Shiisa's random findings

scientificillustration:

Evolutionary Developmental Model for the Origin of the Turtle Shell

“Results of a phylogenetic analysis of shelled reptiles and characters important in constructing a shell are plotted against the ontogeny of pleurodire turtles. Thin sections through turtle embryos show the initial outgrowth of (sub)dermal bone through the costals first (carapace length [CL] = 13.0mm in the pleurodire Emydura subglobosa) and then the neurals (CL = 18.0 mm in the pleurodire Pelomedusa subrufa). The timing of ontogenetic transformations of those features (in red) important in the construction of the shell (i.e., the number of dorsal vertebrae or ribs does not change through ontogeny) is congruent with the phylogenetic transformation of those same features based on our recovered tree topology. Our model makes explicit morphological and histological predictions for the lineage prior to the most recent common ancestor of Eunotosaurus africanus and turtles that are met by the morphology found in Milleretta rubidgei. Numbers above each node represent bootstrap frequencies obtained in the phylogenetic analysis.”

Evolutionary Origin of the Turtle Shell Lyson, Tyler R.; Bever, Gabe S.; Scheyer, Torsten M.; Hsiang, Allison Y.; Gauthier, Jacques A. Current biology : CB doi:10.1016/j.cub.2013.05.003 

See also:

How the turtle got its unique hard shell

http://news.yale.edu/2013/05/30/how-turtle-got-its-shell

headlikeanorange:

A rock hyrax, whose closest living relative is the African elephant. (Wild Arabia - BBC)

(via theanimalblog)

scientificillustration:

“A phylogenetic blueprint for a modern whale (Balaenoptera musculus). The topology traces the inferred evolutionary history of an extant cetacean based on results summarized in Figs. 7–9 and Table 1. Changes extend back to the base of Artiodactyla (A–D). The long sequence of character transformations on the stem lineage to crown Cetacea (branches E–O), on the stem lineage to crown Mysticeti (branches a–f), and within crown Mysticeti (branches g–h) has culminated in the extant blue whale. A subset of the changes on these internal branches (Table 1) are marked by colored circles that indicate the internode where each character evolved and, when applicable, the approximate anatomical position of each derived character state (delayed transformation optimization): B-1 = three primary lung bronchi and multi-chambered stomach, B-2 = fibro-elastic penis with sparse cavernous tissue, C-1 = sparse hair, sebaceous glands absent, and transition to freshwater, C-2 = scrotum absent, can give birth underwater, and can nurse underwater, D = involucrum (thickening of medial wall of auditory bulla), E = robust tail, F–G = transition to saltwater, G = incisive foramina absent and vomeronasal organ inferred absent, H = short cervical (neck) vertebrae, K = posterior positioning of nasal aperture, L = no articulation between vertebrae and pelvis (sacroiliac joint absent), M1 = very short hindlimbs, M2 = tail flukes inferred present, O-1 = external ears absent, O-2 = immobile elbow joint, O-3 = sweat glands absent, a = broad rostrum, b = thin lateral margins of maxillae, c-1 = lateral nutrient foramina on palate and baleen inferred present, c-2 = unsutured mandibular symphysis, d = no teeth in adults, e-1 = telescoping of skull (anterior extension of occipital shield), e-2 = bowed mandibles, g-1 = fibrous temporomandibular joint, g-2 = muscle of tongue reduced (predominantly connective tissue) and ventral throat pouch with numerous grooves, h = enormous body size. Branch lengths are not proportional to time. Artwork is by Carl Buell. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)”

A phylogenetic blueprint for a modern whale. Gatesy J, Geisler JH, Chang J, Buell C, Berta A, Meredith RW, Springer MS, McGowen MR. Mol Phylogenet Evol. 2012 Oct 26. pii: S1055-7903(12)00418-6. doi: 10.1016/j.ympev.2012.10.012. (pdf) 

lostbeasts:

gallantcannibal:

Prehistoric whale evolution, illustrated by Tiffany Turrill.

Ambulocetus, my sweet baby

(via scientificillustration)

oneheadtoanother:

Evolution of Therapsids

(via scientificillustration)

laboratoryequipment:

Water-Wrinkled Fingers Hold Evolutionary Purpose

Wrinkly fingers caused by soaking them in water for a long time, such as in the bath or doing the dishes, have been shown to improve our grip on wet objects or objects under water. Scientists at Newcastle Univ. studied people taking objects out of water with wrinkled fingers and again without wrinkled fingers to explain why the effect occurs.

Author Tom Smulders, publishing the paper in Biology Letters says, “We have shown that wrinkled fingers give a better grip in wet conditions – it could be working like treads on your car tires which allow more of the tire to be in contact with the road and gives you a better grip. Going back in time this wrinkling of our fingers in wet conditions could have helped with gathering food from wet vegetation or streams. And as we see the effect in our toes too, this may have been an advantage as it may have meant our ancestors were able to get a better footing in the rain.”

