sábado, 21 de março de 2009

Cenozoic Pterosaurs

This topic is about speculative biology, so if you're a cryptozoologist, well, no cookies for ya. Okay, maybe, but not for creationists who uselessly attempt to use supposed living pterosaurs as evidence against evolution. JTFFDP (Já Te Fodi, Filho/a Da Puta [portuguese sentence, so usefull for insulting])

As you can possibly imagine, speculating about a world were the K-T event didn't occured brings pterosaurs into the conversation.

The situation of these flying sauropsids in the Cretaceous is somewhat controversial; it is pretty obvious they achieved their golden age in the Early Cretaceous, when pterodactyloids produced a gigantic variety of forms, following the demise of basal pterosaurs, though anurognathids are present in laggerstaten fossil sites which only date in the Mesozoic from the Late Jurassic and Early Cretaceous (see below); interestingly, most ctenochasmatoid pterodactyloids also were found in laggerstaten fossil sites (again, see below). Pratically all pterodactyloid clades (aside from azhdarchids and pteranodontians) date from this era, and diversification within such clades is quite evident, specially in ctenochasmatoids, ranging from the very specialized filter feeder Pterodaustro to the equally specialized fisher Cearadactylus. Other clades show less extreme variations, but still notable (note the difference from the fishing ornithocheirids and the scavenging istiodactylids, both within Ornithocheiroidea).

Then, the fossil record seems to suggest a sudden disappearence of clades, and so only lonchodectids, ornithocheirids, pteranodontids and azhdarchids make it into the Late Cretaceous, and out of these only two clades survived beyond the Turonian (however, I pretty much assume the two last clades outcompeted the first two, since pteranodonts and azhdarchs only became notable in the late Cretaceous, following the dcline of the previous two clades). This, obviously, could be seen as that pterosaurs were suddenly declining and in the way of meeting a dire fate...

However, this might not be the case. As pointed out before, anurognathids are only known from laggerstaten fossil sites, and they appear in the Early Cretaceous, not just on the Late Jurassic. As a whole, these clade might actually have had a history as a Lazarus taxon, because all evidence points for a Triassic origin (they were the most basal known pterosaurs), and yet we lack Triassic fossils (and Triassic laggerstaten). Thus, its possible that they endured until the K-T event. Also, note that ctenochasmatoids were also mainly found in laggerstaten, thus probably also implying that they endured until the end.

Thus that leaves us with what? Four clades? Enough for me. Out of these clades, I'm assuming most would survive into the Cenozoic, had the asteroid not collided and ruined all the fun, except perhaps pteranodontians, because they were very specialized to a pelagic lifestyle, and the Paelocene/Eocene Thermal Maximum would probably exterminate them, as oceans are specially sensitive to climatic changes so extreme as those. Even if they survive they wouldn't pass the Eocene/Oligocene extinction event anyway. Of course, they could become smaller via neoteny, thus being reduced to small, adaptable forms. Whatever.

The other pterosaurs, well more adaptable, would obviously survive and diversify. In particular I can see a pterosaur diversity radiation lasting from the Eocene to the Miocene. Then, with the cooling of the climate, I'm assuming the flying reptiles would be hitten. Probably death to european and perhaps north american denizens, and the survivors could colonise those lands from the south, once the climate became warmer (such cycles, between retreat and return, would occur many times, since there were at least 32 ice ages in the last 2 million years).

Flightlessness in pterosaurs is likely, specially in azhdarchids and/or ctenochasmatoids, but I'd expect it to evolve only one or two times; bats never produced flightless forms after all, and while I hate the bat/pterosaur comparation I do have to agree that both were similar in one thing: the wing membrane, which extended unto the legs, would make it more difficult for them to produce fully flightless forms (birds, on the other hand, only need to loose the wing feathers to be flightless; they have their legs seperated from the wings after all). However, because pterodactyloids had reduced uropatagia, and an upright leg stance (like mammals and dinosaurs), it makes a flightless pterosaur more plausible than a flightless bat. For more info on wingless pterosaurs, see Darren Naish's post:


sábado, 7 de março de 2009

Why pterosaurs weren't replaced by birds

Copyrighted from Richard Butler, Paul Barrett, Steven Nowbath & Paul Upchurch: "Estimating the effects of the rock record on pterosaur diversity patterns: implications forhypotheses of bird/pterosaur competitive replacement, SVP meeting abstracts2008, 59A":

"Pterosaurs formed an important component of terrestrial and marginal marine ecosystems during the Mesozoic, and were the first flying vertebrates. The fossil record appears to indicate a decline in pterosaur taxic diversity [ =species count] in the Late Cretaceous, followed by extinction at theCretaceous/Paleogene boundary. This reduction in species-richness has beenlinked to the ecological radiation of birds in the Early Cretaceous -- it has been proposed that early birds competitively excluded pterosaurs from many key niches. Hypotheses of competitive replacement are frequently posited based on the fossil record, but few have been tested in detail. Here we present a detailed examination of pterosaur diversity through time based upon a new comprehensive database of the spatial and temporal distribution of pterosaurs. We use this database to calculate taxic and phylogenetically corrected diversity estimates, and compare these estimates with a model describing temporal variation in rock availability. We use numbers of pterosaur-bearing formations (PBFs) as a proxy for rock availability;temporal variation in the number of PBFs is then used to generate a model in which rock availability is a perfect predictor of diversity. Both taxic and phylogenetic diversity curves are strongly correlated with numbers of PBFs, suggesting that a significant part of the signal contained within pterosaur diversity patterns may be controlled by geological and taphonomic megabiases rather than macroevolutionary processes. Moreover, significant differences between observed diversity and the diversity predicted by the rock availability model coincide with the occurrence of sites of exceptional preservation (Lagerstätten), again indicating major biases in the pterosaur fossil record. There is no evidence for a long-term decline in pterosaur diversity during the Cretaceous, although a reduction in species-richness might have occurred in the Late Cretaceous. Available data provide little support for the long-term competitive replacement of pterosaurs by birds."

