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Lameta Formation
Lameta Formation
Lameta Formation
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The Lameta Formation, also known as the Infratrappean Beds (not to be confused with the contemporaneous Intertrappean Beds), is a sedimentary geological formation found in Madhya Pradesh, Gujarat, Maharashtra, Telangana, and Andhra Pradesh, India, associated with the Deccan Traps.[1] It is of the Maastrichtian age (Late Cretaceous), and is notable for its dinosaur fossils.

Key Information

History

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The first fossils found in the Lameta Formation were discovered between 1917 and 1919.[2]

The Lameta Formation was first identified in 1981 by geologists working for the Geological Survey of India (GSI), G. N. Dwivedi and Dhananjay Mahendrakumar Mohabey, after being given limestone structures–later recognised as dinosaur eggs–by workers of the ACC Cement Quarry in the village of Rahioli near the city Balasinor in the Gujarat state of western India.[3]

Lithology

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Paleoart of the Deccan trap illustrating the paleoenvironment of Lameta formation

The formation is underlain by the Lower Cretaceous sedimentary "Upper Gondwana Sequence" also known as the Jabalpur Formation, and is overlain by the Deccan Traps basalt. The Lameta Formation is only exposed at the surface as small isolated outcrops associated with the Satpura Fault. The lithology of the formation, depending on the outcrop, consists of alternating clay, siltstone and sandstone facies, deposited in fluvial and lacustrine conditions. The environment at the time of deposition has alternatively been considered semi-arid, or tropical humid.[4][5]

Fossil content

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Many dubious names have been created for isolated bones, but several genera of dinosaurs from these rocks are well-supported, including the titanosaur sauropods Isisaurus and Jainosaurus and the Abelisaurs Indosaurus, Indosuchus, and Rajasaurus and Noasaurids Laevisuchus.[6] Synapsids are also known form the formation, such as the possibly late surviving Avashishta,possibly the last known non- mammalian synapsid the possibly youngest known stegosaurian ichnogenus Deltapodus, madtsoiid snakes and other fossils.

Dinosaurs

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Dinosaurs of Lameta Formation in which a group of Rajasaurus (Middle) hunting an Isisaurus (Middle) with an Indosuchus (bottom left) watching it with her chicks and a Laevisuchus (Bottom right) running with two Jainosaurus (Top Left) in the background
Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Ornithischians

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Genus Species Location Stratigraphic position Material Notes Images
Ankylosauria? Indeterminate Rahioli Isolated vertebrae, scapulocoracoid, humerus, femur, and several armor fragments such as hollow lateral spikes and solid dorsal scutes.[7] Described as a nodosaurid, but the limb bones are titanosaurian.[8]
Brachypodosaurus B. gravis Chota Simla Hill "Humerus."[9] May not be dinosaurian
Ceratopsia? Indeterminate Kheda Horncore base. Originally described as a ceratopsian horncore,[10] but likely represents a theropod limb element or a dorsal rib of a theropod or a titanosauriform.[11]
Deltapodus[12] sp. Jetholi Solitary footprint. A Possible Late Cretaceous Stegosaur, Like Dravidosaurus.
Hypsilophodontidae?[13] Indeterminate. Vikarabad. Teeth. Hypsilophodontidae is not a natural grouping.
Ornithischia[14] Indeterminate Kheda Braincase. Indeterminate Ornithischian.
Spheroolithus? sp. Polgaon,

Tidkepar

Egg fossils. Questionably assigned to this genus[15]

Sauropods

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Genus Species Location Stratigraphic position Material Notes Images
Isisaurus I. colberti Dongargaon Hill Holotype skeleton consists of cervical, dorsal, sacral, caudal vertebrae, ribs, pelvis, scapula, coracoid, left forelimb, and other bones. Other specimens, such as the skull, hindlimb, and foot bones, are unknown. A lithostrotian titanosaur.
Isisaurus
Jainosaurus
Megaloolithus
Jainosaurus J. septentrionalis Bara Simla "Basicranium and partial postcranial skeleton."[16] A titanosaur
Titanosaurus T. blanfordi
  • Panchgaon
  • Pisdura Hill
 Caudal vertebrae.[17] A dubious genus of titanosaur.[18]
T. indicus Pisdura Hill Teeths, Caudal vertebrae and chevron.[19]
Megaloolithus[20] M. cylindricus Chui Hill, Bara Simla, Nand region, Pavan, Ghorpend, Bagh Caves, Dhar, Indwan, Kadwal, Dholiya Raipuriya village, Akhada village, Jhaba village, Padlya village, Jhabua, Dohad, Jhalod, Garadi, Kheda, Rahioli, Dholi Dungri. Multiple specimens consist of fossilized egg shells that are covered in volcanic sediments Sauropod egg fossils
M. dhoridungriensis
M. jabalpurensis
M. khempurensis
M. megadermus
M. problematica
M. walpurensis
M. sp.
Titanosauriform[21] Indeterminate Ukala. Dorsal vertebrae, parts of the ilia and pelvis, and limb bones. A titanosauriform.

