Fossil question that goes with evolution.

[Dobber]

Since Theropod dinosaurs are the ancestors to modern birds, I was wondering, if there has been any fossil discoveries of dinosaurs AFTER/ABOVE the KT boundary? Obviously, some species survived the mass extinction, hence why we have birds, so why no fossils of dinosaurs after the mass extinction. Sort of like the missing links between Dinos and birds. Surely dinosaurs as we know them lasted for thousands of years....at least.....after the mass extinction since evolution takes time. Sorry if this is a stupid question, but it's been on my mind lately.

Chris

[Nanuqsaurus]

Since Theropod dinosaurs are the ancestors to modern birds, I was wondering, if there has been any fossil discoveries of dinosaurs AFTER/ABOVE the KT boundary? Obviously, some species survived the mass extinction, hence why we have birds, so why no fossils of dinosaurs after the mass extinction. Sort of like the missing links between Dinos and birds. Surely dinosaurs as we know them lasted for thousands of years....at least.....after the mass extinction since evolution takes time. Sorry if this is a stupid question, but it's been on my mind lately.

Chris

Birds evolved from dinosaurs before the K-Pg extinction event, and they survived it. Non-avian dinosaurs didn't. All theropod fossils from after the event are bird fossils.

[Halichoeres]

Good question! Whereas the crown-group birds have virtually no fossil evidence before the K-T, archaic bird groups were quite common for 50 million years prior. Moreover, estimates based on mutation rates suggest that living bird groups had direct antecedents in the Campanian/Maastrichtian, even though there are no fossils. This shouldn't be too surprising, because most of the animals that we know from that period are fossilized in ways that don't preserve birds well (i.e., not in lagerstätten).

The other thing that springs to mind is that mass extinctions seem to be particularly hard on very large animals. Part of the mechanism for that seems to be a diminution of productivity. In the wake of either Chicxulub, the Deccan Traps eruptions, or some combination of the two, sunlight might have been attenuated for a period of several years. The cascading effect on plant life could have been enough to wipe out animals that require large amounts of food. Some species would probably have gone extinct in that first year, but others might have persisted decades. Maybe small animals like troodontids or small ornithopods would have persisted for thousands of years, as you suggest, and I for one wouldn't be terribly surprised if some were found just north of the boundary someday. But even thousands of years don't look like much in the context of the total rock record, considering that it covers sixty six thousand thousand years since the K-T.

EDIT: Forgot to add that fossilization probability is pretty low in almost all circumstances, so even if there were a few animals kicking around with very small population sizes, the chance of them dying where we could find them isn't great.

[amargasaurus cazaui]

A few things to add, mostly being we no longer term it the KT boundary...it is now considered the K-PG boundary or event generally.
  Another thing to consider in the discussion is what is known as the "lag" zone. By this I am referring to an area as much as eleven feet between the analomy layer used to identify or  that marks the event and any known dinosaur remains. To date there is a single published specimen known to be associated with the event layer, a triceratops horn, which seems to be firmly determined as not reworked and valid. Everything else dinosaur related that has had the proper study done , has found to be lower in the sediment record and older than the event. What we do not find are layers of dinosaur remains associated with the event or directly afterwards. In fact above the layer and immediately preceding, the lag exists....a potential puzzle for those advocating dinosaur extinction by impact.

[Dobber]

Thanks for the responses everyone! Stupid me, was looking at the evolution as a linear thing...archosaurs to dinosaurs to birds. Not thinking that the would have groups inside each evolving at different times so there would be overlap, so to speak.  Let me make sure I'm understanding this correctly. Birds as we know them, evolved from dinosaurs, but, not necessarily from species that existed at the end of the Cretacious, but rather from Avians that already evolved from dinosaurs earlier in the Cretacious or even Jurassic.

Chris

[Newt]

That's correct. The term "bird" does not have an official phylogenetic definition, so you can argue over whether Jurassic bird-relatives such as Archaeopteryx can properly be called birds, but certainly by the Late Cretaceous there was already a large diversity of undisputed true birds, whose ancestors must have diverged from what we might think of as "typical" theropods much earlier.

[Gwangi]

And it's also important to note that there were entire groups of birds that went extinct along with the dinosaurs at the end of the Cretaceous. Not to make things more confusing. Most notably, the Enantiornithes, which were the most abundant bird group during the Cretaceous. This is a group of birds that kept their clawed hands and teeth but went extinct entirely at the end of the Cretaceous. So did the sea-going toothed Hesperornithes, among others. So although birds survived it was only what we call modern birds (Aves) that made it through. A lot of other birds, entire groups of birds, died out with the other dinosaurs.

But yes, it is best to think of evolution as a tree or bush, with each limb representing a distinct evolutionary divergence. A branch grows from a tree, but there are more branches that grow from that branch with smaller limbs growing from them and so on. They can all live alongside each other, until an event happens that destroys a limb or two, or an entire arm of the tree. So although birds evolved from dinosaurs they did so while dinosaurs were still very much alive and well and lived alongside them and alongside other lineages of now extinct birds as well as dinosaurs that would have appeared very birdy without actually being birds themselves.

