Just waffling here to sort out my own thoughts.

The oldest fossil of a true bird in 70 million years ago, a loon, Gaviiformes, in the age of dinosaurs but only just. It is also uncertain whether this fossil (Enaliornis) is a true loon or a Hesperornithes type of Ornithurae. There is also Limenavis of the same age.

The oldest unequivocal true loon, gaviform, dates to 35 million years ago.

If we take 70 million years ago as the separation point of loons and other birds, and combine that with the multitude of Eocene fossils of true birds, then the date of divergence of the ratites (Paleognathae) from other birds (Neognathae) comes out at 140 million years ago grom genetic analysis.

140 million years ago is early. The first paraves date from 160 million years ago. The date of Archaeopteryx fossils is somewhere in the range of 150.8–148.5 million years ago.

Even if we don’t accept the 70 million year old fossil as a true bird, the last universal common ancestor of all true birds dates well back into the age of dinosaurs. So where are the fossils of true birds from the Cretaceous? A serious question, and we can’t sweep it under the rug as thousands of flying birdlike creatures have preserved fossils from the Cretaceous.

Among fossils, the defining feature of a true bird (Aves) is taken to be the occurrence of a “plowshare-shaped” pygostyle. “Pygostyles probably began to evolve very early in the Cretaceous period, perhaps 140-130 million years ago”, but there are pygostyles that are not “plowshare-shaped” beloinging to for example Confuciusornis.

This brings us to the Ornithurae. These have the “characteristic tail morphology of all extant birds”. They include the true birds (Neoornithes) together with the diving birds Ichthyornis, Hesperornithes and Limenavis. Icnthyornis differs from modern birds in having teeth.

“Hesperornitheans were originally combined with Ichthyornis in the paraphyletic group “Odontornithes” by Othniel Charles Marsh, in 1873. In 1875, they were separated as Odontolcae. The group was often considered to be related to loons and grebes, or to the Paleognathae (based on perceived similarities in the bony palate). These similarities, however, as the more recently determined fact that the osteons of their bones – at least in Hesperornis – were arranged in a pattern similar to that in Neognathae, are today considered to be due to convergent evolution.”

What does this all boil down to?

• Possibility 1. The similarity of Hesperornithes and Neognathae is not due to convergent evolution, but Hesperornithes is a true bird. This points to the truth of circa 140 million years ago as the date of last universal ancestor of all true birds (Neoornithes = Paleognathae + Neognathae).
• Possibility 2. In addition to Possibility 1. Perhaps the plowshare-shaped pygostyle came first and rod-shaped pygostyles evolved from that. That would make Confuciusornis a true bird as well, a Neornithes. The earliest Confuciusornis fossil, E. zhengi, dates to 131 Ma. At a guess, it would make Confuciusornis more closely related to the sparrows than to the ostrich.
• Possibility 3. Hesperornithes is not a true bird, but evolved in parallel with true birds for perhaps 30 million years from 100 to 70 million years ago. The last common ancestor of sparrow and ostrich was more recent than genetics sugests, perhaps of order 100 million years ago.

The beak. One factor that led to the dominant acceptance of Possibility 3 is that Confuciusornis from 131 Ma has a beak but not a ploughshare-shaped pygostyle whereas Ichthyornis at 89 Ma, an older relative of Hesperornithes, has a ploughshare-shaped pygostyle but teeth rather than a beak.

Could it be that teeth developed twice, once once way back but also redeveloped much later? Or three times: “Modern birds all lack teeth, except for the South American hoatzin, Opisthocomus, whose hatchlings have a small tooth that they use to help them escape from their egg and then shed.”

Dang it. Perhaps I should stick to the obvious.

• Confuciusornis resembles modern passerines because it was closely related to ancient passerines.
• Ichthyornis closely resembles modern gulls/terns because it was closely related to modern gulls/terns.
• Hesperornithes closely resembles modern loons because it was closely related to modern loons

The timing would then be a close match to evolution of modern birds from genetic studies. And it would help explain the absense of fossils of true from the Jurassic Era. The fossils were there but were not recognised as true birds and instead thought to be examples of convergent evolution.

Do they need feathers to be considered a bird

Cymek said:

Do they need feathers to be considered a bird

All birds have feathers but not all animals with feathers are birds. T-rex had feathers.

dv said:

Cymek said:

Do they need feathers to be considered a bird

All birds have feathers but not all animals with feathers are birds. T-rex had feathers.

So an animal with all the characteristics of a bird bar feathers isn’t considered a bird ?

Cymek said:

dv said:

Cymek said:

Do they need feathers to be considered a bird

All birds have feathers but not all animals with feathers are birds. T-rex had feathers.

So an animal with all the characteristics of a bird bar feathers isn’t considered a bird ?

There are no such animals. I’m just telling you what’s the case. It happens that in the real universe all birds have feathers.

dv said:

Cymek said:

dv said:

All birds have feathers but not all animals with feathers are birds. T-rex had feathers.

