onceforgivennowfree

[he_who_is_nobody]

​

 

[he_who_is_nobody]

I would say A + B are (would have been) birds as their:
- 'toes' look like claws
- feed-bones are very filigree and seem to allow an easy embracing of e.g. branches
--- both aspects don't support a walking over ground as default locomotion
- heels seem to allow a full streching of the feed, to reduce air drag

Now this also applies to C, but here the (2) claws are not so obviously build and thickness of the 'middle-finger' and the femur indicate a larger animal and more strenght for walking.
This could be an ancester of the birds ... a flying dinosaur?

Well D is much different:
- all bones look very strong, and made to hold huge muscles implying a walking as default usage
- the foot doesn't seem to allow much radius of movement in the heel, whereas the upwards bending of the middle-finger-bones indicate a support of rolling over, which speaks for walking too
I'd assume this could be a dinosaur too BUT I do not know how the legs/bones of ostrichs look like, who are also birds but they surely run around a lot and rather have feed-bones like in this example. ... So I might be misslead and D is a bird as well.

I just noticed this, I wanted to answer your question (finally), but I am wondering if you want to give it another go, because I noticed that you thought the arms (forelimbs) in that image were legs (hind limbs). Just to be clear, the picture is of four animals’ arms/wings, not their legs. I was wondering if that will change your thinking or if you want to stick with what you have said.

 

[Vivre]

I just noticed this, I wanted to answer your question (finally)

Great ~ I was wondering the other day if you'd remember

... and I guess you missed my hint

addendum (13.06): I found it ['parahomology'] ... and dug a bit around and met some cute rap guys

I wondered if you'd disguised the source of your picture - but you didn't .. so I found it out the next day ... and I learned I was pretty wrong to assume these were all 'legs' ;-) (twisted to make it a smaller, more condensed display)

Unfortunately I only got the picture description, as the source article is gone. ... As talkorigin doesn't have too much specific infos on these dinosaurs (except for Archaeopteryx) I widened my search and came across all the following informations:

▶ Sinosauropteryx is the first non-flying dinosaur (via picture-description)
▶ Explore the Family Tree of Birds (AMNH)
▶ Are Birds Really Dinosaurs? (very nice page)

on youtube American Museum of Natural History (AMNH) :
>> Pterosaurs adopted for flight
>> Sinornithosaurus...feathers (such a cute raptor)
>> Hypothetical Placental Mammal Ancestor Traced via MorphoBank (treebuild via phenom/morphology/anatomie) - ot, but great project
>> 30min. Docu: Dinosaur Fossils at the American Museum
[showmore=rap it]

[/showmore]
Some days later Isoletus left 3 links to his excursions-threads which made me find these interesting art-works:

▶ A pack of Troodon (by the master himself)
▶ tip about feathered dinosaurs: Group Deinonychosauria
>> Skeletals and anatomy studies
>> Theropod Foot Comparison

▶ Give Oviraptorosaurs a Hand (don't miss this great free bone study)
>> original size picture, CC
>> the according blog pageThe Changeling – The Hand

▶ Oviraptorosaur tail forms and functions (see pdfs)
▶ The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds

This is not to spam nobody :lol:
... but I hope you find something new among it .

I was wondering if that will change your thinking or if you want to stick with what you have said.

Too late. ... But there was one thing, I didn't mention, that I found the femoral head of A+B looking so flat, that it reminded me more of a bladebone, which would only allow a movement on one axis without much rotary movement. But as it is 'only' a thin scheme I rather dismissed it.

~

 

[he_who_is_nobody]

Hats off to you. I am impressed.

Well, if you enjoy learning about fossils, I hope you will take the time to stop by my blog and take a guess at my monthly blog series, Know Your Bones.

 

[Dragan Glas]

Greetings,

Interesting find re Archaeopteryx:

Early bird Archaeopteryx 'wore feather trousers' for display

Also, confirmation that birds are the legacy of dinosaurs:

Do dinosaurs still live amongst us?

Kindest regards,

James

 

[Isotelus]

Greetings,

Interesting find re Archaeopteryx:

Early bird Archaeopteryx 'wore feather trousers' for display

Also, confirmation that birds are the legacy of dinosaurs:

Do dinosaurs still live amongst us?

Kindest regards,

James

Good links!

In regards to the BBC page, here's an open-access article that people might be interested in regarding evolution of integument including feathers: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7580.2008.01041.x/full

This one is also really interesting, but not open access: http://www.ncbi.nlm.nih.gov/pubmed/17784647
Feather keratin was found in embryonic alligator scales, which is later suppressed in the adults. From the abstract:

The morphogenesis of barb ridges has to be considered as an evolutionary novelty that permitted the evolution of feathers from a generalized archosaurian embryonic epidermis.

Back to that BBC site, a couple of things with this particular paragraph:

There is a bewildering range in the size and shape of modern birds’ beaks, mainly adapted for specific feeding strategies. This avian feature might have evolved to help herbivorous dinosaurs chew their food, placing less stress and strain on the skull than a jaw and teeth. The lighter weight of a beak without teeth then became useful before these dinosaurs took to the air.

That's probably coming from here: http://www.pnas.org/content/early/2013/11/27/1310711110.full.pdf, which attributes the stress-reducing advantage of beaks to non-avian theropods...not to birds, as suggested above. They state right in the conclusion that beaks may have had different functions in birds, as is the case with feathers.

The notion that the loss of teeth in birds correlates with weight reduction is also not really the best explanation; more recent studies suggest that edentulism is linked with the appearance of the crop and gizzard, which are very efficient at processing food and extracting energy needed for high energetic demands: http://www.cell.com/trends/ecology-evolution/abstract/S0169-5347(11)00264-3. Besides, a modern flight apparatus evolved before teeth were lost in their entirety, at least in some lineages, including the one closest to modern birds (e.g., see Ichthyornis).

 

[Dragan Glas]

Greetings,

Good links!

