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Docodontans (Mammaliaformes) from the Late Jurassic of Germany
Historical Biology
Abstract
Docodon hercynicus sp. nov. from the Upper Jurassic (upper Kimmeridgian) Süntel Formation of the Langenberg
Quarry in Lower Saxony is the first docodontan recorded from Central Europe. The two lower molars available are
characterised by vertical enamel ridges at the distal flank of cusp a, which are typical for Docodon. This is only
the second record of Docodon from Europe with the genus otherwise restricted to the Kimmeridgian-Tithonian of
the Morrison Formation in western North America. A distal fragment of a much smaller lower molar from the same
strata exhibits similar vertical enamel ridges and indicates the possible presence of a second Docodon species in
the Langenberg Quarry. Docodon hercynicus n. sp. is further evidence for the close terrestrial faunal interrelationships
between Europe and North America. It represents only the third record of a docodontan from Late Jurassicearliest
Cretaceous strata of Europe and supports a relic occurrence and late survival of mammaliaforms on
a palaeo-island in the Lower Saxony Basin within the European Archipelago.
Three new lower molars of Storchodon cingulatus and a fragmentary upper molar confirm its morganucodontan affinities. Cusps b and c are relatively higher than in Morganucodon, and cusp c is larger than cusp b. Cusp a is asymmetric, with slightly distally recurved tip. All known lower Storchodon molars have a pronounced furcation between the roots on the labial and lingual sides. The wear pattern of Storchodon corresponds to that observed in Morganucodon. Cusp A of the upper molar occludes into the valley between cusps a and c of the lower antagonist, causing large confluent wear facets. The smaller wear facets present on the mesiolabial flank of cusp b and the distolabial flank of cusp c were caused by cusp C of the upper antagonist that occluded into the embrasure between two lower molars. So far, the Morganucodon-like occlusal mode is restricted to the morganucodontans Morganucodon, Dinnetherium nezorum, Cifellilestes ciscoensis, and Storchodon cingulatus, whereas Megazostrodon and Erythrotherium exhibit embrasure occlusion. Although Storchodon belongs to the larger morganucodontans, it is questionable if it represents a case of island gigantism as suggested earlier.
A tegotheriid docodontan Sibirotherium rossicum from the Early Cretaceous of Western Siberia, Russia, was considered to have six lower premolars, as in the tegotheriids Agilodocodon and Microdocodon from the Middle Jurassic of China. The micro-computed tomography of two dentary specimens with a supposed submolariform ultimate deciduous premolar (dp6) revealed absence of a replacing tooth germ in this locus. Also, the morphology of the roots of this tooth is more consistent with that of molariform teeth. Based on the new data, we interpret Sibirotherium to possess five lower premolars rather than six and that the supposed dp6 might in fact be better interpreted as the first molariform (m1). The results of our phylogenetic analysis suggest that this is a plesiomorphic condition for Docodonta and, under slow character optimization, for Tegotheriidae, with the number of premolars reduced to three to four in Docodontidae (Haldanodon, Docodon, and Docofossor).
The Late Jurassic docodontan Haldanodon exspectatus from the Guimarota coal mine in Portugal provides important information on the evolution of the dental replacement pattern in mammaliaforms. Haldanodon shows diphyodont replacement of antemolars and non-replacement of molars. Lower incisors are replaced in alternating order with early replacement of i2 and i4, and late replacement of i1 and i3. Upper and lower premolars were replaced sequentially from front to back. In the maxilla and mandible, four deciduous premolar positions are present (dP1-4, dp1-4), but only three permanent premolars (P1/p1, P3/p3, P4/p4) erupt with loss of the dP2/dp2 position. The anterior deciduous premolars (dP1-2/dp1-2) are small and peg-like, dP3-4/dp3-4 are much larger and molariform. The lower canine and dp4 are the last lower teeth to be replaced. The permanent lower premolars are premolariform and consist mainly of large main cusp a. The ultimate permanent lower premolar (p4) erupts at the same time as m4. After replacement of the antemolars, one or two more molars (m5-6) are added at the posterior end of the tooth row of the mandible. Growth of the ramus occurs at the anterior and posterior ends as evident from the much larger permanent canine and addition of m5-6. In the maxilla, all permanent premolars differ morphologically clearly from the molars. The replacing P1 is small and consists mainly of labial cusps A, B, and C. The P3 and P4 are increasingly larger and show a lingual extension with cusps X and Y which is shorter than in the molars. The adult dental formula of Haldanodon is 6I/4i, 1C/1c, 3P/3p, 5 M/5-6m, the deciduous dental formula is ?dI/4di, 1dC/1dc, 4dP/4dp. The tooth eruption sequence in the mandible is m1 → p1 + m2 → i2 + i4 → ?i1 + ?i3 → p3 + m3 → c + p4 + m4 → m5 → m6. Our results corroborate the earlier suggestions that "Peraiocynodon inexpectatus" is based on deciduous lower premolars (dp1-4) of Docodon victor, and that "Peraiocynodon major" and Cyrtlatherium canei are based on deciduous lower premolars.
