67-422: Haramiyida is a possibly paraphyletic order of mammaliaform cynodonts or mammals of controversial taxonomic affinites. Their teeth, which are by far the most common remains, resemble those of the multituberculates . However, based on Haramiyavia , the jaw is less derived; and at the level of evolution of earlier basal mammals like Morganucodon and Kuehneotherium , with a groove for ear ossicles on
134-479: A "single common ancestor" organism. Paraphyly is common in speciation , whereby a mother species (a paraspecies ) gives rise to a daughter species without itself becoming extinct. Research indicates as many as 20 percent of all animal species and between 20 and 50 percent of plant species are paraphyletic. Accounting for these facts, some taxonomists argue that paraphyly is a trait of nature that should be acknowledged at higher taxonomic levels. Cladists advocate
201-592: A cell nucleus, a plesiomorphy ) from its excluded descendants. Also, some systematists recognize paraphyletic groups as being involved in evolutionary transitions, the development of the first tetrapods from their ancestors for example. Any name given to these hypothetical ancestors to distinguish them from tetrapods—"fish", for example—necessarily picks out a paraphyletic group, because the descendant tetrapods are not included. Other systematists consider reification of paraphyletic groups to obscure inferred patterns of evolutionary history. The term " evolutionary grade "
268-423: A combination of synapomorphies and symplesiomorphies . If many subgroups are missing from the named group, it is said to be polyparaphyletic. The term received currency during the debates of the 1960s and 1970s accompanying the rise of cladistics , having been coined by zoologist Willi Hennig to apply to well-known taxa like Reptilia ( reptiles ), which is paraphyletic with respect to birds . Reptilia contains
335-904: A cusp on the inner half of the upper molar grinds into a basin on the front half of the lower molar, like a mortar-and-pestle . This is a case of convergent evolution with the tribosphenic teeth of therian mammals. There is much uncertainty for how docodont teeth developed from their simpler ancestors. Their closest relatives may have been certain Triassic " symmetrodonts ", namely Woutersia , and Delsatia . The shuotheriids , another group of Jurassic mammaliaforms, also shared some dental characteristics with docodonts. One study has suggested that shuotheriids are closely related to docodonts, though others consider shuotheriids to be true mammals, perhaps related to monotremes . For much of their history of study, docodont fossils were represented by isolated teeth and jaws. The first docodont known from decent remains
402-411: A fairly consistent cusp pattern. A distinct concavity or basin is apparent in the front half of each lower molar, between cusps a, g, and b. This basin has been named the pseudotalonid. When the upper and lower teeth occlude (fit together), the pseudotalonid acts as a receptacle for cusp Y of the upper molar. Cusp Y is often termed the "pseudoprotocone" in this relationship. At the same time, cusp b of
469-419: A group of dinosaurs (part of Diapsida ), both of which are "reptiles". Osteichthyes , bony fish, are paraphyletic when circumscribed to include only Actinopterygii (ray-finned fish) and Sarcopterygii (lungfish, etc.), and to exclude tetrapods ; more recently, Osteichthyes is treated as a clade, including the tetrapods. The " wasps " are paraphyletic, consisting of the narrow-waisted Apocrita without
536-439: A kind of lizard). Put another way, viviparity is a synapomorphy for Theria within mammals, and an autapomorphy for Eulamprus tympanum (or perhaps a synapomorphy, if other Eulamprus species are also viviparous). Groupings based on independently-developed traits such as these examples of viviparity represent examples of polyphyly , not paraphyly. The following list recapitulates a number of paraphyletic groups proposed in
603-445: A lot of", and refers to the fact that a polyphyletic group includes organisms arising from multiple ancestral sources. Groups that include all the descendants of a common ancestor are said to be monophyletic . A paraphyletic group is a monophyletic group from which one or more subsidiary clades (monophyletic groups) are excluded to form a separate group. Philosopher of science Marc Ereshefsky has argued that paraphyletic taxa are