In regards to the BBC page, here's an open-access article that people might be interested in regarding evolution of integument including feathers: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7580.2008.01041.x/full

This one is also really interesting, but not open access: http://www.ncbi.nlm.nih.gov/pubmed/17784647
Feather keratin was found in embryonic alligator scales, which is later suppressed in the adults. From the abstract:

The morphogenesis of barb ridges has to be considered as an evolutionary novelty that permitted the evolution of feathers from a generalized archosaurian embryonic epidermis.

Back to that BBC site, a couple of things with this particular paragraph:

There is a bewildering range in the size and shape of modern birds’ beaks, mainly adapted for specific feeding strategies. This avian feature might have evolved to help herbivorous dinosaurs chew their food, placing less stress and strain on the skull than a jaw and teeth. The lighter weight of a beak without teeth then became useful before these dinosaurs took to the air.

That's probably coming from here: http://www.pnas.org/content/early/2013/11/27/1310711110.full.pdf, which attributes the stress-reducing advantage of beaks to non-avian theropods...not to birds, as suggested above. They state right in the conclusion that beaks may have had different functions in birds, as is the case with feathers.

The notion that the loss of teeth in birds correlates with weight reduction is also not really the best explanation; more recent studies suggest that edentulism is linked with the appearance of the crop and gizzard, which are very efficient at processing food and extracting energy needed for high energetic demands: http://www.cell.com/trends/ecology-evolution/abstract/S0169-5347(11)00264-3. Besides, a modern flight apparatus evolved before teeth were lost in their entirety, at least in some lineages, including the one closest to modern birds (e.g., see Ichthyornis).

Just re-read this, and thought ... "Eh?"

The underlined sentence above suggests that the evolution of beaks were due to "herbivorous dinosaurs" - which would appear to mean the same thing as "non-avian theropods", in contradiction to what you're saying, Isotelus.

I'm particularly thinking of Triceratops' "beak":

Kindest regards,

James

 

[Isotelus]

The underlined sentence above suggests that the evolution of beaks were due to "herbivorous dinosaurs" - which would appear to mean the same thing as "non-avian theropods", in contradiction to what you're saying, Isotelus.

I'm particularly thinking of Triceratops' "beak":

Kindest regards,

James

I suppose I should have made my point more clear.

I also initially thought they were referring to beaked ornithischians like Triceratops, but that doesn't make any sense. Those guys chewed their food in the posterior (caudal) end of their jaws, which were actually built to take the force placed on their back teeth. The underlined sentence implied chewing in the anterior portion of the mouth to dissipate stress and strain on the jaw and teeth, which is why I assumed the BBC site got their reference from here: http://www.pnas.org/content/early/2013/11/27/1310711110.full.pdf. It talks about beaked herbivorous non-avian theropods (Therizinosaurs, in particular) processing their food with their beaks and front teeth to reduce stress on the jaw. I felt that the BBC article was overstating the relevance of beak function in other dinosaurs to that of birds, and regardless of what they meant or what their sources were, it's a sentence on a topic that has little to do with bird evolution directly. There are plenty of great articles specifically about evolution of bird beaks...why didn't they write a sentence on those? Hopefully that makes more sense . Not that I want to make too big of a deal about it all, but these types of science sites have the potential to really give people the wrong (or at least slightly inaccurate) impression about what the science says.

 

[Dragan Glas]

Greetings,

The underlined sentence above suggests that the evolution of beaks were due to "herbivorous dinosaurs" - which would appear to mean the same thing as "non-avian theropods", in contradiction to what you're saying, Isotelus.

I'm particularly thinking of Triceratops' "beak":

Kindest regards,

James

I suppose I should have made my point more clear.

I also initially thought they were referring to beaked ornithischians like Triceratops, but that doesn't make any sense. Those guys chewed their food in the posterior (caudal) end of their jaws, which were actually built to take the force placed on their back teeth. The underlined sentence implied chewing in the anterior portion of the mouth to dissipate stress and strain on the jaw and teeth, which is why I assumed the BBC site got their reference from here: http://www.pnas.org/content/early/2013/11/27/1310711110.full.pdf. It talks about beaked herbivorous non-avian theropods (Therizinosaurs, in particular) processing their food with their beaks and front teeth to reduce stress on the jaw. I felt that the BBC article was overstating the relevance of beak function in other dinosaurs to that of birds, and regardless of what they meant or what their sources were, it's a sentence on a topic that has little to do with bird evolution directly. There are plenty of great articles specifically about evolution of bird beaks...why didn't they write a sentence on those? Hopefully that makes more sense . Not that I want to make too big of a deal about it all, but these types of science sites have the potential to really give people the wrong (or at least slightly inaccurate) impression about what the science says.

Yes, I now see what you mean - remember, I'm not a scientist, just from "the IT crowd".

The Wiki article on Triceratops did say that the beak was believed to have evolved as a less stressful means of pulling vegetation - "at grasping and plucking than biting" - although, as you say, the teeth did all the masticating.

The interesting thing would be to find the equivalent of gizzard stones in non-avian theropods - which would be a possible "missing link" to avian dinosaurs and thus birds losing their teeth.

There appears to be some evidence of such in sauropods.

Kindest regards,

James

 

[Isotelus]

Yes, I now see what you mean - remember, I'm not a scientist, just from "the IT crowd".

The Wiki article on Triceratops did say that the beak was believed to have evolved as a less stressful means of pulling vegetation - "at grasping and plucking than biting" - although, as you say, the teeth did all the masticating.

The interesting thing would be to find the equivalent of gizzard stones in non-avian theropods - which would be a possible "missing link" to avian dinosaurs and thus birds losing their teeth.

There appears to be some evidence of such in sauropods.

Kindest regards,

James

Ah, but you get science! Even I was confused by what the site meant by "herbivorous dinosaurs"...anyone would think Triceratops right off the bat.

Hopefully I'll be working on Ornithischian beaks at some point in the next two years.