The new spalacotheriid “symmetrodontan” Cifellitherium suderlandicum gen. et sp. nov. from the Barremian–Aptian
of the Balve locality in northwestern Germany is the first record of spalacotheriids in Central Europe. The new taxon is
based on one lower and two upper molars. Cifellitherium is similar to Spalacotherium, but differs by smaller stylocone
and larger paraststyle on the upper molars, and a labially interrupted cingulid on the lower molar. The new dryolestid
Minutolestes submersus gen. et sp. nov. is based on one lower and two upper molars of small size. Phylogenetic anal�ysis revealed it as sister taxon of the clade comprising Laolestes, Krebsotherium, Dryolestes, and Guimarotodus. A
dryolestid mandible with unevenly rooted molars and extremely worn down teeth cannot be attributed to Minutolestes
submersus gen. et sp. nov. due to possessing molars twice as large in size. The mandible is assigned to a new dryolestid
taxon, Beckumia sinemeckelia gen. et sp. nov., and has the dental formula 3i, 1c, 4p, 8m and a fully reduced Meckel’s
groove. The mandible lacks any trace of a coronoid or splenial. In the phylogenetic analysis, it appears as sister taxon
of a clade comprising Achyrodon, Phascolestes, Crusafontia, and Hercynodon. The new mammals are the stratigraph�ically youngest European representatives of their clades. The late survival of Beckumia sinemeckelia gen. et sp. nov.
and Minutolestes submersus gen. et sp. nov. is possibly the result of isolated evolution in an Early Cretaceous island
environment. This finding of new spalacotheriid and dryolestid mammals from Central Europe adds to an emerging
paleobiogeographic pattern that Europe was distinct from Asia in the constituents of mammalian faunas during the
Barremian–Aptian.
The Middle Jurassic witnessed the early diversification of mammal groups, including the stem‐mammalian clade, Docodonta. Recent discoveries in China indicate docodontans exhibited ecomorphological diversity akin to small‐bodied mammals living >100 million years later, in the Cenozoic. Our understanding of the emergence of this ecological diversity is hindered by a lack of Middle Jurassic fossil material from other parts of the world. The two partial postcranial skeletons of Borealestes described here come from the Kilmaluag Formation, Scotland. These are the most complete Mesozoic mammaliaform skeletons currently known from the UK, and among the best preserved in Europe. As an early member of Docodonta, Borealestes provides key anatomical information for understanding the clade’s evolution, and the emergence of mammaliaform ecomorphological diversity. Using digital reconstructions from micro‐CT and synchrotron scans, we describe the postcranial anatomy of Borealestes and provide an updated phylogenetic analysis incorporating cranial and postcranial characters. We find Borealestes species form a sister group to a clade comprising Agilodocodon and Microdocodon. To complement observational analyses of the skeleton, we carry out principal components analyses using 3D landmarks on a comparative dataset of 42 extant mammal taxa. Our results indicate Borealestes lacked specializations for derived locomotor behaviour. We detect some similarity in the humerus between Borealestes and Ornithorhynchus. Borealestes is morphologically intermediate between the robust morphology of fossorial and semi‐fossorial/semi‐aquatic Haldanodon and Docofossor, and the gracile morphology for scansorial Agilodocodon and Microdocodon. We suggest ecological diversity in Docodonta may arise from an unspecialized basal bauplan, of which Borealestes may be representative.
The Langenberg Quarry near Bad Harzburg has yielded the first Jurassic stem therian mammal of Germany, recovered from Kimmeridgian (Late Jurassic) near shore deposits of a palaeo-island within the Lower Saxony Basin of the European archipelago. The new stem therian is represented by one lower and three upper molars. Hercynodon germanicus gen. et sp. nov. is attributed to the Dryolestidae, a group of pretribosphenic crown mammals that was common in western Laurasia from the Middle Jurassic to the Early Cretaceous. The new taxon is characterised by small size, a reduced cusp pattern in the upper molars lacking a metacone, and enhancement of the shearing crests paracrista and metacrista. Phylogenetic analysis identified Hercynodon gen. nov. as sister taxon of Crusafontia from the Lower Cretaceous (Barremian) of Spain. Both taxa belong to an endemic European clade of dryolestids, including also Achyrodon and Phascolestes from the earliest Cretaceous (Berriasian) of England. Despite its greater geological age, Hercynodon gen. nov. is the most derived representative of that clade, indicated by the complete reduction of the metacone. The discrepancy between derived morphology and geological age may be explained by an increased rate of character evolution in insular isolation. Other insular phenomena have earlier been observed in vertebrates from the Langenberg Quarry, such as dwarfism in the small sauropod Europasaurus , and possible gigantism in the morganucodontan mammaliaform Storchodon and the pinheirodontid multituberculate mammal Teutonodon which grew unusually large.
The Late Jurassic was a period of great diversity for sauropod dinosaurs, with different lineages of Neosauropoda flourishing, including several camarasauromorph taxa. Efforts made in recent years have resulted in a great increase in our current knowledge of basal camarasauromorph evolution, including both the detailed description of new and previously poorly known sauropods and expanded phylogenetic analyses. Although most recent phylogenies converge in their results on early camarasauromorph diversification, the phylogenetic position of Europasaurus, from the Late Jurassic of Germany, remains controversial despite the completeness of the material representing this species. Although Europasaurus was recovered as a relatively basal camarasauromorph in all phylogenetic analyses to date, some of them retrieved this taxon in a slightly more derived position, among basal brachiosaurids. Europasaurus is not only one of the most complete camarasauromorphs but also the first unequivocal dwarf that evolved through paedomorphosis, retaining several plesiomorphic characters, especially in the cranium. Cranial and axial material of Europasaurus has been described in detail but the appendicular skeleton has not. The current paper rectifies this by providing detailed descriptions and illustrations of its appendicular skeleton. In addition, an extensive re-evaluation of the systematic position of Europasaurus was done based on the three most substantial data sets published in recent years. These analyses resolved Europasaurus as a basal camarasauromorph in all cases, but brachiosaurid affinities remain plausible, especially considering the heterochronic evolution of the taxon.