Read more: http://www.laboratoryequipment.com/news/2013/01/water-wrinkled-fingers-hold-evolutionary-purpose

writingcapital:

A third [evolutionary] advance is in a way the most important, since it is the one used by paleontologists to distinguish reptiles from mammals. The lower jaw of reptiles contains several bones, of which two are important to us. One of these, the dentary, bears the teeth while the other, the articular, smaller and at the hind end of the jaw, forms part of the hinge between the lower and upper jaw (Figure 9-8). The other part of this hinge is the quadrate, a small bone in the head portion of the skull, or cranium. Immediately behind these two small jaw bones is the middle ear, within which sound waves are amplified and transmitted from a special nerve to the brain. In reptiles, amphibians, and fishes, this amplification is carried out by a single small bone. By contrast, the lower jaw of mammals consists only of the tooth-bearing (dentary) bone, which is hinged to another bone, the squamosal, also in the cranium. The two bones that form the hinge of the reptilian jaw have not disappeared. They are represented in mammals by two small bones in the middle ear connected with the counterpart of the single reptilian ear bone. In reptiles, amplification of sound waves in the middle ear, carried out by a single bone, is relatively inefficient. The three bones in the mammalian ear do this job much more effectively, so that the hearing of mammals is much better than that of reptiles.

In order to classify fossil animals neatly and clearly as either reptiles or mammals, most paleontologists and nearly all textbooks classify as reptiles all bony-limbed animals that have a liquid-filled amniotic egg and a jaw hinge formed by the two small bones, articular and quadrate, along with a single ear bone. Mammals differ in having the tooth-bearing (dentary) lower jaw bone articulated directly with a bone of the cranium (squamosal), plus three small bones in the middle ear. Tooth structure also helps in classifying them. Nevertheless, an animal that has almost mammalian teeth but a reptilian jaw hinge and middle ear bone is called a reptile. Mammallike reptiles are all classified as reptiles on the basis of this character, even though the advanced dog-tooth has teeth that resemble those of primitive mammals more than they resemble the teeth of the earliest mammallike reptiles or their immediate ancestors, the pelycosaurs. Likewise, the earliest animals having three bones in the middle ear are called mammals, although, like the primitive mammals of modern Australia—the spiny anteater and platypus (monotremes)—they may well have laid eggs, lacked nipples or teats, had skeletons showing some reptilian features such as shoulder girdles, and had chromosomes resembling those of reptiles.

— Stebbins - Darwin to DNA, Molecules to Humanity, pp. 289-91

I find this strangely profound: everyone knows the difference between a reptile and a mammal upon seeing one, but once all the fragile details are stripped away, there’s only a single, trivial difference between them; it’s this one silly little criterion that informs all of our (taxonomical) knowledge about species long-extinct. I suspect that the taxonomies of many disciplines are like this.

The text alongside fig. 9-8 reads:

Figure 9-8.
A series of skulls showing a few of the numerous transitional forms that, via a series of adaptive radiations, resulted eventually in the origin of modern mammals (a)–(c): Three typical reptiles. (a) A primitive Captorhinus that, like early amphibians and modern turtles, has only one pair of openings in the skull in addition to the nostrils. (b) A primitive ancestor of lizards, Youngina. (c) A modern lizard, Varanus. (d)–(i): Six reptiles that were on or near the line leading to mammals. (d) and (e) Two pelycosaurs that were typical reptiles but show the beginnings of tooth differentiation. Note that the hindmost bone of the lower jaw (angular, a) is nearly as large as the tooth-bearing bone (dentary, dn). (f) and (g) Two early mammallike reptiles, showing further tooth differentiation, plus reduction in size of the angular bone. (h) and (i) Two later forms of reptiles that, with respect to tooth differentiation and reduction of the angular bone, were much like mammals. Diarthrognathus was almost completely intermediate between reptiles and mammals. (j)–(l): Three kinds of mammals. (j) Sinoconodon, the earliest of these, still retained a number of reptilian features. (k) A later form, Deltatheridium, was very similar to modern shrews. (l) A modern opossum (Didelphys). The skulls are drawn at different scales of magnification. Those in the center column are at natural size or somewhat reduced; those in the right column are somewhat magnified.

(via scientificillustration)

rhamphotheca:

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Early humans linked to large-carnivore extinctions

Hominins could have triggered broad changes to the numbers and diversity of meat-eaters in Africa, researcher says.

by Jeff Tollefson  (26 April 2012)

Animal lovers around the world know modern otters as cute, playful and unthreatening. But the mustelid’s giant cousins in ancient Africa may have engaged in a life-and-death competition with humanity’s ancestors — and come out on the losing end.

The demise of the gigantic ‘bear otter’ (Enhydriodon dikikae) was part of a broader decline in large-carnivore diversity in Africa, which accelerated around 2 million years ago — roughly the time that the first representatives of the genus Homo appeared on the scene. Lars Werdelin, a curator at the Swedish Museum of Natural History in Stockholm has been building a case that our forebears had something to do with the change. Although direct evidence of any causal connection is sorely lacking, Werdelin says, the transition in the carnivore fossil record coincides nicely with advances in tool-making and dietary shifts among early hominins.

“The way I see it, this is one of the first ways in which we manipulated our environment on a large scale,” says Werdelin, who presented his latest findings at a symposium on human evolution and climate change at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York. Werdelin argues that hominins may have competed indirectly with some of these carnivores by occupying prime habitat, thus forcing the animals to change their behavior without ever coming into direct contact with them. In some cases, the hominins may have out-competed carnivores directly by forcing them to surrender fresh kills. Regardless, the emergence of early humans could have cascaded through the food chain — ultimately wiping out many of Africa’s larger meat-eaters…

(read more: Nature)              

(images via NovaTaxa: TR - Victor Leshyk; B - Cal. Academy of Sci.)

(via scientificillustration)

troistetesdechien:

Carl Zimmer (2011), Histoires de plumes; Quand les poules avaient des dents, National Geographic France 2011

(via prehistoric-birds)