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Topic: Therapsids

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	Therapsida - Wikipedia, the free encyclopedia
		Therapsids became the dominant land animals during the Middle Permian, and consisted of three major clades, the dinocephalians, the herbivorous anomodonts, and the mostly carnivorous theriodonts, with the carnivorous biarmosuchians as a paraphyletic assemblage of primitive forms.
		After a brief burst of evolutionary diversity, the dinocephalians died out in the later Middle Permian (Guadalupian), but the anomodont dicynodonts and the theriodont gorgonopsians and therocephalians flourished, and were joined at the very end of the Permian by the first cynodonts.
		Like all land animals, the therapsids were seriously affected by the end Permian extinction event, with the very successful gorgonopsians dying out altogether, and the remaining groups being represented by only one or two families of a few species each surviving into the Triassic.
	en.wikipedia.org /wiki/Therapsida (251 words)

	The Anvil of Evolution (Site not responding. Last check: 2007-10-20)
		Therapsid vision was largely peripheral, which is fine for many herbivores but a disadvantage for predators focusing on something lumbering away in front of them.
		Not as dependent as their predecessors on the sun's warming rays to jumpstart their metabolism, therapsids may have been able to move faster than their ancestors, but the basic model was largely the same: limbs that sprawled out to the sides and paddled one at a time.
		True, therapsids had managed to rotate their limbs partially under the body, so their bellies didn't hug the ground as a salamander's, and the stocky predatory models were only dog- or cat-sized.
	www.earthwatch.org /pubaffairs/news/sill_text.html (3828 words)

	[No title]
		Thus, the fossil record demonstrates, during the transition from therapsid reptile to mammal, various bones in the skull slowly migrated together to form a second functional jaw joint, and the now-superfluous original jaw bones were reduced in size until they formed the three bones in the mammalian middle ear.
		The entire series of therapsid transitionals are each fully functional, completely capable of chewing their food and detecting airborne sounds (just as modern snakes eat with a double jaw joint and detect sounds through bones connected to their skull and jawbones).
		Cross sections of therapsid bones reveal a series of small holes called Haversian canals, which are typical of fast-growing, warm-blooded animals (and which are absent in cold-blooded reptiles), indicating that the therapsids developed a progressively more mammalian warm-blooded metabolism as time went on.
	www.geocities.com /CapeCanaveral/Hangar/2437/therapsd.htm (2573 words)

	Biology 356 (Site not responding. Last check: 2007-10-20)
		Therapsids probably had a less sprawling stance than sphenacodontines and perhaps they had a parasagittal stance, at least in the hind limb.
		All anomodonts have a gently concave shelf on the dorsal surface of the skull table from which the jaw adductor musculature originates, and an area of insertion for the adductor externus lateralis on the lateral surface of the lower jaw.
		The histology of the bones of dicynodonts is similar to that of other therapsids such as dinocephalians, but this is not a proof that anomodonts were endothermic.
	www.erin.utoronto.ca /~w3bio356/lectures/therapsids.html (2380 words)

	The Compass Rose: From Reptile to Mammal
		As the therapsid carnivores became more and more effective, the early prey of their more primitive relatives, the pelycosaurs and other early reptiles, such as the cotylosaurs, began to decrease.
		Therapsids were not quick to adapt to these changes and consequently receded to a very minor role, while other reptiles, most noticeably the dinosaurs, took to the forefront.
		The therapsids were likely forest-dwellers and needed to develop senses other than sight to help them navigate through their darkened forest home.
	www.dragonlordsnet.com /crfrm.htm (2518 words)

