Dinosauria broad-scale relationships + Triassic climate and dinosaur rise in South America

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Ben Creisler

Jun 5, 2024, 2:15:47 PM (9 days ago) Jun 5
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Ben Creisler

Recent dino papers:

Free pdf:

Jack Lovegrove, Paul Upchurch & Paul M. Barrett (2024)
Untangling the tree or unravelling the consensus? Recent developments in the quest to resolve the broad-scale relationships within Dinosauria
Journal of Systematic Palaeontology 22(1): 2345333
doi: https://doi.org/10.1080/14772019.2024.2345333

Free pdf:

The phylogenetic relationships of the major lineages within Dinosauria have come under intense scrutiny in recent years. In 2017, a radical new hypothesis of early dinosaur evolution, the ‘Ornithoscelida hypothesis’, was proposed, prompting a flurry of work in this area. However, instead of untangling the phylogenetic tree of dinosaurs as hoped, this further research unravelled the scientific consensus on dinosaur origins and their early relationships. Multiple hypotheses have now been proposed, including several that position the ‘traditionally’ non-dinosaurian silesaurids within Dinosauria. There is no sign of an emerging consensus, with all possible combinations of the three major dinosaur clades (Ornithischia, Theropoda and Sauropodomorpha) having been recovered by recent phylogenetic analyses. The existence of several ‘wildcard taxa’ and clades with uncertain affinities around the base of Dinosauria complicates efforts to differentiate these hypotheses. Recent studies have suggested that the data sets used to investigate the phylogenetic relationships of Dinosauria might be fatally flawed. The construction of new data sets with a stronger focus on the logical underpinning of characters, in addition to the inclusion of newly described or redescribed taxa, will likely hold the key to resolving this debate.


Leonardo Corecco, Matthew J. Kohn & Cesar L. Schultz (2024)
Triassic climate and the rise of the dinosaur empire in South America
Journal of South American Earth Sciences 104977
doi: https://doi.org/10.1016/j.jsames.2024.104977


An update of the Triassic climates over the last decade of studies.
Special focus in South America Triassic strata (Brazil and Argentina).
New information about the CPE and its connection with dinosaurs’ empire.
Current hypotheses of the rise of the dinosaurs.


The Triassic period (251.9 to 201.4 Ma) is the first period of the Mesozoic Era, initiating after the Permian-Triassic mass extinction and ending at the Triassic-Jurassic mass extinction. This period witnessed the origin of modern ecosystems, and also the rise of the dinosaurs. This influence on both geological and ecological history of the Earth has prompted close attention to the paleoclimate and paleoecology of the Triassic period over the last 60 years. This review builds on past work to summarize knowledge of Triassic climate and ecology, especially focusing on data acquired over the last decade for key South American strata. The main climatic events that occurred in the Triassic period can be subdivided in three key intervals, from the base to top: pre-, syn- and post-Carnian Pluvial Episode (CPE). Each of these three intervals corresponds with major climatic events or episodes, positioned relative to the Permian-Triassic mass extinction, CPE, and Triassic-Jurassic mass extinction. The pre-CPE interval of the Early and Middle Triassic represents relatively warm and dry conditions. The CPE of the earliest Late Triassic marks a global increase in effective precipitation (precipitation minus evaporation) for at least 1-2 Myr, causing major floristic and faunal turnovers and possibly triggering the rise of the dinosaurs. The post-CPE interval of the Late Triassic represents a return to warm and dry conditions. Triassic deposits in Brazil and Argentina represent windows for investigating the interrelationship(s) between changes in climate, floras, and faunas. Alternate triggers for dinosaur diversification are also evaluated, including classical considerations of competition, opportunism, and body temperature, in addition to more novel and subtle factors.



Jun 5, 2024, 5:42:42 PM (9 days ago) Jun 5
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This was well timed given the recent discussion on the list on whether or not the Ornithoscelida hypothesis was all that serious.


Gregory Paul

Jun 6, 2024, 7:59:00 AM (9 days ago) Jun 6
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Yep, it's big problem, and it's resolution is problematic. 

I have been skeptical about the Saurischia thing since way back. It is weakly supported. All the more so because the evidence that prosauropods had an air-sac complex is poor. That is a reason why I thought for awhile that therizinosaurs were a link between prosauropods and ornithischians, although it has turned out they are protobirds, probably secondarily flightless. 

Basal dinosaurs are so generalized that it may not be possible to every sort out their relationships to the big groups, especially on the limited fossil record we have and that may never be fully adequate. 