670-549: A more inclusive clade, it often makes sense to study the paraphyletic group that remains without considering the larger clade. For example, the Neogene evolution of the Artiodactyla (even-toed ungulates, like deer, cows, pigs and hippopotamuses - Cervidae , Bovidae , Suidae and Hippopotamidae , the families that contain these various artiodactyls, are all monophyletic groups) has taken place in environments so different from that of
737-521: A new clade, Docodontiformes, to encompass the two groups. Docodonts and other Mesozoic mammals were traditionally thought to have been primarily ground dwelling and insectivorous , but recent more complete fossils from China have shown this is not the case. Castorocauda from the Middle Jurassic of China, and possibly Haldanodon from the Upper Jurassic of Portugal, were specialised for
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#1732844941517804-412: A paraphyletic Haramiyida closely related to Multituberculata outside of crown Mammalia: † Tritylodontidae † Sinoconodon † Morganucodonta † Docodonta + Shuotheriidae † Hadrocodium † Haramiyavia † Thomasia † Euharamiyida † Multituberculata (including Gondwanatheria ) Paraphyly Paraphyly is a taxonomic term describing a grouping that consists of
871-736: A paraphyletic Haramiyida within crown Mammalia as ancestral to Multituberculata: † Tritylodontidae † Morganucodonta † Docodonta Monotremata † Eutriconodonta Cladotheria (including Theria ) † Haramiyavia † Thomasia † Euharamiyida † Multituberculata Cladogram from Hoffmann et al. 2020, showing a diphyletic Haramiyida. † Thomasia † Haramiyavia † Megaconus † Tritylodontidae † Morganucodonta † Docodonta Monotremata † Eutriconodonta Cladotheria (including Theria ) † Multituberculata † Euharamiyida † Cifelliodon † Gondwanatheria Simplified cladogram from Mao et al. 2024, showing
938-467: A paraphyletic grouping, because they exclude the eukaryotes , a descendant group. Bacteria and Archaea are prokaryotes, but archaea and eukaryotes share a common ancestor that is not ancestral to the bacteria. The prokaryote/eukaryote distinction was proposed by Edouard Chatton in 1937 and was generally accepted after being adopted by Roger Stanier and C.B. van Niel in 1962. The botanical code (the ICBN, now
1005-424: A phylogenetic species concept that does not consider species to exhibit the properties of monophyly or paraphyly, concepts under that perspective which apply only to groups of species. They consider Zander's extension of the "paraphyletic species" argument to higher taxa to represent a category error When the appearance of significant traits has led a subclade on an evolutionary path very divergent from that of
1072-487: A pointed spur on its ankle, similar to defensive structures observed in male monotremes and several other early-branching mammals. Like other mammaliaforms, docodont teeth include peg-like incisors , fang-like canines , and numerous interlocking premolars and molars . Most mammaliaforms have fairly simple molars primarily suited for shearing and slicing food. Docodonts, on the other hand, have developed specialized molars with crushing surfaces. The shape of each molar
1139-420: A saddle-shaped hyoid apparatus , and reduced postdentary jaw bones which are beginning to develop into middle ear ossicles . On the other hand, the postdentary bones are still attached to the jaw and skull, the nares (bony nostril rims) have yet to fuse, and in most species the spine's thoracic - lumbar transition is rather subdued. Docodonts have a long and low mandible (lower jaw), formed primarily by
1206-506: A semi-aquatic lifestyle. Castorocauda had a flattened tail, similar to that of a beaver , and recurved molar cusps, which suggests a possible diet of fish or aquatic invertebrates. It was thought possible that docodonts had tendencies towards semi-aquatic habits, given their presence in wetland environments, although this could also be explained by the ease with which these environments preserve fossils compared with more terrestrial ones. Recent discoveries of other complete docodontans such as
1273-432: A slower metabolism and lower growth rates relative to modern mammals of the same size. The juvenile, which was 7 to 24 months old at the time of its death, was only 49% through the process of replacing its deciduous teeth with permanent (adult) teeth . Based on jaw length, the juvenile was 51-59% the weight of the 7-year-old adult. The closest comparisons among modern mammals were monotremes and hyraxes , though Krusatodon
