Transitional fossil: Difference between revisions

Revision as of 21:54, 29 October 2022

Revision as of 15:30, 15 January 2023

Line 38:

{{main|Australopithecus afarensis|Human evolution}}

{{see also|List of human evolution fossils}}

[[File:Lucy Skeleton cropped.jpg|thumb|75px|''[[Australopithecus afarensis|A. afarensis]]'' - walking posture.]]

The hominid ''Australopithecus afarensis'' represents an evolutionary transition between modern bipedal humans and their quadrupedal [[ape]] ancestors. A number of traits of the ''A. afarensis'' skeleton strongly reflect bipedalism, to the extent that some researchers have suggested that bipedality evolved long before ''A. afarensis''.<ref name="Lovejoy1988">{{cite journal |last=Lovejoy |first=C. Owen |author-link=Owen Lovejoy (anthropologist) |date=November 1988 |title=Evolution of Human walking |url=http://users.clas.ufl.edu/krigbaum/proseminar/Lovejoy_1988_SA.pdf |journal=[[Scientific American]] |volume=259 |issue=5 |pages=82–89 |doi=10.1038/scientificamerican1188-118 |issn=0036-8733 |pmid=3212438 |bibcode=1988SciAm.259e.118L }}</ref> In overall anatomy, the pelvis is far more human-like than ape-like. The [[Ilium (bone)|iliac blades]] are short and wide, the sacrum is wide and positioned directly behind the hip joint, and there is clear evidence of a strong attachment for the [[Rectus femoris muscle|knee extensors]], implying an upright posture.<ref name="Lovejoy1988" />{{rp|122}}

Line 74:

{{Main|Flatfish#Evolution}}

[[File:Pseudopleuronectes americanus.jpg|thumb|left|Modern [[flatfish]] are asymmetrical, with both eyes on the same side of the head.]]

[[File:Amphistium.JPG|thumb|Fossil of ''[[Amphistium]]'' with one eye at the top-center of the head.]]

[[Pleuronectiformes]] (flatfish) are an [[order (biology)|order]] of [[Actinopterygii|ray-finned fish]]. The most obvious characteristic of the modern flatfish is their asymmetry, with both eyes on the same side of the head in the adult fish. In some families the eyes are always on the right side of the body (dextral or right-eyed flatfish) and in others they are always on the left (sinistral or left-eyed flatfish). The primitive [[spiny turbot]]s include equal numbers of right- and left-eyed individuals, and are generally less asymmetrical than the other families. Other distinguishing features of the order are the presence of protrusible eyes, another adaptation to living on the [[seabed]] ([[benthos]]), and the extension of the dorsal fin onto the head.<ref>{{harvnb|Chapleau|Amaoka|1998|pp=223–226}}</ref>