	Palaeos Vertebrates: 400.000 Therapsida Overview
		Members of all the basic therapsid lineages apart from the Theriodonta occur in the earliest therapsid fauna of Russia, the early Middle Permian Ocher fauna (Wordian Epoch).
		Of the therapsids, only our own lineage, the Cynodontia, survived into the Jurassic; and this group is covered in the next Unit.
		Although the dentary does become progressively larger over the course of the Mesozoic, the Permian evolution of the therapsid condition does not seem to involve growth of the dentary so much as a progressive restriction of the angular to the posterior portion of the jaw.
	www.palaeos.com /Vertebrates/Units/400Therapsida/000.html (3031 words)

	Palaeos Vertebrates 400.100 Therapsida : Therapsida
		However, whether Tetraceratops is a therapsid or just a close cousin, it is plainly a reasonably good guide to the sorts of forms which connect the "pelycosaurs" with the Therapsida.
		It is quite likely that proto-therapsids such as Tetraceratops (and many others which never became fossilised) evolved in an upland environment where they were not easily fossilised, away from the swamps and deltas frequented by the Pelycosaurs (the only upland Pelycosaur lineages were the Caeseidae and, most certainly, their eothyrid ancestors).
		This early Permian upland evolution proceeded paraelle to the Permocarboniferous lowland fauna, and probably originally derived from reptiles that adapted to dry habitats during the long Kazimovian arid period.
	www.palaeos.com /Vertebrates/Units/400Therapsida/100.html (1793 words)

	therapsid -- Encyclopædia Britannica (Site not responding. Last check: 2007-10-20)
		Therapsids were the stock that gave rise to mammals.
		On land the vertebrates are represented in the Triassic by labyrinthodont amphibians and reptiles, the latter consisting of cotylosaurs, therapsids, eosuchians, thecodontians, and protorosaurs.
		All these tetrapod groups suffered a sharp reduction in diversity at the close of the Permian; 75 percent of the early amphibian families and 80 percent of the early reptilian...
	www.britannica.com /eb/article-9072058 (485 words)

	Therapsida
		Therapsids are where the parasagittal gait of mammals begins to appear.
		Primitive therapsids may have been endothermic, hairy, and had mammary glands, but these things don't fossilize well (if at all), so this is impossible to determine.
		The therapsid phylogeny is pretty straighforward, although the chiniquodontoid branching is guesswork.
	homepage.mac.com /pfhreak/paleontology/clade/T/therapsida.html (127 words)

	Origin of Dinosaurs and Mammals - Erickson
		Therapsids and dinosaurs belonged to two distinct subclasses of reptiles: the therapsids were synapsid reptiles and the dinosaurs were diapsids.
		By the end of the Triassic, the therapsids were on the brink of extinction; their descendants, the mammals, barely survived into the Jurassic and beyond.
		Therapsids were typically compact with their mass concentrated in the trunk.
	www.microlnx.com /dinosaurs/Synapsid_Diapsid.html (2440 words)

	Emergence of Warm Bloodedness. Who Lies Sleeping? The Dinosaur Heritage. AskWhy! Publications.
		The therapsids, undoubtedly used active methods of gaining sexual dominance, like head butting, which required surplus energy compared with that used by the earlier animals and which showed they were warm-blooded.
		The predator:prey ratio for therapsids indicated a marked move towards warm-blood and indeed the explosive adaptive radiation with which they replaced the pelycosaurs is typical of the warm-bloods.
		The earliest therapsids suffered a mass extinction after about ten million years and were replaced by new therapsids evolved from the old.
	web.ukonline.co.uk /michael.magee/awwls/00/wls117.html (917 words)

	THERAPSIDA (Site not responding. Last check: 2007-10-20)
		The therapsids (mammal-like reptiles) were advanced synapsids and the direct ancestors of the mammals.
		DICYNODONTIA - these very successful therapsids owed their success to greatly enlarged synapsid openings in the skull that allowed for longer, stronger jaw muscles, and a hinge between lower jaw and skull that enabled them to eat with a strong shearing action ideal for herbivores.
		Perhaps the best known are the carnivores Thrinaxodon and Cynognathus, but there were also herbivores such as Massetognathus and Oligokyphus (the only cynodont to survive into the Jurassic).
	www.dinoruss.org /de_4/5c5d4a6.htm (223 words)