Theropods

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Abelisaurs
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Genus Species Location Stratigraphic position Material Notes Images
Abelisauroidea Indeterminate Multiple specimens.[22] Could be referred to Abelisauridae or Noasauridae.[23]
Rajasaurus
Indosuchus
Rahiolisaurus
Abelisauridae Indeterminate Multiple specimens. Include form similar to Majungasaurus and forms similar to Carnotaurus.[22]
Compsosuchus C. solus Bara Simla "Vertebrae" Previously considered a Noasaurid now considered an indeterminate Abelisaurid[24]
Indosaurus I. matleyi Bara Simla Partial skeleton, including a partial skull.[25] An abelisaurid
Dryptosauroides D. grandis Bara Simla "Vertebrae."[26] An abelisaurd
Ellipsoolithus[27] E. khedaensis Kheda Eggs Theropod egg fossils.
Indosuchus I. raptorius Bara Simla Cranial remains, including two braincases, as well as a nearly complete skeleton.[25] An abelisaurid
Ornithomimoides O. barasimlensis Bara Simla "Vertebrae."[26] An abelisaurid[28]
O. mobilis Bara Simla "Vertebrae"[26]
Orthogoniosaurus O. matleyi Bara Simla "Tooth"[26] An abelisaurid[29]
Rahiolisaurus R. gujaratensis Rahioli Village Cervical, dorsal, sacral, and caudal vertebrae, portions of pectoral and pelvic girdles, and several hind limb bones of different individuals. An Abelisaurid
Rajasaurus R. narmadensis Temple Hill, Rahioli A partial skeleton consists of maxillae, premaxillae, braincase, and quadrate bone on the skull; and spine, hip bone, legs, and tail in post-cranial remains. An Abelisaurid
Noasaurids
[edit]
Genus Species Location Stratigraphic position Material Notes Images
Laevisuchus L. indicus Bara Simla Only vertebrae.[25] A noasaurid.
Noasaurinae Indeterminate Pisdura Hill A partial dentary.[28] A noasaurine noasaurid.
Noasauridae Indeterminate Multiple specimens.[22] May include femora from very large individuals.[23]
Other Theropods
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Genus Species Location Stratigraphic position Material Notes Images
Coeluroides C. largus Bara Simla "Isolated vertebrae."[26] A Indeterminate theropod also known from Dabrazhin Formation of Kazakhstan
Jubbulpuria J. tenuis Bara Simla "Vertebrae."[26] Likely junior synonym of Laevisuchus[28]
?Megalosaurus Referred to as the 'E' morphotype Rahioli A solitary tooth.[30] Originally identified as belonging to Megalosaurus, however may instead represent a troodontid.[31]
Ornithomimidae?[32] Indeterminate Bara Simla Ceratosaurian taxa from the Lameta Formation have been erroneously referred to ornithomimdae.
Theropoda Indeterminate Cervical vertebra. Initially described as allosauroid. Not an abelisaurid, possibly representing a member of a clade outside of abelisauroidea.[22]
Trachoolithus[33] T. faticanus Bara Simla Eggs. Theropod egg fossils.

