Discussion on Classification of dinosaurs and Related

[kileskus]

Kileskus was a proceratosaurid, a group of tyrannosauroids that were on the small side compared to the type species of the tyrannosauroids. (Palaeontology uses the phylogenetic framework based on shared evolution as opposed to the Linnaean system based on anatomical similarity, so height isn't a classification trait but rather a similarity shared more by species of this subgroup than other tyrannosauroid subgroups.) I like dinosaurs and I am short.

It would be a pity if anyone changed their handles as I've come to associate writing styles (and humour styles) with them.

 

[RooFlyer]

Palaeontology uses the phylogenetic framework based on shared evolution as opposed to the Linnaean system based on anatomical similarity, so height isn't a classification trait but rather a similarity shared more by species of this subgroup than other tyrannosauroid subgroups.)

Never knew that. Has it been a long-standing thing? What happens with the classification systems when the birds diverge?

 

[kileskus]

Never knew that. Has it been a long-standing thing? What happens with the classification systems when the birds diverge?

The widespread adoption of phylogenetics as the basis of classification in palaeontology occurred about 40 years ago I think, so it has been around for a while. Of course evolutionary relationships were studied long before, but the classification system was Linnaean until a conscious effort was made to switch over. So it is fairly longstanding. That said, when I was a kid in the early 2000s devouring books about dinosaurs a lot of them said they were cold-blooded, decades after the community started to accept the warm-blooded hypothesis, so the vestiges of old/traditional paradigms probably hang around longer in palaeontology than in other sciences and even more so in pop palaeontology.

Phylogenetic relationships are categorised using phylograms (with branches whose lengths vary based on the degree of evolutionary change) and cladograms (with branches of the same length, designed to only show the ancestors/branching points and not the degree of change). This is a phylogram of archosaurs, the ancestors of dinosaurs and some other ancient animals, including birds and crocodiles:


You can see here the major division of dinosaurs into ornithiscians and saurischians. Theropods were saurischians and are generally speaking the bipedal dinosaurs we think of. Then, if you take a cladogram of theropods:



There is a clade within the theropods called the paraves. Going further, a 'cladogram' of paraves with years written in and the inclusion of modern birds:


It's not a true cladogram in the strict sense and doesn't label the families within paraves but rather just singles out examples and describes some typical features at the points of diversion. The velociraptor/microraptor family is the dromaeosauridae and between archaeopteryx and velociraptor I would also add troodontidae. If you take the type species of those two families, dromaeosaurus and troodon, and compare them to archaeopteryx, there are a lot of similarities in body design. I note this because archaeopteryx is the classic transitional fossil between birds and dinosaurs but I think some people don't realise that it had a lot more similarities to the two aforementioned terrestrial families.

Archaeopteryx likely couldn't fly very well. Its musculature wouldn't have been conducive to flapping so it likely glided more than it flapped and it would've likely needed a fairly decent run up (like a 747 taxiing) before it could take off. I'm not sure how the Linnaean system handles dinosaurs and birds together but roughly speaking I'd imagine it would put archaeopteryx closer to modern birds, or at least imply archaeopteryx is more similar to modern birds than to dromaeosauridae, which is not accurate evolutionarily speaking.

The groups to the right of archaeopteryx are the ones even closer in evolutionary relationship to modern birds than archaeopteryx. The four animals in this diagram are all from the Cretaceous period. There is a label "short tail/pygostyle" - a pygostyle is a section of fused vertebrae that allowed for the development of short-tailed animals. The long to short tail transition is very important in bird evolution as modern birds have short tails. A very recent discovery (from 2023, but the interpretation of that discovery is so recent the some of the relevant Wikipedia pages haven't been updated) of a creature called baminornis shows a pygostyle, so it would belong somewhere in between sapeornis and confuciusornis in this diagram. The interesting thing about baminornis is that it was from the Jurassic, and it was the contemporary of if not older than archaeopteryx. So that could have a lot of implications for when exactly modern birds started to evolve, although with the caveat that pygostyles likely evolved twice independently and there is debate currently on where baminornis would fit into the phylogenetic tree.

You could go further into avialae cladograms but I'll leave the lecture there. I hope that answers your question, if I understood it correctly. I have fact checked but there might still be inaccuracies, but I hope at least it gives a broad overview of bird evolution and how it's classified in palaeontology.

 

[DejaBrew]

You could go further into avialae cladograms but I'll leave the lecture there. I hope that answers your question, if I understood it correctly. I have fact checked but there might still be inaccuracies, but I hope at least it gives a broad overview of bird evolution and how it's classified in palaeontology.

I can safely say I have learnt multiple new things today! Thank you for the explanation

 

[VPS]

The widespread adoption of phylogenetics as the basis of classification in palaeontology occurred about 40 years ago I think, so it has been around for a while. Of course evolutionary relationships were studied long before, but the classification system was Linnaean until a conscious effort was made to switch over. So it is fairly longstanding. That said, when I was a kid in the early 2000s devouring books about dinosaurs a lot of them said they were cold-blooded, decades after the community started to accept the warm-blooded hypothesis, so the vestiges of old/traditional paradigms probably hang around longer in palaeontology than in other sciences and even more so in pop palaeontology.

