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Journal of Vertebrate Paleontology, Volume 40, Issue sup1 (2020)
Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar
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Adalatherium hui is a latest Cretaceous (Maastrichtian) gondwanatherian mammal based on only a single specimen, a virtually complete, articulated, and well-preserved skull and postcranial skeleton. The specimen is the most complete and best preserved of any mammaliaform from the Mesozoic of the southern supercontinent Gondwana. It was discovered in the Anembalemba Member of the Maevarano Formation in the Mahajanga Basin of northwestern Madagascar. The holotype specimen includes the only complete lower jaw and the only postcranial remains known for Gondwanatheria, which, other than the cranium of Vintana sertichi (also from the latest Cretaceous of Madagascar), are represented only by isolated teeth and fragmentary dentaries. Despite being represented by an immature individual, A. hui is third only to V. sertichi and Coloniatherium cilinskii as the largest Mesozoic mammaliaform (based on body fossils) from Gondwana. Here, we (1) review the paucity of mammaliamorph skull and postcranial skeletal material from the Mesozoic of Gondwana relative to the record from Laurasia; (2) review the systematic paleontology of A. hui; (3) provide an overview of the history of discovery of the holotype specimen; (4) detail the preservation of the holotype, its preparation history, and the imaging techniques used to study it; (5) provide an overview of the geological context of A. hui, which indicates that the species lived close to the end-Cretaceous extinction event in a highly seasonal, semiarid climate; and (6) estimate the body mass of A. hui in the context of other Mesozoic mammaliaforms.
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David W. Krause, Simone Hoffmann, James B. Rossie, Yaoming Hu, John R. Wible, Guillermo W. Rougier, E. Christopher Kirk & Joseph R. Groenke (2020)
Craniofacial morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar.
Journal of Vertebrate Paleontology 40 Supplement 1: Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: 19-66
DOI: 10.1080/02724634.2020.1808665
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1808665The cranium of Adalatherium hui, as represented in the holotype and only specimen (UA 9030), is only the second known for any gondwanatherian mammal, the other being that of the sudamericid Vintana sertichi. Both Adalatherium and Vintana were recovered from the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar. UA 9030 is the most complete specimen of a gondwanatherian yet known and includes, in addition to the cranium, both lower jaws and a complete postcranial skeleton. Aside from Adalatherium and Vintana, gondwanatherians are otherwise represented only by isolated teeth and lower jaw fragments, belonging to eight monotypic genera from Late Cretaceous and Paleogene horizons of Madagascar, the Indian subcontinent, Africa, South America, and the Antarctic Peninsula. Although the anterior part of the cranium is very well preserved in UA 9030, the posterior part is not. Nonetheless, comparable parts of the crania of Adalatherium and Vintana indicate some level of common ancestry through possession of several synapomorphies, primarily related to the bony composition, articular relationships, and features of the snout region. Overprinted on this shared morphology are a host of autapomorphic features in each genus, some unique among mammaliaforms and some convergent upon therian mammals. The cranium of Adalatherium is compared with the crania of other mammaliamorphs, particularly those of allotherians or purported allotherians (i.e., haramiyidans, euharamiyidans, multituberculates, Cifelliodon, and Megaconus). Particular emphasis is placed on several recently described forms: the enigmatic Cifelliodon from the Early Cretaceous of Utah and several new taxa of euharamiyidans from the Late Jurassic of China.
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Simone Hoffmann & E. Christopher Kirk (2020)
Inner ear morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar.