Indeterminate or chimaeric taxa

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Genus Species Location Stratigraphic position Material Notes Images
"Dubeynarainsaurus" "D. sahni" Sirolkhal "Partial dentary with associated teeth."[34] May instead be a later cretaceous pterosaur,[34] proposed to be either belonging to the Infratrappean or Intertrappean beds, although if it were a pterosaur it would not be Maastrichtian.[35]
Lametasaurus L. indicus Bara Simla "Sacrum, ilia, tibia."[26] "Sacrum, ilia, tibia, spines, armor."[36] Includes crocodylomorph, titanosaur scutes and possibly ankylosaurian osteoderms.[8] Also includes abelisaurid material now removed from the type and is being assigned to the Rajasaurus.[3]

Reptiles

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Snakes

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Genus Species Location Stratigraphic position Material Notes Images
Madtsoia M. pisdurensis[37] Pidura Hill Upper A madtsoiid snake.
Sanajeh S. indicus Dholi Dungri A skull, precloaca vertebrae and ribs. A madtsoiid snake.
Sanajeh about to attack a titanosaur hatchling

Crocodylomorphs

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Genus Species Location Stratigraphic position Material Notes Images
Dyrosauridae[38][13][39] Indeterminate. Kisalpuri and Vikarabad. Vertebrae, eggs and teeth. Non-Phosphatosaurinae Dyrosaurid Crocodylomorphs.

Turtles

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Genus Species Location Stratigraphic position Material Notes Images
Jainemys J. pisdurensis Pisdura hill A bothremydid side-necked turtle.
Pelomedusidae[40][41] Indeterminate A turtle.

Mammals

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Genus Species Location Stratigraphic position Material Notes Images
Avashishta A. bacharamensis[42] Bacharam A Haramiyida Mammal.

Mollusca

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Genus Species Location Notes
Mollusca Indeterminate
Gastropoda Indeterminate
Viviparus V. normalis
Physa P. sp.
Paludina P. deccanensis
Lymnaea L. subulata
Unio U. sp.

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Lameta Formation

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The Lameta Formation is a () sedimentary geological formation exposed across central and western India, primarily in the Narmada Basin spanning , , and . It overlies older units such as the Jabalpur Formation with a paraconformity or and is unconformably capped by the volcanic sequence, marking the terminal infra-trappean deposits associated with the Deccan Large Igneous Province. The formation, named after its type section at Lameta Ghat near , attains thicknesses of 18 to 45 meters and is dated to the late (ca. 70–66 Ma), with recent paleomagnetic studies constraining parts to ~67 Ma within Chron C30N or adjacent to magnetic Chron C29R (ca. 66.4–65.7 Ma). Comprising a sequence of lithofacies that reflect a fluvial to pedogenic , the Lameta Formation is divided into distinct units including the basal Green Sandstone (calcareous and glauconitic), Lower Limestone (freshwater carbonates with charophytes), Mottled Nodular Bed (pedogenic calcretes and nodular limestones), and Upper Calcified Sandstone (carbonate-cemented sands). These deposits, formed over a few hundred thousand years, exhibit evidence of semi-arid to sub-humid palaeoclimates with episodic aridity, influenced by evapotranspirative processes and calcium sourcing from underlying marbles. Multiproxy analyses, including micromorphology, , and stable isotopes, indicate a palaeoenvironment dominated by seasonal rivers, wetlands, and development under varying precipitation regimes tied to Deccan volcanic activity. The Lameta Formation holds significant palaeontological value as one of the few dinosaur-bearing units globally, yielding skeletal remains of titanosaurian sauropods (e.g., , ) and abelisaurid theropods (e.g., ), alongside possible ankylosaur fragments and a rare troodontid tooth suggesting faunal exchange. It is particularly noted for extensive dinosaur nesting sites over 1,000 km across its outcrops, preserving eggshells of the oofamily Megaloolithidae (e.g., Megaloolithus cylindricus) in fluvial sediments, which indicate colonial breeding behaviors among sauropods. These fossils underscore biogeographic links between and , reflecting dispersal patterns before the -Paleogene extinction. Associated non-dinosaurian remains include turtles, fishes, ostracods, and palynomorphs like Aquilapollenites indicus, enriching reconstructions of the latest .

Geological Context

Geographic Extent and Type Localities

The Lameta Formation is primarily exposed across central and western India, with major outcrops in Madhya Pradesh (including the Jabalpur and Bagh areas), Gujarat (particularly Kheda District), Maharashtra, and extending eastward to Andhra Pradesh. These exposures occur in a patchwork distribution, largely preserved beneath the overlying Deccan Traps volcanic sequence, where erosion has revealed the underlying sediments in isolated basins along river valleys such as the Narmada. The formation's preservation is uneven due to post-depositional erosion and tectonic activity that has differentially exposed sections. The type locality of the Lameta Formation is designated at Lameta Ghat, a prominent exposure along the near in , where the sequence was first systematically described. Additional key sites include Bara Simla Hill, also near , which provides well-preserved sections representative of the formation's typical , as well as exposures in the Narmada Valley and surrounding regions that have been critical for regional mapping. These localities, often interbedded with or underlying the , serve as reference points for correlating the Lameta Formation with infratrappean beds across the Indian peninsula. Thickness of the Lameta Formation varies regionally from about 20 to 50 meters, with thinner sections (around 12-18 m) in areas like , and thicker accumulations (up to 45 m) near , influenced by local tectonic and depositional controls. This variability reflects the formation's deposition in a series of interconnected fluvial-lacustrine basins prior to the extensive volcanism of the .

