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Re: Most dinosaurs were scaly



I found this to be the best poster at SVP this year. Ever since the discovery 
of structures associated with Tianyulong and (to a lesser extent) that one 
Psittacosaurus individual, there seems to be a growing trend in dinosaur 
paleontology to assume that all dinosaurs were filamented (all ornithodirans 
even), in spite of a large collection of scale impressions from all major 
lineages. Barrett and Evan's analysis represents an actual test of this 
hypothesis. That neither parsimony analysis nor max likelihood (the latter of 
which is more amenable to reversals) found filaments to be ancestral to 
dinosaurs suggests that ancestrally scaly dinos is still the most parsimonious 
explanation. Admittedly, without data on the tree support values (available for 
the max likelihood tree at least) or a more detailed look at the methods we can 
only say so much about these results. 

I would caution against arguments for unique scale-filament intermingling, 
based on hair distribution in armadillos. Armadillo "scales" are not actually 
scales but are a unique form of agglutinated hairs (Wu et al. 2004). Pangolins 
are even weirder as their armour seems to have evolved from the same 
germinative layers as claws/nails (Spearman 1967). In fact, according to 
evo-devo studies synapsids probably never had "true" scales (= sauropsid type) 
as beta-keratin (a hallmark of most sauropsid scales) has never been found in 
the integument of mammals (although pangolins do have an analogue). 

As for whether we might be mislead into thinking some pebbly skin texture is 
actually scaly, it is a cause for concern. Dinosaur skin impressions tended not 
to receive much description unless they involve filaments. It has only been 
rather recently that there has been an interest in the scaly coverings of 
dinosaurs, with Bell (2012) and Davis (2012) offering insights into scale 
structures and distribution among dinosaurs. Paik et al. (2010) gave the only 
analysis I'm aware of regarding potential misinterpretation of lithological 
structures as being integumental, 
 can occur. A key factor to determining scales vs. lithology (or pebbly skin) 
seems to be the regularity of the structures. Pebbly skin has raises and cracks 
that are randomly distributed. Similarly, rainprints and ripple marks may be 
more uniform but don't interlock and often vary greatly in size from print to 
print. Scaly skin, on the other hand, tends
 to show a more regular patterning of interlocking polygons.   

It's unfortunate that this is only a press release. I talked with Paul at SVP 
about this being coming out as a paper and he mentioned that it would be 
published soon. It's too bad this press release may take away a lot of the 
impact. 


Jason


References

Bell, P.R. 2012. Standardized Terminology and Potential Taxonomic Utility for 
Hadrosaurid Skin Impressions: A Case Study for Sauroplophus from Canada and 
Mongolia. PLOS One. 7(2):e31295.

Davis, M. 2012. Census of Dinosaur Skin Reveals Lithology may Not Be the Most 
Important FActor in Increased Preservation of hardorsaurid Skin. Acta. 
Paleontological Polonica. 

Paik, S., Kim, H.J., Huh, M. 2010. Impressions of Dinosaur Skin from the 
Cretaceous Haman Formation in Korea. Journal of Asian Earth Sciences 39:270–274.

Spearman, R.I.C. 1967. On the Nature of the Horny Scales of the Pangolin. 
Journal of the Linnean Society (Zoology). 46(310):267–273.

Wu, P., Hou, L., Plikus, M., Hughes, M., Scehnet, J., Suksaweang, S., Widelitz, 
R.B., Jiang, T-X, Chuong, C-M. 2004. Evo-Devo of Amniote Integuments and 
Appendages. International Journal of Developmental Biology. 48:249–270.





