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Data from vertebrate microsites are important in paleoecological reconstructions, but their usefulness has been limited because of undemonstrated repeatability of sampling data and the time- and labor-intensive nature of their retrieval. Re-examination of a previously studied vertebrate microsite revealed that repeatable diversity and abundance data are obtainable using a controlled sorting methodology. It was found that a curve fitted to a plot of empirical diversity vs. sampling frequency will tend toward an asymptote as sampling frequency increases, indicating that the likelihood of discovery of new taxa having a major impact upon a paleoecological interpretation is diminishing. Rarefaction analysis was applied to the data obtained, and the rarefaction curve provided support for the behavior of the empirical diversity curve. It was also found that as sampling frequency increases, rank orders of relative abundance stabilize among the most common taxa in the sample, indicating that the likelihood of discovery of highly abundant taxa is diminishing. Adequate sampling of a vertebrate microsite can thus be achieved by dividing the original field sample into many small subsamples, and additively plotting diversity and relative abundance data. Once the diversity curve begins to tend toward an asymptote, and the abundance ranks among the most common taxa have stabilized, it is necessary to continue sampling only until double this number of subsamples has been analyzed in order to confirm the established patterns. Proceeding in this fashion will verify that ostensible exhaustion of the taxa present has been achieved. Standardization of sampling methodology will allow similarly compiled data to be compared, both from a single site and among multiple sites, improving the reliability of palaeoecological interpretations generated from vertebrate microsites.
Muscle morphology in the Placodermi can be inferred by comparison to extant gnathostomes (Chondrichthyes (Actinopterygii Sarcopterygii)). Examination of the chondrichthyan hypobranchial musculature suggested a comparable musculature for placoderms, including the coracomandibularis and coracohyoideus, acting separately to depress the mandible and hyoid arch. In sharks, this was associated with the absence of a mandibulohyoid ligament functioning in mandible depression, a characteristic feature of actinopterygians and sarcopterygians. Additionally, the coracobranchiales muscles depress the chondrichthyan ventral gill arches, the clavobranchiales being the corresponding muscles in actinopterygians and sarcopterygians. These muscles and ligaments are not preserved in placoderms, but their attachments can be compared to those of extant gnathostomes. On the placoderm lower jaw, attachment surfaces for the mandibulohyoid ligament are only present in derived taxa and position relative to the jaw joint suggests the ligament functioned poorly (or not at all). This compares to the chondrichthyan condition, but attachment surfaces on the placoderm trunkshield indicate that while some primitive placoderms possessed a coracobranchialis musculature, other derived taxa possessed a clavobranchialis.
The Osteostraci are the most closely related agnathans to the jawed vertebrates, and lack muscles involved in active inspiration, the evolution of which was linked to increased activity near the origin of jawed vertebrates. Since overall morphology suggests osteostracans were active animals, absence of these muscles may instead relate to the absence of segmented gill arches and the anterior position of the osteostracan pectoral fin. The latter may affect development of the hypobranchial musculature, questioning homology of these muscles in lampreys and jawed vertebrates.
A growth series of 97 specimens of the dissorophoid temnospondyl Micromelerpeton credneri from the Permo-Carboniferous of Central Europe is taken as a basis for ontogenetic investigations. Whereas the dermal skull roof is already ossified and sutured in the smallest specimen with a skull length of 6 mm, the ossification sequence of the postcranium can be reconstructed. Compared to branchiosaurids and Recent urodeles, the ossification of the postcranial skeleton is delayed. For the first time, external gills are described in Micromelerpeton credneri. Their three pairs of branches shorten proportionally during ontogeny. A Cartesian transformation and biometric analyses show allometric changes in the dermal skull roof. Whereas the preorbital region elongates slightly (due to positive allometric growth of nasal length and negative allometric growth of orbits) and grows in width isometrically, the postorbital skull table shows isometry in length (due to positive allometry of frontal length and negative allometry of parietal length) and distinct negative allometry in width (due to negative allometry of parietal and supratemporal width). The interorbital width relatively decreases. The cheek region shows positive allometry both in length and in width, shifting the jaw articulation posteriorly. In this way proportionally more space and attachment area for the adductor musculature are provided and the gape enlarges proportionally. The positive allometric growth of the diameter of the sclerotic ring indicates increased importance of the optical sense. Transformation into the adult stage took place gradually and in a longer period of time during ontogeny than in extant amphibians.