[Megalosaurus]

A few things to add, mostly being we no longer term it the KT boundary...it is now considered the K-PG boundary or event generally.
  Another thing to consider in the discussion is what is known as the "lag" zone. By this I am referring to an area as much as eleven feet between the analomy layer used to identify or  that marks the event and any known dinosaur remains. To date there is a single published specimen known to be associated with the event layer, a triceratops horn, which seems to be firmly determined as not reworked and valid. Everything else dinosaur related that has had the proper study done , has found to be lower in the sediment record and older than the event. What we do not find are layers of dinosaur remains associated with the event or directly afterwards. In fact above the layer and immediately preceding, the lag exists....a potential puzzle for those advocating dinosaur extinction by impact.

That "lag" existence is pretty intereting.
It brings to my memory that some scientists think that dinosaurs were already struggling for its lives before the KT event. I remember someone who said that probably acidification of the soils (and environmet in general) may had caused thinner eggshells and weaker bones. That is a teory, but there are more.
So may be the mass extinction occured before the KT event, and that event just closed that chapter in Earth story.

[Nanuqsaurus]

A few things to add, mostly being we no longer term it the KT boundary...it is now considered the K-PG boundary or event generally.
  Another thing to consider in the discussion is what is known as the "lag" zone. By this I am referring to an area as much as eleven feet between the analomy layer used to identify or  that marks the event and any known dinosaur remains. To date there is a single published specimen known to be associated with the event layer, a triceratops horn, which seems to be firmly determined as not reworked and valid. Everything else dinosaur related that has had the proper study done , has found to be lower in the sediment record and older than the event. What we do not find are layers of dinosaur remains associated with the event or directly afterwards. In fact above the layer and immediately preceding, the lag exists....a potential puzzle for those advocating dinosaur extinction by impact.

That "lag" existence is pretty intereting.
It brings to my memory that some scientists think that dinosaurs were already struggling for its lives before the KT event. I remember someone who said that probably acidification of the soils (and environmet in general) may had caused thinner eggshells and weaker bones. That is a teory, but there are more.
So may be the mass extinction occured before the KT event, and that event just closed that chapter in Earth story.

If I recall correctly, some groups of animals were already in decline by the end of the Cretaceous. Sauropods were still around, but they were not as numerous as in the Late Jurassic and Early Cretaceous. Because of overspecialisation and competition with birds, most pterosaurs were gone except for the Azdarchids, who might have had a mostly terrestial lifestyle. Many groups weren't doing so well when the K-Pg event happened anyway, so maybe dinosaurs would've gone extinct pretty quickly even if that asteroid hadn't hit Earth.

[amargasaurus cazaui]

I have had much of this debate here before in the forum and with several people who all view the evidence differently. We really cannot say for sure what did in fact happen....a few things aside from the "lag" I mentioned , that could prove troublesome to the impact alone idea do come to mind.
    We know the Deccan traps had begun erupting prior to the impact event and was doing its best to make a mess of things. To this day the volcanic rock laid down by the event covers most of india in places 11 miles thick. It is the single largest volcanic feature remaining on earth to this day. We also know that some five million years ahead of the impact event we had a massive impact in what would be northern Russia today...forgot the name of the bolide event responsible but it was large as well. The evidence also points to a massive marine regression that dates favorably to the time period we are looking at. A few other possible factors, that might be overlooked. The impact given the credit for so much damage was quite possibly not the single impact event we are often told. There are impacts in the north sea at silvertip, another in russia and a few others I have long forgotten the locations for, that date agreeably to suggest that perhaps rather than a single impacting event, it might have been several or a larger body that broke up when it entered earths gravity.My own personnal belief....and it is only that, is that the dinosaurs were in trouble a long time before the end game. Jack Horner once commented he was sure that the impact killed the last of the dinosaurs...all two of them. Who knows for sure though? There is alot of evidence and arguments on all sides of the discussion as I learned once before.

[Dinoguy2]

Great responses so far, but just to add more bit so well known info, there were already proto-ducks, proto-chickens, and proto-shorebirds very similar to gulls and sandpipers living directly alongside T. rex and kin at the end of the Cretaceous. One early duck (a presbyornithid, I can't remember which, maybe Anatalavis?) been found living both before and after the extinction.

There were also flying ancestors of ostriches, emu, Tinamou, kiwi etc. (lithornithids) around at that time. After the other theropods became extinct a bunch of them became flightless different times on different continents and evolved into all the large flightless birds of today.

All other bird groups besides ducks, chickens, shorebirds, and ratites seem to have evolved after the extinction once the enantiornithines were gone and competition for forest habitats was lessened.

[fleshanthos]

Those Deccan traps. Man. This planet went through some major trouble. Massive strikes due to several impactors at the end of the Cretaceous might have struck a fatal blow, or a death blow to an already struggling ecosystem; or may have caused the Deccan traps...

Not to mention Earth had to have passed through some very hostile regions of space in the Solar System's 260 MY orbit around the galaxy.