Age and Stratigraphy

The Lameta Formation is dated to the stage of the , spanning approximately 72 to 66 million years ago, with recent studies constraining it to 72.17–70.33 Ma during magnetic Chron C29R. This age assignment is supported by multiple lines of evidence, including based on non-marine ostracode assemblages, such as those dominated by genera like Cypridea and Paracypris, which characterize Maastrichtian zones in Indian Gondwanan deposits. Magnetostratigraphic studies of the formation's sedimentary sections reveal a polarity sequence consistent with Chron C29R, aligning it with the global Cretaceous-Paleogene boundary timeline. Additionally, U-Pb dating of interbedded or immediately overlying Deccan Trap volcanics constrains the upper limit of the formation to just prior to the main eruptive phase at around 66.04 ± 0.05 Ma, confirming its pre-extinction placement. Stratigraphically, the Lameta Formation occupies the uppermost position in the sequence of , directly underlying the and representing the final pre-volcanic sedimentary unit. In its type area near , it is divided into units including the basal Green Sandstone (calcareous and glauconitic), Lower Limestone (freshwater carbonates with charophytes), Mottled Nodular Bed (pedogenic calcretes and nodular limestones), and Upper Calcified Sandstone (carbonate-cemented sands), with total thicknesses ranging from 20 to 50 meters depending on local preservation. The basal boundary is an over older sediments, such as the underlying Jabalpur Formation, marking a significant hiatus in deposition. The upper boundary features a sharp, conformable to paraconformable contact with the overlying intertrappean beds and the basal lavas, indicating minimal erosion prior to the onset of . Regionally, the Lameta Formation correlates with other units in , such as the Kallamedu Formation in the Cauvery Basin, based on shared biostratigraphic markers including charophyte and ostracode taxa, as well as continental vertebrate elements like titanosaurian dinosaurs and crocodyliforms. Globally, it shows faunal affinities with the of the , particularly through comparable assemblages of abelisaurid theropods, hadrosaurids, and multituberculate mammals, suggesting biotic exchanges across Gondwana-Laurasia connections in the latest .

Research History

Early Discoveries and Naming

The initial geological surveys of in the early laid the groundwork for recognizing the sedimentary layers now known as the Lameta Formation, with the term "Lameta beds" appearing in reports by the starting in the mid-1800s to describe the distinctive and sandstone exposures underlying the . The name was formally established as the "Lameta Formation" by H.B. Medlicott in 1860, honoring the prominent outcrops at Lameta Ghat along the near , , where these strata are prominently exposed. These early surveys, conducted amid broader mapping efforts by British geologists, highlighted the unit's intercalation with volcanic rocks, though its precise stratigraphic significance remained unclear at the time. The first dinosaur fossils from the Lameta Formation were uncovered in 1828 by Captain W.H. Sleeman of the Bengal Army, who collected isolated caudal vertebrae of a sauropod near Jabalpur while surveying the Narmada Valley; these remains were later identified as belonging to a titanosauriform. Systematic paleontological exploration began in earnest between 1917 and 1919, when Charles A. Matley, working for the Geological Survey of India, led excavations in the Jabalpur region, recovering numerous sauropod vertebrae and other fragments from sites like Bara Simla Hill. Matley's efforts marked the first major concentrated collection from the formation, yielding over 200 specimens that included early evidence of diverse dinosaurian taxa. Key early publications advanced understanding of these finds, including Matley's 1923 description of an armored (Minmi-like ornithischian) based on osteoderms from , and his collaboration with Friedrich von Huene in 1933, which detailed theropod and ornithischian fragments such as those assigned to and Lametasaurus. In 1922, American paleontologist toured and collected carnosaur (theropod) remains from Lameta exposures, contributing informal notes that highlighted the formation's potential for large predatory s, though these were not formally published until later integrations. Early interpretations placed the Lameta Formation in the Eocene due to its stratigraphic position beneath the , which were then dated to the early Tertiary based on limited evidence and regional correlations. This misattribution persisted until the , when palynological analyses of spores and from the strata, including studies revealing Gondwanan assemblages, firmly established its Late () age.

