SVP 2018: Ancestral dinosaur integument

Holtz 2018 tackles the question:
What sort of dermal covering did basal dinosaurs, like Herrerasaurus have? Naked skin (Fig. 1)? Scales? Dorsal osteoderms? Pre-feather filaments? Or combinations thereof?

We looked at this question
earlier. In the poultry section of grocery stores chickens are nude and have no scales.

Holtz concludes,
“In some of these analyses, the more likely ancestral status for Dinosauria or Ornithoscelida was recovered as filamentous. However, the fact that the basal relationships are indeed poorly resolved at present requires an acceptance of ambiguity for the integumentary condition of the original dinosaur.”

Figure 2. Primordial feathers on the back of a 10-day-old chick embryo.

Figure 1. Primordial feathers on the back of a 10-day-old chick embryo. Ontogeny sometimes recapitulates phylogeny. Perhaps this embryo provides just such a clue.

In the non-ambiguous
large reptile tree (LRT,  1315 taxa) the ancestral state (based on phylogenetic bracketing) is nudity with filaments and dorsal osteoderms transformed into subcutaneous spine tables that disappear shortly thereafter. Given that Holtz did not recover a clade Phytodinosauria, he is not likely to have included basal bipedal crocs as proximal outgroups, as recovered in the LRT.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

References
Holtz TR 2018. Integumentary status: It’s complicated: phylogenetic sedimentary, and biological impediments to resolving the ancestral integument of Mesozoic Dinosauria. SVP abstracts.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.