Crocodile variable bone growth marks + crocodilian neural canal ridges + procolophonid tooth morphologies + Iguana intraspecific skeletal variation (free pdfs)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

Some recent reptile papers:

(Note cautions on interpreting variations in bone growth marks and skeletal features within a single species in first and last listed...)

Free pdf:

Anusuya Chinsamy & Maria-Eugenia Pereyra (2025)
Stochastic growth marks in Crocodylus niloticus
Scientific Reports (unedited preprint)
doi: https://doi.org/10.1038/s41598-025-31384-5
https://www.nature.com/articles/s41598-025-31384-5


Skeletochronology combined with growth curve reconstruction is routinely used to assess the age and growth dynamics of extinct and extant vertebrates. Here we performed in vivo labelling studies of the bone histology of four 2 years-old Crocodylus niloticus individuals. We found that all the crocodiles have more growth marks in their compacta than expected for their age, i.e., they deposited stochastic growth marks in their bones. Using the fluorochrome markers we determined that these stochastic growth marks were deposited during their favourable season of growth. The variable preservation of growth marks in the crocodile bones highlights developmental plasticity in their growth, which can be extrapolated to extinct archosaurs, and other reptiles. We caution the use of growth marks in fossil bones as a reliable estimator of age and discuss the far-reaching implications this has for growth curve reconstruction and life history assessments of extinct vertebrates, such as nonavian dinosaurs.

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Free pdf:

William Jude Hart, Jessie Atterholt, and Mathew J. Wedel (2025)
First occurrences of neural canal ridges in Crocodylia
Acta Palaeontologica Polonica 70(4): 749-753
doi:10.4202/app.01269.2025
https://www.app.pan.pl/article/item/app012692025.html


Crocodylia is a crown group inclusive of the last common ancestor of extant crocodylians, followed by successive extinct and extant taxa forming Alligatoroidea, Crocodyloidea, and Gavialoidea. Rigorous work on fossil and extant crocodylian postcrania is vital for understanding the evolution of their functional morphology. Here, we document neural canal ridges (NCRs) in the genera Thecachampsa and Deinosuchus. The morphology of the NCRs in these taxa is consistent with bony spinal cord supports that anchor the denticulate ligaments in extant taxa. To date, we have only found NCRs in the caudal vertebrae of Thecachampsa and Deinosuchus, consistent with the serial distribution of NCRs in non-avian dinosaurs. However, NCRs are present in more regions of the vertebral column in non-amniotes, and absent in Anura, Aves, and Mammalia. Many vertebrate clades await systematic surveys for NCRs, in both fossil and extant representatives. Additional methods, such as osteohistology and embryology, may shed further light on the functional morphology and biomechanical underpinnings of neural canal ridge development and evolution. Our findings expand known axial postcranial morphology in Crocodylia and broaden the known distribution of NCRs in vertebrates.

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Free pdf:

Selena A. Martinez and Kelsey M. Jenkins (2025)
Procolophonids display unique tooth morphologies in relation to reptilian herbivory
Journal of Paleontology (advance online publication)
DOI: https://doi.org/10.1017/jpa.2025.10195
https://www.cambridge.org/core/journals/journal-of-paleontology/article/procolophonids-display-unique-tooth-morphologies-in-relation-to-reptilian-herbivory/091C49F58B880D3DD8B1EEFADC2E1E35



Procolophonidae, a clade of stem reptiles, are hypothesized to be some of the first highly specialized herbivores to evolve following the end-Permian mass extinction event. That hypothesis is largely based on qualitative observations of tooth shape, which are highly subjective and not generalizable. Quantitative studies of reptilian tooth shape have employed relatively sophisticated methods to capture tooth complexity, but these approaches often require expensive equipment and software and are time intensive. In this study, we built a predictive model based on extant lizards to quantitatively predict the diets of procolophonids using simple measures of tooth morphology. We use linear discriminant analysis (LDA) to predict dietary ecology from tooth dimensions and phylogenetic MANOVA to test for significant differences in tooth dimensions for different diet categories. We report two key findings: (1) procolophonids are largely predicted as herbivorous but occupy a different area of the LDA space from extant lizards, and (2) simple metrics return similar results as complex methods, but with less confidence. We hypothesize that Triassic flora posed different mechanical and processing challenges from modern plants, which contributed to the unique tooth morphologies of procolophonids and likely other Triassic taxa.