Key Paleontological Expeditions

During the 1970s and 1980s, paleontologist P. M. Mohabey of the led key expeditions in central and western India, focusing on the Lameta Formation's vertebrate remains. These efforts uncovered significant eggshell fragments and nesting sites at Dongargaon in Maharashtra's Nand-Dongargaon Basin, where articulated skeletons and eggs were documented in calcareous sandstones, and at in Gujarat's Balasinor-Jhabua Basin, yielding additional eggshell assemblages in infratrappean limestones. In the , ongoing debates centered on the precise placement of the Cretaceous-Paleogene (K-Pg) boundary within or near the Lameta Formation, with some interpretations suggesting parts might postdate the boundary due to stratigraphic overlaps with early . These uncertainties were largely resolved in the through high-precision U-Pb of crystals from the , which established the main eruptive phase as beginning around 66.04 Ma, contemporaneous with the Chicxulub impact and firmly anchoring the underlying Lameta Formation to the stage of the . Post-2010 research has advanced through targeted field surveys, including the 2023 documentation of 92 titanosaur clutches containing 256 from the Lameta Formation in Dhar District, , by a team led by Dhanvan Singh, enhancing understanding of reproductive behaviors in the formation's biota. Ongoing surveys have revealed new theropod material, such as abelisaurid fossils from Rahioli in , contributing to refined biostratigraphic correlations. International collaborations, notably French-Indian teams in the , applied to Deccan intertrappean sequences overlying the Lameta, confirming its age through polarity zone matches with global standards. These expeditions built upon initial 1910s discoveries of bones in the Narmada Valley, shifting focus to systematic recovery and geochronological integration.

Sedimentology and Depositional Environment

Lithological Composition

The Lameta Formation primarily consists of interbedded limestones, sandstones, mudstones, and minor conglomerates. The limestones, which form prominent units such as the Lower and Upper Limestones, are predominantly and composed mainly of algal-derived grains, often containing fragments including bioclasts and shell debris in a micritic matrix. Sandstones vary from subarkosic to quartzose types, with content ranging from trace amounts to around 5-15% in some localities alongside (often >95% of grains), bioclasts, and ; grains are subangular to subrounded and poorly to moderately sorted, while mudstones include clay-rich layers with , , , , and . Heavy minerals in the sandstones and mudstones are sparse but include , , , , , and opaques, with minor iron oxides and silica cementation. Palaeosol horizons, particularly in the mottled nodular beds, exhibit pedogenic features such as calcretes with nodular to massive accumulations, reflecting periods of in a semi-arid setting. Geochemically, the limestones show high (CaO) contents, indicative of elevated levels, while the overall sediments display signatures—such as enriched Zr, Hf, and REE patterns—consistent with fluvial derivation from the Craton's granite-gneiss terrains. Immobile s in the clay fractions further align with products of nearby basaltic sources, supporting mixed inputs. Lithological variations occur across basins, with basal conglomerates featuring well-rounded pebbles in a sandy-argillaceous matrix, marking unconformable contacts with underlying basement. Upper units in some exposures include more sandstones and nodular clays, transitioning to the overlying volcanics.

Sedimentary Facies and Structures

The Lameta Formation exhibits distinct sedimentary associations that reflect a dynamic depositional system. Fluvial channel deposits are characterized by cross-bedded sandstones, representing and channel-fill environments within meandering rivers. Overbank floodplains are dominated by mudstones and silty clays containing traces and concretions, indicative of periodic flooding and exposure. Lacustrine margin include laminated limestones and nodular carbonates, suggesting shallow, intermittent water bodies along the basin margins. Key sedimentary structures provide insights into the formative processes. Trough cross-bedding in the facies points to migrating bedforms in sinuous, low-gradient fluvial channels. and desiccation cracks in finer-grained overbank and lacustrine deposits indicate episodic low-energy flow and seasonal drying, consistent with fluctuating water levels. nodules, often rooted and irregularly distributed within mudstones, result from pedogenic processes involving evaporation and soil development. The overall depositional model reconstructs an traversed by meandering rivers and punctuated by intermittent lakes, influenced by a with wet and dry seasons promoting cyclic . provenance derives primarily from the western Indian , including plutonic and metamorphic terrains, as evidenced by and compositions in sandstones. The formation displays fining-upward sequences, typically 10-20 m thick, comprising basal coarse sandstones grading into mudstones and capped by carbonates, reflecting prograding fluvial-lacustrine systems and repeated episodes of channel avulsion and .

