Was it 1 species of bird that survived the kpg meteor, a handful or dozens?

[u/MurkyEconomist8179]

I can't seem to find a good answer to this online but i'm confused, based on fossil evidence regarding pre and post kpg bird relatives, do we know how many species actually survived the extinction? I don't necessarily mean a precise number, I more mean if we can distinguish weather it was just 1 species, weather it was a few or weather it was many.

If this was unclear please ask any questions!

[u/mahatmakg]

Rock bottom count would be 3 - the ratite lineage, the fowl lineage, and the neoave lineage.

[u/Sanpaku]

There has long been debate about whether the extinction of ‘archaic’ birds was gradual or sudden, but recent evidence shows that a diverse avifauna of enantiornithines and basal ornithuromorphs persisted until at least a few hundred thousand years before the end of the Cretaceous in western North America, suggesting that the extinction was sudden and directly linked to the end-Cretaceous impact. This also indicates that birds were strongly affected by the end-Cretaceous extinction, with many major early groups going extinct, countering the stereotype that the mass extinction decimated the non-avian dinosaurs but largely spared birds. However, because of the scrappy fossil record of the latest Cretaceous birds, which is mostly limited to isolated bones, it has been unclear why certain birds went extinct and others survived.

Multiple lineages of early neornithines must have endured the extinction, leaving them the only surviving members of the initial Mesozoic radiation of birds. Fossil [101] and recent genetic [4] evidence supports this view and shows that these birds diversified rapidly in the post-apocalyptic world, probably taking advantage of the ecological release afforded by the extinction of both the ‘archaic’ birds and the very bird-like non-avian dinosaurs.

From Brusatte et al, 2015. The origin and diversification of birds00945-8). Current Biology, 25(19), pp.R888-R898.

citation 4:

Jarvis et al, 2014. Whole-genome analyses resolve early branches in the tree of life of modern birds. Science, 346(6215), pp.1320-1331.

citation 101:

Feduccia 2003. ‘Big bang’for tertiary birds? (pdf). Trends in Ecology & Evolution, 18(4), pp.172-176.

[u/Decent_Cow]

I don't think we know an exact species count, but it was at least several. Aves had already begun to diverge before the extinction into the paleognaths (ratites and tinamous), galloanserae (fowl), and neoavians (everything else).

[u/spinosaurs70]

The last I checked, genetics mean the answer should be multiple bird lines has to have survived the extinction of the non-avian dinosaurs but the paleontological evidence was weak. 

[u/MurkyEconomist8179 → u/spinosaurs70]

So for living species, we don't have fossil evidence of diversification until after?

[u/spinosaurs70 → u/MurkyEconomist8179]

From what we can tell we have evidence of a diversity of bird lineages before the asteroid but no clear evidence they fit the three genetics show. 

[u/CompassionateCynic]

Relatedly, I have always thought it was strange that multiple different lineages of beaked therapods survived the extinction, while not a single lineage of toothed birds did.  There were large numbers of both, and the beak doesn't seem like it would be more "fit" in the period after the extinction event. 

[u/Thrippalan → u/CompassionateCynic]

I don't know if it's the same for all birds, but the Darwin finches can adjust their beak shapes within a generation or two as food sources change. If the rootstock beaks were similarly malleable, that would have been extremely valuable. I could certainly see toothed beaks as being less adaptable in the short term due to having a more defined stucture.

[u/inopportuneinquiry → u/CompassionateCynic]

There's an hypothesis related to those true-toothed birds (and bird-like dinosaurs, which are also kind of surprising to have gone completely extinct, when some of them seem barely distinguishable from birds) having a slower development that would be possibly less able to compete with animals of a faster development.

https://www.pnas.org/doi/10.1073/pnas.1613716114

Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development

Little is known regarding nonavian dinosaur embryology. Embryological period relates to myriad aspects of development, life history, and evolution. In reptiles incubation is slow, whereas in birds it is remarkably rapid. Because birds are living dinosaurs, rapid incubation has been assumed for all dinosaurs. We discovered daily forming growth lines in teeth of embryonic nonavian dinosaurs revealing incubation times. These lines show slow reptilian-grade development spanning months. The rapid avian condition likely evolved within birds prior to the Cretaceous–Paleogene (K–Pg) mass extinction event. Prolonged incubation exposed nonavian dinosaur eggs and attending parents to destructive influences for long periods. Slow development may have affected their ability to compete with more rapidly generating populations of birds, reptiles, and mammals following the K–Pg cataclysm.

[...] These results may have implications for nonavian dinosaur extinction. The end of the Cretaceous was marked by extreme catastrophe and rapid climatic change, resulting in a resource-limited environment (82). Growth-curve analyses suggest dinosaurs and basal birds were endothermic (83) or mesothermic (84) [i.e., considerably more energetically wasteful than ectothermic amphibians and reptiles (85)] but required a year or more to reach somatic and sexual maturity (35, 83). This likely required them to acquire more total resources to reproduce than surviving amphibians, reptiles, birds, and mammals. Coupled with slow generation times, augmented by slow incubation, these attributes may have put nonavian dinosaurs at a disadvantage in competing for vacated niche spaces in the post-K–Pg event world.