So an animal with all the characteristics of a bird bar feathers isn’t considered a bird ?

There are no such animals. I’m just telling you what’s the case. It happens that in the real universe all birds have feathers.

Well on this planet, yeah.

what about baby birds

Cymek said:

Do they need feathers to be considered a bird

No. There are three types of feathers by the way. Fluffy downy feathers are shared not just with dinosaurs (dinofluff) but pterosaurs.
Symmetric feathers and asymmetric flight feathers are the other two.

Here’s what I was looking for. I’m proposing (as a tentative possibility only) that Confusciusornis could perhaps be true birds.(Neornithes).

Hold on, perhaps Enantiornithes are related to the ratites after all. That would explain the absense of ratite fossils, they’re not missing just mislabled. https://en.wikipedia.org/wiki/Enantiornithes. In terms of age, the best known Enantiornithes is Longipteryx at 120.3 million years ago. That ties in with the above timing. The shape is kingfisher-like. Kingfishers aren’t ratites. “Some researchers classify enantiornitheans, along with the true birds, in the class Aves.” from wikipedia.

Gonna do up a little chart showing the timing of the development of feathers in Dinosauria.

It should be noted that it is now known that simple filamental structures that appear identical to feathers have been found in the fossils of some pterosaurs. All up it appears that feathers arose “independently” at least four times among vertebrates.

The reason that I’ve put the independently in doubt-quotes is that it’s clear enough that the reptilian integument is predisposed to evolving this trait.

Btw I will never stop being salty about the fact that Ornithischia is not the branch that birds are descended from. They really messed up on that one.

dv said:

Btw I will never stop being salty about the fact that Ornithischia is not the branch that birds are descended from. They really messed up on that one.

Confuses a lot of people, which may have been their plan.

Post 1 of 4

So here’s a mudmap I’ve done up showing the feathering of various clades of dinosaurs.

Feathers, broadly defined, have arisen at least four times among vertebrates.

Simple, filamentous feathers arose in the genus Tianyulong, a heterodontosaurid that lived around 160 mya and was extinct by 150 mya. Also, similar structures are found in several species of Psittacosauridae, which arose around 125 mya and was extinct soon after 100 mya. Both of these are in Ornithischia, the branch of Dinosauria that includes Stegosaurs and Triceratops etc, and which did NOT contain birds.

Filamentous feathers have also been found on some Pterosaur fossils from 160 mya. They aren’t shown on this diagram (since pterosaurs weren’t dinosaurs). There’s some dispute about whether these Pterosaur pycnofibers really do represent primitive feathers: if they are, it suggests that perhaps the potential to produce feathers was present in the most recent common ancestor of pterosaurs and dinosaurs, some 240 mya.

Finally of course, feathers arose among the ancestors of birds, over on the Saurischia side of the table. Coelurosauria and all their descendants have some kind of feathering. Tyrannosauroidea, Composognathidae, Ornithomimosauria, Oviraptorosauria did not develop pennaceous feathers.

Pennaceous feathers:

However, some Oviraptorosauria and at least one member of Tyrannosauroidea (Ubirajara) had long plumes, presumably for display purposes only.

Artist’s conception of Ubirajara and its ribbony plumes

Paraves contains all the beasts with proper pennaceous feathers: Dromosauridea, Troodontidae, Enantiornithes, Hesperornithes, Aves. All of these feathery groups survived right up until the K-T extinction event but of course only Aves survived the event. I found it interesting compiling this information because I honestly had no idea there were so many non-avian feathery clades that were wiped out by K-T. I wonder why it was Aves that survived.

I was also interested to learn that the separation of the two major groups of birds (Palaeognathae such as emus, tinamous and kiwis and such, versus Neognathae which is everything else) occurred before the extinction event.

The definition of Aves is “the most recent common ancestor of all living birds and all that ancestor’s descendants”.

(You can click the image for somewhat better resolution: the forum does some compression)

Post 2 of 4

This image is the same except that I’ve roped up the completely toothless (edentulous) beasts. The loss of teeth occurred gradually: after the development of the beak, there was a period where several small back teeth remained as grinders. After their loss, some birds relied on swallowing stones to be used as grinders in the belly.

The later members of Oviraptorosauria also went toothless not long after the birds did. Ornithomimosauria went the same way around 100 mya: as the name suggests, they “mimic birds” in many ways, with beaked and toothless jaws, often competing directly with birds for the same niches. (No pennaceous feathers though).

(You can click the image for somewhat better resolution: the forum does some compression)

Post 3 of 4

We normally associate wings with flight but its now clear enough that there were winged dinosaurs long before they were capable of flight. Perhaps they were capable of supporting small glides. Perhaps they were for display. Perhaps they helped with running. I’ve seen various theories.