The below brings us to a problem that is going pretty much ignored. Those mega cladistic studies with many hundreds of characters. There is no practical way to sufficiently verify their reliability. That would require traveling all over the place to check them out, and even then the person/s doing so are likely to make their own boo-boos. This is a reason I am not a big fan of cladistics. The data base is likely to be contaminated. I have come across a few errors in the standard character lists, but my ability to check them is too limited to be of much use. This is a problem because many contend that taxonomy must be based on cladistic phylogenetics -- a paper I submitted was rejected because I did not use them -- which is scientifically dubious. And not all paleos agree, I have gotten other papers through without the cladistics, as have others as I noted recently. 


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Mike Taylor

Jun 6, 2024, 8:16:32 AM (9 days ago) Jun 6
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Postcranial skeletal pneumaticity is well attested in at least some prosauropods(*). See for example

-- Mike.

(*) Anyone who wants to call them "non-sauropod sauropodomorphs" should feel free, if it makes them feel more scientific.

Tim Williams

Jun 6, 2024, 11:40:20 PM (8 days ago) Jun 6
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Gregory Paul <DinosaurMa...@googlegroups.com> wrote:

> The below brings us to a problem that is going pretty much ignored. Those mega cladistic studies with many hundreds of characters. There is no practical way to 
> sufficiently verify their reliability. That would require traveling all over the place to check them out, and even then the person/s doing so are likely to make their own boo-
> boos. This is a reason I am not a big fan of cladistics.

What's the alternative?  Pick a small number of 'key characters' from a handful of taxa, and reconstruct a narrative history of evolution based on these?  This is way things used to be done.  All it gave us was a bunch of paleo 'just-so' stories.  Give me cladistics (mega or not) any day.

Mickey Mortimer

Jun 8, 2024, 6:49:19 AM (7 days ago) Jun 8
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This seems unrealistically defeatist.  We actually have very good material of basal dinosaurs, from Herrerasaurus, to Eoraptor, Buriolestes, Silesaurus, Gnathovorax, Tawa, Eodromaeus, Pampadromaeus, Mbiresaurus, Saturnalia, Lewisuchus, etc..  We do need some of these to be described in detail still after being published in tabloids, Tawa and Eodromaeus in particular (can the latter overcome the Sereno description curse?  Only Afrovenator and Jobaria know).

As for the problem of character reliability, it's not solved because a: people have too much trust in classic matrices and b: no one has yet done the non-flashy work of creating a database of defended character scores.  Langer et al. (2017) nipped the first issue in the bud for Baron's terribly constructed/scored basal dinosaur matrix, saying "Our critical revision of the scorings of Baron et al. indicates that the original version of that dataset is not reliable for testing the phylogenetic relationships of early dinosaurs."  What we need is something like I proposed over a decade ago here https://theropoddatabase.blogspot.com/2011/04/maxillary-fenestra-preview.html mixed with utilizing an online source like Morphobank to create a database of images of each taxon for each character like Gauthier et al. (2012) did in their squamate analysis but for every taxon.  Ideally there should be a way for approved experts to comment as well, considering the many ways taphonomy and other variables can affect scoring.  Twenty years ago it would have not seemed feasible, but new papers will often have comparative figures with photos of every taxon since most people are more comfortable sharing images now.

Mickey Mortimer

e w

Jun 10, 2024, 1:52:53 PM (4 days ago) Jun 10
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"What we need is something like I proposed over a decade ago here https://theropoddatabase.blogspot.com/2011/04/maxillary-fenestra-preview.html mixed with utilizing an online source like Morphobank to create a database of images of each taxon for each character like Gauthier et al. (2012) did in their squamate analysis but for every taxon. Ideally there should be a way for approved experts to comment as well, considering the many ways taphonomy and other variables can affect scoring."

By all means, yes!!!

I noted in crown Aves matrices that character scoring is often too subjective or at least too context-sensitive. Some analyses go to great lengths to precisely describe characters and delimit scorings, but many use ambiguous/relational terminology (e.g. "large" vs "small" - what constitutes "large" or "small" is often dependent on taxon sample in a particular analysis). Thus, a character that is "relationally" scored one way in a specific taxon when compared to one particular taxon set may be scored differently when using a different set of comparison taxa. This a) limits the ability to compare different analyses[*], and b) introduces analytical error by re-applying scores within altered taxon sets and without verifying that the "ambiguous" scorings are unaffected by the change in analyzed taxa.

