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Mbiresaurus enters the LRT as the last common ancestor of Sauropodomorpha + Ornithischia within Phytodinosauria

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A few days ago
Griffen et al. 2022 set forth the hypothesis that African dinosaurs, like Mbiresaurus (Figs 1, 2), were limited by climatic barriers that fenced them in “until these barriers relaxed”. As shown a few days ago, no other coeval archosauriformes were limited in distribution across Pangaea throughout the Triassic. So that hypothesis seems poorly supported.

Figure 1. Click to play 6:42 minute YouTube video from the Zim (Zimbabwe) News.

Today we’ll take a closer look
at Mbiresaurus itself (Fig 2) and add it to the LRT.

Figure 2. Mbiresaurus from Griffen et al. 2022. Note the postobital (lower left) is a complex of bones relected in the new head reconstruction (upper (left).

Despite having a near complete skeleton
to score (Fig 2), Griffen et al. had a tough time consistently nesting taxa surrounding Mbiresaurus (Fig 3) from borrowed cladograms, even after manipulating them by excluding taxa and a character. On the other hand, all attempts consistently nested Mbiresaurus near the base of the Sauropodomorpha.

Figure 3. Nine cladograms borrowed and modifief by Griffen et al 2022 extended figure 4. These all suffer from taxon exclusion. Note how clades bounce around here. This is a failure. This is not the situation in the LRT (Fig. 5) where the cladogram is fully resolved. Lavendar = theropoda. Yellow = basal Dinosauria. Green = basal Phytodinosauria. Blue = Ornithischia. Pink = Sauropodomorpha.

Perhaps this is so because the authors borrowed imperfect cladograms
(Fig 3) suffering from taxon exclusion (i.e. omitting the basalmost yet Late Jurassic ornithschian, Chilesaurus, omitting several basal bipedal crocs other than poorly known Saltopus and Lewisuchus, and omitting basal poposaurs like Turfanosuchus and Poposaurus). These cladograms also suffered from irrelevant taxon inclusion (like Dimorphodon, silesaurids, Ixaerpeton and lagerpertids).

Workers should build their own large reptile tree (LRT, 2140 taxa, subset Fig 5). Eleven years after its genesis the LRT now iincludes such a wide gamut of taxa that taxon exclusion and irrelevant taxon inclusion are increasingly not an issue.

Figure 4 from Griffen et al 2022 extended figure 6. This is the cladogram, still suffering from taxon exclusion, published by the authors to present the phylogeny of Mbiresaurus (silhouette). Overlying colors reflect clades in the LRT (see figure 5).

Griffen et al. considered Mbiresaurus a new genus of basal sauropodomorph.
Likewise, the LRT also nested Mbiresaurus at that node (Fig 5).

But there’s more to this hypothesis of interrelationships.

In the LRT,
which includes many more taxa, Mbiresaurus nests as the last common ancestor of Sauropodomorpha + Ornithischia within the Phytodinosauria (Bakker 1986). That’s a newsworthy opportunity squandered by the authors due to simple, traditional taxon exclusion.

This is what you miss out on with taxon exclusion.
When you exclude taxa you too risk missing the real prize and leaving this sort of low-hanging fruit for amateurs to pluck.

Build your own LRT so you won’t have to borrow flawed and incomplete cladograms. Don’t leave the more exciting discovery to outsiders, especially when it was your team that did all the hard work (e.g finding, digging, cleaning, describing, winning grants, gathering fellow workers and authors, publicizing). It’s not fair. All that blogger did was find a small, but basic flaw without cost in time and treasure and in only a few hours alone. Do the phylogenetic work. Don’t let this sort of thing happen again.

Figure 5. Added to the LRT Mbriesaurus nests at the base of Sauropodomorpha + Ornithischia.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a prior citation so I can promote it here.

The top six problems in paleontology:
Number one: taxon exclusion (= the streetlight effect).
Number two: borrowing cladograms that exclude taxa.
Number three: trusting genomic results.
Number four: trusting textbooks and academic traditions.
Number five: freehand reconstructions.
Number six: “Pulling a Larry Martin” = focusing on one to a dozen traits, rather than a complete suite.
Solution: Keep adding taxa to your own trait-based cladogram. Trace specimens with transparent colors and from those tracings create more accurate and verifiable reconstructions.

Bakker RT 1986. The Dinosaur Heresies. William Morrow.
Griffin C et al. 2022. Africa’s oldest dinosaurs reveal early suppression of dinosaur distribution. Nature 609: 313–319.


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