Journal of Vertebrate Paleontology 40 Supplement 1: Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: 67-80
DOI: 10.1080/02724634.2020.1800719
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1800719
The cochlear canal of Adalatherium hui, from the Late Cretaceous of Madagascar, exhibits a combination of features previously unknown among mammaliaforms. The cochlear canal of Adalatherium is short and âCâ-shaped (curved through at least 210Â). A presumptive lagenar nerve canal extends from the apex of the cochlea to the internal acoustic meatus. In conjunction with an apical expansion of the cochlear canal, this morphology suggests that Adalatherium retained a lagenar macula. Adalatherium is derived among mammaliaforms in possessing primary and secondary osseous laminae, a cribriform plate, and a distinct cochlear ganglion canal. Strikingly, Adalatherium shows a single-layered primary osseous lamina that lacks internal, radially oriented canaliculi for auditory nerve fibers. In this respect, the primary lamina of Adalatherium is structurally different from the double-layered primary lamina containing habenulae perforatae of extant therians. Furthermore, Adalatherium resembles the gondwanatherian Vintana in possessing a secondary canal running parallel to the cochlear ganglion canal. Although its exact role and homology are uncertain, the morphology of this secondary canal and its tributary canaliculi is most consistent with a vascular function. The inner ear of Adalatherium augments a growing list of characters (or character combinations) in which gondwanatherians are not only different from the inferred plesiomorphic condition for mammaliaforms but also distinct from the derived characters of therians. Collectively, the new morphological and phylogenetic data support homoplastic transformation of such structures as the cribriform plate and primary osseous lamina in mammals and independent loss of the lagenar macula within gondwanatherians.
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David W. Krause, Simone Hoffmann, John R. Wible & Guillermo W. Rougier (2020)
Lower jaw morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar.
Journal of Vertebrate Paleontology 40 Supplement 1: Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: 81-96
DOI: 10.1080/02724634.2020.1805456
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1805456
The lower jaw of the holotype of Adalatherium hui, from the Late Cretaceous of Madagascar, is the most complete yet known for a gondwanatherian mammal. It reveals for the first time the morphology of the character-rich ascending ramus of the dentary in a gondwanatherian. Each half of the lower jaw is composed of only one bone, the dentary, which is short and deep and houses only five teeth: an enlarged, procumbent incisor and four postcanine teeth. In comparable parts of its anatomy, the dentary of Adalatherium is strikingly similar to that of Sudamerica but differs slightly from that of Galulatherium (conformation anterior to first postcanine, mental foramen position), the only two other gondwanatherians represented by complete horizontal rami. Among other Mesozoic mammaliaform taxa, the dentary of Adalatherium is most similar to those of the largely Laurasian group Multituberculata, most notably in absence of postdentary trough and Meckelian sulcus; presence of short, deep dentary with sizable diastema and articulating with squamosal via mediolaterally narrow condyle that continues onto posterior surface (i.e., no distinct peduncle); possession of much reduced dentition; absence of angular process; possession of large pterygoid fossa and pterygoid shelf, ventral surface of which is flat; absence of coronoid bone; and possession of unfused mandibular symphysis. Most of these features are clearly derived and stand in stark contrast to the much more plesiomorphic morphology exhibited by the lower jaw of the haramiyaviid Haramiyavia. The lower jaws of euharamiyidans, although derived in their own right, are also relatively plesiomorphic.
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David W. Krause, Yaoming Hu, Simone Hoffmann, Joseph R. Groenke, Julia A. Schultz, Alistair R. Evans, Wighart von Koenigswald & Guillermo W. Rougier (2020)
Dental morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar.
Journal of Vertebrate Paleontology 40 Supplement 1: Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: 97-132
DOI: 10.1080/02724634.2020.1811292
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1811292 The dentition in the only known specimen of Adalatherium hui, a gondwanatherian mammal from the Late Cretaceous of Madagascar, is markedly different from that of any previously known mammaliaform, extinct or extant. The two preserved upper incisors and single lower incisor of Adalatherium are each very large, open-rooted, and bear a restricted band of enamel. A shallow-rooted, rudimentary upper canine is present. The upper postcanine dentition is composed of a small, simple, two-rooted tooth mesially and four large, multiple-rooted (five roots or more) teeth distally. The latter are quadrangular in outline, each with four major cusps and three perimetric ridges bordering a central valley that opens buccally. There are four lower postcanines, also with four major cusps each. The first postcanine has two roots, but the following ones each have (or likely had) at least four. The two distal lower postcanines bear a prominent mesiobuccal basin. The cusps and other topographic features of the postcanines cannot be unambiguously homologized with those of other known mammaliaforms. Diastemata are present in the upper dentition between the incisors and canines and between the canines and postcanines, and in the lower dentition between the incisors and postcanines. Adalatherium, like several gondwanatherians from the Late Cretaceous and Paleogene of Argentina, retains relatively plesiomorphic, ânormalâ radial enamel (i.e., single-layered schmelzmuster, non-decussating small prisms, interprismatic matrix anastomosing around prisms). This stands in contrast to the modified radial enamel found in other gondwanatherians from the Late Cretaceous of India and Madagascar, which exhibit prominent interrow sheets of interprismatic matrix.
