Actually archaeopteryx wasn’t a bird or bird ancestor. It was a side branch.
Depends on how “bird” is defined. Obviously, a crown-group cladistic definition eliminates it, but purely cladistic definitions and especially crown-group-only cladistic definitions and “let’s name every clade in our analysis” aren’t useful for anyone other than those doing phylogenies. I would be perfectly happy using “bird” as a paraphyletic term for any member of Theropoda capable of flight or descended from one capable of flight, which would make Archaeopteryx a bird.
Silly me thought the grammatical error would be the problem!
BLASPHEMY!!! The Monophyletic police have been notified!
I will ask Danny Anduza, the dinosaur paleontologist, who has a wonderful paleontology channel on Twitch.
But was it capable of flight? Or did it descend from some animal capable of flight?
The asymmetric vanes on the remiges of Archaeopteryx suggest that it was well capable of powered flight.
To me monophyly is all but irrelevant for common names (How many unrelated clades are called “vitrinellas” or “limpets” or “bubbles”?). Even within technical terms, I’m comfortable using paraphyletic and polyphyletic groupings, recognized and labelled as such, when convenient, e.g. Skeneidae is definitely polyphyletic, but members of it sensu latu all look similar, and no one has a better place for most members, so I’ll use it sensu latu and labelled as such to refer to any minute trochoid that hasn’t been placed somewhere else; or another: “turrids” are paraphyletic to Conidae, Conorbidae, and Terebridae, but still form a handy morphological grouping for trying to identify things.
Yeah, they really get on the nerves of someone working with fossils of multiple ages:
If it has to be monophyletic, then how can any group with descendants be named as a clade?
Just thought I’d give this its own space. It was getting a little too serious in the humor thread.
Just for the record, I had tongue firmly in cheek when accusing you of cladistic blasphemy.
Paraphyletic and even polyphyletic groups are still used in the primary literature, so I don’t have a problem as long as it is widely known that they are no monophyletic or are labled as not being monophyletic. 99% of the time I will use the paraphyletic ape group and compare them to humans since it is easier for the laity to understand it. The “but humans are apes” juice isn’t worth the squeeze.
Yes, that was obvious to me.
For those less into nomenclature, the issue being discussed is in use of names. The cladistic approach to biological classification gained popularity starting in the 1970’s because it took a more objective approach to analyzing relationships than “As an expert on this group, I say…”. Instead, it sought to explicitly identify evolutionary similarities between organisms. Because of this focus on the similarities, distinctive features found only in a single group are not of interest. For example, humans are morphologically and behaviorally very unusual apes. The more traditional approach tends to focus on “Very Unusual!” and give humans their own category, whereas a cladistic approach focuses on “they originate within the ape group”. Which of these approaches is more useful depends on what questions you are asking.
The debate over cladistics became quite vigorous, often leading to people being dedicated to a particular method of analysis of evolutionary relationships rather than to seeking the best approximation of reality. In particular, it is often more accurate to admit uncertainty than to assume that my latest analysis is the final word. However, some use the justification “we can’t know the exact details of prehistoric evolution, so therefore we just follow this method.” Keeping uncertainty about past events in mind is useful, but there is no biological point in doing the analyses in the first place if they have no connection to biological reality - it becomes just a highly computerized version of “as an expert on this group, I say”.
One particular and ongoing challenge is how to apply cladistics to nomenclature - should the names that we use for organisms convey cladistic information, and if so, how strictly? Approaches to this question range from extreme “we should redo all names to indicate cladistic relationships” to unsurprising strong reactionary conservatism. Such extremes tend to neglect the practical point that a name needs to be a useful way to communicate about things. The best way to show proposed relationships is actually a diagram, such as an evolutionary tree; trying to make a few words exhaustively convey that does not work well. For example, proposals that one can make the meaning of names explicitly connected to a specific concept by replacing Toxicodendron radicans with Toxicodendron radicans T495475THd.34 are not particularly helpful - no one will be able to keep track of such names. Also, the current system of naming organisms has been established since the 1750’s; radical changes disrupt existing understandings. At the same time, few would disagree with the principle that names that refer to groups that are now known to be clumping unrelated organisms should be revised. But deciding how much change in concept requires a new name is not easy.
Thus, for Archaeopteryx, the question is “To what group of organisms should one apply the name ‘bird’?” Many dinosaurs had some sort of fuzz, and in some the fuzz is definitely feathery. Some small dinosaurs were able to glide from tree to tree. At what point do they qualify as the first birds? If we imagine alien biologists observing the late Jurassic world, they would probably have considered the first birds as highly distinctive dinosaurs; it is because the birds went on to become a major group in their own right and the rest of the dinosaurs died out that we think of “bird” as a major division of vertebrates.