Gizzard stones have in fact been found in Caudipteryx, which is indeed a non-avian theropod, but the organ specifically associated with loss of teeth in birds is the crop, which store food, and not gizzard stones (aka gastroliths). Check it out: http://www.pnas.org/content/108/38/15904.long
The primitive birds Hongshanornis and Sapeornis have both been found with seed-filled crops and reduced teeth. Jeholornis, a very primitive bird has not been found with a crop, but may have had one because it too was discovered with seeds and had reduced teeth. What's known for sure is that a crop, as well as associated tooth-loss, occurred a couple of times in different lineages of basal birds. As such, crops are probably a bird synapomorphy.

 

[Dragan Glas]

Greetings,

Yes, I now see what you mean - remember, I'm not a scientist, just from "the IT crowd".

The Wiki article on Triceratops did say that the beak was believed to have evolved as a less stressful means of pulling vegetation - "at grasping and plucking than biting" - although, as you say, the teeth did all the masticating.

The interesting thing would be to find the equivalent of gizzard stones in non-avian theropods - which would be a possible "missing link" to avian dinosaurs and thus birds losing their teeth.

There appears to be some evidence of such in sauropods.

Kindest regards,

James

Ah, but you get science! Even I was confused by what the site meant by "herbivorous dinosaurs"...anyone would think Triceratops right off the bat.

Hopefully I'll be working on Ornithischian beaks at some point in the next two years.

Gizzard stones have in fact been found in Caudipteryx, which is indeed a non-avian theropod, but the organ specifically associated with loss of teeth in birds is the crop, which store food, and not gizzard stones (aka gastroliths). Check it out: http://www.pnas.org/content/108/38/15904.long
The primitive birds Hongshanornis and Sapeornis have both been found with seed-filled crops and reduced teeth. Jeholornis, a very primitive bird has not been found with a crop, but may have had one because it too was discovered with seeds and had reduced teeth. What's known for sure is that a crop, as well as associated tooth-loss, occurred a couple of times in different lineages of basal birds. As such, crops are probably a bird synapomorphy.

Interesting article on crops.

From the "Discussion" section, I gather that my main point - which I didn't make clear - is correct: that the evolution of the gizzard in dinosaurs pre-dated/facilitated(?) the evolution of the crop, which itself was either a pre-cursor or synchronous with the loss of teeth in birds.

What's particularly interesting is that a later paper explores the possibility of seasonal diet being indicative of "plasticity" in the crop and gizzard's function. Gizzards also appear to date back to fish, which pre-date crocodilia both of whose function appear to be related to buoyancy rather than digestion, though I can't help feeling that - in early aquatic species - it would be dual-functional; related to buoyancy and digestion. With later purely land-based species, the buoyancy function presumably would be irrelevant/lost, and the digestion function would become the norm.

Also interesting (in your cited article) is the fact that the hoatzin, which is considered a "primitive" bird, has a crop which functions more like a rumen, in which fermentation occurs. Equally, birds of prey and hummingbirds have crops which don't appear to be applicable to their diet - crops being thought indicative of herbivores.

I'm wondering if the evolution of the crop and its function depends upon which non-avian lineage subsequent avian lineages evolved: herbivorous, piscivorous, insectivorous, etc. Particularly omnivorous for seasonal "plasticity" in their functions.

All the above is speculation on my part - it would be interesting if any of it was confirmed by suitable studies.

I gather that there are no lineages where crops exist without pre-existing gizzards? If correct, then my main point above would appear to be supported.

Kindest regards,

James

 

[Rumraket]

How many DNA "letters" are required to build an ATP motor? A thousand? A million? More?

Exactly all the letters required to encode all the proteins and regulatory regions relevant to the synthesis and regulation of an ATP-synthase. So probably over tens of thousands.

Isn't this kind of obvious? Why do creationists ask these intensely stupid questions they must know the answer to?

 

[Vivre]

Hats off to you. I am impressed.

Well, if you enjoy learning about fossils, I hope you will take the time to stop by my blog and take a guess at my monthly blog series, Know Your Bones.

Thanks
... and for the push to check out the blog which I'd been putting off 'til the right time window apears. ... I'm on my way.

 

[Vivre]

Isn't this kind of obvious? Why do creationists ask these intensely stupid questions they must know the answer to?

Yes. Even if it's not understandable for all the specifics (how can it without studying?), it is possible to get the basic comprehensions and I think that is what nags at them.

I too think that the whole agreement to this debate served nothing but to misuse it for pushing ones own agenda. If you regard Ofnf's and his companions video-history they've long been searching for this kind of opportunity. Their recent videos are an obvious proof that it was all about harvesting fresh food for lying. (To my understanding they committed report-worthy calumny.)

Respect for AronRa that he manages to stay out of that rotten morass and rather points to it for anybody to check it out for themselves.

... and besides - thanks for that biologs-link ... I've now started reading the whole series after I found this specific page very helpful

 

[Isotelus]

Interesting article on crops.

From the "Discussion" section, I gather that my main point - which I didn't make clear - is correct: that the evolution of the gizzard in dinosaurs pre-dated/facilitated(?) the evolution of the crop, which itself was either a pre-cursor or synchronous with the loss of teeth in birds.

I don't know about facilitated...can you elaborate? I'm not aware of any evidence that there is any connection. Just to be clear we're on the same page, crops and gizzards are totally different and unassociated organs with different functions (aside from the fact that they're both part of the digestive system), yes? But as you say, gizzards definitely pre-dated crops. They have been found in both ornithischian and saurischian dinosaurs, crocodillians (as you noted below), and pterosaurs, so gizzards are likely a trait shared by Archosaurs as a whole.

What's particularly interesting is that a later paper explores the possibility of seasonal diet being indicative of "plasticity" in the crop and gizzard's function. Gizzards also appear to date back to fish, which pre-date crocodilia both of whose function appear to be related to buoyancy rather than digestion, though I can't help feeling that - in early aquatic species - it would be dual-functional; related to buoyancy and digestion. With later purely land-based species, the buoyancy function presumably would be irrelevant/lost, and the digestion function would become the norm.

I didn't see any reference to crops in that paper...but maybe I missed it. Where were they discussed? Also, are you saying that fish gizzards are homologous to crocodile gizzards?