Marine limestones and marls in the Langenberg Quarry provide unique insights into a Late Jurassic island ecosystem in central Europe. The beds yield a varied assemblage of terrestrial vertebrates including extremely rare bones of theropod from theropod dinosaurs, which we describe here for the first time. All of the theropod bones belong to relatively small individuals but represent a wide taxonomic range. The material comprises an allosauroid small pedal ungual and pedal phalanx, a ceratosaurian anterior chevron, a left fibula of a megalosauroid, and a distal caudal vertebra of a tetanuran. Additionally, a small pedal phalanx III-1 and the proximal part of a small right fibula can be assigned to indeterminate theropods. The ontogenetic stages of the material are currently unknown, although the assignment of some of the bones to juvenile individuals is plausible. The finds confirm the presence of several taxa of theropod dinosaurs in the archipelago and add to our growing understanding of theropod diversity and evolution during the Late Jurassic of Europe.
An upper “triconodont” molar from the Late Jurassic (late Kimmeridgian) of the Langenberg Quarry in northern Germany is attributed to Storchodon cingulatus gen. et sp. nov. of Morganucodonta. The molar is characterized by continuous lingual and buccal cingula, and a relatively large, buccally-shifted cusp D which is not integrated in the buccal cingulum. With a length of 3.07 mm, the tooth is less than 10 % smaller than the lower holotype molar of Paceyodon davidi , the largest known morganucodontan. The Langenberg morganucodontan possibly represents an example of insular gigantism on an adjacent paleoisland.
The Middle Jurassic docodont Borealestes serendipitus was the first Mesozoic mammal found in Scotland over 40 years ago. Its affinities and morphology have remained poorly understood. Although multiple dentary fragments and isolated teeth have been recovered from Scotland and England, they have not yet been described in sufficient detail. We report new, more complete specimens collected during recent field work on Skye, Scotland, combined with previously collected material. This includes upper and lower dentition and an almost complete right dentary. We present an updated description and diagnosis of the genus Borealestes, based on high-resolution micro-computed tomography (micro-CT) and synchrotron scans. We identify seven key features that distinguish Borealestes from other docodonts, including a pronounced a–c crest, absence of the a–g crest on cusp a, an anterior fovea at the buccolingual midpoint of the upper molar, and the convergence of the Meckel’s groove with the ventral margin of the mandible. We also present a revised diagnosis for the second species, B. mussettae. Our phylogenetic analysis supports a clade formed by Borealestes, Haldanodon, Docofossor, and Docodon. Ontogenetic variation in the mandibular morphology of Borealestes is similar to that seen in Docodon and Haldanodon, with the delayed emergence of the ultimate lower molar, the shift of the last molar to the front of the coronoid process, and a posterior shift of the Meckel’s sulcus in successively older individuals. This supports a distinctive growth pattern in the clade including Borealestes and Docodon, one that may be present in Docodonta as a whole.
Early suckler?
One trait that is unique to mammals is milk suckling. Suckling requires the presence of stability and motion in the throat, both of which require a complex hyoid apparatus. Zhou et al. describe a mammaliform docodontan fossil from the Jurassic that was preserved with a nearly intact hyoid (see the Perspective by Hoffmann and Krause). The structure is complex and saddle shaped, like that seen in modern mammals, suggesting that a muscularized throat was present before the development of mammals.
Science , this issue p. 276 ; see also p. 222
The Early Cretaceous (?Berriasian-Barremian) Teete vertebrate locality in Western Yakutia, East Siberia, Russia, has produced mammal remains that are attributed to three taxa: Eleutherodontidae indet. cf. Sineleutherus sp. (Haramiyida; an upper molariform tooth), Khorotherium yakutensis gen. et sp. nov. (Tegotheriidae, Docodonta; maxillary fragment with three molariform teeth and dentary fragment with one molariform tooth), and Sangarotherium aquilonium gen. et sp. nov. (Eutriconodonta incertae sedis; dentary fragment with one erupted molariform tooth and one tooth in crypt). This is the second occurrence of Mesozoic mammals in high latitudes (paleolatitude estimate N 63–70°) of the Northern Hemisphere. In spite of the presumed Early Cretaceous age based on freshwater mollusks, the Teete mammal assemblage has a distinctive Jurassic appearance, being most similar to the Middle-Late Jurassic mammal assemblages known from Siberia, Russia and Xinjiang, China. The smooth transition from Jurassic to Cretaceous biota in Northern Asia is best explained by stable environmental conditions.
Docodon was the first described docodont, and has long featured prominently in the comparative and functional morphology of mammaliaform mandibles and teeth. We have now re-examined the dental and mandibular fossils of Docodon from Yale Quarry 9 at the Como Bluff site in the Late Jurassic Morrison Formation, using Computed Tomography (CT) scans and 3D image analyses. Our CT study revealed that some features used to distinguish the several Docodon “species” in historical studies many decades ago were based on incorrect manual restoration of mandibles, and on variable features of deciduous premolars, which are replaced in typical mammaliaform fashion. This supports a long-held notion that the multiple species of Docodon from the same quarry of the Morrison Formation are over-split and should be synonymized. We formally propose that the specimens examined in this study be synonymized under Docodon victor. Our new Occlusal Fingerprint Analysis (OFA) of Docodon molars supports the hypothesis that Docodon had a consistent dorso-posterior or palinal component in chewing in the disto-distolingual to distolingual direction. This helps to resolve the controversial historical alternative hypotheses postulated for tooth occlusion in the taxon. The Docodon occlusal pattern is likely a derived feature, evolved within Docodonta. A posterior component in the occlusal trajectory is a functional convergence of Docodon on unrelated traversodontid cynodonts.
