Haramiyida
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| Haramiyida Fossil range: Jurassic-Oligocene |
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Haramiyidans 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" (Butler PM, 2000). It’s tempting to infer that this order represents the ancestors of the multis, a group which appears to have survived until about 40 million years ago. Whilst 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," (Monastersky 1996, p.379). This taxon is in some disgrace for being paraphyletic, (Butler & Hooker 2005, p.185). It doesn't consist of one ancestor and all of its descendants. Kemp, 2005 (p.140-141) provides a concise overview of the postcanines. Harami molars are larger than many of their equivalents from contemporary mammals, but not by much. These are blessed with lots 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. As there's a connecting ridge at one end and a basin in between, the general idea is a crater surrounded by a number of hills. 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," (Cifelli, 2001). 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 multis 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 multis as the sister line of other mammals. It's not a scheme I presently follow. 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. For those of a technical persuasion, it may be safer to refer to this group as haramyioidens rather than 'haramiyidans'. It's a wider (and uglier) term. '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. Nobody had informed it of any extinction. If Butler and Hooker are correct with their interpretaion of hahnodontidids, members of the group even made it as far as the Lower Cretaceous: Hahnodon and Denisodon. I'm presently treating that pair as multituberculates, and waiting for further opinions on the matter.
