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Mammaliaformes

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Mammaliaformes

Mammaliaformes
Temporal range: Carnian – Present 225–0Ma
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Life restoration of Castorocauda lutrasimilis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Order: Therapsida
Suborder: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Rowe, 1988
Subgroups

Mammaliaformes ("mammal-shaped") is a Docodonta and Hadrocodium as well as the Triassic Tikitherium, the earliest known member of the group.[3][4]

Mammaliaformes is a term of Adelobasileus and Sinoconodon in Mammalia, though they fall outside the Mammaliaformes definition. These genera are included in the broader clade Mammaliamorpha, defined phylogenetically as the clade originating with the last common ancestor of Tritylodontidae and the crown group mammals.[2] This wider group includes some families that trait-based taxonomy does not include in Mammalia, in particular Tritylodontidae and Brasilodontidae.

Animals in the Mammaliaformes clade are often called mammaliaforms, without the e. Sometimes, the spelling mammaliforms is used.

The origin of true mammals (Mammalia) extends back to the Jurassic, with extensive findings in the Late Jurassic outcrops of Portugal and China.

Mammaliaformes in life

Early mammaliaforms were generally shrew-like in appearance and size, and most of their distinguishing characteristics were internal. In particular, the structure of the mammaliaform (and mammal) jaw and arrangement of teeth is nearly unique. Instead of having many teeth that are frequently replaced, mammals have one set of baby teeth and later one set of adult teeth which fit together precisely. This is thought to aid in the grinding of food to make it quicker to digest.[5] Warm-blooded animals require more calories than those that are cold-blooded, so quickening the pace of digestion is a necessity. The drawback to the fixed dentition is that worn teeth cannot be replaced, as was possible for the reptilian ancestors of mammaliaforms. To compensate, mammals developed prismatic enamel, characterized by crystallite discontinuities that helped spread out the force of the bite.[6]

[8] Prior to hatching, the milk glands would provide moisture to the leathery eggs, a situation still found in monotremes.[9]

The early mammaliaforms did have an Castorocauda, further removed from crown group mammals than Hadrocodium, had two layers of fur, guard hairs and underfur, as do mammals today.[11]

It is possible that early mammaliaforms had vibrissae; Tritheledontidae, a group of Cynodonts, probably had whiskers.[12] A common ancestor of all therian mammals did so.[13] Indeed, some humans even still develop vestigial vibrissal muscles in the upper lip.[14] Thus, it is possible that the development of the whisker sensory system played an important role in mammalian development, more generally.[13]

Like monotremes today, the legs of early mammaliaforms were somewhat sprawling, giving a rather "reptilian" type of gait. In some forms the hind feet likely bore a spur similar to those found in the platypus and echidnas. Such a spur would have been connected to a venom gland for protection or mating competition.[15]

Hadrocodium lacks the multiple bones in its lower jaw seen in reptiles. These are still retained, however, in earlier mammaliaforms.[16]

Phylogeny

Cladogram based on Rougier et al. (1996)[17] with Tikitherium included following Luo and Martin (2007).[3]
  Mammaliamorpha

Tritylodontidae



Adelobasileus



Sinoconodon

Mammaliaformes

Morganucodontidae   Morganucodon





Tikitherium

Docodonta


Haldanodon


Castorocauda




Crown-group Mammalia
Monotremata

Ornithorhychus (Platypus)


Tachyglossidae (Echidna)


Theriiformes

Triconodonts, Multituberculates,
Marsupials, and Placentals








See also

References

  1. ^ Abdala, F. (2007). "Redescription of Platycraniellus Elegans (Therapsida, Cynodontia) from the Lower Triassic of South Africa, and the cladistic relationships of eutheriodonts". Palaeontology 53 (3): 591–618.  
  2. ^ a b Rowe, T. S. (1988). "Definition, diagnosis, and origin of Mammalia". Journal of Vertebrate Paleontology 8 (3): 241–264.  
  3. ^ a b Luo, Zhe-Xi; Martin, Thomas (2007). "Analysis of Molar Structure and Phylogeny of Docodont Genera". Bulletin of Carnegie Museum of Natural History (39): 27–47.  
  4. ^ Datta, P. M. (2005). "Earliest mammal with transversely expanded upper molar from the Late Triassic (Carnian) Tiki Formation, South Rewa Gondwana Basin, India". Journal of Vertebrate Paleontology 25 (1): 200–207.  
  5. ^ Minkoff,  
  6. ^ Line, S. R. P.; Novaes, P. D. (2005). "The development and evolution of mammalian enamel: Structural and functional aspects". Brazilian Journal of Morphological Sciences 22 (2): 67–72.  
  7. ^ Oftedal, O.T. (2002). "The origin of lactation as a water source for parchment-shelled eggs". Journal of Mammary Gland Biology and Neoplasia 7 (3): 253–266.  
  8. ^ Mammals of the Mesozoic: The least mammal-like mammals
  9. ^ Oftedal, O.T. (2002). "The mammary gland and its origin during synapsid evolution". Journal of Mammary Gland Biology and Neoplasia 7 (3): 225–252.  
  10. ^ Ruben, J.A., and Jones, T.D. (2000). "Selective Factors Associated with the Origin of Fur and Feathers". American Zoologist 40 (4): 585–596.  
  11. ^ Qiang Ji et al. (2006). "A Swimming Mammaliaform from the Middle Jurassic and Ecomorphological Diversification of Early Mammals". Science 311: 1123–27.  
  12. ^ "Your Inner Fish: Episode Guide". PBS. 2014. Retrieved August 7, 2014. 
  13. ^ a b Mitchinson, B.; Grant, R. A.; Arkley, K.; Rankov, V.; Perkon, I.; Prescott, T. J. (12 November 2011). "Active vibrissal sensing in rodents and marsupials". Phil. Trans. R. Soc. B 366 (1581): 3037–3048.  
  14. ^ Tamatsu, Yuichi; Tsukahara, Kazue; Hotta, Mitsuyuki; Shimada, Kazuyuki (August 2007). "Vestiges of vibrissal capsular muscles exist in the human upper lip". Clin Anat 20 (6): 628–31.  
  15. ^  
  16. ^ Kemp, T. S. (2005). The Origin and Evolution of Mammals. Oxford University Press. p. 149.  
  17. ^ Rougier, G. W.; Wible, J. R.; Hopson, J. A. (1996). (Triconodontidae, Mammalia) from the Late Jurassic of Colorado, and a Reappraisal of Mammaliaform Interrelationships"Priacodon fruitaensis"Basicranial Anatomy of . American Museum Novitates (American Museum of Natural History) (3183).  

External links

  • Mammaliforms and Mammaliaformes from Palaeos
  • Mesozoic Mammals; Basal Mammaliaformes, an internet directory
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