypoxia and anoxia. Comparative Biochemistry and Physiology, Part B 141, 347 – 355

Lopez-Fernandez, Hernan et al. 2005. Molecular phylogeny and evidence for an adaptive radiation of geophagine cichlids from South America (Perciformes: Labroidei). Molecular Phylogenetics and Evolution 34, 227–244

Musilova, Zuzana et al. 2008. Molecular phylogeny and biogeography of the Neotropical cichlid
fish tribe Cichlasomatini (Teleostei: Cichlidae: Cichlasomatinae). Molecular Phylogenetics and Evolution 46, 659–672.

Sloman, Katherine A. et al. 2006. Tribute to R. G. Boutilier: The effect of size on the physiological and behavioural responses of oscar, Astronotus ocellatus, to hypoxia. The Journal of Experimental Biology 209, 1197-1205

Winemiller, Kirk O. 1990. Caudal Eyespots as Deterrents against Fin Predation in the Neoptropical Cichlid Astronotus ocellatus. Copeia, Vol. 1990, No. 3, pp. 665-673

Wednesday, May 14, 2008


I had previously mentioned teratorns all the way back here, noting that family Teratornithidae is grouped with the New World vultures (Cathartidae) - possibly in the order Cathartiformes. The "possibly" is partially due to the fact that traditional grouping in Falconiformes or Ciconiiformes has been challenged and cathartids may require their own order. It should be mentioned that some workers feel that they may be more closely related to storks or Pelicaniformes, but unfortunately there seems to be a lack of available information. Welcome to the world of teratorns!

Teratornis merriami was a Pleistocene teratorn of North America that recently had isotopes from its collagen analyzed by Fox-Dobbs et al. 2006. 2H isotope levels possibly suggested a marine diet in one specimen, but 13C and 15N isotope levels suggest teratorns fed in a terrestrial c3 environment (i.e. the non-arid plants). The 15N isotope levels suggested a mixed diet of browsers and grazers, and the authors suggested the teratorn was a scavenger with wide dietary flexibility due to its size. The authors appear to have assumed that teratorns were obligate scavengers by their large numbers in the tar pits, but of course carnivorous birds will engage in facultative scavenging. If teratorns were large enough to require a broad diet, then perhaps they exploited the tar pits in great numbers despite usually preying on something else. I say preying because two morphological studies cited by Fox-Dobbs et al. strongly suggest just that.

Campbell and Toni 1983 mention a 1981 study by them (which I can't access) documenting the plane of rotation of the quadrates, maxillary rostrum and mandible structures and concluded that the birds swallowed prey whole and could not tear pieces off a carcass like a vulture. Hertel 1995 used a number of indices to classify avian skulls into ecomorphs; scavenging species were well separated from other ecomorphs with fairly high confidence (caracaras were somewhat hard to determine) and were marked by such distinctive features as smaller orbits, greater occipital distance, a deep and narrow ramus, large foramen magnum angle and other features related to twisting food off from a carcass and eating it quickly (and apparently less need for acute vision). Teratorns did not show these vulture-like features and in many features it was classified as a piscivore - except for mandibular and maxillary indices (which apparently classified it as a scavenger and mammalivore/generalist, respectively). Hertel speculates that it could have fed from fish from the surface (the feet were not strongly raptorial), but the isotopes from Fox-Dobbs et al. suggest this was either rare or not the case. I think that the mandibular and maxillary features interpreted by Campbell and Toni as being from a predator and the other features resembling a piscivore (and the facultative scavenging) indicate that this was either a generalized species or occupied an ecomorph with no modern counterparts. Fox-Dobbs et al.'s implication that teratorns went extinct directly because of the loss of megafauna is thus probably not correct. Even if it was fairly generalized, it was still fairly large (12.5-15 kg or 27-33 lbs - Campbell and Toni 1983), presumably had fairly large home ranges and was probably more prone to extinction.

Campbell and Toni 1983 further noted that T. merriami* has always been portrayed as a super-condor (this is still true 25 years later) despite the fact that we now know that the skull indices indicated a much different niche. And since when do birds in different families look identical down to the coloration? The post-cranial skeleton apparently shows a mosaic of cathartid, ciconiid and unique features; the flight was apparently condor-like, the pelvis was stork-like and indicated that sustained walking was possible and the stout legs indicated that running was not likely. I'm guessing that this teratorn could have hunted mammals, reptiles and amphibians on the ground and possibly fish in freshwater, although the short legs would have been a hindrance. However it "earned a living", relatives with similar bauplans existed for millions of years.

*Some material from Cuba may indicate that there is another species in the genus, or that there is yet another genus of teratorn (Olson and Alvarenga 2002). This article mentions a "Teratornis" olsoni. Nothing has been published to my knowledge.