Also interesting (in your cited article) is the fact that the hoatzin, which is considered a "primitive" bird, has a crop which functions more like a rumen, in which fermentation occurs. Equally, birds of prey and hummingbirds have crops which don't appear to be applicable to their diet - crops being thought indicative of herbivores.

I'm wondering if the evolution of the crop and its function depends upon which non-avian lineage subsequent avian lineages evolved: herbivorous, piscivorous, insectivorous, etc. Particularly omnivorous for seasonal "plasticity" in their functions.

All the above is speculation on my part - it would be interesting if any of it was confirmed by suitable studies.

For modern birds like birds of prey and hummingbirds, the crop's primary function (first and foremost: storage) has been fairly well-maintained, although it certainly may have been co-opted in terms of the type of food it stores. The hoatzin is wierd, to say the least. It has some primitive aspects (I'm assuming you're thinking of those clawed digits), though it's grouped variably within Neognathae (which includes all birds you could ever imagine except for the ratites). It would be equally important to consider the birds that are more primitive than the hoatzin, which include ducks, geese, chickens, pheasants, etc (the most basal neognaths) and perhaps most importantly, the ratites (paleognaths). Incidentally, all of these have herbivorous to omnivorous diets. This could be indicative of the state of the very earliest and unequivocal modern birds. Whatever it was, it would have been a paleognath, and it would have had no teeth (a synapomorphy for modern birds, as it happens). I would also assume it had a crop, as most modern birds do (and if they don't, I'm fairly sure they're considered to have been lost secondarily). The annoying thing is there's no Mesozoic fossil record of paleognaths as of yet. That alone could open a whole new can of worms of terms of our discussion. I wrote a 12 page single-spaced paper for a class that reviewed the current knowledge on the evolution of modern birds and their closest relatives (which included loss of teeth), so I could go on and on and on and on about this. You probably don't want to get me started. I even had hwin read it, poor guy. :lol:

Btw, I don't know if I really had a point in anything above, and it doesn't necessarily address your main point...I'm just writing out my thoughts on the subject. Heh.

In regards to the non-avian lineage birds are derived from, Zheng et al., (2011) (aka the crop paper) state that the earliest birds were likely eating insects or other types of small prey, so it would follow that their closest non-avian ancestors were likely much the same. Archaeopteryx is often considered to be an early bird, if not the earliest, but Dromaeosaurid dinosaurs group closely to the base of the bird lineage, and are indeed insectivores/carnivores. Interesting to note that the seed-eating Jeholornis, which I mentioned earlier, groups near Archaeopteryx (which it superficially resembles very closely). Sapeornis, which is one of the fossils found with reduced teeth and a crop, often groups near Jeholornis. We can continue to speculate here, but I don't know if any studies have looked at early birds and diet comprehensively.

And speaking of speculation, I think there was a study by Longrich that discussed the possibility of Neornithine birds (aka modern birds) being better adapted for seasonal change, and so were potentially predisposed to make it through the hullabaloo in the late Cretaceous.

I gather that there are no lineages where crops exist without pre-existing gizzards? If correct, then my main point above would appear to be supported.

Not in birds, no, but again, I'm not sure if crops and gizzards have much to do with one another evolutionarily speaking.

 

[Dragan Glas]

Greetings,

Interesting article on crops.

From the "Discussion" section, I gather that my main point - which I didn't make clear - is correct: that the evolution of the gizzard in dinosaurs pre-dated/facilitated(?) the evolution of the crop, which itself was either a pre-cursor or synchronous with the loss of teeth in birds.

I don't know about facilitated...can you elaborate? I'm not aware of any evidence that there is any connection. Just to be clear we're on the same page, crops and gizzards are totally different and unassociated organs with different functions (aside from the fact that they're both part of the digestive system), yes? But as you say, gizzards definitely pre-dated crops. They have been found in both ornithischian and saurischian dinosaurs, crocodillians (as you noted below), and pterosaurs, so gizzards are likely a trait shared by Archosaurs as a whole.

My line of thinking went like this:

In humans, as with other animals that masticate their food, chewing comprises a combination of (pre-)molars and saliva to break down food before it's swallowed. Indeed, chewing provides time to allow saliva to "pre-digest" food - particularly carbohydrates (as the acid in the stomach deals with proteins).

Bearing this in mind, my idea was that the evolution of the gizzard, along with the presence of gastroliths, allows the breaking-down of harder fibrous material in the diet. Effectively, it performs the same function as (pre-)molars - thus, begging the question as to their necessity. If this is the case, then (pre-)molars would tend to be lost prior to other teeth, rather than simultaneously. If there was any fossil evidence of this, it would support the idea that the gizzard essentially supplanted the need for (pre-)molars.

However, since chewing allows time for saliva to pre-digest food, the gradual loss of such teeth would mean that that part of the digestive process would have to be done elsewhere - hence the evolution of the crop: not just as a mere storage facility for later digestion but to take the place of the saliva's role. This is what your paper appears to indicate:

In modern seed-eating birds the crop provides storage, so that a number of seeds can be gathered quickly and then processed later in a more secure location without interference from competitors and/or predators. The mucus in the crop softens hard seeds so that they are more easily ground by the gizzard. The gizzard may be a more basal feature for birds, because it is widely distributed in sister groups, such as modern crocodilians. In recent birds the gizzard is posterior to the proventriculus or glandular part of the stomach. The practice of collecting large numbers of small stones in the gizzard is characteristic of seed eaters among modern birds and is often correlated with a well-developed crop.

Which neatly summarises my main idea - that the gizzard supplanted the function of (pre-)molars and the loss of such teeth required that the role of saliva be done later in the digestive process than in the mouth, hence the evolution of the crop and its mucus to "soften" the seeds. Its storage function is more related to softening by mucus rather than, say, a pelican's gullet or rodents' cheek-pouches providing mere storage.

At least to my mind...