Paleoenvironmental Reconstruction

Climate and Paleosols

The paleosols of the Lameta Formation provide key evidence for reconstructing the climate in , indicating a tropical humid characterized by seasonal rainfall and hot conditions. Red-colored paleosols, primarily alfisols developed on deposits, display vertic features such as slickensides and wedge-shaped peds, alongside gleying indicative of fluctuating tables and periodic inundation during wet phases amid predominantly dry intervals. These profiles suggest a of alluvial plains with limited cover, where exceeded for much of the year, punctuated by episodic heavy rainstorms that promoted soil cracking and bioturbation. Paleosol types in the formation include well-developed calcretes with Bwk horizons marked by nodular and rhizocretionary , reflecting pedogenic maturation under humid thresholds. Quantitative estimates derived from geochemical indices, such as the chemical index of alteration (CIA), point to mean annual of approximately 779–1150 mm, sufficient for moderate but insufficient for lush tropical forests. Stable analyses of pedogenic yield δ¹³C values ranging from -8 to -9‰ (VPDB), consistent with a dominance of C3 vegetation in the zone, and δ¹⁸O values of -4 to -5‰ (VPDB), implying formation from meteoric waters with δ¹⁸O around -10 to -11‰ and mean annual temperatures of 25–30°C. These proxies collectively support a warm, seasonally variable conducive to during dry periods. Recent studies (as of 2024) indicate paleoclimate variability from semi-arid to sub-humid conditions, with two shorter arid episodes in the middle and upper parts of the Mottled Nodular Beds. Micromorphological examination of paleosol thin sections reveals alternating laminae of clay illuviation and Fe-Mn oxide coatings, evidencing repeated wet-dry cycles that align with seasonal dynamics. Such features mirror modern semi-arid soils in the of , where seasonal rains (typically 700–1200 mm annually) cause vertic swelling and gley reduction, followed by prolonged dry seasons promoting calcrete formation. This analogy underscores a proto-monsoonal circulation pattern influencing the during the , prior to intensified Himalayan orogeny. These findings refine earlier models by highlighting climatic variability, potentially linked to or regional , while floral indicators like reinforce the prevalence of drought-tolerant .

Floral and Faunal Indicators

The Lameta Formation preserves a limited but informative record of floral elements that point to freshwater environments. Charophyte gyrogonites, including species such as Platychara cf. sahnii, Nemegtichara grambastii, and Microchara sp., are commonly found in the and argillaceous units, indicating the presence of shallow lacustrine and palustrine settings within a system. These gyrogonites suggest growth in low-energy, freshwater habitats conducive to charophyte , which thrived in seasonal ponds and marshes. Palynological analyses reveal sparse , dominated by types, alongside spores, reflecting a of open woodlands fringing these wetlands rather than dense forests. Faunal indicators in the formation include traces that illuminate animal activities in riparian and zones. Coprolites, primarily from herbivorous dinosaurs like titanosaurs, contain plant fragments, fungal spores, and isotopic signatures (δ¹³C around -24‰) consistent with a diet of C₃ vascular such as gymnosperms and ferns, further supporting a riparian with accessible browse. burrows, including ichnogenera like Arenicolites and Thalassinoides, occur in fine-grained deposits, indicating bioturbation by arthropods or annelids in moist, vegetated soils. Ostracode assemblages provide evidence of low-diversity aquatic communities in seasonal water bodies, with non-marine species such as Cypridea and Ilyocypris dominating but occasional brackish forms like Pongawa suggesting minor fluctuations in interconnected wetlands. These bivalved crustaceans favored shallow, oxygenated waters with emergent vegetation, pointing to a mosaic of freshwater to slightly brackish habitats. Overall, the biotic traces depict a low-diversity structured around riverine corridors, with herbivores exploiting woodland edges and colonizing periodically inundated plains. Taphonomic patterns in the Lameta Formation highlight biases favoring robust remains over delicate ones. Fluvial reworking in the dynamic alluvial environment led to poor preservation of fragile structures, with most floral evidence limited to resistant gyrogonites, , and inclusions, while leaf litter or stems are scarce. In contrast, durable bones and eggshells accumulated in channel lags and overbank deposits, creating a skewed record that overrepresents large animals and underrepresents the full plant diversity of these wetlands.

