Pre-mammals Dianoconodon and Sinoconodon compared
Sometimes a side-by-side demonstration can be useful.
Yes, there are differences here between Sinoconodon and Dianoconodon. That’s why these two took so long to get together in the LRT. Both were late survivors in the Early Jurassic of an earlier Triassic radiation of pre-mammals.
Figure 1. Sinoconodon is known from several specimens showing tooth eruptions and losses that indicate more than one set of replacement teeth. Smaller Dianoconodon is similar in morphology.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg?w=289″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg?w=584″ class=”size-full wp-image-92666″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg” alt=”Figure 1. Sinoconodon is known from several specimens showing tooth eruptions and losses that indicate more than one set of replacement teeth. Smaller Dianoconodon is similar in morphology. ” width=”584″ height=”607″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg?w=584&h=607 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg?w=144&h=150 144w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg?w=289&h=300 289w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/sinoconodon_dianoconodon.skulls588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Sinoconodon is known from several specimens showing tooth eruptions and losses that indicate more than one set of replacement teeth. Smaller Dianoconodon is similar in morphology.
Pre-mammal cynodonts
have more than one set of replacement teeth. When a single eruption of adult teeth follows the original eruption of milk teeth from presumeably toothless jaws, that indicates infant suckling on the mammae of its mother, THE KEY trait in describing a mammal.
The definition of a mammal is the last common ancestor of Megazostrodon, Morganocodon and its descendants in the LRT because those taxa have single replacement teeth = milk then adult teeth.
Others may tell you fur, warm blood, complex brain, middle ear bones detached from the jaw and live birth. Those came earlier, concurrently or later.
Figure 1. Sinoconodon growth series including jaws and teeth, here colorized from Zhang et al. 1992.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg?w=584″ class=”size-full wp-image-31858″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg” alt=”Figure 1. Sinoconodon growth series including jaws and teeth, here colorized from Zhang et al. 1992.” width=”584″ height=”527″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg?w=584&h=527 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg?w=150&h=135 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg?w=300&h=271 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2018/07/sinoconodon_mandibles588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2 Sinoconodon growth series including jaws and teeth, here colorized from Zhang et al. 1992.
Sinoconodon rigneyi
(Patterson & Olson, 1961. Early Jurassic) almost had a mammal jaw joint, and continued to replace teeth throughout its lifetime, but oddly loses all premolars early in ontogeny. See figure below.
Dianoconodon youngi
(Mao et al 2024b, Early Jurassic, IVPP-V4257) is a tiny Sinonodon relative. Note the anterior position of the orbit, distinct from Sinoconodon. This created more room for larger jaw muscles.
References
Mao F et al. (8 co-authors) 2024b. Fossils document evolutiionary changes of jaw joint to mammalian middle ear. Nature 1759(266): onlline
Patterson B and Olson EC 1961. A triconodont mammal from the Triassic of Yunnan. In Vandebroek G (ed.), International Colloquium on the Evolution of Lower and Non Specialized Mammals. Koninklijke Vlaamse Academir voor Wetenschappen, Letteren en Schone Kunsten can Belgie 129-191.
wiki/Sinoconodon
wiki/Docodon
wiki/Triconodon
wiki/Therioherpeton
wiki/Adelobasileus
wiki/Dianoconodon – not yet posted
Source: https://pterosaurheresies.wordpress.com/2025/05/03/pre-mammals-dianoconodon-and-sinoconodon-compared/
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