New Jurassic mammaliaform sheds light on early evolution of mammal-like hyoid bones

Abstract

We report a new Jurassic docodontan mammaliaform found in China that is preserved with the hyoid bones. Its basihyal, ceratohyal, epihyal, and thyrohyal bones have mobile joints and are arranged in a saddle-shaped configuration, as in the mobile linkage of the hyoid apparatus of extant mammals. These are fundamentally different from the simple hyoid rods of nonmammaliaform cynodonts, which were likely associated with a wide, nonmuscularized throat, as seen in extant reptiles. The hyoid apparatus provides a framework for the larynx and for the constricted, muscularized esophagus, crucial for transport and powered swallowing of the masticated food and liquid in extant mammals. These derived structural components of hyoids evolved among early diverging mammaliaforms, before the disconnection of the middle ear from the mandible in crown mammals.

The making of calibration sausage exemplified by recalibrating the transcriptomic timetree of jawed vertebrates

“…Indeed, the Sinemurian record of mammalomorphs (tritylodontids, tritheledontids, Sinoconodon , morganucodontans, Hadrocodium ) from North America, southern Africa and China is fairly rich and diverse, but has not yielded mammals so far. However, ghost lineages encompassing almost the entire Early Jurassic to the middle of the Middle Jurassic occur for haramiyidans and docodonts, both of which have been found in the Rhaetian and the Bathonian, but not so far in between; and while the Rhaetian and/or possibly Norian Thomasia and Haramiyavia lie outside the smallest clade of all other haramiyidans, the Rhaetian Tikitherium is the sister-group of all Jurassic docodonts except the probably Middle Jurassic Gondtherium (Zhou et al, 2019: supp. inf.…”

“…Currently, the former is recovered by parsimony, the latter by Bayesian analysis of the same matrix (Huttenlocker et al, 2018: extended data fig. 9; Zhou et al, 2019: supp. inf.…”

“…: 4), which has meanwhile been dated to between 160.889 ± 0.069 Ma and 160.254 ± 0.045 Ma (Jia and Gao, 2019). Meng (2014: 526, 529–530), however, doubted this, called the specimen “floating”, and pointed out its great similarity to Eomaia in particular (found as its sister-group in the very different matrices of Bi et al, 2018, and Zhou et al, 2019: supp. inf.…”

How the earliest mammals thrived alongside dinosaurs

“…In July, Luo published a paper revealing a 165-million-year-old vole-sized docodont -a close relative of true mammals -that had the hyoid bones of its throat preserved 14 . Microdocodon gracilis is the earliest animal known to have been able to suckle like a modern mammal.…”

Conflict Resolution for Mesozoic Mammals: Reconciling Phylogenetic Incongruence Among Anatomical Regions

“…In practice, these theoretical benefits are tempered by extensive character incompleteness, temporal gaps in the fossil record, and models that do not closely reflect morphological evolution, such as assuming constant rather than episodic evolutionary rates across lineages and character complexes. Nevertheless, phylogenetic inference has been enhanced by a recent explosion in sampling Mesozoic mammals (especially from China), including early members of many clades (Meng, 2014;Luo et al, 2017;Zhou et al, 2019).…”