What's particularly interesting is that a later paper explores the possibility of seasonal diet being indicative of "plasticity" in the crop and gizzard's function. Gizzards also appear to date back to fish, which pre-date crocodilia both of whose function appear to be related to buoyancy rather than digestion, though I can't help feeling that - in early aquatic species - it would be dual-functional; related to buoyancy and digestion. With later purely land-based species, the buoyancy function presumably would be irrelevant/lost, and the digestion function would become the norm.

I didn't see any reference to crops in that paper...but maybe I missed it. Where were they discussed?

No, Isotelus, you didn't miss it. :facepalm:

As I was typing, I was synthesizing the two papers in my mind and extrapolated that the paper's reference to "plasticity" of the gizzard's function might also extend to that of the crop - hence my reference to the hoatzin's crop being more reminiscent of the rumen. And, later, my speculation that their functions in later avians may have depended on which earlier (non-avian/basal avian) species from which they evolved.

I apologise for the faux pas.

Also, are you saying that fish gizzards are homologous to crocodile gizzards?

No - also part of my thinking being ahead of what I'm actually writing.

Since fish have bladders for buoyancy, their gizzards - along with gastroliths - don't have the same function. Equally, those in birds don't appear to have the same function as in other aquatic theropods with diving adaptations, such as crocodilians and pinnipeds - as my cited paper notes. The latters' gizzards appear to act as buoyancy devices - in place of fishes bladders - rather than being used in grinding down harder digested foodstuffs. (Although, again, I can't help the feeling that they must have some digestive function rather than being solely buoyancy-related.)

Also interesting (in your cited article) is the fact that the hoatzin, which is considered a "primitive" bird, has a crop which functions more like a rumen, in which fermentation occurs. Equally, birds of prey and hummingbirds have crops which don't appear to be applicable to their diet - crops being thought indicative of herbivores.

I'm wondering if the evolution of the crop and its function depends upon which non-avian lineage subsequent avian lineages evolved: herbivorous, piscivorous, insectivorous, etc. Particularly omnivorous for seasonal "plasticity" in their functions.

All the above is speculation on my part - it would be interesting if any of it was confirmed by suitable studies.

For modern birds like birds of prey and hummingbirds, the crop's primary function (first and foremost: storage) has been fairly well-maintained, although it certainly may have been co-opted in terms of the type of food it stores. The hoatzin is wierd, to say the least. It has some primitive aspects (I'm assuming you're thinking of those clawed digits), though it's grouped variably within Neognathae (which includes all birds you could ever imagine except for the ratites). It would be equally important to consider the birds that are more primitive than the hoatzin, which include ducks, geese, chickens, pheasants, etc (the most basal neognaths) and perhaps most importantly, the ratites (paleognaths). Incidentally, all of these have herbivorous to omnivorous diets. This could be indicative of the state of the very earliest and unequivocal modern birds. Whatever it was, it would have been a paleognath, and it would have had no teeth (a synapomorphy for modern birds, as it happens). I would also assume it had a crop, as most modern birds do (and if they don't, I'm fairly sure they're considered to have been lost secondarily). The annoying thing is there's no Mesozoic fossil record of paleognaths as of yet. That alone could open a whole new can of worms of terms of our discussion. I wrote a 12 page single-spaced paper for a class that reviewed the current knowledge on the evolution of modern birds and their closest relatives (which included loss of teeth), so I could go on and on and on and on about this. You probably don't want to get me started. I even had hwin read it, poor guy. :lol:

Your comment about the possibility of birds that don't have crops would be a possible counter-evidence to my suggestion of the crop with mucus fulfilling the role of saliva. Unless the lack of a crop implies non-herbivorous diets?!

Are there birds known to not have crops? (Although you later say not... :? )

If there are, and they lost them secondarily, was that due to change in environment and/or diet?

In your paper, it mentioned Jeholornis' gizzard but didn't seem to mention the presence of a crop, which was why I searched for articles trying to confirm whether it had one - this led me to the paper I cited, though it didn't clarify my question.

Btw, I don't know if I really had a point in anything above, and it doesn't necessarily address your main point...I'm just writing out my thoughts on the subject. Heh.

At least yours are well-informed - easily better than mine. Embarrassing, since I'm interested in ornithology - although not from the perspective of your speciality.

In regards to the non-avian lineage birds are derived from, Zheng et al., (2011) (aka the crop paper) state that the earliest birds were likely eating insects or other types of small prey, so it would follow that their closest non-avian ancestors were likely much the same. Archaeopteryx is often considered to be an early bird, if not the earliest, but Dromaeosaurid dinosaurs group closely to the base of the bird lineage, and are indeed insectivores/carnivores. Interesting to note that the seed-eating Jeholornis, which I mentioned earlier, groups near Archaeopteryx (which it superficially resembles very closely). Sapeornis, which is one of the fossils found with reduced teeth and a crop, often groups near Jeholornis. We can continue to speculate here, but I don't know if any studies have looked at early birds and diet comprehensively.

And speaking of speculation, I think there was a study by Longrich that discussed the possibility of Neornithine birds (aka modern birds) being better adapted for seasonal change, and so were potentially predisposed to make it through the hullabaloo in the late Cretaceous.

It would seem to be case, as most evolutionary "action" occurs at the margins - wetlands, where sometimes it's wet and sometimes it's dry, hence the need for maximal adaptability to environmental change. Earlier birds, which could adapt to seasonal availability of food, would be better off than those with a monotonous diet.

I gather that there are no lineages where crops exist without pre-existing gizzards? If correct, then my main point above would appear to be supported.

Not in birds, no, but again, I'm not sure if crops and gizzards have much to do with one another evolutionarily speaking.

Which goes back to my earlier question and your statement that:

Incidentally, all of these have herbivorous to omnivorous diets. This could be indicative of the state of the very earliest and unequivocal modern birds. Whatever it was, it would have been a paleognath, and it would have had no teeth (a synapomorphy for modern birds, as it happens). I would also assume it had a crop, as most modern birds do (and if they don't, I'm fairly sure they're considered to have been lost secondarily). The annoying thing is there's no Mesozoic fossil record of paleognaths as of yet. That alone could open a whole new can of worms of terms of our discussion.

