December 11th, 2024 
Riffin @WFS,World Fossil Society, Athira, Riffin T Sajeev, Russel T Sajeev
A storeroom specimen that changed the origins of modern lizards by millions of years has had its identity confirmed.
The tiny skeleton, unearthed from Triassic-aged rocks in a quarry near Bristol, is at least 205 million years old and the oldest modern-type lizard on record.
Recently, the University of Bristol team’s findings came under question, but fresh analysis, published today in Royal Society Open Science, proves that the fossil is related to modern anguimorphs such as anguids and monitors. The discovery shifts the origin of the whole lizard-snake group, called Squamata, back by 35 million years.
In the original study, Dr David Whiteside, Dr Sofia Chambi-Trowell and Professor Mike Benton, named the little critter Cryptovaranoides microlanius, meaning ‘hidden lizard, small butcher’ because of its identification as a lizard and its sharp teeth, probably used for cutting up prey animals for food. The Bristol team identified many anatomical features of the skull and skeleton that allowed them to place it well within Squamata, and even close to the Anguimorpha.
Figure 1. Images from the holotype NHMUK PV R36822 of C. microlanius, separate isolated bones referable to the taxon and a palatine of †Tanystropheus longobardicus for comparison. (a) Distal end of left humerus in anterior view exposed on the surface of the holotype rock showing an ectepicondylar and an entepicondylar foramen and the capitellum. (b) NHMUK PV 38911 isolated larger specimen of the distal end of left humerus of †Cryptovaranoides microlanius in (above) anterior and (below) posterior views showing similar features except the condyle of the capitellum. (c) Right maxilla, right vomer in ventral view, right septomaxilla in dorsal view and both premaxillae exposed on the surface of the holotype rock. (d) Scan of right septomaxilla in posteromedial view. (e) Scan of NHMUK PV R36822, mainly in ventral view, showing right lower jaw, orbitosphenoid, right jugal, right quadrate, basioccipital, sphenoid, anterior vertebrae and ribs as well as pectoral and forelimb bones. (f) Scan of left jugal in lateral view for comparison. (g,h) Fragment of right otoccipital from scan of NHMUK PV R36822 showing position of vagus foramen, in (g) medial and (h) lateral views. (i,j) NHMUK PV 38889, fragment of left exoccipital part of otoccipital in (i) lateral and (j) medial views, annotated to show vagus foramen. (k) Isolated right palatine NHMUK PV R 38916 of †Cryptovaranoides microlanius in ventral view, showing extent of the choanal sulcus (fossa). (l) Right palatine of †Tanystropheus longobardicus PIMUZ T 2484 showing position of choanal channel. Scale bars all 2 mm except (a) = 0.5 mm and (d) = 1 mm. Arrows show anterior.ant, anterior; at, atlas; ax, axis; ba, basioccipital; bi, bicapitate; cap, capitellum; cen, centrum; ch, choana; chn, channel; cv, cavity; ect, ectepicondyle; ent, entepecondyle (entepicondylar); fct, facet; fo, foramen (foramina); for, foramen; fos, fossa; hg, hypoglossal; hu, humerus (humeral); hyo, hyoid; in, intercentrum; ju, jugal; l., left; lj, lower jaw; msof, margin of suborbital fenestra; mx, maxilla (maxillary); ne, neural; od, odontoid; orbs, orbitosphenoid; oto, otoccipital; pcf, posterior of the choanal fossa; pm, premaxilla; posl, posterolateral; post, posterior; pmd, posteromedial; proc, process; pt, pterygoid; q, quadrate; r, right; ra, radius; raul, radioulnar; ri, rib; s, spine; sp, septomaxilla; sph, sphenoid; th, tooth (teeth); thr, tooth row; tr, trochlea; unc, unicapitate; vf, vagus foramen; vo, vomer (vomerine).
“We knew our paper would be controversial,” explained Dr Whiteside. “But we were confident that we had looked at every possible feature and compared it with everything we could.”
Professor Benton said: “We were therefore surprised, perhaps even shocked, that in 2023 another team of academics suggested that Cryptovaranoides was not a lizard or even a lizard relative, but in fact an archosauromorph, more closely related to crocodilians and dinosaurs.”
In checking their original work, and the questions posed in the rival paper, the Bristol team explored all the data, including the original specimen as well as the X-ray scans that show the details hidden within the rock. “We had the marvellous images from those CT scans as well as further access to the fossil which enabled us to check all their suggestions,” said Dr Chambi-Trowell. “We found that most of the concerns raised were wrong.”
Figure 2. Photographs and CT scan images of NHMUK PV R36822 holotype bones of †Cryptovaranoides microlanius and isolated quadrate, prefrontal and premaxillae. (a–c) Left side of holotype skull and lower jaw of †Cryptovaranoides microlanius. (a) Close-up of left lacrimal in medial view. (b) Left side of skull and lower jaw in medial view. (c) Computed tomography (CT) scan of left lacrimal in lateral view. (d) Holotype right quadrate CT scan in medial view. (e) Isolated left quadrate NHMUK PV R 37606 digitally removed from matrix. (f) CT scan image of holotype right pterygoid in ventromedial view. (g) CT scan of holotype left and right premaxillae in posteroventral views. (h) Isolated left premaxilla NHMUK PV R 38914 in posteroventral view. (i) Isolated right premaxilla NHMUK PV R 38913 in posterior view. (j) Isolated right prefrontal NHMUK PV R 38912 in medial view. (k) Lateral view of right prefrontal NHMUK PV R 38912 showing palpebral fossa. Scale bars all 2 mm except (a) which is 0.5 mm. Arrows show anterior. an, angular; ant, anterior; ar, articular; c, crest; con, condyle; conc, conch; cor, coronoid; ct, contact; den, dentary; dor, dorsal; ec, ectopterygoid; ep, epipterygoid; f, frontal; fct, facet; fo, foramen (foramina); fos, fossa; gr, groove; ju, jugal; l., left; lac, lacrimal; mar, missing anterior region; me, medial; mth, missing tooth; mx, maxilla (maxillary); nal, nasolacrimal; not, notch; olcw, olfactory chamber wall; pa, palatine; pal, palbebral; pm, premaxilla; post, posterior; proc, process; prf, prefrontal; pt, pterygoid; ram, ramus; re, resorption; q, quadrate; r, right; slf, shelf, th, tooth (teeth); trc, tract; ty, tympanic.
Professor Benton added: “All the details of the skull, the jaws, the teeth, and the limb bones confirm that Cryptovaranoides is a lizard, not an archosauromorph.
“In our new paper, we provide great detail of every criticism made and we provide more photographs of the specimen and 3D images from the scans, so everyone can check the detail.”
Dr Whiteside concluded: “The result of all this had to be tested by a phylogenetic analysis.
“This is where we code hundreds of anatomical features in Cryptovaranoides and other modern and fossil lizards, as well as various archosauromorphs.
“We ran the analysis time after time, and it gave our original result, that the little Bristol reptile is indeed the world’s oldest modern-type lizard.”
Source : University of Bristol. “World’s oldest lizard wins fossil fight.” ScienceDaily. ScienceDaily, 26 November 2024. <www.sciencedaily.com
Ref: David I. Whiteside, Sofía A. V. Chambi-Trowell, Michael J. Benton. Late Triassic †Cryptovaranoides microlanius is a squamate, not an archosauromorph. Royal Society Open Science, 2024; 11 (11) DOI: 10.1098/rsos.231874
@WFS,World Fossil Society, Athira, Riffin T Sajeev, Russel T Sajeev
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