1340-492: A unique common ancestor. Conversely, the term monophyly , or monophyletic , builds on the Ancient Greek prefix μόνος ( mónos ), meaning "alone, only, unique", and refers to the fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor. By comparison, the term polyphyly , or polyphyletic , uses the Ancient Greek prefix πολύς ( polús ), meaning "many,
1407-433: Is allowed as a synonym of Magnoliopsida. Phylogenetic analysis indicates that the monocots are a development from a dicot ancestor. Excluding monocots from the dicots makes the latter a paraphyletic group. Among animals, several familiar groups are not, in fact, clades. The order Artiodactyla ( even-toed ungulates ) as traditionally defined is paraphyletic because it excludes Cetaceans (whales, dolphins, etc.). Under
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#17328449415171474-409: Is defined by a characteristic pattern of conical cusps , with sharp, concave crests connecting the center of each cusp to adjacent cusps. When seen from below, the upper molars have an overall subtriangular or figure-eight shape, wider (from side to side) than they are long (from front to back). The bulk of the tooth makes up four major cusps: cusps A, C, X, and Y. This overall structure is similar to
1541-468: Is not certain, and in recent analyses, Gondtherium falls outside the docodont family tree, albeit as a close relative to the group. Reigitherium , from the Late Cretaceous of Argentina , has previously been described as a docodont, though it is now considered a meridiolestidan mammal. Some authors have suggested splitting Docodonta into two families (Simpsonodontidae and Tegotheriidae), but
1608-437: Is not paraphyletic or monophyletic can be called polyphyletic. Empirically, the distinction between polyphyletic groups and paraphyletic groups is rather arbitrary, since the character states of common ancestors are inferences, not observations. These terms were developed during the debates of the 1960s and 1970s accompanying the rise of cladistics . Paraphyletic groupings are considered problematic by many taxonomists, as it
1675-433: Is not possible to talk precisely about their phylogenetic relationships, their characteristic traits and literal extinction. Related terms are stem group , chronospecies , budding cladogenesis, anagenesis, or 'grade' groupings. Paraphyletic groups are often relics from outdated hypotheses of phylogenic relationships from before the rise of cladistics. The prokaryotes (single-celled life forms without cell nuclei) are
1742-405: Is positioned lingual to cusp B. The lower molars are longer than wide. On average, they have seven cusps arranged in two rows. The labial/outer row has the largest cusp, cusp a, which lies between two more cusps. The other major labial cusps are cusp b (a slightly smaller cusp in front of cusp a) and cusp d (a much smaller cusp behind cusp a). The lingual/inner row is shifted backwards (relative to
1809-472: Is potentially another case of convergent evolution, as shuotheriid are often considered true mammals related to modern monotremes . Docodont and shuotheriid teeth are so similar that some genera, namely Itatodon and Paritatodon , have been considered members of either group. A 2024 study, describing the new shuotheriid Feredocodon , even proposed that shuotheriids and docodonts were most closely related to each other among mammaliaforms. The study named
1876-529: Is prominent in Woutersia . Another proposed docodont relative, Tikitherium from India , was originally considered to have been a very early mammaliaform which lived during the Carnian stage of the Triassic. Later investigation found that Tikitherium was likely a misidentification of Neogene shrew teeth, completely unrelated to docodonts or any Mesozoic mammaliaforms. Unambiguous docodonts are restricted to
1943-482: Is sometimes used for paraphyletic groups. Moreover, the concepts of monophyly , paraphyly, and polyphyly have been used in deducing key genes for barcoding of diverse group of species. Current phylogenetic hypotheses of tetrapod relationships imply that viviparity , the production of offspring without the external laying of a fertilized egg, developed independently in the lineages that led to humans ( Homo sapiens ) and southern water skinks ( Eulampus tympanum ,