Your proposal is absolutely sensible and perhaps the only way to tackle this problem (or at least I cannot think of any better, FWIW): Rather than scoring characters using whatever limited comparative material is at hand, and subsequent authors having to drag these scores from one study to the next without being able to verify them, there should be a database documenting the actual material evidence in question, so that ambiguous scorings can be argued for or against based on a comparison of the next best thing after directly inspecting the actual material: specimen photos, with sufficient resolution, and documenting a wide taxon set. And if that is not available, the third-best thing are high-quality drawings; digitization projects such as BHL have provided lots of high-resolution scans of papers from the lithography era, and e.g. for material lost in World War 2 there is often no other way but to resort to historical publications. And an expert comment/discussion feature to resolve the most disputable cases (e.g. when characters are obfuscated by damage, or for ontogeny-related issues especially in nonavian theropods).
A further step would be to allow for inclusion of never-figured material. This is probably not pressing for stem dinosaurs, but for crown dinos there is a considerable amount of highly interesting material that has never been figurewd an only ever described in relative/qualitative terms (by comparison to better-documented taxa, like in a differential diagnosis) - which are often enough quite useful for cladistic analysis, if they would only be methodically collated: e.g. if a humerus is merely described as having a "stronger curvature than [comparison taxon]", this can already permit a sufficiently precise scoring (if the comparison taxon has a strongly curved humerus already).

This would ideally yield a maximally comprehensive taxon set as an open-access database, wherein all pertinent characters ever proposed are collated, and even low-hypodigm taxa are scored in a way that is defensible and reproducible. The latter are less useful for studies across a wide set of taxa, but for more restricted analyses (e.g. specific analyses of less-comprehensive clades, or of anatomical/evolutionary "modules") or for dedicated hypothesis-testing (e.g. by testing sensitivity to inclusion/exclusion of taxa with small hypodigms), etc, they are often crucial. And given the state of analytical theory (I do not expect major conceptual breakthroughs here, and the current methodological research focus is on handling "big data"sets like whole-genome anyway), and seeing the results of the current molecular supermatrices in Aves, I do not expect that the morph data, at the present state - with little cross-study validation, and quality control being essentially ad-hoc and at each author's individual discretion -, are capable of addressing questions like Ornithoscelida or the initial radiation of Neoaves in a reproducible fashion (QED). Such a database would also facilitate analyses whose taxon sets are tailored to represent a particular timespan of rapid radiation - putting roughly coeval more ancestral taxa into a framework held up by more advanced members of their putative clades. (Conventionally, outgroup choice is more important, but for rapid radiations near the base of a clade, there should probably be more focus on which more-advanced ingroup taxa to include.)

(And technically, if one wants to do an analysis that truly supposes as little as possible in advance, one would have to treat each set of articulated material - such as every individual "Archaeopteryx sensu lato" fossil - as an independent OTU. At least in "species" of disputed circumscription, a specimen-based rather than taxon-based approach for such a database is certainly warranted. Sure, little harm is done by considering all the iguanodontids from the Sainte-Barbe Clays at Bernissart to represent a single species/population/OTU - but the same cannot be said for the Daiting/Langenaltheim/Eichstätt Archies, or for the Gargantuavis hypodigm if all "referred to" material is included, etc.)

That being said: perhaps the first step could be a literature index collating the sources of published illustrations - possibly using a primarily specimen-based format right from the start, and treating taxonomic assignment as secondary, so that a specimen may have more than one taxonomic assignment (the least-inclusive clade to which it can be assigned with high confidence, plus various competing higher-level taxa - e.g. Brontornis material being covered by Neognathae, Galloanseres, and Cariamiformes).
Mickey has already done incredible work in this regard, assembling a vast literature index (see e.g. https://www.theropoddatabase.com/Ornithothoraces.htm). But the workload for comprehensive coverage is immense, and different skillsets are required to evaluate the literature, define characters, score material, and finally assemble all this into a usable database. Thus, a crowd-sourced expert-vetted approach seems to be the way to go. I started a literature survey for (mostly) Telluraves in that regard - specifying published descriptions, published illustrations, and published scorings for each named taxon as well as for unassigned material -, but due to the aforementioned problems never progressed beyond that, and I would love to feed these data into a more comprehensive project. (I am no database expert, but I *think* it would be wise to keep the "descriptive/discussion", "literature/references", "image-file" and "scorings" databases distinct and having them interface only via the output - a Web page that may ultimately even be used to pre-generate Nexus datablocks for a selected set of OTUs.)

[*] I found it often necessary to consider specimens to even understand how authors actually *defined* their characters - what consititutes a "large" tubercle, for example, can in retrospect not usually be easily understood without taking an analysis' scorings and comparing them to actual specimens, across the entire taxon set! This *should* not be necessary, but the absence of such a comprehensive database does make it necessary, and I suspect many of the issues Gregory mentions are caused to this subjectivity ands need to double-check (which practical constraints such as time pressue or lack of access to specimens often preclude, leading to inadvertent mis-scorings).

Best regards,

Eike Wulfmeyer

Am Samstag, 8. Juni 2024 um 12:49:23 MESZ hat Mickey Mortimer <therizino...@gmail.com> Folgendes geschrieben:

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