Shallow-marine Kimmeridgian (Late Jurassic) deposits in the Lower Saxony Basin (LSB) composed of alternating limestone, marl and claystone attract great palaeontological interest due to their rich invertebrate and vertebrate assemblages. Unfortunately, the absence of open-marine marker fossils and numerous sedimentary gaps in combination with lateral facies changes hamper the precise stratigraphic correlation of these strata on both a local and global scale. Here, an integrated approach combining carbonate microfacies analysis, ostracod biostratigraphy and high-resolution sequence stratigraphy is applied to two Kimmeridgian sections (Langenberg and Bisperode, 60 km apart) in the southeastern LSB. High-resolution carbonate microfacies analysis enables the definition of 19 microfacies types and seven microfacies associations, which can be arranged into facies belts along a carbonate ramp. Vertical microfacies, bed thickness and diagnostic surfaces define stacking patterns that are interpreted as small-, medium- and large-scale sequences. The ostracod biostratigraphic framework established in this study provides the required stratigraphic control. Correlation of the two studied sections reveals a more proximal setting for Bisperode than Langenberg and an overall shallowing-up trend from mid-ramp to proximal inner ramp developed in both sections. Furthermore, the majority of the medium-scale sequence boundaries defined in this study can be found in similar biostratigraphic positions in other European basins. Synsedimentary tectonics combined with high sediment accumulation rates can be identified as important controlling factors for the distribution and composition of the Kimmeridgian deposits in the LSB based on detailed correlation on both a regional and super-regional scale.
We report a new, small-sized atoposaurid crocodyliform from the Upper Jurassic of Langenberg, Northeastern Germany. Atoposaurids are small-sized Mesozoic crocodyliforms of mainly European distribution, which are considered to be phylogenetically close to the origin of Eusuchia. Knoetschkesuchus langenbergensis gen. nov. sp. nov. is represented by two well-preserved skulls and additional cranial and postcranial remains representing different ontogenetic stages. 3D reconstructions of a juvenile skull based on micro-computed tomography allow the most detailed description of cranial remains of any atoposaurid hitherto presented. Our new analysis contradicts previous preliminary assignment of the Langenberg atoposaurids to Theriosuchus. Knoetschkesuchus gen. nov. is characterized in particular by the presence of two dental morphotypes in the maxilla and dentary, slit-like secondary choanae within a narrow groove on the surface of the pterygoid, absence of lacrimonasal contact, presence of an antorbital foramen and an external mandibular fenestra, and proportional characters of the interorbital and intertemporal region. A similar combination of characters allows attribution of Theriosuchus guimarotae to Knoetschkesuchus, forming the new combination Knoetschkesuchus guimarotae. Our analysis provides an osteological basis for the separation of Theriosuchus and Knoetschkesuchus and helps further delineate generic differences in other closely related crocodylomorphs. Our phylogenetic analysis corroborates inclusion of Knoetschkesuchus into Atoposauridae and supports a position of Atoposauridae within Eusuchia.
Remains of theropod dinosaurs are very rare in Northern Germany because the area was repeatedly submerged by a shallow epicontinental sea during the Mesozoic. Here, 80 Late Jurassic theropod teeth are described of which the majority were collected over decades from marine carbonates in nowadays abandoned and backfilled quarries of the 19th century. Eighteen different morphotypes (A—R) could be distinguished and 3D models based on micro-CT scans of the best examples of all morphotypes are included as supplements. The teeth were identified with the assistance of discriminant function analysis and cladistic analysis based on updated datamatrices. The results show that a large variety of theropod groups were present in the Late
Bulk sampling of a Late Jurassic (Kimmeridgian) section east of Goslar (North Germany) yielded 6.385 isolated teeth of actinopterygians (Osteichthyes). The fauna comprises 72 taxa: Lepidotes sp., Macromesodon sp., Proscinetes sp., Coelodus sp., Macrosemius sp. ? / Notagogus sp. ?, Histionotus sp., Ionoscopus sp., Callopterus sp., Caturus sp., Sauropsis sp., Belonostomus sp., and Thrissops subovatus Münster in Agassiz 1844. Considering the entire material, Lepidotes dominates the fauna. A bed-by-bed consideration of the actinopterygian fauna revealed an oszillating mode of change in the predominance of presumed euryhaline taxa (Lepidotes, Coelodus,and Callopterus) and stenohaline forms (remaining taxa). The changes in faunal composition are possibly caused by changes in the palaeosalinity.
Systematic sampling of the Kimmeridgian (Late Jurassic) sequence in a working quarry (Langenberg at Oker, near Goslar) and an Autobahn cut (BAB 7 at Uppen near Hildesheim) in northwest Germany has yielded a rich material of vertebrate remains including 59 teeth of the dwarf crocodile cf. Theriosuchus sp. It is the first record of this taxon from the Upper Jurassic (Kimmeridgian) of Germany. From dental morphology and taphonomical and geochemical evidence it is concluded that cf. Theriosuchus sp. from the Kimmeridgian of northwest Germany was a piscivorous crocodile which inhabited coastal areas. The palaeogeographical and stratigraphical distribution of European atoposaurids is considered.
Here we describe dinosaur tracks from the Langenberg Quarry near Goslar (Lower Saxony) that represent the first footprints from the Late Jurassic of Germany discovered outside the Wiehen Mountains. The footprints are preserved in Kimmeridgian marginal marine carbonates. They vary in length from 36 to 47 cm and were made by theropod dinosaurs. The original tracksite with 20 footprints was destroyed by quarrying soon after its discovery in 2003. Only the five best defined footprints were excavated. Based on scanned-in analog photographs which were taken during the excavation, a three-dimensional (3-D) model of the original tracksite was generated by applying historical photogrammetry. The resulting model is accurate enough to allow a detailed description of the original tracksite. Different preservation types result from changing substrate properties and include both well-defined footprints and deeply impressed footprints with elongated heel and variably defined digit impressions. The tracksite was discovered stratigraphically close to the bone accumulation of the dwarfed sauropod dinosaur Europasaurus holgeri and probably records a sea level fall along with a faunal interchange, which would likely have eliminated the resident dwarf island fauna. The two largest and best preserved footprints differ from most other Late Jurassic theropod footprints in their great width. Two different trackmaker species might have been present at the site. Several hypotheses presented in a recent paper on Late Jurassic dinosaur tracks from the Wiehen Mountains by Diedrich (2011b) are commented upon herein.
