If an Asteroid wiped out the Dinosaurs how did Evolution continue?

[Anomalocaris]

Thanks for the link. There's a "long line" for the evolution of everything. I'm not talking about grass ex nihilo, but the appearance of "grass ex nihilo".

We still have the post kt explosion of grass, regardless, eh?

I don't know about that. The previous temporal coincidence between what was thought to be the first appearence of grass and what was thought to be the first explosion of grass was very convenient, and resulted in a set of nicely muturally supporting beliefs.

Now that one of the two muturally supporting pillars have been knocked down, I wouldn't wager too much on the other pillar remaining standing for too much longer.

[The Grand Nudger]

Just skimming through, the new date falls within the range given prior, still 5mil we could push it back and be within what the genome tells us. Similarly, there's an -even larger- gap now between the earliest evidence of grasses and the earliest evidence of their diversification and distribution. If anything, I'd say that this makes the situation even more impressive for grass.

Where once we imagined a desolate earth that grass crept across, we now see a densely vegetated earth with some grasses who were busy doing (apparently nothing) until 55ish mya being overtaken by said grass in the face of competition. Grazing mammalians are much better represented from the time period thence and hence in any case (relative to whats been pointed at for grazing dinos). Don't you think?

[Anomalocaris]

Where once we imagined a desolate earth that grass crept across, we now see a densely vegetated earth with some grasses who were busy doing (apparently nothing) until 55ish mya being overtaken by said grass in the face of competition. Grazing mammalians are much better represented from the time period thence and hence in any case (relative to whats been pointed at for grazing dinos). Don't you think?

If you are trying to make the case that grass were not abundant before 50 million years ago because grass grazing animals was not abundant, I think you have to make allowance for abundance of quadrupad ceretopsian dinosaurs who were probably at least partial grass grazers, but who were not recognized as such because no one thought there were grass for them to graze on.

[The Grand Nudger]

No, the case is more aptly we have no reason to assume that grass was abundant before 55mya because evidence is exceedingly sparse ( a single find.......), whereas after 55mya we have the evidence to show that it was very abundant. Simultaneously, as we go about sequencing grass (mostly for ag purposes, mind you, we likey da cereals) we get an estimate of 55-70mya for an lca (that accounts for 90% of existent species). While it's feasible that the family diverged pre kt - only just, and still wouldn't become prominent until about 10mil years afterwards so far as we can tell. I don't have any dogs in the dino race personally, whether or not any particular member of ceratopsia was a grazer would be awesome to know, but there has to be grass there (or it's lca) - in abundance - before we could call anything a grazer on said grass, eh? As far as the big kt winners, grass qualifies either way, in my opinion. Right alongside we humble mammals

(and I think it's fitting that we've stayed so close since..lol)

[Anomalocaris]

The problem with using genome to determine the time of origin of the entire class of animals or plants is the fact that what you are really dating is not the time that has elapsed since the origin of the entire group, but instead the time that has elapsed since the last common ancester of the living members of the group. The group itself may be considerably more ancient than that.

The fact that Ica does not even represent all living members of grass family even today further weakens the case that its genome can be used to determine the time of last common ancester of all grass, and therefore the true origin of grass.

[The Grand Nudger]

All groups can be "considerably more ancient" so long as we include the lca and wherever it may have hailed from (which again...we don't find the sort of evidence for we would expect, certainly nothing to suggest anything like prairies or even fields of grass/proto grass capable of supporting grazing -anythings- pre 55mya anyways). I'd say that when a genome matches fossils we're on to something though Chuck...that's just me.

[Anomalocaris]

All groups can be "considerably more ancient" so long as we include the lca and wherever it may have hailed from (which again...we don't find the sort of evidence for we would expect, certainly nothing to suggest anything like prairies or even fields of grass/proto grass capable of supporting grazing -anythings- pre 55mya anyways).

No, not everything that it could hail from. If you keep tracing the linage of Ica back in time, eventually you will arrive at an bacteria.

But long before reaching the obsurdly distant single cell ancester, more recent ancesters of Ica would have already lost so many of the derived traits of grass that it is no longer a grass. Even more recently there would be ancesters of Ica would have lost so many derived traits of Ica that it was no longer an Ica, but was still a grass.

Assuming Ica is a monophyletic taxa (ie grouped by evolutionary relationship instead of convenience), when you compare the genomes of Ica, the best you can do is determine when the first Ica ancester that was already itself an Ica (by cladistic taxenomy) first arose. You can not determine when the first Ica ancester that wasn't yet Ica, but is already grass, arose.

It is that second ancester - the earliest to have all the basic traits needed to be grass, but none yet of any of the incremental traits needed to be an Ica - that would mark the origin of grass.

Looking just at Ica it would be hard for you to pin point that.

Incidentally, if you assert the first ica happen to also have been the first grass, then that would mean there could subsequently have been no grass that is not also an ica. You already said that wasn't true, meaning first grass wasn't the first ica, and must have predated the first ica.

I'd say that when a genome matches fossils we're on to something though Chuck...that's just me.

Absence of fossil evidence is not evidence of absence of what might make the fossil. The best you can say is genome study and available fossil evidence does not grossly contradict and falsify each other, such as discovery if ica fossil in strata 110 million years old.

The best you can do is to assert a strong statistical correlation between existemce, or prevelence, with fossil record.

Good luck with that.