>________________________________
> From: Zach Armstrong <zach.armstrong64@yahoo.com>
>To: "dinosaur@usc.edu" <dinosaur@usc.edu> 
>Sent: Saturday, 28 December 2013 4:53 PM
>Subject: Re: Most dinosaurs were scaly
> 
>
>
>
>I concur with what Mickey has said. I would also like to raise the question of 
>how confidant we can be that the all the scales of dinosaurs are true scales, 
>and are not epidermal structures secondarily derived from feathers due to 
>evo-devo mechanisms? 
>
>
>At least some evo-devo studies suggest that the reticula scales on the plantar 
>surface of avian feet are actually developmentally stunted feathers. To quote 
>from Dhouailly (2009), "[R]eticula are not true cutaneous appendages, and 
>appear to be feathers 
>arrested in the initiation step of their morphogenesis: formation of a 
>slight bump, without a pla
lar suggestions were made by Sawyer and Knapp (2003).
>
>At least some non-scale epidermal structures in modern avians morphologically 
>mimic scales too. For instance, the facial wattles of Philepitta schlegeli 
>(Schlegel's Asity) have an appearance to me that mimics scales: 
>http://thefeaturedcreature.com/wp-content/uploads/2012/10/Screen%2Bshot%2B2011-06-05%2Bat%2B7.26.20%2BPM2.png
>
>A similar thing can be said about the bare skin on the head and neck of 
>Coragyps atratus (Black Vulture): 
>http://en.wikipedia.org/wiki/File:Coragyps-atratus-002.jpg
>
>If all we had were fossilized impressions of these bare skin structures, might 
>we erroneously conclude they were true scales?
>
>I also think inferring from osteoderms in thyreophorans and sauropods that 
>their ancestors never had filamentous integumentary appendages (FIAs) might be 
>misleading. Hair sprouts amongst the osteoderms of armadillos for instance: 
>http://upload.wikimedia.org/wikipedia/commons/b/b4/Nine-banded_Armadillo.jpg 
>Do fossil cingulates preserve hair impressions amongst their osteoderms? Seems 
>unlikely.
>
>
>The same might be true for scaled dinosaurs, even those with osteoderms. 
>Additionally, feathers erupt from scutate scales in some birds on occasion. 
>Sawyer & Knapps (2003) noted, "The growth of feathers from the distal ends of 
>scutate scales occurs occasionally in normally scaled [chicken] breeds such as 
>White Plymouth Rock and White Leghorn.
>have been observed growing from the tips of the definitive scale ridges at 12 
>days of incubation." So scales and feathers intermingling are not de facto 
>impossible, although there appears to be significant developmental 
>constraints. Maybe these constraints were more relaxed during the initial 
>evolution of FIAs in dinosaurs.
>
>-Zach
>
>>________________________________
>
>> From: Mickey Mortimer <mickey_mortimer111@msn.com>
>>To: "dinosaur@usc.edu" <dinosaur@usc.edu> 
>>Sent: Friday, December 27, 2013 11:48 PM
>>Subject: RE: Most dinosaurs were scaly
>> 
>>
>>Is it just me, or does this study seem to suffer fr
aively assuming body covering doesn't covary with other factors we can test?  
In other words, it's obvious if you just plug in known skin coverings over a 
cladogram, scales will be the ancestral state for Dinosauria.  No one's ever 
doubted that, Greg Paul included.  The additional factor which has been 
discussed ever since his 1988 work is of course size.  What happens if you only 
plot small specimens on the cladogram?  Ornithischians are all fuzzy/spiny, and 
sauropodomorphs are unknown unless the titanosaur embryos count.  Even if the 
latter do count, Sciurumimus makes theropods primitively fuzzy despite 
Juravenator, so that's ambiguous basal Saurischia and fuzzy basal Dinosauria, 
which only gets more support if pterosaurs are avemetatarsalians.  Maybe 
Barrett and Evans include a caveat about this assumption, but since taking it 
into account nullifies their entire conclusion, I don't think
>it could help.  This isn't even getting into the metabolic and growth evidence 
>that 
>>shows increasingly basal archosauromorphs weren't like living 
>>'reptiles'.  You might as well determine ornithischians don't have cheeks 
>>based only on their lack in birds, crocs and lepidosaurs.
>>
>>Mickey Mortimer
>>
>>
>>----------------------------------------
>>> Date: Fri, 27 Dec 2013 10:13:58 -0800
>>> From: bcreisler@gmail.com
>>> To: dinosaur@usc.edu
>>> Subject: Most dinosaurs were scaly
>>>
>>> From: Ben Creisler
>>> bcreisler@gmail.com
>>>
>>>
>>> A news item and the original abstract from the 2013 SVP meeting:
>>>
>>> Nature news:
>>>
>>> http://www.nature.com/news/feathers-were-the-exception-rather-than-the-rule-for-dinosaurs-1.14379
>>>
>>>
>>> The abstract from the SVP Meeting:
>>>
>>>
>>> Poster Session III (Friday, November 1, 2013, 4:15 - 6:15 PM)
>>> DINOSAUR INTEGUMENT: WHAT DO WE REALLY KNOW?
>>> BARRETT, Paul, The Natural History Museum, London, United Kingdom; EVANS,
>>> David, Univ of Toronto at Mississauga, Toronto, ON, Canada
>>>
>>> Osteoderms and scaly skin impressions are historically well known in n
saurs
>>> these structures,
>>> many dinosaur taxa possessed other integumentary features, including a
>>> range of ‘quills,'
>>> filaments, and feathers in non-avian theropods and ornithischians.
>>> Feathers and their
>>> homologs are commonly regarded as a synapomorphy of either coelurosaurian or
>>> tetanuran theropods, but some authors have gone further, using the presence 
>>> of
>>> ornithischian feather-like structures to suggest that these structures
>>> are plesiomorphic for
>>> Dinosauria. This inference has wide-ranging implications for dinosaur
>>> biology and
>>> evolution.
>>> However, to date, no studies have attempted to assess rigorously the
>>> evolution of
>>> dinosaur integumentary structures within a broad phylogenetic context.
>>> We compiled a
>>> complete database of all epidermal integumentary structures reported
>>> in dinosaurs, by
>>> major body region, in order to investigate the origin of feather
>>> homol
>nd the
>>> evolution of integumentary structures in the clade. Scales are
>>> definitively present in
>>> virtually all major ornithischian clades. This, and the presence of
>>> extensive armour in
>>> thyreophorans suggests that genasaurian skins were primitively scaly. 
>>> Similarly,
>>> sauropodomorphs lack evidence for anything other than scales or
>>> osteoderms. Fitch
>>> optimization of integument types on dinosaur phylogenies shows that there 
>>> is no
>>> unequivocal support for inferring a deep origin of feather-like
>>> structures, a result
>>> supported by maximum likelihood ancestral state reconstructions for
>>> these characters.
>>> The structures in Tianyulong and Psittacosaurus are best regarded as
>>> autapomorphic
>>> integumentary modifications, and there is currently no strong evidence
>>> that these features
>>> are feather homologs. Further work on the chemical composition of
>>> these structures, and
>>> those in several non-coelurosaurian theropods, is needed. Although
>>> ornithodirans exhibit
>>> a range of integumentary novelties that may be related to the origin
re currently the only dinosaurs that display unequivocal e
>>> feathers and their
>>> direct homologs.                           
>>
>>
>>
>
>
>