Although, as you note, there appears to be a lack of relevant fossils to clear up this question.

I hope all the above clarifies my "black box" thinking in the earlier post ... somewhat.

If not, you can always ask me to "resubmit" my thoughts!

Kindest regards,

James

 

[Isotelus]

Greetings,

My line of thinking went like this:

In humans, as with other animals that masticate their food, chewing comprises a combination of (pre-)molars and saliva to break down food before it's swallowed. Indeed, chewing provides time to allow saliva to "pre-digest" food - particularly carbohydrates (as the acid in the stomach deals with proteins).

Bearing this in mind, my idea was that the evolution of the gizzard, along with the presence of gastroliths, allows the breaking-down of harder fibrous material in the diet. Effectively, it performs the same function as (pre-)molars - thus, begging the question as to their necessity. If this is the case, then (pre-)molars would tend to be lost prior to other teeth, rather than simultaneously. If there was any fossil evidence of this, it would support the idea that the gizzard essentially supplanted the need for (pre-)molars.

However, since chewing allows time for saliva to pre-digest food, the gradual loss of such teeth would mean that that part of the digestive process would have to be done elsewhere - hence the evolution of the crop: not just as a mere storage facility for later digestion but to take the place of the saliva's role. This is what your paper appears to indicate:

In modern seed-eating birds the crop provides storage, so that a number of seeds can be gathered quickly and then processed later in a more secure location without interference from competitors and/or predators. The mucus in the crop softens hard seeds so that they are more easily ground by the gizzard. The gizzard may be a more basal feature for birds, because it is widely distributed in sister groups, such as modern crocodilians. In recent birds the gizzard is posterior to the proventriculus or glandular part of the stomach. The practice of collecting large numbers of small stones in the gizzard is characteristic of seed eaters among modern birds and is often correlated with a well-developed crop.

Which neatly summarises my main idea - that the gizzard supplanted the function of (pre-)molars and the loss of such teeth required that the role of saliva be done later in the digestive process than in the mouth, hence the evolution of the crop and its mucus to "soften" the seeds. Its storage function is more related to softening by mucus rather than, say, a pelican's gullet or rodents' cheek-pouches providing mere storage.

At least to my mind...

Gotcha. That clears things up for me for the most part, although there's one thing that confuses me. You're suggesting that the gizzard supplanted the need for molars (which would follow logically; no disagreement there)...but the dinosaurs we're talking about didn't have molars. Archosaurs in general (aside from certain herbivorous ones, of course) couldn't masticate or chew their food, and that includes birds, primitive or not. Going back to bird evolution in particular, both the jaws and teeth of those near or on the avian lineage were adapted for shearing and cutting prey items so they could fit down the throat, and so neither the teeth or saliva played the major pre-processing role for gizzards to supplant. The underlined sentence from the above quote also doesn't necessarily imply a direct connection between the evolution of the crop and the gizzard; an indirect involvement of both in the loss of teeth and evolution of the beak is perhaps more plausible given what is currently known. In regards to crop function, I would reinstate the importance of storage, one because of the first sentence from the above quote, and two (and more importantly) because there's something else about birds that involves and is necessitated both by the ability of the crop to store/mushify food and the gizzard to efficiently process it. Something about metabolism...

No, Isotelus, you didn't miss it. :facepalm:

As I was typing, I was synthesizing the two papers in my mind and extrapolated that the paper's reference to "plasticity" of the gizzard's function might also extend to that of the crop - hence my reference to the hoatzin's crop being more reminiscent of the rumen. And, later, my speculation that their functions in later avians may have depended on which earlier (non-avian/basal avian) species from which they evolved.

I apologise for the faux pas.

No need to apologize (you're not misrepresenting or quote-mining as can occur on these forums....)! I figured that's what happened after I did the whole Ctrl F trick.

No - also part of my thinking being ahead of what I'm actually writing.

Since fish have bladders for buoyancy, their gizzards - along with gastroliths - don't have the same function. Equally, those in birds don't appear to have the same function as in other aquatic theropods with diving adaptations, such as crocodilians and pinnipeds - as my cited paper notes. The latters' gizzards appear to act as buoyancy devices - in place of fishes bladders - rather than being used in grinding down harder digested foodstuffs. (Although, again, I can't help the feeling that they must have some digestive function rather than being solely buoyancy-related.)

Right, so effectively you're describing analogous structures in a sense. It would make sense to me that gizzards in crocs do help with digestion, because they can't chew. I can't remember where I saw this, but some newer research suggests that gastroliths may stabilize the body in water, because at least in some cases, their mass is too small to have an effect on buoyancy.

Your comment about the possibility of birds that don't have crops would be a possible counter-evidence to my suggestion of the crop with mucus fulfilling the role of saliva. Unless the lack of a crop implies non-herbivorous diets?!

Are there birds known to not have crops? (Although you later say not... :? )

If there are, and they lost them secondarily, was that due to change in environment and/or diet?

In your paper, it mentioned Jeholornis' gizzard but didn't seem to mention the presence of a crop, which was why I searched for articles trying to confirm whether it had one - this led me to the paper I cited, though it didn't clarify my question.

Yep. Owls and buttonquails (which aren't actually quails, btw) lack crops entirely. In some cases the crop is also somewhat under-developed in comparison to most birds, as is the case with ducks and geese. I don't know why this is the case, or if it's really been looked into. Geese for sure do most of their digestion in their enlarged caeca.

Now when you asked this:

I gather that there are no lineages where crops exist without pre-existing gizzards? If correct, then my main point above would appear to be supported.

I thought you were asking if there were any birds that had crops, but no gizzards, to which the answer is no. All birds have gizzards, but as above, not all birds have crops. Hopefully that's clear.

The authors surmised that Jeholornis easily could have had a crop, but it just hasn't preserved. They pointed to other specimens of which they have over a 100 examples, and evidence of crops occurring only in two individuals.

At least yours are well-informed - easily better than mine. Embarrassing, since I'm interested in ornithology - although not from the perspective of your speciality.