The Incredible teratorn (Aiolornis incredibilis) was one of three teratorn species that lived in North America in the late Pleistocene (from the early Pliocene) and was primarily differentiated from T. merriami by its size. Where T. merriami had a 3.5 to 4 m (11-13') wingspan, A. incredibilis was more along the lines of 5-5.5 m (16.5 to 18') and it presumably weighed around 36 kg (80 lbs) or more. Campbell et al. 1999 examined new and old specimens and determined there were enough characteristics to establish a new genus (it was originally in Teratornis) and suggested that Pliocene specimens may actually belong to other species and/or genera. Clearly a lot remains to be discovered and written about this species, Campbell et al. thought that it had distinctive flight capabilities but didn't (probably couldn't) expand upon that. The beak was deeper than Teratornis, although without much skull material nothing about potential ecomorphology has been written. I doubt it was a "super condor" as alleged by some, and presumably it shared the same walking abilities (since Argentavis did...) and specialized on some other food source. It seems dubious that three large generalists could have co-existed in the North American southwest in the late Pleistocene.

As I've been hinting at, the third species in question is Cathartornis gracilis which is very rarely discussed (it is known from two tarsometatarsi). Campbell et al. 1999 discuss it briefly; it is comparable in size to Teratornis but more gracile, although Campbell et al are not convinced it belongs in its own genus. Olson and Alvarenga 2002 mention that more material has apparently been found and Campbell now thinks it is worthy of genus-level distinction. Like the Cuban material, I haven't heard of any publications.

Teratorns aside from Merriam's aren't discussed too frequently, with the exception of the gigantic Miocene Argentavis magnificens from South America. This was the largest flying species of bird with a span of around 7 meters (23 feet) and a mass of around 70 kg (150 lbs) (The azhdarchid pterosaur Hatzegopteryx dwarfed this) and so has received a lot of attention. Campbell and Toni 1983 stated that Argentavis was simply a larger version of the Teratornis morphotype on the basis of wing and leg bone similarities (i.e. condor-like flight and stork-like walking); apparently the 1981 paper by the authors documented features of the 55 cm+ skull which indicated it was predatory (Chatterjee et al. 2007). Palmqvist and Vizcaino 2003 determined that a falconiform the size of Argentavis would have a territory of about 542 square kilometers (~200 sq. miles) and would take about three days to patrol its territory and would eat around 5-10 kg of meat per day. The authors feel that since scavenging birds do not have defined territories and can exist at higher densities that predatory ones - and they suggest that predatory sabertoothed marsupials opened up a new niche for giant vultures (they seemed to imply that Argentavis ate bones). Most recently, Chatterjee et al. 2007 stuck with the morphological implications that this was a predatory species capable of eating rabbit-size animals whole. So why gigantism? Palmqvist and Vizcaino note that while giant species have low populations, low population density, small clutch size and long breeding cycles they are resilient against predation (maybe even engaging in kleptoparasitism) and can withstand famine.

Very seldom discussed is the earliest teratorn Taubatornis (with 6 Google hits) from the late Oligocene of Brazil that had not reached the proportions of later species (the distal width of the tibiotarsus was about 70% that of Teratornis). This fossil also demonstrates that South America is likely the place of origin for this family and that teratorns in North America (and Cuba?) were a fairly recent phenomenon. Olson and Alvarenga also mention the curious fact that teratorns and cathartids are almost always found together, which would support frequent scavenging habits (the authors are neutral).

That about ends the story for teratorns thus far, and as usual there are more questions than answers. For birds with no obvious adaptations for eating carrion, teratorns sure did hang out with vultures and get stuck in tar pits a lot. Teratorns also seem very different from living birds of prey that hunt on the ground, and exactly how a short-legged bird unable to run well hunts a sufficient number of small animals per day is beyond me. Perhaps Teratornis was somewhat like a marabou stork or adjutant (Leptoptilos sp.) in that it was a presence at kills but otherwise occupied a different niche it was morphologically adapted towards. The presence of three sympatric genera (and their extinction) certainly hints that these were not all generalists. It is increasingly clear that teratorns were not "super condors", but what exactly they were is still rather unclear. Hopefully some of the unpublished material will come to light and new discoveries will be made to clear up the basic life histories of this enigmatic group.


Campbell, Kenneth E. and Tonni, Eduardo P. 1983. Size and locomotion in teratorns (Aves: Teratornithidae). The Auk 100: 390-403.

Campbell, Kenneth E. et al. 1999. A New Genus for the Incredible Teratorn. Smithsonian Contributions to Paleobiology No. 89: 169–175. Available (Huge file)

Chatterjee, Sankar et al. 2007. The aerodynamics of Argentavis, the world’s largest
flying bird from the Miocene of Argentina. PNAS. Published online (for free)

Fox-Dobbs, Kena. 2006. Dietary controls on extinction versus survival among avian
megafauna in the late Pleistocene. Geology V. 34, No. 8 pp. 685-689

Hertel, Fritz. 1995. Ecomorphological indicators of feeding behavior in Recent and fossil raptors. The Auk 112(4): 890-903

Olson, Storrs. L and Alvarenga, Herculano M. F. 2002. A new genus of small teratorn from the Middle Tertiary of Taubate Basin, Brazil (Aves: Teratornithidae). Proceedings of the Biological Society of Washington 115 (4) pp. 701-705

Palmqvist, Paul and Vizcaino, Sergio F. 2003. Ecological and reproductive constraints of body
size in the gigantic Argentavis magnificens(Aves, Teratornithidae) from the Miocene of Argentina. Ameghiniana 40 (30) pp. 379-385

Monday, May 12, 2008

Like a Child's Bad Drawing...