A revised diagnosis and expanded description are presented for the amphiumid salamander Proamphiuma cretacea based on the original topotypic collection of vertebrae and on new atlantes, trunk vertebrae, and caudal vertebrae from the holotype locality. P. cretacea is the type and only species in the genus and is reliably known only from the Bug Creek Anthills (late Maastrichtian or early Paleocene in age), in the Hell Creek Formation, Montana, USA. A referred dentary originally believed to be from the same locality is shown to have come from the upper part (late Paleocene in age) of the Ravenscrag Formation of Saskatchewan, Canada, and is re-interpreted as belonging to an indeterminate amphiumid genus and species. Contrary to a recent claim, P. cretacea is a diagnosable amphiumid taxon and stands as the geologically oldest member of the family. Proamphiuma differs from the type and only other unequivocal amphiumid genus, Amphiuma (four species: late Paleocene–Recent, USA), in primitively retaining weaker vertebral crests and processes. Proamphiuma differs further from the three extant Amphiuma species (conditions unknown for the late Paleocene A. jepseni) in three character states that are potentially autapomorphic within the family—indistinct postzygapophyseal process on atlas, vertebrarterial canal closed posteriorly in trunk vertebrae, and spinal foramen present in anterior caudals—plus vertebral plesiomorphies and one vertebral character state of uncertain polarity. The following relationships are hypothesized within the Amphiumidae: Proamphiuma (A. jepseni (A. pholeter (A. meansA. tridactylum))). This phylogeny and fossil occurrences imply that the characteristic atlanto–cranial joint and elongate trunk and the unique vertebromuscular complex of amphiumids were established by the Cretaceous–Tertiary boundary, while elongation of the snout and associated cranial modifications seen in living amphiumids appeared after the late Paleocene. In terms of its morphology and provenance, Proamphiuma remains a good structural ancestor for, if not directly ancestral to, Amphiuma.
The holotype of Judithemys sukhanovi gen et. sp. nov. from the Late Cretaceous (Campanian) Dinosaur Park Formation of Alberta, Canada, has been included in four cladistic analyses. New material allows for a more complete description of this taxon. Judithemys sukhanovi is represented by 65 specimens (most very fragmentary) including one virtually complete skeleton (the holotype) and several partial shells. It differs from all other “macrobaenids” in the combination of wide vertebral scales, absence of central plastral fontanelles, and lack of strongly upturned peripherals. The morphology of Judithemys reiterates a suite of characters (large size, well-differentiated neurals reduced to eight, and greater overlap of the twelfth marginal scales onto the second suprapygal) common to Late Cretaceous–Paleocene “macrobaenids” and distinct from Early Cretaceous members. Judithemys and “Clemmys” backmani are close in morphology, geography, and stratigraphic position and are possibly closely related phylogenetically. A preliminary phylogenetic analysis supports the hypothesis that Judithemys is not part of the crown group.
Omphalosaurus is a marine reptile known from the latest Early Triassic to the Middle Triassic. It has a wide distribution in the northern hemisphere, occurring in the eastern Pacific realm, in Spitsbergen, and in the western Tethys, but remains poorly known. A recently discovered partial skeleton from the northern Alps is the only specimen showing cranial and postcranial bones together. It is described here in detail and compared to the other known material, especially the holotype skull from Nevada.
Although numerous disarticulated skull bones are present in the Alpine specimen, their identification and interpretation is difficult. The lower jaw and the dentition are sufficiently well preserved to reconstruct morphology, function, and tooth replacement. Remarkably, the snout of Omphalosaurus was rather elongate with the crushing dentition placed anteriorly. The dentition is concentrated along the skull midline and forms a convex upper and concave lower pavement of button-like teeth, set in the premaxillae and the dentaries, respectively. The combination of the forward placement of the dentition and the high tooth replacement rates (as deduced from CT scans) suggests highly abrasive food requring relatively low masticatory forces.