I was considering going into ornithology myself before I decided to pursue paleontology. I wanted to work on conservation of endemic Hawaiian birds.

It would seem to be case, as most evolutionary "action" occurs at the margins - wetlands, where sometimes it's wet and sometimes it's dry, hence the need for maximal adaptability to environmental change. Earlier birds, which could adapt to seasonal availability of food, would be better off than those with a monotonous diet.

Indeed! And herein lies the rub: why did none of the more primitive birds, some of which could vary their diet accordingly, not make it past the Cretaceous? It's a question without a clear answer. Granted, the fossil birds with crops we were discussing are all from the Early Cretaceous. But good 'ol Ichthyornis was for all intents and purposes a modern bird with teeth, albeit reduced. At the beginning of the Cenozoic, modern birds take off (pun intended), and there are a fair number of fossils to show for this. It actually probably relates on some level to my rather cryptic comment on metabolism above. As always...need more evidence.

And are we derailing the thread, or can we make an argument that our discussion doesn't sufficiently deviate from the overall topic of this debate?

 

[Dragan Glas]

Greetings,

Greetings,

My line of thinking went like this:

In humans, as with other animals that masticate their food, chewing comprises a combination of (pre-)molars and saliva to break down food before it's swallowed. Indeed, chewing provides time to allow saliva to "pre-digest" food - particularly carbohydrates (as the acid in the stomach deals with proteins).

Bearing this in mind, my idea was that the evolution of the gizzard, along with the presence of gastroliths, allows the breaking-down of harder fibrous material in the diet. Effectively, it performs the same function as (pre-)molars - thus, begging the question as to their necessity. If this is the case, then (pre-)molars would tend to be lost prior to other teeth, rather than simultaneously. If there was any fossil evidence of this, it would support the idea that the gizzard essentially supplanted the need for (pre-)molars.

However, since chewing allows time for saliva to pre-digest food, the gradual loss of such teeth would mean that that part of the digestive process would have to be done elsewhere - hence the evolution of the crop: not just as a mere storage facility for later digestion but to take the place of the saliva's role. This is what your paper appears to indicate:

[...]

Which neatly summarises my main idea - that the gizzard supplanted the function of (pre-)molars and the loss of such teeth required that the role of saliva be done later in the digestive process than in the mouth, hence the evolution of the crop and its mucus to "soften" the seeds. Its storage function is more related to softening by mucus rather than, say, a pelican's gullet or rodents' cheek-pouches providing mere storage.

At least to my mind...

Gotcha. That clears things up for me for the most part, although there's one thing that confuses me. You're suggesting that the gizzard supplanted the need for molars (which would follow logically; no disagreement there)...but the dinosaurs we're talking about didn't have molars.

:facepalm:

Which neatly pulls the teeth of my argument. :lol:

(Serves me right for not reading up about it first before posting.

* Makes note to self: don't type before reading. *)

Archosaurs in general (aside from certain herbivorous ones, of course) couldn't masticate or chew their food, and that includes birds, primitive or not. Going back to bird evolution in particular, both the jaws and teeth of those near or on the avian lineage were adapted for shearing and cutting prey items so they could fit down the throat, and so neither the teeth or saliva played the major pre-processing role for gizzards to supplant. The underlined sentence from the above quote also doesn't necessarily imply a direct connection between the evolution of the crop and the gizzard; an indirect involvement of both in the loss of teeth and evolution of the beak is perhaps more plausible given what is currently known. In regards to crop function, I would reinstate the importance of storage, one because of the first sentence from the above quote, and two (and more importantly) because there's something else about birds that involves and is necessitated both by the ability of the crop to store/mushify food and the gizzard to efficiently process it. Something about metabolism...

At the time, I was thinking that what was really needed was a phylogeny of the digestive system, from mouth to anus, to identify who had what, and - hopefully - why?

I found a interesting paper - Gizzards versus Teeth - that touches on a lot of what we've been discussing, including your cryptic metabolism comment. It also included a simple "tree" of the relationship between gizzards, teeth, etc, and references two other papers with more detailed "trees" - here and here. Their review of the possible reasons for one or the other being present is particularly fascinating: perhaps the most interesting being the fact that the gizzard is ideal for flight as it places digestion nearest the centre of gravity, whereas teeth mean a large head (strong jawbones and masticatory muscles for chewing), which would make flight awkward. Hence, gizzards favour flight - which explains why all birds have them.

A interesting corollary to this is that most birds fly with their head out-front, including tall birds. Cranes, for example, do this. In contrast, shoe-billed storks (aka, "whale-heads"), which have large heads/bills, fly with their head resting back between their wings. A interesting exception to the long-necked birds flying with their heads out-front are larger herons and egrets - like the (Great Blue/Grey) heron and large egret - which also fly with their heads back between their wings - it's the key identifier to distinguishing between cranes and these particular birds in flight. (Also, divers tend to fly with their heads at a lower level than the plane of their bodies.)

This would appear to suggest that the heron's head is heavier relative to that of cranes and/or the length/strength of the neck's ability to support it out-front during flight. (Perhaps divers' heads are relatively heavy too but not so heavy that they require the heron's adaptation!?)

I'm sure there's a study/paper on birds to be written, by a under-graduate who's lost for an idea for their degree, on the relationship between the centre of gravity, the weight of the head, the head's distance from the centre-of-gravity and the length/strength of the neck.

No, Isotelus, you didn't miss it. :facepalm:

As I was typing, I was synthesizing the two papers in my mind and extrapolated that the paper's reference to "plasticity" of the gizzard's function might also extend to that of the crop - hence my reference to the hoatzin's crop being more reminiscent of the rumen. And, later, my speculation that their functions in later avians may have depended on which earlier (non-avian/basal avian) species from which they evolved.

I apologise for the faux pas.

No need to apologize (you're not misrepresenting or quote-mining as can occur on these forums....)! I figured that's what happened after I did the whole Ctrl F trick.

Thank you.

(* Makes note to self: don't synthesize whilst typing. *)

No - also part of my thinking being ahead of what I'm actually writing.