2010-399: Is variable between docodonts, as with many other mammaliaforms. The components of the atlas are unfused, attaching to the large and porous occipital condyles of the braincase. Vertebrae at the base of the tail often have expanded transverse processes (rib pedestals), supporting powerful tail musculature. Most docodonts have gradually shrinking ribs, forming a subdued transition between
2077-503: The Cetacea (whales, dolphins, and porpoises) that the Artiodactyla are often studied in isolation even though the cetaceans are a descendant group. The prokaryote group is another example; it is paraphyletic because it is composed of two Domains (Eubacteria and Archaea) and excludes (the eukaryotes ). It is very useful because it has a clearly defined and significant distinction (absence of
Haramiyida - Misplaced Pages Continue
2144-569: The ICN ) abandoned consideration of bacterial nomenclature in 1975; currently, prokaryotic nomenclature is regulated under the ICNB with a starting date of 1 January 1980 (in contrast to a 1753 start date under the ICBN/ICN). Among plants, dicotyledons (in the traditional sense) are paraphyletic because the group excludes monocotyledons . "Dicotyledon" has not been used as a botanic classification for decades, but
2211-756: The Northern Hemisphere , abruptly appearing in the fossil record in the Middle Jurassic . Very few docodonts survived into the Cretaceous Period ; the youngest known members of the group are Sibirotherium and Khorotherium , from the Early Cretaceous of Siberia . One disputed docodont, Gondtherium , has been described from India, which was previously part of the Southern Hemisphere continent of Gondwana . However, this identification
2278-638: The ants and bees . The sawflies ( Symphyta ) are similarly paraphyletic, forming all of the Hymenoptera except for the Apocrita, a clade deep within the sawfly tree. Crustaceans are not a clade because the Hexapoda (insects) are excluded. The modern clade that spans all of them is the Tetraconata . One of the goals of modern taxonomy over the past fifty years has been to eliminate paraphyletic "groups", such as
2345-576: The crown group of Mammalia ), or whether all living mammals (including therians and monotremes) are more closely related to each other than to haramiyidans (and thus placing Haramiyida outside crown Mammalia) and whether or not haramiyidans are closely related to multituberculates , an important of group of Mesozoic mammaliaforms typically regarded as crown group mammals, as part of the group Allotheria . While many studies recover Triassic haramiyidans and Jurassic euharamiyidans as closely related, some phylogenetic studies have recovered them as unrelated, find
2412-414: The nares (bony nostril holes) are small and paired, rather than fused into a single opening, and the rear edge of each naris is formed by a large septomaxilla , a bone which is no longer present in mammals. The nasal bones expand at the back and overlook thick lacrimals . The frontal and parietal bones of the skull roof are flat and broad, and there is no postorbital process forming the rear rim of
2479-472: The orbit (eye socket). Docodonts also see the first occurrence of a mammalian-style saddle-shaped complex of hyoids (throat bones). Microdocodon has a straight, sideways-oriented basihyal which connects to two pairs of bony structures: the anterior hyoid cornu (a jointed series of rods which snake up to the braincase), and the posterior thyrohyals (which link to the thyroid cartilage ). This hyoid system affords greater strength and flexibility than
2546-405: The thoracic and lumbar regions of the spine. However, this developmental trait is not universal. For example, Agilodocodon lacks lumbar ribs, so it has an abrupt transition from the thoracic to lumbar vertebrae like many modern mammals. The forelimbs and hindlimbs generally have strong muscle attachments, and the olecranon process of the ulna is flexed inwards. All limb bones except
2613-431: The tibia lack epiphyses , plate-like ossified cartilage caps which terminate bone growth in adulthood. This suggests that docodont bones continued growing throughout their lifetime, like some other mammaliaforms and early mammals. The ankle is distinctive, with a downturned calcaneum and a stout astragalus which connects to the tibia via a trochlea (pulley-like joint). The only known specimen of Castorocauda has