Fossil Assemblage

Dinosaurs

The Lameta Formation has yielded a diverse assemblage of dinosaurs, primarily from Maastrichtian-aged sediments in central and , representing some of the last non-avian dinosaurs on the before the Cretaceous-Paleogene . The s, mostly fragmentary and disarticulated due to fluvial transport in riverine depositional environments, include representatives from and , highlighting Gondwanan endemism with close affinities to taxa from , , and . Numerous fragmentary skeletal specimens have been documented, alongside extensive egg clutches that provide insights into reproductive behavior. Sauropods dominate the assemblage, with titanosaurs being the most common herbivores. Valid taxa include septentrionalis, indicus, and colberti, known from partial skeletons including vertebrae, limb bones, and a skull fragment of collected from Dongargaon Hill in ; these feature long necks, tails, and slender limbs adapted for browsing in forested floodplains. Lametasaurus indicus, based on partial remains from including osteoderms and limb elements, was initially described as an armored dinosaur but is now considered a dubious theropod taxon, potentially an abelisauroid, due to chimaeric elements including theropod bones. Evidence of nesting behavior comes from extensive titanosaur egg clutches assigned to the oogenus Megaloolithus, with a 2023 discovery in the District of uncovering 92 nests containing 256 eggs in circular, linear, and combination patterns within sandy , indicating colonial breeding in palustrine settings. Theropods are represented mainly by abelisaurids, large carnivores that preyed on the abundant sauropods. , from , is known from skull roof elements, vertebrae, and limb bones such as a , , and dentary, exhibiting abelisauroid traits like robust phalanges and a deep jaw suited for bone-crushing bites. , discovered near Rahioli in , preserves a partial including the braincase, vertebrae, pelvic girdle, and hind limbs, distinguished by elongated supratemporal fenestrae, a median nasal horn, and a robust ilium, suggesting it was a top predator about 9 meters long. Ornithischians are scarce, with no valid taxa identified; past reports of armored forms have been reclassified as theropods. Many specimens form chimaeric assemblages, with mixed titanosaur and abelisaurid elements often jumbled in fluvial channels, complicating and indicating post-mortem transport over distances. These dinosaurs represent the terminal Gondwanan , with abelisaurids and titanosaurs showing strong phylogenetic ties to southern continents, underscoring India's role as a biogeographic crossroads before isolation and the K-Pg mass extinction around 66 million years ago.

Reptiles

The Lameta Formation preserves a notable record of non-dinosaurian reptiles, reflecting a predominantly with indeterminate mesoeucrocodylians, , and snakes as key components. These taxa, adapted to lacustrine and riverine settings, include piscivorous predators and that interacted with the broader community, such as through predation on nests. Fossils are primarily preserved in carbonate-rich sediments, where taphonomic conditions favored the accumulation of robust bones and shells in low-energy depositional environments. Crocodilian nests have been reported from the formation, indicating habits in shallow waters. Turtles belong to the Bothremydidae, with bothremydids such as Carteremys leithii and Jainemys pisdurensis documented by complete shells and skulls suggestive of riverine habitats. Over 50 specimens, including well-preserved carapaces and plastra, occur in the Bagh area outcrops correlated with the Lameta Formation, indicating adaptation to slow-moving freshwater bodies amid semiarid conditions. Snakes include madtsoiids like Sanajeh indicus and Madtsoia pisdurensis, discovered in the 2000s from sites such as Pisdura and . A remarkable articulated specimen of S. indicus preserves gut contents with a sauropod and hatchling skeleton, evidencing predation on nesting sites and highlighting ecological overlap with dinosaurs. These fossils, found in sandstones, underscore the snakes' terrestrial-aquatic lifestyle. Overall, the reptile assemblage comprises around a dozen identified taxa, predominantly freshwater-adapted forms whose preservation in carbonates and marls reflects selective taphonomic biases toward durable skeletal elements.