Since fish have bladders for buoyancy, their gizzards - along with gastroliths - don't have the same function. Equally, those in birds don't appear to have the same function as in other aquatic theropods with diving adaptations, such as crocodilians and pinnipeds - as my cited paper notes. The latters' gizzards appear to act as buoyancy devices - in place of fishes bladders - rather than being used in grinding down harder digested foodstuffs. (Although, again, I can't help the feeling that they must have some digestive function rather than being solely buoyancy-related.)

Right, so effectively you're describing analogous structures in a sense.

Agreed.

It would make sense to me that gizzards in crocs do help with digestion, because they can't chew. I can't remember where I saw this, but some newer research suggests that gastroliths may stabilize the body in water, because at least in some cases, their mass is too small to have an effect on buoyancy.

I did look for some more information regarding gastroliths in crocodiles to clarify this but all I could find was a Google Books reference (pages 36-39 regarding "Digestion")

Your comment about the possibility of birds that don't have crops would be a possible counter-evidence to my suggestion of the crop with mucus fulfilling the role of saliva. Unless the lack of a crop implies non-herbivorous diets?!

Are there birds known to not have crops? (Although you later say not... :? )

If there are, and they lost them secondarily, was that due to change in environment and/or diet?

In your paper, it mentioned Jeholornis' gizzard but didn't seem to mention the presence of a crop, which was why I searched for articles trying to confirm whether it had one - this led me to the paper I cited, though it didn't clarify my question.

Yep. Owls and buttonquails (which aren't actually quails, btw) lack crops entirely. In some cases the crop is also somewhat under-developed in comparison to most birds, as is the case with ducks and geese. I don't know why this is the case, or if it's really been looked into. Geese for sure do most of their digestion in their enlarged caeca.

If the main purpose of crops is storage (for later digestion), owls might not need it due to less likelihood of being disturbed - at least, nocturnal species, since there are diurnal owls.

Diurnal birds-of-prey would face stiffer competition and likelihood of disturbance on kills, hence the need for crops.

However, it appears that - genetically - owls are more related to nightjars and their allies than falconiformes, which may be a more relevant factor.

Button quails though...?

Description[/url]"]The buttonquails are a group of small terrestrial birds. The smallest species is the quail-plover, the only species in the genus Ortyxelos, which is 10 cm (3.9 in) in length and weighs only 20 g (0.71 oz). The buttonquails in the genus Turnix range from 12–23 cm (4.7–9.1 in) in length and weigh between 30–130 g (1.1–4.6 oz). They superficially resemble the true quails of the genus Coturnix, but differ from them in lacking a hind toe and a crop. The females of this family also possess a unique vocal organ created by an enlarged trachea and inflatable bulb in the oesophagus, which they use to produce a booming call.

This would appear to suggest that not all button quails are without crops - just the Turnix genus: and it's possible that, in the latter case, it was sacrificed for the enlarged trachea and inflatable oesophagus for mating calls!? (On a side-note, songbirds appear to have only a small dilation of the oesophagus where the crop would be.)

As for ducks and geese, this may be more related to their being "weeders" - preferring grasses - rather than (broad) leaves and/or seeds.

Gulls and penguins don't appear to have crops either, though this could be due to their diet being almost exclusively piscine in nature.

Now when you asked this:

I gather that there are no lineages where crops exist without pre-existing gizzards? If correct, then my main point above would appear to be supported.

I thought you were asking if there were any birds that had crops, but no gizzards, to which the answer is no. All birds have gizzards, but as above, not all birds have crops. Hopefully that's clear.

The authors surmised that Jeholornis easily could have had a crop, but it just hasn't preserved. They pointed to other specimens of which they have over a 100 examples, and evidence of crops occurring only in two individuals.

So it appears that they may well have had crops - just that the fossilized evidence is sparse.

At least yours are well-informed - easily better than mine. Embarrassing, since I'm interested in ornithology - although not from the perspective of your speciality.

I was considering going into ornithology myself before I decided to pursue paleontology. I wanted to work on conservation of endemic Hawaiian birds.

As a child, my mother encouraged an interest in Nature - birds, animals, flowers, trees, and astronomy.

I am a member of Birdwatch Ireland, Irish Wildlife Trust and Astronomy Ireland (in the UK, I was a member of the RSPB).

It would seem to be case, as most evolutionary "action" occurs at the margins - wetlands, where sometimes it's wet and sometimes it's dry, hence the need for maximal adaptability to environmental change. Earlier birds, which could adapt to seasonal availability of food, would be better off than those with a monotonous diet.

Indeed! And herein lies the rub: why did none of the more primitive birds, some of which could vary their diet accordingly, not make it past the Cretaceous? It's a question without a clear answer. Granted, the fossil birds with crops we were discussing are all from the Early Cretaceous. But good 'ol Ichthyornis was for all intents and purposes a modern bird with teeth, albeit reduced. At the beginning of the Cenozoic, modern birds take off (pun intended), and there are a fair number of fossils to show for this. It actually probably relates on some level to my rather cryptic comment on metabolism above. As always...need more evidence.

Ichthyornis appears to have been a piscivore rather than a omnivore - although that's not the reason for its name, as you'll be aware! - thus may have been more prone to an extinction event where the sea-level dropped by over 150m.

It should not be surprising that the extinction of omnivores was a case of hit-or-miss depending on where and how the flora/fauna were affected by the change in climate at the time.

As you note, metabolism.

And are we derailing the thread, or can we make an argument that our discussion doesn't sufficiently deviate from the overall topic of this debate?

I don't think so - we're still discussing evolution being a better explanation than creationism for all of this, aren't we? Besides, others already have taken it on a meandering course.

Kindest regards,

James

 

[Dragan Glas]

Greetings,

Interesting study and implications:

Researchers declassify dinosaurs as being the great-great-grandparents of birds

Kindest regards,

James

 

[ldmitruk]

Greetings,

Interesting study and implications:

Researchers declassify dinosaurs as being the great-great-grandparents of birds

Kindest regards,

James

Que creationists saying once again science got it wrong in 3, 2, 1...