A look at transitions of reptiles to mammals

Values not in the table can be calculated by using linear interpolation. Slum is stellar luminosity, it is the Lum column on the table. BC is bolometric correction, it is the Bolo.

A look at transitions of reptiles to mammals

Joined external nares Mammals: Separate external nares The reptiles evolved into four major groups; the anapsids, which produced the turtles, the diapsids which produced the dinosaurs, and an offshoot group, the eurapsids, which produced the icthyosaurs.

The final group, the synapsids, took a radically different path than the other groups and produced the therapsids, which concentrated on osteo- and pysiological changes which eventually produced the mammals.

The group called the cynodontia dog tooth produced a lineage of forms intermediate between reptiles and mammals. The group looks like this: Saggital crest for greater muscle attachment; nares separated; lumbar free.

Additional cusps on cheek teeth; teeth double rooted; 'double' jaw joint, the quadrate-articular and the dentary-squamosal bones articulate, but the quadrate-articular bones are very much reduced and only loosely constrained in a groove in the dentary bone; cervical ribs very short; lumbar free; phalangeal arrangement mammalian - loss of some bones.

Double occipital condyle; secondary palate; separated nares; dentary bone covers almost all lower jaw; differentiated dentition; double rooted teeth; lumbar free; scapulare with spine; pelvic elements fused; fused clavical ribs; but quadrate-articular although very much reduced, still participate in the jaw joint.

This feature classifies the organism as a reptile, even though it has far more mammal characters than reptile ones.

A look at transitions of reptiles to mammals

However, the basic principle still holds. There is a diagram showing the difference between mammals and reptiles here: There were afew other things about the teeth i.

I don't think it's true that "their focus seemed to be on the splitting of the jawbone and how that could have evolved into the formaiton of the ear" since the jawbone transformation was just one of a large number of changes mentioned on the links I gave, and in the case of the jawbone the focus was on the changes in the jaw itself and not the inner ear Early tetrapods such as pelycosaurs possessed mandibles lower jaws composed of a dentary tooth-bearing bone associated with a number of thin plates of bone that originally served to strengthen the jaw as a whole.

The hindmost of these bones, the articular, articulated hence the nameor hinged, with the quadrate bone of the skull. In therapsids this arrangement persisted, but the new life-style of these progressive animals, with its growing emphasis on high consumption of energy for lots of activity, required precise manipulation of food in the mouth in order that it might be better broken down for efficient digestion.

In these animals, the act of chewing was forcing changes in the structure of the lower jaws to strengthen them further and increase their biting leverage. In this process, the dentary bone was becoming longer and thicker in response to the increase in stress to which it was subjected.

In addition, as the molar teeth came into being and were put to grinding up food, changes in jaw musculature forced changes in jaw conformation to permit good chewing. The most primitive therapsids had jaws whose muscles were mainly attached to the inner surfaces of both jaws and skull.

In later models, however, the new masseter chewing muscles gradually appeared on the outside of the dentary bone, connecting this to the cheekbone.

Other muscles arose from a new coronoid crownlike process that extended the rear of the dentary bone upward inside the arch of the cheekbone. These muscles inserted along the top and back of the skull, along the temporal bones, and hense are collectively called temporal muscles.

Because of the increasing power of these muscles in higher therapsids, the dentary bone was becoming bigger and heavier at the expense of all the other little jawbones.

You can see all of this in the sequence of skulls on the mammal-like reptile page at http: Is there more than the jawbones and other dental fossils? It seemed that there seemed to be a little bit about ribs for a couple but it seemed mostly to revolve around the skulls.

Claim CC215:

A lot of the most interesting skeletal differences between mammals and reptiles are in the skulls not just the jawbones as you seem to be saying above but there are some significant ones in the rest of the skeleton which are also seen transforming in parallel with the skull changes.

The biggest one is the change in gait--reptiles walk in a sprawled-out posture, lifting one leg at a time and bending their spine in an s-shape as they move, while mammals carry their legs straight beneath them and flex their spine up and down rather than from side to side.

In the mammal-like reptiles we see a series of intermediate gaits, finally leading to a basically modern mammal-like gait. Other differences between mammals and reptiles which can be observed transforming are fused vs. From the page on "transitional forms" at http: In most reptiles, the phalangeal formula iswhereas the mammaliam formula is The early therapsids possessed the reptilian formula.

In Thrinaxodon, the phalangeal formula is reduced toclose to the mammalian count, but still intermediate between the two conditions. The "extra" phalanges in digits 3 and 4 are very small, presaging their later absense. In later cynodonts, the count is reduced to the mammalian formula of Whereas reptiles generally display ribs all the way back to the pelvis, mammals lack ribs in the pelvic region.

The gradual loss of these pelvic ribs can be seen in the cynodonts or mammal-like reptiles. Probelesodon, for example, displays ribs all the way back to the pelvis, but the last several ribs are greatly attenuated. In other advanced cynodonts, such as Thrinaxodon or the tritylodonts, the pelvic ribs are absent altogether, as in the mammalian configuration.

Do we know anything about their internal organs? I don't know anything about this either way; you'd have to ask a practicing paleontologist. It may be that certain aspects of the skeleton would allow scientists to infer things about their internal organs, but maybe not.

There was something about there being some evidence of fur.For the vast majority of science fiction worldbuilding, the major alteration to the laws of physics is allowing some species of faster-than-light propulsion for their starships. Others will add things like psionics/psychic regardbouddhiste.com besides those, the rest of the laws of physics operate exactly as in real life.

Nowhere is this better illustrated than with the reptile -> mammal transition. Before documenting this transition, it is probably a good idea to list various characteristics of reptiles and see how these change with the evolution of the mammals. Transitions of Reptiles to Mammals A long long time ago, in a galaxy not too far away, was a little blue planet called Earth, and on this world not a single mammal lived.

However a lot of time has past since then and we now have lots of furry creatures that are collectively called mammals. The so-called mammal-like reptiles are believed by evolutionists to be the ancestors of the mammals and to have become more mammal-like with the passage of time.

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