Nowe dinozaury 2024

[Taurovenator]

Mamy pierwszego tegorocznego "silezauryda". Gondwanax paraisensis został opisany na postawie szczątków pochodzących od wielu osobników (głównie kręgi, elementy miednicy i nóg). Wiekiem jest bardzo zbliżony do Gamatavus (obydwa taksony zostały odnalezione w tej samej formacji). Autorzy publikacji kolejny raz odzyskali "silezaurydy" jako dinozaury ptasiomiedniczne.

R. Temp Müller, A new “silesaurid” from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs, Gondwana Research (2024), doi: https://doi.org/10.1016/j.gr.2024.09.007

Był tylko jeden autor, i to ten, który mocno wspiera tą hipotezę (ja również jestem jej przychylny). Tak czy inaczej, dobra rzecz, prawdopodobnie najstarszy znany zaawansowany "silezauryd".

[Danu]

Jedna rzecz mnie zastanawia. Autor podaje, że Silesaurus miał sacrum zlożone z 3 kręgów, podczas gdy w publikacji z 2010 roku autorzy podali, że 4.

Piechowski & Dzik 2010. THE AXIAL SKELETON OF SILESAURUS OPOLENSIS
"The sacrum of Silesaurus is composed of four fused vertebrae."

kontra:
"The sacrum resembles that of Silesaurus opolensis (Dzik & Sulej, 2007), which includes three sacral vertebrae (Piechowski & Tałanda, 2020). According to Nesbitt (2011), the sacrum of Silesaurus opolensis is
composed of two primordial sacral vertebrae plus one “insertion” between these
elements."

[nazuul]

Co jest kręgiem krzyżowym?
Z cytowanych prac:

It appears thus to be on the dinosaurian level in the development of sacrum, with three sacrals firmly connected by their ribs with the ilium (Fig. 19)

The medial surface of the ilium bears facets for three sacral ribs.

Sprawa ze Silesaurus jest jednak szczególna (nie wiem czy tak się powinno rozumować i dlaczego przesunięcie się kręgu miałoby być mniej prawdopodobne niż nowy kręg):

Silesaurus (ZPAL unnumbered) was reported
as having four sacral vertebrae (Dzik,
2003; Dzik and Sulej, 2007). However, only
three sacral ribs attach to the ilium. Silesaurus
is unique in that four centra are
coossified together by sharing three sacral
ribs (see character 208). The three sacral ribs
attach in a similar location as the sacral ribs
of Arizonasaurus and Batrachotomus. Conversely,
the sacral ribs are much more
delicate than those of Euparkeria and crocodylian-
line archosaurs (see Dzik, 2003; Dzik
and Sulej, 2007). Nonetheless, the first sacral
rib of Silesaurus attaches in the same location
as primordial sacral rib one in plesiomorphic
forms, whereas the third sacral rib of
Silesaurus attaches with the anteroposteriorly
trending ridge on the medial side of the ilium
and is posteriorly elongated as with primordial
sacral two of plesiomorphic forms.
Therefore, the third sacral of Silesaurus is
homologous with that of primordial sacral
two.

Jeszcze podana przez Ciebie praca:

The first sacral vertebra is
placed behind the tip of the anterior iliac spine. This bone is
morphologically similar to the preceding presacrals, except that
it is firmly co-ossified with the rest of the sacrum and its neural
spine is higher and more stout, with the dorsal extremity greatly
thickened. The transverse processes and sacral ribs diverge from
each other. The transverse processes of first sacral vertebra are
anteroposteriorly narrow and buttressed ventrally by delicate
thin laminae. The processes project anterolaterally to contact the
ilia close to the iliac spine. This vertebra lacks a rib and thus may
be considered a dorsosacral rather than a true sacral.
The second sacral vertebra has its broad transverse processes
modified into wing-like structures that project anterolaterally.
Similar structures are present in next sacral vertebrae but they
are broad and oriented transversely. In the last sacral vertebra, an
additional wing-like process extends posterodorsally; its centrum
and neural arch are similar to those in proximal caudal vertebrae.
All specimens show an extensive fusion of transverse processes
and corresponding sacral ribs. The second sacral vertebra bears
fan-like ribs broadly attached to the ilia, forming an anterior vertical
blade.