Although ichthyosaurian affinities of Omphalosaurus have been controversial, the postcranial skeleton of the Alpine specimen and an improved understanding of cranial and dental anatomy provides further evidence for such affinities. Omphalosaurus possesses four synapomorphies placing it within the ichthyosaurs (preorbital region distinctly longer than postorbital region, pterygoid flange strongly reduced, interpterygoid vacuity absent or strongly reduced, cervical ribs without distinctive anterior process) and five characters suggestive of ichthyosaurian affinities (splenial contributing extensively to jaw symphysis, shortened vertebral centra, dorsal ribs single-headed and articulating largely with centrum, lack of compact bone, microunit enamel).
Recent discovery of an almost complete skull of Sphagesaurus huenei, a previously poorly known form from the Late Cretaceous of southern Brazil, shows unexpected morphology for a crocodyliform, including an extreme heterodonty with small lower incisors, large upper caniniforms, and reversed triangle-like postcanines; edentulous anterior region of premaxilla; and maxilla with posterior wall over the anterior margin of the suborbital fenestra. The postcanine teeth have extensive wear facets, implying an alternate unilateral occlusion and suggesting the presence of both lateral and fore-aft movement of the jaw. These characteristics appear unique within the crocodyliform lineage, showing that feeding diversity was wider than thought in this clade.
The phylogenetic relationships of Sphagesaurus huenei are evaluated through a parsimony analysis. Sphagesaurus lies within a monophyletic group formed by Cretaceous and Tertiary taxa traditionally referred as notosuchians and sebecosuchians. Interestingly, several mammal-like tooth morphologies were present in this clade of terrestrial crocodyliforms.
Three new specimens of the rare alligatoroid Brachychampsa montana from the upper Campanian Kirtland Formation (De-na-zin Member), San Juan Basin, New Mexico, are the first bona fide examples of this taxon from this stratigraphic interval. The most complete specimen (SMP VP-1312) consists of much of the skull table and snout and a nearly complete mandible. SMP VP-1264 consists solely of an incomplete partial skull table (parietal, right squamosal), partial basicranium (basioccipital, otoccipital), and incomplete right quadrate, whereas NMMNH P-7988 is an isolated frontal. Together, these new specimens supplement and allow for further comparison to other globidontans and to previously documented specimens of Brachychampsa.
?Brachychampsa sealeyi, from the Menefee Formation of the San Juan Basin, New Mexico, is based on a juvenile specimen that cannot be distinguished from B. montana, so it is a subjective junior synonym. The crocodylian assemblage of the Kirtland Formation consists of Brachychampsa montana, Leidyosuchus sp. and Denazinosuchuskirtlandicus. It is doubtful that tooth morphology alone can be correlated with “cheloniphagous” diet within the globidontans.
We report here the first unequivocal record of a pre-Late Pleistocene lizard from the island of Madagascar, based on a nearly complete lower jaw, elements of both the pectoral and pelvic girdles, several vertebrae and ribs, and numerous osteoderms of what is presumed to be a single individual. The specimen, recovered from the Upper Cretaceous (Maastrichtian) Anembalemba Member, Maevarano Formation, Mahajanga Basin, northwestern Madagascar, is identified as a scincoid scincomorph and, more specifically, a new genus and species of ?Cordylidae (Cordyliformes), based on a combination of gnathic, dental, and postcranial characters. The new taxon is the first identifiable lizard from the Late Cretaceous of the African continent (sensu lato).
If the new taxon is correctly attributed to the Cordylidae, it constitutes a significant temporal and geographic range extension for the clade since cordylids have no definite representatives in the fossil record and extant forms are restricted to the sub-Saharan portion of mainland Africa. This new record also indicates that cordylids, after their occurrence in the Maastrichtian, became extinct on Madagascar, leaving only zonosaurine Gerrhosauridae as extant representatives of Cordyliformes on the island. Owing to limited knowledge concerning the time of divergence for cordylids and gerrhosaurids relative to the tectonic separation of Africa and Madagascar, and in light of the paucity of Mesozoic lizard fossils in general, and from Gondwana in particular, the discovery of the new taxon in the Late Cretaceous of Madagascar does little to otherwise constrain scenarios concerning the biogeographic history of early cordyliforms.
