That one might simply be a mistake, "Theropoda" and "Thecodontia" are fairly similar-looking words.
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From: firstname.lastname@example.org <email@example.com> on behalf of Tim Williams <firstname.lastname@example.org>
Sent: October 24, 2017 8:10 PM
Subject: Re: [dinosaur] Jehol Biota rise and fall + protoceratopsids from Alxa, Inner Mongolia, China + more free pdfs
Brad McFeeters <email@example.com> wrote:
> Shao et al. 2017 strangely refer to _Liaoningornis_ as "the only member of
> the Neornithes in the Yixian Formation." Has anyone else ever considered it
> to be that derived?
My guess is that the authors have confused 'Neornithes' with
'Ornithurae'. _Liaoningornis_ was originally described as a member of
the Ornithurae (Hou, 1997; Chinese Science Bulletin 42: 413-417),
where it was described as a "carinate bird" on account of its keeled
sternum. However, it was assigned to a new order
(Liaoningornithiformes) at the base of the Ornithurae, not the crown
Since then, _Liaoningornis_ has been redescribed and referred to the
Enantiornithes (O'Connor 2012; Vertebrata Palasiatica 50: 25-37).
This review (Shao et al. 2017) contains a few dodgy statements.
There's also this: "After the Yale conference, many feathered
dinosaurs such as _Beipiaosaurus_, _Sinornithosaurus_, _Microraptor_,
_Sinovenator_, provided new evidences for the "Thecodontia-origin" of
birds..." Elsewhere, the review makes it clear that birds are
descended from dinosaurs, so this statement is odd.