One approach promoted by certain cladists is to use “crown-group” names. This defines the name as applying to the last common ancestor of all living members of the group and all descendants of that ancestor. For example, wooly mammoths are more closely related to Indian elephants than to African elephants. A crown-group definition of elephant would include the living species, wooly mammoths, and other extinct forms that are close relatives of the modern forms. However, mastodons split off earlier from the living elephants, so under this concept they aren’t true elephants. It’s also often very difficult to be certain whether certain fossils are within or outside the crown group. For certain analyses, a crown group is a useful concept (and for certain analyses, assuming something is part of the crown group when it isn’t gives significant errors, e.g. molecular clocks), but I don’t find it very practical for a basis for names. Does it really make sense to imply that, if platypus and echidna became extinct, that “mammal” would suddenly become a much smaller group?
Although analyses have varied somewhat, many support the idea that Archaeopteryx is on a side branch relative to modern birds, possibly more closely related to the Enantiornithines (a group of birds that died out along with the dinosaurs) than to modern birds. Do we say it’s not a true bird until they are part of the group that lost teeth? Then Archaeopteryx is out.
Do we draw the line earlier and say it’s the first ones to achieve powered flight, along with their descendants? Then Archaeopteryx is in, and this probably is the best match for the general popular concept of what is a bird.
The issue also ties to a bad antievolutionary argument: “If Archaeopteryx is a bird, then it cannot be a transition between reptiles and birds.” Again, the problem is in the relationship between names and reality. Evolution produces a gradient of differences between organisms; to have useful names we must draw lines somewhere.
I would say cladistics also gained popularity because it better modeled the branching structure of evolutionary relationships as compared to Linnaean taxonomy. For example, genera are equal in rank and sit next to each other in Linnaean taxonomy without any underlying relationships between them. This isn’t surprising since Linnaean taxonomy was founded 100 years before the theory of evolution.
Aren’t all species related to one another?
We can apply the name “bird” to anything we want since it is a human abstraction. In my non-expert view, the advantage of cladistics is that whatever you call a bird you also have to include the common ancestor of all species you call birds and all the descendants of that common ancestor. This would include extinct species. So we could decide to include Archaeopteryx in the bird group, and we would have to also include the common ancestor of Archaeopteryx, the common ancestor of Archae and all other species we want to call birds, and all of the descendants of that common ancestor. That is, the crown group.
Figuring out who that common ancestor was and who all the descendants are is tough, and nigh on impossible without DNA. Fossils don’t give enough information for an understanding of fine detailed relationships. I think that is part of the problem you are talking about. We can use different methods and different data sets that often give different answers, and that may be the best we can do.
Birds are still in the reptile clade, or rather in the diapsid clade.
I just asked Dr. Anduza, a dinosaur paleontologist, if paleontologists consider archaeopteryx to be a bird. It seems that the jury is still out on that question; some say yes, some say no. Dr. Anduza will be on a dig out West this summer and will attempt to live-stream his work. Something I’m looking forward to.
Just as a thought, are penguins, kiwis, and ostriches still birds?
Yes, of course. But the penguin is also a Batman villian, and Kiwi can also refer to somebody from NZ.
Help me understand this. Because it sounds to me like you’re saying that if ‘X’ is a bird, then we are obliged to include all the common ancestors preceding ‘X’ in what we call ‘birds’ as well. But … one can keep going back until you reach common ancestors that are no longer birds, right? I mean - nobody is insisting that some microbial ancestor of us all qualifies as a bird!
Or if we only go back to the ‘crown group’ (which I gather is what you’re saying), then doesn’t that chosen ‘crown group’ represent an arbitrary cutoff (or cuttoff of convenience according to fossils that have been found)?
Naming ‘species’ to various higher taxa/groups is not an exact science. Cladistics appears to give some structure to the business and is therefore helpful in some cases but has its own problems. Cladistics usually plays with external features (morphology) while genetics would give more accurate information about evolution. It is possible to use the methodology of cladistics for genetic data, so these can be combined. I am not sure if even the genetic data would yield accurate conclusions about classification. There is still a need for subjective decisions about where to draw the line between different labels.
Before we start to group ‘species’ to higher taxa, maybe we should first determine what is a species. That is not as easy task as many imagine.
Anyhow, I accept the attitude that we can have labels for groups that are not monophyletic. Even for such groups that most people today would say are ‘wrong’, like the classification used in the OT.
I basically agree with T_aquaticus.
We all know clades only get us so far. But they are still very useful since it’s based off of ancestry.
Consider dinosaurs. Within that we find the clade Paraves. Not all of these seemed to fit the bird narrative. But within them is the Avialae which seems to include what we all consider birds , or had descendants that we classify as birds. The Avialae would have had a common ancestor in the Paraves that we may even consider a bird, not not all the others.
Within the bird clade it’s not problematic to consider penguins as birds because of this ancestry just like it’s ok to consider humans primates even though there is a lot of physical distinctions between us, chimps and gorillas.
To be bird is a taxonomic group vs something like tree which is a form. By that I mean not all trees have a direct common ancestor as you step up each clade. It’s a convergent form within the plant world just like the shape of fish is convergent with the shape of the dolphin. It seems like seals are also working in that direction as well.