Mammals and Other Vertebrates

The mammalian fossil record from the Lameta Formation and associated intertrappean beds is sparse, dominated by isolated teeth and fragments indicative of early Gondwanan radiations. Gondwanatheres, particularly sudamericids such as Dakshina jederi, are represented by hypsodont molariform teeth (mf3 and mf4) and incisors from Maastrichtian intertrappean mudstones at Naskal () and Gokak (); these exhibit multiple-layered enamel and V-shaped islets, suggesting adaptations for processing abrasive plant material or possibly . Additionally, a late-surviving haramiyid is known from infratrappean beds near Bacharam and Jaidpalli (), based on microvertebrate screen-washing residues. Fish remains in the Lameta Formation are rare and restricted to actinopterygians preserved in lacustrine limestones and mudstones, reflecting freshwater or brackish depositional environments. The holostean Pycnodus lametae is documented by a nearly complete skeleton and isolated teeth from sites in Maharashtra (e.g., Dongargaon), featuring a deep-bodied form with specialized crushing dentition suited to durophagous feeding on mollusks and crustaceans. Other taxa include gar (Lepisosteus indicus), osteoglossids, and siluriform catfishes from Telangana localities, indicating mixed fluvial-lacustrine habitats influenced by marine incursions. No chondrichthyans are known from these deposits. Amphibian fossils are exceedingly rare, limited to anuran (frog) remains suggesting occupation of riparian and wetland niches. A discoglossid frog, represented by fragmentary ilia and other elements (approximately 5 specimens total), occurs in Maastrichtian intertrappean beds at Naskal (Andhra Pradesh), with morphology implying a Laurasian affinity and possible dispersal via terrestrial corridors. The non-dinosaurian, non-reptilian assemblage of the Lameta Formation exhibits low diversity, with roughly 10 taxa overall, primarily microvertebrate elements concentrated in fine-grained mudstones that favored preservation of small-bodied forms. This paucity underscores an early stage of Gondwanan diversification amid fluvial-lacustrine settings, with biases toward aquatic and semi-aquatic taxa.

Invertebrates

The invertebrate record of the Lameta Formation is dominated by freshwater mollusks and preserved primarily in and carbonate beds, reflecting lacustrine and fluvial environments during the stage of the . Gastropods and bivalves occur abundantly in these deposits, with representatives such as the gastropod (including L. subulata) and the bivalve Unio (including U. deccanensis), indicating stable, low-energy aquatic settings like lakes and river channels. Approximately 20 species of mollusks have been documented across these assemblages, primarily from sites in and Pisdura, underscoring their role as indicators of perennial freshwater bodies amid a semi-arid . These shelled mollusks, often found articulated or as molds in fine-grained limestones, suggest oligotrophic to mesotrophic water conditions with minimal salinity. Ostracods form a diverse component of the Lameta invertebrate fauna, with over 40 species reported from key localities such as , serving as important biostratigraphic markers for the . Genera including Cypridea (e.g., C. (Pseudocypridina) sp.) and Ilyocypris dominate the assemblages, alongside others like Eucypris, Candona, and Cyclocypris, totaling up to 41 freshwater species in some sections. These microcrustaceans exhibit variations in carapace morphology and size (up to 4.1 mm in rare gigantic forms), reflecting fluctuations in from freshwater to slightly brackish conditions, likely tied to episodic drying and flooding in lakes. Their biogeographic affinities link the Lameta fauna to contemporaneous non-marine assemblages in and , supporting correlations within the Upper of . Other invertebrates and related traces include charophyte algae gyrogonites, often treated as pseudo-invertebrate indicators due to their calcified reproductive structures, with species such as Platychara cf. sahnii and Nemegtichara grambastii preserved in palustrine carbonates. These gyrogonites, measuring 360–580 μm in length, point to shallow, vegetated water bodies within the floodplain. Palynomorphs, such as Aquilapollenites indicus, are also present, providing evidence of angiosperm-dominated flora. Trace fossils, including burrows attributable to annelids (e.g., Planolites-like forms) and possible insect pupation chambers, occur sporadically in the finer sediments, evidencing bioturbation by soft-bodied invertebrates in moist substrates. The high abundance of these in the carbonate-rich units of the Lameta Formation provides critical palaeoecological insights into water chemistry, with low-diversity, high-abundance assemblages signaling seasonal and stable freshwater habitats. Recent taxonomic reviews in the have refined identifications, incorporating new finds from Pisdura and Dongargaon to update the systematics of both mollusks and ostracods, enhancing correlations with intertrappean beds above the .

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