Finally, we document here the observation that lizards appear to have been much less speciose than snakes in Late Cretaceous faunas of Gondwana, whereas the reverse is true in Laurasia. Lizards do not appear to become common in Gondwana until the Early Tertiary.
The postcranial skeleton of Ukhaatherium nessovi, a eutherian mammal from the Upper Cretaceous of the Gobi Desert, Mongolia, is described. Nearly the entire skeleton is represented by three skeletal assemblages associated with each other, found at Ukhaa Tolgod, a locality in the Nemegt Basin. Morphological comparisons of Ukhaatherium are made with several other mammals, including placentals, marsupials, and Asioryctes, another Cretaceous eutherian from Mongolia. As has been previously pointed out, Ukhaatherium and Asioryctes possess a number of characters that suggest they occupy a basal position in the eutherian evolutionary tree. Ukhaatherium has epipubic bones, an unexcavated astragalar trochlea, and a depressed calcaneum, among other primitive characters. Derived characters that link it with eutherians include an upper ankle joint which is more restricted to the parasagittal plane than in basal marsupials and other outgroups, and an astragalar neck that is superimposed on the sustentacular facet, as opposed to the condition found in metatherians and other outgroups, in which the sustentacular facet is either medial to the astragalus, or it is ventral to the astragalar neck but the latter overhangs the sustentacular facet medially. Ukhaatherium offers some intermediate conditions between placentals and its outgroups which facilitate a better understanding of character evolution at the root of Placentalia.
A reanalysis of the upper and lower molar morphology of the early Paleocene marsupial Roberthoffstetteria nationalgeographica led to an interpretation of the molar homologies of the Polydolopinae (Polydolopimorphia). Several derived features support the attribution of Roberthoffstetteria to the Polydolopimorphia: thick dentary, molars with thick enamel, upper molars with reduced preparacrista that points to stylar cusp A, open centrocrista (that is, postparacrista not connected to the premetacrista), and metaconule large to very large, forming a “hypocone.” Other derived features support the monophyly of Roberthoffstetteria polydolopines: alignment of paraconule, protocone, and metaconule in a lingual row; well-expanded anterior and posterior cingula, which are level with the trigon basin; variable occurrence of accessory cuspules at the labial face of the upper molars; and the labially placed paraconid with respect to the metaconid in the lower molars. Both Roberthoffstetteria and the polydolopines are plesiomorphic in having stylar cusp E, which is absent in most other South American marsupials. Several character complexes may be involved in the evolution of the polydolopine molar pattern.
The origin of the small, Miocene horse Archaeohippus is poorly known. A recently collected specimen from the late Oligocene or earliest Miocene (Arikareean) of Florida represents Archaeohippus mannulus, sp. nov. It includes a complete upper dentition, a partial left dentary with dp1–m3, and most of the right and left manus. It is the most nearly complete skeleton of an Arikareean Archaeohippus. Distinguishing characteristics of A. mannulus include: on upper P2–P3, anteroposteriorly narrow hypocone with a pronounced medivallum ridge originating on the metaloph; lower cheek teeth with a mediolaterally broad and flat hypoconulid; and extremely small body size with very gracile limb elements. Body mass of this individual is estimated at 10 kg. The revised generic diagnosis includes derived features of Archaeohippus relative to Miohippus and Anchitherium such as crochets on upper cheek teeth and reduced tridactyly, which link it with Parahippus, merychippine-grade equids, hipparionines, and equines.
Thalassocnus antiquus, sp. nov., is a marine nothrothere from the late Miocene Aguada de Lomas vertebrate horizon (ca. 7 to 8 Ma) of the Pisco Formation in the Sacaco area of the southern coast of Peru. It is similar to the slightly younger latest Miocene Thalassocnus natans, but smaller and distinctly more gracile. The sloping morphology of the lateral border of the nares in T. antiquus differs from the probably plesiomorphic subvertical edge of the nares in T. natans. Parsimony analysis does not resolve the relative positions of T. antiquus and T. natans, and, therefore, does not fully confirm the possibility of a single Thalassocnus lineage, which spans over 4 Ma. However, Thalassocnus is an endemic genus and the stratigraphic distribution of its four species is well known. Furthermore, some characters indicate a continuous evolution from the oldest (T. antiquus) to the youngest species (T. carolomartini). Therefore, we prefer the hypothesis of a single Thalassocnus lineage, although a more complex evolutionary scenario is not discarded.