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Free pdf:

Vieno Rosa, Marcos Vinícius Coelho & Camila Cupello (2025)
The skeleton of the green Iguana iguana (Squamata: Iguanidae) and its intraspecific morphological variation
The Anatomical Record (advance online publication)
doi:  https://doi.org/10.1002/ar.70108
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70108

The green iguana (Iguana iguana) is an iguanine lizard with herbivorous and arboreal habits, whose distribution spans through South America, Central America to the south of North America. Although the genus Iguana is well-known, the species still lacks a comprehensive and up-to-date anatomical study, particularly addressing the axial skeleton, including intraspecific variation. This study provides an anatomical revision of the species, providing a detailed redescription of its cranial skeleton and the first comprehensive analysis of its axial skeleton. Here we use X-ray computed tomography, 3D segmentation and osteological analyses to examine nine specimens. Significant individual variability was observed in the shape and proportions of skull bones, the presence and absence of a neural spine in the atlas vertebra, rib count and caudal vertebrae morphotypes. Notably, the nasal and frontal bones exhibited shape variation related with specimen size. The caudal vertebrae exhibited considerable variation across specimens, presenting seven distinct morphotypes with consistent sequence but individual variation in their quantity and presence. Moreover, the caudal vertebrae variability contrasts with the previously known caudal pattern for the species. These findings expand our understanding of the morphological diversity within I. iguana.

[Mickey Mortimer]

"Vieno Rosa, Marcos Vinícius Coelho & Camila Cupello (2025)
The skeleton of the green Iguana iguana (Squamata: Iguanidae) and its intraspecific morphological variation"

This is a very cool paper that is just what Curtice implied we need more of on his blog this week when he said "There is, to me, an almost complete disdain for the massive range of variation present in extant taxa." Iguanids aren't titanosaurs, but is there pectoral shape variation in Iguana iguana that might be relevant to Alamosaurus and Utetitan? Rosa et al. report "The arrow-like shape of the interclavicle remains consistent across all specimens; however, its curvature varies, ranging from a nearly straight angle (Ig04) to an acute angle (Ig02, Ig03). The Ig01, UF: Herp:181922, and DZ UERJ specimens exhibit curvatures that fall between these extremes. ... The lateroventral process found in the procoracoid is only present in Ig04, while it is absent in the DZ UERJ, Ig01, Ig02, Ig03, Ig05, and UF:Herp:181922 specimens." So the profile of pectoral elements can certainly vary within I. iguana.

Interestingly, "The bones of both forelimbs and hindlimbs, including carpal and tarsal elements, displayed no significant variations across specimens", and to the possible detriment of sauropod workers, vertebrae exhibited the most variation. And perhaps most detrimental to titanosaur workers "The most significant intraspecific morphological variation in I. iguana was observed in the caudal structure, as all specimens exhibited distinct patterns..."

Now how about a paper like this for Alligator mississippiensis and Struthio camelus?

Mickey Mortimer

[James Napoli]

Can happily say that work similar in Alligator mississippiensis is in progress. My posted preprint on ontogenetic variation will be formally published soon (with minimal changes, happily), and work on variation within and between species is continuing. 

I'm very happy to see the Iguana paper, but one potential caveat that I don't see noted is the provenance of the specimens. Many of the specimens are from Brown University's XROMM lab, and I suspect they were acquired commercially on the pet trade (as is normal for in vivo experimentation in reptiles), rather than wild-caught; a life in captivity has well-known effects throughout the skeleton that could introduce variation beyond the "normal" for the taxon. 

[Gregory Paul]

This is important for assorted reasons. It suggests that the growth rates of dinosaurs may in some cases be underestimated by the presumption the rings are annual, rather than sometimes multi-annual. Could apply to the recent paper indicating Tyrannosaurus grew more slowly than had been thought. Or maybe not.  May explain the seemingly erratic growth of some dinosaurs. Or maybe not. 

I knew and have published that growth rings are not reliable age indicators. Came across bird biology papers observing and in some cases warning that bone rings are not reliable for that purpose because of numerous examples of birds of known age having too many rings for that time period, sometimes lots more of them. That growth stoppages can occur more than once a year is not surprising, can occur because of more than one bad feeding period in a year, reproduction in females, illness. I detailed this with references in the Complete Dinosaur 2nd edition in 2012. Which is not cited in the below work.

GSPaul

 

[Heinrich Mallison]

If you, Paul, happen to have those papers handy, I'd greatly appreciate if you could either send them or at least list them - please?

_______________________________________________________
Dr. Heinrich Mallison

cell: +49 (0)179 5429922
email: heinrich...@gmail.com
blog: dinosaurpalaeo.wordpress.com

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[Thomas Yazbek]

I've always been a little skeptical of the various estimates of dinosaur growth rates/maturation. They seem way too long for endothermic + r-selected animals. We really don't have any modern analogues to dinosaurs in that regard. Yes, they were massive, but modern megafauna are all K-selected mammals whose brains take years to develop, so not very good analogues with sauropods which laid a zillion eggs & exhibited less parental care than most mammals/birds. Crocodilians are ectotherms so also not the best comparison. Sexual maturity surely came way before skeletal maturity, but I have a hard time imagining T.rex taking 30 years to get to full size.

Thomas

[Russell Engelman]

One would think given the huge populations of green iguanas (and a few other large lizards like Tupinambis and Ctenosaura) in Florida, combined with the high mortality rates during cold snaps and the significant culling efforts, it would be really easy to put together a reference collection of wild-born lizard skeletons to study individual variation. I wouldn't be surprised if they just used the pet trade but there are other potential options.