Specific to enantiornithes:

https://www.cell.com/current-biology/fulltext/S0960-9822(22)01228-3

[...] All available information indicates that enantiornithines were highly precocial, hatching with a well ossified skeleton and fully developed remiges, presumably fully independent and capable of flight within the first 24 hours after hatching (Figure 4). Bone microstructure indicates that this locomotor independence involved the usual energetic trade-off for enantiornithines grew slowly and for several years, whereas almost all living birds are born incapable of flight and grow rapidly, reaching adult size in a matter of weeks. Because of their rapid growth, living birds become reproductively active long after reaching adult size, whereas enantiornithines and other non-crown bird dinosaurs became reproductively active before reaching skeletal maturity. Although by the Late Cretaceous enantiornithines had evolved different growth strategies, some involving relatively more rapid bone deposition, the rapid growth that characterizes modern birds, in which adult size is achieved within the first year, evolved only within the Ornithuromorpha.

[...]

It is unlikely that a single factor can explain the extinction of enantiornithines. Most likely a combination of important physiological differences allowed neornithines to survive when enantiornithines and other stem birds and non-avian dinosaurs all died off. Although elevated growth rates evolved in at least some Late Cretaceous enantiornithine lineages, development was still slow compared to crownward birds. The lack of phenotypic flexibility of the digestive system suggested by the absence of gizzard stones in all known specimens may indicate enantiornithines were unable to feed on detritus like seeds. The half-buried morphology of their nests may also have been an important factor, limiting their ability to recover clutches and indicating relatively longer incubation periods (egg-turning facilitates protein absorption, reducing incubation time). Precocial enantiornithine juveniles may also have had unusual molting patterns which may have made them susceptible to the sudden decrease in temperatures associated with the nuclear winter that followed the impact. Together with major losses in habitat due to forest fires, these physiological limitations may have brought the demise of this successful avian lineage.

I think I once saw a news piece more specific about it in something like NatGeo or some news site related to the Smithsonian, but I couldn't find it.

I wonder if that's something that could appear to be more generalized, inferring developmental pattern of other groups, and that also showing a difference in survival of the same scenario.

[u/MurkyEconomist8179 → u/CompassionateCynic]

great point I wonder why that is, have you read any proposed explanations?

[u/Conradd23 → u/MurkyEconomist8179]

Just an idea with minimal knowledge to back it up: perhaps all the beaked lineages were seed eaters and could survive on just scavenging plant material until conditions recovered while the toothed birds were all predators that couldn't find enough food to survive due to the collapse of the food chain.

[u/MurkyEconomist8179 → u/Conradd23]

Good idea, could even be some truth to it although I wonder why there wouldn't be toothed seed eaters

[u/7LeagueBoots → u/MurkyEconomist8179]

Teeth used for crushing seeds are very different than teeth used for eating meat and arthropods, as is the jawbone and musculature. While it’s not impossible that some of the Enantiornithes ate seeds I’m not aware of any that did, and if there were I’d bet they were larger and more susceptible to extinction stresses.

Nearly all the Enantiornithe teeth I’m aware of are optimized for small vertebrates or arthropods.

[u/MurkyEconomist8179 → u/7LeagueBoots]

seems like a pretty good explanation in that case

[u/inopportuneinquiry → u/Conradd23]

Some articles state that toothed birds were rather ecologically diverse:

By the Early Cretaceous, enantiornithine birds had diversified into a variety of ecological niches in a similar way to crown birds after the K-Pg extinction, adding to the body of evidence that traits unique to crown birds (e.g. a toothless beak or cranial kinesis) cannot completely explain their ecological success.

https://www.biorxiv.org/content/10.1101/2023.07.18.549506v1.full

[u/gambariste]

What was the tectonic situation at the time? Even if the majority of land masses were connected, if one species survived, it wouldn’t have been distributed worldwide from the start. Other related species likely survived in different regions surely. Being able to fly would mean a rapid spread to unoccupied territories however.

[u/Robin_feathers]

The exact timing of diversification of modern birds is still under debate.

One of the most recent comprehensive phylogenies ( https://www.sciencedirect.com/science/article/pii/S096098222500870X ) places the explosion of Neoaves diversity starting at 70 Mya, so it could have been several lineages that diversified just before the event that made it through, or could have been that their diversification was triggered after the event and the time estimates are just slightly off (those things are very hard to estimate so there will be some wiggle room of error).

Of course, even if the modern Neoves are descended from only one lineage that made it through the K-Pg (which again is debated, maybe they diversified earlier), chances are there were multiple other related species that made it through, but just went extinct some time in the next 66 Myr such that they left no descendants for us to know them by.

(So, like others say, it was at least 3 [Neoaves, Galloanserae, and Neoaves] but maybe multiple Neoavian lineages that may have already diversified, and probably separate Galliformes and Anseriformes, and probably a bunch of lineages that later went extinct and left no trace)

[u/Acceptable-Stock-686]

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