An isolated upper fourth premolar (P4) of the extinct red panda Parailurus was recovered from the Pliocene (3–4 Ma) Ushigakubi Formation near Tochio, Niigata Prefecture, Japan. This is the first report of Parailurus from Asia, a genus previously known from Europe and northwestern North America. The Tochio P4 is about 50 percent larger than that of the extant Ailurus fulgens, lacks an entostyle, but has a lingual cingulum, protoloph with paraconule, a marked posterior cingulum with fine wrinkles, and a distal buccolingual groove. The transverse width of the P4 is greater than the anteroposterior length; the reverse is true of Parailurus anglicus from Europe.
Mammalian fossils of the Konso Formation (southwestern Main Ethiopian Rift) derive from stratigraphic intervals dated to between 2.0 Ma and younger than 1.3 Ma. Systematic paleontological collecting resulted in almost 8,000 identifiable mammalian specimens representing 8 orders, 22 families, and more than 68 species including Australopithecus boisei and Homo erectus. Despite geographic proximity to the Turkana Basin (approximately 200 km), aspects of the Konso fauna are distinctive, with its 1.9–1.7 Ma assemblage showing some degree of endemism. Bovids Megalotragus, Parmularius altidens, Parmularius eppsi, Menelikia, and Pelorovis, all common at Turkana and/or Olduvai, are rare or absent at Konso, while Parmularius cf. pandatus, Simatherium, and Notochoerus n. sp. of the Konso assemblages are the youngest known records of these taxa in eastern Africa. The dominant suid of this assemblage is Kolpochoerus majus, a previously poorly known taxon. Subsequent to circa 1.7 Ma, an influx of external elements occurred, possibly related to a general East African trend of climatic drying between 1.8 and 1.6 Ma. The post-1.5 Ma Konso fauna is characterized by apparently immigrant dry grassland adapted bovids, such as Damaliscus niro and Parmularius angusticornis. Metridiochoerus compactus, Metridiochoerus hopwoodi and Metridiochoerus modestus are common in the 1.5 to 1.3 Ma levels at Konso, whereas the latter two suids are rare at Turkana. The post-1.5 Ma Kolpochoerus limnetes/olduvaiensis of Konso is morphologically more conservative than time-equivalent Turkana specimens. The post-1.5 Ma Konso Elephas recki represents an evolutionary grade immediately preceding the fully advanced E. recki recki condition.
Synaptomys morgani, sp. nov. is described from the early Pleistocene (ca. 1.0–1.6 Ma) of Florida. It is more primitive in certain features than Synaptomys cooperi and Synaptomys australis, and in one evolutionary scenario may be ancestral to both, assuming S. australis is distinct from S. cooperi. The schmelzmuster, or microscopic enamel prism banding pattern, is described for samples of extinct and extant bog lemmings from North America. Two hypotheses for the origin of Synaptomys are considered. The first, a revision of the Repenning and Grady concept of a rapid origin of Synaptomys from Mictomys, holds that the Cheetah Room population of Synaptomys from Hamilton Cave, West Virginia, evolved from Mictomys landesi or a related species, probably between 1.3 and 1.6 Ma. The second proposes that Synaptomys originated from a North American species similar to Plioctomys rinkeri. Based on current information, neither hypothesis can be rejected. Mictomys kansasensis from the Java l.f. of South Dakota appears more primitive than populations of this species from other early Pleistocene Great Plains localities, as the trailing edges of triangles in upper and lower molars in the Java sample retain thicker layers of lemming enamel. The “long” condition of the lower incisor (growing end of the incisor posterior to m3), previously assumed to be primitive, appears to be derived for Synaptomys.