	Part 6: The Gulf Between Reptiles and Mammals (Site not responding. Last check: 2007-10-20)
		Then, at the beginning of the Triassic Period, another group of therapsid "protomammals" appeared in the fossil record for a few million years, and were extinguished.
		The structure of the teeth, among other features, shows that pelycosaurs and therapsids, although not necessarily the direct ancestors of mammals, may certainly be regarded as their ancient uncles and aunts.
		The fossil record does not tell us whether therapsids were warm-blooded, whether they had hair instead of scales and whether they nursed their young.
	www.geocities.com /osarsif/ce06.htm (4151 words)

	artskep3.htm
		The therapsids all have 6 bones in their jaw (in profile), with an enlarged dentary bone in comparison to other reptiles.
		Lystrosaurus (Shovel-nosed Lizard) is one of the first therapsids to develop a closed palate; this is also considered to be a step in the evolutionary ladder towards becoming a mammal.
		Finally, note that most of the attention towards therapsids is on the skulls; the rest of the skeleton of these animals is definitely reptilian.
	www.ligstryders.org /artikels/artskep3.htm (1360 words)

	Biology 356 (Site not responding. Last check: 2007-10-20)
		Although both pelycosaurs and early thrapsids are paraphyletic taxa at the base of the clade that includes advanced therapsids and mammals, these Paleozoic reptiles have played a pivotal role in considerations of synapsid evolution, including the origin of mammals.
		As primitive synapsids, pelycosaurs are characterized by the presence of an anteriorly inclined plate-like occiput, the small posttemporal fenestra is bordered by the supraoccipital, tabular, and opisthotic bones; the lateral temporal fenestra bordered is by jugal, squamosal and postorbital bones, the pillar-like septomaxilla has a broad base that straddles the maxilla-premaxillary suture.
		As the oldest known therapsid, this form shares with other early therapsids a number of derived cranial features, but numerous primitive features that appear in derived form in all other therapsids Tetraceratops is therefore the sister taxon to all other therapsids.
	www.erin.utoronto.ca /~w3bio356/lectures/permo_carb_synapsid.html (3046 words)

	Origin of Dinosaurs and Mammals - Erickson
		Ousted from the niches for large-scale animals, therapsids declined in size, number, and variety during the Middle and Late Triassic.
		Therapsids already had a relatively advanced physiology by the Triassic Period.
		But, whereas the archosaurs could move quickly and effortlessly in an elastic hopping gait, therapsids were limited by their limb architecture to a slower ballistic walking or aerobic trotting gait.
	microlnx.com /dinosaurs/Physiology.html (1260 words)

	Untitled Document (Site not responding. Last check: 2007-10-20)
		In reptiles (non-synapsid amniotes), and in all pelycosaurs and the majority of therapsids, the articular and quadrate bones form the hinge axis for the lower jaw.
		In the most advanced (toward the mammalian condition) group of cynodont therapsids and the most primitive mammals, both the older "reptilian" joint between articular and quadrate, and a second, "mammalian" jaw joint between the dentary of the lower jaw and the squamosal bone were present.
		Within therapsids, the articular and quadrate were already transmitting vibrations to the ear as well as serving as surfaces of articulation.
	ijolite.geology.uiuc.edu /01SprgClass/geo143/lect/lect21.html (1209 words)

	BIRDS CAME FIRST
		The beginnings of such an existence are traced back to the late Permian era, some 260 million years ago, when the ruling reptiles were the therapsids.
		Among the casualties of the mass extinction at the end of the Palaeozoic era, 245 million years ago, were the therapsids.
		Their departure left wide open the role of dominant land animals, a role soon filled by their successors, the archosaurs, which ruled the world for the next 180 million years.
	www.dinoruss.org /de_4/5c60bbe.htm (1371 words)

