Haramiyida

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Haramiyida
Temporal range: Late Triassic-Middle Jurassic, 216.5–183Ma
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Order: Therapsida
Suborder: Cynodontia
Clade: Mammaliaformes
Suborder: Haramiyida
Hahn, Sigogneau-Russell & Wouters, 1989
Subgroups

Haramiyidans (incl. Eleutherodontida Kermack et al., 1998) seem to be the earliest known herbivores amongst basal mammals, assuming they are mammals. Their teeth, which are by far the most common remains, resemble those of the multituberculates. The jaw however, based on Haramiyavia, is less derived; "at the level of evolution of Morganucodon and Kuehneotherium, with a groove for ear ossicles on the dentary".[1]

Ancestry[edit]

It is tempting to infer that this order represents the ancestors of the multituberculates, a group which appears to have survived until about 40 million years ago. While this is not impossible, the evidence available is insufficient to be conclusive. As an illustration and with reference to material from Greenland:

"Jenkins' group identified haramiyid jaws with the teeth in place, as well as additional parts of the skeleton. Among other revelations from the fossils, the teeth in the upper jaw do not fit the classic multituberculate arrangement, with the second molar offset towards the centre of the mouth.

"That shows rather well that haramiyids are not closely related to multituberculates," says William A. Clemens of the University of California, Berkeley, one of the leaders of the multituberculate symposium.[2] This taxon is in some disgrace for being paraphyletic;[3] i.e. it doesn't consist of one ancestor species and its descendants. Kemp provides a concise overview of the post-canines.[4] Harami Molars are larger than many of their equivalents from contemporary mammals, but not by much. These have many of cusps and are generally double-rooted. The crowns are wide and have a line of three large cusps on one edge, with five smaller ones on the opposing side.

Originally, it was thought that upper and lower molars were pretty much mirror images of each other, and minor details lead to the establishment of two genera: Thomasia and Haramiya. The suggestion was subsequently made that these could also represent lowers and uppers of only one genus, and the discovery of Haramiyavia provided confirmation for that. The teeth of Theroteinida and Eleutherodontida, (nothing more is yet known), are perhaps more accurately described as 'haramiyidan'-like. "But haramiyids are known from beds as old as Norian: hence, if they are related to multituberculates, an astonishingly early divergence of crown mammals (not to mention a series of putative sister taxa to crown mammals) is implied".[5]

More precise affinities will probably remain unclear until better evidence is forthcoming. Butler & Hooker, (2005) maintain that 'haramiyids' are still stronger candidates for having given rise to the multituberculates than morganucodontids are: "As long as we only have teeth to of the critical taxa, we feel it necessary to adopt the Allotheria concept as a working hypothesis; no doubt the discovery of mammalian skeletal material in the Jurassic will throw new light on the problem", (p. 206). The concept of Allotheria unites haramis and multituberculates as the sister line of other mammals.

Most fossils have been reported from Europe, but some are known from Africa and Greenland. A description in January 2005 extended the published range to the Junggar Basin of Inner Mongolia. It may be safer to refer to this group as haramyioidens rather than 'haramiyidans'. 'Haramiyan' fossils first appear in the Upper Triassic. Until 1999, the last traces were Middle Jurassic. However, Allostaffia then turned up in the Upper Jurassic of Tanzania.

Notes[edit]

  1. ^ Butler PM, 2000
  2. ^ Monastersky 1996, p.379
  3. ^ Butler & Hooker 2005, p.185
  4. ^ Kemp, 2005 (p.140-141)
  5. ^ Cifelli, 2001

External links[edit]

References[edit]

  • Zofia Kielan-Jaworowska, Richard L. Cifelli, and Zhe-Xi Luo, Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure (New York: Columbia University Press, 2004), 249-260.