In any case, all the Pennaraptora have wings of some kind. This includes all the Paraves with proper pennaceous feathers (Dromaeosauria, Troodontidae, Enantiornithes, Hesperornithes, Aves) but also includes Oviraptorosauria.

(You can click the image for somewhat better resolution: the forum does some compression)

Post 4 of 4

Finally, flight. This is a contested one, and there are disputes about exactly which species were capable of flight and which were only capable of gliding.

It is widely thought that every major group under Avialae had at least some members capable of flight. This includes Aves: these days a lot of the Palaeognathae cannot fly (the exception being tinamous) but it appears that in their early era, they mostly fly.

Hesperornithes was largely aquatic but also had some flying members. Enantiornithes appears to have mainly been capable of flight, with some flightless members.

There’s some dispute about whether other branches of Paraves had members capable of flight. There’s a school of thought that suggests the four-winged Microraptors, part of Dromaeosauria, was capable of true flight while others opine that it was probably a glider. Similarly, Jinfengopteryx, which is part of Troodontidae, was well equipped to fly.

(You can click the image for somewhat better resolution: the forum does some compression)

Well done and thanks dv.

:)

Michael V said:

Well done and thanks dv.

:)

^ ditto.

roughbarked said:

Michael V said:

Well done and thanks dv.

:)

^ ditto.

Cheers

dv said:

That’s sort of part of my hypothesis. The hypothesis that some true birds had teeth and lost them later than other true birds. The true birds that lost their teeth first were the passerines.

Thanks for the parts 1,2,3,4. Archiving a copy.

dv said:

That’s sort of part of my hypothesis. The hypothesis that some true birds had teeth and lost them later than other true birds. The true birds that lost their teeth first were the passerines.

Thanks for the parts 1,2,3,4. Archiving a copy.

Had a look though it now. That’s actually a masterful summary.

Problem is, and what prompted this thread in the first place, is that genetic analysis puts the separation of paleaognathae and neograthae at 140 million years ago. On the chart it’s placed at 70 million years ago.

If that 140 million year old date is correct then the enantiornethes and hesperornithes may be, or may not be true birds, ie. hesperornithes may be descended from the ancestral neograthae.

Mollwolf: There are a few different kinds of genetic comparison.

Some are based on assumed rates of molecular evolution. There are larger error bars on these because mitochondrial DNA mutation rates do in fact vary.

Others are based on individual markers to establish priority. These are absolute and more or less incontrovertible. If several markers are found in A and B but not C then A and B diverged first.

Mt-DNA and nuclear DNA “molecular clock” studies have thus come up with very different answers on the date of the Neognathae/Palaeognathae split.

Hedges, S. B., Parker, P. H., Sibley, C. G. & Kumar, S. Continental breakup and the ordinal diversification of birds and mammals (Nature 381, 226-229 ) came up with 97 +- 12 mya from nuclear DNA studies, and anywhere from 68 to 131 mya from mt-DNA studies.

Mass Survival of Birds Across the Cretaceous- Tertiary Boundary: Molecular Evidence (March 1997Science 275(5303):1109-13) by Cooper and Penny produced an estimate range from 100 to 180 mya using combined mt-DNA and nuclear DNA.

The very recent Phylogenomics and Morphology of Extinct Paleognaths Reveal the Origin and Evolution of the Ratites by Yonezawa et al gives 104.7–115.5 mya, using mt- and nuclear DNA tied with fossil and morphology constraints.
Notably, this paper and the Cooper one both indicated that multiple lineages of Neognathes survived the KT extinction event.

Meanwhile, A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing by Prum et al 2015 gave an estimate of 73 mya.

A new time tree reveals Earth history’s imprint on the evolution of modern birds, Claramunt et al 2015, gives 95 mya. This paper also suggest that Galloanseres diverged before the KT extinction event, but all three groups underwent explosive diversification after that event.

The Prum and the Cooper papers are the two outer estimates, and the central estimates are the Yonezawa, Claramunt, and Parker papers (110 mya, 95 mya and 98 mya).

But as you allude, the obv question is: where are the fossils? If Aves were massively diverse for 30 million years prior to the KT, why is no one finding diverse fossils in this era?
A Vegavis iaai fossil found in Antarctica, dated to 68 million years, showed significantly “duck-like” morphology. This suggest that at least some diversification had occurred by 68 mya. There are no fossils that are widely accepted as palaeognathae prior to the KT: zero, nul.

Of course there could be explanations that are compatible with an earky diversification of Aves: maybe they were rare, maybe they were in an isolated area that did not have a lot of places likely to preserve fossils, maybe they showed little morphological change in the early phase, so specimens that don’t look paleognathae but were ulimately the ancestors of modern palaeonathae are being overlooked.

It’s an unresolved issue and I suppose it is unlikely to be resolved unless more fossils show up.

Corrected: A and B diverged last

We have heard about feathers and teeth.. But where do the bones come in? Avian bones are rather thin and hollow. Not the greatesrt at leaving fossil traces.