domingo, 1 de março de 2009

Niche map for WIW part 2

Note: I've replaced the "Filter Feeder" and "Diver" niches with "Waterbird" and "Fishing mammal", for accuracy reasons.


Tall Browser: Sauropod, Therizinosaur
Low Browser: Hadrosaur, Ceratopsid
Large Grazer: Sauropod/Ankylosaur, Hadrosaur
Medium Grazer: Hadrosaur, Therizinosaur, Pseudoungulate
Small Grazer: Bipedal Ornithopod, Pseudoungulate
Aquatic Herbivore: Ceratopsid, Afrothere, Multituberculate, Herbivorous Crocodillian*
Large Omnivore: Ornithomimid*/Troodontid, Oviraptor, Ceratopsid
Small Omnivore: Afrothere, Pseudoungulate, Glire, Galliforme/Paleognath/Oviraptor
Large Insectivore: Afrothere, Alvarezsaurid, Specialized Troodontid/Unenlagiine/Noasaur/Therizinosaur (see below)
Small Insectivore: Afrothere, Metatherian, Cimolestan
Top Predator: Abeliosaur/Noasaur, Tyrannosaur
Medium Predator: Tyrannosaur, Dromeosaur, Hyeanodont/Mesonychian/Metatherian, Crocodillian
Small Predator: Troodontid/Unenlagiine, Hyeanodont/Mesonychian, Crocodillian, Monitor, Metatherian
Aquatic Predator: Crocodillian, Mosasaur, Plesiosaur
Arboreal Herbivore: Specialized Primate, Gondwanaviforme, Multituberculate, Arboreal Ornithopod
Arboreal Omnivore/Frugivore: Primate, Cimolestan, Dromeosaur, Glire, Scadentian, Metatherian
Arboreal Predator: Hyeanodont/Mesonychian, Dromeosaur, Metatherian
Winged Frugivore/Nectar Feeder: Volaticothere, Flying Cimolestan/Primate, Galliforme, Apsaraviforme, Enantiornithe
Winged Insectivore: Enantiornithe/Neornithe*/Apsaraviforme, Anurognathid, Volaticothere
Winged Predator: Volaticothere, Enantiornithe, Anurognathid*
Winged Scavenger/Terrestrial Stalker: Pterosaur, Unenlagiine, Pseudodontorn, Paleognath
Waterbird: Anseriforme, Paleognath, Flamingo/Presbyornid, Grebe/Loon/Similar Bird, Hesperornithe, Pseudodontorn
Diving Mammal: Cimolestan, Afrothere, Metatherian
Random Oddity: Panda like Ceratopsid/Therizinosaur, Anteating Therizinosaur

*1.An idea I got just now. Probably it will replace the aquatic ceratopsids, or make them water buffalo analogues, while herbivore crocodillians would be hippo analogues
2.I think I'll replace them by either troodontids or flightless pterosaurs
3.I don't know if I should have insect/nectar eating neornithes; therefore, I'll only reffer insect/nectar eating birds as "birds"
4.Another idea I got just now

North America

Tall Browser: Therizinosaur, Hadrosaur/Sauropod
Low Browser: Hadrosaur, Ceratopsid, Meridiungulate
Large Grazer: Hadrosaur, Therizinosaur, Sauropod/Ankylosaur
Medium Grazer: Hadrosaur, Therizinosaur, Pseudoungulate
Small Grazer: Pseudoungulate, Bipedal Ornithopod, Xenarthran/Meridiungulate
Large Omnivore: Troodontid, Oviraptor, Ceratopsid
Small Omnivore: Metatherian, Glire, Xenarthran, Galliforme/Oviraptor/Screamer
Insectivore: Afrothere, Metatherian, Cimolestan, Xenarthran
Top Predator: Tyrannosaur
Medium Predator: Tyrannosaur, Dromeosaur, Hyeanodont/Mesonychian, Metatherian
Small Predator: Troodontid/Unenlagiine, Hyeanodont/Mesonychian, Metatherian
Aquatic Predator: Plesiosaur, Champsosaur, Crocodillian
Arboreal Omnivore: Cimolestan, Multituberculate, Glire, Dromeosaur, Metatherian
Arboreal Predator: Metatherian, Dromeosaur
Winged Omnivore: Volaticothere, Galliforme, Apsaraviforme, Enantiornithe
Winged Insectivore: Bird, Anurognathid, Volaticothere
Winged Predator: Volaticothere, Enantiornithe, Anurognathid
Winged Scavenger/Terrestrial Stalker: Pterosaur, Paleognath, Unelagiine, Ichthyorniforme
Waterbird: Anseriforme, Paleognath, Loon/Grebe/Similar bird, Hesperornithe
Diving Mammal: Cimolestan, Metatherian
Random Oddity: Can't think off