	Comparative Anatomy Topic 3 - Mammals (Site not responding. Last check: 2007-10-20)
		Therapsids are often referred to as mammal-like reptiles.
		Some even speculate that some latter therapsids had hair, but the only evidence of skin in a therapsid comes from a hairless, more primitive species from the end of the Permian, millions of years before therapsids went extinct.
		In all likelihood therapsids were endotherms and they occupied a diverse array of habitats, so it probably is likely that at least some had hair.
	www.auburn.edu /academic/classes/zy/0301/Topic3e/Topic3e.html (841 words)

	Internet Public Library: Dinosaur Floor of the Exhibit Museum
		Therapsids were mammal-like reptiles derived from Pelycosaurs in Permian Time (248 to 286 million years ago).
		The carnivorous therapsids gave origin to the mammals in the Triassic Time (213 to 248 million years ago).
		The last of the therapsids died out in the Jurassic (144 to 213 million years ago).
	www.ipl.org /div/dino/sauropod.html (517 words)

	MESOZOIC ERA
		Therapsid fossils are found in many areas, including the southwestern United States; their remains occur in many of the red-bed successions that are preserved in Texas, Oklahoma, New Mexico, Utah (photo above) and Arizona.
		Therapsids (mammal-like reptiles) and true mammals were present in the Triassic, yet the diapsid reptiles became the group.
		Conventional wisdom suggests that therapsids and mammals were "warm-blooded" and reptiles "cold-blooded".
	www-rohan.sdsu.edu /~rhmiller/chordates2/Chordates2.htm (3172 words)

	Synapsid Reptiles
		But the sphenacodonts were the group of pelycosaurs that evolvedinto the Therapsids, an animal that you have in the IllustratedNotes there which is the one that may be familiar to you.
		And so at the same timethat the Therapsids are undergoing this tremendous decrease, theArchosaurs are undergoing an increase in their diversity.
		It appears to be the case for some reason, the reason the Archosaurswere out competing with the Therapsids and causing a tremendousreduction in their numbers and in diversity.
	www.csupomona.edu /~dfhoyt/classes/zoo138/SYNAPSID.HTML (4532 words)

	Chapter 13 Study Guide
		The therapsids are considered mammal-like reptiles because of differences from typical reptiles in jaw structure, teeth, and positioning of legs beneath the body.
		It has been suggested that therapsids were also endothermic (know what this term means), as were mammals.
		Therapsids underwent a rapid diversification in the Permian but most were victims of the Permian extinction.
	www.uvm.edu /~cmehrten/courses/historical/ch16sg.html (1164 words)

	[No title]
		Although the Karoo may be best recognized for providing evidence as to how mammals evolved in the course of Therapsid evolution, it is also important to realize that Pareiasaurs were once thought to be the predecessors for all modern-day reptiles.
		Therocephalians They are another group of carnivorous therapsids which is often compared to the Gorgonopsids, though they are not in the same taxon.
		Fossil therapsids counterparts were found on all three continents, providing support for the theory of continental drift.
	www.ucmp.berkeley.edu /mesozoic/triassic/karoo.txt (2612 words)

	Untitled Document (Site not responding. Last check: 2007-10-20)
		Rowe and van den Heever (1986) argue for a simpler interpretation in which the mammalian formula originated once within therapsids directly from the unreduced sphenacodont condition, with disc-like elements in gorgonopsians and cynodonts being partial reversals or neomorphs.
		The phylogenetic distribution of discs in early cynodonts suggests that the hypothesis of Rowe and van den Heever must be modified to include reacquisition of these elements in ancestral cynodonts and subsequent re-loss in advanced cynodonts.
		Extensive homoplasy in the manus and pes of therapsids, and in other parts of the appendicular skeleton, appears related to the acquisition of a more upright, parasagittal, stance and gait.
	www.vertpaleo.org /jvp/15-615-639.html (327 words)

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