Phylogenetic relationships are categorised using phylograms (with branches whose lengths vary based on the degree of evolutionary change) and cladograms (with branches of the same length, designed to only show the ancestors/branching points and not the degree of change). This is a phylogram of archosaurs, the ancestors of dinosaurs and some other ancient animals, including birds and crocodiles:
View attachment 450390

You can see here the major division of dinosaurs into ornithiscians and saurischians. Theropods were saurischians and are generally speaking the bipedal dinosaurs we think of. Then, if you take a cladogram of theropods:

View attachment 450389

There is a clade within the theropods called the paraves. Going further, a 'cladogram' of paraves with years written in and the inclusion of modern birds:
View attachment 450391

It's not a true cladogram in the strict sense and doesn't label the families within paraves but rather just singles out examples and describes some typical features at the points of diversion. The velociraptor/microraptor family is the dromaeosauridae and between archaeopteryx and velociraptor I would also add troodontidae. If you take the type species of those two families, dromaeosaurus and troodon, and compare them to archaeopteryx, there are a lot of similarities in body design. I note this because archaeopteryx is the classic transitional fossil between birds and dinosaurs but I think some people don't realise that it had a lot more similarities to the two aforementioned terrestrial families.

Archaeopteryx likely couldn't fly very well. Its musculature wouldn't have been conducive to flapping so it likely glided more than it flapped and it would've likely needed a fairly decent run up (like a 747 taxiing) before it could take off. I'm not sure how the Linnaean system handles dinosaurs and birds together but roughly speaking I'd imagine it would put archaeopteryx closer to modern birds, or at least imply archaeopteryx is more similar to modern birds than to dromaeosauridae, which is not accurate evolutionarily speaking.

The groups to the right of archaeopteryx are the ones even closer in evolutionary relationship to modern birds than archaeopteryx. The four animals in this diagram are all from the Cretaceous period. There is a label "short tail/pygostyle" - a pygostyle is a section of fused vertebrae that allowed for the development of short-tailed animals. The long to short tail transition is very important in bird evolution as modern birds have short tails. A very recent discovery (from 2023, but the interpretation of that discovery is so recent the some of the relevant Wikipedia pages haven't been updated) of a creature called baminornis shows a pygostyle, so it would belong somewhere in between sapeornis and confuciusornis in this diagram. The interesting thing about baminornis is that it was from the Jurassic, and it was the contemporary of if not older than archaeopteryx. So that could have a lot of implications for when exactly modern birds started to evolve, although with the caveat that pygostyles likely evolved twice independently and there is debate currently on where baminornis would fit into the phylogenetic tree.

You could go further into avialae cladograms but I'll leave the lecture there. I hope that answers your question, if I understood it correctly. I have fact checked but there might still be inaccuracies, but I hope at least it gives a broad overview of bird evolution and how it's classified in palaeontology.

‘Dragon prince’ dinosaur discovery 'rewrites' T.rex family tree

The dinosaur skeletons, found hidden in a museum collection in Mongolia, is an ancestor of the mighty tyrannosaurs.

www.bbc.co.uk

And it changes all the time

 

[RooFlyer]

That’s really interesting thank you @kileskus .

The reason it piqued my interest was because when I was an undergraduate in the late 1970s doing zoology ( as a minor subject ) I recall doing a paper on, I think what was then called Systematic Taxonomy for extant creatures and vague memory says that it was much along what you are describing above.

I do recall, again with bad memory, that my conclusion was that this newfangled way of taxonomy really wouldn’t take off.

But it was adopted for palaeontology?? I was more of a hard-rocker (economic geology) rather than a soft-rocker ( fuels and palaeo) but I never heard about that. Have they gone back and reclassified all of the untold number of fossil species? Or did I misunderstand you and they have only applied it to dinosaurs or maybe vertebrate palaeontology?

 

[kileskus]

It was in the 70s and 80s that it became phased in to palaeontology so probably at the time you were writing the paper it wasn't really a thing. I think Linnaean naming is still used sometimes especially with higher order taxa as they're more convenient, but they don't like the hierarchical structure, maybe because of the long timeline and the increased relevance of macroevolution when evaluating extinct organisms as opposed to extant ones. That's my theory anyway. Molecular palaeontology has also rapidly grown in the past few decades due to biotechnological advancements allowing for increasing molecular material to be identified from fossils and sequenced.

I think it's invertebrates as well. I don't read much about them, but from what I have read cladistics is predominantly used for categorisation. Since invertebrates survived extinction events better and have more extant successors, in my opinion phylogenetic taxonomy would be more useful to represent the continuity and diversification of species. This paper traces the evolution of angiosperms from the Cretaceous Terrestrial Revolution and contextualises it within broader trends of plant, invertebrate and vertebrate evolution. Admittedly it's a bit of a straw man example as it doesn't really deal with species-level analysis, fossilised or not, but its integration of phylogenetics suggests a) the widespread adoption of this kind of mindset throughout palaeontology, and b) the utility of cladistics for classifying both extinct and living organisms, much the same way birds can be logically included into cladograms of vertebrates.

But now that you mention it I'll probably keep a closer eye on new research regarding invertebrates.

Is there a link to your paper somewhere? It would be interesting to see how it can - or can't - be applied to extant biology. Though I'm not very familiar with Linnaean taxonomy to begin with.

I know nothing about rocks or geologists either but would imagine their classification could also be based on their formation processes and environments as much as on their characteristics.

 

[RooFlyer]

Is there a link to your paper somewhere?

A third years zoology undergraduate paper. Even predates word processors

I know nothing about rocks or geologists either but would imagine their classification could also be based on their formation processes and environments as much as on their characteristics.

First tier is formation process: igneous, metamorphic and sedimentary.

Then, as to what we technically call a given igneous rock, it’s a combination of its chemical analysis (each element calculated as its oxide), it’s mineralogical composition and it’s texture.

For metamorphic and sedimentary rocks, it’s mainly mineralogy and texture.