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Simone Hoffmann, Yaoming Hu & David W. Krause (2020)
Postcranial Morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar.
Journal of Vertebrate Paleontology 40 Supplement 1: Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: 133-212
DOI: 10.1080/02724634.2020.1799818
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1799818 The holotype and only known specimen of Adalatherium hui from the Late Cretaceous of Madagascar preserves the first postcranial skeleton for the Gondwanatheria. It represents only the fourth Mesozoic mammaliaform described from articulated postcranial material from Gondwana (the others being the morganucodontans Megazostrodon and Erythrotherium and the stem therian Vincelestes). The postcranial skeleton of Adalatherium is virtually complete, and its preservation is exceptional; even costal cartilages and manual and pedal sesamoids are preserved. Adalatherium exhibits a variety of derived and plesiomorphic traits, probably reflective of a long evolutionary history in geographic isolation on Madagascar. Among the bizarre features are a mediolaterally compressed and anteroposteriorly bowed tibia, an unusually high number of trunk vertebrae (at least 16 thoracic and 12 lumbar vertebrae), a short tail, and a trochleated navicular facet on the astragalus. Aside from these features, Adalatherium displays derived and plesiomorphic characteristics in its pectoral girdle: the coracoid is well developed and contributes to half of the glenoid fossa, a separate procoracoid is absent, and the sternoclavicular joint appears to have been mobile. A ventrally facing scapular glenoid and the well-developed humeral trochlea suggest a relatively parasagittal forelimb posture. Notable features of the hind limb and pelvic girdle include a large obturator foramen similar in size to that of therians, a large parafibula, and the presence of epipubic bones. Articulation between the pelvic girdle and hind limb is in contrast to that between the pectoral girdle and the forelimb in that it is indicative of a sprawling posture.
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Simone Hoffmann, Robin M. D. Beck, John R. Wible, Guillermo W. Rougier & David W. Krause (2020)
Phylogenetic placement of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: implications for allotherian relationships.
Journal of Vertebrate Paleontology 40 Supplement 1: Memoir 21: Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: 213-234
DOI: 10.1080/02724634.2020.1801706
https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1801706The phylogenetic position of Gondwanatheria within Mammaliaformes has historically been controversial. The well-preserved skeleton of Adalatherium hui from the Late Cretaceous of Madagascar offers a unique opportunity to address this issue, based on morphological data from the whole skeleton. Gondwanatheria were, until recently, known only from fragmentary dental and mandibular material, as well as a single cranium. The holotype of A. hui provides the first postcranial skeleton for gondwanatherians and substantially increases the amount of character data available to score. We sampled 530 characters and 84 cynodonts (including 34 taxa historically affiliated with Allotheria) to test the phylogenetic relationships of Gondwanatheria and Allotheria using parsimony, undated Bayesian, and tip-dated Bayesian methods. We tested three lower dental formulae for Adalatherium, because its postcanines are distinctly different from those of other mammaliaforms and cannot readily be homologized with any known dental pattern. In all analyses, Adalatherium is recovered within Gondwanatheria, most frequently outside of Sudamericidae or Ferugliotheriidae, which is congruent with establishment of the family Adalatheriidae. The different dental coding schemes do not greatly impact the position of Adalatherium, although there are differences in character optimization. In all analyses, Gondwanatheria are placed within Allotheria, either as sister to Multituberculata, nested within Multituberculata, or as sister to Cifelliodon (and Euharamiyida), or in a polytomy with other allotherians. The composition of Allotheria varies in our analyses. The haramiyidans Haramiyavia and Thomasia are placed outside of Allotheria in the parsimony and tip-dated Bayesian analyses, but in a polytomy with other allotherians in the undated Bayesian analyses.
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