Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth

  title={Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth},
  author={Eva A. Hoffman and Timothy B. Rowe},
Transformations in morphology, physiology and behaviour along the mammalian stem lineage were accompanied by profound modifications to reproduction and growth, including the emergence of a reproductive strategy characterized by high maternal investment in a small number of offspring1,2 and heterochronic changes in early cranial development associated with the enlargement of the brain3. Because direct fossil evidence of these transitions is lacking, the timing and sequence of these modifications… 

Reptile-like physiology in Early Jurassic stem-mammals

It is reported, using synchrotron X-ray tomographic imaging of incremental tooth cementum, that the Early Jurassic Morganucodon and Kuehneotherium had maximum lifespans considerably longer than comparably sized living mammals, but similar to those of reptiles, and so they likely had reptilian-level basal metabolic rates.

Multituberculate Mammals Show Evidence of a Life History Strategy Similar to That of Placentals, Not Marsupials

It is found that proportions of different bone tissue microstructures in the femoral cortices of small extant marsupials and placentals correlate with length of lactation period, and this histological correlate of reproductive strategies to members of Multituberculata is applied.

The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals

The earliest-known mandibular fossil of a mammaliaform with double molariform roots and a crown with two rows of cusps from the Late Triassic of Greenland is described and indicates that teeth with two roots can better withstand stronger mechanical stresses like those resulting from tooth occlusion, than teeth with a single root.

Developmental bias, macroevolution, and the fossil record

  • D. Jablonski
  • Biology, Environmental Science
    Evolution & development
  • 2019
Assessing the “heritability” of an ancestral bias across phylogeny, and the tendency for bias change in strength and orientation over evolutionary time will help find a set of general rules for the macroevolutionary effects of developmental bias, including its impact on and interactions with the other intrinsic and extrinsic factors governing the movement, expansion, and contraction of clades in morphospace.

New tools suggest a middle Jurassic origin for mammalian endothermy

We suggest that mammalian endothermy was established amongst Middle Jurassic crown mammals, through reviewing state‐of‐the‐art fossil and living mammal studies. This is considerably later than the

Colobops: a juvenile rhynchocephalian reptile (Lepidosauromorpha), not a diminutive archosauromorph with an unusually strong bite

The skull of Colobops was strongly dorsoventrally compressed post-mortem, with most bones out of life position, and the cranial anatomy is consistent with that of other rhynchocephalian lepidosauromorphs, not rhynchosaurs.

Evolution and identity of synapsid carpal bones

The observations provided here provide an updated revision of synapsid carpal homologies, mainly on the basis of position and anatomical contacts and also taking into account the results of embryological studies.

Comparative skeletal anatomy of neonatal ursids and the extreme altriciality of the giant panda

Whether ursid neonates have exceptionally altricial skeletons at birth compared with other caniform neonates is asked and it is found that most bear neonates are similar to outgroup neonates in levels of skeletal ossification, with little variation in degree ofOssification between ursine bears neonates (i.e. bears of the subfamily Ursinae).

The evolution of anteriorly directed molar occlusion in mammals

It is posited that therian mammals (eutherians and metatherians) evolved anteriorly directed chewing strokes, which are absent in other synapsid lineages, and this evolutionary transition might have been a crucial prerequisite for the dietary diversification of therians.

A new non-mammalian eucynodont from the Chinle Formation (Triassic: Norian), and implications for the early Mesozoic equatorial cynodont record

Recently collected non-mammalian eucynodontian jaws from the middle Norian Blue Mesa Member of the Chinle Formation in northeastern Arizona shed light on the Triassic cynodont record from western equatorial Pangaea, indicating that the faunal dissimilarity previously recognized between the western and eastern portions of equatorialPangaea is overstated.



Developmental palaeontology in synapsids: the fossil record of ontogeny in mammals and their closest relatives

  • M. Sánchez-Villagra
  • Environmental Science, Geography
    Proceedings of the Royal Society B: Biological Sciences
  • 2010
Developmental palaeontology is relevant for the discourse of ecological developmental biology, an area of research where features of growth and variation are fundamental and accessible among fossil mammals.

The Emergence of Mammals

  • T. Rowe
  • Biology
    Evolutionary Neuroscience
  • 2020

Reproduction in Early Amniotes

Exceptional insights into early amniote reproduction are offered by recent fossil discoveries, and the fact that these fossils come from ancient seas and lakes and not from dry land helps to explain the paradox that there is an older fossil record for live-bearing amniotes than for egg laying in ammiotes.

Heterochrony in limb evolution: developmental mechanisms and natural selection.

The tetrapod limb provides several examples of heterochrony-changes in the timing of developmental events. These include species differences in the sequence of skeletal chondrogenesis, in gene

Mammalian skull heterochrony reveals modular evolution and a link between cranial development and brain size

It is argued that cranial heterochrony in mammals has occurred in concert with encephalization but within a conserved modular organization.

Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution

Tests of competing phylogenetic hypotheses with new data show that Late Triassic haramiyids are a separate clade from multituberculate mammals and are excluded from the Mammalia, suggesting that dietary diversification is a major factor in the earliest mammaliaform evolution.

Ontogeny of the Early Triassic Cynodont Thrinaxodon liorhinus (Therapsida): Cranial Morphology

The large number of changes in the temporal region of the skull of Thrinaxodon may indicate a greater development of the posterior fibres of the temporalis musculature from an early ontogenetic stage, indicating a strong posterodorsal movement of the mandible in Thrinrix.


  • V. Weisbecker
  • Biology
    Evolution; international journal of organic evolution
  • 2011
The first postcranial ossification sequences of the monotreme echidna and platypus are presented, and these are compared with published data from other mammals and amniotes to suggest marsupials may not represent the ancestral mammalian condition.

Larger mammals have longer faces because of size-related constraints on skull form

It is demonstrated that cranial size and shape co-vary in adults across a range of mammalian groups, similar to how large individuals tend to be long-faced and small individuals have large braincases.

Definition, diagnosis, and origin of Mammalia

Triassic and Early Jurassic taxa commonly referred to as mammals, including Morganucodontidae, Kuehneotheriidae, and Haramiyidae, were found to lie outside of Mammalia.