Remains of a fossil lizard were discovered during the 2012 field season of the Europasaurus-Project in the Langenberg Quarry in Oker, Lower Saxony. The bone fragments are between 1.5 and 4 mm in size and derive from a middle Kimmeridgian (154 my) micritic, marly limestone layer deposited under shallow marine conditions. Besides a femur, the majority of the identifiable bones belongs to the skull. Parts of both dentaries, a frontal, a jugal, a supposed squamosal and a part of a premaxillary bone are well-preserved. Another tooth-bearing fragment is situated below the main bone conglomeration; osteoderms are not preserved. The characteristic teeth with their chisellike morphology and marked, oblique cutting edges and the unpaired frontal with its rugose surface define this specimen as belonging to Paramacellodidae. Thus, it represents the first Mesozoic lizard from northern Germany. The tiny bones of the Langenberg lizard are disarticulated, although right and left dentary fragments are preserved side by side, the right one on top. Taphonomic interpretation follows known disarticulation stages of complete lizards (Messel Pit, Eocene, Germany) and lizard skulls (Uña, Barremian, Spain). The best comparison can be made with lizard bone aggregates from the Kimmeridgian of Guimarota, Portugal. Its predominantly terrestrial coal sedimentation has preserved a rich paramacellodid lizard fauna with several genera and species. We describe their taphonomy for the first time and compare it to the preservation of the Langenberg lizard. Two bone aggregates of Portuguese paramacellodids are especially suitable for comparison. One coal slab contains both dentaries and postdentary bones plus one maxillary, still adducted, but all other skull elements are slightly disarticulated. The other specimen shows less skull bones, but both dentaries lie aside. With only a small distance between the mandible tips, the two bones still keep their original orientation. Disarticulation of the Langenberg paramacellodid must range between these two stages. The skull and especially the snout tip remained rather complete during the beginning decay and it is very likely that all bones belong to the same individual. The find shows that the marine sediments in the Langenberg Quarry have not only potential for large terrestrial vertebrates such as the dwarfed sauropod Europasaurus, but also for fragile and minute remains.
A new Late Jurassic docodontan shows specializations for a subterranean lifestyle. It is similar to extant subterranean golden moles in having reduced digit segments as compared to the ancestral phalangeal pattern of mammaliaforms and extant mammals. The reduction of digit segments can occur in mammals by fusion of the proximal and intermediate phalangeal precursors, a developmental process for which a gene and signaling network have been characterized in mouse and human. Docodontans show a positional shift of thoracolumbar ribs, a developmental variation that is controlled by Hox9 and Myf5 genes in extant mammals. We argue that these morphogenetic mechanisms of modern mammals were operating before the rise of modern mammals, driving the morphological disparity in the earliest mammaliaform diversification.
Copyright © 2015, American Association for the Advancement of Science.
A new docodontan mammaliaform from the Middle Jurassic of China has skeletal features for climbing and dental characters indicative of an omnivorous diet that included plant sap. This fossil expands the range of known locomotor adaptations in docodontans to include climbing, in addition to digging and swimming. It further shows that some docodontans had a diet with a substantial herbivorous component, distinctive from the faunivorous diets previously reported in other members of this clade. This reveals a greater ecological diversity in an early mammaliaform clade at a more fundamental taxonomic level not only between major clades as previously thought.
Copyright © 2015, American Association for the Advancement of Science.
One of the most interesting Mesozoic Lagerstätten, Shar Teg in southwestern Mongolia, is
reviewed. The geological structure and oryctocoenoses of Shar Teg are described. Shar Teg is one of the most diverse Jurassic Lagerstätten in terms of fossils represented. Fossils from Shar Teg include aquatic and terres� trial plants, mollusks, crustaceans, insects, fishes, amphibians, reptiles, and mammals. Insects are the most diverse group. To date, a total of 297 species of 161 families and 22 orders have been described or recorded in Shar Teg, making it possible to reconstruct comprehensively the Jurassic biota of the locality. The orycto�coenosis composition is peculiar; it includes only six species described from other localities. The orycto�
coenosis appears to link the faunas of eastern Asia, Central Asia, and Europe. A total of 31 new species are
described.
Nils Knötschke (2014): Cranial anatomy of the Late Jurassic dwarf sauropod Europasaurus holgeri (Dinosauria, Camarasauromorpha): ontogenetic changes and size dimorphism, Journal of Systematic Palaeontology, makes every effort to ensure the accuracy of all the information (the "Content") contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at
Neosauropods are well represented in the Late Jurassic fossil record, both in Laurasia and Gondwana. Among Macronaria, Europasaurus represents one of the most basal forms of this group. In addition to its systematic importance, Europasaurus is also the first unequivocal dwarf sauropod from which adult and juvenile material is available. Despite the abundance of sauropods in the fossil record, early juvenile specimens are rare, limiting knowledge about sauropod ontogeny. Therefore, the great amount of material of Europasaurus provides an excellent opportunity to improve our knowledge on the early evolution of Macronaria, as well as to shed light on some morphological changes through ontogeny. The postcranial axial skeleton of sauropods is extremely modified with respect to the anatomy observed in its ancestors, the ‘prosauropods’, proving to be one of the most informative regions of the body. Here we provide a detailed description of the axial skeleton of Europasaurus, including adult and juvenile elements, discussing its systematic and ontogenetic importance. We also analyse the phylogenetic position of Europasaurus through a cladistic analysis using TNT, which retrieves this taxon in a basal position among Camarasauromorpha. Additionally, the presence/absence of discrete characters and the comparison of juvenile elements with adult specimens allowed us to recognize different morphological ontogenetic stages (MOS). Whereas early stages lack derived characters (e.g. spinodiapophyseal lamina and prespinal lamina on dorsal vertebrae), all derived characters (including autapomorphies) are present in late immature specimens. Therefore, while late immature specimens provide the same phylogenetic signal as adult specimens of Europasaurus, more immature stages are recovered in a basal position among sauropods. Finally, we apply the MOS to other maturity criteria (e.g. neurocentral closure, sexual maturity) in a search for a wider definition of maturity.