[The Grand Nudger]

No, not everything that it could hail from. If you keep tracing the linage of Ica back in time, eventually you will arrive at an bacteria.

But long before reaching the obsurdly distant single cell ancester, the ancesters of Ica would have already lost so many of the derived traits of grass that it is no longer a grass. Before even that other more recent ancetsres of Ica would have lost so many derived traits of Ica that it was no longer an Ica, but was still a grass.

I might just be confused here, but you seem to have reversed the order of a top down system of classification while trying to maintain top down priority. All descendants of the lca are grass, we could call the lca grass itself. It's not necessarily the case that the ancestor of the lca was grass.

Though that could certainly be the case, the lca representing some spur that survived on the otherwise annihilated family tree. Else-wise it would be the only representative of what it is to be grass. The trouble that thinking of it this way runs into is the "what-if" category. What if, despite having no evidence that this is the case, the lca was just a representative of a larger group? Where did all of the other reps of that group go (remember, 90% of all existent grasses trace to an lca...the other ten haven't been studied conclusively)? Why don't we find any evidence of either group? We don't know how long the lca was around, that's true, but we do know that it isn't well represented in the fossil record, and certainly nowhere near as well it's descendants are represented a scant 10-15my later. If I wanted to make the case for multiple reps of grass via lca, or the lcas "length of service" as it were, I'd be looking for the kind of evidence we don't find where we expect we should. I would certainly try to accomplish this before I imagined some sort of buffalo on the plains scenario sans buffalo plus dinosaurs.

When you compare the genomes of Ica, the best you can do is determine when the first Ica ancester that was already itself an Ica first arose. You can not determine when the first Ica ancester that wasn't yet Ica, but is already grass, arose.

As above, there's no reason for the lca's ancestors to have been grass, and we have no evidence that this was so. The lca already encompasses all known finds -including- the one you linked. We don't know how long it was around, but we do know that it wasn't gently waving all over the plains. That type of growth would be immediately recognizable (pollination by air means a hell of alot of opportunity for evidence to be left behind).

It is that second ancester which was the first to have all the traits needed to be grass, but none yet of any of the incremental traits needed to be an Ica, that would mark the origin of grass.

Looking just at Ica it would be hard for you to pin point that.

I disagree, I think the lca offers us the best evidence yet as to where to even -start looking- for evidence of it's ancestors. If they were grass..if they had the defining characteristics - we'd expect evidence that we have not found, again. We simply cant put grass much further back than the lca without any evidence, because it really does offer fantastic potential for being found in the fossil record due to what it means to be a member of the family.

The best you can say is genome study and available fossil evidence does not grossly contradict and falsify each other (for example discovery of what is very much an Ica like grass fossil 100 mya). I am not sure if they really support each other.

Well, they establish that up to 5my before kt there was an lca for said grasses doing it's thing (for an indeterminate period before), that very near kt reps of a few of it's descendants found their way into a dinos stomach. That 10my -after- kt all existent grasses had likely diverged from that lca, and that a few short my after the world was covered with the shit. No other "horizontal relative" of that lca is found in the genomes of any existent species (nor are we sitting on a mound of fossilized grasses -more accurately fossilized evidence of reproduction- which do not appear to be representative of that lineage). I'd say that paints a hell of a picture. It's not a polaroid, granted, but before the genome and this recent find we had bupkiss...lol.

(Mind you, I'm not an advocate of colonizer grass speeding across a desolate impact cratered landscape. There's a 10my gap between kt and the "grass explosion" leading into the cenozoic. I doubt that the flora hadn't rebounded by the time 10my had passed. Neverthless, both the genome and the what we have of the fossil record tell us that grass was at one point, not all that important or widely distributed - and then, post kt...it become a veritable force of nature. Could we chalk that down to the kt event? Sure, but not in the way you'd likely object to, a way I;d object to as well.)

[orogenicman]

It's just a shame to think that foraging dinosaurs of the Jurassic didn't enjoy the finer things in life, like a meadow of ganja.

[Anomalocaris]

It's just a shame to think that foraging dinosaurs of the Jurassic didn't enjoy the finer things in life, like a meadow of ganja.

The foraging dinosaurs of middle Cretaceous certainly did, and it might just be possible that Jurassic dinosaurs also did

Cretaceous evidence:

1. There was a major change in the composition of foraging dinosaurs population around 120 mya. Big herding quadrupedal herbavores built for browsing very low to the ground, and dentition showing adaptations for, and signs of, working with highly abrasive plant material (such as grass with their intra-cellular silicate crystals) became much more numerous. High browsers became comparative much less well represented. This change does not require any anatomicaly breakthrough on the part of dinosaurs, so it must be an adaptation to the composition of available plant material. There must have a been a major increase in neutritious ground hugging plants around 120 million years ago.

2. Some of the low browsers may have eaten woody brush like plants, but others like hedrosaurs and titanosaurs have cow like adaptations that seem specifically targets ground hugging, abrasive, but not tough, plants like grass.

Jurrasic evidence:

The late cretaceous grass evidence has been found in dinosaurs dung fossils from India and Africa. These evidence points to existence of diversified grass during late cretaceous that had already some evolutionary distance from any original ancesteral grass. How far is suggested by India and Africa have been separated during the break up anf Pangea 140 million ago. This suggests the original ancesteral had already existsed 140 million years ago. That's so close to Jurrasic that it might as well be jurrasic.