2680-466: The tribosphenic teeth found in true therian mammals, like modern marsupials and placentals . However, there is little consensus for homologizing docodont cusps with those of modern mammals. Cusps A and C lie in a row along the labial edge of the tooth (i.e., on the outer side, facing the cheek). Cusp A is located in front of cusp C and is typically the largest cusp in the upper molars. Cusp X lies lingual to cusp A (i.e., positioned inwards, towards
2747-431: The 1880s, but their relationships and diversity have only recently been well-established. Monographs by George Gaylord Simpson in the 1920s argued that they were specialized " pantotheres ", part of a broad group ancestral to true therian mammals according to their complex molars. A 1956 paper by Bryan Patterson instead argued that docodont teeth were impossible to homologize with modern mammals. He drew comparisons to
Haramiyida - Misplaced Pages Continue
2814-586: The Triassic haramiyidians as non-mammalian cynodonts, while recovering the Euharamiyida as crown-group mammals closely related to multituberculates. Cladogram from Luo et al 2017, showing a monophyletic Haramiyida outside of crown Mammalia unrelated to Multituberculata: † Tritylodontidae † Morganucodonta † Docodonta † Haramiyavia † Thomasia † Euharamiyida Monotremata † Eutriconodonta † Multituberculata Cladotheria (including Theria ) Cladogram from Han et al. 2017, showing
2881-533: The closest relatives of Docodonta have been identified as certain Late Triassic "symmetrodonts", such as Delsatia and Woutersia (from the Norian - Rhaetian of France ). These "symmetrodonts" have three major cusps (c, a, and b) set in a triangular arrangement on their lower molars. These cusps would be homologous to cusps c, a, and g in docodonts, which have a similar size and position. The lingual cusp (cusp X)
2948-613: The dentary. Some authors have placed them in a clade with Multituberculata dubbed Allotheria within Mammalia. Other studies have disputed this and suggested the Haramiyida were not crown mammals, but were part of an earlier offshoot of mammaliaformes instead. It is also disputed whether the Late Triassic species are closely related to the Jurassic and Cretaceous members belonging to Euharamiyida/Eleutherodontida , as some phylogenetic studies recover
3015-402: The dentary. The ectotympanic bone, also known as the angular , fits into a deep slot on the dentary which opens backwards, a characteristic unique to docodonts. The malleus (also known as the articular ) sends down a particularly well-developed prong known as the manubrium, which is sensitive to vibrations. The incus (also known as the quadrate ) is still relatively large and rests against
3082-450: The examples given here, from formal classifications. Species have a special status in systematics as being an observable feature of nature itself and as the basic unit of classification. Some articulations of the phylogenetic species concept require species to be monophyletic, but paraphyletic species are common in nature, to the extent that they do not have a single common ancestor. Indeed, for sexually reproducing taxa, no species has
3149-442: The grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic with respect to the excluded subgroups. In contrast, a monophyletic grouping (a clade ) includes a common ancestor and all of its descendants. The terms are commonly used in phylogenetics (a subfield of biology ) and in the tree model of historical linguistics . Paraphyletic groups are identified by
3216-556: The island of Taiwan . Docodonta See text. Docodonta is an order of extinct Mesozoic mammaliaforms (advanced cynodonts closely related to true crown-group mammals ). They were among the most common mammaliaforms of their time, persisting from the Middle Jurassic to the Early Cretaceous across the continent of Laurasia (modern-day North America, Europe, and Asia). They are distinguished from other early mammaliaforms by their relatively complex molar teeth. Docodont teeth have been described as "pseudotribosphenic":
3283-428: The labial row) and has two large cusps: cusp g (at the front) and cusp c (at the back). Two additional lingual cusps may be present: cusp e and cusp df. Cusp e lies in front of cusp g and is roughly lingual to cusp b. Cusp df (“docodont cuspule f”) lies behind cusp c and is lingual to cusp d. There is some variation in the relative sizes, position, or even presence of some of these cusps, though docodonts in general have