A docodontan mammaliaform from the Middle Jurassic of China possesses swimming and burrowing skeletal adaptations and some dental features for aquatic feeding. It is the most primitive taxon in the mammalian lineage known to have fur and has a broad, flattened, partly scaly tail analogous to that of modern beavers. We infer that docodontans were semiaquatic, convergent to the modern platypus and many Cenozoic placentals. This fossil demonstrates that some mammaliaforms, or proximal relatives to modern mammals, developed diverse locomotory and feeding adaptations and were ecomorphologically different from the majority
of generalized small terrestrial Mesozoic mammalian insectivores.
Mammalia is defined by its ancestry as the taxon originating with the most recent common ancestor of extant Monotremata and Theria. To diagnose Mammalia as so defined, 176 character transformations in the skull and postcranial skeleton, distributed among Placentalia, Marsupialia, Multituberculata, Monotremata, Morganucodontidae, Tritylodontidae, and Exaeretodon, were polarized, scored, and subjected to PAUP. Only one most parsimonious tree was identified (BL = 190, CI = 0.926): (Exaeretodon (Tritylodontidae (Morganucodontidae (Monotremata (Multituberculata (Marsupialia, Placentalia)))))).Thirty-seven osteological synapomorphies diagnose Mammalia. Triassic and Early Jurassic taxa commonly referred to as mammals, including Morganucodontidae, Kuehneotheriidae, and Haramiyidae, were found to lie outside of Mammalia. These fossils document that the mammalian lineage had diverged from other known synapsid lineages by the Norian (Late Triassic). However, the earliest evidence that Monotremata and Theria had diverged from their most recent common ancestor, and thus the earliest evidence of Mammalia itself, is of Bathonian (Middle Jurassic) age. Many of the diagnostic attributes of Mammalia are associated with either the sensory organs housed in the skull, the masticatory system, or the craniovertebral and atlas-axis articulations. Modification of each of these regions has long been tied to the origin of mammals. However, other synapomorphies are identified which suggest that additional factors must be sought to fully understand the origin of Mammalia.
Henkelotherium guimarotae Krebs 1991 is an important Jurassic mammal for understanding therian evolution. We are presenting a new study of extensive, previously undescribed, mandibles and dentitions. The revised dental formula is: I4? or 5?/i4, C1/c1, P4/p4, M6/m7. The canine and premolars show an alternate replacement that ends with M4/m4 eruption, and is followed by a late sequential eruption of the last three lower (m5-7) and last two upper (M5-6) molars. The lower premolars erupted in the following order: p1 → p3 → p2 → p4, and the canine erupted most probably shortly before p4. The timing of the premolar replacement before the late molar eruption is similar to that of Dryolestes leiriensis, and is a characteristic of dryolestidans. Henkelotherium lower molars have subequal roots, a plesiomorphy of non-dryolestidan mammals, and the upper molars are supported by a strong, curved lingual root; a derived character. In the upper molars, the postvallum wear surface is contiguous to the parastyle wear surface of the succeeding molar, which differs from dryolestids. The parastylar lobe of the succeeding molar, and the postvallum of the preceding molar, are imbricated, and can develop strong, continuous wear surfaces, matching the prevallid crest of the lower molar. Henkelotherium differs from dryolestids in having an inflected, shelf-like mandibular angular process with a foramen. This large sample of Henkelotherium shows a significant variation gradient along the molar series, with the strongest wear occurring only in two to three consecutive molars. The extraordinarily long molar row is correlated with the late growth of jaws; and the jaw with late addition of molars sustained an effective mastication, much longer in older adults of dryolestidans than in other Mesozoic stem therians. The late eruption of several more molars after completion of antemolar replacement suggests that dryolestidans had either a longer-lived life, or slower life-history traits, or a combination of both, than crown therians.
The Upper Cretaceous (Cenomanian) Mata Amarilla Formation in western Central Santa Cruz Province of Argentina has yielded fragmentary teeth of a large ?docodontan, an australosphenidan, a meridiolestidan (Amarillodon meridionalis gen. et sp. nov.), and a stem dryolestid (Treslagosodon shehuensis gen. et sp. nov.). These represent the first possible records for docodontans, Cretaceous australosphenidans, and stem dryolestids in South America. Both ?docodontan tooth fragments are unusually large and exhibit potential durophagous adaptation. The Amarillodon gen. nov. lower (?deciduous) posterior premolar has a trigonid angulation of 100° and is autapomorphic by a large and exoedaenodont distolabial accessory cusp on the distal cingulid. Both the mesial and distal cingulid are shelf-like. The mesiolabial upper molar fragment of the ausktribosphenid australosphenidan is similar to an upper M1 of aff. ?Bishops from the lower Albian (Lower Cretaceous) of Australia by its large stylar cusp ?C and breached paracone. The lower molar of the new stem dryolestid is characterized by a large talonid cusp d and a mesio-distally strongly compressed mesial root that is weaker than the distal one. The australosphenidan, if corroborated, suggests faunal interrelationships between Australia and South America by the late Early/early Late Cretaceous.