Well, I've survived another round of finals, on with the blogging!

Unexpectedly, fishes in the deepest parts of the oceans (Hadal zone) have rather conservative bauplans (like Abyssobrotula) and only in the bathy- and abyssalpelagic species do the truly bizarre forms exist. I'm guessing that while such divergent forms are efficient at capturing prey/food particles, they can only be practical up to a certain point. Recently I discussed a denizen from the Zone of Bizarre Fishes, the stoplight loosejaw, which had odd characters such as a mouth with no floor that could somehow capture copepods and modified chlorophyll (from the copepods) that was used to detect red light emitted in order to see prey (like...copepods). Even with these peculiar features, the stoplight loosejaw is still recognizably a dragonfish, albeit a rather extreme one.

The genus Lasiognathus ("Wolftrap anglers") is a member of the order Lophiiformes (anglerfish) and the suborder Ceratioidei (Deep sea anglers), although this is rather hard to recognize at first. I was wondering if the artists who drew these species screwed up horribly - until I saw a photograph:

L. amphirhamphus from Pietsch 2005, used with permission.

Lasiognathus is recognizable as a lophiiform due to the presence of a modified first dorsal fin or illicium and bioluminescent "bait" or an esca at the end. The lack of pelvic fins unites this with other ceratioids and the characteristic dwarfed males have yet to be found (which would hint at them being small of course). Along with the sister taxa Thaumatichthys* (in the family Thaumatichthyidae) Lasiognathus has denticles on the esca and a bizarre premaxillary that can flip down to form a venus flytrap-like cage. The features of the esca have established 5 species of Lasiognathus (Pietsch 2005) known from only 27 adult female specimens (Pietsch 2005a).

*Pietsch and Orr 2007 mention some possible morphological and preliminary genetic evidence that may suggest otherwise. Support for maintaining the family is still convincing. Also, if you have access check out the Lasiognathus skeleton on page 14.

While the esca is key to differentiating species, the genus is still riddled with apomorphies. Thaumatichthys shares the massive overbite and premaxillary cage - but it has an esca in the roof of its mouth (how does a fin ray wind up there?) and looks broadly different. The head is extremely long (>60% standard length) and narrow (Pietsch 2005); the pterygiophore is 85% of the SL and can slide back and forth in a deep cranial trough, forming a tentacle when retracted(!); the illicium supported by the pterygiophore is 50% of the SL (Bertelsen and Pietsch 1996); illustrations of the flipped-down premaxillaries can be found here and here.

Unfortunately, that about wraps it up for Lasiognathus. Anatomically it seems pretty well known (particularly the esca), but there still are a great deal of unanswered questions for this taxa. Several of the species co-exist and I can't help but wonder if the different esca shape can attract different prey items. And who knows what genetic tests will do to the species count (some specimens lacked the critical esca) and the monophyly of Thaumatichthyidae. With only 27 specimens known, there undoubtedly is a great deal more to learn about this bizarre taxa.

I guess this was some sort of bloated picture-of-the-day post. I have no idea what to do next, but fortunately I have a lot of time to do it.


Bertelsen, E. and Pietsch, Theodore W. 1996. Revision of the Ceratioid Anglerfish Genus Lasiognathus (Lophiiformes: Thaumatichthyidae). Copeia, Vol. 1996, No. 2, pp. 401-409

Pietsch, Theodore W. and Orr, James Wilder. 2007. Phylogenetic Relationships of Deep-sea Anglerfishes of the Suborder Ceratioidei (Teleostei: Lophiiformes) Based on Morphology. Copeia, Vol. 2007, No. 1, pp. 1-34.

Pietsch, Theodore W. 2005. New Species of the Ceratioid Anglerfish Genus Lasiognathus Regan
(Lophiiformes: Thaumatichthyidae) from the Eastern North Atlantic off Madeira. Copeia, 2005(1), pp. 77–81

Pietsch, Theodore W. 2005a. Thaumatichthyidae. Wolftrap Seadevils. Version 06 November 2005 (under construction). in The Tree of Life Web Project,

Pietsch, Theodore W. and Kenaley, Christopher P. 2007. Ceratioidei. Seadevils, Devilfishes, Deep-sea Anglerfishes. Version 02 October 2007 (under construction). in The Tree of Life Web Project,