3350-528: The last common ancestor of reptiles and all descendants of that ancestor except for birds. Other commonly recognized paraphyletic groups include fish , monkeys , and lizards . The term paraphyly , or paraphyletic , derives from the two Ancient Greek words παρά ( pará ), meaning "beside, near", and φῦλον ( phûlon ), meaning "genus, species", and refers to the situation in which one or several monophyletic subgroups of organisms (e.g., genera, species) are left apart from all other descendants of
3417-605: The literature, and provides the corresponding monophyletic taxa. The concept of paraphyly has also been applied to historical linguistics , where the methods of cladistics have found some utility in comparing languages. For instance, the Formosan languages form a paraphyletic group of the Austronesian languages because they consist of the nine branches of the Austronesian family that are not Malayo-Polynesian and are restricted to
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#17328449415173484-504: The lower molar shears into an area labial to cusp Y. Occlusion is completed when the rest of the upper molar slides between adjacent lower molar teeth, letting the rear edge of the preceding lower molar scrape against cusp X. This shearing-and-grinding process is more specialized than in any other early mammaliaform. "Pseudotalonid" and "pseudoprotocone" are names which reference the talonid -and- protocone crushing complex which characterize tribosphenic teeth . Tribosphenic teeth show up in
3551-432: The midline of the skull). A distinct wear facet is found on the labial edge of cusp X, extending along the crest leading to cusp A. Cusp Y, a unique feature of docodonts, is positioned directly behind cusp X. Many docodonts have one or two additional cusps (cusps B and E) in front of cusp A. Cusp B is almost always present and is usually shifted slightly labial relative to cusp A. Cusp E, which may be absent in later docodonts,
3618-561: The oldest fossils of therians , the mammalian subgroup containing marsupials and placentals . This is a case of convergent evolution , as therian talonids lie at the back of the lower molar rather than the front. The opposite is true for docodont teeth, which have been described as "pseudotribosphenic". Pseudotribosphenic teeth are also found in shuotheriids , an unusual collection of Jurassic mammals with tall pointed cusps. Relative to docodonts, shuotheriids have pseudotalonids which are positioned further forwards in their lower molars. This
3685-450: The origin of living mammals: monotremes , marsupials , and placentals . In other words, docodonts are outside of the mammalian crown group , which only includes animals descended from the last common ancestor of living mammals. Previously, docodonts were sometimes regarded as belonging to Mammalia , owing to the complexity of their molars and the fact that they possess a dentary-squamosal jaw joint . However, modern authors usually limit
3752-426: The petrosal bone of the braincase, a remnant of a pre-mammalian style jaw joint. In true mammals, the postdentary elements detach fully and shrink further, becoming the ossicles of the middle ear and embracing a circular eardrum . Docodont skulls are generally fairly low, and in general form are similar to other early mammaliforms such as morganucodonts . The snout is long and has several plesiomorphic traits:
3819-675: The ranks of the ICZN Code , the two taxa are separate orders. Molecular studies, however, have shown that the Cetacea descend from artiodactyl ancestors, although the precise phylogeny within the order remains uncertain. Without the Cetaceans the Artiodactyls are paraphyletic. The class Reptilia is paraphyletic because it excludes birds (class Aves ). Under a traditional classification, these two taxa are separate classes. However birds are sister taxon to
3886-445: The result of anagenesis in the excluded group or groups. A cladistic approach normally does not grant paraphyletic assemblages the status of "groups", nor does it reify them with explanations, as in cladistics they are not seen as the actual products of evolutionary events. A group whose identifying features evolved convergently in two or more lineages is polyphyletic (Greek πολύς [ polys ], "many"). More broadly, any taxon that