Docodonta are one of the earliest diverging groups of mammaliaforms, and their morphology provides key information on the transition between non-mammalian cynodonts and Mammalia. We describe the partial skulls of two docodontans Borealestes serendipitus and Borealestes cuillinensis sp. nov. from the Kilmaluag Formation (Middle Jurassic: Bathonian), Isle of Skye, Scotland. We visualize their cranial anatomy using laboratory and synchrotron X-ray micro-CT. The skulls belong to two partial skeletons, currently comprising the most complete Mesozoic mammal fossils reported from the British Isles. The associated upper and lower dentitions show that the lower dentition of Borealestes is not diagnostic to species level. We establish, B. cuillinensis, based on upper molar characters, and re-identify upper molars previously assigned to ‘Borealestes’ mussettae as belonging to B. cuillinensis. ‘Borealestes’ mussettae, based on distinctive lower molars, is found to be morphologically and phylogenetically distinct from Borealestes, necessitating assignment to a new genus, Dobunnodon gen. nov. The skulls of Borealestes retain many plesiomorphic features seen in Morganucodon but absent in more crownward mammaliaforms. Our study highlights that generic and species taxonomy of docodontans are more reliable when based on both upper and lower teeth, while lower molar morphology may underrepresent the true diversity of Mesozoic mammaliaforms.
The Late Jurassic (late Kimmeridgian) multituberculate assemblage from the Langenberg Quarry in Northern Germany includes Paulchoffatiidae indet., the pinheirodontid Teutonodon langenbergensis, and Cimbriodon multituberculatus gen. et sp. nov. of the paulchoffatiid line. A fragmentary m1 that was formerly attributed to Eobaataridae indet. is now assigned to the paulchoffatiid line. Teutonodon langenbergensis is one of the largest known Jurassic multituberculates and most derived known member of Pinheirodontidae. Cimbriodon multituberculatus, a derived member of the paulchoffatiid line is characterised by the upper premolars P4 and P5 showing three rows of cusps, with P5 having numerous cusps and being distinctly longer than P4, and the lower premolars p3 and p4 showing five serrations with long ridges. The new taxon is unique among multituberculates by the presence of several lingual cusps on p3 and p4. Rugosodon from the Late Jurassic of China differs from Paulchoffatiidae or Pinheirodontidae by seven serrations on p4, significantly reduced buccal cusps on p4, a p3 that has half the length of p4, and a simple bicuspid I3, and is referred to the paulchoffatiid line. Allodontidae is known only from western North America, Paulchoffatiidae and Pinheirodontidae only from Western and Central Europe (Portugal, Spain, Great Britain, and Germany). Plagiaulacidae is known from the earliest Cretaceous of Great Britain and of western North America.
Zoobank: urn:lsid:zoobank.org:pub:D8ECDD1D-931D-47E3-AAEE-D421B4C7079D
The upper Bathonian Kirtlington mammal bed of England is one of the rare Middle Jurassic sites in the world to have yielded mammalian remains and undoubtedly the richest. A few taxa have so far been described, among which the genus Cyrtlatherium Freeman, 1979, assigned by its author to the Kuehneotheriidae and subsequently included in the Symmetrodonta. In this note I argue that Cyrtlatherium represents a docodont of which it is possibly a milk premolar.
The dryolestid fauna of the Lower Kimmeridge lignite of the Guimarota coal mine (Leiria, Central Portugal) is dominated by two genera, Dryolestes leiriensis sp. nov. and Krebsotherium lusitanicum gen. et sp. nov. Both taxa are represented by upper and lower dentitions which can unambiguously be attributed to each other on the base of size and relative abundance. The lower jaw (length about 3.5 cm) of the larger taxon Dryolestes leiriensis sp. nov. is very similar to the lower jaw taxon Dryolestes priscus MARSH 1878 from the Morrison Formation, and the corresponding upper jaw closely resembles the upper jaw taxon "Herpetairus arcuatus" SIMPSON 1927. Therefore "Herpetairus" SIMPSON 1927 is a junior synonym of Dryolestes MARSH 1878. Krebsotherium lusitanicum gen. et sp. nov. with a lower jaw length of about 2.5 cm is considerably smaller and its lower molars are characterized by pointed cusps and an anteriorly-projecting paraconid; the upper molars have a strikingly small stylocone and a median ridge in the trigon basin. On the base of these characters Krebsotherium nov. gen. is placed in the lineage leading to Amblotherium OWEN 1871. Guimarotodus inflatus gen. et sp. nov. is only represented by lower jaws and characterized by an inflated metaconid with chisellike tip. From Late Jurassic/Early Cretaceous sediments of Porto Pinheiro near Lourinhã at the mid-Portuguese Atlantic coast a new species of the genus Laolestes SIMPSON 1927, Laolestes andresi sp. nov., is described on the base of upper molars; these are characterized by a very large stylocone being isolated from the paracrista and an extremely strong median ridge in the trigon basin. Portopinheirodon asymmetricus gen. et sp. nov. is represented by a strikingly asymmetrical upper molar with strongly enlarged metastylar region without any cusps. On the basis of the Guimarota material the Dryolestidae of the Morrison Formation is revised. "Herpetairus" SIMPSON 1927 is the upper dentition of Dryolestes MARSH 1878 and "Melanodon" SIMPSON 1927 the upper dentition of Laolestes SIMPSON 1927. Amblotherium "debilis" SIMPSON 1929 is a synonym of Amblotherium gracilis SIMPSON 1927 and "Kepolestes coloradensis" SIMPSON 1927 is synonymized with Amblotherium SIMPSON 1927. "Malthacolestes osborni" SIMPSON 1927 is dP3 and dP4 of an upper milk dentition and belongs most probably to Laolestes SIMPSON 1927. Euthlastus cordiformis SIMPSON 1927 and Comotherium richi PROTHERO 1981 are not Dryolestidae but upper dentitions of Paurodontidae. Among the Guimarota Dryolestidae three upper and eight lower juvenile dentitions in various stages of tooth replacement have been found. As in Eutheria, all antemolar tooth positions are replaced (I1-4, C, P1-4). First and second milk premolars (dP1 and dP2) are premolariform, while dP3 and dP4 are molariform. Tooth replacement in the lower jaw is alternating and takes place in two waves; dI2, dI4 dP1, and dP3 are replaced in the first wave and dI1, dI3, dC, dP2, and dP4 in the second. P4 is the last premolar to erupt and appears when M6 starts to break through. Tooth replacement at all antemolar positions is the primitive condition for Theria, and the reduced tooth replacement of marsupials (only dP3 is replaced postnatally) is derived. From this evidence it can be deduced that the mode of reproduction of Late Jurassic Theria was not like that of marsupials. The Dryolestidae of the Guimarota coal mine are more primitive than those of the Morrison Formation (Wyoming) or from southeastern England. Advanced genera like Laolestes are missing, and in all lower jaws examined an insertion pit of a rudimentary coronoid bone has been detected. Laolestes andresi sp. nov. from Porto Pinheiro with a stylocone isolated from the paracrista indicates relationships to Late Cretaceous Dryolestidae of South America (e.g., Leonardus BONAPARTE 1990). A cladistic analysis of Dryolestidae based on 20 dental and mandibular characters yielded three groups (Dryolestes + Peraspalax; Phascolestes + Guimarotodus + Laolestes + Leonardus; Krebsotherium + Crusafontia + Amblotherium) which are not formally named here.
