Headless Huayracursor enters the LRT, but not within Sauropodomorpha
From the Hechenleitner et al 2025 abstract:
“Compared to its generally small and short-necked Carnian counterparts, Huayracursor is larger and exhibits an incipient elongation of its cervical vertebrae, representing an intermediate condition for size and cervical elongation between known Carnian and Norian sauropodomorph. This discovery provides one of the oldest pieces of evidence of increased body mass and neck elongation in early Sauropodomorpha.”
From the publicity
“Among sauropodomorphs, Huayracursor jaguensis provides the earliest evidence of synchronous body mass increase and neck elongation in Sauropodomorpha, suggesting that these key traits emerged at the dawn of dinosaurs.”
“H. jaguensis likely lived during the Late Triassic period, between 201 million and 237 million years ago.”
“H. jaguensis is estimated to have measured at nearly 5 feet long and weighed about 40 pounds. It had a shorter neck compared to later sauropodomorphs, but its cervical vertebra showed signs of elongation.”
Figure 1. Huayracursor reconstruction and parts.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg?w=584″ class=”size-full wp-image-94984″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg” alt=”Figure 1. Huayracursor reconstruction and parts.” width=”584″ height=”430″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg?w=584&h=430 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg?w=150&h=110 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg?w=300&h=221 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-jaguensis588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Huayracursor reconstruction and parts.
By contrast
in the large reptile tree (LRT, 2339 taxa, subset Fig 5) headless Huayracursor nested basal to Sauropodomorpha, as the proximal outgroup taxon, between Mbiresaurus (Fig 3) and Sauropodomorpha + Chilesaurus + the rest of the Phytodinosauria = Ornithischia.
Mbiresaurus and Chilesaurus were not included in the phylogenetic analysis published at Wikipedia – Huayracursor, reflecting the Nature article, which is behind a paywall.
Figure 2. Huayracursor bones in dorsal view.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg?w=584″ class=”size-full wp-image-94985″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg” alt=”Figure 2. Huayracursor bones in dorsal view.” width=”584″ height=”438″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg?w=584&h=438 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg?w=150&h=113 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg?w=300&h=225 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/huayracursor-skeleton-pieces588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Huayracursor bones in dorsal view.
Acccording to the LRT, taxon exclusion remains
(in 2025) the number one problem hobbling paleontology. Too many taxa is always better than too few.
Figure 2. Mbiresaurus, the last common ancestor of Sauropodomorpha and Ornithischia, typifies the morphology of basal Phytodinosauria.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg?w=584″ class=”size-full wp-image-71860″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg” alt=”Figure 2. Mbiresaurus, the last common ancestor of Sauropodomorpha and Ornithischia, typifies the morphology of basal Phytodinosauria.” width=”584″ height=”366″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg?w=584&h=366 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg?w=150&h=94 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg?w=300&h=188 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2022/09/mbiresaurus_recon588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Mbiresaurus, the last common ancestor of Sauropodomorpha and Ornithischia, typifies the morphology of basal Phytodinosauria.
An almost overlooked phalanx…
Huayracursor appears to have a pedal phalanx 5.1 perhaps created by splitting metatarsal 5. Ancestors, like Mbiresaurus (Fig 3) had a long slender metatarsal 5, but no pedal digit 5. Descendant sauropodomorphs, like Plateosaurus (Fig 4), had two short phalanges on pedal digit 5.
That’s interesting: apparently the reactivation of a long lost gene recreated pedal digit 5 phalanges in a step-by-step fashion in this clade. Something similar occurred with the posterior jaw bones of embryo multituberculates retained into adulthood and the loss of molar and premolar shapes in odontocetes.
Figure 2. Plateosaurus skeleton digitized.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg?w=584″ class=”size-full wp-image-51114″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg” alt=”Figure 2. Plateosaurus skeleton digitized.” width=”584″ height=”467″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg?w=584&h=467 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg?w=150&h=120 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg?w=300&h=240 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2020/11/plateosaurus-skeleton588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 4. Plateosaurus skeleton digitized. Note pedal digit 5 has two phalanges.
Two sacrals
appear to be present in Huayracursor (Fig 2). That’s a primitive trait. Sauropodomorphs have more, sometimes many more sacrals (Fig 4). There are several other pre-sauropodomorph traits in Huayracursor in the manus and pes.
Figure 4. Subset of the LRT focusing on Phytodinosauria and Huayracursor.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg?w=160″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg?w=547″ class=”size-full wp-image-94992″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg” alt=”Figure 4. Subset of the LRT focusing on Phytodinosauria and Huayracursor. ” width=”584″ height=”1094″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg?w=584&h=1094 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg?w=80&h=150 80w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg?w=160&h=300 160w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/lrtsauropodomorpha588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 5. Subset of the LRT focusing on Phytodinosauria and Huayracursor.
Bottom line:
In the LRT Huayracursor is so close to Sauropodomorpha that additional taxa might push it in someday at the very base. But not today. Today it is the proximal outgroup = last common ancestor for the Sauropodomorpha + Ornithischia, which is a great overlooked headline for this taxon.
Apparently the Hechenleitner et al paper did not recognize the clade Phytodinosauria due to taxon exclusion. Too many taxa is always better than too few.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
References
Hechenleitner EM et al (6 co-authors) 2025. A long-necked early dinosaur from a newly discovered Upper Triassic basin in the Andes. Nature: 1–6. doi:10.1038/s41586-025-09634-3
Publicity
sci.news/paleontology/huayracursor-jaguensis-14287
sciencealert.com/near-complete-fossil-in-argentina-is-one-of-the-worlds-oldest-dinosaurs
abcnews.go.com/International/new-species-long-necked-dinosaur-discovered-mountains-argentina/story
Source: https://pterosaurheresies.wordpress.com/2025/10/20/headless-huayracursor-enters-the-lrt-but-not-within-sauropodomorpha/
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