3953-492: The same data is put through a Bayesian analysis . Cladogram based on a phylogenetic analysis of Zhou et al. (2019) focusing on a wide range of mammaliamorphs: † Morganucodonta Haldanodon Docofossor Castorocauda Agilodocodon Microdocodon † Hadrocodium † Haramiyida Yinotheria (including Monotremata ) † Fruitafossor Theriimorpha (including Metatheria and Eutheria ) Docodont fossils have been recognized since
4020-409: The simple, U-shaped hyoids of earlier cynodonts . It allows for a narrower and more muscular throat and tongue, which are correlated with uniquely mammalian behaviors such as suckling . The oldest unambiguous fossil evidence of hair is found in a well-preserved specimen of the docodont Castorocauda , though hair likely evolved much earlier in synapsids . The structure of the vertebral column
4087-399: The specialised digging species Docofossor , and specialised tree-dweller Agilodocodon suggest Docodonta were more ecologically diverse than previously suspected. Docofossor shows many of the same physical traits as the modern day golden mole , such as wide, shortened digits in the hands for digging. A 2024 study on adult and juvenile Krusatodon specimens found that docodonts had
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#17328449415174154-481: The teeth of Morganucodon and other " triconodont " mammaliaforms, which had fairly simple lower molars with a straight row of large cusps. However, re-evaluations of mammaliaform tooth homology in the late 1990s established that docodonts were not closely related to either morganucodonts or therians. Instead, they were found to be similar to certain early " symmetrodonts ", a broad and polyphyletic grouping of mammaliaforms with triangular upper molars. In particular,
4221-590: The term "Mammalia" to the crown group, excluding earlier mammaliaforms like the docodonts. Nevertheless, docodonts are still closely related to crown-Mammalia, to a greater extent than many other early mammaliaform groups such as Morganucodonta and Sinoconodon . Some authors also consider docodonts to lie crownward of the order Haramiyida , though most others consider haramiyidans to be closer to mammals than docodonts are. Docodonts may lie crownward of haramiyidans in phylogenetic analyses based on maximum parsimony , but shift stemward relative to haramiyidans when
4288-494: The tooth-bearing dentary bone. The dentary connects to the cranium via a joint with the squamosal , a connection which is strengthened relative to earlier mammaliaforms. The other bones in the jaw, known as postdentary elements, are still connected to the dentary and lie within a groove (the postdentary trough ) in the rear part of the dentary's inner edge. Nevertheless, they are very slender, hosting hooked prongs which start to converge towards an oval-shaped area immediately behind
4355-676: The two groups as unrelated, recovering the Triassic haramiyidians as non-mammalian cynodonts, while recovering the Euharamiyida as crown-group mammals closely related to multituberculates. Order † Haramiyida Hahn, Sigogneau-Russell & Wouters, 1989 [Haramiyoidea Hahn, 1973 sensu McKenna & Bell, 1997 ] The relationships of haramiydans to other mammals and mammaliaform cynodonts are controversial and have been subject to numerous conflicting phylogenetic analysis results. Major unresolved questions are whether or not haramiyidans are more closely related to marsupials and placental mammals ( Theria ) than they are to monotremes (and thus inside
4422-616: Was Haldanodon , from the Late Jurassic Guimarota site of Portugal . Recently, exceptionally preserved skeletons have been discovered in the Jurassic Tiaojishan Formation of China . Chinese docodonts include otter -like, mole -like, and squirrel -like species, hinting at impressive ecological diversity within the group. Many docodonts have muscular limbs and broad tail vertebrae, adaptations for burrowing or swimming. Like true mammals, docodonts have hair,
4489-479: Was much smaller than either, at fewer than 156 g in adult body mass. The authors propose that the standard condition in modern small mammals (very high metabolism, rapid growth, and short lifespan) would not be adopted until true mammals in the Jurassic mammals. In addition, docodonts contradict earlier assumptions that high metabolism evolved in sync with ecological diversity, since their diversity far outpaces their metabolism. The lineage of Docodonta evolved prior to
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