Isolated bones of forelimb and pelvic girdle (two humeri, five ulnae, and an ilium) recovered from the Late Jurassic (Kimmeridgian) Guimarota coal mine in western central Portugal are attributed to the docodont Haldanodon exspectatus, dryolestoids, and a ?paulchoffatiid multituberculate. The larger of the two humeri is assigned to the dryolestid Dryolestes leiriensis based on size and shape. It clearly exhibits an incipient trochlea at the distal joint, suggesting that this derived character was well established among Late Jurassic dryolestidans, including Henkelotherium. Plesiomorphic characters are the prominent spherical radial condyle and the weakly developed ulnar condyle. An incipient medial keel is present in distal aspect of the humerus trochlea. The shallow olecranon fossa of the humerus corresponds to the small anconeal process of the radius. The smaller humerus with damaged distal joint is 50% smaller and cannot be assigned to a specific dryolestoid taxon. It is in the size range of the smaller Guimarota dryolestoids Krebsotherium, Drescheratherium, and Henkelotherium. One ulna differs from the dryolestoid ulnar shape by the nearly semicircular articular surface for the ulnar condyle of the humerus, the asymmetric olecranon with medial overhang, as well as the prominent anconeal process and is tentatively attributed to a paulchoffatiid multituberculate.
Turtles are frequently found in fluviatile to lagoonal and shallow marine sediments in the Upper Jurassic of Western Europe. These turtles usually show a mixture of basal and derived characters, but phylogenetic relationships are still largely unresolved. This is mainly due to the incompleteness of fossils and the lack of taxonomically unambiguous characters and is also related to the presence of different ontogenetic stages, which are not easy to compare. The morphological description of a new turtle from the Upper Jurassic of Langenberg Quarry (Oker, Lower Saxony, Germany) gives further insights into the ontogeny of basal eucryptodire turtles as well as into aquatic adaptation of Upper Jurassic turtles. The specimen is herein left in open nomenclature, due to the fact that it represents a juvenile individual. Several characters define the specimen as juvenile: its small size (7.28 cm carapace length); lateral carapacial fontanelles; enlarged vertebral scutes; a radial striation pattern covering the entire carapace; and the grade of ossification of preserved skull and limb elements. A clear aquatic adaptation of the individual is the elongated manus, a feature that is independent of ontogenetic age. The elongated manus may indicate a marine lifestyle and the individual possibly inhabited nearshore to offshore areas around the former Jurassic islands, which today form the Saxony Basin. The ossification pattern of the carapace of this eucryptodire turtle resembles that of known Jurassic paracryptodires and thus provides new insights to the ontogeny of Jurassic turtles.
Records of mammals in Mesozoic strata are rare: the earliest are of late Triassic age in Wales, S. Africa and China: two primitive mammal families (Eozo-strodontidae and Kuehneotheridae) are represented in these faunas. There then follows a long time gap until Late Jurassic, when mammals are known from the U.S.A., U.K., Portugal and Tanzania: these faunas include pantotheres, the stock from which almost all the later mammals arose. Between the Late Trias and Late Jurassic, the only known fauna is that of the Middle Jurassic of Stonesfield in Oxfordshire. Thus the discovery of a second site is of great importance: it occurs in the Estuarine Series of Skye in Scotland, and contains a fauna of tritylodonts and docodont mammals. The discovery of this fauna was made in August 1971 by Dr. M. Waldman and Mr. J. B. Dobinson during the course of a search for terrestrial vertebrates in the non-marine strata of Skye.
Stratigraphy
Since Hugh Miller (1858) described the occurrence of Jurassic vertebrate fossils on the Isle of Eigg, further vertebrates of similar age have been found in the Hebridean region. The richest material so far recovered has been from the Bathonian (Middle Jurassic) of Eigg (Hudson 1966), and the most recent find is that of plesiosaur remains from the Bearreraig Sandstone (Bajocian) near Rigg, Isle of Skye (Hudson & Morton 1969). All the Jurassic vertebrate remains known from this area are those of fish and reptiles and occur in a variety of localities. (Miller 1858, Peach 1910, Arkell